Cu对390 MPa级CrNiMo系低合金船用钢板力学性能的影响

Effect of Cu on mechanical properties of 390 MPa grade CrNiMo series low-alloy ship steel plates

以不含Cu(961-Base)和含1wt%Cu(961-Cu)的CrNiMo系低合金船用钢板为研究对象,测试其经两次淬火+高温回火后的室温拉伸和低温冲击力学性能。通过热膨胀相变仪、光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)等技术手段研究了Cu对试验钢显微组织、力学性能、析出相和织构特征的影响。结果表明,不含铜钢的Ac_(1)和Ac_(3)温度分别为767℃和905℃,含Cu钢的Ac_(1)和Ac_(3)温度分别为762℃和895℃,且含铜钢的铁素体/贝氏体转变温度范围更低。经热处理后试验钢的显微组织均为板条贝氏体(LB)和少量准多边形铁素体(QPF),含铜钢的板条细化使大角度晶界比例提高了6.8%,更有利于阻碍裂纹扩展。含铜钢的屈服强度和抗拉强度分别比不含铜钢提升了84 MPa和68 MPa,低温冲击吸收能量从220 J提升到267 J。二者的冲击断口均以剪切唇和纤维区为主,含铜钢具有更大的剪切断面率。fcc结构的富Cu相在基体和位错线处非均匀析出,呈球状或棒状,产生析出强化作用。两种试验钢均以α和γ织构为主要织构特征,其中含铜钢含有更高比例的有利于变形的γ织构。

CrNiMo low-alloy marine steels without Cu(961-Base)and with 1wt%Cu(961-Cu)quenched twice and then tempered at high temperature were prepared,and then the effect of Cu on microstructure,mechanical properties,precipitated phase and texture characteristics of the steel was investigated by thermal dilatometer,optical microscope(OM),scanning electron microscope(SEM),electron backscatter diffractometer(EBSD)and transmission electron microscope(TEM).The results show that the Ac_(1)and Ac_(3)temperatures of the 961-Base steel are 767℃and 905℃,and that of 961-Cu steel are 762℃and 895℃,respectively.The ferrite/bainite transformation temperatures of the 961-Cu steel are lower than that of the 961-Base steel.The microstructure of the tested steels after heat treatment is dominated by lath bainite(LB)and a small amount of quasi-polygonal ferrite(QPF).The lath of the 961-Cu steel is more refined,which increases the proportion of large-angle grain boundaries by 6.8%and is more beneficial to hinder crack propagation.Compared with that of the 961-Base steel,the yield strength and tensile strength of the 961-Cu steel are increased by 84 MPa and 68 MPa,respectively,and the low-temperature impact absorbed energy are increased from 220 J to 267 J.The impact fracture of the tested steels is dominated by the shear lip and fiber zone,with the 961-Cu steel having a greater shear section ratio.The Cu-rich phase(fcc structure)is non-uniformly precipitated in the matrix and on dislocation line in the form of globular or rods,producing a precipitation strengthening effect.Both the tested steels are characterized byαandγtextures,with the 961-Cu steel containing a higher proportion ofγtextures that is conducive to deformation.