贝氏体区等温处理对钒微合金化TRIP钢组织性能的影响

Effect of heat treatment in bainite region on microstructure and mechanical properties of V-microalloyed TRIP-aided sheet steel

通过连续退火实验,研究了贝氏体区等温处理对钒微合金化TRIP钢组织性能的影响。等温≤60 s时,组织由铁素体、分布不均匀且成堆聚集的残留奥氏体及贝氏体/马氏体组成。等温120～180 s后,组织中马氏体减小,残奥含量趋于稳定且分布弥散、均匀,基体上存在钒的析出。EBSD分析结果表明等温时间达到120 s后,大、小角度晶界的分布趋于稳定,以大角度晶界为主。所有等温时间范围内,铁素体晶粒尺寸大体呈正态分布,其中2～3μm的铁素体晶粒占很大比例。等温时间较短时,连续退火钢板呈现出高抗拉强度(1100 MPa)、低屈服强度(495 MPa)和低伸长率(20.3%)的特性。随着等温时间的延长,呈现出相对低抗拉强度(885 MPa)、高屈服强度(570 MPa)和高伸长率(27.8%)的特性,而且加工硬化指数(0.29)、各向异性指数(1.04)和强塑积(24603 MPa.%)也较为优良。

Effects of isothermal treatment in bainite transformation region on microstructural characteristics and mechanical properties of a V-microalloyed TRIP steel after cold rolling and continuous annealing were investigated. The results show that, when holding for ≤60 s, the microstructure consists of ferrite, retained austenite distributed unevenly in flock-shape, and bainite and martensite. After holding for 120- 180 s, the volune fraction of martensite decreases, the volume fraction of retained austenite tends to be stable and distributes dispersedly, and the vanadium carbonitrides both disperse and precipitate within matrix. EBSD results show that grain boundaries distribution tends to be stable and is dominated by large angle grain boundaries after holding for 120 s. The ferrite grain sizes of the isothermally treated steel roughly obey normal distribution for all isothermal time and a large amount of grain sizes is in the range of 2 - 3 p,m. When holding for shorter isothermal time, a relatively higher tensile strength （1100 MPa） , lower yield strength （495 MPa） and elongation （20.3%） of continuous annealing sheet steel are obtained. With the increase of isothermal time, a relatively lower tensile strength （885 MPa）, higher yield strength （570 MPa） and elongation （27.8%） for the steel can be obtained, and its strain-hardening exponent （0.29）, anisotropy exponent （1.04） and product of tensile strength-to elongation （24603 MPa. % ） are also excellent.