CN116814918A - Composite treatment process for AM austenitic stainless steel regulated and controlled by residual stress - Google Patents
Composite treatment process for AM austenitic stainless steel regulated and controlled by residual stress Download PDFInfo
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- CN116814918A CN116814918A CN202310784450.3A CN202310784450A CN116814918A CN 116814918 A CN116814918 A CN 116814918A CN 202310784450 A CN202310784450 A CN 202310784450A CN 116814918 A CN116814918 A CN 116814918A
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- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims abstract description 35
- 239000002131 composite material Substances 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 title claims abstract description 30
- 230000001105 regulatory effect Effects 0.000 title claims description 5
- 238000010438 heat treatment Methods 0.000 claims abstract description 38
- 239000000654 additive Substances 0.000 claims abstract description 21
- 230000000996 additive effect Effects 0.000 claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 claims abstract description 19
- 238000005255 carburizing Methods 0.000 claims description 13
- 238000005498 polishing Methods 0.000 claims description 12
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 9
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 8
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 7
- 150000001875 compounds Chemical class 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- 230000003746 surface roughness Effects 0.000 claims description 5
- 230000004913 activation Effects 0.000 claims description 4
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 4
- 239000012153 distilled water Substances 0.000 claims description 4
- 235000011187 glycerol Nutrition 0.000 claims description 4
- 239000003792 electrolyte Substances 0.000 claims description 3
- 229910000831 Steel Inorganic materials 0.000 claims description 2
- 239000010959 steel Substances 0.000 claims description 2
- 238000005868 electrolysis reaction Methods 0.000 claims 1
- 238000005516 engineering process Methods 0.000 abstract description 6
- 238000009826 distribution Methods 0.000 abstract description 2
- 230000000977 initiatory effect Effects 0.000 abstract description 2
- 238000005728 strengthening Methods 0.000 description 15
- 230000000694 effects Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 210000003850 cellular structure Anatomy 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 238000007517 polishing process Methods 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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Abstract
The invention discloses a composite treatment method for manufacturing austenitic stainless steel by additive, which belongs to additive manufacturing technology, and the innovative mode of combining heat treatment and low-temperature gas carburization can effectively reduce the integral tensile residual stress (< 50 MPa) of the austenitic stainless steel by additive manufacturing, and can introduce extremely large compressive residual stress (> 2000 MPa) on the surface of a part with a complex structure. The distribution rule of the residual stress can effectively inhibit the initiation of fatigue cracks. After the composite treatment of the invention, the fatigue performance of the austenitic stainless steel component manufactured by additive can be obviously improved by more than 30 percent.
Description
Technical Field
The invention belongs to additive manufacturing technology, and particularly relates to a composite treatment process for Additive Manufacturing (AM) austenitic stainless steel aiming at residual stress regulation.
Background
Austenitic stainless steel (austenitc stainless steel) has excellent corrosion resistance, good toughness and easy workability, and is widely used in various light industries such as chemical industry, energy, ships, food, medical industry, and the like, and advanced manufacturing industry, and the like. However, austenitic stainless steel has low surface hardness, and is insufficient in wear resistance and fatigue resistance in practical application, and further application is limited.
The rapid development of science and technology has led to an increasing interest in Additive Manufacturing (AM) technology. The additive manufacturing technology overcomes the trouble caused by the traditional technology for manufacturing metal parts with complex shapes, and can directly form the metal parts which are nearly fully compact and have good mechanical properties. However, extensive research has shown that the surface of additively manufactured parts inevitably has a large tensile residual stress (> 500 MPa). And the existence of larger tensile residual stress ensures that the parts are easy to be subjected to fatigue damage in actual working conditions, thereby seriously affecting the service life and the reliability of equipment.
The post heat treatment mode can effectively reduce the overall tensile residual stress level, thereby improving the fatigue life of the parts. But only by means of heat treatment, there is a limited improvement in fatigue performance. Riemer et al, onthafacigulrackwhbehaviorin 316Lstainlesssteelmanufacturedby selectivelasermelting, in which AM austenitic stainless steel is heat treated at 650℃, found that only about 10% improvement in fatigue performance was achieved and the desired strengthening effect was not achieved.
Surface strengthening can improve the fatigue life of parts by introducing surface compressive residual stress. The surface strengthening process is widely used in parts conventionally manufactured, and Huang et al in Fatigue behaviorsofAISI Lstainless steelwithagnradientnanostructuredsurfacelayer demonstrate the effectiveness of surface strengthening for fatigue performance improvement by surface strengthening austenitic stainless steel. However, for additive manufactured parts with complex structures, it is difficult to obtain effective strengthening effect by the conventional surface strengthening method.
Disclosure of Invention
The invention provides a composite treatment process for AM austenitic stainless steel aiming at residual stress regulation, which improves the fatigue resistance of a material by regulating the residual stress of the AM austenitic stainless steel.
The technical scheme for realizing the invention is as follows: a composite treatment process for AM austenitic stainless steel for regulating residual stress is characterized in that an austenitic stainless steel forming member is prepared by adopting an additive manufacturing method, and then the austenitic stainless steel forming member is subjected to composite treatment, and the composite treatment process comprises the following steps:
and a first step of carrying out heat treatment on the austenitic stainless steel forming component manufactured by the additive with the tensile residual stress of more than 500MPa, wherein the heat treatment temperature is 850-950 ℃, the heat preservation is carried out for 1-4 hours, then air cooling is carried out, the component after heat treatment is obtained, the tensile residual stress is controlled within 50MPa, and the second step is carried out.
Step two, the component after heat treatment is subjected to electrolytic polishing treatment, and 0.1 to 0.5A/cm is used 2 The current density of the steel sheet is treated for 2 to 6 hours to obtain an electropolished component, so that the surface roughness of the electropolished component can be effectively reduced, and the third step is carried out.
And thirdly, performing low-temperature gas carburizing treatment on the member subjected to electrolytic polishing to obtain a member subjected to compound treatment, and introducing compressive residual stress of more than 2000MPa on the surface of the member subjected to compound treatment to obtain the AM member with the reinforced surface.
Compared with the prior art, the invention has the remarkable advantages that:
(1) After the heat treatment (1-4 h at 850-950 ℃) in the composite treatment process provided by the invention is used, the integral residual stress level of the AM austenitic stainless steel component can be reduced from the original value of 500MPa to 50MPa or less. The stress level of the component in the service process can be remarkably reduced through greatly reducing (more than 95%) the tensile residual stress, so that the fatigue resistance of the component is improved.
(2) After the low-temperature gas carburization surface strengthening treatment in the composite treatment process provided by the invention, a uniform strengthening layer with the thickness of 30 micrometers can be introduced on the surface of an AM austenitic stainless steel component with a complex structure, and the strengthening layer has compressive residual stress of more than 2000 MPa. By introducing extremely large compressive residual stress, the initiation of fatigue cracks can be effectively inhibited, and the fatigue resistance of the component is improved.
(3) After the composite treatment process (heat treatment and low-temperature gas carburization) is used, huge compressive residual stress (> 2000 MPa) can be introduced on the surface while the overall tensile stress level (< 50 MPa) is reduced. After the composite treatment, the special distribution of the residual stress can obviously improve the fatigue resistance of the component, and the fatigue limit can be improved by more than 30%.
Drawings
FIG. 1 is a flow chart of the composite treatment process of the present invention.
FIG. 2 is a graph showing the residual stress along the depth of the member before and after the heat treatment of the composite treatment according to the present invention.
FIG. 3 is a microstructure of the component before and after the heat treatment of the composite treatment of the present invention.
FIG. 4 is a time-temperature flow chart of the composite treatment process of the present invention.
FIG. 5 is a graph showing the comparison of fatigue life before and after the composite treatment under 300MPa stress.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by one of ordinary skill in the art without creative efforts, are within the scope of the present invention based on the embodiments of the present invention.
In addition, the technical solutions of the embodiments of the present invention may be combined with each other, but it is necessary to base that the technical solutions can be implemented by those skilled in the art, and when the technical solutions are contradictory or cannot be implemented, the combination of the technical solutions should be considered to be absent, and not included in the scope of protection claimed in the present invention.
The following describes the specific embodiments, technical difficulties and inventions of the present invention in further detail in connection with the present design examples.
Referring to FIGS. 1 to 5, an AM austenitic stainless steel composite treatment process for residual stress regulation is firstly adopted to prepare an austenitic stainless steel forming component (SLM 316L sample adopts selective laser melting additive manufacturing equipment (SLM-125 HL), and the process parameters are as follows, the laser power is 200W, the scanning speed is 800mm/s, the layer thickness is 30 mu m, and the scanning interval is 120 mu m). And (3) carrying out composite treatment on the AM component after the tensile residual stress of the obtained formed component is more than 500MPa, wherein the composite treatment process comprises the following steps of:
and firstly, placing the AM component in a heat treatment furnace, heating to 850-950 ℃ along with the furnace, preserving heat for 1-4h, and then air-cooling to obtain the AM component after heat treatment, wherein the tensile residual stress level of the AM component after heat treatment is reduced to be less than 50MPa.
Further, the heat treatment furnace is heated to 850-950 ℃ at a heating rate of 5-15 ℃/min, and the heating rate can ensure the uniformity of temperature.
A second step of placing the heat-treated AM component obtained in the first step in an electrolytic polishing solution at a concentration of 0.1-0.4A/cm 2 The current density of (2) is treated for 2 to 6 hours to obtain an AM component after electrolytic polishing, and the step can reduce the surface roughness of the component.
Further, the electrolytic polishing solution is prepared from phosphoric acid, distilled water, sulfuric acid and glycerin according to the following ratio of 18:15:14:53, the heating temperature in water bath is 40-50 ℃.
And thirdly, placing the AM component obtained in the second step in a low-temperature gas carburizing furnace for low-temperature gas carburizing treatment to obtain the AM component after the compound treatment, wherein the step can introduce compressive residual stress of more than 2000GPa on the surface to obtain the AM component with the reinforced surface. The low temperature gas carburizing treatment is divided into two stages:
when the low-temperature gas carburizing treatment is carried out, the method is divided into two stages:
in the first stage, the volume group used is HCl: n (N) 2 (2:1-1:3) the surface of the mixed gas removing memberThe passivation film is treated at 200-300 deg.c for 3-5 hr.
In the second stage, the reuse volume composition is CO: h 2 ：N 2 (1:2:3-1:4:6), the treatment temperature is 450-480 ℃, and the carburizing time is 25-40h.
Example 1
As shown in fig. 1, a composite treatment process for AM austenitic stainless steel for residual stress regulation, comprising the following steps:
sample preparation: a 316L austenitic stainless steel forming member was made using a selective laser melting additive manufacturing method.
A sample model with the size of 10mm by 10mm is modeled by computer CAD software, then the model is layered according to a slice with the thickness of 30 mu m of each layer, the rotation of 66.7 degrees is arranged between the layers, and a scanning path is planned by using special software for additive manufacturing. The 316L austenitic stainless steel coupon preparation was then performed using SLM-125HL additive manufacturing equipment. The set additive manufacturing printing parameters are as follows: the laser power was 200W, the scanning speed was 800mm/s, the layer thickness was 30 μm, and the scanning pitch was 120. Mu.m.
The first step: heat treatment for the purpose of reducing residual stress of the sample
And (3) placing the prepared sample into a heat treatment furnace, heating to 900 ℃ along with the furnace, preserving heat for 1h, and then air-cooling. After heat treatment, the peculiar cellular structure and the fusion line of the additive manufacturing material are disappeared, the microstructure before and after heat treatment is shown in figure 3, and the residual stress is reduced to within 50MPa, which is shown in figure 2.
And a second step of: electrolytic polishing treatment for the purpose of reducing the surface roughness of a sample
Conventional mechanical polishing processes have difficulty in reducing additive manufactured specimens having complex structures, and thus use electrolytic polishing to remove the surface roughness of the specimens. Placing the sample after the first heat treatment in electrolyte (90 ml of phosphoric acid, 75ml of distilled water, 70ml of sulfuric acid and 265ml of glycerin), heating to 45deg.C in water bath, and maintaining 0.14A/cm 2 The surface-treated sample was obtained by treating the sample with a current density for 4 hours, and the oxide layer resulting from the heat treatment was removed by electrolytic polishing.
And a third step of: low temperature gas carburizing treatment for surface strengthening
The conventional surface strengthening treatment is difficult to be applied to additive manufacturing samples with complex structures, and can be used for carrying out surface strengthening on parts with any complex shape due to the diffusibility of low-temperature gas carburization, and the flow of the low-temperature gas carburization process stage is shown in fig. 4. Firstly, placing the sample after electrolytic treatment into a low-temperature gas carburizing furnace, uniformly heating for 40min to 250 ℃, preserving heat for 2h, and then introducing activated gas (HCl and N) 2 Mixed gas of (d) for 4 hours. After the surface activation is finished, the temperature is increased at a constant speed in the same furnace for 40min to 470 ℃ for 2H, and then the carbon-permeable gas (CO and H) is introduced 2 And N 2 Is mixed gas of (2) for 30h and furnace cooling. FIG. 3 shows the microstructure of the reinforced layer after the compounding treatment according to the present invention. The fatigue effect after the composite strengthening treatment can be shown in fig. 5, and it can be found that the fatigue failure cycle number of the original sample is 1.3E5 under the same stress of 300MPa after the composite treatment, and the fatigue failure cycle number is 1E7 after the composite treatment, so that the service life is improved by 100 times, and the fatigue limit is reached. And the fatigue failure cycle numbers are 5.9E5 and 1.7E6 respectively only by means of heat treatment and surface strengthening, and are improved by about 5 times and 10 times. Therefore, the fatigue life of the parts can be effectively prolonged by the mode of compound treatment.
Claims (7)
1. A composite treatment process for AM austenitic stainless steel for regulating residual stress is characterized in that an austenitic stainless steel forming member is prepared by adopting an additive manufacturing method, and then the austenitic stainless steel forming member is subjected to composite treatment, and the composite treatment process comprises the following steps:
firstly, carrying out heat treatment on an austenitic stainless steel forming component manufactured by additive manufacturing, wherein the tensile residual stress of the austenitic stainless steel forming component is greater than 500MPa, the heat treatment temperature is 850-950 ℃, the temperature is kept for 1-4 hours, then air cooling is carried out, a component after heat treatment is obtained, the tensile residual stress is controlled within 50MPa, and the process is shifted to the second step;
step two, the component after heat treatment is subjected to electrolytic polishing treatment, and 0.1 to 0.5A/cm is used 2 The current density of the steel is treated for 2 to 6 hours to obtain a component after electrolytic polishing, and the electrolysis can be effectively reducedThe surface roughness of the polished member is shifted to the third step;
and thirdly, performing low-temperature gas carburizing treatment on the member subjected to electrolytic polishing to obtain a member subjected to compound treatment, and introducing compressive residual stress of more than 2000MPa on the surface of the member subjected to compound treatment to obtain the AM member with the reinforced surface.
2. The composite treatment process for AM austenitic stainless steel for residual stress regulation according to claim 1, wherein in the first step, the heat treatment is carried out by adopting a heat treatment furnace, the austenitic stainless steel forming member is heated to 850-950 ℃ along with the furnace, and the heating rate is controlled to 5-15 ℃/min.
3. The composite treatment process for AM austenitic stainless steel for residual stress control according to claim 1, wherein the member after heat treatment is subjected to electropolishing treatment in the second step, specifically comprising the following steps:
the water bath heating temperature adopted by the electrolytic polishing is 40-50 ℃, and the electrolyte is prepared from phosphoric acid, distilled water, sulfuric acid and glycerin.
4. The composite treatment process for AM austenitic stainless steel for residual stress regulation and control according to claim 3, wherein the specific proportion of the electrolyte is phosphoric acid: distilled water: sulfuric acid: glycerol = 18:15:14:53.
5. the composite treatment process for AM austenitic stainless steel for residual stress control according to claim 1, wherein in the third step, the electropolished component is subjected to low-temperature gas carburizing treatment, specifically comprising the following steps:
the low-temperature gas carburizing treatment is divided into two stages:
in the first stage, the gas used in the activation treatment is HCl: n (N) 2 The treatment temperature is 200-300 ℃ and the activation time is 3-5h;
in the second stage, the gas used in the activation treatment is carburizing gas CO：H 2 ：N 2 The treatment temperature is 450-480 ℃, and the carburizing time is 25-40h.
6. The composite treatment process for AM austenitic stainless steel for residual stress control according to claim 5, wherein HCl: n (N) 2 The ratio of the mixed gas is 2:1 to 1:3.
7. the composite treatment process for AM austenitic stainless steel for residual stress control according to claim 5, wherein CO: h 2 ：N 2 The ratio of the mixed gas is 1:2: 3-1: 4:6.
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| CN202310784450.3A CN116814918A (en) | 2023-06-29 | 2023-06-29 | Composite treatment process for AM austenitic stainless steel regulated and controlled by residual stress |
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