轧后冷却工艺对海洋平台用钢组织性能的影响

Effect of cooling mode on microstructure and mechanical properties of offshore platform steel

轧后采用空冷、加速冷却和两段式(前段超快冷+后段加速冷却,简称超快冷)三种冷却模式进行控制冷却,研究了冷却工艺对海洋平台用钢组织性能的影响。结果表明,空冷工艺所得试验钢的组织为多边形铁素体和马氏体,铁素体晶粒内位错密度较低,析出相数量较少,尺寸粗大;加速冷却所得试验钢的显微组织由多边形铁素体、针状铁素体和细小弥散的M/A岛组成,铁素体晶粒较空冷工艺明显细化,位错密度提高,析出物细小弥散;两段式所得试验钢的相变组织主要为针状铁素体,板条明显细化,位错密度进一步提高,析出物细小而数量降低。三种冷却工艺中,空冷工艺所得试验钢的屈强比最低,塑性最好;加速冷却工艺所得试验钢的低温韧性最佳;而采用两段式冷却工艺所得试验钢抗拉强度最高。

In order to investigate the effect of cooling routes on microstructure and mechanical properties of offshore platform steel,three types of cooling mode which includes air cooling,accelerated cooling（ACC）,and two-stage cooling（ultra fast cooling（UFC）＋ ACC）was applied after hot rolling.The results show that polygonal ferrite and martensite are obtained by air cooling process.Dislocation density in polygonal ferrite is relatively lower and precipitates are larger,and sparsely distributed.The microstructure of the steel consists of polygonal ferrite,acicular ferrite and fine dispersed M/A island after treating by accelerated cooling mode.Compared with air cooling mode,ferrite grain is refined and dislocation density increases and fine dispersed precipitates are observed in the steel by ACC.The microstructure attained from two-stage cooling mode mainly consists of fine acicular ferrite with high dislocation density and less fine dispersed precipitates.Among the three cooling modes,the lowest yield ratio and highest plasticity are achieved by air cooling.Optimal low-temperature toughness and highest strength of the steel are obtained by accelerated cooling and two-stage cooling treatment,respectively.