CN116213751A - A kind of 316L stainless steel surface treatment method - Google Patents

Abstract

The invention discloses a surface treatment method of 316L stainless steel, which is used to solve the technical problem of poor application performance caused by the disadvantages of poor surface quality, many pores, large residual stress and weak corrosion resistance of 316L stainless steel rapidly formed by laser powder bed fusion . The method is to firstly use laser powder bed fusion technology to perform rapid prototyping treatment on 316L stainless steel, and perform stress relief annealing on the formed 316L stainless steel, put the annealed LPBF 316L stainless steel into a high-energy shot blasting chamber, and treat the surface of LPBF 316L stainless steel Perform shot peening. Due to the high-energy shot peening treatment on the surface, severe plastic deformation with high strain and high strain rate was introduced, resulting in the gradient nanostructure on the surface of 316L, and the original molten pool structure no longer appeared. After testing, the nanocrystalline layer formed on the surface of 316L stainless steel can reach 212 μm.

Description

A kind of 316L stainless steel surface treatment method

technical field

The invention relates to the field of stainless steel surface treatment, in particular to a 316L stainless steel surface treatment method.

Background technique

LPBF 316L stainless steel has good corrosion resistance, high temperature resistance and creep resistance, and is widely used in aerospace, robotics, construction machinery and other fields. Because LPBF 316L stainless steel is mostly used in harsh working environments such as high temperature and high pressure , so higher requirements are put forward for its surface performance and reliability. Nanocrystals have the characteristics of small size, high interface density, and grain boundary structure similar to ordinary high-angle grain boundaries. Compared with LPBF 316L original grains, nanocrystals can significantly improve material properties. In order to improve the overall performance and service life of LPBF 316L stainless steel conditions are created.

Document 1 "Wu Jiahao, Research on Microstructure and Properties of 316L Stainless Steel Formed by Selective Laser Melting [J]. Weapon Materials Science and Engineering" reported that 316L stainless steel samples were formed by selective laser melting (SLM) technology. The results show that the mechanical properties of vertical planes are better than those of parallel planes due to the influence of grain size and porosity. Document 2 "Ma Chunyu, Twin crystal behavior during high-speed compaction of 316L stainless steel powder for decoration [J]. Forging Technology, 2022, 47(08)" reported the effect of impact energy on twin crystal structure during high-speed compaction of 316L powder , and the density of the twin structure determines the corrosion resistance of 316L stainless steel. It was found that under higher impact energy, a denser twin structure can be obtained, which can improve its corrosion resistance and help reduce corrosion. rate. Document 3 "Zhu Derong, Effect of solution aging on the microstructure and hardness of 316L stainless steel blocks formed by SLM [J]. Metal Heat Treatment, 2022, 47 (08)" reported that different aging processes were used in selective laser melting technology The influence on the microstructure and hardness of 316L stainless steel after forming, the results show that: the microstructure of 316L stainless steel block formed by SLM is mainly composed of fine columnar grains and honeycomb grains, "layer-layer" and "road-road "The molten pool boundary is clearly visible, but after solid solution aging, the boundary disappears and the grain boundary is clearly visible. At a higher aging temperature, M ₂₃ C ₆ is generated at the grain boundary of the sample, and the microhardness is significantly improved.

Generally speaking, the smaller the surface grain size and the greater the thickness of the severe plastic deformation layer, the better the mechanical properties of 316L stainless steel. In addition, the introduction of high strain and high strain rate is an effective measure to change the surface properties of 316L stainless steel. In the above method, although the 316L stainless steel structure is prepared, the surface grain size of the prepared 316L stainless steel is relatively large, and the severe plastic deformation layer ratio is small, which restricts its effective application.

Contents of the invention

In order to improve the surface properties of 316L stainless steel formed by LPBF and expand the technical problems of its practical application, the present invention provides a surface strengthening method for additively manufacturing 316L stainless steel. In this method, LPBF 316L stainless steel is subjected to stress relief annealing treatment, and then its surface is shot peened under high pressure. After a long period of shot peening, the surface of LPBF 316L stainless steel undergoes severe plastic deformation with large strain and high strain rate. Achieve surface gradient nanostructures.

The technical scheme that the present invention adopts to solve its technical problem comprises the following steps: a kind of 316L stainless steel surface treatment method, this method comprises the following steps:

(1) Perform laser powder bed fusion rapid prototyping on 316L stainless steel powder to obtain 316L stainless steel samples;

(2) Perform stress relief annealing on the formed 316L stainless steel sample;

(3) Shot peening is performed on the 316L stainless steel sample after the stress relief annealing treatment to realize the surface gradient nanostructure. The shot peening conditions are that the air pressure is 0.3 or 0.4 MPa, and the shot peening time is 30 or 45 min.

Further, in step (1), the 316L stainless steel powder is calculated according to the mass fraction, and the specific composition of the powder is: C is 0.03%, Mn is 0.02%, Ni is 12.5%~13.0%, Cu is 0.50%, and Si is 0.75%, P is 0.025%, Cr is 17.5%~18.0%, Mo is 2.25%~2.50%, and the balance is Fe.

Further, in step (1), the scanning strategy is Meader, and the process parameters are selected as follows:

Layer thickness: 50μm, spot size: 70μm, scanning pitch: 110μm, laser power: 200W, spot pitch: 60μm, exposure time: 80μs, scanning speed, 750mm/s.

Further, in step (2), the stress relief annealing treatment conditions are as follows: the annealing temperature is 1280° C., the holding time is 60 minutes, and air cooling to room temperature.

Further, in step (3), the 316L stainless steel sample was subjected to high-energy shot peening using ASH230 projectiles with a diameter of 0.6 mm.

Compared with prior art, beneficial result of the present invention is:

The grain size on the surface of the 316L stainless steel prepared by the invention is greatly reduced, and the thickness of the severe plastic deformation layer on the surface is increased at the same time. The nanocrystal size on the surface of the stainless steel is 25nm, which has reached the ultra-fine grain scale, and the thickness of the plastic deformation layer can reach 212 μm, which is much smaller than the grain size in the background technology, and the thickness of the deformed layer is obviously increased.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Figure 1 is a schematic diagram of the nanogradient structure on the surface of 316L stainless steel prepared in Example 1.

Figure 2 shows the scanning strategy and forming samples of laser powder bed fusion rapid prototyping technology.

Fig. 3 is the transmission electron microscope bright field, dark field and electron diffraction photos of the surface nanostructures of 316L stainless steel prepared in Example 1.

Fig. 4 is the photo of the nanostructure plastic deformation layer on the surface of 316L stainless steel prepared in Example 2.

Fig. 5 is a photograph comparing the thickness of the plastically deformed layer of Example 3 and Example 1.

Detailed ways

The specific embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings.

Embodiment 1: the present invention provides a kind of 316L stainless steel surface treatment method, concrete steps are as follows:

(1) Laser powder bed fusion (LPBF) rapid prototyping treatment is performed on 316L stainless steel powder. The 316L stainless steel powder used is a spherical particle formed by gas atomization, with a particle size diameter between 20 and 65 μm. The diameter is about 50 μm; 316L stainless steel powder is calculated according to the mass fraction. The specific composition of the powder is: C is 0.03%, Mn is 0.02%, Ni is 12.5%~13.0%, Cu is 0.50%, Si is 0.75%, and P is 0.025%. , Cr is 17.5%~18.0%, Mo is 2.25%~2.50%, and the balance is Fe.

The scanning strategy is Meader. The scanning route of each layer is shown in (a) in Figure 2. The specific processing parameters are shown in Table 1. After printing each layer of 316L stainless steel, rotate 67° to continue to maintain the scanning route, and finally form The flat 316L stainless steel sample of 70×19×4mm ³ is shown in (b) in Figure 2;

Table 1

(2) Perform stress-relieving annealing treatment on the formed 316L stainless steel sample, the annealing temperature is 1280°C, the holding time is 60min, and air-cooled to room temperature;

(3) ASH230 cast steel projectiles with a diameter of 0.6 mm were used to perform high-energy shot peening on the 316L stainless steel sample after stress relief annealing to achieve surface gradient nanostructures. As shown in Figure 1, the shot peening condition was that the air pressure was 0.40 MPa, the shot peening time is 45min;

(a) in Fig. 3 is that embodiment 1 prepares the transmission electron microscope bright field of 316L stainless steel surface nanocrystal, (b) among Fig. 3 is the dark field that embodiment 1 prepares 316L stainless steel surface nanocrystal, (c among Fig. 3 ) is the electron diffraction pattern corresponding to the bright field of the nanocrystals on the surface of 316L stainless steel prepared in Example 1. It can be seen from the bright field and dark field images that the grains on the surface of the 316L stainless steel sample are extremely small; from the grain size range of the dark field image, it can be seen that the grains on the surface of the 316L stainless steel sample have been refined into ultrafine nanocrystals , the minimum grain size is 25nm. It can be seen from (b) in Figure 5 that the plastic deformation layer in Example 1 can reach 231 μm, and at the same time, the molten pool structure of the plastic deformation layer is basically eliminated.

Example 2

According to the strengthening method of Example 1, the shot peening time in step (3) is changed to 30min, and the shot peening air pressure is 0.3MPa, and the surface of the 316L stainless steel that has been formed in Example 1 is strengthened, as shown in Figure 4, the stainless steel The thickness of the severe plastic deformation layer reaches 212μm, and the molten pool structure of the plastic deformation layer is basically eliminated.

Example 3

According to the strengthening method of Example 1, step (1) and step (2) are selected to treat 316L stainless steel, as shown in (a) in Figure 5, it can be found that the surface of 316L stainless steel formed by LPBF has no plastic deformation layer, and LPBF The molten pool structure on the surface is basically not eliminated during forming.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, are all included in the scope of patent protection of the present invention in the same way.

Claims (5)

1. a 316L stainless steel surface treatment method is characterized in that the method may further comprise the steps: (1) Perform laser powder bed fusion rapid prototyping on 316L stainless steel powder to obtain 316L stainless steel samples; (2) Perform stress relief annealing on the formed 316L stainless steel sample; (3) Shot peening is performed on the 316L stainless steel sample after the stress relief annealing treatment to realize the surface gradient nanostructure. The shot peening conditions are that the air pressure is 0.3 or 0.4 MPa, and the shot peening time is 30 or 45 min. 2. A 316L stainless steel surface treatment method according to claim 1, characterized in that, in step (1), the 316L stainless steel powder is calculated according to the mass fraction, and the specific composition of the powder is: C is 0.03%, and Mn is 0.02%, Ni is 12.5%~13.0%, Cu is 0.50%, Si is 0.75%, P is 0.025%, Cr is 17.5%~18.0%, Mo is 2.25%~2.50%, and the balance is Fe. 3. A 316L stainless steel surface treatment method according to claim 1, characterized in that, in step (1), the scanning strategy is Meader, and the process parameters are selected as follows: Layer thickness: 50μm, spot size: 70μm, scanning pitch: 110μm, laser power: 200W, spot pitch: 60μm, exposure time: 80μs, scanning speed, 750mm/s. 4. A method for surface treatment of 316L stainless steel according to claim 1, characterized in that in step (2), the stress relief annealing treatment conditions are as follows: annealing temperature is 1280°C, holding time is 60 minutes, and air cooling to room temperature. 5. A 316L stainless steel surface treatment method according to claim 1, characterized in that in step (3), the 316L stainless steel sample is subjected to high-energy shot peening using ASH230 projectiles with a diameter of 0.6 mm.

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