Method for enhancing mechanical property of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing

Abstract

The invention discloses a method for enhancing the mechanical property of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, and belongs to the field of high-end equipment manufacturing and new materials.The method comprises the following steps that S1, an alloy powder raw material is prefabricated through a high-energy ball mill, and dried GCr15 powder and VN powder are mixed and then put into the high-energy ball mill to be fully and evenly mixed; s2, the gas environment of the laser additive manufacturing equipment construction cavity is set to be nitrogen, original air of the construction cavity is exhausted into a waste gas cabin through the nitrogen, and the oxygen concentration in the cavity is reduced to 200 ppm or below; and S3, nitrogen is used as circulating gas, and the whole process of preparation, production and cooling of laser additive manufacturing is carried out. According to the method, the microstructure of the alloy is regulated and controlled by increasing the N element content and the V element content in the alloy. Nitrogen atoms enable a strengthening phase to be more easily and uniformly distributed in a solid solution, vanadium can enable fine grain strengthening and precipitation strengthening to be generated in the steel, and the mechanical property of the GCr15 bearing steel alloy is greatly improved through the two reasons.

Description

Technical Field

[0001] The present invention belongs to the field of high-end equipment manufacturing and new materials, and specifically relates to a method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing. Background Art

[0002] Bearings play an extremely important role in industrial equipment and equipment such as machinery, transportation, aerospace, and electricity, and are widely used in major equipment fields such as metallurgical equipment, power and electrical equipment, and large machine tools. This requires that bearing steel needs to have good strength, wear resistance, contact fatigue strength, and toughness. Adding vanadium nitride (VN) material to GCr15 material can significantly improve the strength and toughness of bearing steel. Among them, nitrogen as an intermediate alloy element has more advantages than adding carbon. N and C are the main elements for generating interstitial phases. They exist in the form of interstitial solute atoms in steel. Since nitrogen atoms occupy the interstitial position of the octahedron and the nitrogen atomic radius is smaller than that of carbon, it is easier to be evenly distributed in the solid solution; and the addition of vanadium can significantly improve the strength of steel, which is due to the mechanism of grain refinement and precipitation strengthening.

[0003] Compared with traditional metallurgical methods, laser additive manufacturing is easier to control the element content in the alloy by directly adding simple substances or compounds, thereby improving the mechanical properties of the alloy. By adding uniform reinforcing phase powder to the matrix powder and utilizing the processing characteristics of additive manufacturing, an alloy with uniform internal structure and excellent performance can be produced. Commonly used powder mixing methods include physical and chemical methods. The specific implementation method of the crushing method in the physical method is to use a high-energy ball mill to evenly mix the several powders to be added, so as to achieve the effect of nano-sized particle size powder evenly adhering to the surface of micron-sized particle size powder. Summary of the invention

[0004] The present invention provides a method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, which can fully and evenly mix two powders of different particle sizes, and regulate the element ratio and processing parameters through the laser additive manufacturing method to manufacture a new alloy with excellent mechanical properties.

[0005] The technical solution of the present invention is: a method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, and the specific steps of the method are as follows:

[0006] S1: pre-prepare alloy powder raw materials by high-energy ball mill, mix the dried GCr15 powder and VN powder and put them into the ball mill for full and uniform mixing;

[0007] S2: Set the gas environment of the laser additive manufacturing equipment's build chamber to nitrogen and wait for the ventilation process; specifically, select "Nitrogen" on the operation panel, and the equipment's self-made nitrogen will exhaust the original air in the build chamber into the exhaust chamber, reducing the oxygen concentration in the chamber to below 200ppm;

[0008] S3: Use nitrogen as the circulating gas for the entire process of preparation, production, and cooling of laser additive manufacturing.

[0009] The GCr15 powder described in the present invention has a particle size range of 15 to 53 μm.

[0010] The particle size of the VN powder of the present invention is in the range of 60 to 160 nm.

[0011] The alloy powder raw material prefabricated by high-energy ball mill of the present invention is to mix GCr15 powder and VN powder in a mass ratio of (90-99):(10-1), the high-energy ball mill speed is 150r / min, the speed ratio is -1.5 (the rotation direction is opposite, the speed ratio is 1.5), and the ball milling time is 2-8h.

[0012] The present invention uses nitrogen gas produced by the equipment as circulating gas to prevent oxidation of the sample during the manufacturing process and ensure the effective increase of nitrogen element.

[0013] The substrate preheating temperature of the additive manufacturing process of the present invention is 80°C, the laser power is 100-300W, the powder feeding amount is 40g / h, the laser scanning path is 67° rotating alternating scanning between layers, the scanning speed is 200-800mm / s, the scanning spacing is 0.05mm, and the stacking layer height is 0.03mm.

[0014] A GCr15 bearing steel with enhanced mechanical properties by adding vanadium nitride through laser additive manufacturing is manufactured by the additive manufacturing method. Experimental results show that the peak strength of the sample prepared by the method of the present invention reaches 1100MP.

[0015] Beneficial effects of the present invention:

[0016] The present invention proposes a method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing. This method can regulate the alloy microstructure by increasing the N element content and the V element content in the alloy. Since the radius of nitrogen atoms is smaller than that of carbon atoms, by replacing their atomic occupancy, the strengthening phase is easier to be evenly distributed in the solid solution. The addition of vanadium elements can produce two strengthening mechanisms in steel: fine grain strengthening and precipitation strengthening. These two reasons together lead to a significant improvement in the mechanical properties of the GCr15 bearing steel alloy. At the same time, the strength and plasticity of the material can be regulated by subsequent heat treatment in the future.

[0017] In the traditional alloy smelting process, elements are usually added to the alloy in the form of compounds. This method often leads to an inevitable increase in the content of another element while adding a target element. Sometimes, even only another element can be added, and the amount of the target element added cannot be accurately controlled. However, the additive manufacturing technology (3D printing technology) used in the present invention is essentially different from the traditional smelting method. Even when the element content is exactly the same, additive manufacturing technology can print out specific shapes as needed. More importantly, additive manufacturing technology can control the content of the target element to achieve precise and quantitative control of the performance improvement caused by the addition of elements, which is difficult to achieve with traditional smelting methods. The application of this technology provides higher flexibility and precision for alloy design and manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a physical picture of VN nanopowder attached to GCr15 fine powder at the micrometer scale;

[0019] Figure 2 Based on Figure 1 The line graph of element content given by the centerline scanning path;

[0020] Figure 3 This is the mapping image scanned by the energy spectrum experiment;

[0021] Figure 4 The tensile performance curves of the GCr15 bearing steel after performance enhancement manufactured by the method of the present invention and the conventional process (forging + annealing) are shown;

[0022] Figure 5 The tensile fracture morphology and energy dispersive X-ray spectrum of the performance-enhanced GCr15 bearing steel manufactured by the method of the present invention;

[0023] Figure 6 The tensile performance curve of the GCr15 bearing steel produced in Comparative Examples 1 and 2 of the present invention;

[0024] Figure 7 This is a metallographic diagram of the GCr15 bearing steel manufactured in Comparative Example 3 of the present invention;

[0025] The numbers in the figure are: 1-line scanning path selected in the SEM image, 2-schematic diagram of the substrate area in mapping, 3-schematic diagram of the attached VN area in mapping. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] Example 1: A method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, wherein the powder used is commercial powder, GCr15 is spherical fine powder with a particle size of 15 to 53 μm, and VN is nano-scale powder with a particle size of 60 to 160 nm. The preformed powder is made by mixing VN alloy powder and GCr15 powder in a high-energy ball mill. In terms of mass percentage, the GCr15 powder is 98% and the VN alloy powder is 2%. The speed of the high-energy ball mill is 150 r / min, the speed ratio is -1.5, and the ball milling time is 4 hours. The actual effect of VN nanopowder attached to GCr15 fine powder at the micron scale is as follows: Figure 1 As shown. Figure 1 The element content line graph given by the centerline scanning path is as follows Figure 2 As shown; the mapping image scanned by the energy spectrum experiment is as follows Figure 3 shown.

[0028] Before the additive manufacturing process, prepare the program file, put the mixed powder into a vacuum drying oven for drying for 6 hours at 80°C, and add the dried mixed powder into the powder bin. Select a stainless steel substrate, sandpaper polish and ultrasonically clean its surface, fix the substrate on the workbench, and tighten it with a clamp after leveling. Set the gas atmosphere to nitrogen, and preheat the substrate on the other hand. When the oxygen content is lower than 200ppm and the substrate temperature reaches the preheating set value, laser metal additive manufacturing is performed. The process parameters for the laser metal additive manufacturing process are: substrate preheating temperature is 80°C, laser spot diameter is 100μm, laser power is 100W, laser scanning path is 67° rotation alternating scanning between layers, scanning speed is 200mm / s, scanning spacing is 0.05mm, and stacking layer height is 0.03mm.

[0029] The workpiece size is set to 30*12*3mm in the operating system. After the processing is completed, the material block is removed from the substrate by wire cutting and processed into a tensile specimen. Then, a static tensile test is performed using a tensile testing machine according to the ASTM E8 standard to obtain a stress-strain curve such as Figure 4 The experimental results show that the peak strength of the sample is about 1100MPa, which is much higher than the peak strength of 700MPa of bearing steel made of GCr15 powder by traditional metallurgical process (hot rolling, hot forging, spheroidizing annealing, carburizing and nitriding, etc.).

[0030] The present embodiment relates to a method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing. Nitrogen is used instead of traditional argon to speed up the cooling rate of the SLM process and help to increase the nitrogen content. The microstructure of the alloy is regulated by increasing the N element content and the V element content in the alloy. Since the atomic radius of nitrogen is smaller than that of carbon atoms, by replacing its atomic position, the strengthening phase is easier to be evenly distributed in the solid solution. The addition of vanadium can produce two strengthening mechanisms in steel: fine grain strengthening and precipitation strengthening. These two reasons together lead to a significant improvement in the mechanical properties of the GCr15 bearing steel alloy.

[0031] like Figure 5 As shown, V and N are evenly distributed on the tensile fracture section, which indicates that the two strengthening elements are successfully introduced into the material by the method of the present invention. At the same time, no element segregation is observed, which indicates that V and N are well compatible with the material and have a great contribution to the performance improvement of the material.

[0032] Example 2: A method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, the powder used is commercial powder, GCr15 is spherical fine powder with a particle size of 15 to 53 μm, and VN nanopowder with a particle size of 60 to 160 nm. The preformed powder is made by mixing VN powder and GCr15 powder in a high-energy ball mill, and in terms of mass percentage, GCr15 powder is 98% and VN powder is 2%. The speed of the high-energy ball mill is 150 r / min, the speed ratio is -1.5, and the ball milling time is 4 hours.

[0033] Before starting laser metal deposition additive manufacturing, prepare the program file, put the mixed powder into a vacuum drying oven for 6 hours at 80°C, and add the dried mixed powder into the powder bin. Select a stainless steel substrate, sandpaper polish and ultrasonically clean its surface, fix the substrate on the workbench, and tighten it with a clamp after leveling. Adjust the posture of the laser cladding head to keep it vertically downward. Check the coaxiality of the laser spot and the powder spot to ensure that the laser beam and the powder flow can converge coaxially and confocally on the substrate surface.

[0034] When laser metal deposition additive manufacturing starts, under the control of a computer program, the robotic arm drives the adjustable zoom cladding head to move according to the preset manufacturing path. The parameters of the printing process are: laser power 300 W, scanning speed 420 mm / s, powder feeding amount 40 g / h, overlap 0.5 mm, and layer height 0.05 mm.

[0035] Comparative Example 1: A method for enhancing the mechanical properties of GCr15 bearing steel by laser additive manufacturing, wherein the powder used is commercial powder, and GCr15 is spherical fine powder with a particle size of 15 to 53 μm.

[0036] Before the additive manufacturing process, prepare the program file, put the GCr15 powder into a vacuum drying oven for 6 hours, the parameter is 80℃, and the dried powder is added to the powder bin. Select a stainless steel substrate, sandpaper polish and ultrasonically clean its surface, fix the substrate on the workbench, and tighten it with a clamp after leveling. Set the gas atmosphere to nitrogen, and preheat the substrate on the other hand. When the oxygen content is lower than 200ppm and the substrate temperature reaches the preheating set value, laser metal additive manufacturing is performed. The process parameters for the laser metal additive manufacturing process are: substrate preheating temperature is 80℃, laser spot diameter is 100μm, laser power is 100W, laser scanning path is 67° rotation alternating scanning between layers, scanning speed is 200mm / s, scanning spacing is 0.05mm, and stacking layer height is 0.03mm.

[0037] The workpiece size is set to 30*12*3mm in the operating system. After the processing is completed, the material block is removed from the substrate by wire cutting and processed into a tensile specimen.

[0038] Comparative Example 2: A method for enhancing the mechanical properties of GCr15 bearing steel by laser additive manufacturing, wherein the powder used is commercial powder, and GCr15 is spherical fine powder with a particle size of 15 to 53 μm.

[0039] Before the additive manufacturing process, prepare the program file, put the GCr15 powder into a vacuum drying oven for 6 hours, the parameter is 80℃, and the dried powder is added to the powder bin. Select a stainless steel substrate, sandpaper polish and ultrasonically clean its surface, fix the substrate on the workbench, and tighten it with a clamp after leveling. Set the gas atmosphere to nitrogen, and preheat the substrate on the other hand. When the oxygen content is lower than 200ppm and the substrate temperature reaches the preheating setting value, laser metal additive manufacturing is performed. When the laser metal additive manufacturing process is performed, the parameters are: substrate preheating temperature is 80℃, laser spot diameter is 100μm, laser power is 250W, laser scanning path is 67° rotation alternating scanning between layers, scanning speed is 300mm / s, scanning spacing is 0.05mm, and stacking layer height is 0.03mm.

[0040] The workpiece size is set to 30*12*3mm in the operating system. After the processing is completed, the material block is removed from the substrate by wire cutting and processed into a tensile specimen.

[0041] The static tensile test was performed by a tensile testing machine according to ASTM E8 standard to obtain the stress-strain curves of Comparative Example 1 and Comparative Example 2 as shown in Figure 6The experimental results show that the peak strengths of the two samples are about 960MPa and 900MPa, respectively, which are higher than the peak strength of 700MPa of bearing steel made of GCr15 powder by traditional metallurgical processes (hot rolling, hot forging, spheroidizing annealing, carburizing and nitriding, etc.), but the strength and elongation are lower than the sample prepared by adding VN powder, which proves that adding VN powder and adopting the process of the present invention are beneficial to strengthening bearing steel materials.

[0042] Comparative Example 3: A method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, the powder used is commercial powder, GCr15 is spherical fine powder with a particle size of 15-53μm, and VN is nano-powder with a particle size of 60-160nm. The preformed powder is made by mixing VN powder and GCr15 powder in a high-energy ball mill. In terms of mass percentage, GCr15 powder is 98% and VN powder is 2%. The speed of the high-energy ball mill is 150r / min, the speed ratio is -1.5, and the ball milling time is 4h.

[0043] Before the additive manufacturing process, prepare the program file, put the mixed powder into a vacuum drying oven for drying for 6 hours at 80°C, and add the dried mixed powder into the powder bin. Select a stainless steel substrate, sandpaper polish and ultrasonically clean its surface, fix the substrate on the workbench, and tighten it with a clamp after leveling. Set the gas atmosphere to nitrogen, and preheat the substrate on the other hand. When the oxygen content is lower than 200ppm and the substrate temperature reaches the preheating set value, laser metal additive manufacturing is performed. The process parameters for the laser metal additive manufacturing process are: substrate preheating temperature is 80°C, laser spot diameter is 100μm, laser power is 400W, laser scanning path is 67° rotation alternating scanning between layers, scanning speed is 1000mm / s, scanning spacing is 0.05mm, and stacking layer height is 0.03mm. Figure 7 This is a metallographic photograph of the bearing steel prepared in Comparative Example 3. There are large irregular unfused holes and scattered micropores on its surface. The defects are large and numerous, which will have a negative impact on the material properties.

[0044] In order to make the logical thinking of the present invention clearer, Table 1 lists the relevant parameters and final effects of the embodiments and comparative examples.

[0045] Table 1 Relevant process parameters and performance data of examples and comparative examples

[0046]

[0047] Two specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing, characterized in that: The following steps are involved: S1: pre-prepare alloy powder raw materials by high-energy ball mill, mix the dried GCr15 powder and VN powder and put them into high-energy ball mill for full and uniform mixing; S2: The gas environment of the laser additive manufacturing equipment build chamber is set to nitrogen, and the nitrogen exhausts the original air in the build chamber into the exhaust chamber, reducing the oxygen concentration in the chamber to below 200ppm; S3: Use nitrogen as the circulating gas for the entire process of preparation, production, and cooling of laser additive manufacturing.

2. A method for enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing according to claim 1, characterized in that: The particle size of the GCr15 powder is in the range of 15 to 53 μm.

3. The method of enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing according to claim 1, characterized in that: The particle size of the VN powder is between 60 and 160 nm.

4. The method of enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing according to claim 1, characterized in that: The alloy powder raw material is prepared by high-energy ball mill by mixing GCr15 powder and VN powder in a mass ratio of (90-99): (10-1), the speed of the high-energy ball mill is 150r / min, the speed ratio is -1.5, and the ball milling time is 2-8h.

5. The method of enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing according to claim 1, characterized in that: The substrate preheating temperature of the additive manufacturing process is 80°C, the laser power is 100-300W, the powder feeding amount is 40g / h, the laser scanning path is 67° rotating alternating scanning between layers, the scanning speed is 200-800mm / s, the scanning spacing is 0.05mm, and the stacking layer height is 0.03mm.

6. The method of enhancing the mechanical properties of GCr15 bearing steel by adding vanadium nitride through laser additive manufacturing according to claim 1, characterized in that: Nitrogen was used as the circulating gas to prevent oxidation of the sample during the manufacturing process while ensuring the effective addition of nitrogen.

7. A GCr15 bearing steel reinforced with vanadium nitride by laser additive manufacturing, characterized in that: The method is prepared by any one of claims 1 to 6.

8. The GCr15 bearing steel reinforced with vanadium nitride added by laser additive manufacturing according to claim 7, characterized in that: The peak strength of the prepared bearing steel sample reaches 1100MPa.

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