高强度热轧双相钢分段相变行为及性能

Transformation behavior and properties of high strength hot-rolled dual phase steel

研究了C-Mn-P-Cr成分设计热轧双相钢分段冷却过程的相变行为,分析了分段冷却工艺参数和卷取温度对铁素体和马氏体相变组织及性能的影响。结果表明,在分段冷却控制相变过程中,两段水冷间隔空冷开始温度和空冷时间影响铁素体转变体积分数、形态和晶粒尺寸,从而也影响残留亚稳奥氏体的体积分数和分布。卷取温度影响亚稳奥氏体的转变,进而也影响马氏体的自回火过程和铁素体的过时效过程。两段水冷间隔空冷温度宜控制在650~660℃,以促进多边形铁素体均匀充分转变。空冷开始温度降为630~640℃,则会出现针状铁素体。当650~660℃空冷时间从5 s延长到8 s,铁素体体积分数从65%增加到87%,且马氏体明显细化。卷取温度250~300℃时,铁素体马氏体两相界面处有约300 nm的较大碳化物颗粒,且马氏体内部有一定程度的回火,析出了少量的细小碳化物,会使得屈服强度偏高约80 MPa。采用150~200℃卷取可获得较为理想的双相组织和力学性能。

Dual phase steel with composition design of C-Mn-P-Cr was used to study the transformation behavior during step cooling process.Effects of step cooling process data and coiling temperature on ferrite and martensite transformation and properties of the steel were analyzed.The results show that air cooling temperature and time between two step water cooling effect the volume fraction,morphology and grain size of ferrite,which also effect the volume fraction and distribution of retained metastable austenite.Coiling temperature effects transformation of metastable austenite,and it influences the self tempering of martensite and over aging of ferrite.Air cooling from 650-660 ℃ is benefit to uniform transformation of polygonal ferrite.When cooling temperature decreases to 630-640 ℃,there is some acicular ferrite.When cooling time at 650-660 ℃ increases from 5 s to 8 s,volume fraction of ferrite increases from 65% to 87%,meanwhile martensite refines markedly.At the coiling temperature of 250-300 ℃,there is large carbide particle with size of 300 nm occurs in dual phase boundary,and fine carbides precipitate in tempered martensite.When coiling temperature is 150-200 ℃,well dual phase microstructure and mechanical properties are obtained.