Heat treatment process for additively manufactured RAFM steel

Abstract

A heat treatment process for additively manufactured RAFM steel, comprising the following steps: (1) additive manufacturing of RAFM steel; (2) normalizing heat treatment on the RAFM steel: the normalizing temperature is 900-1060°C, the holding time is 30-60 min, and after holding, air cooling to room temperature is performed; and (3) tempering heat treatment on the RAFM steel treated in step (2): the tempering temperature is 600-800°C, the heating rate is 5-15°C / min, the holding time is 60-120 min, and after holding, air cooling to room temperature is performed. The present application achieves grain refinement by means of a rapid melting and cooling process of selective laser melting, and improves the comprehensive mechanical properties of the RAFM steel by means of heat treatment.

Description

A heat treatment process for additive manufacturing of RAFM steel

[0001] The present application claims priority to the Chinese patent application No. 202411288963.6, filed on September 14, 2024, and entitled "A heat treatment process for additive manufacturing of RAFM steel", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of manufacturing process of reduced activation ferritic / martensitic steel (RAFM steel) components in nuclear fusion reactor, and in particular to a heat treatment process for additive manufacturing of RAFM steel. BACKGROUND

[0003] Reduced activation ferritic / martensitic steel (RAFM steel) has become the most promising candidate structural material in international thermonuclear experimental reactor (ITER) and future thermonuclear demonstration fusion reactor due to its high thermal conductivity, low thermal expansion coefficient and irradiation activation, and excellent comprehensive mechanical properties. The first wall (FW) as a component directly facing the plasma bears long-term aging effects such as neutron irradiation, high thermal load and mechanical load, tritium breeder corrosion, and the RAFM steel structural material applied to the first wall should meet quite severe environmental requirements.

[0004] The design of the FW structure is limited by the complex geometry, and its processing and manufacturing have great challenges. The traditional manufacturing method mainly includes multiple steps such as bending, milling, hot isostatic pressing (HIP), fusion welding, mechanical processing and heat treatment, and has long manufacturing cycle and low processing precision. Additive manufacturing (AM) technology has attracted widespread attention from scholars due to its advantages in manufacturing complex three-dimensional shape structures. Selective laser melting (SLM) based on powder bed melting has the advantages of high material utilization rate, short production cycle, high forming precision, good surface quality and excellent mechanical properties compared with traditional processes.

[0005] The sample after SLM forming has a large thermal stress inside due to the influence of heat accumulation, and the material as a whole has high strength and brittleness, so heat treatment is needed to regulate the microstructure and mechanical properties. SUMMARY

[0006] The application aims to overcome the deficiencies of the prior art and provide a heat treatment process for additive manufacturing of RAFM steel. The application refines grains through a selective laser melting rapid melting and cooling process and improves the comprehensive mechanical properties of the RAFM steel through normalizing and tempering heat treatment.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0008] A heat treatment process for additive manufacturing of RAFM steel, comprising the following steps:

[0009] (1) Additive manufacturing of RAFM steel;

[0010] (2) Normalizing heat treatment of the RAFM steel, the normalizing temperature being 900-940 DEG C, the holding time being 30-60 min, and air cooling to room temperature after holding;

[0011] (3) Tempering heat treatment of the RAFM steel treated in step (2), the tempering temperature being 600-730 DEG C, the heating rate being 5-15 DEG C / min, the holding time being 60-80 min, and air cooling to room temperature after holding;

[0012] In the step (1), the preparation method of the RAFM steel comprises the following steps:

[0013] S1: Melting, refining and degassing of RAFM steel raw materials through a vacuum induction furnace to obtain a molten alloy, placing the molten alloy into a gas atomization nozzle system, atomizing the molten alloy into small droplets by inert gas flow, and then rapidly solidifying to form RAFM steel powder;

[0014] S2: Drying the RAFM steel powder in an oven, and then forming the RAFM steel through SLM powder bed melting;

[0015] The RAFM steel raw material comprises the following components by mass percentage:

[0016] C: 0.08-0.15%; Cr: 8.0-9.6%; Mn: 0.3-0.8%; W: 1.0-2.5%; V: 0.1-0.5%; Ta: 0.05-0.2%; the rest being Fe and impurity elements;

[0017] The impurity elements include Al, Si, Ni, Cu, P, S, Co, Nb, Mo, Ag, Sn, As, Sb, B, O, N; wherein, B≤0.001%, N≤0.003%.

[0018] In some embodiments, Al≤0.02%, Si, Ni, Cu≤0.01%, P, S, Co, Nb, Mo≤0.005%, Ag, Sn, As, Sb≤0.001%, O≤0.028%.

[0019] In some embodiments, in S1, the powder particle size of the RAFM steel raw material is in the range of 15-53μm, the particle size distribution is D10=20.0μm, D50=33.1μm, D90=54.2μm, the average particle size is 33.1μm, the Hall flow rate is less than 15s / 50g, the loose bulk density is less than 4g / cm3, and the sphericity is greater than 90%.

[0020] In some embodiments, in S2, the drying temperature of the RAFM steel powder is 100-120℃, and the holding time is 2-5h.

[0021] In some embodiments, in S2, the parameters of the melt forming are: laser power 160-320W, laser scanning speed 600-1200mm / s, scanning interval 70-90μm, layer thickness 25-50μm, preheating temperature 80-120℃, oxygen content in the forming bin less than 100ppm, argon purity 99.999%, cooling time 50-100s, and the scanning path is set as long straight line bidirectional scanning with a layer interlayer deflection angle of 90°.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] The application obtains fine-grained high-performance RAFM steel by combining SLM technology with heat treatment process, uses the rapid melting and cooling characteristics of laser to obtain fine martensite structure, and the process of laser selective melting is three-dimensional modeling→slicing→scanning path planning→printing. The near two-dimensional plane is stacked into a three-dimensional structure by controlling the laser scanning path, without the need for molds, low cost, short cycle, high precision, and unique advantages in preparing complex and precise metal structural parts. Subsequently, the heat treatment process is used to homogenize the structure to obtain higher ductility, and the problem of porosity defects formed in the casting process of large metal components is solved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Fig. 1 is a microstructure diagram of the RAFM steel without heat treatment according to the application;

[0025] Fig. 2 is a microstructure diagram of the RAFM steel after heat treatment according to the application of Example 1;

[0026] Fig. 3 is a microstructure diagram of the RAFM steel after heat treatment according to the application of Comparative Example 1;

[0027] Fig. 4 is a microstructure diagram of the RAFM steel after heat treatment according to the application of Comparative Example 2;

[0028] Figure 5 is a comparison chart of the room temperature tensile properties of RAFM steels of Examples 1-3 and the control group;

[0029] Figure 6 is a comparison chart of the room temperature impact properties and microhardness of RAFM steels of Examples 1-3 and the control group;

[0030] Figure 7 is a comparison chart of the tensile properties of RAFM steels of Examples 4-10 and the control group. DETAILED DESCRIPTION

[0031] The D10, D50, and D90 are the particle sizes at which 10%, 50%, and 90% of the cumulative particle size distribution is reached, respectively. In the present application, the cumulative particle size distribution values can be determined, for example, from the particle size distribution obtained by image analysis.

[0032] The "average particle size" refers to the average diameter of the steel grains, which is measured according to GB / T 6394-2017 "Metallic average grain size determination method".

[0033] The term "Hall flow rate" refers to the time (in seconds / 50g) required for 50g of metal powder to pass through a funnel of a specific gauge (typically 2.5mm aperture) under standard conditions, with shorter times indicating better powder flowability. This index is specified by the national standard GB / T 1482-2022 "Metal powder flowability determination standard funnel method", using a non-magnetic corrosion-resistant metal funnel, with a measurement accuracy requirement of ±0.1 seconds.

[0034] The term "bulk density" refers to the mass per unit volume of steel powder or bulk material in a naturally accumulated state, which is usually measured by three-dimensional laser scanning method (error ±3%) 1 or natural filling method (GB / T 5162-2023 standard).

[0035] The term "sphericity" refers to the closeness of the actual shape of the steel particles or steel balls to an ideal sphere, which is usually quantified by parameters such as diameter deviation and surface roundness.

[0036] To better illustrate the purpose, technical solutions and advantages of the present application, specific examples will be used to further illustrate the present application below, but the scope of protection and implementation of the present application is not limited thereto.

[0037] The present application provides a heat treatment process for additive manufacturing of RAFM steel, comprising the following steps:

[0038] (1) Additive manufacturing of RAFM steel;

[0039] (2) normalizing heat treatment of the RAFM steel, the normalizing temperature is 900-1060℃, the holding time is 30-60min, and after holding, air cooling to room temperature;

[0040] (3) The RAFM steel treated in step (2) is subjected to a tempering heat treatment, the tempering temperature is 600-800℃, the heating rate is 5-15℃ / min, the holding time is 60-120min, and the holding is followed by air cooling to room temperature.

[0041] In some embodiments, the preparation method of the RAFM steel in step (1) comprises the following steps:

[0042] S1: Melting, refining and degassing of the RAFM steel raw material by a vacuum induction furnace to obtain a molten alloy, placing the molten alloy into a gas atomization nozzle system, atomizing the molten alloy into small droplets by inert gas flow, and then rapidly solidifying to form a RAFM steel powder;

[0043] S2: Drying the RAFM steel powder in an oven, and then forming the RAFM steel by SLM powder bed fusion.

[0044] In some embodiments, in S1, the rate of the inert gas flow is 1000-1500Nm3 / h.

[0045] In some embodiments, the RAFM steel raw material comprises the following components by mass percentage:

[0046] C: 0.08-0.15%; Cr: 8.0-9.6%; Mn: 0.3-0.8%; W: 1.0-2.5%; V: 0.1-0.5%; Ta: 0.05-0.2%; the rest is Fe and impurity elements.

[0047] In some embodiments, the impurity elements include: Al, Si, Ni, Cu, P, S, Co, Nb, Mo, Ag, Sn, As, Sb, B, O, N; wherein, Al≤0.02%, Si, Ni, Cu≤0.01%, P, S, Co, Nb, Mo≤0.005%, Ag, Sn, As, Sb, B≤0.001%, O≤0.028%, N≤0.003%.

[0048] In some embodiments, in S1, the powder particle size range of the RAFM steel raw material is 15-53μm, the particle size distribution is D10=20.0μm, D50=33.1μm, D90=54.2μm, the average particle size is 33.1μm, the Hall flow rate is less than 15s / 50g, the loose bulk density is less than 4g / cm 3 , and the sphericity is greater than 90%.

[0049] In some embodiments, in S2, the drying temperature of the RAFM steel powder is 100-120℃, and the holding time is 2-5h.

[0050] In some embodiments, in S2, the parameters of the melt forming are: laser power 160-320 W, laser scanning speed 600-1200 mm / s, scanning pitch 70-90 pm, layer thickness 25-50 pm, preheating temperature 80-120 °C, oxygen content in the forming chamber less than 100 ppm, argon purity 99.999%, cooling time 50-100 s, and the scanning path is set as long straight line bidirectional scanning with an interlayer deflection angle of 90°.

[0051] In some embodiments, the normalizing temperature in step (2) is 940-1050 °C, and can be specifically 940 °C, 950 °C, 960 °C, 970 °C, 980 °C, 990 °C, 1000 °C, 1020 °C, or 1050 °C.

[0052] In some embodiments, the tempering temperature in step (3) is 650-740 °C, and can be specifically 650 °C, 660 °C, 670 °C, 680 °C, 690 °C, 700 °C, 710 °C, 720 °C, 730 °C, or 740 °C.

[0053] In some embodiments, the heating rate during the tempering heat treatment in step (3) is any one or a range value of two of 5 °C / min, 6 °C / min, 8 °C / min, 10 °C / min, 12 °C / min, or 15 °C / min.

[0054] In the present application, if the heating rate is too fast, the RAFM steel is not uniformly heated; if the heating rate is too slow, the heat treatment efficiency is low, the time is too long, and the long heating time will coarsen the grains, affecting the performance of the RAFM steel. Therefore, by controlling the heating rate during tempering within the above range, the comprehensive performance of the RAFM steel is improved.

[0055] In some embodiments, the tempering holding time in step (3) is 60-90 min, and can be specifically 60 min, 70 min, 80 min, or 90 min.

[0056] The present application also provides a RAFM steel obtained by the heat treatment process of the additive manufacturing RAFM steel.

[0057] The materials, reagents, etc. used in the following examples are commercially available reagents and materials unless otherwise specified.

[0058] Example 1

[0059] The present embodiment discloses a heat treatment process of an additive manufacturing RAFM steel, comprising the following steps:

[0060] (1) Additive manufacturing of the RAFM steel:

[0061] S1: melting, refining and degassing the RAFM steel raw material by a vacuum induction melting furnace to obtain a molten alloy, placing the molten alloy into a gas atomization nozzle system, atomizing the molten alloy into small droplets by using a high-speed inert gas flow, and then rapidly solidifying to form a RAFM steel powder;

[0062] The RAFM steel raw material comprises the following components by mass percentage:

[0063] C: 0.10%; Cr: 8.61%; Mn: 0.63%; W: 1.5%; V: 0.3%; Ta: 0.11%; and the rest is Fe and impurity elements;

[0064] The impurity elements include: Al≤0.02%, Si, Ni, Cu≤0.01%, P, S, Co, Nb, Mo≤0.005%, Ag, Sn, As, Sb, B≤0.001%, O≤0.028%, and N≤0.003%.

[0065] The powder particle size range of the RAFM steel raw material is 15-53 μm, the particle size distribution is D10=20.0 μm, D50=33.1 μm, D90=54.2 μm, the average particle size is 33.1 μm, the Hall flow rate is 12.5 s / 50 g, the loose bulk density is 3.8 g / cm 3 , and the sphericity is 95%.

[0066] S2: drying the RAFM steel powder in a drying oven, the drying temperature is 100℃, the holding time is 5h, and then the RAFM steel is obtained by SLM powder bed melting forming;

[0067] The parameters of the melting forming are: laser power 160 W, laser scanning speed 600 mm / s, scanning interval 90 μm, layer thickness 30 μm, preheating temperature 80℃, oxygen content in the forming bin less than 100 ppm, argon purity 99.999%, cooling time 50 s, and the scanning path is set as long straight line bidirectional scanning with a layer deflection angle of 90°.

[0068] (2) normalizing the RAFM steel, the normalizing temperature is 900℃, the holding time is 30 min, and the RAFM steel is air cooled to room temperature after holding.

[0069] (3) tempering the RAFM steel treated in step (2), the tempering temperature is 600℃, the heating rate is 5℃ / min, the holding time is 60 min, and the RAFM steel is air cooled to room temperature after holding.

[0070] The size of the additive manufactured RAFM steel in this embodiment is 150×60×16 mm, and the printing thickness is 20 mm.

[0071] Example 2

[0072] The present embodiment discloses a heat treatment process for additive manufacturing of RAFM steel, comprising the following steps:

[0073] (1) Additive manufacturing of RAFM steel:

[0074] S1: Melting, refining and degassing of RAFM steel raw materials by vacuum induction melting furnace, placing the molten alloy into a gas atomization nozzle system, atomizing the alloy liquid into small droplets by using high-speed inert gas flow, and then rapidly solidifying to form RAFM steel powder;

[0075] The RAFM steel raw material comprises the following components by mass percentage:

[0076] C: 0.10%; Cr: 8.61%; Mn: 0.63%; W: 1.5%; V: 0.3%; Ta: 0.11%; the rest is Fe and impurity elements;

[0077] Among them, the impurity elements include: Al≤0.02%, Si, Ni, Cu≤0.01%, P, S, Co, Nb, Mo≤0.005%, Ag, Sn, As, Sb, B≤0.001%, O≤0.028%, N≤0.003%.

[0078] The powder particle size range of the RAFM steel raw material is 15-53 μm, the particle size distribution is D10=20.0 μm, D50=33.1 μm, D90=54.2 μm, the average particle size is 33.1 μm, the Hall flow rate is 12.5 s / 50 g, the loose bulk density is 3.8 g / cm 3 , and the sphericity is 95%.

[0079] S2: Drying the RAFM steel powder in a drying oven at a drying temperature of 100°C for 2h, and then forming by SLM powder bed melting to obtain the RAFM steel;

[0080] Among them, the parameters of the melting forming are: laser power 320W, laser scanning speed 1200mm / s, scanning interval 120μm, layer thickness 50μm, preheating temperature 100°C, oxygen content in the forming bin less than 100ppm, argon purity 99.999%, cooling time 100s, scanning path setting long straight line bidirectional scanning, and interlayer deflection angle 90°.

[0081] (2) Normalizing heat treatment of the RAFM steel, normalizing temperature is 1060°C, holding time is 60min, and holding after air cooling to room temperature.

[0082] (3) The RAFM steel treated in step (2) is subjected to a tempering heat treatment, the tempering temperature is 800℃, the heating rate is 15℃ / min, the holding time is 120min, and the holding is air-cooled to room temperature.

[0083] The size of the additive manufactured RAFM steel in this embodiment is 150x60x16mm, and the printing thickness is 20mm.

[0084] Example 3

[0085] This embodiment discloses a heat treatment process for additive manufacturing of RAFM steel, comprising the following steps:

[0086] (1) Additive manufacturing of RAFM steel:

[0087] S1: The RAFM steel raw material is melted, refined and degassed by a vacuum induction melting furnace, the molten alloy is placed into a gas atomization nozzle system, the alloy liquid is atomized into small droplets by using high-speed inert gas flow, and then rapid solidification is carried out to form RAFM steel powder;

[0088] The RAFM steel raw material comprises the following components by mass percentage:

[0089] C: 0.10%; Cr: 8.61%; Mn: 0.63%; W: 1.5%; V: 0.3%; Ta: 0.11%; the rest is Fe and impurity elements;

[0090] Among them, the impurity elements include: Al≤0.02%, Si, Ni, Cu≤0.01%, P, S, Co, Nb, Mo≤0.005%, Ag, Sn, As, Sb, B≤0.001%, O≤0.028%, N≤0.003%.

[0091] The powder particle size range of the RAFM steel raw material is 53μm, the particle size distribution is D10=20.0μm, D50=33.1μm, D90=54.2μm, the average particle size is 33.1μm, the Hall flow rate is 12.5s / 50g, the loose bulk density is 3.8g / cm 3 , and the sphericity is 95%.

[0092] S2: The RAFM steel powder is placed in a drying oven for drying, the drying temperature is 120℃, the holding time is 4h, and then the SLM powder bed melting is formed to obtain the RAFM steel;

[0093] The parameters of the melt forming are as follows: laser power 240 W, laser scanning speed 600 mm / s, scanning interval 70 μm, layer thickness 25 μm, preheating temperature 120 ℃, oxygen content in the forming bin less than 100 ppm, argon purity 99.999%, cooling time 80 s, and the scanning path is set as long straight line bidirectional scanning with an interlayer deflection angle of 90°.

[0094] (2) The RAFM steel is subjected to normalizing heat treatment, the normalizing temperature is 940 ℃, the holding time is 55 min, and the steel is air-cooled to room temperature after holding.

[0095] (3) The RAFM steel subjected to step (2) is subjected to tempering heat treatment, the tempering temperature is 650 ℃, the heating rate is 10 ℃ / min, the holding time is 70 min, and the steel is air-cooled to room temperature after holding.

[0096] The size of the additive manufactured RAFM steel in this embodiment is 150×60×16 mm, and the printing thickness is 20 mm.

[0097] Example 4

[0098] A heat treatment process for additive manufacturing of RAFM steel, which is different from example 1 in that the normalizing temperature in step (2) is 940 ℃, the holding time is 45 min; the tempering temperature in step (3) is 740 ℃, the holding time is 90 min, and the others are the same as example 1.

[0099] Example 5

[0100] A heat treatment process for additive manufacturing of RAFM steel, which is different from example 1 in that the normalizing temperature in step (2) is 980 ℃, the holding time is 45 min; the tempering temperature in step (3) is 740 ℃, the holding time is 90 min, and the others are the same as example 1.

[0101] Example 6

[0102] A heat treatment process for additive manufacturing of RAFM steel, which is different from example 1 in that the normalizing temperature in step (2) is 1020 ℃, the holding time is 45 min; the tempering temperature in step (3) is 740 ℃, the holding time is 90 min, and the others are the same as example 1.

[0103] Example 7

[0104] A heat treatment process for additive manufacturing of RAFM steel, which is different from example 1 in that the normalizing temperature in step (2) is 1050 ℃, the holding time is 45 min; the tempering temperature in step (3) is 740 ℃, the holding time is 90 min, and the others are the same as example 1.

[0105] Example 8

[0106] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that the normalizing temperature in step (2) is 980℃, the holding time is 45min; the tempering temperature in step (3) is 650℃, the holding time is 90min, and the others are the same as example 1.

[0107] Example 9

[0108] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that the normalizing temperature in step (2) is 980℃, the holding time is 45min; the tempering temperature in step (3) is 700℃, the holding time is 90min, and the others are the same as example 1.

[0109] Example 10

[0110] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that the normalizing temperature in step (2) is 980℃, the holding time is 45min; the tempering temperature in step (3) is 780℃, the holding time is 90min, and the others are the same as example 1.

[0111] Comparative example 1

[0112] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that only hot isostatic pressing (HIP) heat treatment is performed on the RAFM steel, and the process parameters are: pressure is 120MPa, heating temperature is 920℃, holding time is 120min, furnace cooling, and heating rate is 10℃ / min.

[0113] Comparative example 2

[0114] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that after the RAFM steel is subjected to the tempering heat treatment of step (3), hot isostatic pressing heat treatment is additionally performed, and the heat treatment process parameters are: pressure is 120MPa, heating temperature is 920℃, holding time is 120min, furnace cooling, and heating rate is 10℃ / min.

[0115] Comparative example 3

[0116] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that the normalizing temperature in step (2) is 800℃, and the others are the same as example 1.

[0117] Comparative example 4

[0118] A heat treatment process for additive manufacturing of RAFM steel, different from example 1 in that the normalizing temperature in step (2) is 1100℃, and the others are the same as example 1.

[0119] Comparative Example 5

[0120] A heat treatment process for additive manufacturing of RAFM steel, which is different from Example 1 in that the heating rate during tempering heat treatment in step (3) is 2°C / min, and the others are the same as Example 1.

[0121] Comparative Example 6

[0122] A heat treatment process for additive manufacturing of RAFM steel, which is different from Example 1 in that the heating rate during tempering heat treatment in step (3) is 20°C / min, and the others are the same as Example 1.

[0123] Comparative Example 7

[0124] A heat treatment process for additive manufacturing of RAFM steel, which is different from Example 1 in that the tempering temperature in step (3) is 500°C, and the others are the same as Example 1.

[0125] Comparative Example 8

[0126] A heat treatment process for additive manufacturing of RAFM steel, which is different from Example 1 in that the tempering temperature in step (3) is 850°C, and the others are the same as Example 1.

[0127] Comparative Example 9

[0128] A heat treatment process for additive manufacturing of RAFM steel, which is different from Example 1 in that the tempering holding time in step (3) is 50 min, and the others are the same as Example 1.

[0129] Comparative Example 10

[0130] A heat treatment process for additive manufacturing of RAFM steel, which is different from Example 1 in that the tempering holding time in step (3) is 180 min, and the others are the same as Example 1.

[0131] Control group

[0132] RAFM steel without any heat treatment.

[0133] Performance test

[0134] 1. Tensile strength: The tensile strength is the maximum bearing capacity of the metal under quasi-static tensile conditions, which is the critical value of the transition from uniform plastic deformation to local concentrated plastic deformation of the metal, and is expressed by σ b .

[0135] 2. Yield strength: the yield strength is the yield limit when the metal material has a yield phenomenon, for the RAFM steel without obvious yield phenomenon, the stress value causing 0.2% residual deformation is defined as the yield strength, and is represented by σ s .

[0136] 3. Elongation: the elongation is the ratio of the original gage length after fracture elongation to the initial gage length when the metal material is in quasi-static tension, and is represented by δ.

[0137] 4. Static toughness: the static toughness is used to reflect the anti-fracture ability of the material in the process of force, and can be approximately represented by 0.5*(σ b +σ s )*δ.

[0138] The above indexes are obtained by tensile test, and the metal material tensile test is performed according to GB / T228.1-2021 test standard.

[0139] 5. Impact work: the impact work is an index for measuring the toughness of the material, and is the ability of the material to absorb plastic deformation work and fracture work under impact load, and is represented by A k . The Charpy impact test is performed according to GB / T229-2007 test standard.

[0140] 6. Vickers hardness: used to describe the ability of the material to resist the pressure of hard objects into its surface, and is represented by HV. The Vickers hardness test is performed according to GB / T4340.1-2009 test standard.

[0141] The above test results are shown in Table 1.

[0142] Table 1

[0143] According to Table 1 and Figures 5-7, the tensile strength and yield strength of the RAFM steel decrease after normalizing and tempering heat treatment, because the dislocations are absorbed after heat treatment, the dislocation strengthening mechanism is weakened, so the strength decreases, and the small grains grow during the heat treatment process, and the strength decreases. However, the elongation of the RAFM steel increases after heat treatment. And, by controlling the temperature and holding time during normalizing heat treatment and tempering heat treatment, the RAFM steel has high plasticity and toughness, so that the comprehensive performance of the RAFM steel is greatly improved.

[0144] According to Examples 1-10, the RAFM steel is refined by laser selective melting rapid melting and cooling process, and the plasticity and toughness of the RAFM steel are effectively improved by normalizing and tempering heat treatment, and according to the calculation of the static toughness, the normalizing and tempering heat treatment process has a significant effect on improving the comprehensive mechanical properties of the material.

[0145] According to figures 1-4, the fine-grained high-performance RAFM steel provided by the application can regulate the internal microstructure through a heat treatment process. Before heat treatment, the microstructure is chessboard-shaped, with orderly arrangement of coarse columnar crystals and small equiaxed crystals, and the grain growth has a preferred orientation in the <101> direction. The structure has anisotropy. After heat treatment, the grain orientation is more uniform, and the grains are refined during the recrystallization process, and the alloy elements continuously precipitate carbides. According to the strength theory, the grain refinement and carbide precipitation have a significant impact on the mechanical properties of the RAFM steel.

[0146] According to table 1, examples 4-10, when the tempering temperature remains unchanged at 740℃, and the normalizing temperature changes from 940℃ to 980℃ to 1020℃ to 1050℃, the static toughness is 8500.17MPa·%, 9839.51MPa·%, 9740.70MPa·%, and 9338.80MPa·%, respectively. When the normalizing temperature remains unchanged at 980℃, and the tempering temperature changes from 650℃ to 700℃ to 740℃ to 780℃, the static toughness is 8349.12MPa·%, 9446.80MPa·%, 9839.51MPa·%, and 9764.44MPa·%, respectively. Compared with the static toughness (3345.73MPa·%) of the RAFM steel sample without heat treatment, the static toughness is significantly improved.

[0147] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application and not to limit the scope of protection of the application. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the application.

Claims

1. A heat treatment process for additive manufacturing of RAFM steel, comprising the following steps: (1) Additive manufacturing of RAFM steel; (2) Normalizing heat treatment of the RAFM steel, the normalizing temperature being 900-940℃, the holding time being 30-60min, and the holding being followed by air cooling to room temperature; (3) Tempering heat treatment of the RAFM steel after step (2), the tempering temperature being 600-730℃, the heating rate being 5-15℃ / min, the holding time being 60-80min, and the holding being followed by air cooling to room temperature; wherein the preparation method of the RAFM steel in step (1) comprises the following steps: S1: Melting, refining and degassing of RAFM steel raw materials by a vacuum induction furnace to obtain a molten alloy, placing the molten alloy into a gas atomization nozzle system, atomizing the molten alloy into small droplets by inert gas flow, and then rapidly solidifying to form RAFM steel powder; S2: Drying the RAFM steel powder in an oven, and then forming the RAFM steel by SLM powder bed fusion; the RAFM steel raw materials comprising the following components by mass percentage: C: 0.08-0.15%; Cr: 8.0-9.6%; Mn: 0.3-0.8%; W: 1.0-2.5%; V: 0.1-0.5%; Ta: 0.05-0.2%; the rest being Fe and impurity elements; the impurity elements including: Al, Si, Ni, Cu, P, S, Co, Nb, Mo, Ag, Sn, As, Sb, B, O, N; wherein B≤0.001%, N≤0.003%.

2. The heat treatment process for additively manufactured RAFM steel of claim 1, wherein, Al≤0.02%, Si, Ni, Cu≤0.01%, P, S, Co, Nb, Mo≤0.005%, Ag, Sn, As, Sb≤0.001%, O≤0.028%.

3. The heat treatment process for additively manufactured RAFM steel of claim 1, wherein, In S1, the powder particle size of the RAFM steel raw material is in the range of 15-53 μm, the particle size distribution is D10=20.0 μm, D50=33.1 μm, D90=54.2 μm, the average particle size is 33.1 μm, the Hall flow rate is less than 15 s / 50 g, the loose bulk density is less than 4 g / cm 3 , and the sphericity is greater than 90%.

4. The heat treatment process for additively manufactured RAFM steel of claim 1, wherein, In S2, the drying temperature of the RAFM steel powder is 100-120℃, and the holding time is 2-5h.

5. The heat treatment process for additively manufactured RAFM steel of claim 1, wherein, In S2, the parameters of the fusion forming are: laser power 160-320W, laser scanning speed 600-1200mm / s, scanning pitch 70-90μm, layer thickness 25-50μm, preheating temperature 80-120℃, oxygen content in the forming bin less than 100ppm, argon purity 99.999%, cooling time 50-100s, scanning path set as long straight line bidirectional scanning, and layer deflection angle 90°.

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