CN116574976A - A flexible second phase production control method suitable for bearing steel and its application - Google Patents

Abstract

The invention discloses a flexible second phase production control method suitable for bearing steel and its application, belonging to the technical field of metal product production. The control methods include composition control, smelting control, high temperature diffusion and billet opening control, hot rolled billet heating control and wire rod rolling control. The invention obtains good shape, size and quantity of inclusions and carbides by controlling the production process parameters of the bearing steel, so that the product can meet the requirements of downstream users for stable and efficient production of rolling elements with high fatigue life. Through the appropriate metallurgical process, the appropriate number and type of inclusions can be obtained; through the intermediate blanking and diffusion process, the nature and shape of the inclusions can be changed; through the control of rolling process parameters, the composite precipitation of inclusions and carbides can be suppressed, and finally Get good product quality.

Description

A flexible second phase production control method suitable for bearing steel and its application

technical field

The invention relates to a flexible second phase production control method suitable for bearing steel and its application, belonging to the technical field of metal product production.

Background technique

High-quality bearing steel is mostly used to manufacture rolling elements such as precision steel balls. The parameters such as the quantity, shape, and size of hard second phases such as inclusions and carbides significantly affect the fatigue life, crushing load, and corrosion resistance of rolling elements. and other performance. A large number of scholars have studied the relationship between oxide inclusions, carbide particles and fatigue life of rolling elements. At present, bearing steel production enterprises adopt suitable smelting equipment and continuous casting process, which can stably reduce the oxygen content in bearing steel to below 8ppm, greatly reduce the amount of oxide inclusions in steel, and then undergo appropriate high-temperature diffusion treatment to make rolling elements The lifespan is greatly improved. But on the other hand, although the oxygen content of the bearing steel produced by electroslag remelting method reaches 18ppm, the fatigue life of the rolling elements is still 1.4 times of the life of L ₁₀ of bearing steel with 8ppm of oxygen content produced by continuous casting, and 1.4 times of the life of L ₅₀ . 1.3 times, which shows that in addition to the influence of oxygen content, the size and shape of the hard second phase are also critical to the fatigue life of bearing steel. The reduction of the relative fatigue life of TiN particles, eutectic carbide particles and other hard secondary particles has attracted extensive attention and research. The harm of the hard second phase to steel is essentially that the elastic modulus, linear expansion coefficient and plasticity of the hard second phase particles and the steel matrix are different. Uncoordinated synchronization, resulting in cracks and voids at the junction, eventually leading to early crack source initiation and fatigue failure.

Therefore, in the production process of bearing steel, special control means are needed to optimize the hard second phase. Through flexible control methods, the desired inclusion shape and carbide state can be obtained, and the hardness of the hard second phase of bearing steel can be reduced. harm and improve product quality.

Contents of the invention

The problem to be solved by the present invention is to provide a flexible second-phase production control method suitable for bearing steel. By controlling the production process parameters of bearing steel, good inclusions, carbide shapes, sizes and quantities can be obtained, so that the product can meet the downstream requirements. The user's requirements for stable and efficient production of rolling elements with high fatigue life. Through the appropriate metallurgical process, the appropriate number and type of inclusions can be obtained; through the intermediate blanking and diffusion process, the nature and shape of the inclusions can be changed; through the control of rolling process parameters, the composite precipitation of inclusions and carbides can be suppressed, and finally Get good product quality.

At the same time, the invention provides an application of the wire rod obtained by the flexible second phase production control method suitable for bearing steel in the rolling body.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A flexible second phase production control method suitable for bearing steel, comprising the steps of:

1) Ingredient control:

The weight percentage of chemical composition of bearing steel is C: 0.95-1.05%, Mn: 0.25-0.45%, Si: 0.15-0.35%, S: 0.01-0.025%, Cr: 1.40-1.65%, P: ≤0.025%, Ti: ≤0.002%, Ni: ≤0.30%, Mo: ≤0.10%, Cu: ≤0.25%, and the rest are Fe and trace impurities.

For the control of S content, when the S content is too low, the sulfide will not form the form with oxide and nitride as the core, but only an independent sulfide. When the S content is too high, the level of sulfide formed is too high, which deteriorates the fatigue performance. At the same time, the sulfide reacts eutectically with carbon at the interdendritic position, resulting in the formation of large-sized eutectic carbides, which also deteriorates the fatigue performance.

Excessively high sulfide levels refer to the large number and large size of sulfides. According to the method of "Determination of the Content of Non-metallic Inclusions in Steel in GB/T 10561", the level of sulfide inclusions detected is high.

The control of Ti content is mainly to avoid the formation of large-grained titanium inclusions.

2) Smelting control:

Through suitable converter tapping and alloying (firstly, it is required that the molten iron loaded into the converter has a C content of 3.7-4.5%, a Si content of 0.2-0.5%, a Mn content of 0.2-0.3%, and the lower the other elements, the better. The molten iron enters After the converter, use an oxygen lance to blow for 700-1000 seconds, and control the carbon pulling temperature at 1560-1670 ° C. During the converter smelting process, add appropriate lime, fluorite, dolomite, iron oxide balls, etc. to ensure that the converter slag composition: CaO : 45-55%, SiO ₂ : 10-15%, MgO: 5-8% and the balance of FeO. Carry out alloying when tapping and pay attention to the amount of slag lower than 3Kg/t, when the amount of molten steel in the ladle is about 4 When the amount of molten steel in the ladle is about 8-12t, add carburizer (the composition of the carburizer is C), ferrosilicon, ferromanganese, ferrochrome, synthetic slag (synthetic slag It mainly includes 48-50% CaO, 34-35% Al ₂ O ₃ , 14-15% SiO ₂ and the balance of MgO), so that the molten steel composition meets the following content), and the molten steel with the following composition and temperature is obtained as LF refining treatment early guarantee.

Molten steel composition: C: 0.89-0.95%, Si: 0.10-0.15%, Mn: 0.27-0.32%, P: 0.0087-0.0109%, S: 0.005-0.01%, Al: 0.0086-0.0559%, Ti: 0.0007-0.0074 %, Cr: 1.33-1.43%, the rest is Fe and trace impurities.

The molten steel temperature is: 1505-1570°C. The LF refining process adopts a suitable slagging process (at the beginning of LF refining, add 500Kg of synthetic slag (synthetic slag mainly includes 48-50% CaO, 34-35% Al ₂ O ₃ , 14-15% SiO ₂ and the balance MgO) , Lime 100Kg, Calcium Carbide 50Kg and Ferrosilicon Powder 100Kg, and then fine-tuned by observing the color and consistency of the slag material on site, and finally obtained a good white slag), and obtained a good white slag, that is, the final slag, and the composition of the final slag is as follows : CaO: 40-57.2%, SiO ₂ : 15-25%, MgO: 6-10%, Al ₂ O ₃ : 21-25% and FeO: 0.8-1.2%. The basicity R of the final slag is 3-4.5. During the LF refining process, according to the composition inspection of the molten steel, carbon wire, ferromanganese, ferrochromium and other alloys are added to fine-tune the composition, and alloys with high Ti content are avoided to ensure that the molten steel obtained by LF refining has C: 0.89-0.95%. Si: 0.10-0.15%, Mn: 0.27-0.32%, P: 0.0087-0.0109%, S: 0.005-0.01%, Al: 0.0086-0.0559%, Ti: 0.0007-0.0074%, Cr: 1.33-1.43%, the rest For Fe and trace impurities.

After LF refining, the molten steel enters the RH station for further refining. The RH vacuum treatment cycle time is 40-50min, and the vacuum degree is 50-100Pa to further remove the inclusions and degassing in the molten steel.

Calcium treatment is strictly prohibited throughout the smelting process, that is, no calcium wire is added to molten steel during the LF refining process.

After the above-mentioned smelting treatment and continuous casting (the ladle after RH vacuum treatment enters the continuous casting machine, it is produced at a casting speed of 0.65-0.8m/min, the temperature of the tundish is controlled at 1475-1500°C, and protection is added to the crystallizer. Slag. The crystallizer adopts electromagnetic stirring, the current is set to 480-520A, and the frequency is 2.35-2.45Hz. For the secondary cooling water volume, the total water volume is controlled at 100-130L/min, and dynamic light reduction is adopted at the end, and the total reduction volume is controlled After 8.5-11mm) into a slab, the second phase in the continuous casting slab has the following types: 1) Inclusions, which are divided into the following categories: ①Ti(C,N) type inclusions, with edges and corners, are orange-red, and a small amount appears alone , mostly accompanied by MnS; Ti(C,N) is TiA, where A includes C and/or N. ②MnS inclusions, MnS inclusions mainly exist in two forms: massive pure MnS, and MnS with other inclusions (mostly oxides) as the core. ③Oxide inclusions are mainly two types: a small amount of magnesia-aluminum spinel inclusions and a large amount of alumina + calcium aluminate + sulfide composite inclusions. 2) Carbide, divided into the following categories: ① Granular eutectic carbide between dendrites. ② Coarse intergranular carbides.

The mold slag is continuously consumed along with the billet continuous casting, so it should be continuously added according to the actual consumption on site to keep the molten steel from being exposed. The general consumption is 0.2-1.0Kg/t (0.2-1.0Kg of mold slag consumed per ton of molten steel). The mold powder composition mainly includes: 35% SiO ₂ , 22% CaO, 4% Al ₂ O ₃ , 10% K ₂ O+Na ₂ O (K ₂ O and Na ₂ O are arbitrary proportions), 19% C , and the balance Fe.

3) High temperature diffusion and billet opening:

The continuous casting slab undergoes slow cooling, or direct hot charging for high temperature diffusion, and the temperature control of each section is as follows:

Preheating section: temperature ≤900°C, time ≥180min;

Heating section: temperature 1200-1250℃, time 100-120min;

Soaking section: temperature 1250-1270°C, time 60-90min.

The main function of high-temperature diffusion is to dissolve carbides. Sufficient high-temperature diffusion temperature and time are used to ensure the dissolution of carbide second-phase particles and reduce its impact on fatigue life. After high-temperature diffusion (high-temperature diffusion is completed in the furnace, after the diffusion is completed, it directly enters the blanking machine through the roller table for 6 times of heavy reduction. The temperature is gradually lowered, and the billet temperature is 1060-1100°C after the billet opening is completed), and the billet is rolled into a hot-rolled billet with a cross-section of 160×160mm by 6 passes of heavy reduction. In order to ensure the reduction effect of the core area of the billet, the reduction process of each pass is as follows:

Pass 1: slot width B: 320mm; slot bottom width b: 285mm; height h: 160mm;

Pass 2: slot width B: 256mm; slot bottom width b: 220mm; height h: 160mm;

Pass 3: slot width B: 226mm; slot bottom width b: 190mm; height h: 160mm;

Pass 4: slot width B: 201mm; slot bottom width b: 170mm; height h: 160mm;

Pass 5: slot width B: 175mm; slot bottom width b: 155mm; height h: 160mm;

Pass 6: slot width B: 162mm; slot bottom width b: 157mm; height h: 160mm.

After the above-mentioned high-temperature diffusion treatment and rolling into a hot-rolled slab, the second phase in the slab has the following types: 1) Inclusions, which are divided into the following categories: ①Ti(C,N)-type inclusions, a small number of large lumps precipitated separately The Ti(C,N) inclusions have basically been broken, and most of the Ti(C,N) accompanying MnS have not been deformed. ②MnS-type inclusions, MnS-type inclusions all become long strips, and part of MnS appears together with oxides and Ti(C,N) inclusions. ③Oxide inclusions are mainly two types of magnesium aluminum spinel, alumina + calcium aluminate + sulfide composite, most of which are wrapped by MnS inclusions. 2) Carbides: ① The granular eutectic carbides between dendrites have all been solid-dissolved into the matrix. ②Reticular carbide precipitates at the grain boundary, with a thickness of <0.5 μm.

4) Heating of hot rolled slab:

The hot-rolled slab is rolled after being heated, and the temperature of each section is controlled as follows when the hot-rolled slab is heated:

Preheating section: temperature ≤ 800 ℃, time 60-70min;

Heating section: temperature 1150-1210°C, time 30-40min;

Soaking section: temperature 1190-1230°C, time 30-40min.

All kinds of second-phase particles in the hot-rolled slab will change again after being heated and kept warm after cooling. The main manifestations are: ①The number of small particles of Ti(C,N) in the matrix increases, and the amount of Ti(C,N) in the billet increases. The voids in the matrix caused by crushing are healed after reheating at high temperature and rolling. The Ti(C,N) associated with MnS is further wrapped by MnS to reduce its harmfulness. ②The strip-shaped MnS in the hot-rolled slab will be broken and tend to be spherical at the weak point after heating and heat preservation, and finally become isolated MnS particles. MnS with oxide inclusions as the core tends to become a spherical shell, and the Ca content of the shell further increases, eventually becoming CaS-MnS composite inclusions. ③ After the hot-rolled slab is heated and kept warm, almost all oxide inclusions appear together with MnS. Most of the oxide inclusions are small and are wrapped by MnS inclusions; a small amount of oxide inclusions are relatively large, and they share a certain proportion with MnS.

After the above treatment, almost all the carbide second-phase particles in the hot-rolled slab are in solid solution, and most of the inclusion second-phase particles are wrapped by sulfide, which significantly reduces the hazard of the hard second relative fatigue life. Pure brittle second-phase particles and sulfide-wrapped second-phase particles are rolled into wire rods, and then rolled into rolling elements through drawing and cold heading processes. It can be seen that after being wrapped with sulfide, the damage of the second phase particles to the matrix during the deformation of the wire can be significantly reduced.

5) Wire rolling:

The control points of wire rod rolling: 1) The temperature of entering and finishing rolling is 850-880°C, the temperature of entering and reducing sizing is 850-880°C, and the temperature of spinning is 780-810°C. scope. It is required to have at least 2 sections of water tanks before finishing rolling, the number of nozzles in each water tank is ≥10, and the length of the entire water cooling section before finishing rolling is ≥40m; there are at least 3 sections of water tanks between finishing rolling and reducing sizing, and the number of nozzles in each water tank ≥10, the length of the entire water-cooling section before finishing rolling is ≥50m; there are at least 2 sections of water tanks between the reducing sizing and the laying head, the number of nozzles in each water tank is ≥10, and the length of the entire water-cooling section before finishing rolling is ≥20m. During production, it is required that the cooling water temperature is ≤35°C, the cooling nozzle pressure is ≥0.5MPa, and the blowback nozzles are all opened, and the pressure is ≥0.5MPa. The cooling nozzles control the water flow according to the actual temperature. It is required to preferentially open the nozzles near the heating furnace side, and use a small flow rate or close the nozzles near the laying machine side.

The main purpose of wire rod rolling is to deform the core of the rolled material at low temperature, and through a suitable water tank nozzle cooling and sufficient recovery section, the temperature of the core of the rolled material is always at a low temperature to avoid the precipitation of the second coarse carbide phase. At the same time, the lower deformation temperature enhances the strength of the steel matrix and further reduces the damage of the second phase of hard inclusions. At this time, most of the hard inclusions are wrapped by sulfides, which can cooperate with the matrix to deform during the deformation process, and the danger of forming pores is greatly reduced.

In the wire, the ratio of the number of oxide and sulfide-associated second phase particles to [the total number of pure oxide particles and Ti(C,N) particles] is (1.52-2.09):1.

The application of the wire rod obtained by the flexible second phase production control method suitable for bearing steel in the rolling body, the wire rod is made into the rolling body through drawing and cold heading processes.

A rolling element is made from the wire obtained by the flexible second phase production control method suitable for bearing steel of the present invention.

The smelting control of the present invention: the desired second phase type is obtained through appropriate converter tapping, LF slagging, RH and continuous casting processes. High-temperature diffusion and billet opening: Dissolve the second phase of carbide through an appropriate high-temperature diffusion process to reduce its impact on fatigue life. After high-temperature diffusion, 6-pass rolling was used to form a hot-rolled slab with a cross-section of 160×160 mm to obtain the desired second phase type of inclusions. Hot-rolled slab heating process: After the hot-rolled slab heating process, almost all the carbide second-phase particles in the hot-rolled slab are in solid solution, and most of the second-phase particles of inclusions are wrapped by sulfide, which significantly reduces the hardness of the second relative fatigue. life-threatening hazards. Wire rolling control: By controlling the deformation of the core of the rolled material at low temperature, the precipitation of the second coarse carbide phase is avoided. At the same time, the lower deformation temperature enhances the strength of the steel matrix and further reduces the damage of the second phase of hard inclusions. At this time, most of the hard inclusions are wrapped by sulfide, and can deform synchronously with the matrix tissue during the deformation process.

Compared with the bearing steel wire rod obtained by the current conventional control method, the beneficial effects of the present invention are as follows: through flexible control, the probability of scratching the matrix by the hard second phase is reduced, and a low-hazard matrix structure is obtained. The rolling contact fatigue life test was carried out. Under the load of the maximum contact stress of 4.5GPa, the L ₁₀ life reached 1.5×10 ⁷ cycles.

Description of drawings

Fig. 1 is when the hot-rolled slab of the present invention is heated, and the Ti (C, N) particle that is accompanied by MnS is further wrapped by the microstructure diagram of MnS;

Fig. 2 is the microstructure diagram of elongated MnS in the hot-rolled slab of the present invention;

Fig. 3 is a microstructure diagram of the elongated MnS in Fig. 2, which finally becomes CaS-MnS composite inclusion particles after heating;

Fig. 4 is the microstructural figure of the particle that oxide of the present invention is wrapped by sulfide;

Fig. 5 is the microstructural figure of the particle of oxide and sulfide each proportion of the present invention;

Figure 6 is a morphological diagram of the second phase of cold heading deformation of the wire rod without sulfide wrapping;

Fig. 7 is a morphological diagram of the second phase of wire rod cold heading deformation after sulfide wrapping in the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. The following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

Example 1

A flexible second phase production control method for bearing steel, Specifications, including composition control, smelting control, high temperature diffusion and billet opening control, hot-rolled slab heating control and wire rolling control, the production steps are as follows:

1) Composition control: The weight percentage of chemical composition of bearing steel is C: 1.0%, Mn: 0.35%, Si: 0.25%, S: 0.015%, Cr: 1.50%, P: 0.012%, Ti: 0.002%, Ni: 0.02 %, Mo: 0.01%, Cu: 0.02%, and the rest are Fe and trace impurities.

2) Smelting control: LF final slag composition: CaO: 46%, SiO ₂ : 21%, MgO: 10%, Al ₂ O ₃ : 22%, FeO: 1.0%. The RH vacuum treatment time is 45min, and the vacuum degree is 67Pa.

Through proper converter tapping and alloying, the molten steel composition meets the following content, and the molten steel with the following composition and temperature is obtained as the early guarantee of LF refining treatment.

The process of tapping and alloying in the converter is as follows: the molten iron loaded into the converter is required to have a C content of 4.0%, a Si content of 0.4%, a Mn content of 0.25%, and the rest of the elements are not required; For 850 seconds, the carbon pulling temperature is controlled at 1600°C; during the converter smelting process, one or more of lime, fluorite, dolomite, and iron oxide balls are added to ensure that the converter slag composition: CaO: 50%, SiO ₂ : 12%, MgO: 6% and the balance of FeO; carry out alloying when tapping and pay attention to the amount of slag lower than 3Kg/t, when the amount of molten steel in the ladle is 5t, add 100Kg of Al block; when the amount of molten steel in the ladle is 10t, Add recarburizer, ferrosilicon, ferromanganese, ferrochrome and synthetic slag in sequence to make the composition of molten steel meet the requirements. Synthetic slag includes 49% CaO, 35% Al ₂ O ₃ , 15% SiO ₂ and the balance MgO. The carburant is C.

Molten steel composition: C: 0.90%, Si: 0.12%, Mn: 0.30%, P: 0.0095%, S: 0.008%, Al: 0.023%, Ti: 0.005%, Cr: 1.40%, the rest is Fe and trace impurities; The molten steel temperature is: 1550°C. LF refining is through the slagging process (the slagging process is: at the beginning of LF refining, add 500Kg of synthetic slag, 100Kg of lime, 50Kg of calcium carbide and 100Kg of ferrosilicon powder, and then make fine adjustments by observing the color and consistency of the slag on site, and finally get white slag, i.e. final slag), to obtain the final slag, the composition of the final slag is as follows: CaO: 44%, SiO ₂ : 20%, MgO: 10%, Al ₂ O ₃ : 25% and FeO: 1%; the alkali of the final slag The degree R is 3.5; during the LF refining process, carbon wire, ferromanganese, and ferrochrome are added to fine-tune the composition according to the composition inspection of molten steel, so as to ensure that the composition of molten steel obtained by LF refining is the same as that obtained after converter tapping and alloying;

The steel ladle after RH vacuum treatment enters the continuous casting machine and is produced at a casting speed of 0.7m/min. The temperature of the tundish is controlled at 1490°C, and mold slag is added to the crystallizer (consumption of mold slag is: per ton of molten steel consumption protection Slag 0.5Kg; Mold flux components include: 35% SiO ₂ , 22% CaO, 4% Al ₂ O ₃ , 10% K ₂ O+Na ₂ O, 19% C, and the balance Fe); the crystallizer adopts electromagnetic stirring , the current is set to 500A, and the frequency is 2.4Hz; for the secondary cooling water volume, the total water volume is controlled at 120L/min, and dynamic light reduction is adopted at the end, and the total reduction is controlled at 10mm to obtain continuous casting slabs;

The second phase in the continuous casting slab has the following types: 1) Inclusions, which are divided into the following categories: ①Ti(C,N) type inclusions, with edges and corners, are orange-red, a small amount appears alone, and most of them appear together with MnS. ②MnS inclusions, MnS inclusions mainly exist in two forms: massive pure MnS, and MnS with other inclusions (mostly oxides) as the core. ③Oxide inclusions are mainly two types: a small amount of magnesia-aluminum spinel inclusions and a large amount of alumina + calcium aluminate + sulfide composite inclusions. 2) Carbide, divided into the following categories: ① Granular eutectic carbide between dendrites. ② Coarse intergranular carbides.

3) High-temperature diffusion and billet opening: the temperature of the preheating section is 850°C, and the heat preservation is 180 minutes; the temperature of the heating section is 1230°C, and the heat preservation is 120 minutes; the temperature of the soaking section is 1260°C, and the heat preservation is 70 minutes. After 6 times of blanking, it is rolled into a hot-rolled billet with a cross-section of 160mm.

After the high temperature diffusion is completed, it directly enters the blanking machine through the roller table for 6 times of heavy reduction. The temperature of the billet is 1200°C when the rolling is started; as the blanking progresses, the temperature of the billet gradually decreases, and the temperature of the billet is 1080°C after the blanking is completed. , using 6 times of heavy reduction to roll into a hot-rolled billet with a cross-section of 160×160mm;

The reduction process of each pass using 6-pass large reduction is as follows:

Pass 1: slot width B: 320mm; slot bottom width b: 285mm; height h: 160mm;

Pass 2: slot width B: 256mm; slot bottom width b: 220mm; height h: 160mm;

Pass 3: slot width B: 226mm; slot bottom width b: 190mm; height h: 160mm;

Pass 4: slot width B: 201mm; slot bottom width b: 170mm; height h: 160mm;

Pass 5: slot width B: 175mm; slot bottom width b: 155mm; height h: 160mm;

Pass 6: slot width B: 162mm; slot bottom width b: 157mm; height h: 160mm.

After the above-mentioned high-temperature diffusion treatment and rolling into a hot-rolled slab, the second phase in the slab has the following types: 1) Inclusions, which are divided into the following categories: ①Ti(C,N)-type inclusions, a small number of large lumps precipitated separately The Ti(C,N) inclusions have basically been broken, and most of the Ti(C,N) accompanying MnS have not been deformed. ②MnS-type inclusions, MnS-type inclusions all become long strips, and part of MnS appears together with oxides and Ti(C,N) inclusions. ③Oxide inclusions are mainly two types of magnesium aluminum spinel, alumina + calcium aluminate + sulfide composite, most of which are wrapped by MnS inclusions. 2) Carbides: ① The granular eutectic carbides between dendrites have all been solid-dissolved into the matrix. ②Reticular carbide precipitates at the grain boundary, with a thickness of <0.5 μm.

4) Heating of hot-rolled slabs: the temperature of the preheating section is 750°C, and the heat preservation is 60 minutes; the temperature of the heating section is 1190°C, and the heat preservation is 40 minutes; the temperature of the soaking section is 1220°C, and the heat preservation is 30 minutes.

All kinds of second-phase particles in the hot-rolled slab will change again after being heated and kept warm after cooling. The main manifestations are: ①The number of small particles of Ti(C,N) in the matrix increases, and the amount of Ti(C,N) in the billet increases. The voids in the matrix caused by crushing are healed after reheating at high temperature and rolling. The Ti(C,N) associated with MnS is further wrapped by MnS to reduce its harmfulness, as shown in Figure 1. ②The strip-shaped MnS in the hot-rolled slab will be broken and tend to be spherical at the weak point after heating and heat preservation, and finally become isolated MnS particles. MnS with oxide inclusions as the core tends to become a spherical shell, and the Ca content of the shell further increases, and finally becomes CaS-MnS composite inclusions, as shown in Figure 2-3. ③ After the hot-rolled slab is heated and kept warm, almost all oxide inclusions appear together with MnS. Most of the oxide inclusions are small and are wrapped by MnS inclusions; a small amount of oxide inclusions are relatively large, and each accounts for part of the proportion with MnS, as shown in Figures 4 to 5. The FEI inclusion scanning analyzer is used to make statistics on the size and proportion of oxides and MnS, as shown in Table 1 below.

Table 1 scan analysis results

It can be seen from Table 1 that the higher the number of oxide particles wrapped by sulfide, the better. For the hazard of fatigue life, when the total amount of the second phase is determined, the pure sulfide second phase < the second phase particles of the oxide wrapped by sulfide < the second phase particles of the proportion of oxide and sulfide < the pure Oxide, Ti(C,N), carbide second phase. For example, 2335 inclusions were scanned in this test (the second carbide phase has almost been eliminated), the number of oxide and sulfide associated particles is 1124, and the number of pure oxide particles and Ti(C,N) particles are respectively 387, 151, the ratio of the number of oxide and sulfide associated particles to the total number of pure oxide particles and Ti(C,N) particles is 1124/538=2.09. The invention reduces the amount of the hard second phase of pure oxide particles and Ti(C,N) particles, and the ratio of the number of oxides and sulfide associated particles to the total number of pure oxide particles and Ti(C,N) particles ≥1.5, good fatigue life can be obtained. In Comparative Example 1, most of the oxides and Ti(C,N) are not associated with sulfides, resulting in a reduced fatigue life.

5) Wire rod rolling: entering the finishing mill at 850°C, entering into the reducing and sizing at 880°C, and spinning temperature at 790°C. Open the 1st and 2nd water tanks before finishing rolling, the 1st, 2nd and 3rd water tanks between finishing rolling and reducing sizing, and the 1st and 2nd water tanks before sizing and laying head. The first 5 nozzles of all water tanks are opened, the cooling water temperature is 30°C, the nozzle pressure is 0.6MPa, all the blowback nozzles are opened, and the gas pressure is 0.6MPa.

In this embodiment, the water tanks of each section are controlled by the nozzle + recovery section, so that the wire rod finishing temperature reaches 850°C, the cutting and sizing temperature reaches 880°C, and the spinning temperature reaches 790°C.

After the above treatment, almost all the carbide second-phase particles in the hot-rolled slab are in solid solution, and most of the inclusion second-phase particles are wrapped by sulfide, which significantly reduces the hazard of the hard second relative fatigue life. Pure brittle second-phase particles and sulfide-wrapped second-phase particles are rolled into wire rods, and then rolled into rolling elements through drawing and cold heading processes. The morphology is shown in Figures 6 to 7. It can be seen that after being wrapped with sulfide, the damage of the second phase particles to the matrix during the deformation of the wire can be significantly reduced.

In Figure 6, the hard oxide particles are not wrapped by sulfide. During the cold heading deformation and drawing deformation of the steel, the oxide particles are broken into strings and scratch the matrix to form holes, which lead to early fatigue failure. source, reducing the fatigue life of the material. In Figure 7, the hard oxide particles are wrapped by sulfide. During the deformation of the steel, the sulfide protects the oxide particles from being broken, causing less damage to the steel matrix and improving the fatigue life.

The wire is made into rolling elements through drawing and cold heading processes.

A rolling element is made of a wire obtained by a flexible second phase production control method suitable for bearing steel in this embodiment.

Example 2

A flexible second-phase production control method suitable for bearing steel, with a specification of φ12mm, including composition control, smelting control, high-temperature diffusion and billet opening control, hot-rolled billet heating control, and wire rod rolling control. The production steps are as follows:

1) Composition control: The weight percentage of chemical composition of bearing steel is C: 1.01%, Mn: 0.34%, Si: 0.25%, S: 0.012%, Cr: 1.55%, P: 0.011%, Ti: 0.002%, Ni: 0.02 %, Mo: 0.01%, Cu: 0.02%, and the rest are Fe and trace impurities.

2) Smelting control: LF final slag composition: CaO: 44%, SiO ₂ : 22.9%, MgO: 10%, Al ₂ O ₃ : 22%, FeO: 1.1%. The RH vacuum treatment time is 47min, and the vacuum degree is 67Pa.

Through proper converter tapping and alloying, the molten steel composition meets the following content, and the molten steel with the following composition and temperature is obtained as the early guarantee of LF refining treatment.

The process of tapping and alloying in the converter is as follows: the molten iron loaded into the converter is required to have a C content of 4.2%, a Si content of 0.3%, a Mn content of 0.22%, and the rest of the elements are not required; For 800 seconds, the carbon pulling temperature is controlled at 1650°C; during the converter smelting process, one or more of lime, fluorite, dolomite, and iron oxide balls are added to ensure that the converter slag composition: CaO: 55%, SiO ₂ : 13%, MgO: 7% and FeO in the balance; carry out alloying when tapping and pay attention to the amount of slag lower than 3Kg/t, when the amount of molten steel in the ladle is 5t, add 100Kg of Al block; when the amount of molten steel in the ladle is 10t, Add recarburizer, ferrosilicon, ferromanganese, ferrochrome and synthetic slag in sequence to make the composition of molten steel meet the requirements. Synthetic slag includes 49% CaO, 35% Al ₂ O ₃ , 15% SiO ₂ and the balance MgO. The carburant is C.

Molten steel composition: C: 0.92%, Si: 0.13%, Mn: 0.29%, P: 0.01%, S: 0.006%, Al: 0.035%, Ti: 0.006%, Cr: 1.37%, the rest is Fe and trace impurities; The molten steel temperature is: 1530°C. LF refining is through the slagging process (the slagging process is: at the beginning of LF refining, add 500Kg of synthetic slag, 100Kg of lime, 50Kg of calcium carbide and 100Kg of ferrosilicon powder, and then make fine adjustments by observing the color and consistency of the slag on site, and finally get white slag, i.e. final slag), to obtain the final slag, the composition of the final slag is as follows: CaO: 51%, SiO ₂ : 18%, MgO: 8%, Al ₂ O ₃ : 22% and FeO: 1%; the alkali of the final slag The degree R is 4.2; during the LF refining process, according to the composition inspection of molten steel, carbon wire, ferromanganese, and ferrochrome are added to fine-tune the composition, so as to ensure that the composition of molten steel obtained by LF refining is the same as that obtained after converter tapping and alloying;

The steel ladle after RH vacuum treatment enters the continuous casting machine and is produced at a casting speed of 0.7m/min. The temperature of the tundish is controlled at 1495°C, and mold slag is added to the crystallizer (consumption of mold slag is: per ton of molten steel consumption protection Slag 0.6Kg; Mold flux composition includes: 35% SiO ₂ , 22% CaO, 4% Al ₂ O ₃ , 10% K ₂ O+Na ₂ O, 19% C, and the balance Fe); the crystallizer adopts electromagnetic stirring , the current is set to 500A, and the frequency is 2.4Hz; for the secondary cooling water volume, the total water volume is controlled at 110L/min, and dynamic light reduction is adopted at the end, and the total reduction is controlled at 9mm to obtain continuous casting slabs; 3) High temperature diffusion and Billet opening: the temperature in the preheating section is 880°C, and the heat preservation is 200 minutes; the temperature in the heating section is 1220°C, and the heat preservation is 110 minutes; the temperature in the soaking section is 1260°C, and the heat preservation is 70 minutes. After 6 times of blanking, it is rolled into a hot-rolled billet with a cross-section of 160mm.

After the high temperature diffusion is completed, it directly enters the blanking machine through the roller table for 6 times of heavy reduction. The temperature of the billet is 1200°C when the rolling is started; as the blanking progresses, the temperature of the billet gradually decreases, and the temperature of the billet is 1080°C after the blanking is completed. , using 6 times of heavy reduction to roll into a hot-rolled billet with a cross-section of 160×160mm;

The reduction process of each pass using 6-pass large reduction is as follows:

Pass 1: slot width B: 320mm; slot bottom width b: 285mm; height h: 160mm;

Pass 2: slot width B: 256mm; slot bottom width b: 220mm; height h: 160mm;

Pass 3: slot width B: 226mm; slot bottom width b: 190mm; height h: 160mm;

Pass 4: slot width B: 201mm; slot bottom width b: 170mm; height h: 160mm;

Pass 5: slot width B: 175mm; slot bottom width b: 155mm; height h: 160mm;

Pass 6: slot width B: 162mm; slot bottom width b: 157mm; height h: 160mm.

4) Heating of hot-rolled slabs: the temperature in the preheating section is 760°C, and the heat preservation is 60 minutes; the temperature in the heating section is 1190°C, and the heat preservation is 40 minutes;

5) Wire rod rolling: 850°C into the finishing mill, 880°C into the reducing and sizing, and 780°C for spinning. Open the 1st and 2nd water tanks before finishing rolling, the 1st, 2nd and 3rd water tanks between finishing rolling and reducing sizing, and the 1st and 2nd water tanks before sizing and laying head. The first 5 nozzles of all water tanks are opened, the cooling water temperature is 30°C, the nozzle pressure is 0.7MPa, all the blowback nozzles are opened, and the gas pressure is 0.7MPa.

The wire is made into rolling elements through drawing and cold heading processes.

A rolling element is made of a wire obtained by a flexible second phase production control method suitable for bearing steel in this embodiment.

Example 3

A flexible second phase production control method suitable for bearing steel, comprising the following steps:

Step 1, composition control: the weight percentage of chemical composition of bearing steel is C: 0.95%, Mn: 0.25%, Si: 0.15%, S: 0.01%, Cr: 1.40%, P: 0.025%, Ti: 0.001%, Ni: 0.30%, Mo: 0.10%, Cu: 0.25%, the rest is Fe and trace impurities;

Step 2, smelting control: through converter tapping and alloying, molten steel with the following composition and temperature is obtained, which is used as the early guarantee for LF refining treatment;

The process of tapping and alloying in the converter is as follows: the molten iron loaded into the converter is required to have a C content of 3.7%, a Si content of 0.2%, a Mn content of 0.2%, and other elements are not required; after the molten iron enters the converter, it is blown with an oxygen lance 700 seconds, the carbon pulling temperature is controlled at 1560°C; during the converter smelting process, one or more of lime, fluorite, dolomite and iron oxide balls are added to ensure that the converter slag composition: CaO: 45%, SiO ₂ : 10%, MgO: 5% and the balance of FeO; carry out alloying when tapping and pay attention to the amount of slag lower than 3Kg/t, when the amount of molten steel in the ladle is 4t, add 80Kg of Al block; when the amount of molten steel in the ladle is 8t, Add recarburizer, ferrosilicon, ferromanganese, ferrochrome and synthetic slag in sequence to make the composition of molten steel meet the requirements. Synthetic slag includes 48% CaO, 34% Al ₂ O ₃ , 14% SiO ₂ and the balance MgO. The carburant is C.

Molten steel composition: C: 0.89%, Si: 0.10%, Mn: 0.27%, P: 0.0087%, S: 0.005%, Al: 0.0086%, Ti: 0.0007%, Cr: 1.33%, the rest is Fe and trace impurities; The molten steel temperature is: 1505°C. LF refining is through the slagging process (the slagging process is: at the beginning of LF refining, add 500Kg of synthetic slag, 100Kg of lime, 50Kg of calcium carbide and 100Kg of ferrosilicon powder, and then make fine adjustments by observing the color and consistency of the slag on site, and finally get White slag, i.e. final slag), to obtain final slag, the composition of final slag is as follows: CaO: 40%, SiO ₂ : 25%, MgO: 8.8%, Al ₂ O ₃ : 25% and FeO: 1.2%; the alkali of final slag The degree R is 3; during the LF refining process, according to the composition inspection of molten steel, carbon wire, ferromanganese, and ferrochrome are added to fine-tune the composition, so as to ensure that the composition of molten steel obtained by LF refining is the same as that obtained after converter tapping and alloying;

After LF refining, the molten steel enters the RH station to continue refining, the RH vacuum treatment cycle time is 40min, and the vacuum degree is 50Pa;

The steel ladle after RH vacuum treatment enters the continuous casting machine and is produced at a casting speed of 0.65m/min. The temperature of the tundish is controlled at 1475°C, and mold slag is added to the crystallizer (consumption of mold slag is: per ton of molten steel consumption protection Slag 0.2Kg; Mold flux composition includes: 35% SiO ₂ , 22% CaO, 4% Al ₂ O ₃ , 10% K ₂ O+Na ₂ O, 19% C, and the balance Fe); the crystallizer adopts electromagnetic stirring , the current is set to 480A, and the frequency is 2.35Hz; for the secondary cooling water volume, the total water volume is controlled at 100L/min, and dynamic light reduction is adopted at the end, and the total reduction is controlled at 8.5mm to obtain continuous casting slabs;

Step 3, high-temperature diffusion and billet opening: the continuous casting billet is subjected to high-temperature diffusion, and the temperature of each section is controlled as follows:

Preheating section: temperature 900°C, time 180min;

Heating section: temperature 1200℃, time 100min;

Soaking section: temperature 1250℃, time 60min;

After the diffusion is completed, it directly enters the blanking machine through the roller table for 6 times of heavy reduction. The temperature of the billet is 1180°C when the rolling is started; as the billeting progresses, the temperature of the billet gradually decreases. After the blanking is completed, the temperature of the billet is 1060°C. Using 6 passes of heavy reduction, it is rolled into a hot-rolled slab with a cross-section of 160×160mm;

The reduction process of each pass using 6-pass large reduction is as follows:

Pass 1: slot width B: 320mm; slot bottom width b: 285mm; height h: 160mm;

Pass 2: slot width B: 256mm; slot bottom width b: 220mm; height h: 160mm;

Pass 3: slot width B: 226mm; slot bottom width b: 190mm; height h: 160mm;

Pass 4: slot width B: 201mm; slot bottom width b: 170mm; height h: 160mm;

Pass 5: slot width B: 175mm; slot bottom width b: 155mm; height h: 160mm;

Pass 6: slot width B: 162mm; slot bottom width b: 157mm; height h: 160mm.

Step 4, heating the hot-rolled slab: the hot-rolled slab is rolled after being heated, and the temperature of each section is controlled as follows when the hot-rolled slab is heated:

Preheating section: temperature 800℃, time 60min;

Heating section: temperature 1150℃, time 30min;

Soaking section: temperature 1190℃, time 30min;

Step five, wire rolling:

The control points of wire rod rolling: the temperature of entering and finishing rolling is 850°C, the temperature of entering and reducing sizing is 850°C, and the temperature of spinning is 780°C. The water tanks of each section pass through the nozzle + recovery section to reach the above temperature to obtain wire rods. It is required that there are 2 sections of water tanks before finishing rolling, and the number of nozzles in each water tank is 10. The length of the water cooling section before finishing rolling is 50m; there are 2 sections of water tanks between the reducing sizing and the laying head, the number of nozzles in each water tank is 10, and the length of the entire water cooling section before finishing rolling is 20m; during production, the cooling water temperature is required to be 35°C. The pressure of the cooling nozzle is 0.5MPa, and the blowback nozzle is fully opened with a pressure of 0.5MPa.

The wire is made into rolling elements through drawing and cold heading processes.

A rolling element is made of a wire obtained by a flexible second phase production control method suitable for bearing steel in this embodiment.

Example 4

A flexible second phase production control method suitable for bearing steel, comprising the following steps:

Step 1, composition control: the weight percentage of chemical composition of bearing steel is C: 1.05%, Mn: 0.45%, Si: 0.35%, S: 0.025%, Cr: 1.65%, P: 0.01%, Ti: 0.001%, Ni: 0.20%, Mo: 0.03%, Cu: 0.10%, the rest is Fe and trace impurities;

Step 2, smelting control: through converter tapping and alloying, molten steel with the following composition and temperature is obtained, which is used as the early guarantee for LF refining treatment;

The process of tapping and alloying in the converter is as follows: the molten iron loaded into the converter is required to have a C content of 4.5%, a Si content of 0.5%, a Mn content of 0.3%, and the rest of the elements are not required; For 1000 seconds, the carbon pulling temperature is controlled at 1670°C; during the converter smelting process, one or more of lime, fluorite, dolomite, and iron oxide balls are added to ensure that the converter slag composition: CaO: 55%, SiO ₂ : 15%, MgO: 8% and the balance of FeO; carry out alloying when tapping and pay attention to the amount of slag lower than 3Kg/t, when the amount of molten steel in the ladle is 6t, add 120Kg of Al block; when the amount of molten steel in the ladle is 12t, Add recarburizer, ferrosilicon, ferromanganese, ferrochrome and synthetic slag in sequence to make the composition of molten steel meet the requirements. Synthetic slag includes 50% CaO, 35% Al ₂ O ₃ , 14% SiO ₂ and the balance MgO. The carburant is C.

Molten steel composition: C: 0.95%, Si: 0.15%, Mn: 0.32%, P: 0.0109%, S: 0.01%, Al: 0.0559%, Ti: 0.0074%, Cr: 1.43%, the rest is Fe and trace impurities; The molten steel temperature is: 1570°C. LF refining is through the slagging process (the slagging process is: at the beginning of LF refining, add 500Kg of synthetic slag, 100Kg of lime, 50Kg of calcium carbide and 100Kg of ferrosilicon powder, and then make fine adjustments by observing the color and consistency of the slag on site, and finally get white slag, i.e. final slag), to obtain the final slag, the composition of the final slag is as follows: CaO: 57.2%, SiO ₂ : 15%, MgO: 6%, Al ₂ O ₃ : 21% and FeO: 0.8%; the alkali of the final slag The degree R is 4.5; during the LF refining process, carbon wire, ferromanganese, and ferrochrome are added to fine-tune the composition according to the composition inspection of molten steel, so as to ensure that the composition of molten steel obtained by LF refining is the same as that obtained after converter tapping and alloying;

After LF refining, the molten steel enters the RH station to continue refining, the RH vacuum treatment cycle time is 50min, and the vacuum degree is 100Pa;

The steel ladle after RH vacuum treatment enters the continuous casting machine and is produced at a casting speed of 0.8m/min. The temperature of the tundish is controlled at 1500°C, and mold slag is added to the crystallizer (consumption of mold slag is: per ton of molten steel consumption protection Slag 1.0Kg; mold flux composition includes: 35% SiO ₂ , 22% CaO, 4% Al ₂ O ₃ , 10% K ₂ O+Na ₂ O, 19% C, and the balance Fe); the crystallizer adopts electromagnetic stirring , the current is set to 520A, and the frequency is 2.45Hz; for the secondary cooling water volume, the total water volume is controlled at 130L/min, and dynamic light reduction is adopted at the end, and the total reduction is controlled at 11mm to obtain continuous casting slabs;

Step 3, high-temperature diffusion and billet opening: the continuous casting billet is subjected to high-temperature diffusion, and the temperature of each section is controlled as follows:

Preheating section: temperature 850℃, time 200min;

Heating section: temperature 1250℃, time 120min;

Soaking section: temperature 1270℃, time 90min;

After the diffusion is completed, it directly enters the blanking machine through the roller table for 6 times of heavy reduction. The temperature of the billet is 1230°C when the rolling is started; as the blanking progresses, the temperature of the billet gradually decreases, and the temperature of the billet is 1100°C after the blanking is completed. Using 6 passes of heavy reduction, it is rolled into a hot-rolled slab with a cross-section of 160×160mm;

The reduction process of each pass using 6-pass large reduction is as follows:

Pass 1: slot width B: 320mm; slot bottom width b: 285mm; height h: 160mm;

Pass 2: slot width B: 256mm; slot bottom width b: 220mm; height h: 160mm;

Pass 3: slot width B: 226mm; slot bottom width b: 190mm; height h: 160mm;

Pass 4: slot width B: 201mm; slot bottom width b: 170mm; height h: 160mm;

Pass 5: slot width B: 175mm; slot bottom width b: 155mm; height h: 160mm;

Pass 6: slot width B: 162mm; slot bottom width b: 157mm; height h: 160mm.

Step 4, heating the hot-rolled slab: the hot-rolled slab is rolled after being heated, and the temperature of each section is controlled as follows when the hot-rolled slab is heated:

Preheating section: temperature 750℃, time 70min;

Heating section: temperature 1210°C, time 40min;

Soaking section: temperature 1230℃, time 40min;

Step five, wire rolling:

The control points of wire rod rolling: the temperature of entering and finishing rolling is 880°C, the temperature of entering and reducing sizing is 880°C, and the temperature of spinning is 810°C. The water tanks of each section pass through the nozzle + recovery section to reach the above temperature to obtain wire rods. It is required that there are 3 sections of water tanks before finishing rolling, the number of nozzles in each water tank is 12, and the length of the entire water cooling section before finishing rolling is 50m; there are 4 sections of water tanks between finishing rolling and reducing sizing, and the number of nozzles in each water tank is 15. The length of the water cooling section before finishing rolling is 70m; there are 3 sections of water tanks between the reducing sizing and the laying head, the number of nozzles in each water tank is 15, and the length of the entire water cooling section before finishing rolling is 30m; during production, the cooling water temperature is required to be 30°C. The pressure of the cooling nozzle is 0.6MPa, and the blowback nozzle is fully opened with a pressure of 0.6MPa.

The wire is made into rolling elements through drawing and cold heading processes.

A rolling element is made of a wire obtained by a flexible second phase production control method suitable for bearing steel in this embodiment.

Comparative example 1: (the difference between this comparative example and embodiment 1 is only: the S content is too low)

A flexible second-phase production control method suitable for bearing steel, with a specification of φ12mm, including composition control, smelting control, high-temperature diffusion and billet opening control, hot-rolled billet heating control, and wire rod rolling control. The production steps are as follows:

1) Composition control: The weight percentage of chemical composition of bearing steel is C: 1.0%, Mn: 0.34%, Si: 0.22%, S: 0.002%, Cr: 1.50%, P: 0.015%, Ti: 0.003%, Ni: 0.02 %, Mo: 0.01%, Cu: 0.02%, and the rest are Fe and trace impurities.

2) Smelting control: LF final slag composition: CaO: 45%, SiO ₂ : 22%, MgO: 10%, Al ₂ O ₃ : 22%, FeO: 1.0%. The RH vacuum treatment time is 47min, and the vacuum degree is 67Pa.

3) High-temperature diffusion and billet opening: the temperature of the preheating section is 850°C, and the heat preservation is 180 minutes; the temperature of the heating section is 1228°C, and the heat preservation is 120 minutes; the temperature of the soaking section is 1250°C, and the heat preservation is 70 minutes. After 6 times of blanking, it is rolled into a hot-rolled billet with a cross-section of 160mm.

4) Heating of hot-rolled slabs: the temperature of the preheating section is 750°C, and the heat preservation is 60 minutes; the temperature of the heating section is 1195°C, and the heat preservation is 40 minutes; the temperature of the soaking section is 1222°C, and the heat preservation is 30 minutes.

5) Wire rod rolling: 850°C for finishing mill, 878°C for sizing, and 800°C for spinning. Open the 1st and 2nd water tanks before finishing rolling, the 1st, 2nd and 3rd water tanks between finishing rolling and reducing sizing, and the 1st and 2nd water tanks before sizing and laying head. The first 5 nozzles of all water tanks are opened, the cooling water temperature is 30°C, the nozzle pressure is 0.6MPa, all the blowback nozzles are opened, and the gas pressure is 0.6MPa.

Comparative example 2: (The difference between this comparative example and Example 1 is only: in the high temperature diffusion and billet opening, the temperature of the heating section and the soaking section are all too low)

A flexible second-phase production control method suitable for bearing steel, with a specification of φ10mm, including composition control, smelting control, high-temperature diffusion and billet opening control, hot-rolled billet heating control, and wire rod rolling control. The production steps are as follows:

1) Composition control: The weight percentage of chemical composition of bearing steel is C: 1.0%, Mn: 0.35%, Si: 0.25%, S: 0.015%, Cr: 1.50%, P: 0.012%, Ti: 0.002%, Ni: 0.02 %, Mo: 0.01%, Cu: 0.02%, and the rest are Fe and trace impurities.

2) Smelting control: LF final slag composition: CaO: 46%, SiO ₂ : 21%, MgO: 10%, Al ₂ O ₃ : 22%, FeO: 1.0%. The RH vacuum treatment time is 45min, and the vacuum degree is 67Pa.

3) High-temperature diffusion and billet opening: the temperature of the preheating section is 850°C, and the heat preservation is 150 minutes; the temperature of the heating section is 1100°C, and the heat preservation is 100 minutes; the temperature of the soaking section is 1100°C, and the heat preservation is 50 minutes. After 6 times of blanking, it is rolled into a hot-rolled billet with a cross-section of 160mm.

4) Heating of hot-rolled slabs: the temperature of the preheating section is 750°C, and the heat preservation is 60 minutes; the temperature of the heating section is 1180°C, and the heat preservation is 36 minutes; the temperature of the soaking section is 1190°C, and the heat preservation is 30 minutes.

5) Wire rod rolling: entering the finishing mill at 850°C, entering into the reducing and sizing at 880°C, and spinning temperature at 790°C. Open the 1st and 2nd water tanks before finishing rolling, the 1st, 2nd and 3rd water tanks between finishing rolling and reducing sizing, and the 1st and 2nd water tanks before sizing and laying head. The first 5 nozzles of all water tanks are opened, the cooling water temperature is 30°C, the nozzle pressure is 0.6MPa, all the blowback nozzles are opened, and the gas pressure is 0.6MPa.

Comparative example 3: (the difference between this comparative example and Example 1 is only: in the heating of the hot-rolled slab, the temperature of the heating section and the soaking section are all too low, and the temperature of entering the finishing mill and the spinning temperature are all too high)

A flexible second-phase production control method suitable for bearing steel, with a specification of φ14mm, including composition control, smelting control, high-temperature diffusion and billet opening control, hot-rolled billet heating control, and wire rolling control. The production steps are as follows:

1) Composition control: The weight percentage of chemical composition of bearing steel is C: 1.0%, Mn: 0.33%, Si: 0.23%, S: 0.018%, Cr: 1.50%, P: 0.012%, Ti: 0.002%, Ni: 0.02 %, Mo: 0.01%, Cu: 0.02%, and the rest are Fe and trace impurities.

2) Smelting control: LF final slag composition: CaO: 40%, SiO ₂ : 25.1%, MgO: 8%, Al ₂ O ₃ : 26%, FeO: 0.9%. The RH vacuum treatment time is 50min, and the vacuum degree is 70Pa.

3) High-temperature diffusion and billet opening: the temperature of the preheating section is 850°C, and the heat preservation is 150 minutes; the temperature of the heating section is 1230°C, and the heat preservation is 120 minutes; the temperature of the soaking section is 1260°C, and the heat preservation is 70 minutes. After 6 times of blanking, it is rolled into a hot-rolled billet with a cross-section of 160mm.

4) Heating of hot-rolled slabs: the temperature of the preheating section is 750°C, and the heat preservation is 60 minutes; the temperature of the heating section is 1100°C, and the heat preservation is 40 minutes; the temperature of the soaking section is 1120°C, and the heat preservation is 30 minutes.

5) Wire rod rolling: 900°C into the finishing mill, 880°C into the reducing and sizing, and 900°C for spinning. Open the 1st water tank before finishing rolling, the 1st, 2nd and 3rd water tanks between finishing rolling and sizing, and the 1st water tank before sizing and laying machine. The first 5 nozzles of all water tanks are opened, the cooling water temperature is 30°C, the nozzle pressure is 0.6MPa, all the blowback nozzles are opened, and the gas pressure is 0.6MPa.

The effect comparison results of Example 1-Example 4 and Comparative Example 1-Comparative Example 3 are shown in Table 2 below.

Table 2: Effect comparison

It can be seen from Table 2 that in Comparative Example 3, the presence of network carbon carbides reduces the L ₁₀ life, but the degree of reduction is not as harmful as other second phases.

L ₁₀ life test steps are as follows:

1) Install the test steel ball in the specimen fixture, which is clamped on the test shaft and rotates with the test shaft, and the accompanying test steel ball is installed in the hole of the supporting circular table. Turn the handwheel clockwise to raise the lead screw, and when the test steel ball contacts with the test steel ball, turn the handwheel clockwise again to make the test piece slightly stressed, and the test can be carried out at this time. The test fixture is equipped with temperature and vibration sensors, which can detect the temperature and vibration of the test piece respectively.

During the test, lubricating oil provides lubrication and cooling for the sample, and the return oil is pumped back to the oil tank through the oil pipe.

2) Set the test load to 15KN (the maximum load of the instrument: 19.6kN);

3) Set the transmission shaft speed to 2500r/min (the maximum speed of the instrument is 3000r/min);

4) The instrument starts to transfer, and records the relevant measurement parameters (load, speed, temperature, current, vibration, etc.) in the computer;

5) When the load, current, vibration and other parameters reach the set alarm value, it is considered that the steel ball has fatigue failure, and the life value of the steel ball at this time is recorded.

It should be appreciated that in the above description of exemplary embodiments of the invention, in order to streamline this disclosure and to facilitate understanding of one or more of the various inventive aspects, various features of the invention are sometimes grouped together in a single embodiment, figure, or in its description. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, inventive aspects lie in less than all features of the foregoing disclosed embodiments, as the claims reflect. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

While the invention has been described in terms of a limited number of embodiments, it will be apparent to a person skilled in the art having the benefit of the above description that other embodiments are conceivable within the scope of the invention thus described. In addition, it should be noted that the language used in the specification has been chosen primarily for the purpose of readability and instruction rather than to explain or define the inventive subject matter. Accordingly, many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. With respect to the scope of the present invention, the disclosure of the present invention is intended to be illustrative rather than restrictive, and the scope of the present invention is defined by the appended claims.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (10)

1. A method of controlling the production of a flexible second phase suitable for use in bearing steel, comprising the steps of:

Step one, component control: the steel composition of the bearing steel comprises the following components in percentage by weight: 0.95-1.05%, mn: 0.25-0.45%, si: 0.15-0.35%, S: 0.01-0.025%, cr: 1.40-1.65%, P: less than or equal to 0.025 percent, ti: less than or equal to 0.002 percent, ni: less than or equal to 0.30 percent, mo: less than or equal to 0.10 percent, cu: less than or equal to 0.25 percent, and the balance of Fe and trace impurities;

step two, smelting control: tapping and alloying by a converter to obtain molten steel with the following components and temperature, wherein the molten steel is used as a preliminary guarantee of LF refining treatment;

molten steel composition: c: 0.89-0.95%, si: 0.10-0.15%, mn: 0.27-0.32%, P: 0.0087-0.0109%, S: 0.005-0.01%, al: 0.0086-0.0559%, ti:0.0007 to 0.0074%, cr: 1.33-1.43%, and the balance of Fe and trace impurities; the temperature of molten steel is as follows: 1505-1570 ℃; LF refining is carried out by a slag forming process to obtain final slag, wherein the final slag comprises the following components: caO: 40-57.2%, siO ₂ ：15~25%，MgO：6~10%，Al ₂ O ₃ : 21-25% and FeO: 0.8-1.2%; the alkalinity R of the final slag is 3-4.5; in the LF refining process, according to the component inspection condition of molten steel, adding carbon wires, ferromanganese and ferrochrome for component fine adjustment, so as to ensure that the molten steel obtained by LF refining is identical to the molten steel obtained after converter tapping and alloying;

after LF refining, the molten steel enters an RH station to be refined continuously, the circulation time of RH vacuum treatment is 40-50 min, and the vacuum degree is 50-100 Pa;

The ladle subjected to RH vacuum treatment enters a continuous casting machine, is produced by adopting a pulling speed of 0.65-0.8 m/min, the temperature of a tundish is controlled to be 1475-1500 ℃, and casting powder is added into a crystallizer; the crystallizer adopts electromagnetic stirring, the current is set to be 480-520A, and the frequency is 2.35-2.45 Hz; controlling the total water quantity to be 100-130L/min for the secondary cooling water quantity, and adopting dynamic soft reduction at the tail end, and controlling the total reduction to be 8.5-11 mm to obtain a continuous casting blank;

step three, high-temperature diffusion and cogging: the continuous casting billet is subjected to high-temperature diffusion, and the temperature of each section is controlled as follows:

preheating section: the temperature is less than or equal to 900 ℃ and the time is more than or equal to 180min;

and (3) heating: the temperature is 1200-1250 ℃ and the time is 100-120 min;

and (3) a soaking section: the temperature is 1250-1270 ℃ and the time is 60-90 min;

after the diffusion is finished, directly entering a cogging machine through a roller way to carry out 6 times of large reduction, wherein the temperature of a billet is 1180-1230 ℃ during initial rolling; gradually reducing the temperature of the steel billet along with the cogging, rolling the steel billet into a hot rolled billet with a section of 160 multiplied by 160mm by adopting 6 times of large reduction, wherein the temperature of the steel billet is 1060-1100 ℃ after the cogging is completed;

step four, heating a hot rolled blank: the hot rolled blank is rolled after being heated, and the temperature of each section of the hot rolled blank is controlled as follows when the hot rolled blank is heated:

preheating section: the temperature is less than or equal to 800 ℃ and the time is 60-70min;

And (3) heating: the temperature is 1150-1210 ℃ and the time is 30-40min;

and (3) a soaking section: the temperature is 1190-1230 ℃ and the time is 30-40min;

step five, rolling the wire rod:

the control key points of wire rod rolling are as follows: the finishing rolling temperature is 850-880 ℃, the reducing sizing temperature is 850-880 ℃, the spinning temperature is 780-810 ℃, and the water tanks of each section reach the temperature range through the nozzles and the recovery sections to obtain the wire rod.

2. The method for controlling the production of a flexible second phase suitable for bearing steel according to claim 1, wherein the converter tapping and alloying process is as follows: molten iron is filled into a converter, wherein the content of C is required to be 3.7-4.5%, the content of Si is required to be 0.2-0.5%, and the content of Mn is required to be 0.2-0.3%; after molten iron enters a converter, blowing for 700-1000 seconds by an oxygen lance, and controlling the carbon pulling temperature to 1560-1670 ℃; in the converter smelting process, one or more of lime, fluorite, dolomite and ferric oxide balls are added to ensure the components of converter slag: caO: 45-55%, siO ₂ : 10-15%, mgO: 5-8% of FeO and the balance;alloying during tapping, paying attention to slag quantity lower than 3Kg/t, and adding 80-120 Kg of Al blocks when the molten steel quantity in the ladle is 4-6 t; and when the molten steel amount in the ladle is 8-12 t, adding carburant, ferrosilicon, ferromanganese, ferrochromium and synthetic slag in sequence to ensure that the molten steel components meet the requirements.

3. The method for controlling production of flexible second phase suitable for bearing steel according to claim 2, wherein the synthetic slag comprises 48-50% CaO, 34-35% Al ₂ O ₃ 、14~15%SiO ₂ And the balance MgO.

4. A method of controlling the production of a flexible second phase suitable for use in bearing steel according to claim 3, wherein the slag formation process is: when LF refining is started, adding 500Kg of synthetic slag, 100Kg of lime, 50Kg of calcium carbide and 100Kg of ferrosilicon powder, and then carrying out fine adjustment by observing the color and the consistency of slag materials on site to finally obtain white slag, namely final slag.

5. The flexible second phase production control method for bearing steel according to claim 1, wherein the mold flux consumption is: 0.2-1.0 Kg of protective slag is consumed per ton of molten steel; the covering slag comprises the following components: 35% SiO ₂ ，22%CaO，4%Al ₂ O ₃ ，10%K ₂ O+Na ₂ O,19% c, and balance Fe.

6. A method of controlling the production of a flexible second phase suitable for use in bearing steels according to claim 1, wherein each pass of reduction process using 6 passes of high reduction is as follows:

pass 1: notch width B:320mm; groove bottom width b:285mm; height h:160mm;

pass 2: notch width B:256mm; groove bottom width b:220mm; height h:160mm;

Pass 3: notch width B:226mm; groove bottom width b:190mm; height h:160mm;

pass 4: notch width B:201mm; groove bottom width b:170mm; height h:160mm;

pass 5: notch width B:175mm; groove bottom width b:155mm; height h:160mm;

pass 6: notch width B:162mm; groove bottom width b:157mm; height h:160mm.

7. The flexible second phase production control method for bearing steel according to claim 1, wherein in the fifth step, at least 2 sections of penetrating water tanks are required before finish rolling, the number of nozzles of each water tank is more than or equal to 10, and the length of the water cooling section before the whole finish rolling is more than or equal to 40m; at least 3 sections of water penetrating tanks are arranged between finish rolling and reducing sizing, the number of nozzles of each water penetrating tank is more than or equal to 10, and the length of the water cooling section before the whole finish rolling is more than or equal to 50m; at least 2 sections of water penetrating tanks are arranged between the reducing sizing machine and the wire laying machine, the number of nozzles of each water penetrating tank is more than or equal to 10, and the length of the water cooling section before the whole finish rolling is more than or equal to 20m; when the production is carried out, the cooling water temperature is required to be less than or equal to 35 ℃, the pressure of the cooling nozzle is more than or equal to 0.5MPa, and the back blowing nozzle is fully opened, and the pressure is more than or equal to 0.5MPa.

8. The method for controlling production of a flexible second phase suitable for bearing steel according to claim 1, wherein the ratio of the number of oxide-sulfide associated second phase particles to the total number of pure oxide particles and TiA particles in the wire is (1.52-2.09): 1, a step of; in TiA, A includes C and/or N.

9. The application of the wire rod obtained by the flexible second phase production control method suitable for bearing steel according to any one of claims 1-8 in rolling bodies, wherein the wire rod is manufactured into the rolling bodies through drawing and cold heading procedures.

10. A rolling element characterized by being made of a wire rod obtained by the flexible second phase production control method for bearing steel according to any one of claims 1 to 8.