Molding method of composite stainless steel molded body and composite stainless steel molded body

Abstract

The invention provides a forming method of a composite stainless steel forming body and the composite stainless steel forming body. The molding method of the composite stainless steel molded body comprises the following steps: performing injection molding on a first injection material to obtain a first green body, wherein the first injection material comprises precipitation hardening type stainless steel, and the average powder size is 8-12 [mu] m; a second injection material is adopted to carry out wrapping injection molding on the surface of the first green body to obtain a second green body, the second injection material comprises austenitic stainless steel, and the average powder size is 4-10 microns; sequentially degreasing and sintering the first green body and the second green body to obtain a molded body, wherein the sintering temperature is 1280-1320 DEG C; according to the forming method of the composite stainless steel forming body, precipitation hardening type stainless steel and austenitic stainless steel can be combined at low temperature, high strength and high hardness of the precipitation hardening type stainless steel are maintained, meanwhile, high polishing performance and high corrosion resistance of the austenitic stainless steel can be maintained, and the forming body with good comprehensive performance can be prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of powder material injection molding, in particular to the technical field of stainless steel material injection molding, and further to a molding method of a composite stainless steel molded body and the composite stainless steel molded body. Background Art

[0002] Traditional high-end hardware products are mostly made of copper alloys and zinc alloys. However, as industry demand increases, the demand for high corrosion resistance and high strength is increasing, and high-end high-end hardware products are turning to stainless steel for manufacturing.

[0003] Stainless steel materials typically include austenitic stainless steel and precipitation-hardening stainless steel. Austenitic stainless steels such as 304, 304L, 316, and 316L offer high corrosion resistance and are widely used in product exterior components. However, while austenitic stainless steels offer excellent corrosion resistance, they also suffer from low hardness and poor wear and impact resistance. Precipitation-hardening stainless steels such as 17-4PH (SUS 630), 15-5PH (XM12), and 13-8Mo (XM13) offer high hardness and strength and are widely used in structural components. However, precipitation-hardening stainless steels fail chemical testing and, as they do not meet corrosion resistance requirements, are not suitable for use in product exterior components.

[0004] Generally speaking, austenitic stainless steels require higher sintering temperatures. For example, SUS 316L stainless steel requires a sintering temperature between 1360°C and 1380°C to achieve a dense sintered part. Sintering temperatures that are too low can easily result in insufficient sintered density, preventing the surface from achieving a mirror-like finish. Precipitation-hardening stainless steels, on the other hand, typically require a lower sintering temperature. For example, SUS 630 stainless steel typically requires a sintering temperature of 1300°C to achieve densification. However, sintering at 1380°C results in the formation of a larger amount of hard and brittle ferrite, forming a continuous phase and reducing the strength and ductility of the sintered part. Therefore, it is difficult to combine austenitic and precipitation-hardening stainless steels at the same sintering temperature to produce a molded part with high polishability, hardness, and strength. Currently, austenitic stainless steel is commonly used for exterior components, with high-hardness ceramic materials used for internal structural components, or precipitation-hardening stainless steel is used for structural components, with corrosion-resistant plastic used for exterior components. Although this composite can meet the requirements of strength and corrosion resistance, the performance of the two types of materials is quite different, the bonding performance is poor, and the bonding interface will have defects such as warping, cracks, and delamination, which cannot meet the needs of long-term use. It is still necessary to focus on how to composite austenitic stainless steel and precipitation hardening stainless steel.

[0005] Therefore, how to complete the sintering of the two materials at a lower sintering temperature and combine the two together through sintering, while maintaining the high strength and high hardness of the precipitation hardened stainless steel, while also maintaining the high polishability and high corrosion resistance of the austenitic stainless steel, has become a problem that ordinary technicians in this field are committed to solving. Summary of the Invention

[0006] In response to the above-mentioned problems, the present invention provides a method for forming a composite stainless steel formed body and the composite stainless steel formed body. This method combines precipitation-hardening stainless steel and austenitic stainless steel at a relatively low sintering temperature, maintaining the high strength and hardness of the precipitation-hardening stainless steel while also maintaining the high polishability and corrosion resistance of the austenitic stainless steel, resulting in a formed body with excellent overall performance.

[0007] To achieve the above-mentioned object, the present invention provides a first aspect of a method for forming a composite stainless steel formed body, comprising the steps of: (1) Preparation of the first embryo injection molding a first shot material to obtain a first green body, wherein the first shot material comprises precipitation hardened stainless steel and has an average powder size of 8 to 12 μm; (2) Preparation of the second embryo A second green body is obtained by injection molding a second shot material on the surface of the first green body, wherein the second shot material comprises austenitic stainless steel and has an average powder size of 4 to 10 μm; (3) Degreasing and sintering The first green body and the second green body are degreased and sintered in sequence to obtain a formed body, and the sintering temperature is 1280-1320°C.

[0008] In the method for forming a composite stainless steel formed body of the present invention, a second green body of austenitic stainless steel is coated with a first green body of precipitation-hardened stainless steel. The resulting formed body combines the corrosion-resistant austenitic stainless steel with the high-strength precipitation-hardened stainless steel, resulting in a composite stainless steel formed body with high strength, high hardness, and high corrosion resistance. Furthermore, the average powder size of the precipitation-hardened stainless steel is 8-12 μm, while the average powder size of the austenitic stainless steel is 4-10 μm. Using austenitic stainless steel powder with a finer average powder size for coating enhances the sintering driving force. Even at relatively low sintering temperatures of 1280-1320°C, the difficult-to-sinter austenitic stainless steel can be densified. After polishing, the resulting formed body achieves a mirror-finish finish (surface roughness <0.03 μm), resulting in high polishability.

[0009] As a technical solution of the present invention, the first shot material is subjected to a first injection molding in a first molding mold to obtain the first green embryo.

[0010] As a technical solution of the present invention, the inlet melt temperature of the first molding mold is 190~210℃, the mold wall temperature is 90~100℃, the maximum injection pressure is 100MPa, the holding pressure is 75MPa, the holding time is 3~4s, the first injection molding time is 2s and the interval period is 25~30s, cooling water is used for cooling for 10s after the first injection molding, and the mold opening time is 1~5s.

[0011] As a technical solution of the present invention, the first green body is placed in a second molding die, and the second shot material is used to injection-mold the second green body onto the surface of the first green body.

[0012] As a technical solution of the present invention, the inlet melt temperature of the second molding mold is 190~210℃, the mold wall temperature is 100~120℃, the maximum injection pressure is 90MPa, the holding pressure is 60MPa, the holding time is 2~5s, the second injection molding time is 2~5s and the interval period is 30~40s, cooling water is used for cooling for 15s after the second injection molding, and the mold opening time is 1~5s.

[0013] As a technical solution of the present invention, the first green embryo has a limiting portion, and the second green embryo has a receiving portion, and the limiting portion and the receiving portion are fixedly engaged.

[0014] As a technical solution of the present invention, the composition of the precipitation hardening stainless steel includes 15.50-17.50 wt.% chromium, 3.00-5.00 wt.% nickel, 0.15-0.45 wt.% niobium, 3.00-5.00 wt.% copper, ≤1.00 wt.% manganese, ≤0.07 wt.% carbon, 70.00-78.00 wt.% iron and ≤1.0 0wt.% of other non-metallic elements, the composition of the austenitic stainless steel includes 16.00~18.00wt.% of chromium, 12.00~14.00wt.% of nickel, 2.00~3.00wt.% of molybdenum, ≤2.00wt.% of manganese, ≤0.03wt.% of carbon, 63.00~68.00wt.% of iron and ≤1.00wt.% of other non-metallic elements.

[0015] As a technical solution of the present invention, the degreasing includes acid degreasing and thermal degreasing. The temperature of the acid degreasing is 110~135℃, and the time of the acid degreasing is 7.5~12.0h. The temperature of the thermal degreasing is 350~600℃, and the time of the thermal degreasing is 2.0~6.0h.

[0016] As a technical solution of the present invention, the sintering includes pre-sintering and partial pressure sintering. The temperature of the pre-sintering is 1020~1080℃, the time of the pre-sintering is 140~180min, the time of the partial pressure sintering is 140~180min, the pressure of the partial pressure sintering is 1~10Pa, and argon is introduced during the sintering.

[0017] The second aspect of the present invention provides a composite stainless steel formed body obtained by a forming method of a composite stainless steel formed body, wherein the surface roughness of the composite stainless steel formed body after polishing is less than 0.03 μm, and the sintered density of the composite stainless steel formed body is 7.90-7.95 g / cm 3 , hardness is 220~275HV, tensile strength is 700~950MPa, yield strength is 500~700MPa, and nickel release is less than or equal to 0.05μg / cm3 per week 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a flow chart of the forming method of the composite stainless steel formed body of the present invention. DETAILED DESCRIPTION

[0019] The composite stainless steel formed body obtained by the forming method of the present invention has excellent comprehensive performance, including high strength, high hardness, high polishability, and high corrosion resistance. Furthermore, the composite stainless steel formed body has a hardness of 220 to 275 HV. For example, the hardness may be, but is not limited to, 220 HV, 225 HV, 230 HV, 235 HV, 240 HV, 245 HV, 250 HV, 255 HV, 260 HV, 265 HV, 270 HV, and 275 HV, which is much higher than the 120 to 140 HV hardness of austenitic stainless steel. The tensile strength of the composite stainless steel formed body is 700-950 MPa. As an example, the tensile strength may be, but is not limited to, 700 MPa, 750 MPa, 800 MPa, 850 MPa, 900 MPa, and 950 MPa. The yield strength is 500-700 MPa. As an example, the yield strength may be, but is not limited to, 500 MPa, 520 MPa, 540 MPa, 560 MPa, 580 MPa, 600 MPa, 620 MPa, 640 MPa, 660 MPa, 680 MPa, and 700 MPa. Its tensile strength and yield strength are higher than those of austenitic stainless steel (tensile strength of 480-620 MPa and yield strength of 170-300 MPa). Therefore, the composite stainless steel formed body of the present invention combines precipitation-hardened stainless steel on the basis of austenitic stainless steel, greatly improving the strength and hardness. The surface roughness of the composite stainless steel formed body of the present invention after polishing is less than 0.03 μm. As an example, the surface roughness can be, but is not limited to, 0.029 μm, 0.027 μm, 0.025 μm, 0.023 μm, 0.020 μm, 0.019 μm, 0.017 μm, 0.015 μm, 0.013 μm, and 0.010 μm, and has good high polishability. The sintered density is 7.90-7.95 g / cm 3 As an example, it can be, but not limited to, 7.90 g / cm 3 , 7.91g / cm 3 , 7.92g / cm 3 、7.93g / cm 3 , 7.94g / cm 3 , 7.95g / cm 3 This indicates that the present invention can achieve densification of both austenitic stainless steel and precipitation-hardening stainless steel at a relatively low sintering temperature of 1300±10°C. The composite stainless steel formed body of the present invention exhibits no defects such as warping, cracking, or delamination at the interface between the austenitic stainless steel and precipitation-hardening stainless steel. It can pass 24-hour artificial sweat and 96-hour salt spray tests with no significant corrosion, and a weekly nickel release of less than or equal to 0.05 μg / cm 2 .

[0020] The forming method of the composite stainless steel formed body of the present invention comprises the steps of (1) preparing a first green body; (2) preparing a second green body; and (3) degreasing and sintering.

[0021] Wherein, step (1) of preparing the first green body comprises injection molding the first shot to obtain the first green body. The first shot comprises precipitation hardening stainless steel, and the composition of the precipitation hardening stainless steel comprises 15.50-17.50 wt.% of chromium, 3.00-5.00 wt.% of nickel, 0.15-0.45 wt.% of niobium, 3.00-5.00 wt.% of copper, ≤1.00 wt.% of manganese, ≤0.07 wt.% of carbon, 70.00-78.00 wt.% of iron and ≤1.00 wt.% of other non-metallic elements, wherein the other non-metallic elements refer to inevitable impurities such as silicon, phosphorus and sulfur. The precipitation hardening stainless steel can be 17-4PH (SUS 630), 15-5PH (XM12), 13-8Mo (XM13), preferably 17-4PH (SUS 630). The average powder size of the precipitation-hardening stainless steel is 8-12 μm. For example, the average powder size can be, but is not limited to, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm. The powder particle size is 1000-1600 mesh. For example, the particle size can be, but is not limited to, 1000 mesh, 1100 mesh, 1200 mesh, 1300 mesh, 1400 mesh, 1500 mesh, or 1600 mesh. The first green body can be obtained by subjecting the first shot to a first injection molding process in a first molding die. The parameters of the first molding die can be: an inlet melt temperature of 190-210°C, a mold wall temperature of 90-100°C, a maximum injection pressure of 100 MPa, a holding pressure of 75 MPa, a holding time of 3-4 seconds, a first injection molding time of 2 seconds with an interval of 25-30 seconds, cooling water cooling for 10 seconds after the first injection molding, and a mold opening time of 1-5 seconds.

[0022] Step (2) of preparing the second green body comprises: using a second shot material to injection mold the surface of the first green body to obtain the second green body. The second shot material comprises austenitic stainless steel, and the composition of the austenitic stainless steel comprises 16.00-18.00wt.% chromium, 12.00-14.00wt.% nickel, 2.00-3.00wt.% molybdenum, ≤2.00wt.% manganese, ≤0.03wt.% carbon, 63.00-68.00wt.% iron, and ≤1.00wt.% other non-metallic elements, wherein the other non-metallic elements refer to inevitable impurities such as silicon, phosphorus, and sulfur. The austenitic stainless steel can be 304, 304L, 316, or 316L, preferably 316L. The average powder size of the austenitic stainless steel is 4-10μm, which is smaller than the average powder size of the precipitation hardening stainless steel. For example, the average powder size of austenitic stainless steel can be, but is not limited to, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. The powder particle size is 1300-3000 mesh. For example, the particle size can be, but is not limited to, 1300 mesh, 1500 mesh, 1700 mesh, 1900 mesh, 2000 mesh, 2200 mesh, 2400 mesh, 2600 mesh, 2800 mesh, or 3000 mesh. The second green body can be formed by placing the first green body into a second forming mold and then using the second shot to cover the surface of the first green body with the material. The parameters of the second molding mold can be: inlet melt temperature of 190~210℃, mold wall temperature of 100~120℃, maximum injection pressure of 90MPa, holding pressure of 60MPa, holding time of 2~5s, second injection molding time of 2~5s and interval period of 30~40s, cooling water is used for cooling for 15s after the second injection molding, and mold opening time is 1~5s.

[0023] Step (3) degreasing and sintering includes: degreasing and sintering the first green embryo and the second green embryo in sequence to obtain a molded body.

[0024] Degreasing includes acid degreasing and thermal degreasing. The temperature of acid degreasing is 110-135°C. As an example, the temperature can be, but is not limited to, 110°C, 115°C, 120°C, 125°C, 130°C, and 135°C. The time of acid degreasing is 7.5-12.0 hours. As an example, the time can be, but is not limited to, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10.0 hours, 10.5 hours, 11.0 hours, 11.5 hours, and 12.0 hours. The temperature of thermal degreasing is 350-600°C. As an example, the temperature can be, but is not limited to, 350°C, 400°C, 450°C, 500°C, 550°C, and 600°C. The time for thermal debinding is 2.0~6.0h. As an example, the time can be but not limited to 2.0h, 3.0h, 4.0h, 5.0h, and 6.0h. Staged heating is used during thermal debinding to ensure complete debinding. Sintering includes pre-sintering and partial pressure sintering. The pre-sintering temperature is 1020~1080℃. As an example, the temperature can be but not limited to 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, and 1080℃. The time for pre-sintering is 140~180min. As an example, the time can be but not limited to 140min, 150min, 160min, 170min, and 180min. The efficiency of partial pressure sintering can be improved by pre-sintering in advance. The temperature of the partial pressure sintering is 1280~1320℃. As an example, the temperature can be but not limited to 1280℃, 1290℃, 1300℃, 1310℃, 1320℃, and is preferably 1300℃. The time of the partial pressure sintering is 140~180min. As an example, the time can be but not limited to 140min, 150min, 160min, 170min, and 180min. The pressure of the partial pressure sintering is 1~10Pa, and argon is introduced during sintering. As an example, the pressure can be but not limited to 1Pa, 3Pa, 5Pa, 7Pa, 9Pa, 10Pa, and is preferably 1Pa.

[0025] The flow chart of the forming method of the composite stainless steel formed body of the present invention can be shown as follows: Figure 1 The forming method of the composite stainless steel formed body comprises the following steps: S1. The first shot 10 is injection molded to obtain a first green embryo 1; S2. The second shot 20 is injection molded to obtain a second green embryo 2. This step may be specifically to place the first green embryo 1 into the second green embryo 2 of the molding mold 4, and the second shot 20 is injection molded into the second green embryo 2 outside the first green embryo 1, and form a preform 3; S3. The preform 3 is degreased and sintered to form a composite molded body.

[0026] In addition, the first green body 1 has a limiting portion 11, and the second green body 2 has a receiving portion 21 corresponding to the limiting portion 11, and the limiting portion 11 and the receiving portion 21 are fixed by snapping. The limiting portion 11 can be, but is not limited to, a barb, a cone, or a convex structure. During the injection molding process of the second green body 2, the second shot 20 is injected into the molding mold by injection molding, so that the green body is formed with a receiving portion 21 having a shape corresponding to the limiting portion. The receiving portion 21 and the limiting portion 11 form a self-engaging and stable joint structure, thereby improving the joint stability of the first shot 10 and the second shot 20. This joint method is different from the method of adding solder for welding and can avoid the problem of local corrosion resistance and strength reduction of the molded body due to the heat-affected zone caused by solder or welding.

[0027] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0028] Example 1 This embodiment is a method for forming a composite stainless steel formed body, which includes the following steps.

[0029] (1) Preparation of the first embryo Precipitation-hardened stainless steel was injected into a first mold to produce a first green body having a barb. The first mold had an inlet melt temperature of 200°C, a mold wall temperature of 95°C, a maximum injection pressure of 100 MPa, a holding pressure of 75 MPa, a holding time of 3.5 seconds, a first injection molding time of 2 seconds, and a 27.5-second interval. After the first injection molding, cooling water was used for 10 seconds, and the mold opening time was 3 seconds. The precipitation-hardened stainless steel had an average powder size of 8 μm and a composition consisting of 16.50 wt.% chromium, 4.50 wt.% nickel, 0.35 wt.% niobium, 4.00 wt.% copper, 0.50 wt.% manganese, 0.03 wt.% carbon, 74.12 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0030] (2) Preparation of the second embryo The first green body was placed in a second mold, and a second green body was injection-molded onto the surface of the first green body using austenitic stainless steel. The second green body had a stopper corresponding to and engaging the barb. The second mold had an inlet melt temperature of 195°C, a mold wall temperature of 110°C, a maximum injection pressure of 90 MPa, a holding pressure of 60 MPa, and a holding time of 3 seconds. The second injection molding time was 1.5 seconds with a 33-second interval. After the second injection molding, cooling water was used for 15 seconds, and the mold opening time was 3 seconds. The average powder size of the austenitic stainless steel was 6 μm. The austenitic stainless steel composition included 17.50 wt.% chromium, 12.00 wt.% nickel, 2.50 wt.% molybdenum, 0.20 wt.% manganese, 0.02 wt.% carbon, 67.78 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0031] (3) Degreasing and sintering The first and second green bodies were acid debinded, thermally debinded, pre-sintered, and pressure-sintered together to obtain a molded body. Acid debinding was performed using oxalic acid at a temperature of 130°C for 10 hours. Thermal debinding was performed at a temperature of 450°C for 3 hours. Pre-sintering was performed at a temperature of 1050°C for 160 minutes. Pressure-sintering was performed at a temperature of 1300°C for 160 minutes at a pressure of 1 Pa, with argon gas introduced for sintering.

[0032] Example 2 This embodiment is a method for forming a composite stainless steel formed body, which includes the following steps.

[0033] (1) Preparation of the first embryo Precipitation-hardened stainless steel was injected into a first mold to produce a first green body having a barb. The first mold had an inlet melt temperature of 195°C, a mold wall temperature of 90°C, a maximum injection pressure of 100 MPa, a holding pressure of 75 MPa, a holding time of 3.5 seconds, a first injection molding time of 2 seconds, and a 30-second interval. After the first injection molding, cooling water was used for 10 seconds, and the mold opening time was 3 seconds. The precipitation-hardened stainless steel had an average powder size of 10 μm and a composition of 16.50 wt.% chromium, 4.50 wt.% nickel, 0.35 wt.% niobium, 4.00 wt.% copper, 0.50 wt.% manganese, 0.03 wt.% carbon, 74.12 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0034] (2) Preparation of the second embryo The first green body was placed in a second mold, and a second green body was injection-molded onto the surface of the first green body using austenitic stainless steel. The second green body had a stopper corresponding to and engaging the barb. The second mold had an inlet melt temperature of 205°C, a mold wall temperature of 100°C, a maximum injection pressure of 90 MPa, a holding pressure of 60 MPa, and a holding time of 3 seconds. The second injection molding time was 2 seconds with a 35-second interval. After the second injection molding, cooling water was used for 15 seconds, and the mold opening time was 3 seconds. The average powder size of the austenitic stainless steel was 8 μm. The austenitic stainless steel composition included 17.50 wt.% chromium, 12.00 wt.% nickel, 2.50 wt.% molybdenum, 0.20 wt.% manganese, 0.02 wt.% carbon, 67.78 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0035] (3) Degreasing and sintering The first and second green bodies were sequentially subjected to acid debinding, thermal debinding, pre-sintering, and partial pressure sintering to produce a molded body. Acid debinding was performed using oxalic acid at a temperature of 130°C for 10 hours. Thermal debinding was performed at a temperature of 500°C for 3 hours. Pre-sintering was performed at a temperature of 1050°C for 160 minutes. Partial pressure sintering was performed at a temperature of 1300°C for 160 minutes at a pressure of 5 Pa, with argon gas flowing through the sintering chamber.

[0036] Comparative Example 1 This comparative example is a method for forming a composite stainless steel formed body, which includes the following steps.

[0037] (1) Preparation of the first embryo Precipitation-hardened stainless steel was injected into a first mold to produce a first green body having a barb. The first mold had an inlet melt temperature of 200°C, a mold wall temperature of 95°C, a maximum injection pressure of 100 MPa, a holding pressure of 75 MPa, a holding time of 3.5 seconds, a first injection molding time of 2 seconds, and a 27.5-second interval. After the first injection molding, cooling water was used for 10 seconds, and the mold opening time was 3 seconds. The precipitation-hardened stainless steel had an average powder size of 10 μm and a composition of 16.50 wt.% chromium, 4.50 wt.% nickel, 0.35 wt.% niobium, 4.00 wt.% copper, 0.50 wt.% manganese, 0.03 wt.% carbon, 74.12 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0038] (2) Preparation of the second embryo The first green body was placed in a second mold, and a second green body was injection-molded onto the surface of the first green body using austenitic stainless steel. The second green body had a stopper corresponding to and engaging the barb. The second mold had an inlet melt temperature of 195°C, a mold wall temperature of 110°C, a maximum injection pressure of 90 MPa, a holding pressure of 60 MPa, and a holding time of 3 seconds. The second injection molding time was 1.5 seconds with a 33-second interval. After the second injection molding, cooling water was used for 15 seconds, and the mold opening time was 3 seconds. The average powder size of the austenitic stainless steel was 23 μm. The austenitic stainless steel composition included 17.50 wt.% chromium, 12.00 wt.% nickel, 2.50 wt.% molybdenum, 0.20 wt.% manganese, 0.02 wt.% carbon, 67.78 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0039] (3) Degreasing and sintering The first and second green bodies were sequentially subjected to acid debinding, thermal debinding, pre-sintering, and partial pressure sintering to produce a molded body. Acid debinding was performed using oxalic acid at a temperature of 130°C for 10 hours. Thermal debinding was performed at a temperature of 450°C for 3 hours. Pre-sintering was performed at a temperature of 1050°C for 160 minutes. Partial pressure sintering was performed at a temperature of 1300°C for 160 minutes at a pressure of 1 Pa, with argon gas flowing through the sintering chamber.

[0040] Comparative Example 2 This comparative example is a method for forming a composite stainless steel formed body, which includes the following steps.

[0041] (1) Preparation of the first embryo Precipitation-hardened stainless steel was injected into a first mold to produce a first green body having a barb. The first mold had an inlet melt temperature of 200°C, a mold wall temperature of 95°C, a maximum injection pressure of 100 MPa, a holding pressure of 75 MPa, a holding time of 3.5 seconds, a first injection molding time of 2 seconds, and a 27.5-second interval. After the first injection molding, cooling water was used for 10 seconds, and the mold opening time was 3 seconds. The precipitation-hardened stainless steel had an average powder size of 8 μm and a composition consisting of 16.50 wt.% chromium, 4.50 wt.% nickel, 0.35 wt.% niobium, 4.00 wt.% copper, 0.50 wt.% manganese, 0.03 wt.% carbon, 74.12 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0042] (2) Preparation of the second embryo The first green body was placed in a second mold, and a second green body was injection-molded onto the surface of the first green body using austenitic stainless steel. The second green body had a stopper corresponding to and engaging the barb. The second mold had an inlet melt temperature of 195°C, a mold wall temperature of 110°C, a maximum injection pressure of 90 MPa, a holding pressure of 60 MPa, and a holding time of 3 seconds. The second injection molding time was 1.5 seconds with a 33-second interval. After the second injection molding, cooling water was used for 15 seconds, and the mold opening time was 3 seconds. The average powder size of the austenitic stainless steel was 6 μm. The austenitic stainless steel composition included 17.50 wt.% chromium, 12.00 wt.% nickel, 2.50 wt.% molybdenum, 0.20 wt.% manganese, 0.02 wt.% carbon, 67.78 wt.% iron, and ≤1.00 wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0043] (3) Degreasing and sintering The first and second green bodies were acid debinded, thermally debinded, pre-sintered, and pressure-sintered together to obtain a molded body. Acid debinding was performed using oxalic acid at a temperature of 130°C for 10 hours. Thermal debinding was performed at a temperature of 450°C for 3 hours. Pre-sintering was performed at a temperature of 1050°C for 160 minutes. Pressure-sintering was performed at a temperature of 1380°C for 160 minutes at a pressure of 1 Pa, with argon gas introduced for sintering.

[0044] Comparative Example 3 This comparative example is a method for forming a composite stainless steel formed body, which includes the following steps.

[0045] (1) Preparation of embryos Austenitic stainless steel is placed in a mold and injection molded to produce a green body. The mold inlet melt temperature is 195°C, the mold wall temperature is 110°C, the maximum injection pressure is 90 MPa, the holding pressure is 60 MPa, the holding time is 3 seconds, the injection molding time is 1.5 seconds with a 33-second interval, and cooling water is used for 15 seconds after injection molding. The mold opening time is 3 seconds. The average powder size of the austenitic stainless steel is 6μm. The austenitic stainless steel composition includes 17.50wt.% chromium, 12.00wt.% nickel, 2.50wt.% molybdenum, 0.20wt.% manganese, 0.02wt.% carbon, 67.78wt.% iron, and ≤1.00wt.% of other non-metallic elements (a mixture of silicon, phosphorus, and sulfur).

[0046] (2) Degreasing and sintering The green body was sequentially subjected to acid debinding, thermal debinding, pre-sintering, and partial pressure sintering to obtain a molded body. Acid debinding was performed using oxalic acid at a temperature of 130°C for 10 hours. Thermal debinding was performed at a temperature of 450°C for 3 hours. Pre-sintering was performed at a temperature of 1050°C for 160 minutes. Partial pressure sintering was performed at a temperature of 1380°C for 160 minutes at a pressure of 1 Pa, with argon gas flowing through the sintering chamber.

[0047] The molded bodies of Examples 1-2 and Comparative Examples 1-3 were subjected to sintering density, hardness, strength, polishing, surface roughness, and chemical tests. The test results are shown in Table 1.

[0048] The sintered density is determined in accordance with MPIF Standard 54. First, the empty weight (W air ), then place the test cube into a vacuum dish, immerse it in oil, and use a machine to remove the air until all bubbles are eliminated. After removing the test cube, wipe off the remaining oil on the surface and measure its weight again (W oil ), and finally put the test cube into the water and measure the weight of the test cube in the water (W water ). The three measured weights (W air 、W oil With W water ) According to the Archimedes method (calculation formula is as follows) the sintered density of the test cube (ρ s ).

[0049]

[0050] Hardness was tested using a Vickers hardness tester with a load of 0.01 kgf. Tensile testing was performed using specimen design according to MPIF E8 / E8M, and tensile strength was tested using a universal tensile testing machine at a test rate of 1 mm / min.

[0051] Polishing is performed using commonly known polishing techniques within the industry. Specifically, the surface is first roughened with low-grit sandpaper to remove roughness. Next, it is polished with coarse and fine grinding wheels, and finally, it is polished to a mirror finish. The surface roughness of the polished molded body is tested using a surface roughness tester.

[0052] Chemical tests include artificial sweat, salt spray, and nickel release testing. Artificial sweat testing is conducted in accordance with NFS 80772. Specifically, 100g of sodium chloride and 50g of lactic acid are added to 850g of purified water to create a one-liter artificial sweat solution with a pH range of approximately 6.5-7.2. The composite stainless steel formed body sample is immersed in the artificial sweat solution, and the test heating cabinet is maintained at 55°C for 24 hours. Salt spray testing is conducted in accordance with ASTM B-117. Specifically, a 1.5% salt solution with a pH range of 6.5-7.2 is atomized into a mist, and the composite stainless steel formed body sample is placed in a heating cabinet maintained at 35°C for 96 hours. Nickel release testing is conducted in accordance with EN 1811. Specifically, artificial sweat was prepared according to the artificial sweat test, the sample was soaked in the artificial sweat, the heating cabinet was maintained at 30°C, the test time was one week (168 hours), and the nickel content in the artificial sweat after the test was detected using an atomic absorption spectrophotometer (AAS).

[0053] Table 1 Test results of molded bodies of Examples 1-2 and Comparative Examples 1-3

[0054] The results in Table 1 show that coating with austenitic stainless steel powders of finer average powder size can enhance the sintering driving force. Even the more difficult-to-sinter austenitic stainless steel can be densified at lower sintering temperatures of 1280-1320°C, resulting in a molded body with excellent surface roughness, polishing, sintered density, hardness, strength, and chemical properties. In Comparative Example 1, however, due to the larger average powder size of the austenitic stainless steel, full densification was not achieved at the lower sintering temperature, resulting in failure to pass chemical testing. Furthermore, the surface was more susceptible to oxidation, resulting in rust spots and poor polishing properties. In Comparative Example 2, the sintering temperature was too high. Although the austenitic stainless steel had a high density after sintering, the resulting product had poor strength and ductility. In Comparative Example 3, no precipitation-hardened stainless steel was compounded, resulting in only austenitic stainless steel. Although the corrosion resistance was excellent, the hardness and strength were low, making it impossible to achieve both strength and corrosion resistance.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for forming a composite stainless steel formed body, characterized in that: Including steps: (1) Preparation of the first embryo injection molding a first shot material to obtain a first green body, wherein the first shot material comprises precipitation hardened stainless steel and has an average powder size of 8 to 12 μm; (2) Preparation of the second embryo A second green body is obtained by injection molding a second shot material on the surface of the first green body, wherein the second shot material comprises austenitic stainless steel and has an average powder size of 4 to 10 μm; (3) Degreasing and sintering The first green body and the second green body are degreased and sintered in sequence to obtain a formed body, and the sintering temperature is 1280-1320°C.

2. The method for forming a composite stainless steel formed body according to claim 1, wherein: The first shot material is subjected to a first injection molding in a first molding mold to obtain the first green embryo.

3. The method for forming a composite stainless steel formed body according to claim 2, wherein: The inlet melt temperature of the first molding mold is 190~210℃, the mold wall temperature is 90~100℃, the maximum injection pressure is 100MPa, the holding pressure is 75MPa, the holding time is 3~4s, the first injection molding time is 2s and the interval period is 25~30s, cooling water is used for cooling for 10s after the first injection molding, and the mold opening time is 1~5s.

4. The method for forming a composite stainless steel formed body according to claim 2, wherein: The first green body is placed in a second molding die, and the second shot material is used to injection-mold the second green body onto the surface of the first green body.

5. The method for forming a composite stainless steel formed body according to claim 4, wherein: The inlet melt temperature of the second molding mold is 190~210℃, the mold wall temperature is 100~120℃, the maximum injection pressure is 90MPa, the holding pressure is 60MPa, the holding time is 1~5s, the second injection molding time is 2~5s and the interval period is 30~40s, cooling water is used for cooling for 15s after the second injection molding, and the mold opening time is 1~5s.

6. The method for forming a composite stainless steel formed body according to claim 1, wherein: The first green embryo has a limiting portion, and the second green embryo has a receiving portion, and the limiting portion and the receiving portion are clamped and fixed.

7. The method for forming a composite stainless steel formed body according to claim 1, wherein: The composition of the precipitation hardening stainless steel includes 15.50-17.50 wt.% of chromium, 3.00-5.00 wt.% of nickel, 0.15-0.45 wt.% of niobium, 3.00-5.00 wt.% of copper, ≤1.00 wt.% of manganese, ≤0.07 wt.% of carbon, 70.00-78.00 wt.% of iron, and ≤1.00 wt.% of other non-metallic elements. The composition of the austenitic stainless steel includes 16.00-18.00 wt.% of chromium, 12.00-14.00 wt.% of nickel, 2.00-3.00 wt.% of molybdenum, ≤2.00 wt.% of manganese, ≤0.03 wt.% of carbon, 63.00-68.00 wt.% of iron, and ≤1.00 wt.% of other non-metallic elements.

8. The method for forming a composite stainless steel formed body according to claim 1, wherein: The degreasing includes acid degreasing and thermal degreasing. The temperature of the acid degreasing is 110-135° C. and the time of the acid degreasing is 7.5-12.0 hours. The temperature of the thermal degreasing is 350-600° C. and the time of the thermal degreasing is 2.0-6.0 hours.

9. The method for forming a composite stainless steel formed body according to claim 1, wherein: The sintering includes pre-sintering and partial pressure sintering. The pre-sintering temperature is 1020-1080° C., the pre-sintering time is 140-180 min, the partial pressure sintering time is 140-180 min, the partial pressure sintering pressure is 1-10 Pa, and argon is introduced during the sintering.

10. The composite stainless steel formed body obtained by the forming method of a composite stainless steel formed body according to any one of claims 1 to 9, characterized in that: The surface roughness of the composite stainless steel formed body after polishing is less than 0.03 μm, and the sintered density of the composite stainless steel formed body is 7.90-7.95 g / cm 3 , hardness is 220~275HV, tensile strength is 700~950MPa, yield strength is 500~700MPa, and nickel release is less than or equal to 0.05μg / cm3 per week 2 .

Images