CN110669997A - Method for laser melting deposition of 24CrNiMo alloy steel - Google Patents

Abstract

The invention relates to a method for laser melting and depositing 24CrNiMo alloy steel, which sets a time interval of 2-10min when adjacent deposition layers are deposited, so that the temperature of the previously deposited deposition layer is reduced to 180-220 ℃ and then the next deposition layer is deposited. Compared with the traditional processing method, the method disclosed by the invention omits complex heat treatment process steps, realizes real-time regulation and control of the phase structure of the laser melting deposition 24CrNiMo alloy steel, reduces energy consumption and labor cost, and shortens the processing period. In addition, the phase structure obtained by real-time regulation and control of the laser melting deposition 24CrNiMo alloy steel is a low-carbon lath martensite structure with high strength and high toughness, the grain size of the phase structure is obviously smaller than that of a part obtained by a traditional processing method, the mechanical property of the alloy steel component is obviously improved, and the phase structure has the practical engineering application potential of reducing the production period and resource consumption.

Description

Method for laser melting deposition of 24CrNiMo alloy steel

Technical Field

The invention relates to a method for laser melting deposition of 24CrNiMo alloy steel. More specifically, the invention relates to laser additive manufacturing of high-performance alloy steel parts, namely phase structure, internal defects, tensile property and the like of 24CrNiMo alloy steel are regulated and controlled through an optimized laser deposition method.

Background

24CrNiMo is a material component system commonly used for low-alloy high-strength steel at the present stage in China, and at present, alloy steel of the system is usually manufactured into alloy steel blanks through the traditional casting and forging processes, and then a heat treatment process is designed according to different use requirements. The alloy steel after processing has the advantages of high specific strength, stable components at high temperature, high impact toughness and good wear resistance, and is widely applied to parts which have high requirements on strength and bear high load, such as a transmission eccentric shaft of a horizontal forging machine, a crankshaft in a forging press, a high-iron brake disc and the like. In addition, the alloy steel of the system is also applied to parts with high requirements on wear resistance and strength, such as transmission gears, petroleum exploration equipment and the like after surface treatment.

The traditional processing method of the 24CrNiMo low-alloy high-strength steel part comprises the processing steps of casting, forging, hot sintering, heat treatment, turning and the like. The traditional processing method has long production period, serious energy consumption and great environmental pollution. The phase structure and the mechanical property of the 24CrNiMo alloy steel obtained in different heat treatment states are different, so that different heat treatment processes can be selected according to the requirements of finished parts on the mechanical property in the traditional machining process. Generally, eccentric shafts, crankshafts, camshafts, and the like in heavy machinery require toughness in the inside and hardness in the outside, so that a granular bainite structure having good toughness is obtained by subjecting a core portion to thermal refining and then to high-temperature or medium-temperature tempering. The gear drill bit in the traditional gear and oil exploration equipment needs parts with higher strength and hardness, so the 24CrNiMo alloy steel is generally subjected to quenching and tempering and low-temperature tempering to obtain a low-carbon martensite structure with higher strength after being forged.

Laser melting deposition (Laser melting deposition) additive manufacturing employs a Laser as a heat source to melt metal powder that is synchronously conveyed and to achieve additive manufacturing of metal components by layer-by-layer buildup. In the additive manufacturing process, technological parameters such as laser energy input, scanning path, scanning speed, powder feeding amount and the like can be accurately controlled according to a part model or a program, and the free forming manufacturing of metal parts with complex shapes is realized. Compared with the traditional manufacturing technology, the laser melting deposition has the advantages of short production period, high material utilization rate and small environmental pollution. At present, research aiming at laser additive manufacturing of 24CrNiMo alloy steel mainly focuses on the influence of laser process parameters on the defect number of deposited parts, phase structure regulation and control of the 24CrNiMo alloy steel are realized by changing a deposition method in a laser melting deposition process, and no scholars conduct research at present. According to the characteristics of the processing technology of 24CrNiMo alloy steel, the phase structure is mainly influenced by the cooling rate between the austenitizing temperature A3 and the room temperature, so that different cooling rates can be obtained by changing the interlayer cooling time interval of a deposition layer in the laser melting deposition process, and further the real-time regulation and control of the phase structure of 24CrNiMo alloy steel laser in the laser material increasing process are realized.

Disclosure of Invention

The Cr-Ni-Mo series low-alloy high-strength steel is widely applied to drill bits in the field of oil exploration with extremely high requirements on strength and toughness, gear parts in the field of heavy machinery, transmission shafts, brake discs and other parts in the field of high-speed railways after being processed by traditional preparation methods such as casting, forging, heat treatment, turning and the like. Different heat treatments are carried out on the forged low-alloy high-strength steel according to the requirements of different parts on mechanical properties such as strength, wear resistance, toughness and the like, and the main heat treatment process is quenching and tempering. The quenching and tempering treatment in the traditional processing method has the problems of long processing period, high labor cost, serious energy consumption and the like. The invention aims to change the highest temperature and the cooling rate of a 24CrNiMo alloy steel deposition layer in the solidification process by changing a laser melting deposition method so as to regulate and control the phase structure and the mechanical property of the 24CrNiMo alloy steel. Compared with the traditional processing method, the method disclosed by the invention omits complex heat treatment process steps, realizes real-time regulation and control of the phase structure of the laser melting deposition 24CrNiMo alloy steel, reduces energy consumption and labor cost, and shortens the processing period. In addition, the phase structure and the grain size obtained by real-time regulation and control of the laser melting deposition 24CrNiMo alloy steel are obviously smaller than those obtained by the traditional processing method, and the mechanical property of the alloy steel member is obviously improved.

In one aspect, the invention relates to a method for depositing 24CrNiMo alloy steel by laser melting, which sets a time interval of 2-10min when adjacent deposition layers are deposited, and reduces the temperature of the deposition layer deposited in advance to 180-220 ℃ before depositing the next layer.

After the laser melting deposition of one layer, in order to avoid generating larger heat accumulation, the laser melting deposition of a new deposition layer can be continued when the temperature of the deposited layer is reduced gradually along with the prolonging of the interval time by stopping a period of time between adjacent deposition layers and measuring the temperature change of the deposition layer by using contact type temperature measuring equipment, and the temperature is reduced to 180-220 ℃. If the temperature of the deposited layer is lower than 180 ℃, then the laser melting is carried out to deposit a new deposited layer, on one hand, the production efficiency can be reduced due to the prolonging of the interlayer time interval, on the other hand, the deposited layer can generate oxide inclusions due to the overlong contact time with oxygen, and then the metallurgical bonding between the deposited layers is influenced, and internal defects are generated, so that the mechanical property is reduced. If the temperature of the deposited layer is higher than 220 ℃, and then the laser melting is carried out to deposit a new deposited layer, the heat accumulation is generated in the deposited layer, and the cooling rate of the deposited layer is further reduced, and because the cooling rate of the deposited layer is lower than the critical cooling rate for generating lath martensite, a lath martensite structure with excellent mechanical property cannot be obtained finally.

In a preferred embodiment, each deposition layer is deposited using a reciprocating scan, the scan direction between adjacent deposition layers being the same or different, preferably rotated by 90 °.

In a preferred embodiment, the method uses a fiber laser, a semiconductor laser or CO under inert gas shielding₂The laser melts and deposits 24CrNiMo alloy steel powder on the substrate material.

In a preferred embodiment, the method parameters are set as follows: the laser power is 2500 w-10000 w, preferably 2500 w-4000 w, the scanning speed is 5 mm/s-100 mm/s, preferably 5 mm/s-20 mm/s, the lap joint rate is 40% -50%, the powder feeding speed is 8 g/min-100 g/min, preferably 8 g/min-20 g/min, the Z-axis lifting amount of each layer is 1 mm-4 mm, preferably 1 mm-4 mm, the laser spot diameter is 3 mm-4 mm, and the defocusing amount is 2 mm.

The specific process parameters of the laser melting deposition and the time interval between adjacent deposition layers are properly selected according to the sizes of the substrate and the deposition layers, and only the temperature of the deposition layer deposited in advance is reduced to 180-220 ℃ and then the next layer is deposited.

In a preferred embodiment, the 24CrNiMo alloy steel powder has a grain diameter of 40-180 μm, and comprises the following elements in percentage by mass: c: 0.2 to 0.25%, Ni: 1-1.49%, Cr: 1-1.2%, Mn: 0.5-1%, Mo: 0.4-1%, O: less than 0.034%, and the balance Fe.

In a preferred embodiment, the substrate material is selected from 304L, 316L, Q195, Q215, Q235, Q255, or Q275.

In a preferred embodiment, the inert gas is argon or nitrogen with a purity higher than 99.99%.

In a preferred embodiment, the method comprises the steps of:

(1) pretreatment of 24CrNiMo alloy steel powder: placing 24CrNiMo alloy steel powder in a vacuum drying oven for dehydration treatment, setting the temperature to be 100-120 ℃, and continuing for 4-6 h;

(2) pretreatment of a substrate material: polishing the surface of the substrate material by using a grinding wheel to remove rust or oxide skin; sequentially polishing the surface of the substrate by using 200# and 400# abrasive paper, cleaning the surface by using absolute ethyl alcohol after polishing, and drying for later use;

(3) laser melting deposition forming: the 24CrNiMo alloy steel material with the lath martensite phase structure is finally obtained by carrying out laser melting deposition according to the method.

In another aspect, the invention relates to a 24CrNiMo alloy steel article obtained by the above method.

Drawings

FIG. 1 is a schematic drawing showing dimensions of a laser fused deposition 24CrNiMo alloy steel tensile test piece.

FIG. 2 is SEM topography of 24CrNiMo alloy steel powder.

FIG. 3 is a normal distribution diagram of the particle size of 24CrNiMo alloy steel powder.

FIG. 4 is a schematic illustration of the preparation of 24CrNiMo alloy steel.

FIG. 5 is a schematic illustration of a process for preparing 24CrNiMo alloy steel.

Fig. 6 is an XRD diffraction pattern of 24CrNiMo alloy steel, fig. 6 (a): sample S1, fig. 6 (b): sample S2, fig. 6 (c): sample S3.

FIG. 7 shows CCT curve simulation results of 24CrNiMo alloy steel.

Fig. 8 is metallographic structure and SEM morphology of 24CrNiMo alloy steel, fig. 8 (a): sample S1, fig. 8 (b): sample S2, fig. 8 (c): sample S3.

FIG. 9 shows TEM morphology and selected area diffraction spots of laser fused deposition 24CrNiMo alloy steel, FIG. 9(a) shows TEM morphology and selected area diffraction spots of S1 sample, FIG. 9(b) shows TEM morphology and selected area diffraction spots of S2 sample, and FIG. 9(c) shows TEM morphology and selected area diffraction spots of S3 sample.

FIG. 10 is a room temperature tensile curve of 24CrNiMo alloy steel.

Fig. 11 is SEM morphology of tensile fracture of 24CrNiMo alloy steel, fig. 11(a) and 11(b) are low and high SEM morphology of S1 sample, respectively, fig. 11(c) and 11(d) are low and high SEM morphology of S2 sample, respectively, and fig. 11(e) and 11(f) are low and high SEM morphology of S3 sample, respectively.

FIG. 12 is a hardness profile of 24CrNiMo alloy steel.

Detailed Description

The principles and features of this invention will be described hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention and are not intended to limit the scope of the invention, which is defined solely by the claims appended hereto.

The laser used in the invention is a YSL-4000 fiber laser, and a pw3040/60 type X-ray diffraction analyzer is used for analyzing the phase composition (Cu Kalpha target material, the scanning range is 20-120 degrees, the scanning speed is 2 degrees/min, the tube voltage is 40kv, and the tube current is 200mA) in a deposition sample. The phase structure morphology of the deposition-state sample is analyzed and observed by a Nava Nano SEM 650 type secondary electron scanning microscope. The JEM-2100F type transmission electron microscope is used for observing and analyzing the crystal structure and the TEM appearance of the sample in a deposition state. Microhardness from the substrate to the deposited layer was measured using a MicroMet-5101 hardness tester with a load of 2.945N and a load time of 15 s. Test tensile properties of as-deposited specimens were measured by AG-X100kN testing machine (Suns, China) at room temperature at a tensile rate of 0.6 mm/s. The dimensions of these tensile specimens (according to ISO 6892-1: 2016) are shown in FIG. 1, the thickness of the tensile specimens being 2 mm. In order to ensure the repeatability of the test, samples under the same conditions were prepared and measured and averaged as tensile data, typical tensile data was taken to plot a tensile curve. The cross-sectional morphology of the failed tensile specimens was observed by SEM.

Example 1

The highest temperature and the cooling rate of the 24CrNiMo alloy steel in the deposition state in the solidification process are changed by changing a laser melting deposition strategy, so that different phase structures and mechanical properties are obtained. The specific implementation process comprises the following steps:

(1) pretreatment of 24CrNiMo alloy steel powder: the 24CrNiMo alloy steel powder comprises the following elements in percentage by mass (wt.%): c: 0.25%, Ni: 1.49%, Cr: 1.12%, Mn: 0.65%, Mo: 0.49%, O: 0.030% and the balance Fe. The powder SEM morphology is shown in fig. 2, and exhibits a spherical morphology. The particle size distribution of the powder is shown in FIG. 3, and the average particle size is 79 μm. Placing the powder in a vacuum drying oven, and keeping the temperature at 110 ℃ for 4 hours to remove the water in the powder.

(2) Pretreatment of a substrate material: the substrate material is a rolled Q235 alloy steel plate, and the specific size is 60mm multiplied by 80mm multiplied by 15 mm. First, the oxide scale and rust on the substrate surface were removed with a grinding wheel, and the substrate surface was cleaned with absolute ethanol. And then sequentially polishing the surface of the substrate by using 200# and 400# sandpaper, cleaning the surface by using absolute ethyl alcohol, and drying the surface of the substrate by using a blower for later use.

(3) Laser melting deposition test: adopting a fiber laser, carrying out laser melting and deposition on the pretreated 24CrNiMo alloy steel powder on a Q235 alloy steel substrate, and adopting three different deposition strategies in the deposition process to obtain 24CrNiMo alloy steel deposition layers with three different phase structures, wherein the method comprises the following specific steps:

a) and starting the PLC master controller, the fiber laser, the six-axis joint robot, the water cooling circulation, the protective gas and the powder feeding gas switch, and placing the pretreated Q235 substrate surface on the sample table upwards. The distance from the laser cladding head to the surface of the substrate is adjusted through the robot teaching box, so that the distance from the surface of the substrate to the laser cladding head is 14 mm. In addition, the pretreated 24CrNiMo alloy steel powder was placed in the powder tank of the powder feeder.

b) Fig. 4 is a schematic diagram of a laser melting deposition process, and specific process parameters are set as follows: the laser power is 2500w, the scanning speed is 5mm/s, the lap joint rate is 40%, the powder feeding rate is 11.6g/min, the Z-axis lifting amount of adjacent deposition layers is 1mm, the laser spot diameter is 3mm, and the defocusing amount is 2 mm. The dimensions of the 24CrNiMo alloy steel deposit layer are 50mm x 20mm x10 mm.

c) On the basis of the laser melting deposition process parameters, three laser melting deposition strategies are designed and named as S1, S2 and S3 respectively, and the names of corresponding samples in a deposition state are an S1 sample, an S2 sample and an S3 sample respectively. As shown in fig. 5, three deposition strategies employ a reciprocating scanning strategy within each deposition layer: the strategy of S1 adopts a continuous deposition method without time interval, the strategy of S2 has 2-minute time interval between adjacent deposition layers, and the strategy of S3 has 90 degrees difference between adjacent deposition layers on the basis of having 2-minute time interval between adjacent deposition layers.

Example 2

Phase structure analysis: after the laser melting deposition test, a deposition state sample is cut along a plane perpendicular to the scanning direction of the first layer of laser, 200#, 400#, 600#, 800#, 1000# and 1500# abrasive paper are used for grinding the cross section in sequence, and diamond polishing liquid with the particle size of 2 mu m is used for polishing the cross section until no obvious scratch exists after grinding. Using an etching solution (4ml HNO)₃+96ml C₂H₅OH) cross-section, the sample phase structure was analyzed by optical microscopy (Olympus, Japan), scanning electron microscopy (Zissis, Germany) and high resolution transmission electron microscopy (JEM-2100). The phase composition of the sample is analyzed by X-ray diffraction (XRD), the related process parameters are Cu Ka, the scanning speed is 3 degrees/min, the scanning angle is 20 degrees to 120 degrees, the voltage is 40kV, and the current is 150 mA. The specific test results and analyses were as follows:

1) XRD diffraction analysis

FIGS. 6a, b and C are XRD diffraction patterns of S1, S2 and S3 samples, respectively, and it is known that main phases of the S1, S2 and S3 samples are alpha-Fe (M) with a body-centered cubic structure, wherein M is an alloy element such as C, Ni, Cr, Mo and the like dissolved in the alpha-Fe. Because the content of alloy elements in the 24CrNiMo alloy steel is less, the degree of alpha-Fe lattice distortion is lower, and the alloy steel can be approximately regarded as a body-centered cubic structure.

2) CCT curve of 24CrNiMo alloy steel

The CCT curve of the 24CrNiMo alloy steel shown in the figure 7 can be obtained through thermodynamic simulation software. The CCT curve shows that the 24CrNiMo alloy steel can obtain different phase structures including bainite, martensite and pearlite under different cooling rates, wherein the cooling curve with the cooling rate of 240.5 ℃/s is the critical cooling rate at which the martensite transformation directly occurs. The invention can change the cooling rate by changing the time interval of adjacent deposition layers in the laser melting deposition process, so the CCT curve of the 24CrNiMo alloy steel provides a reference basis for realizing the phase structure regulation and control of the laser melting deposition 24CrNiMo alloy steel.

3) Observation of tissue morphology

FIGS. 8(a), (b) and (c) show the metallographic structure (upper part of the picture) and SEM structure (lower part of the picture) of the middle of the S1, S2 and S3 samples, respectively, and the analysis of the metallographic structure shows that the S1 sample mainly comprises granular bainite which takes bainitic ferrite as a matrix and on which M-A island elements are distributed. The samples S2 and S3 mainly consist of Lath Martensite (LM for short), and a small amount of M-A island elements are distributed on the Lath Martensite. Since the samples S2 and S3 had time intervals during laser melt deposition, the cooling rate was higher than that of the S1 sample prepared by the continuous deposition method. The CCT curve analysis of the combined 24CrNiMo alloy steel shows that the S1 sample undergoes bainite transformation during cooling from an austenite temperature A3 to room temperature, while the S2 and S3 samples directly undergo martensite transformation during cooling because the cooling rate is higher than 240.5 ℃/S.

FIGS. 9(a), (b) and (c) TEM topographies and selected area diffraction spots (shown in the upper right insert) for the S1, S2 and S3 samples, respectively. The microscopic morphology and structure of the M-A island elements in the S1 sample can be observed and analyzed by TEM, the lath martensite morphology in the M-A island elements in the S1 sample can be observed from FIG. 9(a), the low-carbon martensite structure can be determined by diffraction spots, and the stoichiometric ratio of C to Fe is 0.09: 1.91. The TEM morphology and the selected area diffraction spots in fig. 9(b) and (C) can be used to determine that the microstructures in the samples S2 and S3 are low carbon martensite, and the crystal structure, C, and Fe element stoichiometric ratios of the low carbon martensite are the same as those in the sample S1.

Example 3

Mechanical Property test

1) Room temperature tensile Properties

FIG. 10 is a room temperature tensile graph of the S1, S2 and S3 samples, which shows that the S3 sample has the highest room temperature tensile property, an average tensile strength of 1214MPa, an average yield strength of 1011MPa and an average elongation of 18%. The samples of S1 have an average tensile strength of 949MPa, an average yield strength of 873MPa and an average elongation of 15%. The tensile properties of the S2 sample were the worst, with an average tensile strength of 922MPa, an average yield strength of 832MPa, and an average elongation of 12%. The tensile property of the S3 sample is higher than that of the S1 and S2 samples because the low-carbon martensite obtained by the S3 sample has high-strength and high-toughness mechanical property, and the inclusion defects in the sample can be obviously reduced by rotating the adjacent deposition layers by 90 degrees, so that the crack initiation points of the sample in the tensile process are effectively reduced, and the crack propagation rate is reduced. The tensile properties of the S1 specimen were higher than those of the S2 specimen because the 2 minute time interval between adjacent deposits of the S2 specimen resulted in longer metal to oxygen contact time on the surface of the deposited deposits, which resulted in metal oxide inclusions between the deposits, and inclusion defects in the interior of these deposited parts became crack initiation sites that reduced the tensile properties of the specimens.

Fig. 11(a) and (b), (c) and (d), (e) and (f) are low and high power SEM morphologies of tensile fracture for the S1, S2 and S3 samples, respectively. As shown in fig. 11(b), in addition to the dimples and tear edges with quasi-cleavage characteristics observed at the tensile fracture of the S1 specimen, unmelted alloy steel powder particles were also observed at the fracture failure surface. The presence of the unmelted particles in the S1 sample reduced the tensile properties. As shown in fig. 11(c), the fracture of the S2 sample includes two portions, a fiber region and a shear lip region. The S2 sample (fig. 11(d)) consisted primarily of a large number of dimples and a small number of tear edges, and exhibited primarily ductile fracture characteristics. In addition, a void defect was observed in the fractured surface of the sample of S2, such void being generated by the peeling of the unmelted powder inside the sample under tensile load. The fracture of the S3 specimen (fig. 11e) was also divided into two parts, fiber and shear lip, and the dimple on the fracture surface was smaller and deeper in the S3 specimen (fig. 11f) than in the S2 specimen. As can be seen from the observation of the fracture morphology of the sample, the number of holes and unmelted grains of the S3 sample is lower than that of the S1 and S2 samples. Since these defects act as main sites for initiating fracture by inducing cracks and accelerating crack propagation in the tensile test, the tensile properties of the S3 specimen with a smaller number of defects are higher than those of the S1 and S2 specimens.

2) Hardness of

Fig. 12 is a graph showing the hardness distribution of the S1, S2, and S3 test specimens. The average microhardness of the S1, S2 and S3 specimens were 302HV, 328HV and 360HV, respectively. The S2 and S3 samples had smaller grain sizes due to the higher cooling rate of the S2 and S3 samples than the S1 samples during solidification. The microhardness of the S2 and S3 samples was higher than that of the S1 samples under the fine grain strengthening effect. In addition, since the rotation of the adjacent deposition layers by 90 ° can reduce the inclusion defects inside the test specimen, the number of internal defects of the S3 test specimen is lower than that of the S2 test specimen in the case where the difference in grain size is small. These internal defects become weak points at which micro cracks are initiated when subjected to a load, and therefore the S3 test specimen with the smallest number of internal defects has fewer weak points, so that the hardness of the S3 test specimen is higher than that of the S2 test specimen.

Although the present invention has been described in terms of the preferred embodiment, it is not intended that the invention be limited to the embodiment. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also belong to the protection scope of the present invention. The scope of the invention should therefore be determined with reference to the appended claims.

Claims (9)

1. A method for laser melting deposition of 24CrNiMo alloy steel is characterized by comprising the following steps: in the method, when adjacent deposition layers are deposited, a time interval of 2-10min is set, so that the temperature of the deposition layer deposited firstly is reduced to 180-220 ℃ and then the next layer is deposited.

2. The method of claim 1, wherein: each deposition layer is deposited using a reciprocating scan, the scan direction between adjacent deposition layers being the same or different, preferably rotated by 90 °.

3. The method according to claim 1 or 2, characterized in that: the method uses a fiber laser, a semiconductor laser or CO under the protection of inert gas₂The laser melts and deposits 24CrNiMo alloy steel powder on the substrate material.

4. A method according to any one of claims 1 to 3, characterized in that: the method parameter setting is as follows: the laser power is 2500 w-10000 w, preferably 2500 w-4000 w, the scanning speed is 5 mm/s-100 mm/s, preferably 5 mm/s-20 mm/s, the lap joint rate is 40% -50%, the powder feeding speed is 8 g/min-100 g/min, preferably 8 g/min-20 g/min, the Z-axis lifting amount of each layer is 1 mm-4 mm, preferably 1 mm-4 mm, the laser spot diameter is 3 mm-4 mm, and the defocusing amount is 2 mm.

5. The method according to any one of claims 1 to 4, characterized in that: the particle size of the 24CrNiMo alloy steel powder is 40-180 mu m, and the alloy steel powder comprises the following elements in percentage by mass: c: 0.2 to 0.25%, Ni: 1-1.49%, Cr: 1-1.2%, Mn: 0.5-1%, Mo: 0.4-1%, O: less than 0.034%, and the balance Fe.

6. The method according to any one of claims 1 to 5, wherein: the substrate material is selected from 304L, 316L, Q195, Q215, Q235, Q255, or Q275.

7. The method according to any one of claims 1 to 6, wherein: the inert gas is argon or nitrogen with the purity higher than 99.99 percent.

8. The method according to any one of claims 1 to 7, wherein: the method comprises the following steps:

(1) pretreatment of 24CrNiMo alloy steel powder: placing 24CrNiMo alloy steel powder in a vacuum drying oven for dehydration treatment, setting the temperature to be 100-120 ℃, and continuing for 4-6 h;

(2) pretreatment of a substrate material: polishing the surface of the substrate material by using a grinding wheel to remove rust or oxide skin; sequentially polishing the surface of the substrate by using 200# and 400# abrasive paper, cleaning the surface by using absolute ethyl alcohol after polishing, and drying for later use;

(3) laser melting deposition forming: and carrying out laser melting deposition according to the method to finally obtain the 24CrNiMo alloy steel material with the lath martensite phase structure.

9. A24 CrNiMo alloy steel product is characterized in that: prepared according to the process of any one of claims 1 to 8.

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