高氮奥氏体钢粉末的合成及其致密化工艺

Synthesis and densification process of high nitrogen austenitic steel powders

采用机械合金化和高压气雾化两种工艺分别合成了近球形粉末,随后通过粉末注射成形技术制备了0Cr17Mn11Mo3N高氮奥氏体钢材料。用X射线衍射、扫描电镜、拉伸试验等手段研究了粉末和块状材料的结构及性能。结果表明:两种粉末球形度好,颗粒细小,装载量和烧结活性较高,都能够较好满足后续粉末注射成形工艺要求。机械合金化粉末最佳致密化条件是采用真空脱氧+氮气烧结方式,在0.1 MPa氮气压力下于1260℃烧结120 min,烧结体相对密度97.90%,氮含量1.02 mass%,经过1150℃×90 min固溶处理后屈服强度、抗拉强度、伸长率、断面收缩率、维氏硬度分别高达627 MPa、965 MPa、11.3%、16.7%、312HV;高压气雾化粉末最佳致密化条件为0.1 MPa氮气压力下1300℃烧结120 min,烧结体相对密度98.33%,氮含量0.78mass%,经固溶处理后屈服强度、抗拉强度、伸长率、断面收缩率、维氏硬度也分别达到580 MPa、885 MPa、26.0%、29.1%、222HV。由于氮在奥氏体中的强化作用,0Cr17Mn11Mo3N高氮奥氏体钢的强度、硬度等远高于传统注射成形316L奥氏体不锈钢。

Two kinds of nearly spherical powders were synthesized by mechanical alloying method and high pressure gas atomization method, and then high nitrogen 0Cr17Mn11Mo3N austenitie steels were prepared by powder injection molding technology using the two different powders as raw materials. The structure and performances of the powders and bulk materials were investigated by means of X-ray diffraction （XRD） , scanning electron microscopy （SEM） and tensile tests. The results show that both powders are characterized by good sphericity, fine particle size, high powder loading and sintering activity, meeting the process requirements of subsequent powder injection molding. The optimum densifieation conditions for mechanically alloyed powders are determined to be vacuum deoxidation at 1150 ℃ for 40 min and then sintered under 0.1 MPa nitrogen pressure at 1260 ℃ for 120 min, under which the relative density of 97.90% and the nitrogen content of 1.02 mass% can be achieved for the sintered specimens, and after solid solution treatment at 1150 ℃for 90 min, the yield strength, ultimate tensile strength, elongation, reduction of area and Vickers hardness of the specimens can be as high as 627 MPa, 965 MPa, 11.3%, 16.7% and 312 HV, respectively. The optimum densification process conditions for high pressure gas-atomized powders are found to be sintered under 0. 1 MPa nitrogen pressure at 1300 ℃ for 120 min, under which the relative density of 98.33% and the nitrogen content of 0. 78 mass% can be acquired, and after solid solution treatment, the yield strength, ultimate tensile strength, elongation, reduction of area and Vickers hardness can reach 580 MPa, 885 MPa, 26.0% , 29. 1% and 222 HV, respectively. Due to the positive effects of nitrogen in austenite, much higher strength and hardness have been obtained in high nitrogen 0Cr17Mn11Mo3N austenitic steels in contrast with conventional MIM 316L austenitie stainless steels.