CN106119736A - A kind of martensite aged stainless steel - Google Patents

Abstract

It is an object of the invention to provide a kind of novel martensitic aged stainless steel 1Cr14Co13Mo5, it is characterised in that described martensite aged stainless steel is 1Cr14Co13Mo5, it forms and percentage by weight is: Cr:12.8 15.2, Co:12 14.5, Mo:4.0 5.5, Ni:0.5 2, C:0.13 0.19, Mn :≤0.20, Nb:0.2 0.3, Ti:0.2 0.3, P :≤0.02, S :≤0.01, Si :≤0.20, O≤0.005, N≤0.02, Fe surplus.Experiment shows, this strength of alloy reaches 1900Mpa, impact flexibility a_k60J/cm², hardness HRC50, combination of strength and toughness is good.

Description

A maraging stainless steel

technical field

The invention belongs to the field of alloys, and in particular provides a novel maraging stainless steel 1Cr14Co13Mo5 with good strength and toughness coordination.

Background technique

Because of its good strength, toughness and corrosion resistance, maraging stainless steel is widely used in load-bearing and corrosion-resistant (or high-temperature) components in high-tech fields such as aviation, aerospace, nuclear technology, ships, and advanced machinery manufacturing. This type of steel adopts the means of superposition of low-carbon martensitic transformation strengthening and aging strengthening effects to make the steel have super high strength and excellent comprehensive performance. Since the 1970s, maraging stainless steel has risen to a new level in terms of alloy composition design, smelting process and strength level. Especially in 1997, Martin et al. applied for the patent of maraging stainless steel Custom465, which changed the strength level from 1600MPa pushed to 1800Mpa. China successfully designed and developed a new type of ultra-low carbon maraging stainless steel F863 from 2002 to 2005. This steel is a Cr-Ni-Co-Mo maraging stainless steel independently developed by China with independent intellectual property rights. , its intensity reaches the level of 1940Mpa ^[4] .

However, the current development of maraging stainless steel is also facing a prominent problem. The combination of strength and toughness is not excellent enough. How to improve the toughness index while ensuring the high strength of maraging stainless steel has important theoretical significance and application value. . The invention provides a novel maraging stainless steel 1Cr14Co13Mo5 with good corrosion resistance and strength-toughness matching.

Contents of the invention

The object of the present invention is to provide a new type of maraging stainless steel 1Cr14Co13Mo5. Experiments show that the alloy has a tensile strength of 1900Mpa, an impact toughness of a _k 60J/cm ² , a hardness of HRC50, and a good combination of strength and toughness.

The present invention specifically provides a maraging stainless steel, characterized in that the maraging stainless steel is 1Cr14Co13Mo5, and its composition and weight percentage are: Cr: 12.8-15.2, Co: 12-14.5, Mo: 4.0- 5.5, Ni: 0.5-2, C: 0.13-0.19, Mn: ≤0.20, Nb: 0.2-0.3, Ti: 0.2-0.3, P: ≤0.02, S: ≤0.01, Si: ≤0.20, O≤0.005, N≤0.02, Fe balance.

As a preferred solution, the composition and weight percentage of the maraging stainless steel are: Cr: 13.0-15.0, Co: 12-14, Mo: 4.0-5.5, Ni: 0.5-1, C: 0.13-0.19, Mn : ≤0.20, Nb: 0.2-0.3, Ti: 0.2-0.3, P: ≤0.02, S: ≤0.01, Si: ≤0.20, O≤0.005, N≤0.02, Fe balance.

The present invention also provides the preparation method of the maraging stainless steel, which is characterized in that: the raw materials are put into a vacuum induction furnace for melting, the obtained steel ingot is forged at 1050°C-1150°C, and the final forging temperature is 880°C-920°C ℃; forgings were annealed at 850℃～870℃ for 2～3h; solution treated at 1050℃～1150℃ for 40min～90min, water cooled, then subjected to cryogenic treatment, and finally aged twice at 500℃～600℃, each Second heat preservation 1 ~ 2h.

Wherein, the solution treatment is preferably heat preservation at 1100°C-1150°C for 50min-80min, water cooling, and the cooling rate is preferably to cool to room temperature within 2min.

The cryogenic treatment is to use a mixed solution of liquid nitrogen + alcohol to carry out cryogenic treatment at -78°C, preferably to cool the stainless steel to -78°C within 5 minutes.

The aging treatment is preferably two aging treatments at 540° C., each time for 2 hours.

Description of drawings

Fig. 1 The grain state of sample steel after solution treatment at different temperatures (among them, a, 1000°C, b, 1050°C, c, 1100°C, d, 1150°C).

Fig. 2 Effect of solution temperature on grain size of experimental steel.

Fig. 3 Microstructure diagrams of samples after solution treatment at different temperatures (among them, a, 1000°C, b, 1050°C, c, 1100°C, d, 1150°C).

Figure 4 Effect of solution temperature on the amount of retained austenite.

Fig. 5 SEM morphology of precipitates after solution treatment at 1000℃×1h and 1050℃×1h after cryogenic cooling.

Fig. 6 Energy spectrum analysis of the matrix after solution treatment at 1000℃.

Fig. 7 Energy spectrum analysis of precipitates after solution treatment at 1000℃.

Figure 8 Effect of solution temperature on sample hardness.

Figure 9 The effect of solution temperature on the tensile strength and yield strength of the sample.

Figure 10 Effect of solution temperature on sample elongation and reduction of area.

Figure 11 Effect of solution temperature on impact toughness of samples.

Fig. 12 Metallographic structure after aging treatment at different temperatures (among them, a, 520°C, b, 540°C, c, 560°C, d, 580°C).

Fig. 13 Morphology of precipitated phase after solid solution cryogenic cooling at 1100°C + aging at 540°C twice.

Fig. 14 Effect of different aging temperatures on the hardness of samples after solid solution cryogenic cooling at 1100°C.

Fig. 15 Effect of different aging temperatures on the tensile strength of samples after solid solution cryogenic cooling at 1100°C.

Fig. 16 Effect of different aging temperatures on the elongation of the sample after solid solution cryogenic cooling at 1100°C.

Fig. 17 Effect of different aging temperatures on the impact toughness of samples after solid solution cryogenic cooling at 1100°C.

detailed description

Metallographic samples under various heat treatment systems of the present invention, after grinding and polishing, adopt the mixed solution of picric acid+hydrochloric acid+alcohol to corrode, and observe grain structure with Axio Observer ZIm metallographic optical microscope, adopt intercept method to calculate solid solution The grain size of the state alloy was observed, and the structure was observed under the INSPECT F50 field emission scanning electron microscope. The SEM image included general secondary electron images and backscattered electron (BSE) images. Tecnai G ² F20 transmission electron microscope was used to observe and analyze the precipitated phase in steel. The TEM sample was prepared by double spray electrolytic thinning process. The double spray liquid was 10% HClO ₄ +90% C ₂ H ₅ OH (volume fraction) . Phase identification was carried out by combining selected area electron diffraction (SAED) with TEM and energy dispersive spectroscopy (EDS) configured on SEM. D/Max2500PC Cu target X-ray diffractometer (XRD) was used to measure the amount of retained austenite in the experimental steel after solution treatment.

In the mechanical performance test, the tensile sample and the impact sample are GB/T228-2002 and GB/T229-1994 standard samples respectively, the gauge length of the tensile sample is 25mm, the diameter is 5mm, the size of the impact sample is It is 10mm×10mm×55mm. Use a Rockwell hardness tester to test the hardness of maraging stainless steel after heat treatment. The sample is roughly ground and then finely ground so that the upper and lower surfaces are parallel and the roughness is higher than 0.8. Measure at least three points for each sample (when When the hardness values of the measured points differ greatly, several more points should be measured), and the average value should be taken.

Example 1

Preparation of the sample: Select high-purity Fe, electrolytic Ni, Co, high-purity Mo, V, Nb, Si, Mn and other raw materials, and use an ultra-high vacuum induction furnace to melt a 25kg steel ingot. The composition of the sample steel is shown in Table 1. The steel ingot is forged at 1100°C±10°C, the final forging temperature is 900°C±10°C, and it is forged into a Φ40mm bar. The forging is annealed within 24 hours after forging, and annealed at 860°C±10°C for 2-3 hours. Furnace cold and ready to use.

Table 1 embodiment stainless steel chemical composition (mass percentage %)

Example 2

Solution treatment: take sample 1 stainless steel for solution treatment, heat preservation at 1000°C, 1050°C, 1100°C, and 1150°C for 1 hour, water-cool to room temperature, and then perform cryogenic treatment (mixed solution of liquid nitrogen + alcohol -78 ℃), and its grain structure state is shown in Fig. 1.

It can be seen from Figure 1 that the grains after solution treatment at different temperatures are all equiaxed, and the grain size of different temperature treatments is measured, as shown in Figure 2, as the solution temperature increases, the grain size increases , increased from 35um to 65um, no abnormal growth phenomenon. As the solid solution temperature increases, the undissolved substances in the grain boundaries and grains gradually decrease, which accelerates the formation and homogenization of austenite, which is beneficial to the formation of austenite.

Figure 3 (a) to (d) are the microstructure of the sample steel after solid solution treatment at 1000°C, 1050°C, 1100°C, and 1150°C, respectively, and the matrix of the sample steel after solid solution cryogenic cooling The structure is lath martensite, and there is a certain amount of retained austenite on the grain boundary and in the grain. When it is in solid solution at 1000°C and 1050°C, there are still precipitates at the grain boundary. As the solid solution temperature increases, the content of retained austenite gradually increases. When the solid solution temperature rises to 1150°C, it can be seen that there are a large amount of retained austenite in irregular blocks at the grain boundaries. According to the principle of X-ray diffraction, using D/Max2500PC X-ray diffractometer, according to the national standard "YBT5338-2006 X-ray Diffraction Law for Quantitative Measurement of Residual Austenite in Steel", the residual austenite after solid solution treatment at different temperatures is calculated amount, as shown in Figure 4.

It can be seen from (a) and (b) in Figure 5 that after solution treatment at 1000°C and 1050°C, there are also precipitates at the grain boundaries, which are analyzed by scanning electron microscopy and its energy spectrum system after solution treatment at 1000°C The morphology and composition range of the precipitates are shown in (a) and (b) of Figure 5.

Figure 6 and Figure 7 are the energy spectrum analysis of the matrix and precipitates after solution treatment at 1000°C, respectively. The main components of the precipitates are Fe, Mo, Cr, Co and a small amount of Ni, Mn, C, etc. Analyzing the cause of the precipitates, firstly, the solid solution temperature is low, and the alloying elements are not fully dissolved in the steel, so that Mo is combined with other alloying elements to form compounds and precipitates during the process of water cooling to room temperature after solid solution treatment. In addition, , the energy at the grain boundary is higher, which also provides the nucleation site and power for the precipitated phase. Moreover, this Mo-rich precipitate is easy to precipitate at the grain boundary, and grows faster than the precipitate in the grain, resulting in uneven size of the precipitate. The precipitate on the grain boundary is larger than the precipitate in the grain. The precipitates on the inner martensite lath are between 0.1μm-0.2um, and the precipitates at the grain boundaries are larger, about 2μm-3μm. Larger precipitates on the grain boundaries may increase the solid solution strength of the steel, but it will reduce the toughness and elongation of the steel, and will affect the strengthening and toughening effect of the steel during subsequent aging, thereby affecting the final comprehensive mechanical properties of the steel . Therefore, for good coordination of mechanical properties, the solid solution temperature should be raised to about 1100°C, and the generation of intergranular and intragranular precipitates should be avoided as much as possible.

Figures 8 to 11 show the effect of solution temperature on the mechanical properties of the experimental steel. It can be seen that the hardness of the experimental steel decreases continuously with the increase of the solution temperature, and the hardness HRC decreases continuously from 48 to 42. The reason for the analysis is mainly due to the increase of the solution temperature. Grain size gradually increases, the effect of grain boundary strengthening gradually decreases, and the content of retained austenite increases, resulting in a decrease in hardness. The strength index tensile strength Rm and yield strength Rp0.2 generally show a downward trend with the increase of solution temperature, among which the tensile strength first increases sharply and then gradually decreases, reaching a maximum value of 1737Mpa at 1050°C, and the yield strength is first large The amplitude decreases, reaches the lowest point at around 1060°C, and then rises slightly.

The plastic index elongation A% does not change significantly in the range of 1000 ° C to 1100 ° C, but it decreases sharply as the temperature continues to rise, and the reduction of area Z% gradually increases with the increase of the solution temperature, reaching 1100 °C is reaching a maximum value of 17%, after which it starts to decrease slightly. The toughness index aku changes significantly with the increase of the solution temperature. At about 1000 ° C, due to the existence of grain boundary precipitates, it becomes the source of cracks, which is easy to break and has low toughness. However, with the increase of the solution temperature, the solid solution Dissolution treatment can make all the alloying elements and precipitates after hot rolling and cooling fully dissolved in the steel, and the toughness is greatly improved. As the temperature continues to rise, the toughness does not change much and is stable at about 140J/cm ² .

Example 3

Aging treatment: The stainless steel sample 1 treated in Example 2 was further subjected to aging treatment: aging at 520°C, 540°C, 560°C, and 580°C for two times, each time for 2 hours, and air cooling.

Figure 12 (a) to (d) are the microstructure after treatment at 520°C, 540°C, 560°C, and 580°C, respectively. It can be seen that the matrix structure of stainless steel after aging treatment is low carbon lath martensite , there are fine and dispersed aging precipitates on the martensite lath, and there are a small amount of retained austenite and reversed austenite at the grain boundary. With the increase of aging temperature, the reversed austenite increases. After aging treatment at 580℃, there are continuously distributed reverse transformed austenite and retained austenite at grain boundaries and between martensite lath bundles.

Figure 13 (a) and (b) the morphology of the precipitated phase of the sample aged at 540°C. It can be seen that after aging treatment, a large number of dispersed, fine and strengthened precipitated phases are precipitated on the martensite matrix. The precipitation of the precipitated phase improves the strength of the steel. Only the ellipsoidal precipitated phase is seen in the precipitated phase of the stainless steel of the present invention, which can be inferred to be the Laves phase of the Fe ₂ Mo type, and the Laves phase of the Fe ₂ Mo type is also a secondary hardened steel Typical strengthening phase in .

Figures 14 to 17 show the effects of different aging temperatures on the mechanical properties of samples after solid solution cryogenic cooling at 1100°C.

Sample 1 stainless steel has undergone a heat treatment process of 1100°C solution treatment for 1h+(-78°C deep cooling)+540°C aging twice, the tensile strength reaches 1900MPa, the impact toughness reaches a _k 60J/cm ² , the hardness reaches HRC50, and the toughness With a good fit, it can meet the basic performance requirements of engineering applications.

Example 4

Samples 2-9 were taken, solution treated at 1050°C-1150°C for 40min-90min, water-cooled, then subjected to cryogenic treatment, and finally aged twice at 500°C-600°C, each holding for 1-2h. The experimental results show that the obtained maraging stainless steel has a good combination of strength and toughness, and the tensile strength, impact toughness and hardness can all meet the basic performance requirements of engineering applications.

The above-mentioned embodiments are only to illustrate the technical conception and characteristics of the present invention, and its purpose is to allow those familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention with this. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (8)

1. a martensite aged stainless steel, it is characterised in that described martensite aged stainless steel is 1Cr14Co13Mo5, its group Become and percentage by weight be: Cr:12.8-15.2, Co:12-14.5, Mo:4.0-5.5, Ni:0.5-2, C:0.13-0.19, Mn: ≤ 0.20, Nb:0.2-0.3, Ti:0.2-0.3, P :≤0.02, S :≤0.01, Si :≤0.20, O≤0.005, N≤0.02, Fe Surplus.

2. according to martensite aged stainless steel described in claim 1, it is characterised in that the composition of described martensite aged stainless steel And percentage by weight is: Cr:13.0-15.0, Co:12-14, Mo:4.0-5.5, Ni:0.5-1, C:0.13-0.19, Mn :≤ 0.20, Nb:0.2-0.3, Ti:0.2-0.3, P :≤0.02, S :≤0.01, Si :≤0.20, O≤0.005, N≤0.02, more than Fe Amount.

3. the preparation method of martensite aged stainless steel described in a claim 1, it is characterised in that: raw material is put into vacuum sense Answering melting in stove, gained steel ingot opens forging at 1050 DEG C～1150 DEG C, and final forging temperature is 880 DEG C～920 DEG C；Forging is at 850 DEG C ～annealing insulation 2～3h at 870 DEG C；Solution treatment 40min～90min at 1050 DEG C～1150 DEG C, water-cooled, then carry out deep cooling Process, finally Ageing Treatment twice at 500 DEG C～600 DEG C, every time insulation 1～2h.

4. according to the preparation method of martensite aged stainless steel described in claim 3, it is characterised in that: described solution treatment is 50min～80min, water-cooled it is incubated at 1100 DEG C～1150 DEG C.

5. according to the preparation method of martensite aged stainless steel described in claim 3 or 4, it is characterised in that: after solution treatment Room temperature it is cooled in 2min.

6. according to the preparation method of martensite aged stainless steel described in claim 3, it is characterised in that: described subzero treatment is for adopting At-78 DEG C, subzero treatment is carried out with the mixed solution of liquid nitrogen+ethanol.

7. according to the preparation method of martensite aged stainless steel described in claim 3 or 6, it is characterised in that: described subzero treatment Require that rustless steel is cooled to-78 DEG C in 5min.

8. according to the heat treatment method of martensite aged stainless steel described in claim 3, it is characterised in that: described Ageing Treatment is Ageing Treatment twice at 540 DEG C, is incubated 2h every time.