选区激光熔化成形的304L不锈钢硬度和微观结构的研究

Study on Hardness and Microstructure of 304L Stainless Steel by Selective Laser Melting

选区激光熔化成形的奥氏体不锈钢与传统轧制材料相比,其硬度明显高于传统材料,这与其独特的微观结构密不可分。使用纳米压痕技术测量SLM打印态、SLM热处理态以及传统轧制3种304L奥氏体不锈钢的硬度变化,与材料的微观结构表征相结合,发展了一种使用硬度快速评价材料屈服强度的方法,并发现位错强化、细晶强化以及弥散强化是影响SLM 304L硬度的主要3种因素。结合理论计算分析了3种强化机制的作用。结果表明,高密度位错、析出相以及细小的晶粒尺寸共同造成了SLM打印态304L不锈钢具有最高的硬度,其中位错密度与晶粒尺寸是最主要的材料硬化因素。

Selective laser melting(SLM) austenitic stainless steel has higher hardness than its traditional rolled counterparts, which was closely related to its unique microstructure. The nano-indentation measurement was applied to investigate the hardness evolution in three kinds of samples, including as-built and heat-treated SLM, and the traditional rolled 304L austenitic stainless steels. Combining with the microstructure characterization of the materials, a rapid method for evaluating the yield strength of the materials by hardness was developed. Dislocation strengthening, fine grain strengthening and dispersion strengthening are the three main factors affecting the hardness of SLM 304L. The results show that high density dislocations, precipitates and fine grain size jointly cause the highest hardness of 304L stainless steel as-built SLM. The dislocation density and grain size are the two main material strengthening factors.