CN116640978A - Preparation method of non-magnetic 17-4ph material for mirror polishing - Google Patents

Abstract

The invention relates to the technical field of metal powder metallurgy forming, in particular to a preparation method of a non-magnetic 17-4ph material for mirror polishing. The preparation method mainly aims at the problems that nitrogen is perfectly stabilized in grains by combining with MIM technology, thereby stabilizing austenite and achieving the preparation technology of nonmagnetic 17-4ph products, and provides the following technical scheme: the preparation method comprises the following preparation steps: step one: selecting raw materials; step two: preparing a feed; step three: injection molding; step four: degreasing with nitric acid; step five: sintering; step six: and (5) solution treatment. The non-magnetic 17-4PH product has the hardness of about 180-240HV, the salt fog performance of more than 48H, the magnetic permeability of less than 1.02, and the thickness range of a compact layer of the product is larger than the normal polishing requirement, thereby being suitable for most polishing requirements and being mainly applied to the preparation process of the non-magnetic 17-4PH material which can meet the mirror polishing requirements.

Description

Preparation method of non-magnetic 17-4ph material for mirror polishing

technical field

The invention relates to the technical field of metal powder metallurgy forming, in particular to a preparation method of a non-magnetic 17-4ph material used for mirror polishing.

Background technique

Metal powder injection molding technology is a near-net-shaping technology developed from plastic injection molding and ceramic powder metallurgy technology. It breaks through the forming limitations of traditional powder metallurgy technology and occupies a huge role in the mass production of three-dimensional complex shape products. Advantage. Such as stable product performance, high dimensional accuracy, high material utilization rate, etc. Non-magnetic stainless steel generally belongs to austenitic stainless steel, such as 316L, 304, etc., but the 17-4ph of normal composition belongs to precipitation hardening martensitic stainless steel, which is a magnetic steel. If it is to be non-magnetic, its crystal structure must be adjusted to Austenite structure; Nitrogen is an element that forms austenite, and its ability to form austenite is 30 times that of nickel. At high temperature, the solid solubility of nitrogen in austenite is relatively large, and high temperature penetrates nitrogen into the grain. Then it is cooled rapidly, nitrogen is solid-dissolved inside the grains, and the austenite is stabilized, so as to achieve the purpose of non-magnetism. By adjusting the sintering process, a dense layer with a certain thickness is formed on the surface of the product, and the formation of the dense layer is a necessary condition for mirror polishing. In view of this, we propose a method for the preparation of non-magnetic 17-4ph materials for mirror polishing.

Contents of the invention

The purpose of the present invention is to solve the problem in the background technology that there is a lack of a perfect combination of MIM technology to stabilize nitrogen in the grain, thereby stabilizing austenite and achieving the preparation technology of non-magnetic 17-4ph products, and proposes a method for mirror polishing Preparation of nonmagnetic 17-4ph materials.

Technical scheme of the present invention: the preparation method of the nonmagnetic 17-4ph material that is used for mirror surface polishing comprises the following preparation steps:

Step 1: raw material selection: select gas-atomized powdery 17-4ph material, the 17-4ph material includes the following percentages of raw materials by mass: 15.5-17.5% of chromium, 3.0-5.0% of nickel, 3.0-5.0% of copper, 0.05% of manganese -1.0%, silicon 0.05-1.0%, carbon 0.02-0.07%, and the rest is iron;

Step 2: Feed preparation: add the raw material powder weighed in step 1 into the internal mixer and mix it with the binder, knead for 2 hours at a temperature of 150-200 ° C, and after forming a uniform paste, squeeze it out and granulate;

Step 3: Injection molding: Add the feed prepared in step 2 to the barrel of the injection molding machine. After the feed is plasticized by the screw of the injection molding machine, the feed is extruded into the mold cavity by extrusion and filled. After 5 to 15 seconds After cooling, the mold is opened, and the green body is ejected through the ejector mechanism to obtain the blank of the required part;

Step 4: Nitric acid degreasing: take the green body of the part formed in step 3 and put it into the nitric acid degreasing furnace, decompose the binder in the green body into small molecular organic matter, and burn it out at the exhaust port of the equipment to obtain Porous skim base;

Step 5: Sintering treatment: Put the degreased base into a graphite vacuum furnace for thermal degreasing, degrease the remaining adhesive in the product, and proceed to the sintering stage after thermal degreasing;

Step 6: Solution treatment: heat the product at 1100-1200° C. for 1-3 hours and then quickly cool it to obtain the final non-magnetic 17-4ph product.

Preferably, the 17-4ph material in the step 1 includes the following mass percent raw materials: 15.5% chromium, 3.0% nickel, 3.0% copper, 0.05% manganese, 0.05% silicon, 0.02% carbon, and 78.38% iron.

Preferably, the 17-4ph material in step 1 includes the following percentages of raw materials by mass: 17.5% chromium, 5.0% nickel, 5.0% copper, 1.0% manganese, 1.0% silicon, 0.07% carbon, and 70.43% iron.

Preferably, the D90 of the aerosolized powdered 17-4ph material is 10-25 μm.

Preferably, the binder in the second step is any one or more mixtures of POM, PP, EVA or SA; the volume ratio of the raw material powder to the binder is 45-60%: 55-40 %.

Preferably, the granulation in the second step obtains cylindrical feed granules with a length of 2-3 mm.

Preferably, the injection temperature of the injection molding machine in the third step is set at 150-220°C.

Preferably, the temperature of the step four nitric acid degreasing furnace is 110-120°C, and 98% fuming nitric acid is introduced;

The degreasing rate of the nitric acid degreasing furnace is >7.6%.

Preferably, the basic process of thermal degreasing in step five is: slowly warming up from room temperature to 350°C, then keeping it warm for 60-120min, then raising the temperature to 600°C, and keeping it warm for 60-120min;

The process of the sintering stage is: according to a certain heating rate, the temperature is raised from 600°C to 900-1200°C and kept for 60 minutes, raised from 900-1200°C to 1260-1350°C, kept for 1-4 hours under nitrogen, and then cooled to 1130°C ℃, nitrogen for 2 hours, and finally cooled to room temperature.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. The present invention adopts the conventional 17-4ph material, and optimizes the composition of the material, and combines the MIM process to prepare a non-magnetic 17-4ph product that can be used for mirror polishing. The preparation procedure is perfect and systematic, so that the 17-4ph The development of 4ph has been applied and has broad market prospects;

2. The dense layer on the surface of the product prepared by the present invention can reach more than 200 μm, and the polishing allowance of MIM parts is generally between 40-110 μm, so the thickness of the dense layer can meet most polishing requirements and meet the product market demand;

3. The non-magnetic 17-4PH product prepared by the present invention has a hardness of about 180-240HV, salt spray performance>48H, magnetic permeability<1.02, and the dense layer thickness range is greater than the normal polishing requirements, which can meet most polishing requirements.

Description of drawings

Fig. 1 is the sintering curve figure of step 5 of the present invention;

Fig. 2 is the surface effect figure after the product preparation of the present invention is polished;

Fig. 3 is a schematic diagram of the cross-section polishing effect of the product prepared in the present invention.

Explanation: The position marked by the white border in Figure 3 is the thickness of the dense layer.

Detailed ways

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

Embodiment one

As shown in Figures 1-3, the preparation method of the non-magnetic 17-4ph material for mirror polishing proposed by the present invention comprises the following preparation steps:

Step 1: Raw material selection: choose gas-atomized powdery 17-4ph material, D90 is 10-25 μm; 17-4ph material includes the following percentages of raw materials by mass: chromium 15.5%, nickel 3.0%, copper 3.0%, manganese 0.05%, Silicon 0.05%, carbon 0.02%, iron 78.38%;

Step 2: Feed preparation: Add the raw material powder weighed in step 1 into the internal mixer and mix it with the binder. The binder is a mixture of POM, PP, EVA and SA. The volume ratio of the raw material powder to the binder is 45-60%: 55-40%; The quality of raw material powder and binding agent among the present invention is respectively: 17-4ph powder material 40kg, binding agent gets 3500gPOM, 250.4gPP, 120gEVA and 80gSA; At the temperature of 195 ℃ After mixing for 2 hours, after forming a uniform paste, lower the gland and knead for 30min, extrude it and granulate it to obtain cylindrical feeding granules with a length of 3mm;

Step 3: Injection molding: Add the feed material prepared in step 2 to the barrel of the injection molding machine, the maximum material temperature is 200°C, after the feed material is plasticized by the screw of the injection molding machine, the feed material is extruded into the cavity of the mold by extrusion and filled. , after 10 seconds of cooling, the mold is opened, and the green body is ejected through the ejector mechanism to obtain the blank of the required part;

Step 4: Nitric acid degreasing: Take the green part formed in step 3 and put it into the nitric acid degreasing furnace at a temperature of 110 ° C, and feed 98% fuming nitric acid for 8 hours of degreasing; the binder in the green body is decomposed into Small molecular organic matter, and burn them out at the exhaust port of the equipment to obtain a porous degreasing body; the degreasing rate of the nitric acid degreasing furnace is >7.6%

Step 5: Sintering treatment: put the degreased base into a graphite vacuum furnace. The present invention selects a graphite vacuum furnace produced by Ningbo Hengpu Vacuum Technology Co., Ltd. for thermal degreasing. The basic process of thermal degreasing is: slowly warming up from room temperature to 350°C, then keep warm for 120min, then raise the temperature to 600°C, keep warm for 120min; degrease the remaining adhesive in the product, and proceed to the sintering stage after thermal degreasing. The process of the sintering stage is: adopt the vacuum internal firing mode, press A certain heating rate raises the temperature from 600°C to 950°C and keeps it warm for 60 min, then rises from 950°C to 1280°C under nitrogen atmosphere, keeps it under nitrogen for 3 hours, then cools down to 1050°C, keeps it under nitrogen for 2 hours, and finally cools down to room temperature;

Step 6: Solid solution treatment: When the product is sintered, nitrogen will form Cr3N2 with Cr, resulting in poor Cr in the grain boundary, resulting in poor corrosion resistance of the product, insufficient nitrogen content in the grain, and affecting the austenitization effect. Only when N solid dissolves into the grains can the full austenitization effect be achieved. The product is kept at 1180°C for 1 hour and then cooled quickly. During this process, Cr3N2 decomposes and N penetrates into the grains to achieve full austenitization. The effect is to obtain the final non-magnetic 17-4ph product, which improves the corrosion resistance of the product.

Embodiment two

As shown in Figures 1-3, the preparation method of the non-magnetic 17-4ph material for mirror polishing proposed by the present invention, compared with the first embodiment, this embodiment also includes the following preparation steps:

Step 1: Raw material selection: choose gas-atomized powdery 17-4ph material, D90 is 10-25μm; 17-4ph material includes the following percentage mass raw materials: chromium 17.5%, nickel 5.0%, copper 5.0%, manganese 1.0%, Silicon 1.0%, carbon 0.07%, iron 70.43%;

Step 2: Feed preparation: Add the raw material powder weighed in step 1 into the internal mixer and mix it with the binder. The binder is a mixture of POM, PP, EVA and SA. The volume ratio of the raw material powder to the binder is 45-60%: 55-40%; The quality of raw material powder and binding agent among the present invention is respectively: 17-4ph powder material 40kg, binding agent gets 3500gPOM, 250.4gPP, 120gEVA and 80gSA; At the temperature of 195 ℃ After mixing for 2 hours, after forming a uniform paste, lower the gland and knead for 30min, extrude it and granulate it to obtain cylindrical feeding granules with a length of 3mm;

Step 3: Injection molding: Add the feed material prepared in step 2 to the barrel of the injection molding machine, the maximum material temperature is 200°C, after the feed material is plasticized by the screw of the injection molding machine, the feed material is extruded into the cavity of the mold by extrusion and filled. , after 10 seconds of cooling, the mold is opened, and the green body is ejected through the ejector mechanism to obtain the blank of the required part;

Step 4: Nitric acid degreasing: Take the green part formed in step 3 and put it into the nitric acid degreasing furnace at a temperature of 110 ° C, and feed 98% fuming nitric acid for 8 hours of degreasing; the binder in the green body is decomposed into Small molecular organic matter, and burn them out at the exhaust port of the equipment to obtain a porous degreasing body; the degreasing rate of the nitric acid degreasing furnace is >7.6%

Step 5: Sintering treatment: put the degreased base into a graphite vacuum furnace. The present invention selects a graphite vacuum furnace produced by Ningbo Hengpu Vacuum Technology Co., Ltd. for thermal degreasing. The basic process of thermal degreasing is: slowly warming up from room temperature to 350°C, then keep warm for 120min, then raise the temperature to 600°C, keep warm for 120min; degrease the remaining adhesive in the product, and proceed to the sintering stage after thermal degreasing. The process of the sintering stage is: adopt the vacuum internal firing mode, press A certain heating rate raises the temperature from 600°C to 950°C and keeps it warm for 60 min, then rises from 950°C to 1280°C under nitrogen atmosphere, keeps it under nitrogen for 3 hours, then cools down to 1050°C, keeps it under nitrogen for 2 hours, and finally cools down to room temperature;

Step 6: Solid solution treatment: When the product is sintered, nitrogen will form Cr3N2 with Cr, resulting in poor Cr in the grain boundary, resulting in poor corrosion resistance of the product, insufficient nitrogen content in the grain, and affecting the austenitization effect. Only when N solid dissolves into the grains can the full austenitization effect be achieved. The product is kept at 1180°C for 1 hour and then cooled quickly. During this process, Cr3N2 decomposes and N penetrates into the grains to achieve full austenitization. The effect is to obtain the final non-magnetic 17-4ph product, which improves the corrosion resistance of the product.

In the present invention, the non-magnetic 17-4ph material performance test prepared by embodiment one and embodiment two obtains the following data:

Embodiment one Embodiment two Hardness (HV) 225 240 Salt spray performance (H) 52.5 56 Permeability 0.83 1.01 Dense layer thickness (μm) 268 275

The polishing margin of MIM parts is generally between 40-110 μm, so the dense layer on the product surface of the non-magnetic 17-4ph material prepared in Example 1 and Example 2 of this scheme meets most of the polishing requirements and has ample margin.

The above-mentioned specific embodiments are only several preferred embodiments of the present invention. Based on the technical solution of the present invention and the relevant revelations of the above-mentioned embodiments, those skilled in the art can make various alternative improvements and combinations to the above-mentioned specific embodiments. .

Claims (9)

1. A method for producing a nonmagnetic 17-4ph material for mirror polishing, characterized by comprising the following production steps:

step one: raw material selection: selecting an aerosolized powdery 17-4ph material, wherein the 17-4ph material comprises the following raw materials in percentage by mass: 15.5 to 17.5 percent of chromium, 3.0 to 5.0 percent of nickel, 3.0 to 5.0 percent of copper, 0.05 to 1.0 percent of manganese, 0.05 to 1.0 percent of silicon, 0.02 to 0.07 percent of carbon and the balance of iron;

step two: and (2) feeding preparation: adding the raw material powder weighed in the first step into an internal mixer, mixing with a binder, mixing for 2 hours at the temperature of 150-200 ℃ to form a uniform paste, extruding the paste, and granulating;

step three: injection molding: adding the feed prepared in the second step into a charging barrel of an injection molding machine, plasticizing the feed by a screw of the injection molding machine, extruding the feed into a mold cavity by extrusion, cooling for 5-15 seconds, opening the mold, and ejecting a green body by an ejection mechanism to obtain a primary blank of a required part;

step four: degreasing with nitric acid: placing the part green body formed in the third step into a nitric acid degreasing furnace, decomposing a binder in the green body into small molecular organic matters, and discharging the small molecular organic matters after burning the small molecular organic matters at a smoke outlet of equipment so as to obtain a porous degreasing blank;

step five: sintering: placing the degreased blank into a graphite vacuum furnace for thermal degreasing, degreasing the residual adhesive in the product cleanly, and performing a sintering stage after thermal degreasing;

step six: solution treatment: the product is quickly cooled after heat preservation for 1-3 hours at 1100-1200 ℃ to obtain the final nonmagnetic 17-4ph product.

2. The method for preparing a non-magnetic 17-4ph material for mirror polishing according to claim 1, wherein the 17-4ph material in the first step comprises the following raw materials by mass: 15.5% of chromium, 3.0% of nickel, 3.0% of copper, 0.05% of manganese, 0.05% of silicon, 0.02% of carbon and 78.38% of iron.

3. The method for preparing a non-magnetic 17-4ph material for mirror polishing according to claim 1, wherein the 17-4ph material in the first step comprises the following raw materials by mass: 17.5% of chromium, 5.0% of nickel, 5.0% of copper, 1.0% of manganese, 1.0% of silicon, 0.07% of carbon and 70.43% of iron.

4. The method for producing a nonmagnetic 17-4ph material for mirror polishing according to claim 1, wherein the D90 of the aerosolized powdery 17-4ph material is 10-25 μm.

5. The method for producing a nonmagnetic 17-4ph material for mirror polishing according to claim 1, wherein the binder in the second step is any one or a mixture of a plurality of POM, PP, EVA or SA; the volume ratio of the raw material powder to the binder is 45-60%:55-40%.

6. The method for producing a non-magnetic 17-4ph material for mirror polishing according to claim 1, wherein the granulating in the second step yields cylindrical feed particles having a length of 2 to 3 mm.

7. The method for producing a non-magnetic 17-4ph material for mirror polishing according to claim 1, wherein the injection temperature of the injection molding machine in the step three is set to 150 to 220 ℃.

8. The method for preparing a non-magnetic 17-4ph material for mirror polishing according to claim 1, wherein the temperature of the step four nitric acid degreasing furnace is 110-120 ℃, and 98% fuming nitric acid is introduced;

the degreasing rate of the nitric acid degreasing furnace is more than 7.6%.

9. The method for preparing a nonmagnetic 17-4ph material for mirror polishing according to claim 1, wherein the step five thermal degreasing basic process is as follows: slowly heating from room temperature to 350 ℃, then preserving heat for 60-120min, heating to 600 ℃, and preserving heat for 60-120min;

the sintering stage comprises the following processes: raising the temperature from 600 ℃ to 900-1200 ℃ at a certain temperature raising rate, preserving heat for 60min, raising the temperature from 900-1200 ℃ to 1260-1350 ℃, preserving heat for 1-4 hours under nitrogen, then cooling to 1130 ℃, preserving heat for 2 hours under nitrogen, and finally cooling to room temperature.