不锈钢微熔池高压渗氮熔炼与凝固机理研究

The existing preparation method of high nitrogen stainless steel is increasing nitrogen by the methods of electroslag remelting, high pressure bottom blowing and powder metallurgy. Then generated ingot and powder are carried out heat treatment and machining into product finally. The process which is easy to appear micro bubbles has so less efficient and the nitrogen distribution is not uniform that product performance will be effect. Therefore, the application provide a new method that high nitrogen stainless steel is prepared by high pressure metallurgy selectively laser melting. The primary experiment characteristics are rapid laser melting, micro-melting pool nitridation with high pressure, melt fast cold and burst condensate and pressure control of ultrafine bubbles. In this project, the mechanism of micro-melting pool high pressure nitridation, formed in the process of stainless steel powder laser melting, is mainly studied. What’s more, the dissolving and updating of nitrogen on the pool surface are analyzed under high pressure. At the same time, migrate movement behavior of nitrogen and Marangoni effect induced by surface tension in the liquid steel are considered. Carried out experiments of producing high nitrogen stainless profile steel which is high density by the equipment of high pressure metallurgy selectively laser melting, to confirm the effect of pressure, alloying elements, pool size, laser power and scanning speed for the property of high nitrogen stainless steel. The project has scientific research value and a good application prospects. The results of the project will lay the foundation for producing rapidly, stably and personalized customization high nitrogen stainless steel.

目前高氮不锈钢制备一般采用电渣重熔、高压底吹、粉末冶金等形式增氮，形成铸锭或粉体后热处理，最后进行机加工形成产品，效率较低、易出现微气泡、氮分布不均匀，直接影响产品性能。鉴于此，申请者提出了高压冶金选择性激光熔化制备高氮不锈钢的新方法，并开展了初步试验，特点为激光快速熔化、微熔池高压增氮、熔体快冷骤凝、压力控制超微气泡。本项目主要研究不锈钢粉体激光熔化形成的微熔池与高压气氛协同增氮机制，分析高压气氛下氮在熔池表面溶渗与更新的机理，研究钢液中氮的迁移运动行为及表面张力引发的Marangoni效应，在高压冶金选择性激光熔化实验设备上，开展制备高致密度的高氮不锈钢型材实验，确定压力、合金元素、熔池尺寸、激光功率、扫描速度等因素对高氮不锈钢性能的影响。本项目既有科学研究价值，又具有很好的应用前景，项目成果将为快速、稳定、个性化定制生产高性能高氮不锈钢产品奠定基础。

选区激光熔化技术作为金属增材制造技术的重要分支，受国内外众多学者重视。本项目开展了微熔池增氮热力学与动力学基础研究，建立了微熔池传热模型，并计算确定了凝固时间的影响因素及规律。研究了激光系统的光斑自动定位提取算法及传感器测量软件设计，明晰了基于深度神经网络的波前控制算法并得到验证确认。采用常规选区激光熔化CSLM和高压选区激光熔化HPSLM两种方式对含氮不锈钢粉进行了基础成形实验，高压SLM成形过程中存在渗氮行为。腔内压力0.1MPa时，渗氮量为0.064wt%，1.5MPa时，渗氮量为0.73wt%。探究了工艺参数对成形试样最终氮含量影响规律及氮含量对物相组成的影响，分析了工艺参数对单道熔池形貌、单道和块体成形质量、微观组织结构、相对致密度及微观表面硬度的影响，并根据不同评价指标优化了SLM成形高氮不锈钢的工艺参数。在试验参数范围内，各因素对渗氮量显著度的影响次序为腔内压力＞扫描间隔＞铺粉层厚＞扫描速度＞激光功率。CSLM块体试样性能方面，体能量密度为136.36J/mm3（激光功率200W、扫描速度1000mm/s）时，相对致密度达到98.85%，显微硬度达到409HV0.3。CSLM试样相对致密度随激光能量密度的增加呈先增加后降低的趋势，在一定激光能量密度范围内，CSLM试样显微硬度与其成反比，HPSLM试样显微硬度与腔内压力成正比。将选区激光熔化技术用于成形高氮不锈钢，不仅丰富了高氮不锈钢制备方式，同时也开发了选区激光熔化技术成形的新材料，项目成果将为高效、稳定、高质量生产高氮不锈钢构件奠定基础。