High-temperature-resistant nanoparticle strengthened martensitic stainless steel and method for preparing the same

Abstract

The application provides a high-temperature-resistant nano-particle reinforced martensitic stainless steel and a preparation method thereof. The preparation method of the high-temperature-resistant nano-particle reinforced martensitic stainless steel comprises the following steps: uniformly mixing Nb powder and BN powder to obtain mixed powder, uniformly mixing the mixed powder and iron powder according to different mass ratios, and then sequentially placing the mixed powder and the iron powder into an iron thin cylinder to perform fixed welding by using a laser welding technology to prepare an iron-based thin rod containing gradient distribution mixed powder; and placing the iron-based thin rod and the martensitic stainless steel into a vacuum induction melting furnace to melt, and then performing vacuum casting, normalizing and tempering treatment to finally obtain the high-temperature-resistant nano-particle reinforced martensitic stainless steel. The high-temperature-resistant nano-particle reinforced martensitic stainless steel obtained by the application has a yield strength of greater than or equal to 315 MPa, a tensile strength of greater than or equal to 331 MPa and an elongation of greater than or equal to 49.5% at a temperature of greater than or equal to 600 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature-resistant materials, and particularly relates to a high-temperature-resistant nano-particle reinforced martensitic stainless steel and a preparation method thereof. BACKGROUND

[0002] Martensitic stainless steel is widely used in high-temperature pressure components (such as turbine blades, high-temperature bolts, etc.) in the fields of energy, chemical industry and aerospace due to its high strength and toughness, corrosion resistance and good processability. However, as the service temperature increases (usually > 500℃), the martensite softens, and the continuous precipitation and coarsening of carbides (such as M 23 C6, MC type carbides) at the grain boundary significantly reduces the high-temperature mechanical properties of the martensitic stainless steel, which is manifested as a decrease in yield strength and loss of plasticity, which has become a key bottleneck restricting the long-term stable service of the martensitic stainless steel in extreme environments. Therefore, improving the high-temperature mechanical properties of the martensitic stainless steel has become a problem to be solved. Existing researches add > 1 wt.% content of elements such as W and Co to form stable carbides or solid solution strengthening phases during alloy preparation to improve the high-temperature mechanical properties of the martensitic stainless steel, but excessive addition of precious elements will increase the cost, induce brittle Laves phase and worsen the processability; in addition, existing technologies refine the grains and improve the high-temperature strength and plasticity by regulating the heat treatment process such as two-stage aging or deformation heat treatment, but due to the complex process, it is difficult to realize the industrial production of the alloy, and the improvement of the high-temperature strength and plasticity is limited. Therefore, how to reduce the addition amount of raw materials, simplify the process, obtain a martensitic stainless steel with excellent mechanical properties such as high thermal stability and high strength and plasticity and realize industrialized production is a technical problem to be solved at present. SUMMARY

[0003] In order to solve the above technical problems, the present application provides a high-temperature-resistant nano-particle reinforced martensitic stainless steel, and a preparation method thereof, which comprises the following steps:

[0004] (1) at room temperature, uniformly mix Nb powder and BN powder in a ball mill at a rotation speed of 50-80 rpm for 6-10 hours to prepare a mixed powder 1, wherein the mass ratio of the Nb powder to the BN powder is 2.6-3.4:1.6-2.4;

[0005] The particle size of the Nb powder is 30-110 microns, and the particle size of the BN powder is 50-170 microns;

[0006] (2) The mixed powder 1 obtained in step (1) is mixed with iron powder in a mass percentage of 3.6:1-4.4:1, 1.7:1-2.3:1, 2.7:5.3-3.2:5.3 in a ball mill with a rotation speed of 40-60 rpm for 12-14 hours to obtain high, medium and low content of mixed powder 2, mixed powder 3 and mixed powder 4, respectively; the particle size of the iron powder is 90-120 microns;

[0007] (3) The mixed powder 2, mixed powder 3 and mixed powder 4 in step (2) are placed in the upper, middle and lower positions of an iron thin cylinder in a mass percentage of 0.8-1.2:0.8-1.2:2.8-3.2, respectively, and then welded using laser welding technology at a power of 500-800 W and a welding speed of 15-30 mm / s to finally obtain an iron-based rod with gradient distribution of mixed powder;

[0008] (4) The iron-based rod with gradient distribution of mixed powder in step (3) and martensitic stainless steel are placed together in a vacuum induction melting furnace, heated to 1500-1700℃ at a power of 4-9 kW every 5-11 minutes, and held for 30-45 minutes to finally obtain a martensitic stainless steel melt containing nano-particle reinforcement; the mass ratio of the iron-based rod with gradient distribution of mixed powder to the martensitic stainless steel is 0.015%:1-0.065%:1;

[0009] The composition of the martensitic stainless steel ranges, by mass percentage, as follows: C: 0.06-0.15 wt.%; Cr: 8.10-9.70 wt.%; Si: ≤0.60 wt.%; Mn: 0.20-0.70 wt.%; V: 0.10-0.35 wt.%; Mo: 0.20-0.99 wt.%; P: ≤0.030 wt.%; S: ≤0.020 wt.%; Ni: ≤0.50 wt.%; N: 0.02-0.08 wt.%; Cu: ≤0.30 wt.%; Nb: 0.03-0.10 wt.%; Ti: ≤0.02 wt.%; Zr: ≤0.50; Al: ≤0.030; W: 1.10-2.50 wt.%; and the balance being Fe;

[0010] (5) The nano-particle reinforced martensitic stainless steel melt obtained in step (4) is cast under vacuum conditions, normalized and tempered to finally obtain a high-temperature resistant nano-particle reinforced martensitic stainless steel;

[0011] The normalizing treatment is austenitizing at 1040-1070℃ for 1-3 hours and then air cooling;

[0012] The tempering treatment is holding at 740-780℃ for 2-4 hours and then air cooling;

[0013] The high-temperature-resistant nano-particle reinforced martensitic stainless steel has a martensitic lath with a size of 4.5-5.5 microns; the high-temperature-resistant nano-particle reinforced martensitic stainless steel has uniformly dispersed nano-particles with a particle size of 40-160 nm; the high-temperature-resistant nano-particle reinforced martensitic stainless steel has a yield strength of ≥315 MPa, a tensile strength of ≥331 MPa, and an elongation of ≥49.5% at ≥600℃.

[0014] Further, the particle size of the Nb powder in step (1) is 40-100 microns, and the particle size of the BN powder is 60-150 microns.

[0015] Further, the particle size of the iron powder in step (2) is 100-110 microns.

[0016] Further, the laser welding technology in step (3) is performed at a welding speed of 18-28 mm / s under a power of 600-700 W.

[0017] Further, in step (4), the power is increased by 6-8 kW every 8-10 minutes to heat to 1520-1680℃ for 35-40 minutes.

[0018] Further, in step (4), the martensitic stainless steel has a composition range of C: 0.07-0.13 wt.%, Cr: 8.15-9.50 wt.%, Si: ≤0.50 wt.%, Mn: 0.30-0.60 wt.%, V: 0.15-0.25 wt.%, Mo: 0.30-0.98 wt.%, P: ≤0.020 wt.%, S: ≤0.010 wt.%, Ni: ≤0.40 wt.%, N: 0.03-0.07 wt.%, Cu: ≤0.20 wt.%, Nb: 0.04-0.09 wt.%, Ti: ≤0.01 wt.%, Zr: ≤0.40, Al: ≤0.020, W: 1.50-2.00 wt.%, and the rest is Fe.

[0019] Further, in step (4), the mass ratio of the iron-based fine rod to the martensitic stainless steel of the gradient distribution mixed powder is 0.02%:1-0.05%:1.

[0020] Further, in step (5), the normalizing treatment is austenitizing at 1060℃ for 1.5-2.5 hours and then air cooling; and the tempering treatment is holding at 760℃ for 2.5-3.5 hours and then air cooling. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 EBSD microstructure of the high-temperature-resistant nano-particle reinforced martensitic stainless steel 1 in Example 2 of the present application;

[0022] Figure 2 High temperature stress strain curve of the high temperature resistant nano-particle strengthened martensitic stainless steel 1 in Example 2 of the present application at 600℃;

[0023] Figure 3 High temperature stress strain curve of the high temperature resistant nano-particle strengthened martensitic stainless steel 1 in Example 2 of the present application at 650℃;

[0024] Figure 4 EBSD structure diagram of the high temperature resistant nano-particle strengthened martensitic stainless steel 2 in Example 3 of the present application;

[0025] Figure 5 High temperature stress strain curve of the high temperature resistant nano-particle strengthened martensitic stainless steel 2 in Example 3 of the present application at 620℃;

[0026] Figure 6 High temperature stress strain curve of the high temperature resistant nano-particle strengthened martensitic stainless steel 2 in Example 3 of the present application at 680℃;

[0027] Figure 7 EBSD structure diagram of the martensitic stainless steel 3 in Comparative Example 1 of the present application;

[0028] Figure 8 High temperature stress strain curve of the martensitic stainless steel 3 in Comparative Example 1 of the present application at 600℃;

[0029] Figure 9 High temperature stress strain curve of the martensitic stainless steel 3 in Comparative Example 1 of the present application at 650℃. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0031] Example 1

[0032] The preparation method of the gradient distribution mixed powder iron-based thin rod comprises the following steps:

[0033] Step 1, under room temperature conditions, put the Nb powder and BN powder into a ball mill at a mass ratio of 3:2, uniformly mix at a speed of 70 rpm for 8 hours to obtain mixed powder 1;

[0034] The particle size of the Nb powder is 30-80 microns, and the particle size of the BN powder is 70-130 microns.

[0035] Step 2, the mixed powder 1 obtained in step 1 is mixed with iron powder in a mass ratio of 4:1, 2:1 and 3:5 in a ball mill with a rotation speed of 50 rpm for 12 hours to obtain mixed powder 2, mixed powder 3 and mixed powder 4; the Fe powder has a particle size of 80-110 microns;

[0036] Step 3, the mixed powder 2, mixed powder 3 and mixed powder 4 in step 2 are sequentially placed in an iron thin cylinder in a mass ratio of 1:1:3 in the above order, and then fixed welding is performed using a laser welding technique at a power of 560 W and a welding speed of 20 mm / s to finally prepare an iron-based fine rod with gradient distribution of mixed powder.

[0037] Example 2

[0038] The high-temperature-resistant nano-particle reinforced martensitic stainless steel 1 is prepared by the following steps:

[0039] Step 1, the gradient distribution mixed powder iron-based fine rod prepared in Example 1 and martensitic stainless steel are subjected to vacuum induction melting treatment, the vacuum induction melting treatment is as follows: heating to complete melting at a power increasing by 6 kW every 7 minutes, and then maintaining at 1600℃ for 35 minutes to obtain a nano-particle reinforced martensitic stainless steel melt; the mass ratio of the gradient distribution mixed powder iron-based fine rod to the martensitic stainless steel is 0.03%:1;

[0040] According to the mass percentage, the composition of the martensitic stainless steel is as follows: C: 0.11wt.%; Cr: 8.25wt.%; Si: 0.29wt.%; Mn: 0.43wt.%; V: 0.16wt.%; Mo: 0.33wt.%; P: 0.019wt.%; S: 0.002wt.%; Ni: 0.11wt.%; N: 0.047wt.%; Cu: 0.04wt.%; Nb: 0.055wt.%; Ti: 0.0072wt.%; Zr: 0.0020; Al: 0.0004; W: 1.52wt.%; and the rest is Fe;

[0041] Step 2, the nano-particle reinforced martensitic stainless steel melt obtained in step 1 is cast under vacuum conditions, normalized and tempered to obtain the high-temperature-resistant nano-particle reinforced martensitic stainless steel 1;

[0042] The normalizing treatment is austenitizing at 1060℃ for 1 hour and then air cooling;

[0043] The tempering treatment is maintaining at 760℃ for 2.5 hours and then air cooling.

[0044] The EBSD structure of the high-temperature-resistant nano-particle reinforced martensitic stainless steel 1 in this example is as follows:Figure 1 The microstructure is shown to be martensite lath, wherein the average size of the martensite lath is 5.3 microns. The high-temperature nano-particle reinforced martensitic stainless steel 1 uniformly disperses nano-particles (the particle size of the nano-particles is 40-160 nm); Figure 2 and Figure 3 The high-temperature tensile stress-strain curves of the high-temperature nano-particle reinforced martensitic stainless steel 1 at 600°C and 650°C, respectively, can be seen that the yield strength, tensile strength and elongation thereof at 600°C are 315 MPa, 331 MPa and 49.5%, respectively; and the yield strength, tensile strength and elongation thereof at 650°C are 261 MPa, 285 MPa and 57.8%, respectively. It can be concluded that the high-temperature nano-particle reinforced martensitic stainless steel 1 can still maintain good performances in high strength, high plasticity, stability, toughness and the like even under high-temperature conditions.

[0045] Example 3

[0046] The high-temperature nano-particle reinforced martensitic stainless steel 2, the specific method steps include the following:

[0047] Step 1, the gradient distribution mixed powder iron-based rod and the martensitic stainless steel prepared in Example 1 are subjected to vacuum induction melting treatment, wherein the vacuum induction melting treatment is to heat to complete melting by increasing the power by 8 kW every 8 minutes, and then to obtain a nano-particle reinforced martensitic stainless steel melt by maintaining at 1620°C for 40 minutes; the mass ratio of the gradient distribution mixed powder iron-based rod to the martensitic stainless steel is 0.05%:1;

[0048] According to the mass percentage, the composition of the martensitic stainless steel is: C: 0.11wt.%; Cr: 8.25wt.%; Si: 0.29wt.%; Mn: 0.43wt.%; V: 0.16wt.%; Mo: 0.33wt.%; P: 0.019wt.%; S: 0.002wt.%; Ni: 0.11wt.%; N: 0.047wt.%; Cu: 0.04wt.%; Nb: 0.055wt.%; Ti: 0.0072wt.%; Zr: 0.0020; Al: 0.0004; W: 1.52wt.%; and the rest is Fe;

[0049] Step 2, the nano-particle reinforced martensitic stainless steel melt obtained in Step 1 is cast under vacuum conditions, normalized and tempered to obtain the high-temperature nano-particle reinforced martensitic stainless steel 2;

[0050] The normalizing treatment is to perform austenitizing at 1060°C for 1.2 hours and then air cooling,

[0051] The tempering treatment is as follows: air cooling after holding at 760 °C for 2.7 hours.

[0052] The EBSD structure of the high-temperature-resistant nano-particle strengthened martensitic stainless steel 2 in this embodiment is shown in Figure 4 The microstructure is martensitic lath, and the average size of the martensitic lath is 4.8 microns; the high-temperature-resistant nano-particle strengthened martensitic stainless steel 2 uniformly disperses nano-particles (the particle size of the nano-particles is 40-160 nm); the high-temperature tensile stress-strain curves of the high-temperature-resistant nano-particle strengthened martensitic stainless steel 2 at 620 °C and 680 °C are shown in Figure 5 and Figure 6 The yield strength, tensile strength and elongation of the high-temperature-resistant nano-particle strengthened martensitic stainless steel 2 at 620 °C are 323 MPa, 344 MPa and 58.2%, respectively, and the yield strength, tensile strength and elongation of the high-temperature-resistant nano-particle strengthened martensitic stainless steel 2 at 680 °C are 267 MPa, 290 MPa and 73.9%, respectively. It can be seen that the high-temperature-resistant nano-particle strengthened martensitic stainless steel 2 can maintain good high strength, high plasticity, stability, toughness and other performances even at high temperature.

[0053] Comparative Example 1

[0054] The martensitic stainless steel 3 is prepared by the following steps:

[0055] Step 1, the martensitic stainless steel is subjected to vacuum induction melting treatment, and the vacuum induction melting treatment is as follows: heating to complete melting at a power of 6 kW per 5 minutes, holding at 1580 °C for 25 min, and obtaining a martensitic stainless steel melt.

[0056] The composition of the martensitic stainless steel is as follows in terms of mass percentage: C: 0.11 wt.%; Cr: 8.25 wt.%; Si: 0.29 wt.%; Mn: 0.43 wt.%; V: 0.16 wt.%; Mo: 0.33 wt.%; P: 0.019 wt.%; S: 0.002 wt.%; Ni: 0.11 wt.%; N: 0.047 wt.%; Cu: 0.04 wt.%; Nb: 0.055 wt.%; Ti: 0.0072 wt.%; Zr: 0.0020; Al: 0.0004; W: 1.52 wt.%; and the balance is Fe.

[0057] Step 2, the martensitic stainless steel melt obtained in step 1 is cast under vacuum conditions, normalized and tempered to obtain the martensitic stainless steel 3.

[0058] The normalizing treatment is as follows: austenitizing at 1060 °C for 1 hour and air cooling,

[0059] The tempering treatment is as follows: air cooling after holding at 760 °C for 2.5 hours.

[0060] In the present comparative example, the composition of the martensitic stainless steel 3 is the same as that of the examples, and the EBSD structure is as shown in FIG. 2. The average size of the martensite laths in the microstructure of the martensitic stainless steel 3 prepared in Comparative Example 1 is 7.5 microns, which is relatively coarse. Figure 7 The high-temperature tensile stress-strain curves of the martensitic stainless steel 3 obtained in Comparative Example 1 at 600°C and 650°C are as shown in FIG. 3. The high-temperature yield strength, tensile strength and elongation of the martensitic stainless steel 3 obtained in Comparative Example 1 at 600°C are 295 MPa, 304 MPa and 42.0%, respectively, and at 650°C are 238 MPa, 250 MPa and 49.1%, respectively. Figure 8 and Figure 9 The high-temperature yield strength, tensile strength and elongation of the martensitic stainless steel 3 obtained in Comparative Example 1 at 600°C are 295 MPa, 304 MPa and 42.0%, respectively, and at 650°C are 238 MPa, 250 MPa and 49.1%, respectively.

[0061] Examples 2 and 3 of the present application differ from Comparative Example 1 in that:

[0062] The average size of the martensite laths in the microstructure of the high-temperature nano-particle strengthened martensitic stainless steel 1 prepared in Example 2 is 5.3 microns, which is significantly smaller than the average size of the martensite laths in the martensitic stainless steel 3 prepared in Comparative Example 1 (7.5 microns), and the degree of refinement of the martensite laths is 29%. The refined martensite lath structure in Example 2 is more stable at high temperatures, which can delay dislocation climb and grain boundary migration, thereby improving the high-temperature strength. In addition, the refined martensite laths increase the number of grain boundaries, making it easier for the grain boundaries to coordinate the deformation of adjacent grains at high temperatures, thereby improving the high-temperature plasticity. Meanwhile, uniform nano-particles are also formed in the high-temperature nano-particle strengthened martensitic stainless steel 1 prepared in Example 2, and the nano-particles and the fine and uniform martensite laths achieve synergistic regulation, which helps to improve the strength and thermal stability of the stainless steel. The yield strength, tensile strength and elongation of the high-temperature nano-particle strengthened martensitic stainless steel 1 obtained in Example 2 at 600°C are 315 MPa, 331 MPa and 49.5%, respectively, which are 6.8%, 8.9% and 17.9% higher than those of Comparative Example 1, respectively. At 650°C, the yield strength, tensile strength and elongation of the high-temperature nano-particle strengthened martensitic stainless steel 1 obtained in Example 2 are 261 MPa, 285 MPa and 57.8%, respectively, which are 9.7%, 14.9% and 17.7% higher than those of Comparative Example 1, respectively. Therefore, the strength and plasticity of the high-temperature nano-particle strengthened martensitic stainless steel 1 obtained in Example 2 are both significantly better than those of the martensitic stainless steel obtained in Comparative Example 1, and the high-temperature strength and plasticity of the stainless steel are both improved simultaneously.

[0063] The average size of the martensite laths in the microstructure of the high-temperature-resistant nanoparticle-strengthened martensitic stainless steel 2 prepared in Example 3 was 4.8 microns, which was 36% finer than the average size of the martensite laths (7.5 microns) in the martensitic stainless steel 3 prepared in Comparative Example 1, while uniform nanoparticles were also formed. The finer the size of the martensite laths in the martensitic stainless steel, the better the high-temperature resistance, i.e., the higher the strength-to-plasticity ratio. The yield strength, tensile strength, and elongation of the high-temperature-resistant nanoparticle-strengthened martensitic stainless steel 2 obtained in Example 3 at 620 °C were 323 MPa, 344 MPa, and 58.2%, respectively, which were all higher than the corresponding properties of the martensitic stainless steel in Comparative Example 1 at 600 °C, and were increased by 9.5%, 13.2%, and 38.6%, respectively. Meanwhile, uniform nanoparticles were also formed in the high-temperature-resistant nanoparticle-strengthened martensitic stainless steel 2 prepared in Example 3, and the nanoparticles and the fine and uniform martensite laths achieved synergistic regulation, which helped to improve the strength and thermal stability of the stainless steel. The yield strength, tensile strength, and elongation of the high-temperature-resistant nanoparticle-strengthened martensitic stainless steel 2 obtained in Example 3 at 680 °C were 267 MPa, 290 MPa, and 73.9%, respectively, which were all higher than the corresponding properties of the martensitic stainless steel in Comparative Example 1 at 650 °C, and were increased by 12.2%, 16.9%, and 50.5%, respectively. Therefore, the high-temperature-resistant nanoparticle-strengthened martensitic stainless steel 2 obtained in Example 3 still had higher strength and plasticity at a higher temperature than the stainless steel in Comparative Example 1.

[0064] Comparative Example 2

[0065] In the article "Mechanical properties of Grade 91 steel at high temperatures" by Ren et al. published in Journal of Physics: Conference Series, Volume 1168, Issue 2, 2018, the tensile properties of a 91 grade martensitic stainless steel at high temperatures of 565 °C and 650 °C were investigated. The martensitic stainless steel provided was a 91 grade martensitic stainless steel obtained after hot rolling deformation and normalization and tempering treatment, for which a yield strength and a tensile strength and an elongation of 245 MPa, 283 MPa and 41.3% at 650 °C were measured, wherein the chemical composition of the 91 grade martensitic stainless steel was: C: 0.10 wt.%, Si: 0.23 wt.%, Mn: 0.40 wt.%, P: 0.010 wt.%, S: 0.002 wt.%, Cr: 8.34 wt.%, Ni: 0.13 wt.%, Mo: 0.98 wt.%, Nb: 0.079 wt.%, N: 0.044 wt.%, Ti: 0.002 wt.%, Zr: 0.001 wt.%, Al: 0.009 wt.%, Cu: 0.06 wt.%, Sn: 0.005 wt.%, V: 0.229 wt.%, the remainder being Fe.

[0066] Examples 2 and 3 of the present application differ from Comparative Example 2 in that:

[0067] The high-temperature resistant nano-particle reinforced martensitic stainless steel prepared in Example 2 and Example 3 belongs to the same kind of martensitic stainless steel as the 91-grade martensitic stainless steel in Comparative Example 2, and the addition amount of noble metals such as Cr (8.25 wt.%), Mo (0.33 wt.%), Nb (0.055 wt.%) in the high-temperature resistant nano-particle reinforced martensitic stainless steel of the examples is less than the addition amount of the corresponding elements in the comparative example (Cr: 8.34 wt.%, Mo: 0.98 wt.%, Nb: 0.079 wt.%), which greatly reduces the cost; in addition, compared with Comparative Example 2, the high-temperature resistant nano-particle reinforced martensitic stainless steel obtained in Example 2 and Example 3 is a cast martensitic stainless steel, which does not undergo the hot rolling and other processing deformation strengthening processes of the martensitic stainless steel in Comparative Example 2, thereby simplifying the processing process and saving the processing cost. The yield strength, tensile strength and elongation of the high-temperature resistant nano-particle reinforced martensitic stainless steel obtained in Example 2 at a high temperature of 650℃ are increased by 6.5%, 0.7% and 39.9% respectively compared with the 91-grade martensitic stainless steel in Comparative Example 2 at the same temperature. As can be seen, the low-processing-cost high-temperature resistant nano-particle reinforced martensitic stainless steel obtained in the present application has a high temperature strength and plasticity at ≥600℃ which is significantly better than the high-processing-cost hot-rolled deformation strengthened 91-grade martensitic stainless steel in Comparative Example 2. In addition, the strength and plasticity of the high-temperature resistant nano-particle reinforced martensitic stainless steel 2 obtained in Example 3 at 680℃ are still higher than the strength and plasticity of the 91-grade martensitic stainless steel in Comparative Example 2 at 650℃, wherein the yield strength, tensile strength and elongation are increased by 2.3%, 1.8% and 78.9% respectively. Therefore, the high-temperature resistant nano-particle reinforced martensitic stainless steel obtained in the examples of the present application has a more excellent strength and plasticity than Comparative Example 2 at a higher service temperature at a lower cost than the prior art.

[0068] The high-temperature mechanical properties of the martensitic stainless steel in Comparative Example 1 and Comparative Example 2 and the high-temperature resistant nano-particle reinforced martensitic stainless steel in Example 2 and Example 3 are summarized in the following table:

[0069] Table 1 Comparison of high-temperature mechanical properties of martensitic stainless steel in comparative examples and examples

[0070]

[0071] The comparison between example 2 and example 3 proves that the components, the proportioning and the process parameters used in each embodiment of the present application are different, and the excellent properties of the high-temperature-resistant nano-particle reinforced martensitic stainless steel obtained finally are different, thus it is proved that the most excellent property of the present application is not determined by a certain component, the proportioning of components or process parameters, and example 2 and 3 still exhibit the comprehensive performance significantly better than that of comparative example 1 (conventional martensitic stainless steel) and comparative example 2 (rolling-reinforced martensitic stainless steel) at a high temperature of ≥600 DEG C, and the yield strength, the tensile strength and the elongation are simultaneously improved, although the present application obtains the cast state stainless steel, but the obtained performance has exceeded the rolling-reinforced steel, compared with the prior art, a significant technical progress is achieved. The martensite lath is significantly refined only through the synergistic regulation of the component interaction, the proportioning, the process and the process parameters, and the high-temperature grain boundary sliding is inhibited by the interface pinning effect, under the premise of not adding rare earth noble metal and simplifying the process flow (one-step melting and casting + short-time heat treatment), the high-temperature strength and plasticity are simultaneously realized through the synergistic effect of the component, the proportioning, the process and the process parameters, and only within the protection scope of the present application. Compared with the prior art and the traditional rolling process, the process of the present application is simple, the energy consumption is reduced, the cost is reduced, and the material still has high strength and plasticity and thermal stability at a temperature of 600 DEG C and above, and can meet the long-life demand of the extreme environment of the hot end part of an aero-engine, a supercritical power station pipeline and the like. The present application breaks through the contradiction between the high-temperature performance and the process cost through multi-dimensional synergistic optimization, and is suitable for the industrialized production of high-performance martensitic stainless steel.

Claims

1. High-temperature resistant nanoparticle-reinforced martensitic stainless steel, characterized in that, Its preparation method includes the following steps: (1) At room temperature, Nb powder and BN powder are mixed evenly in a ball mill at a mass ratio of 2.6-3.4:1.6-2.4 for 6-10 hours to prepare mixed powder 1. The particle size of the Nb powder is 30-110 micrometers, and the particle size of the BN powder is 50-170 micrometers. (2) The mixed powder 1 obtained in step (1) is mixed with iron powder in a ball mill at a speed of 40-60 rpm for 12-14 hours according to the mass percentages of 3.6:1-4.4:1, 1.7:1-2.3:1, and 2.7:5.3-3.2:5.3, respectively, to obtain mixed powder 2, mixed powder 3, and mixed powder 4 with high, medium, and low contents; the iron powder has a particle size of 90-120 micrometers; (3) The mixed powder 2, mixed powder 3 and mixed powder 4 in step (2) are placed in the upper, middle and lower positions of the iron thin cylinder in the following mass percentages: 0.8-1.2:0.8-1.2:2.8-3.

2. Then, the iron-based fine rod with gradient distribution mixed powder is welded at a power of 500-800W and a welding speed of 15-30mm / s using laser welding technology to finally obtain the iron-based fine rod with gradient distribution mixed powder. (4) The iron-based fine rods containing gradient-distributed mixed powder from step (3) and the martensitic stainless steel are placed together in a vacuum induction melting furnace. The power is increased by 4-9 kW every 5-11 minutes to heat to 1500-1700℃ and held for 30-45 minutes to finally obtain nanoparticle-reinforced martensitic stainless steel melt. The mass ratio of the iron-based fine rods containing gradient-distributed mixed powder to the martensitic stainless steel is 0.015%:1-0.065%:

1. The composition range of the martensitic stainless steel, by weight percentage, is as follows: C: 0.06-0.15wt.%; Cr: 8.10-9.70wt.%; Si: ≤ 0.60wt.%; Mn: 0.20-0.70wt.%; V: 0.10-0.35wt.%; Mo: 0.20-0.99wt.%; P: ≤ 0.030wt.%; S: ≤ 0.020wt.%; Ni: ≤ 0.50wt.%; N: 0.02-0.08wt.%; Cu: ≤0.30wt.%; Nb: 0.03-0.10wt.%; Ti: ≤ 0.02wt.%; Zr: ≤ 0.50; Al: ≤ 0.030; W: 1.10-2.50wt.%; The remainder is Fe; (5) The nanoparticle-reinforced martensitic stainless steel melt obtained in step (4) is cast, normalized and tempered under vacuum conditions to finally obtain high-temperature resistant nanoparticle-reinforced martensitic stainless steel. The normalizing treatment involves austenitizing at 1050-1070℃ for 1-3 hours followed by air cooling. The tempering process involves holding the temperature at 740-780℃ for 2-4 hours, followed by air cooling. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel contains martensitic laths with a size of 4.5-5.5µm; the high-temperature resistant nanoparticle-reinforced martensitic stainless steel contains uniformly dispersed nanoparticles with a particle size of 40-160nm; the high-temperature resistant nanoparticle-reinforced martensitic stainless steel has a yield strength ≥315MPa, a tensile strength ≥331MPa, and an elongation ≥49.5% at ≥600℃.

2. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, The particle size of Nb powder in step (1) is 40-100 micrometers, and the particle size of BN powder is 60-150 micrometers.

3. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, The iron powder in step (2) has a particle size of 100-110 micrometers.

4. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, The laser welding technology described in step (3) is used to perform welding at a power of 600-700W and a welding speed of 18-28mm / s.

5. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, In step (4), the power is increased by 6-8kW every 8-10 minutes to heat to 1520-1680℃ and kept warm for 35-40 minutes.

6. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, The composition range of the martensitic stainless steel mentioned in step (4) is as follows: C: 0.07-0.13wt.%; Cr: 8.15-9.50wt.%; Si: ≤0.50wt.%; Mn: 0.30-0.60wt.%; V: 0.15-0.25wt.%; Mo: 0.30-0.98wt.%; P: ≤0.020wt.%; S: ≤0.010wt.%; Ni: ≤0.40wt.%; N: 0.03-0.07wt.%; Cu: ≤0.20wt.%; Nb: 0.04-0.09wt.%; Ti: ≤0.01wt.%; Zr: ≤0.40; Al: ≤0.020; W: 1.50-2.00wt.%; The remainder is Fe.

7. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, The mass ratio of the iron-based fine rods and martensitic stainless steel in the gradient distribution mixed powder described in step (4) is 0.02%:1-0.05%:

1.

8. The high-temperature resistant nanoparticle-reinforced martensitic stainless steel according to claim 1, characterized in that, The normalizing treatment in step (5) involves austenitizing at 1060℃ for 1.5-2.5 hours and then air cooling; the tempering treatment involves holding at 760℃ for 2.5-3.5 hours and then air cooling.

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