RE与Ti复合变质对铸造5CrNiMo模具钢组织和性能的影响

Influence of Rare Earths and Titanium Complex Modification on the Microstructures and Properties of 5CrNiMo Cast Steel

研究了稀土(RE)与Ti复合变质对5Cr Ni Mo模具钢铸态和热处理组织与性能的影响。结果表明,变质和未变质5Cr Ni Mo铸锭宏观组织由表面细晶区、柱状晶区和中心等轴晶组成,RE、Ti变质缩小柱状晶区宽度、细化中心等轴晶,0.02%RE+0.10%Ti变质使柱状晶宽度与铸锭半径之比由未变质的0.48降低至0.28,中心等轴晶尺寸从1 700μm细化至200μm,RE变质减少钢中Mn S夹杂物数量,并使偏析于晶界的Ti C由杆状转变为粒状。经过900℃×2h+570℃×2 h调质处理后,5Cr Ni Mo钢的组织为回火索氏体,索氏体保留了原马氏体形态。相较于未变质,RE与Ti复合变质试样调质态抗拉强度提高10.7%,达到1 232 MPa,伸长率和硬度分别为16.4%和35.6 HRC。RE与Ti复合变质,细化晶粒,增加回火过程中晶内析出相的数量,产生沉淀强化作用。

The influence of the rare earths （RE） and titanium complex modification and heat treatment on 5CrNiMo cast steel was studied systematically. The results show that the macrostructure of 5CrNiMo is consisted with surface fine crystalline area, columnar area and equiaxed area. RE and Ti modification can shrink CA and refine EA remarkably. And the proportion of columnar area to the diameter of ingot is reduced from 0.48 to 0.28 with 0.02%RE＋0.10%Ti. Meanwhile, equiaxed grains is refined from 1 700 μm to 200μm. The number of MnS inclusions decrease by adding RE, and rod like TiC is formed in the boundary at the same time. After heat treatment, the microstructure of 5CrNiMo cast steel consist of tempered sorbite, which still keep martensite morphology. Compared with un-modified sample, the tensile strength of quenching and tempering sample is increased 10.7%, up to 1 232 MPa, and the elongation and hardness are 16.4% and 35.6 HRC. RE and Ti multi-modification can refine grain size, increase the intragranular nano-sized precipitates, enhance the tensile strength and hardness.