Nano TiC reinforced 316L stainless steel with excellent high-temperature mechanical property

Abstract

The invention discloses nano TiC reinforced 316L stainless steel with excellent high-temperature mechanical property, the content of TiC in the nano TiC reinforced 316L stainless steel is 4-6wt%, TiC is added in the form of nano powder, and the preparation process comprises the following steps: adding nano TiC powder into stainless steel powder, uniformly stirring, and carrying out heat treatment to obtain the nano TiC reinforced 316L stainless steel. Nano TiC powder is evenly attached to the specific surface of 316L stainless steel powder through grinding of a ball mill, then the ground mixed powder is put into laser additive manufacturing equipment, the nano TiC reinforced 316L stainless steel is obtained through laser additive manufacturing, and the technological parameters of laser additive manufacturing are as follows: the laser power is 150-500 W, the scanning speed is 400-1400 mm / s, the interlayer spacing is 0.04-0.1 mm, and the layer thickness is 0.01-0.05 mm; in the additive manufacturing process, argon is adopted as protective gas. The 316L stainless steel with the excellent high-temperature mechanical property can be obtained only through the additive manufacturing machining method, the high-temperature mechanical property of the 316L stainless steel can be comparable with that of nickel-based alloy, and the use environment and the application range of the 316L stainless steel are greatly expanded.

Description

Technical Field

[0001] The invention relates to nano-TiC reinforced 316L stainless steel with excellent high-temperature mechanical properties, belonging to the technical field of new materials and processing. Background Art

[0002] 316L stainless steel is a common and widely used stainless steel material. Due to its excellent corrosion resistance, mechanical properties and machinability, it plays an extremely important role in medical devices, chemical industry, marine engineering, food processing, cosmetics and jewelry, energy electronics, automobiles and aerospace. However, with the advancement of science and technology, various fields now have higher requirements for the strength, hardness, ductility, fatigue resistance, corrosion resistance and other properties of metal materials. However, 316L stainless steel is a typical austenitic stainless steel. The internal crystal structure is mainly FCC solid solution structure, the grains are coarse, and no phase change occurs during cooling. Therefore, the mechanical properties cannot generally be improved by heat treatment. Therefore, the application conditions of 316L stainless steel without strengthening treatment are greatly limited. Laser additive manufacturing has the ability to in-situ regulate the organization and structure of the alloy, and the alloy manufactured has more excellent mechanical properties. However, the high-temperature mechanical properties of additively manufactured 316L stainless steel are poor. How to enhance its high-temperature mechanical properties is an urgent problem to be solved. Solving this problem will expand the application range of 316L stainless steel in extreme temperature environments, such as nuclear fusion devices, aircraft engines, turbine blades, heat exchangers, liquefied gas storage and transportation, superconducting realization and rocket propellant tanks. Summary of the invention

[0003] The purpose of the present invention is to provide a nano-TiC reinforced 316L stainless steel with excellent high-temperature mechanical properties. By optimizing the element ratio and additive manufacturing process, 316L stainless steel with high temperature resistance and ultra-high strength is obtained.

[0004] The technical scheme adopted by the present invention to achieve the purpose of the invention is: a nano-TiC reinforced 316L stainless steel with excellent high-temperature mechanical properties, wherein the TiC content in the nano-TiC reinforced 316L stainless steel is 4-6wt%, and the TiC is added in the form of nano-powder. The preparation process comprises the following steps: adding the nano-TiC powder to the stainless steel powder and stirring evenly, grinding the nano-TiC powder by a ball mill so that the nano-TiC powder is evenly attached to the surface of the 316L stainless steel powder, and then putting the ground mixed powder into a laser additive manufacturing device to obtain the nano-TiC reinforced 316L stainless steel by laser additive manufacturing. The process parameters of the laser additive manufacturing are: laser power 150W-500W, scanning speed 400-1400mm / s, interlayer spacing 0.04-0.1mm, and layer thickness 0.01-0.05mm; argon is used as a protective gas during the additive manufacturing process.

[0005] Furthermore, the process parameters of the ball mill grinding of the present invention are: grinding time 30-120min, and grinding machine speed 400RPM.

[0006] Furthermore, the specific operation of adding nano-TiC powder to stainless steel powder and stirring uniformly according to the present invention is: first, the nano-TiC powder is mixed with the 316L stainless steel powder and then dried, the drying temperature of the drying treatment is 60-100°C, and the drying time is 1-3h; then the dried mixed powder is poured into a powder mixer and stirred and mixed uniformly, and the stirring time is 3-6h.

[0007] Furthermore, the process parameters of the laser additive manufacturing described in the present invention are: laser power 180W-250W, scanning speed 600-1000mm / s, layer spacing 0.07-0.09mm, and layer thickness 0.02-0.04mm.

[0008] Furthermore, the process parameters of the laser additive manufacturing described in the present invention are: laser power 180W, scanning speed 800mm / s, layer spacing 0.07mm, and layer thickness 0.03mm.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. The present invention pre-mixes 316L stainless steel and nano-TiC powder, and then processes them through laser additive manufacturing to obtain nano-TiC-reinforced 316L stainless steel, thereby achieving in-situ regulation of the stainless steel composition and microstructure, and providing a new path for achieving ultra-high strength and high temperature resistant 316L stainless steel.

[0011] 2. The present invention can realize the processing and manufacturing of high-performance 316L stainless steel only through additive manufacturing, which greatly reduces the processing time compared with traditional processing methods and is expected to realize the structural integrated manufacturing of large and complex key equipment.

[0012] 3. The TiC size of the present invention is nanometer-level, which can effectively avoid stress concentration and effectively utilize the strengthening effect of TiC compared to micrometer-level. In addition, through a large number of experiments, it is found that controlling the addition amount of nano-TiC powder to 4-6wt% can maximize the strengthening effect of TiC. 4-6wt% TiC can effectively increase the cooling rate in the additive manufacturing process and provide a position for grain nucleation, thereby helping to produce fine grains and a large number of grain boundaries, thereby playing a role in grain boundary strengthening.

[0013] Fourth, the present invention adopts the addition of 4-6wt% nano-TiC powder to 316L stainless steel powder, which can form nano-sized precipitation phases, a large number of crystalline boundaries, and fine grains, and the rapid solidification and thermal stress in the additive manufacturing process of the present invention are conducive to the formation of high dislocation density. Therefore, the 316L stainless steel prepared by the present invention contains a multi-scale gradient structure, which is conducive to enhancing the mechanical properties of the alloy, especially the high-temperature mechanical properties.

[0014] 5. The present invention controls the specific parameters of additive manufacturing, adopts a small heat input of 150W-500W, a high-speed printing of 400-1400mm / s, selects a layer spacing of 0.04-0.1mm and a layer thickness of 0.01-0.05mm, and obtains stainless steel with fine grains, high dislocation density, and a large amount of nanoparticles. These unique structures are conducive to improving the strength of stainless steel.

[0015] In summary, the stainless steel prepared by the present invention has excellent mechanical properties, and its high-temperature strength is better than that of commonly used steels, titanium alloys, and medium-high entropy alloys, and is comparable to that of nickel-based alloys.

[0016] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an electron backscattering image of the grain boundary and grain morphology and a grain boundary and grain size distribution image of the nano-TiC reinforced 316L stainless steel prepared in Example 1 of the present invention.

[0018] Figure 2 This is an electron microscope morphology image of the material microstructure of nano-TiC reinforced 316L stainless steel prepared in Example 1 of the present invention and a statistical result image of the size and spacing of the precipitated phases.

[0019] Figure 3 The engineering stress-strain curves of the nano-TiC reinforced 316L stainless steel prepared in Example 1 of the present invention at different temperatures.

[0020] Figure 4 A comparison of high temperature mechanical properties of nano-TiC reinforced 316L stainless steel prepared in Example 1 of the present invention and other alloys.

[0021] Figure 5 Grain boundary orientation diagram and projection electron microscope image of nano-TiC reinforced 316L stainless steel prepared in Example 1 of the present invention after deformation at 600°C. DETAILED DESCRIPTION

[0022] Embodiment 1

[0023] A nano-TiC reinforced 316L stainless steel with excellent high-temperature mechanical properties, wherein the TiC content in the nano-TiC reinforced 316L stainless steel is 4wt%, and the TiC is added in the form of nano-powder. The preparation process comprises the following steps: adding the nano-TiC powder into the stainless steel powder and stirring evenly, grinding the powder by a ball mill so that the nano-TiC powder is evenly attached to the specific surface of the 316L stainless steel powder, and then putting the ground mixed powder into a laser additive manufacturing device to obtain the nano-TiC reinforced 316L stainless steel by laser additive manufacturing. The process parameters of the laser additive manufacturing are: laser power of 180W, scanning speed of 800mm / s, interlayer spacing of 0.07mm, and layer thickness of 0.03mm; and argon is used as a protective gas in the additive manufacturing process.

[0024] The process parameters of ball mill grinding in this example are: grinding time 30min, grinding machine speed 400RPM.

[0025] The specific operation of adding nano-TiC powder to stainless steel powder and stirring them evenly in this example is: first, the nano-TiC powder is mixed with the 316L stainless steel powder and then dried at a drying temperature of 60°C for 1 hour; then the dried mixed powder is poured into a powder mixer and stirred for 4 hours.

[0026] Figure 1 The electron backscattering images of the grain and grain boundary morphology and the distribution of grain and grain boundary size of the nano-TiC reinforced 316L stainless steel prepared in this embodiment. (a) The electron backscattering image of the grain and grain boundary morphology of 316L stainless steel. From this image, it can be seen that the grains of 316L stainless steel are of different sizes, including fine grain areas and areas rich in Luan grain boundaries. (b) is the distribution map of grain boundaries with different orientations obtained by statistics. It can be seen that Luan grain boundaries (orientation difference is about 60°) account for as much as 35%. Such a large proportion of Luan grain boundaries has never been achieved in the previous additive manufacturing of 316L stainless steel. (c) is the statistical grain size statistics obtained, and its average value is 1 micron.

[0027] Figure 2 The electron microscope morphology of the material microstructure of the nano-TiC reinforced 316L stainless steel prepared in this example. (a) shows that there are a large number of nano-sized TiC particles in the 316L stainless steel; (b) is a statistical TiC size distribution diagram, the average value is about 40nm, and (c) is a statistical TiC spacing distribution diagram, the average value is 50nm. Figure 1 and Figure 2 The microstructure is shown from the micrometer to the nanometer scale, from which it can be concluded that the prepared 316L stainless steel contains a large number of fine TiC particles, fine grains, and a large proportion of Luan grain boundaries.

[0028] Figure 3 The engineering stress-strain curve of the nano-TiC reinforced 316L stainless steel prepared in this embodiment. It can be seen from the figure that the high-strength stainless steel prepared in this embodiment can reach 1000MPa at room temperature, and the elongation is as high as 20%, and has excellent mechanical properties. At high temperatures, the strength will decrease, but the strength can still reach 800MPa at 600℃, and the elongation is higher than 20%; at 800℃, the strength decreases significantly, but the strength is higher than 450MPa, and the elongation reaches 15%.

[0029] Figure 4 This is a comparison of the high-temperature mechanical properties of the nano-TiC reinforced 316L stainless steel prepared in this implementation and other alloys. It can be seen that in the temperature range from room temperature to 800°C, the strength of the prepared 316L stainless steel is higher than that of titanium alloy, stainless steel, medium-high entropy alloy, and aluminum alloy. The strength of the prepared 316L stainless steel is comparable to that of nickel-based alloys. This high strength in a wide temperature range greatly expands the application range of 316L stainless steel.

[0030] Figure 5 The grain boundary orientation and projection electron microscope image of the nano-TiC reinforced 316L stainless steel prepared in this example after deformation at 600℃. (a) is a statistical diagram of the grain boundary orientation after deformation. It can be seen that the proportion of grain boundaries with an orientation difference of less than 10 is as high as 40%, which shows that a large number of dislocations multiply during the deformation process, providing the necessary conditions for high strength. The large number of dislocations is due to the multi-scale structure of the prepared 316L stainless steel, that is, a large number of fine TiC particles, fine grains, and quenching grain boundaries (see Figure 2). Figure 1 and 2 (b) is the projection electron microscope image after deformation. It can be seen that dislocations are piled up in large quantities at the TiC particles, which increases the dislocation density. In addition, stacking faults are formed during the deformation process, which provides favorable conditions for the accumulation of dislocations.

[0031] Embodiment 2

[0032] A nano-TiC reinforced 316L stainless steel with excellent high-temperature mechanical properties, wherein the TiC content in the nano-TiC reinforced 316L stainless steel is 5wt%, and the TiC is added in the form of nano-powder. The preparation process comprises the following steps: adding the nano-TiC powder into the stainless steel powder and stirring evenly, grinding the nano-TiC powder by a ball mill so that the nano-TiC powder is evenly attached to the specific surface of the 316L stainless steel powder, and then putting the ground mixed powder into a laser additive manufacturing device to obtain the nano-TiC reinforced 316L stainless steel by laser additive manufacturing. The process parameters of the laser additive manufacturing are: laser power 250W, scanning speed 1000mm / s, interlayer spacing 0.07mm, and layer thickness 0.03mm; and argon is used as a protective gas in the additive manufacturing process.

[0033] The process parameters of ball mill grinding in this example are: grinding time 100min, grinding machine speed 400RPM.

[0034] The specific operation of adding nano-TiC powder to stainless steel powder and stirring them evenly in this example is: first, the nano-TiC powder is mixed with the 316L stainless steel powder and then dried at a drying temperature of 80°C for 1 hour; then the dried mixed powder is poured into a powder mixer and stirred for 2 hours.

[0035] Embodiment 3

[0036] A nano-TiC reinforced 316L stainless steel with excellent high-temperature mechanical properties, wherein the TiC content in the nano-TiC reinforced 316L stainless steel is 6wt%, and the TiC is added in the form of nano-powder. The preparation process comprises the following steps: adding the nano-TiC powder into the stainless steel powder and stirring the mixture evenly, grinding the mixture by a ball mill so that the nano-TiC powder is evenly attached to the specific surface of the 316L stainless steel powder, and then placing the ground mixed powder into a laser additive manufacturing device to obtain the nano-TiC reinforced 316L stainless steel by laser additive manufacturing. The process parameters of the laser additive manufacturing are: laser power 300W, scanning speed 1200mm / s, interlayer spacing 0.07mm, layer thickness 0.03mm, and argon is used as a protective gas during the additive manufacturing process.

[0037] The process parameters of ball mill grinding in this example are: grinding time 120min, grinding machine speed 400RPM.

[0038] The specific operation of adding nano-TiC powder to stainless steel powder and stirring them evenly in this example is: first, the nano-TiC powder is mixed with the 316L stainless steel powder and then dried. The drying temperature of the drying treatment is 100°C and the drying time is 1 hour; then the dried mixed powder is poured into a powder mixer and stirred for 3 hours.

Claims

1. A nano-TiC reinforced 316L stainless steel with excellent high temperature mechanical properties, characterized in that: The TiC content in the nano-TiC reinforced 316L stainless steel is 4-6wt%, and TiC is added in the form of nano-powder. The preparation process comprises the following steps: adding the nano-TiC powder into the stainless steel powder and stirring evenly, grinding the powder by a ball mill so that the nano-TiC powder is evenly attached to the specific surface of the 316L stainless steel powder, and then putting the ground mixed powder into a laser additive manufacturing device to obtain the nano-TiC reinforced 316L stainless steel by laser additive manufacturing. The process parameters of the laser additive manufacturing are: laser power 150W-500W, scanning speed 400-1400mm / s, interlayer spacing 0.04-0.1mm, and layer thickness 0.01-0.05mm; argon is used as a protective gas during the additive manufacturing process.

2. The nano-TiC reinforced 316L stainless steel with excellent high temperature mechanical properties according to claim 1, characterized in that: The process parameters of the ball mill grinding are: grinding time 30-120min, grinding machine speed 400RPM.

3. The nano-TiC reinforced 316L stainless steel with excellent high temperature mechanical properties according to claim 1, characterized in that: The specific operation of adding nano-TiC powder to the stainless steel powder and stirring them evenly is: first, the nano-TiC powder is mixed with the 316L stainless steel powder and then dried, the drying temperature of the drying treatment is 60-100°C, and the drying time is 1-3h; then the dried mixed powder is poured into a powder mixer and stirred and mixed evenly, and the stirring time is 3-6h.

4. The nano-TiC reinforced 316L stainless steel with excellent high temperature mechanical properties according to claim 1, characterized in that: The process parameters of the laser additive manufacturing are: laser power 180W-250W, scanning speed 600-1000mm / s, layer spacing 0.07-0.09mm, and layer thickness 0.02-0.04mm.

5. The nano-TiC reinforced 316L stainless steel with excellent high temperature mechanical properties according to claim 4, characterized in that: The process parameters of the laser additive manufacturing are: laser power 180 W, scanning speed 800 mm / s, layer spacing 0.07 mm, and layer thickness 0.03 mm.

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