CN117144242A - On-line quenching HB 450-grade high-strength and high-toughness hot-rolled wear-resistant steel plate with yield ratio not less than 0.85, and manufacturing method and application thereof - Google Patents

Abstract

The invention discloses an online quenching type high strength and toughness HB450 grade hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85 and its manufacturing method and application. The wear-resistant steel plate includes the following chemical components: C, Si, Mn, Ti, Cr, Mo, Nb, B, Als, Ca, and at the same time meet: 3.0%≤2*Mn+Cr+Mo+10*B≤4.5%, 4.5≤Si/C≤8.0; the yield ratio of the hot-rolled wear-resistant steel plate It has reached the level of quenching and tempering heat treatment NM450, and has excellent low-temperature impact toughness and cold bending forming performance, which can better meet the requirements of dump car bodies, crane cantilevers, etc. that have strong resistance to plastic deformation, overall structural stiffness, and safety. The manufacturing of high load-bearing structural parts expands its application scope.

Description

A kind of online quenching type HB450 grade high strength and toughness hot-rolled wear-resistant steel plate with yield-strength ratio ≥0.85 and manufacturing methods and applications thereof

Technical field

The invention belongs to the technical field of wear-resistant steel, and specifically relates to an online quenching type high-strength and toughness HB450 grade hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85 and its manufacturing method and application.

Background technique

With the improvement of process technology and the upgrade of rolling cooling equipment, hot-rolled wear-resistant steel without quenching and tempering heat treatment has become a research hotspot of major steel companies and scientific research institutions. The way to strengthen products is mainly through the ultra-fast cooling system after rolling. Achieved by online quenching, the product hardness covers the HB300~HB450 level.

Compared with quenched and tempered heat-treated wear-resistant steel, online quenched hot-rolled wear-resistant steel has the advantages of short production process, low production cost, and good cold-bending forming performance. In recent years, it has high requirements in mixer tanks or rotating blades. It is widely used in structural parts with high strength, high wear resistance and easy formability. There are currently many published patents related to online quenching hot-rolled wear-resistant steel. According to different laminar cooling modes, they can be divided into one-stage continuous cooling and three-stage segmented cooling modes.

Among them, it is difficult to guarantee the plate shape pass rate, cold bending performance, and low-temperature impact performance of online quenched hot-rolled wear-resistant steel that adopts a continuous cooling mode for laminar flow cooling. For example, the patent publication number is CN112962026A, and the product hardness reaches the HB300-HB400 level. , the yield-to-strength ratio is 0.88 to 0.92, but the cooling rate is fast and the plate shape qualification rate is difficult to guarantee. At the same time, the residual stress of the martensitic structure obtained by the cooling rate is large, and the cold bending performance and low-temperature impact performance are difficult to guarantee and are not guaranteed. Mentioned; the patent number is CN107099727A. The product hardness reaches HB400 level and the yield-to-strength ratio is 0.86~0.90. However, using a continuous cooling mode, the product shape and cold bending performance are difficult to guarantee and are not mentioned.

Although laminar cooling uses a three-stage cooling mode to produce online quenched hot-rolled wear-resistant steel of different hardness levels with good plate shape and cold bending performance, the yield-to-strength ratio of these wear-resistant steels is generally low, basically around 0.80. below, or even as low as 0.50. For example, for patents with publication numbers CN110760752A, CN111334720A, CN108411203A, CN114086084A, CN111057936A, and CN112760560A, the yield-strength ratios are 0.74~0.84, 0.68~0.73, ≤0.75, 0.50~0.65, and 0.6 respectively. 3～0.66, 0.69～0.71, product hardness reaches HB300 level. The patent number is CN111270160A, the yield-to-strength ratio is 0.72 to 0.79. The patent number is CN111593264A, the yield-strength ratio is not mentioned, and the product hardness reaches the HB360 level. The patents with publication numbers CN111440996B, CN113930670A, CN112831731A, and CN113699437A, the yield-strength ratios are ≤0.70, 0.70~0.76, 0.75~0.79, 0.61~0.71 respectively. The product hardness reaches HB400 level; the patent with publication number CN113584378A, the yield-strength ratio is ≤0.70, 0.70~0.76, 0.75~0.79, 0.61~0.71 respectively. The strong ratio is 0.77 ~0.87, the yield-to-strength ratio of the product cannot be stably controlled above 0.85, mostly lower than 0.85, and the low-temperature impact performance of the product is not mentioned. The patent with publication number CN112760559A has a yield-to-strength ratio of 0.72 to 0.73; the patents with publication numbers of CN112501501A, CN113930669A, CN113174530A, CN112708824A, and CN113637894A have a yield-to-strength ratio of 0.70 to 0.73, 0.72 to 0.73, and 0 respectively. .66～0.79, 0.67～0.76, 0.77~0.84, the product hardness reaches HB450 level, and low temperature impact toughness is not mentioned.

The yield ratio of traditional quenched and tempered heat-treated wear-resistant steel is above 0.80, concentrated in the range of 0.84 to 0.90. However, the yield ratio of online quenching-type hot-rolled wear-resistant steel disclosed in the existing technology is relatively low, resulting in the replacement of online quenching-type wear-resistant steel. When quenched and tempered heat-treated wear-resistant steel is used in load-bearing structural parts such as dump carriage bodies or crane arms, when the tensile strength and hardness of the materials are the same, a low yield-strength ratio will cause the load-bearing structural parts to easily or prematurely undergo plastic deformation. The overall stiffness of the structural parts is reduced, and the dump car body or the crane boom is easily deformed, which is not conducive to extending the service life and ensuring structural safety. Therefore, the low yield-to-strength ratio restricts the application range of online quenched hot-rolled wear-resistant steel to a certain extent.

To sum up, the products disclosed in the prior art are online quenched hot-rolled wear-resistant steel with a hardness of HB300 to HB450. Laminar cooling adopts a one-stage continuous cooling mode, and the yield-to-strength ratio reaches more than 0.85, but the product shape qualification rate is , cold bending performance and low temperature impact performance are difficult to guarantee. When laminar cooling adopts the three-stage cooling mode, the yield-strength ratio is basically below 0.80, or even as low as 0.5, or the yield-strength ratio cannot be stably controlled above 0.85 and the low-temperature impact toughness is not mentioned, so the yield-strength ratio is low to a certain extent. Restricts the application scope of online quenched hot-rolled wear-resistant steel.

Contents of the invention

In order to solve the above technical problems, the present invention provides an online quenching type high-strength and tough HB450 grade hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85 and its manufacturing method and application. The yield-strength ratio of the hot-rolled wear-resistant steel plate reaches the quenching and tempering heat treatment It is at the level of NM450 and has excellent low-temperature impact toughness and cold bending forming performance, which can better meet the load-bearing requirements of dump truck bodies, crane cantilevers, etc. that require strong material resistance to plastic deformation, overall structural stiffness and safety. Manufacturing of structural parts has expanded its application scope.

The technical solutions adopted by the present invention are as follows:

A kind of online quenching type HB450 grade high strength and toughness hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85. The chemical composition and weight percentage content of the wear-resistant steel plate are: C: 0.17~0.23%; Si: 1.00~1.50%; Mn: 1.35～1.85%; Ti: 0.08～0.15%; Cr: 0.35～0.85%; Mo: 0.20～0.40%; Nb: 0.015～0.050%; B: 0.0010～0.0030%; Als: 0.020～0.060%; Ca: 0.0015 ~0.0050%; P: ≤0.012%; S: ≤0.003%; N: ≤0.0030%; O: ≤0.0030%; the rest is Fe and inevitable inclusions, and must also meet: 3.0% ≤ 2*Mn+Cr +Mo+10*B≤4.5%, 4.5≤Si/C≤8.0.

The metallographic structure of the wear-resistant steel plate is martensite, ferrite and nanoscale precipitated carbides.

In the metallographic structure of the wear-resistant steel plate, the volume fraction of martensite is ≥95%, the width of martensite laths is ≤0.30 μm; the volume fraction of ferrite is ≤5%, and the average grain size of ferrite is ≤4 μm; nanometer The size of precipitated carbides is ≤25nm and the volume fraction is 0.16~0.25%.

The wear-resistant steel plate has a tensile strength of ≥1250MPa, a tensile strength of ≥1450MPa, a yield ratio of ≥0.85, a hardness of ≥450HB, a -40°C impact energy A _kv of ≥70J, a cold bending performance of 150°, and D=4a.

The invention also provides a manufacturing method for the online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85, which includes the following steps: smelting, continuous casting, heating, rolling, cooling, coiling, leveling and flattening. .

In the continuous casting step, the thickness of the slab is 230mm.

In the heating step, the slab exit temperature is 1250-1300°C, the slab temperature is controlled to be ≥1230°C and the holding time is ≥35 minutes. The last two sections of the heating furnace use a reducing atmosphere, and the air excess coefficient is <1.0.

In the rolling step, a 2-stand rough rolling and a 7-stand finishing hot rolling mill are used for rolling. The rough rolling and final rolling temperature _R2DT is 1080~1130°C, and the cumulative rolling reduction rate of rough rolling is ≥80. %, the cumulative reduction rate of finishing rolling is ≥85%, and the final rolling temperature FDT of finishing rolling is 850~900℃.

In the cooling and coiling steps, the strip is quenched online after rolling, using a segmented cooling mode. The first segment is cooled at a cooling rate of 5 to 10°C/s for 1 to 5 s, and the second segment is cooled at a cooling rate of ≥100°C/s. Rapid cooling to 630~680℃, the third stage air cooling, air cooling time is 8~15s, the fourth stage is cooled to 200~300℃ at a cooling speed of ≥60℃/s for coiling, and after coiling and unloading, cover it with heat preservation The cover should be insulated. After keeping it warm for 60 to 90 minutes, remove the heat preservation cover and air-cool to room temperature.

In the flattening step, the rolling force of the whole machine is 700-1000t, the roll bending force is 90-120t, and the flattening speed is 30-50m/min.

The yield ratio ≥0.85 online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate provided by the invention has a chemical composition of medium C, medium Mn, high Si, high Ti and Cr, Mo, Nb, B alloy design, and at the same time needs to meet 3.0% ≤2*Mn+Cr+Mo+10*B≤4.5%, Mn, Cr, Mo, and B are all alloy elements that improve the stability of austenite and will inhibit the transformation of austenite to ferrite. According to thermal simulation And CCT analysis results show that the content of Mn, Cr, Mo, and B is too high. When 2*Mn+Cr+Mo+10*B>4.5%, there is basically no ferrite formation, which not only reduces the plastic toughness of the material, but also makes TiC difficult to Precipitation occurs in the cooling air cooling section, and the precipitation strengthening effect is greatly weakened; the content of Mn, Cr, Mo, and B is too low, and when 2*Mn+Cr+Mo+10*B<3.0%, the hardenability of the material cannot be guaranteed, and the material cannot be guaranteed. strength and hardness. in,

C: 0.17% ~ 0.23%. As a basic element in steel, C plays a very important role in improving the strength and hardness of steel. In order to ensure that the material hardness reaches 450HB, the material strengthening method is phase change + precipitation + fine grain strengthening. In this case, it is necessary to ensure that the C content is above 0.16%, but the C content should not be too high. On the one hand, according to the solid solubility product formula of the second phase in steel, if the C content is too high, the full solid solution temperature of TiC is >1300°C. As a result, Ti cannot be completely dissolved into the matrix during the heating process, and the subsequent TiC precipitates are all sub-micron in size, which reduces the improvement in strength caused by precipitation strengthening; on the other hand, it is not conducive to the control of the depth of the decarburization layer on the surface of the steel plate, resulting in The surface hardness is reduced, which is not conducive to the control of performance uniformity in the thickness direction; furthermore, it is difficult to form a small amount of ferrite in the air cooling section during the cooling process, which is not conducive to the impact toughness, welding, and cold bending performance of the material.

Si: 1.00% to 1.50%. Si has the effect of solid solution strengthening and can improve the strength of the material. At the same time, the use of high Si composition design can promote the formation of a certain proportion of ferrite structure. The higher the C content, the higher the Si content. However, the C content and Si content need to meet 4.5≤Si/C≤8.0. Considering that this application corresponds The C content is 0.17% ~ 0.23%. According to the results of thermal simulation and CCT analysis, it is difficult to generate a ferrite structure when Si/C<4.5. When Si/C>8.0, the ferrite ratio is >10%, which cannot guarantee the strength of the material. ,hardness. However, if the Si content is too high, the brittleness of the material will increase, which will deteriorate the impact toughness and the red rust on the surface of the strip will be severe and difficult to remove, which is not conducive to the control of surface quality.

Mn: 1.35% ~ 1.85%. As a strengthening element of steel, Mn can significantly improve the hardenability of steel and increase the strength of steel. In order to ensure that the material hardness reaches 450HB, the Mn content needs to be above 1.35%, but the Mn content should not be too high. , Too high Mn content can easily lead to segregation in the center of the billet, and is not conducive to the impact toughness, welding performance and formability of the material.

Cr: 0.35% ~ 0.85%. The purpose of adding Cr is to improve the hardenability of steel and improve the strength, hardness and wear resistance of steel. On the other hand, Cr has good oxidation resistance and is compatible with carbon elements. The affinity is large. Considering that the C and Si content in this application are relatively high, decarburization problems are prone to occur. Adding ≥0.35% Cr can significantly increase the diffusion activation energy of carbon, strongly prevent the diffusion of carbon, and effectively reduce the total decarburization and decarburization of steel. The depth of the semi-decarburized layer is beneficial to the control of the depth of the decarburized layer of steel.

Ti: 0.08% ~ 0.15%. Ti is an important element in the present invention. The purpose of adding a higher content is, on the one hand, to synergize with the Nb element during the heating process to increase the refining effect of the original austenite grains; on the other hand, During the heating process, Ti dissolved in the matrix can precipitate a large amount of nano-scale TiC in the cooling air cooling section, which has a precipitation strengthening effect and improves the strength and hardness of the material. Furthermore, Ti can fix excess B and reduce FeB, etc. The number of grain boundary precipitates makes it dispersedly distributed on the ferrite matrix, which is beneficial to improving the strength of the ferrite matrix, thereby narrowing the difference between the strength of the ferrite matrix and the strength of the martensite phase, and improving the yield strength. ratio as well as strength, hardness and wear resistance. In order to give full play to the precipitation strengthening effect of Ti, the Ti content must be no less than 0.080%. Considering that the corresponding C content of the present invention is 0.17% to 0.23%, according to the analysis of the solid solubility product formula, when the Ti content is greater than 0.15%, all TiC The solid solution temperature is >1346°C. Ti that cannot be completely dissolved in the matrix during the heating process will form a large amount of hard micron-level TiC after rolling and cooling. Micron-level TiC will become the source of crack initiation, which is not conducive to material plasticity, low-temperature impact toughness and Cold forming performance.

Nb: 0.015% ~ 0.050%. The combined addition of Nb and Ti has a more significant effect on austenite grain refinement during heating and rolling than adding Nb or Ti alone. Nb mainly reduces austenite through synergy with Ti during the heating process. The strong solute dragging effect at the grain boundary and the increase in recrystallization temperature during the rolling process refine the austenite grains to achieve the final effect of refining the ferrite and martensite grains, and the refined grains have an important impact on the yield strength of the material. The increase is greater than its increase in tensile strength, which can improve the yield-to-strength ratio of the material. At the same time, adding Nb to refine the grains is beneficial to improving the material's low-temperature toughness and cold bending properties.

Mo: 0.20% ~ 0.40%. On the one hand, Mo has good high-temperature thermal stability, which can prevent the size coarsening of carbides precipitated in the air-cooling section during the cooling process, achieve better precipitation strengthening effects, and thus help improve ferrite. The strength of the matrix improves the yield ratio; on the other hand, there is a strong binding force between Mo and C. Since the C content in the present invention is 0.17% to 0.23% and the C content is relatively high, pearlite structure is easily formed during the cooling process. , adding Mo can fix excess C and avoid the formation of pearlite structure during the cooling process.

B: 0.0010% ~ 0.0030%. As another important element in the present invention, B can improve the stability of austenite. On the one hand, it can avoid the formation of pearlite structure in the cooling air cooling section; on the other hand, it can delay the transformation of austenite into iron. The transformation of the element body avoids the problem of the formation of a large amount of soft phase ferrite structure and the reduction of material strength and hardness due to the need to extend the air cooling time in the cooling air cooling section to increase the amount of TiC precipitation and improve the precipitation strengthening effect. Adding a certain content of B and appropriately extending the air cooling time not only stably controls the proportion of ferrite, but also increases the number and proportion of TiC precipitates, improves the precipitation strengthening effect and the strength of the ferrite base material, which is beneficial to improving the yield ratio.

Als: 0.020% ~ 0.060%. Als is mainly used as a deoxidizer, and can react with N to form AlN nail-rolled grain boundaries, which can refine grains.

Ca: 0.0015% ~ 0.0050%: The affinity of Ca to S is greater than Mn. Ca can change the shape of steel sulfides (MnS) and transform easily deformable long MnS inclusions into spindle-shaped (Ca, Mn) S inclusions while avoiding the formation of Type II sulfides, thereby reducing the anisotropy of the steel plate and improving the plasticity and low-temperature impact toughness of the steel plate. Considering that the S content is controlled at a low level in this application, the Ca content should be controlled between 0.0015% and 0.0050%.

P and S, as impurity elements, will have adverse effects on the plasticity, forming, welding and other properties of steel. The lower their content, the better. Considering production cost factors, in actual production, control P: ≤0.012% and S: ≤0.003%.

O and N are harmful gas elements. Since Ti is extremely active, it will preferentially react with O and N to precipitate, affecting the yield of Ti, the precipitation amount of TiC and the precipitation strengthening effect. Based on the Ti yield and improving the precipitation strengthening effect of TiC Consider, N: ≤0.0030%; O: ≤0.0030%.

In the structure design of hot-rolled wear-resistant steel, the present invention takes martensite, ferrite and nano-precipitated carbides as target structures. By refining the grain size of ferrite and martensite and the width of martensite laths, the strength, yield ratio and low-temperature impact toughness of the material can be improved; by introducing nanoscale carbides on the ferrite matrix, improving The proportion of precipitates, enhancing its pinning effect on dislocations and improving the strength of the ferrite matrix can reduce the difference between the strength of the ferrite matrix and the strength of the martensite matrix, and achieve the purpose of improving the material yield ratio. ; By increasing the proportion of martensite to ≥95%, controlling the self-tempering effect of martensite and its decomposed carbide pinning dislocations, the strength and yield ratio of the material are improved; at the same time, ≤5% of the soft phase iron is retained The purpose of the body is based on the material's cold bending formability and low-temperature impact toughness.

In the manufacturing method of the online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate provided by the present invention with a yield ratio of ≥0.85, high-temperature heating is used in the heating process, and emphasis is placed on extending the heat preservation time of the high-temperature section rather than the total time in the furnace. The purpose of high-temperature heating and casting billet discharge temperature is 1230-1300°C. On the one hand, it is to increase the proportion of Ti atoms dissolved in the matrix and create conditions for the precipitation of a large amount of TiC precipitates during the cooling and coiling process; on the other hand, it is to control The slab temperature during high-pressure water descaling before rough rolling is >1173°C to ensure that the fayalite Fe ₂ SiO ₄ is in a molten state and is easy to remove, and to prevent Fe ₂ SiO ₄ from being nail-rolled on the surface of the steel plate matrix and making it difficult to remove. The purpose of controlling the casting temperature to be ≥1230℃ and the holding time to be ≥35min is to allow sufficient time for Ti atoms to fully dissolve into the matrix, and to prevent the austenite grains from being too coarse and not conducive to improving strength, and the furnace-generated iron oxide scale being too thick is not conducive to improving strength. Surface quality control. The last two sections of the heating furnace use a reducing atmosphere with an excess air coefficient of <1.0. This is mainly based on the control of the depth of the decarburization layer on the surface of the steel plate to avoid the problem of low surface hardness caused by too much depth of the decarburization layer on the surface of the steel plate.

In terms of rolling process, the rough rolling stage gives full play to the characteristics of high temperature and large deformation. The cumulative reduction rate of rough rolling is ≥80% in order to fully recrystallize the original austenite and increase the cumulative deformation amount and control in the non-recrystallized area in the finishing rolling stage. The cumulative reduction rate of finishing rolling is ≥85%, which is conducive to generating larger cumulative strain energy, increasing nucleation sites, refining the austenite grain size, and transforming austenite into ferrite or martensite grains. size, while improving the strength of the material, the increase in the yield strength of refined grains is greater than the increase in the tensile strength, which can significantly increase the material's yield-strength ratio and help improve the low-temperature impact toughness of the material; at the same time, fine grains The austenite grain size can be refined, the martensite grain size transformed from austenite can be refined, and the size of martensite lath bundles and lath blocks can be reduced, while the size of martensite lath bundles and lath blocks can be reduced. and yield strength are consistent with the Hall-Petch formula, which can improve the material yield strength and yield-strength ratio.

In the cooling process, the control strategy of segmented cooling + heat preservation after coiling is adopted. The purpose of the first stage of slow cooling is to add higher content of Mn, Cr, Mo, B and other stabilizing austenite elements, slow cooling after rolling Without forming ferrite or pearlite structure, the deformed austenite can undergo a dynamic recovery process to form equiaxed austenite with a relatively regular shape, which is beneficial to improving the martensite or ferrite structure after phase transformation. Uniformity, improved performance uniformity. The purpose of the second stage of rapid cooling is to increase the degree of phase transformation supercooling, increase nucleation sites, and refine the ferrite grain size formed by austenite transformation and the martensite grain size formed by retained austenite transformation. , the width of the martensite plate can not only improve the material's yield-strength ratio, but also improve the material's low-temperature impact toughness and cold bending formability; the main purpose of cooling to 630~680℃ is to achieve the optimal temperature for ferrite phase transformation in this temperature range interval is also the suitable precipitation temperature range for TiC precipitates. Under the premise that B and Mo elements can control the proportion of ferrite within a certain range, a larger proportion of nanoscale TiC precipitates can be quickly formed per unit time, and TiC can easily be in place. Precipitation near dislocations plays the role of pinning dislocations and enhancing the strength of the ferrite matrix, which can reduce the difference between the strength of the ferrite matrix and the strength of the martensite phase and increase the yield-strength ratio. The purpose of the third stage of air cooling is to give a certain time for TiC to fully precipitate. The present invention controls the time of the third stage of air cooling to be 8 to 15 seconds. If the air cooling time is too short, the amount of TiC precipitated will be small, which will affect dislocation pinning and ferrite. The increase in matrix strength is small; if the air cooling time is too long, the proportion of ferrite increases and the grain size increases, and the proportion of TiC precipitates is large, but the increase in material strength by precipitation strengthening is less than the proportion of ferrite for phase transformation strengthening. Reducing the amount will actually reduce the material strength, hardness and yield-to-strength ratio. The purpose of the fourth stage of cooling is to transform the untransformed austenite structure into a martensite structure. The cooling rate must be greater than the critical cooling rate for martensite structure transformation. The coiling temperature must be between M _f + (30 ~ 80℃ ), if the coiling temperature is too high, the degree of martensite decomposition will be severe and the number of precipitated carbides will be large. Although the pinning effect of carbides on dislocations and the yield ratio can be improved, the material strength and hardness will decrease significantly. It cannot reach 450HB; if the coiling temperature is too low, although the material strength and hardness can reach 450HB, the martensite lath does not decompose, the number of precipitated carbides is small, and the pinning effect on dislocations is small, resulting in yield strength The strength is low, the yield-strength ratio is ≤0.75, and the martensite residual stress corresponding to low-temperature coiling is large, and the impact toughness of the material is poor. After coiling, a thermal insulation cover is used for insulation. On the one hand, it further enhances the martensite self-tempering effect and improves the pinning effect of precipitated carbides on dislocations and the yield ratio; on the other hand, it is beneficial to the temperature in the length and width directions of the hot coil. , mechanical properties and uniformity control of residual stress, which is conducive to improving the plate quality and improving the flatness of the plate.

As an important process of the present invention, smoothing can increase the dislocation density and work hardening degree of the material. Especially for phase change-strengthened high-strength steel, the smoothing process can increase the yield strength by 100 to 200 MPa, while the tensile strength is basically not influence, which can significantly increase the yield strength and yield ratio, ensuring that the yield ratio of the material is ≥0.85. At the same time, smoothing can improve the shape of the wear-resistant steel plate and increase its shape compliance rate.

This invention controls the yield ratio of hot-rolled wear-resistant steel from the perspective of the entire process of steelmaking-heating-rolling-cooling-coiling-smoothing, rather than solely through steelmaking, heating, rolling, cooling, and coiling. Optimize and control a certain process in taking and leveling. The root cause of the yield-strength ratio problem of hot-rolled wear-resistant steel lies in the dislocation state in the ferrite matrix caused by the interaction between soft phase ferrite and hard phase martensite, which involves the volume fraction of soft phase and hard phase. , size, internal microstructure and the degree of pinning of dislocations by precipitates, etc., which further involves chemical composition, heating, rolling, cooling, coiling and other processes that affect the degree of deformation, cooling rate, temperature parameters, and the work hardening of materials. level of smoothing process. Therefore, it is necessary to control the yield-strength ratio from the perspective of the entire process and find out reasonable process parameters that match each process before and after.

Compared with the prior art, the present invention has the following beneficial effects:

1) The hot-rolled wear-resistant steel produced by the method of the present invention has a yield strength of ≥1250MPa, a tensile strength of ≥1450MPa, a yield ratio of ≥0.85, and a hardness of ≥450HB. Both the yield and hardness of the product reach the quenched and tempered heat-treated wear-resistant steel. The physical performance level of NM450 solves the problem of low yield-strength ratio of online quenched hot-rolled wear-resistant steel, and better meets the requirements for materials such as dump truck bodies and crane cantilevers with strong plastic deformation resistance, overall structural stiffness and plastic deformation resistance. The manufacturing of very high load-bearing structural parts, and the production process eliminates the need for quenching and tempering heat treatment, and the production cost is about 1,000 to 1,200 yuan/t lower than that of quenching and tempering heat treatment NM450.

2) The cold-bending performance of the hot-rolled wear-resistant steel produced by the method of the present invention reaches 150°, D=4a is qualified, the impact power A _kv at -40°C is ≥70J, and the cold-bending performance and low-temperature impact toughness are better than those of quenched and tempered steel. Cold bending properties and low temperature impact toughness of heat treated wear-resistant steel NM450.

Description of the drawings

Figure 1 is a metallographic structure diagram of the hot-rolled wear-resistant steel in Example 1, and its metallographic structure is 96.88% M+3.12% F;

Figure 2 is a TEM image of martensite laths in the metallographic structure of the hot-rolled wear-resistant steel in Example 1;

Figure 3 is a TEM image of the precipitates in the metallographic structure of the hot-rolled wear-resistant steel in Example 1

Figure 4 is the metallographic structure diagram of the hot-rolled wear-resistant steel in Comparative Example 1, and its metallographic structure is 87.32%M+12.68%F;

Figure 5 is the metallographic structure diagram of the hot-rolled wear-resistant steel in Comparative Example 2, and its metallographic structure is 91.25%M+8.75%F;

Figure 6 is a metallographic structure diagram of the hot-rolled wear-resistant steel in Comparative Example 3, and its metallographic structure is 93.36%M+6.64%F;

Figure 7 is a metallographic structure diagram of the hot-rolled wear-resistant steel in Comparative Example 5. The metallographic structure is 93.7%M+6.3%F;

Figure 8 is a metallographic structure diagram of the hot-rolled wear-resistant steel in Comparative Example 7, and its metallographic structure is 100% M.

Detailed ways

The invention provides an online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85. The chemical composition and weight percentage content of the wear-resistant steel plate are: C: 0.17~0.23%; Si: 1.00~1.50 %; Mn: 1.35～1.85%; Ti: 0.08～0.15%; Cr: 0.35～0.85%; Mo: 0.20～0.40%; Nb: 0.015～0.050%; B: 0.0010～0.0030%; Als: 0.020～0.060% ; Ca: 0.0015～0.0050%; P: ≤0.012%; S: ≤0.003%; N: ≤0.0030%; O: ≤0.0030%; the rest is Fe and inevitable inclusions, and must also meet: 3.0% ≤ 2 *Mn+Cr+Mo+10*B≤4.5%, 4.5≤Si/C≤8.0.

The manufacturing method of the online quenching HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85 includes the following steps: smelting, continuous casting, heating, rolling, cooling, coiling, leveling and leveling.

In the continuous casting step, the thickness of the slab is 230mm.

In the heating step, the slab exit temperature is 1250-1300°C, the slab temperature is controlled to be ≥1230°C and the holding time is ≥35 minutes. The last two sections of the heating furnace use a reducing atmosphere, and the air excess coefficient is <1.0.

In the rolling step, a 2-stand rough rolling and a 7-stand finishing hot rolling mill are used for rolling. The rough rolling and final rolling temperature _R2DT is 1080~1130°C, and the cumulative rolling reduction rate of rough rolling is ≥80. %, the cumulative reduction rate of finishing rolling is ≥85%, and the final rolling temperature FDT of finishing rolling is 850~900℃.

In the cooling and coiling steps, the strip is quenched online after rolling, using a segmented cooling mode. The first segment is cooled at a cooling rate of 5 to 10°C/s for 1 to 5 s, and the second segment is cooled at a cooling rate of ≥100°C/s. Rapid cooling to 630~680℃, the third stage air cooling, air cooling time is 8~15s, the fourth stage is cooled to 200~300℃ at a cooling speed of ≥60℃/s for coiling, and after coiling and unloading, cover it with heat preservation The cover should be insulated. After keeping it warm for 60 to 90 minutes, remove the heat preservation cover and air-cool to room temperature.

In the flattening step, the rolling force of the whole machine is 700-1000t, the roll bending force is 90-120t, and the flattening speed is 30-50m/min.

The present invention will be described in detail below with reference to examples.

The chemical components and weight percentages in each example and comparative example are shown in Table 1.

Table 1 Chemical compositions of Examples and Comparative Examples

Table 2 Rolling process parameters of Examples and Comparative Examples

Table 3 Cooling process parameters of Examples and Comparative Examples

Table 4. Flattening process parameters of Examples and Comparative Examples

Table 5 Mechanical properties of Examples and Comparative Examples

Note: Comparative Examples 8-9 are all NM450 steel plates produced using the quenching and tempering heat treatment process. Their chemical composition, rolling, and heat treatment production processes are as follows.

Comparative example 8:

NM450 steel plate composition: C: 0.21%; Si: 0.27%; Mn: 1.25%; P: 0.013%; S: 0.002%; Cr: 0.20%; Mo: 0.25%; Nb: 0.025%; Ti: 0.025%; B : 0.0018%; Als: 0.045%.

NM50 steel plate manufacturing method: molten steel is smelted in a converter, refined outside the furnace, and continuously cast into slabs. The heating temperature of the slab is 1230°C, the starting temperature of rough rolling is 1150°C, the cumulative reduction rate of rough rolling is 84.35%, the cumulative reduction rate of finishing rolling is 83.33%, the final rolling temperature of finishing rolling is 895°C, and laminar cooling is performed after rolling. , the coiling temperature is 660°C, and air cooled to room temperature after coiling. After rolling, the steel plate is subjected to quenching and tempering heat treatment, including quenching and tempering. The quenching process is quenching temperature 950°C, holding time 30 minutes; the tempering process is: tempering temperature 220°C, holding time 30 minutes, finished product thickness specification 6.0mm.

Comparative example 9:

NM450 steel plate composition: C: 0.19%; Si: 0.21%; Mn: 1.30%; P: 0.010%; S: 0.001%; Cr: 0.25%; Mo: 0.20%; Nb: 0.022%; Ti: 0.028%; B : 0.0015%; Als: 0.040%.

NM50 steel plate manufacturing method: molten steel is smelted in a converter, refined outside the furnace, and continuously cast into slabs. The slab heating temperature is 1230°C, the rough rolling opening temperature is 1145°C, the finishing rolling temperature is 888°C, the cumulative rolling reduction rate of rough rolling is 84.35%, and the cumulative reduction rate of finishing rolling is 83.33%. Laminar cooling is performed after rolling. , the coiling temperature is 645℃, the steel plate is subjected to quenching and tempering heat treatment after rolling, including quenching and tempering. The quenching process is quenching temperature 945℃, holding time 30min; the tempering process is: tempering temperature 230℃, holding time 30min, the finished product Thickness specification 4.0mm.

The above detailed description of an online quenching type high strength and toughness HB450 grade hot-rolled wear-resistant steel plate with a yield ratio ≥0.85 and its manufacturing method and application is illustrative rather than restrictive. Several embodiments are enumerated, so changes and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims (10)

1. An online quenching-type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85, characterized in that the chemical composition and weight percentage of the wear-resistant steel plate are: C: 0.17 to 0.23%; Si: 1.00 ~1.50%; Mn: 1.35~1.85%; Ti: 0.08~0.15%; Cr: 0.35~0.85%; Mo: 0.20~0.40%; Nb: 0.015~0.050%; B: 0.0010~0.0030%; Als: 0.020~ 0.060%; Ca: 0.0015～0.0050%; P: ≤0.012%; S: ≤0.003%; N: ≤0.0030%; O: ≤0.0030%; The rest is Fe and inevitable inclusions, and must simultaneously meet: 3.0%≤2*Mn+Cr+Mo+10*B≤4.5%, 4.5≤Si/C≤8.0. 2. The online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio ≥ 0.85 according to claim 1, characterized in that the metallographic structure of the wear-resistant steel plate is martensite, ferrite and nanometer Precipitated carbides. 3. The online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio of ≥0.85 according to claim 1, characterized in that, in the metallographic structure of the wear-resistant steel plate, the volume fraction of martensite is ≥95%. , martensite lath width ≤ 0.30 μm; ferrite volume fraction ≤ 5%, average ferrite grain size ≤ 4 μm; nanoscale precipitated carbide size ≤ 25 nm, volume fraction 0.16 to 0.25%. 4. The online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate according to any one of claims 1-3, characterized in that the wear-resistant steel plate has a strength of ≥1250MPa and a tensile strength of ≥1450MPa. , Yield-strength ratio ≥0.85, hardness ≥450HB, -40℃ impact energy A _kv ≥70J, and cold bending performance reaches 150°, D=4a passed. 5. The manufacturing method of the online quenching type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield ratio ≥ 0.85 according to any one of claims 1-4, characterized in that the manufacturing method includes the following steps: smelting, continuous Casting, heating, rolling, cooling, coiling, smoothing and flattening. 6. The manufacturing method according to claim 5, characterized in that in the heating step, the slab exit temperature is 1250-1300°C, and the holding time for controlling the slab temperature ≥ 1230°C ≥ 35 min, the last two sections of the heating furnace Using a reducing atmosphere, the air excess coefficient is <1.0. 7. The manufacturing method according to claim 5, characterized in that, in the rolling step, a 2-stand rough rolling and a 7-stand finishing hot rolling mill are used for rolling, and the rough rolling and final rolling temperature is R ₂ DT is 1080~1130℃, the cumulative rolling reduction rate of rough rolling is ≥80%, the cumulative rolling reduction rate of finishing rolling is ≥85%, and the final rolling temperature FDT of finishing rolling is 850~900℃. 8. The manufacturing method according to claim 5, characterized in that in the cooling and coiling steps, the strip is quenched online after rolling, using a segmented cooling mode, and the first segment is cooled at 5-10°C/s. Rapid cooling is 1~5s, the second stage is cooled to 630~680℃ at a cooling speed of ≥100℃/s, the air cooling and air cooling time of the third stage is 8~15s, and the fourth stage is cooled to a cooling speed of ≥60℃/s. Coil at 200~300℃; after coiling and unloading, cover with an insulation cover for thermal insulation. After 60~90 minutes of insulation, remove the insulation cover and cool to room temperature in air. 9. The manufacturing method according to claim 5, characterized in that, in the flattening step, the rolling force of the flattening machine is 700-1000t, the bending force is 90-120t, and the flattening speed is 30-50m/min. 10. The online quenching-type HB450 grade high-strength hot-rolled wear-resistant steel plate with a yield-strength ratio ≥ 0.85 as described in any one of claims 1-4 is suitable for the application of steel for dump car bodies and crane cantilevers.