FH32-HD和FH36-HD高延性船板钢的开发及控冷工艺

Development and controlled cooling process of FH32-HD and FH36-HD higher ductility ship plate steels

采用低C和Nb+Ti复合添加的成分设计,通过优化“弛豫-层流冷却-空冷”的控冷工艺开发出了FH32和FH36两种强度级别的高延性船板钢,对其拉伸性能及显微硬度进行测试,拉伸采用全厚度A_(5)比例试样,利用扫描电镜和能谱仪对试验钢显微组织和夹杂物进行了观察和分析。结果表明,随着开冷温度的降低,即弛豫时间的延长,会使铁素体更早地产生屈服,平均晶粒尺寸和软硬相之比增大;此外,片状珠光体增多,粒状贝氏体含量显著降低,整体伸长率有所升高,但强度富余量大幅减小。终冷温度的降低会使珠光体片层间距先减小后增大,组织中存在的贝氏体含量逐渐增多,形貌由粒状贝氏体转变为板条状贝氏体,强度呈上升趋势,但伸长率在600℃达到峰值后显著降低。

Using the composition design of low C and Nb+Ti compound addition,two higher ductility ship plate steels FH32 and FH36 were developed by means of optimizing the controlled cooling process of"relaxation-laminar cooling-air cooling".The tensile properties and microhardness were tested,and the full-thickness A_(5)scale specimens were used for tensile testing.The microstructure and inclusions of the tested steels were observed and analyzed by using SEM and EDS.The results show that with the reduction of the initial cooling temperature,that is,the extension of the relaxation time,the ferrite yield earlier,the average grain size and the ratio of soft-hard phases increase.Furthermore,the content of lamellar pearlite increases and the content of granular bainite decreases significantly.The overall elongation increases,but the strength margin greatly decreases.The decrease of the final cooling temperature make the pearlite lamellae reduce firstly and then enlarge,the content of bainite in the structure increases gradually,and the morphology changes from granular bainite to lath bainite.The strength shows an upward trend,but the elongation decreases significantly after reaching a peak at 600℃.