【作者】 姜玉珍；

【导师】 季长涛；

【作者基本信息】 长春工业大学 ， 材料加工工程， 2011， 硕士

【摘要】 与传统的奥氏体不锈钢相比,高氮无镍奥氏体不锈钢保持了高塑性、韧性、无磁性的性能特点,主要是强度明显提高,同时还具有良好的生物相容性及优良的耐腐蚀性能,并且节约了贵重的镍资源,降低了不锈钢生产的成本,因此成为世界各国竞争和研发的焦点。目前国际上普遍采用高压冶金的方法生产高氮无镍奥氏体不锈钢,该方法生产成本高,安全隐患大,不宜进行大规模生产,因此寻求一种常压下冶炼高氮无镍奥氏体不锈钢的方法成为材料科学研究的重点。常压下氮在钢中的溶解度很低,与高压冶金相比,常压下冶炼的高氮无镍奥氏体不锈钢的铸态组织中存在大量的氮气孔,氮元素分布不均,但是在随后的锻造过程中氮气孔会焊合,经固溶处理后氮元素分布均匀,组织为单相奥氏体,在此状态下,试验用钢是否具有优异的抗腐蚀性能是常压冶炼和生产的高氮无镍奥氏体不锈钢能否实际应用的关键。本文以一种常压下冶炼的高氮无镍奥氏体不锈钢Cr18Mn18Mo2NbN0.6为材料,利用扫描电子显微镜、光学显微镜等对铸态、锻造态和固溶处理态进行了显微组织分析；在酸性介质(10%H2SO4和10%HNO3)中对固溶处理后的高氮无镍奥氏体不锈钢和1Cr18Ni9Ti进行了酸浸试验和极化曲线测试；在中性介质(3.5%NaCl)中对其进行了盐雾试验和极化曲线测试；对固溶态、氮化物析出后及压缩变形量分别为10%、20%、30%和40%的试验钢进行了显微组织分析、三氯化铁浸泡试验和极化曲线测试。实验结果表明,高氮无镍奥氏体不锈钢的铸态组织为等轴枝晶,枝晶间存在未溶的片状氮化物和氮气孔,氮气孔在锻造过程中可以焊合。试验钢锻造后的组织为明显的层状组织,基体为奥氏体,氮化物以层片状分布在层状组织界面以及层与层之间。固溶处理后其组织为单相奥氏体,组织中存在大量的退火孪晶,奥氏体晶粒细小；高氮无镍奥氏体不锈钢在10%H2SO4和10%HNO3中的腐蚀速率小于1Cr18Ni9Ti,其自腐蚀电位、点蚀电位较高、钝化区较宽,这是氮元素提高了耐蚀性的结果；高氮无镍奥氏体不锈钢在3.5%NaCl中的盐雾腐蚀速度小于1Cr18Ni9Ti,1Cr18Ni9Ti出现严重的晶间腐蚀,而高氮无镍奥氏体不锈钢表面仅有少量的较小的点蚀坑,高氮无镍奥氏体不锈钢自腐蚀电位较高,钝态电流密度较小,因此,高氮无镍奥氏体不锈钢比1Cr18Ni9Ti有较强的抗Cl-腐蚀的能力；不同冷变形量的试验钢自腐蚀电位、点蚀电位与固溶态近似相等,但变形量越大,点蚀坑的数目越多,蚀坑平均尺寸越大,氮化物析出后,试验钢的点蚀电位明显降低,并出现大面积的点蚀坑。更多还原

【Abstract】 Nickel free high nitrogen austenitic stainless steels keep high plasticity and toughness and without magnetic compared with the traditional austenitic stainless steels. But the strength improves obviously. At the same time they have excellent biocompatibility and corrosion resistance. They become the focus of competition and development in the world because they can save the precious resources of nickel and reduce the costs of production. At present, the production of nickel free high nitrogen austenitic stainless steels adopts high pressure metallurgy method in the world. This method has high production costs and high danger, so it is not suitable for mass production. Thus seeking a way of smelting nickel free high nitrogen austenitic stainless steels at atmospheric pressure is the key of material scientific research. The solubility of nitrogen in steels is very low at atmospheric pressure, so compared with high pressure metallurgy, there are lots of nitrogen porosities in the organization of high nitrogen austenitic stainless steels smelted at atmospheric pressure and the distribution of nitrogen is uneven. But the nitrogen porosities will be welded in subsequent rolling process. The distribution of nitrogen is uniform after solution treatment and the organization is full austenite. In this state, the tested steels smelted at atmospheric pressure have excellent corrosion resistance or not is the key of whether they can be applied in practice.In this paper, (Cr18Mn18Mo2NbN0.6) nickel free high nitrogen austenitic stainless steel smelted in an atmospheric pressure was studied. The microstructures of casting, rolling state and solid solution treatment state were analyzed through scanning electron microscope, optical microscope etc. Acid pickling and polarization curve testing of nickel free high nitrogen austenitic stainless steel after solid solution treatment and 1Cr18Ni9Ti were done in acidic medium (10%H2SO4 and 10%HNO3); Salt spray corrosion testing and polarization curve testing of tested steel after solid solution treatment and 1Cr18Ni9Ti were done in neutral medium (3.5%NaCl); The microstructure analysis, FeCl3 soak testing and polarization curve testing of tested steel after precipitation of nitrides, cold deformation 10%,20%,30%,40% and rolling state were done. The experimental results show that the cast structure of nickel free high nitrogen austenitic stainless steel was equiaxial dendritic crystals. Undissolved sheet nitrides and nitrogen porosities existed between dendritic crystals. The nitrogen porosities will be welded in subsequent rolling process. The microstructure of rolling state of tested steel was obvious layer structure. The matrix was austenite. Layer nitrides distributed on the interface of layer structure and between layers. The microstructure of the tested steel after solid solution treatment was full austenite. Lots of annealing twins existed in the microstructure. The grains of austenite were very small. The corrosion rate of nickel free high nitrogen austenitic stainless steel was less than 1Cr18Ni9Ti in 10%H2SO4 and 10%HNO3.The natural corrosion potential and pitting corrosion potential of nickel free high nitrogen austenitic stainless steel was higher, the passivation was very wide. This was because nitrogen improved corrosion resistance. The corrosion rate of nickel free high nitrogen austenitic stainless steel was less than 1Cr18Ni9Ti in 3.5%NaCl. 1Cr18Ni9Ti appeared serious intergranular corrosion while the surface of nickel free high nitrogen austenitic stainless steel only appeared a small amount of smaller pitting corrosion pits. The natural corrosion potential of nickel free high nitrogen austenitic stainless steel was higher and the current density of passivity was smaller. Therefore nickel free high nitrogen austenitic stainless steel had stronger ability of resisting Cl- corrosion than 1Cr18Ni9Ti. The natural corrosion potential and pitting corrosion potential of tested steel after different cold deformation approximately equal with rolling state. But when distortion was greater, the number of pitting corrosion pits increased, and pitting corrosion pits deepen. The pitting corrosion potential of tested steel after precipitation of nitrides obviously reduced and the pitting corrosion pits appeared vastly.更多还原