Method for injection molding of 316L workpiece with high wear resistance and corrosion resistance

Abstract

The invention relates to a method for injection molding of a 316L workpiece with high wear resistance and corrosion resistance. The method comprises the following steps that S1, raw materials are prepared; s2, feed preparation: uniformly mixing 316L alloy powder, silicon nitride powder, copper powder and a binder to prepare the feed for powder injection molding; wherein the 316L alloy powder is gas atomization powder of which D50 is equal to 10 microns; the particle size range of the copper powder and the silicon nitride powder is 1-20 nm. S3, injection molding is conducted, specifically, the feed is subjected to injection molding through an injection machine to form a green body of the titanium alloy composite material; s4, degreasing: degreasing the green body to form a degreased blank; s5, sintering: sintering the degreased blank to form a sintered part; and S6, the sintered part is subjected to heat treatment. The wear-resistant and corrosion-resistant performance of the 316L workpiece can be synergistically improved, the stability of the passivation film under the dynamic working condition is enhanced, meanwhile, a gradient protection layer can be constructed, and the method adapts to the multi-factor coupling corrosion environment.

Description

Technical Field

[0001] The present invention relates to the field of powder injection molding, and particularly relates to a method for injection molding 316L parts with high wear resistance and corrosion resistance. Background Art

[0002] The birth of 316 stainless steel was to solve the problem of seawater corrosion of bolts on ocean liners. The corrosion resistance of 316 stainless steel in a 5% salt solution environment is 3.2 times that of 304 stainless steel, making it a medical-grade material.

[0003] Due to its molybdenum (Mo) content, 316 stainless steel exhibits better pitting corrosion resistance than 304 stainless steel in general marine environments, but its application in complex seawater working conditions still has significant limitations:

[0004] Limitation 1: The passivation film is prone to failure: Cl- in seawater will preferentially adsorb on the surface of the passivation film and form soluble chlorides with metal cations (such as Fe2+, Cr 3 +), resulting in the rupture of the local passivation film and the initiation of pitting or crack corrosion. Especially in high-temperature (>30°C) or low-oxygen deep-water environments, the stability of the passivation film is further reduced, and the corrosion rate increases significantly.

[0005] Limitation 2: Dynamic wear accelerates corrosion: Marine equipment (such as pumps, valves, propellers) faces fluid erosion and particle wear during operation. Surface wear will damage the integrity of the passivation film, forming active sites for electrochemical corrosion, resulting in the synergistic failure of corrosion and wear. Summary of the Invention

[0006] The object of the present invention is a method for injection molding 316L parts with high wear resistance and corrosion resistance. This method can achieve the synergistic improvement of the wear and corrosion resistance of 316L parts, enhance the stability of the passivation film under dynamic working conditions, and at the same time can construct a gradient protective layer to adapt to the multi-factor coupled corrosion environment.

[0007] The technical solution to achieve the object of the present invention is: The present invention includes the following steps:

[0008] S1. Raw material selection: Select 316L powder. The 316L powder includes the following component raw materials according to weight percentage: chromium 16-20%, nickel 10-15%, molybdenum 0.20-2.00%, manganese 0.35-0.50%, silicon 0.30-0.60%, carbon 0.03-0.05%, sulfur 0.01-0.12%, phosphorus 0.03-0.35%, oxygen 0.02-0.36%, and the remaining balance is iron;

[0009] S2, feed material preparation: 316L powder, silicon nitride powder, copper powder and binder are uniformly mixed to prepare feed material for powder injection molding; wherein the 316L powder is an aerosolized powder with D50=10μm; the particle size range of the silicon nitride powder and the copper powder is 1-20nm; wherein the weight of the 316L powder accounts for 90-93% of the weight of the feed material, the weight of the binder accounts for 6-8% of the weight of the feed material, the weight of the silicon nitride powder accounts for 1-3% of the weight of the feed material, and the weight of the copper powder accounts for 0.1-1.5% of the weight of the feed material;

[0010] S3, injection molding: the feed is injected into a green body by an injection molding machine;

[0011] S4, degreasing: degreasing the green body to form a degreased body;

[0012] S5. Sintering: After the debinded blank is sintered, a sintered part is formed;

[0013] S6. The sintered parts are heat treated.

[0014] The finer the silicon nitride powder particle size, the stronger the strengthening effect. Nitrogen is integrated into the austenite lattice as an interstitial atom, causing lattice distortion and hindering dislocation movement, thereby improving the strength and hardness of the material. At the same time, nitrogen promotes the stabilization of austenite, inhibits the precipitation of harmful phases (such as σ phase), and refines the grains. Nitrogen can also promote the compactness of the passivation film and improve its resistance to pitting and crevice corrosion in chloride ion environments.

[0015] The reason why copper powder is selected with small particle size is similar to that of silicon nitride. The addition of copper can improve the corrosion resistance of stainless steel in non-oxidizing acids such as sulfuric acid and phosphoric acid. Copper will generate ε-Cu phase in stainless steel, producing precipitation strengthening effect.

[0016] The silicon nitride and copper powders need to be taken in a glove box filled with Ar gas as a protective atmosphere. After weighing and mixing, the mixed powder is kneaded with a binder.

[0017] The amount of silicon nitride and copper powder added also needs to be controlled. Copper and silicon nitride will jointly promote grain boundary embrittlement. The thermal brittleness of copper and the brittleness of silicon nitride are superimposed, resulting in poor thermoplasticity. Silicon nitride is a ceramic particle with weak interfacial bonding with the metal matrix, which can easily become a crack source and reduce material performance. When excessive copper powder is added, a liquid copper film will be formed, resulting in hot working cracking.

[0018] When preparing the feed, the 316L powder and the copper powder must be mixed first, stirred at a low speed, and then the silicon nitride powder is added and stirred at a high speed.

[0019] Furthermore, in the above step S4, the degreasing is to first perform acid degreasing on the green body to form an acid-degreasing body; and then perform thermal degreasing on the acid-degreasing body to form a degreasing body;

[0020] The acid degreasing includes five stages. The first stage is pre-rinsing at a temperature of 110°C for 60 minutes of heat preservation. The second to fourth stages are degreasing stage 1, degreasing stage 2, and degreasing stage 3. The temperatures in degreasing stage 1 to degreasing stage 3 are controlled at 125°C, and the heat preservation times are 120 minutes, 120 minutes, and 60 minutes respectively. The nitric acid feeding amount is 1 - 2.5 g / min. The fifth stage is post-rinsing at a temperature of 130°C for 60 minutes of heat preservation. The green compact forms an acid-degreased blank after acid degreasing.

[0021] The thermal degreasing is heated to 550°C at a rate of 1.5°C / min and held for one hour to obtain a degreased blank.

[0022] Furthermore, the volume ratio of the binder in the above-mentioned feedstock is 5% - 10%, and the mass percentage contents of the components of the binder are controlled as follows: polyoxymethylene 80 - 90%, polypropylene 5 - 10%, ethylene-vinyl acetate copolymer 1 - 5%, and stearic acid 1 - 3%.

[0023] Furthermore, the above-mentioned binder includes polyoxymethylene 80 - 90%, polypropylene 5 - 10%, ethylene-vinyl acetate copolymer 1 - 5%, and stearic acid 1 - 3%.

[0024] Furthermore, the technical parameters of injection molding in the above-mentioned step S3 are as follows: the mold temperature is 80 - 120°C, the feedstock heating temperature is 160 - 180°C, the injection pressure is 80 - 120 MPa; the holding pressure time is 1 - 2.5 s.

[0025] Furthermore, in the above-mentioned step S5, first, the degreased blank is pre-sintered at 700 - 900°C for 1 - 2 hours; then sintering is carried out, and the sintering temperature T satisfies the following conditions: 0.6TL ≤ T ≤ 0.95TL; where TL is the theoretical melting point temperature of the metal or alloy.

[0026] Furthermore, in the above-mentioned step S6, the sintered product is placed in a metal furnace and heated to 1100 - 1200°C at a heating rate of 5°C / min and held for 1 - 3 hours.

[0027] The present invention proposes an innovative solution for the following core contradictions:

[0028] Contradiction 1: Synergistic optimization of the surface wear resistance and corrosion resistance of the material: The hardness of the existing 316 stainless steel (~200 HV) is difficult to resist the abrasion of sediment in seawater medium, and simply increasing the hardness (such as carbide strengthening) may sacrifice the corrosion resistance (risk of intergranular corrosion).

[0029] Solution: Silicon nitride (Si3N4) is introduced as a dispersion strengthening phase. Its high hardness (~1500HV) and chemical inertness can improve wear resistance while avoiding galvanic corrosion with the matrix. The addition of copper (Cu) inhibits Cl- penetration through the self-repair mechanism of the passivation film (the oxidation products of Cu+ / Cu2+ fill the film defects), thereby achieving a synergistic improvement in wear resistance and corrosion resistance.

[0030] Contradiction 2: Long-term stability in dynamic seawater environments: Fluctuations in seawater velocity (accumulation of biofilm in stagnant areas or scouring by high-speed flows) and temperature changes cause significant fluctuations in the performance of traditional materials.

[0031] Solution: Optimize the microstructure through Si3N4 / Cu composite doping: Si3N4 particles refine the grains, reduce the precipitation of carbides at grain boundaries, and inhibit intergranular corrosion; Cu elements are selectively oxidized on the worn exposed surface to form a dense CuO / Cr2O3 composite oxide film, which enhances the stability of the passivation film under dynamic conditions.

[0032] Contradiction 3: Adaptability to complex working conditions: Extreme conditions such as deep-sea low oxygen, high temperature or high Cl- concentration place higher demands on the comprehensive performance of materials.

[0033] Solution: Through the "sacrificial anode" effect of Cu (local micro-area potential regulation) and the wear-resistant barrier effect of Si3N4, a gradient protective layer is constructed to adapt to the multi-factor coupled corrosion environment.

[0034] The present invention has positive effects: the present invention improves the problem of poor wear and corrosion performance of 316 parts by adding a certain amount of silicon nitride and copper powder to 316L alloy powder. Specifically, nitrogen is integrated into the austenite lattice as an interstitial atom, resulting in lattice distortion and hindering dislocation movement, thereby improving the strength and hardness of the material. At the same time, nitrogen promotes the stabilization of austenite, inhibits the precipitation of harmful phases (such as σ phase), and refines the grains. Nitrogen can also promote the compactness of the passivation film and improve its resistance to pitting and crevice corrosion in a chloride ion environment. The reason for selecting a small particle size of copper powder is similar to that of silicon nitride. The addition of copper can improve the corrosion resistance of stainless steel in non-oxidizing acids such as sulfuric acid and phosphoric acid. Copper will generate ε-Cu phase in stainless steel, producing a precipitation strengthening effect. The use of silicon nitride and copper powder needs to be completed in a glove box, and the box is filled with Ar gas as a protective atmosphere. After weighing and mixing, the mixed powder is kneaded with a binder. DETAILED DESCRIPTION

[0035] (Example 1)

[0036] This embodiment includes the following steps:

[0037] S1. Raw material selection: Select 316L powder, and the 316L powder includes the following component raw materials by weight percentage: chromium 16 - 20%, nickel 10 - 15%, molybdenum 0.20 - 2.00%, manganese 0.35 - 0.50%, silicon 0.30 - 0.60%, carbon 0.03 - 0.05%, sulfur 0.01 - 0.12%, phosphorus 0.03 - 0.35%, oxygen 0.02 - 0.36%, and the rest is iron;

[0038] S2. Feed preparation: Uniformly mix 316L powder, silicon nitride powder, copper powder and binder to make a feed for powder injection molding; among them, the 316L powder is an air-atomized powder with D50 = 10μm; the particle size ranges of the silicon nitride powder and the copper powder are both 1 - 20nm; among them, the weight of the 316L powder accounts for 90 - 93% of the weight of the feed, the weight of the binder accounts for 6 - 8% of the weight of the feed, the weight of the silicon nitride powder accounts for 1% of the weight of the feed, and the weight of the copper powder accounts for 0.5% of the weight of the feed;

[0039] S3. Injection molding: Inject the feed through an injection machine to form a green body;

[0040] S4. Debinding: Debind the green body to form a debound blank;

[0041] S5. Sintering: Sinter the debound blank to form a sintered part;

[0042] S6. Heat treatment is carried out on the sintered part.

[0043] During feed preparation, first mix the 316L powder and the copper powder, stir at a low speed, and then add the silicon nitride powder and stir at a high speed.

[0044] In the step S4, the debinding is to first perform acid debinding on the green body to form an acid-debound blank; then perform thermal debinding on the acid-debound blank to form a debound blank;

[0045] The acid debinding includes five stages. The first stage is pre-rinsing, with a temperature of 110°C and a heat preservation time of 60 min; the second stage to the fourth stage are the first debinding stage, the second debinding stage, and the third debinding stage. The temperatures of the first debinding stage to the third debinding stage are controlled at 125°C, and the heat preservation times are 120 min, 120 min, and 60 min respectively, and the nitric acid feeding amount is 1 - 2.5 g / min; the fifth stage is post-rinsing, with a temperature of 130°C and a heat preservation time of 60 min; after the green body undergoes acid debinding, an acid-debound blank is formed;

[0046] The thermal debinding is to heat up to 550°C at a rate of 1.5°C / min and keep it warm for one hour to obtain a debound blank.

[0047] The volume ratio of the binder in the feed is 5% - 10%, and the mass percentage contents of the components of the binder are controlled as follows: polyoxymethylene 80 - 90%, polypropylene 5 - 10%, ethylene-vinyl acetate copolymer 1 - 5%, and stearic acid 1 - 3%.

[0048] The binder includes polyoxymethylene 80 - 90%, polypropylene 5 - 10%, ethylene-vinyl acetate copolymer 1 - 5%, and stearic acid 1 - 3%.

[0049] The technical parameters of injection molding in step S3 are as follows: the mold temperature is 80 - 120°C, the feed heating temperature is 160 - 180°C, the injection pressure is 80 - 120 MPa; the holding time is 1 - 2.5 s.

[0050] In step S5, first, the debound billet is pre-sintered at 700 - 900°C for 1 - 2 h; then sintering is carried out, and the sintering temperature T satisfies the following conditions: 0.6TL ≤ T ≤ 0.95TL; where TL is the theoretical melting point temperature of the metal or alloy.

[0051] In step S6, the sintered product is placed in a metal furnace and heated to 1100 - 1200°C at a heating rate of 5°C / min and held for 1 - 3 h.

[0052] The present invention proposes an innovative solution for the following core contradictions:

[0053] Contradiction 1: Synergistic optimization of surface wear resistance and corrosion resistance of materials: The hardness of existing 316 stainless steel (∼200 HV) is difficult to resist sand erosion in seawater media, and simply increasing the hardness (such as carbide strengthening) may sacrifice corrosion resistance (risk of intergranular corrosion).

[0054] Solution idea: Introduce silicon nitride (Si3N4) as a dispersion strengthening phase. Its high hardness (∼1500 HV) and chemical inertness can improve wear resistance, and at the same time, avoid galvanic corrosion with the matrix; the addition of copper (Cu) inhibits the penetration of Cl- through the passivation film self-repair mechanism (the oxidation products of Cu+ / Cu2+ fill the film defects), realizing the synergistic improvement of wear resistance and corrosion resistance.

[0055] Contradiction 2: Long-term stability in a dynamic seawater environment: The performance of traditional materials fluctuates significantly due to seawater flow velocity fluctuations (biofilm accumulation in stagnant areas or erosion by high-speed flow) and temperature changes.

[0056] Solution idea: Optimize the microstructure through the composite doping of Si3N4 / Cu: Si3N4 particles refine the grain, reduce the precipitation of grain boundary carbides, and inhibit intergranular corrosion; Cu elements are selectively oxidized on the worn surface to form a dense CuO / Cr2O3 composite oxide film, enhancing the stability of the passivation film under dynamic working conditions.

[0057] Contradiction 3: Adaptability to complex working conditions: Extreme conditions such as deep - sea hypoxia, high temperature, or high Cl - concentration pose higher requirements for the comprehensive performance of materials.

[0058] Solution idea: By the "sacrificial anode" effect of Cu (local micro - area potential regulation) and the wear - resistant barrier effect of Si3N4, a gradient protective layer is constructed to adapt to the multi - factor coupled corrosion environment.

[0059] In this embodiment, the weight of silicon nitride powder accounts for 2% of the weight of the feed, and the weight of copper powder accounts for 1% of the weight of the feed.

[0060] Others are the same as in Example 1.

[0061] (Example 3)

[0062] In this embodiment, the weight of silicon nitride powder accounts for 3% of the weight of the feed, and the weight of copper powder accounts for 1.5% of the weight of the feed.

[0063] Others are the same as in Example 1.

[0064] (Example 4)

[0065] In this embodiment, the weight of silicon nitride powder accounts for 4% of the weight of the feed, and the weight of copper powder accounts for 2% of the weight of the feed.

[0066] Others are the same as in Example 1.

[0067] (Example 5)

[0068] In this embodiment, the weight of silicon nitride powder accounts for 5% of the weight of the feed, and the weight of copper powder accounts for 2.5% of the weight of the feed.

[0069] Others are the same as in Example 1.

[0070] The test comparison table of Examples 1 to 5 is as follows:

[0071]

[0072] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above - mentioned are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for injection molding 316L parts with high wear and corrosion resistance, characterized in that It includes the following steps: S1. Raw material selection: Select 316L powder, and the 316L powder includes the following component raw materials by weight percentage: chromium 16 - 20%, nickel 10 - 15%, molybdenum 0.20 - 2.00%, manganese 0.35 - 0.50%, silicon 0.30 - 0.60%, carbon 0.03 - 0.05%, sulfur 0.01 - 0.12%, phosphorus 0.03 - 0.35%, oxygen 0.02 - 0.36%, and the balance is iron; S2. Feed preparation: Uniformly mix 316L powder, silicon nitride powder, copper powder and binder to make a feed for powder injection molding; among them, the 316L powder is an air - atomized powder with D50 = 10μm; the particle size ranges of the silicon nitride powder and the copper powder are both 1 - 20nm; among them, the weight of the 316L powder accounts for 90 - 93% of the weight of the feed, the weight of the binder accounts for 6 - 8% of the weight of the feed, the weight of the silicon nitride powder accounts for 1 - 3% of the weight of the feed, and the weight of the copper powder accounts for 0.1 - 1.5% of the weight of the feed; S3. Injection molding: Inject the feed through an injection machine to form a green body; S4. Debinding: Debind the green body to form a debound blank; S5. Sintering: Sinter the debound blank to form a sintered part; S6. Heat - treat the sintered part.

2. The method for manufacturing a 316L part with high wear and corrosion resistance by injection molding according to claim 1, characterized in that: In the step S4, the debinding is to first perform acid debinding on the green body to form an acid - debound blank; then perform thermal debinding on the acid - debound blank to form a debound blank; The acid debinding includes five stages. The first stage is pre - rinsing, with a temperature of 110°C and a holding time of 60 min; The second stage to the fourth stage are the first debinding stage, the second debinding stage, and the third debinding stage. The temperatures of the first debinding stage to the third debinding stage are controlled at 125°C, and the holding times are 120 min, 120 min, and 60 min respectively, and the nitric acid feeding rate is 1 - 2.5 g / min; The fifth stage is post - rinsing, with a temperature of 130°C and a holding time of 60 min; after the green body undergoes acid debinding, an acid - debound blank is formed; The thermal debinding is to heat up to 550°C at a rate of 1.5°C / min and hold for one hour to obtain a debound blank.

3. A method for manufacturing a 316L part with high wear and corrosion resistance by injection molding according to claim 1, characterized in that: The volume ratio of the binder in the feed is 5% - 10%, and the mass percentage contents of the components of the binder are controlled as follows: polyoxymethylene 80 - 90%, polypropylene 5 - 10%, ethylene - vinyl acetate copolymer 1 - 5%, stearic acid 1 - 3%.

4. A method for manufacturing a 316L part with high wear and corrosion resistance by injection molding, as claimed in claim 3, wherein: The binder includes polyoxymethylene 80 - 90%, polypropylene 5 - 10%, ethylene - vinyl acetate copolymer 1 - 5%, stearic acid 1 - 3%.

5. A method for manufacturing a 316L part with high wear and corrosion resistance by injection molding, characterized in that: The technical parameters of the injection molding in the step S3 are: the mold temperature is 80 - 120°C, the feed heating temperature is 160 - 180°C, the injection pressure is 80 - 120 MPa; the holding pressure time is 1 - 2.5 s.

6. A method for manufacturing a 316L part with high wear and corrosion resistance by injection molding according to claim 1, characterized in that: In the step S5, first perform pre - sintering on the debound blank at 700 - 900°C for 1 - 2 h; then perform sintering, and the sintering temperature T satisfies the following condition: 0.6TL ≤ T ≤ 0.95TL; where TL is the theoretical melting point temperature of the metal or alloy.

7. The method for manufacturing a 316L part with high wear and corrosion resistance by injection molding according to claim 1, characterized in that: In the step S6, put the sintered product into a metal furnace, heat it to 1100 - 1200°C at a heating rate of 5°C / min, and hold for 1 - 3 h.

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