稀土元素对Si—Mn—V钢淬火,回火过程中组织结构转变的影响

采用透射电镜,X射线,膨胀仪等方法,对含稀土和不含稀土的4种低、中碳Si—Mn-V钢(20SiMn2V;20SiMn2VRE;40SiMn2V和40SiMn_2VRE)进行了淬火、回火过程中组织结构转变的对比试验,结果表明:稀土元素可以细化低、中碳钢的奥氏体晶粒度;降低M_s点;细化马氏体板条束和板条晶尺寸;并增加中碳钢马氏体中位错亚结构的相对比例。而对低、中碳钢淬火回火组织中残余奥氏体的体积和热稳定性影响甚微。稀土元素明显地抑制了低碳马氏体在低温回火过程中的分解,阻碍板条晶内片状渗碳体的析出,并推迟其长大球化过程。稀土元素也明显地抑制了中碳马氏体中高温回火过程中粒状渗碳体的析出和球化过程。

EFFECTS OF RARE EARTH ELEMENTS ON MICROSTRUCTURAL TRANSFORMATION OF LOW OR MEDIUM CARBON Si-Mn-V STEELS DURING QUENCHING AND TEMPERING

The microstructural transformation of four different low or medium carbon steels: 20SiMn2V, 20SiMn2VRE, 40SiMn2V and 40SiMn2VRE, during quen- ching and tempering have been examined by TEM, X--ray diffraction and dilatometer. It was shown that the rare earth elements added may make not only the fine aus- tenite grains of the low or medium carbon steels, but also the fine packet of lath martensite and lath size, lower the M_s temperature and raise the relative Percenta- ge of dislocation substructure of martensite in medium carbon steel, but influence no more the volume fraction and thermal stability of retained austenite within que- nching and tempering structure of low or medium carbon steels. The rare earth elements may remarkably inhibit the decomposition of low carbon martensite during low temperature tempering, retard the precipitation of cementite plates in lath gra- ins and delay the spheroidization of carbides. They may also restrain obviously the precipitation and spheroidization of cementite in medium carbon martensite during high temperature tempering.