500MPa级冷轧热镀锌双相钢的组织与性能

Microstructure and properties of 500 MPa grade cold rolled and hot-dip galvanized dual phase steels

对500 MPa级两种不同成分冷轧热镀锌双相钢进行不同温度的两相区退火试验,研究了退火温度和Nb对冷轧双相钢组织与性能的影响。结果表明,退火温度为760℃时,试验钢的微观组织为铁素体+马氏体;随着两相区退火温度的升高,铁素体平均晶粒尺寸逐渐减小,并有少量的珠光体出现。NbC能有效地抑制铁素体再结晶晶粒长大,含Nb钢的铁素体晶粒明显小于不含Nb钢,最小达到3.66μm。不含Nb钢中马氏体形状不规则,呈带状聚集分布;在NbC的作用下,含铌钢马氏体晶界圆滑,晶粒尺寸更加细小,呈弥散分布,其马氏体含量低于不含Nb试验钢。含Nb钢的强度、断后伸长率、加工硬化指数(n值)等均高于不含Nb钢。

500 MPa grade cold rolled and hot-dip galvanized dual phase steels with different chemical composition were annealed at two phase region temperature.Effects of annealing temperature and Nb on the microstructure and mechanical properties were investigated.The results indicate that microstructure of the tested steels is main composed of ferrite and martensite.As the annealing temperature increase,the average grain size of ferrite decrease and the pearlite appears.Because of that the growth of recrystallized ferrite grain is prevented by NbC,the grain size of ferrite in the Nb-added steel is smaller than that in the Nb-free steel,and the smallest average ferrite grain size is 3.66 μm.Martensite in Nb-free steel distributes in banded shape.Compared with Nb-free steel,martensite volume fraction of the Nb-added steel is less,the grain boundary is more regular,the grain size is smaller and the distribution is dispersive.The strength,elongation after fracture and n value of the Nb-added steel are higher than those of the Nb-free steel.