氧化物还原对无镍双相不锈钢气-固渗氮奥氏体化的促进机理研究

Porous high-nitrogen Ni-free austenitic stainless steel has relative low elastic modulus. It is therefore suitable for biomedical implant to replace the hazardous Ni-containing stainless steel. It can also be applied in particle filtering devices working under extreme conditions such as high temperature and high corrosive environment. It is a new type of stainless steel with practical application value and research significance. This project proposes to prepare porous high-nitrogen Ni-free austenitic stainless steel by reducing part of the oxides in the CrMn Ni-free dual-phase stainless steel compact first, and then followed by nitriding austenization during the sintering process. Furthermore, the pore characteristic and diffusion bonding behavior of porous high-nitrogen Ni-free austenitic stainless steel are also taken into consideration. The project emphasizes on the research on the mechanism of oxide reduction and gas-solid sintering nitridation of the stainless steel. Experimental techniques such as XPS etc., together with ThermalCal will be applied to calculate, predict and analyze the thermostability of oxides and characteristics of reduzates after reduction, as well as the phase constituents and phase compositions of the stainless steel after nitridation process, so as to clarify the thermodynamic conditions for oxides reduction and gas-solid nitridation. The project may provide a scientific guideline for the optimization of the nitridation process and make a meaningful contribution to the development of high-nitrogen Ni-free austenitic stainless steel.

多孔高氮无镍奥氏体不锈钢有较低的弹性模量，适合用作医用植入材料，代替危害健康的含镍不锈钢；也可用于高温、高腐蚀等极端环境下流体的颗粒过滤；是一种具有实际应用价值和研究意义的新型不锈钢。本课题将对CrMn无镍双相不锈钢粉末压坯先期进行还原，去除部分氧化膜，随后在烧结过程中进行渗氮奥氏体化，制得多孔高氮无镍奥氏体不锈钢，进而分析其孔隙特性与扩散焊接行为。在此基础上，重点研究不锈钢氧化物还原和气-固烧结渗氮机理，利用XPS等手段并协同ThermalCal热力学计算方法，预测、分析多孔不锈钢中氧化物的热稳定性与还原相组成，继而探究在不同温度、氮气氛和时间条件下，不锈钢渗氮后的相组成和相成分，以此计算、评估还原和氮化的热力学和动力学条件。本课题的研究将为多孔无镍不锈钢优化渗氮路线提供理论基础和科学依据，为高氮无镍奥氏体不锈钢的发展做出有意义的贡献。

高氮无镍奥氏体不锈钢（HNASS）具有低成本、耐腐蚀性能好、力学性能优异的特点，克服了传统奥氏体不锈钢中镍元素对人体有害和昂贵等问题，在医用植入材料、海洋工程和装备等领域具有广泛潜在应用价值。本项目以低、中氮不锈钢粉末为原材料，分别利用放电等离子烧结（SPS）与金属注射成型（MIM）制备出了致密HNASS，利用模压成型与气固渗氮烧结工艺制备了孔隙率可控的HNASS，探究了多孔HNASS的真空扩散焊接行为。. （1）以低、中氮不锈钢粉末为原材料，通过粉末渗氮和SPS工艺制备了致密HNASS。探究了渗氮温度对低氮和中氮不锈钢粉末的相组成与含氮量的影响规律，获得氮含量较高且可控的含氮不锈钢粉末；随后通过SPS制备了致密HNASS，并研究了氮含量对其相、组织、耐腐蚀性和力学性能的影响。. （2）以低、中氮双相不锈钢粉末为原材料，采用模压成形和气固渗氮烧结方法制备了多孔HNASS，分析了烧结温度、造孔剂含量和压制压力对其孔隙率和孔隙形貌的影响，建立了工艺参数与其组织、抗压性能和弹性模量的关系。. （3）利用MIM与气固渗氮烧结制备了FeCrMnMoN系致密HNASS，开发了优化注射、脱粘、烧结工艺，成功制备了HNASS，获得了烧结温度、烧结时间、固溶处理对线收缩、氮含量、相转变、组织组成、力学性能、耐腐蚀性能和摩擦磨损性能等的影响规律。. （4）探究氢气还原对中氮双相不锈钢粉末气固渗氮烧结试样组织的影响：分析还原参数对试样相组成的影响，探究还原过程中氧化物的演变规律，探讨还原工艺对渗氮行为的影响；结合材料热力学理论，研究各种氧化物的热力学稳定性。还原工艺参数对析出物含量有影响，随着还原时间延长，CrN相含量小幅增加，Cr2N相含量则小幅下降。. （5）研究了孔隙率为30%的HNASS的真空扩散焊行为，探究了焊接温度和压力对焊接接头和热影响区的影响规律，结果表明1000 ℃的焊接温度与1 MPa焊接压力可获得良好的力学性能。. 本项目研究为粉末冶金制备致密/多孔高氮无镍奥氏体不锈钢提供了新方法，优化了渗氮路线并提供了理论基础和科学依据。