阅读说明：本技术 一种用于17-4产品无磁烧结工艺 (Non-magnetic sintering process for 17-4 products ) 是由 乔永苹 方涛 欧朝辉 于 2021-09-13 设计创作，主要内容包括：本发明公开了一种用于17-4产品无磁烧结工艺,涉及不锈钢烧结技术领域；包括以下步骤：S1,制备黏结剂；S2,混炼；S3,注射成型,制备试样生胚；S4,烧结还原及除碳；S8,在1200℃时再通入氮气,分压压力75KPA,保温210分钟,使烧结炉各层温度更加均匀及对产品进行渗氮；S9：在最高温分压降温至1150℃后再保温2小时,分压压力80KPa,继续对产品进行渗氮,让其奥氏体化完全；本发明通过具体的烧结过程设置,确定通入氮气的时间、流量和时机,确保氮元素形成并稳定奥氏体,同时实现对渗氮深度的控制,获得满足磁性要求的产品,产品烧结完成后通过固溶热处理,能有效的去除产品表面的氮化铬,继而快速获得17-4PH奥氏体化的不锈钢产品。(The invention discloses a non-magnetic sintering process for 17-4 products, relating to the technical field of stainless steel sintering; the method comprises the following steps: s1, preparing an adhesive; s2, mixing; s3, injection molding, and preparing a sample green body; s4, sintering, reducing and decarbonizing; s8, introducing nitrogen at 1200 ℃, keeping the temperature for 210 minutes under the partial pressure of 75KPA, so that the temperature of each layer of the sintering furnace is more uniform and nitriding is carried out on the product; s9: after the highest temperature partial pressure is reduced to 1150 ℃, the temperature is preserved for 2 hours, the partial pressure is 80KPa, and nitriding is continuously carried out on the product to ensure complete austenitizing; according to the invention, through the specific setting of the sintering process, the time, the flow and the time for introducing nitrogen are determined, the formation of nitrogen elements and the stability of austenite are ensured, the control of nitriding depth is realized, a product meeting the magnetic requirement is obtained, the chromium nitride on the surface of the product can be effectively removed through solution heat treatment after the product is sintered, and then the 17-4PH austenitized stainless steel product is quickly obtained.)

1. A non-magnetic sintering process for 17-4 products is characterized by comprising the following steps:

s1, preparing an adhesive;

s2, mixing and refining the adhesive and the pre-alloyed powder;

s3, performing injection molding on the mixed injection material through an injection machine to prepare a sample green body;

s4, heating the sample green blank by a sintering furnace at 30-800 ℃ for degreasing, and removing the adhesive in the sample green blank;

s5, sintering at 800-1050 ℃ in vacuum, preserving heat at 1050 ℃ for 2 hours, and reducing and decarbonizing the green blank metal oxide;

s6, sintering by using argon when 1050 ℃ is reached, and sintering and shrinking the green blank;

s7, using nitrogen at 1200 ℃, keeping the temperature for 30 minutes under the partial pressure of 20KPA, and enabling the carbon content in the front of the furnace and in the furnace to be uniformly distributed;

s8, introducing nitrogen at 1200 ℃, keeping the temperature for 210 minutes under the partial pressure of 75KPA, so that the temperature of each layer of the sintering furnace is more uniform and nitriding is carried out on the product;

s9: and (3) cooling to 1150 ℃ at the highest temperature and partial pressure, then preserving the heat for 2 hours, keeping the partial pressure at 80KPa, and nitriding the product continuously to ensure that the product is completely austenitized.

2. The non-magnetic sintering process for 17-4 products in claim 1, wherein the binder in the step S1 is High Density Polyethylene (HDPE) -Paraffin Wax (PW) -based binder.

3. The nonmagnetic sintering process of claim 1, wherein the prealloyed powder in the step S2 is ultra-high pressure water atomized 17-4PH prealloyed powder with an average particle size of 7 μm, and the temperature during mixing is 135 ℃ and the mixing time is 2.2 hours, so as to obtain the injection material.

4. The nonmagnetic sintering process of claim 1, wherein the degreasing temperature of the sample green body in the step S4 is 600 ℃, and the temperature is kept for 4 hours.

5. The non-magnetic sintering process for 17-4 products, according to claim 1, wherein the flow rates of nitrogen gas introduced in the step S7 and the step S8 are 50L/min and 55L/min respectively.

6. The nonmagnetic sintering process of claim 1, wherein the sintering of the product in the step S9 is completed and then solution heat treatment is performed to remove chromium nitride on the surface of the product, so as to obtain a 17-4PH austenitized stainless steel product.

Technical Field

The invention relates to the technical field of stainless steel sintering, in particular to a non-magnetic sintering process for 17-4 products.

Background

Metal Injection Molding (MIM) is a fast-developing metal part forming technique in the field of powder metallurgy today. The excellent properties and near net shape forming ability of MIM materials are quite attractive. In recent years, MIM development has relied on powder feedstock, stable and reliable binder systems and optimized debinding techniques, as well as the development of material systems and their articles.

The 17-4PH alloy is precipitated, quenched, hardened and martensitic stainless steel composed of copper, niobium/columbium, can meet the requirements of high hardness and strong corrosion resistance after treatment and processing, is mainly used for offshore platforms, helicopter decks, airplane turbine blades, nuclear waste tanks and other mechanical parts at present, but still has considerable technical difficulty in the preparation of large-size 17-4PH alloy parts based on the current MIM process, so that the process for quickly sintering the 17-4PH austenitized stainless steel product has higher practical significance.

Disclosure of Invention

The invention aims to solve the defect that the sintering process of the existing 17-4PH austenitized stainless steel product is complex, and provides a nonmagnetic sintering process for the 17-4 product and an operation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme: a non-magnetic sintering process for 17-4 products specifically comprises the following steps:

s1, preparing an adhesive;

s2, mixing and refining the adhesive and the pre-alloyed powder;

s3, performing injection molding on the mixed injection material through an injection machine to prepare a sample green body;

s4, heating the sample green blank by a sintering furnace at 30-800 ℃ for degreasing, and removing the adhesive in the sample green blank;

s5, sintering at 800-1050 ℃ in vacuum, preserving heat at 1050 ℃ for 2 hours, and reducing and decarbonizing the green blank metal oxide;

s6, sintering by using argon when 1050 ℃ is reached, and sintering and shrinking the green blank;

s7, using nitrogen at 1200 ℃, keeping the temperature for 30 minutes under the partial pressure of 20KPA, and enabling the carbon content in the front of the furnace and in the furnace to be uniformly distributed;

s8, introducing nitrogen at 1200 ℃, keeping the temperature for 210 minutes under the partial pressure of 75KPA, so that the temperature of each layer of the sintering furnace is more uniform and nitriding is carried out on the product;

s9: and (3) cooling to 1150 ℃ at the highest temperature and partial pressure, then preserving the heat for 2 hours, keeping the partial pressure at 80KPa, and nitriding the product continuously to ensure that the product is completely austenitized.

In a preferred embodiment of the present invention, the binder in the step S1 is a High Density Polyethylene (HDPE) -Paraffin Wax (PW) -based binder.

In a preferred embodiment of the present invention, the pre-alloyed powder in the step S2 is a pre-alloyed powder of 17-4PH obtained by ultra-high pressure water atomization with an average particle size of 7 μm, and the temperature during kneading is 135 ℃ and the kneading time is 2.2 hours, thereby obtaining an injection material.

In a preferred embodiment of the present invention, the temperature for degreasing the green sample in the step S4 is 600 ℃, and the green sample is incubated for 4 hours.

Preferably, the flow rates of the nitrogen gas introduced in the step S7 and the nitrogen gas introduced in the step S8 are 50L/min and 55L/min, respectively.

Preferably, after the sintering of the product in the step S9 is completed, solution heat treatment is performed to remove chromium nitride on the surface of the product, so as to obtain a stainless steel product austenitized at 17-4 PH.

The invention has the beneficial effects that:

1) through specific setting of a sintering process, determining the time, flow and opportunity of introducing nitrogen, ensuring the formation of nitrogen and stabilizing austenite, simultaneously realizing the control of nitriding depth, obtaining a product meeting the magnetic requirement, and effectively removing chromium nitride on the surface of the product through solution heat treatment after the product is sintered so as to quickly obtain a 17-4PH austenitized stainless steel product;

2) by selecting the 17-4PH prealloying powder through ultrahigh pressure water atomization and determining the parameters of the prealloying powder such as particle size, heat preservation time and the like, the phase morphology, the sintering density and the post-sintering heat treatment of the obtained product are ensured to reach the expectation, and the requirement of directionally preparing the 17-4PH austenitized target stainless steel product is met.

Detailed Description

The technical solution of the present patent will be described in further detail with reference to the following embodiments.

In describing embodiments of the present patent in detail below, it is to be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated based on the orientation or positional relationship for ease of description and simplicity of description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present patent.

In the description of this patent, it is noted that unless otherwise specifically stated or limited, the terms "mounted," "connected," and "disposed" are to be construed broadly and can include, for example, fixedly connected, disposed, detachably connected, disposed, or integrally connected and disposed. The specific meaning of the above terms in this patent may be understood by those of ordinary skill in the art as appropriate.

A non-magnetic sintering process for 17-4 products specifically comprises the following steps:

s1, preparing an adhesive, wherein the adhesive is a high-density polyethylene (HDPE) -Paraffin (PW) -based adhesive, the adhesive of a (HDPE) - (PW) system has good fluidity, the temperature has little influence on the viscosity, the viscosity can be changed rapidly during cooling, the adhesive is firm and stable after cooling, the production cost is low, no pollution is caused to the environment, and the lubricating performance is good;

s2, proportioning and mixing the adhesive and the pre-alloyed powder, wherein the pre-alloyed powder is ultra-high pressure water atomized 17-4PH pre-alloyed powder with the average particle size of 7 microns, the mixing temperature is 135 ℃, the mixing time is 2.2 hours, and the injection material is obtained;

s3, performing injection molding on the mixed injection material through an injection machine to prepare a sample green body;

s4, heating the green sample blank by a sintering furnace at 30-800 ℃ for degreasing, and removing the adhesive in the green sample blank, specifically, when degreasing, firstly, keeping the temperature at 120 ℃ for 1h, then heating at 4 ℃/min, stopping heating when the temperature reaches 600 ℃, and keeping the temperature for 4 hours, so as to ensure efficient degreasing of the green blank;

s5, sintering at 800-1050 deg.C, keeping temperature at 1050 deg.C for 2 h, reducing and decarbonizing the blank;

s6, sintering by using argon when 1050 ℃ is reached, and sintering and shrinking the green blank;

s7, using nitrogen at 1200 ℃, keeping the temperature for 30 minutes under the partial pressure of 20KPA, and enabling the carbon content in the front of the furnace and in the furnace to be uniformly distributed;

s8, introducing nitrogen at 1200 ℃, keeping the temperature for 210 minutes under the partial pressure of 75KPA, so that the temperature of each layer of the sintering furnace is more uniform and nitriding is carried out on the product;

s9: and (3) cooling to 1150 ℃ at the highest temperature and partial pressure, then preserving heat for 2 hours, continuing nitriding the product at the partial pressure of 80KPa to ensure complete austenitizing, carrying out solid solution heat treatment after sintering the product, and removing chromium nitride on the surface of the product to obtain a stainless steel product with 17-4PH austenitizing.

And when nitrogen is introduced in the S7 step and the S8 step, the flow rates are respectively 50L/min and 55L/min, so that the uniform distribution of the carbon content in the furnace and the uniform nitriding of the product are ensured in the sintering process, the nitrogen is introduced in a three-stage mode in the sintering process, and the progressive continuous pressurization is performed during each nitrogen injection, so that the high-pressure nitriding is realized, the product size can be ensured, and the product with weak magnetism can be obtained.

Specifically, the 17-4PH austenitized stainless steel product is finally prepared, the size precision is high, the product strength is high, the product is nonmagnetic and good in corrosion resistance, and the requirements of nonmagnetic, corrosion resistance, high strength and price deviation in the application field are met.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.