低碳钢气体氮碳共渗及后续淬火研究  

Gaseous Nitrocarburizing and Post-quenching of Low Carbon Steel

作　　者：李楠 洪悦[1] 伍翠兰[1] 徐强 LI Nan;HONG Yue;WU Cui-lan;XU Qiang(School of Material Science and Engineering,Hunan University,Changsha 410082,China)

机构地区：[1]湖南大学材料科学与工程学院,长沙410082

出　　处：《表面技术》2018年第11期9-16,共8页Surface Technology

基　　金：国家自然科学基金(51071064;11427806)~~

摘　　要：目的减少传统氮碳共渗及后续淬火形成的马氏体层中大量孔洞及其性能差的缺陷,寻求优化的工艺参数,在低碳钢表面获得少孔、高强、高韧的强化层。方法采用X射线衍射、扫描电镜、透射电镜及显微硬度计对不同工艺参数条件下制备的强化层的微观组织结构和性能进行表征。结果氮碳共渗化合物层经850℃加热油淬后转变成多孔马氏体,降低淬火温度、缩短共渗时间、减少共渗气氛中的NH3流量、增加CO流量均可减少淬火试样表面孔洞的数量。经680℃加热淬火后,氮碳共渗化合物层转变成马氏体加残余奥氏体的复相强化层,这种复相强化层的硬度可达到1000HV,且具有很好的韧性。经过120℃低温回火后,复相强化层仍保持高硬度和良好韧性。相对于增加CO流量而言,降低NH3流量不仅能减少表面的孔洞,也可保持680℃淬火强化层的高硬度和良好韧性,同时也可缩短氮碳共渗时间,节约成本。结论优化的氮碳共渗淬火工艺能获得由马氏体和奥氏体组成的复相强化层,并显著减少表面孔洞。强化层中广泛分布的奥氏体能显著改善复相强化层的韧性。因此,复相强化层具有高强高韧且少孔的优点。The work aims to decrease the shortcomings of numerous pores and poor performance in the martensitic layers fabricated by traditional nitrocarburizing and post-quenching and find out the optimized process parameters to obtain a strengthened layer with few pore,high strength and high tenacity on low carbon steel.X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and microhardness tester were used to characterize the microstructures and the properties of the strengthened layers formed at different process parameters.Nitrocarburized compound layer was transformed into a porous martensitic layer after re-heating and oil-quenching at 850℃.The quantity of pores on the surface quenched specimen could be decreased by lowering quenching temperature,reducing nitrocarburizing time,decreasing gas fluxes of NH3 and increasing the gas fluxes of CO.After post-quenching at 680℃,the nitrocarburized compound layer could be transformed into a multiphase strengthened layer composed of martensite and retained austenite.The multiphase strengthened layer had the hardness up to 1000HV and good toughness.Even after tempering at 120℃,the multiphase strengthened layer could still keep the high hardness and good toughness.Compared with increasing of the gas fluxes of CO during the nitrocarburizing process,decreasing of gas fluxes of NH3 not only decreased the pores and kept high hardness and good toughness of the strengthened layers,but also reduced the nitrocarburizing time and costing.The optimized nitrocarburizing and post-quenching process can be used to fabricate a multiphase strengthened layer composed of martensite and retained austenite and reduce the surface pores.The widely distributed austenite-blocks in the strengthened layers can greatly improve the toughness.Therefore,the multiphase strengthened layer has advantages of high hardness,high toughness and few pores.

关 键 词：氮碳共渗 淬火 化合物层 复合强化层 马氏体 奥氏体 

分 类 号：TG156.8[金属学及工艺—热处理]