超快冷对X70管线钢组织和性能的影响

Effect of ultra fast cooling on microstructure and properties of X70 pipeline steel

采用MMS-300热/力模拟试验机研究了无Mo和含Mo管线钢X70不同冷却条件的动态相变行为并绘制了试验钢的动态CCT曲线。结合实验室轧制和冷却试验,研究了超快冷和层流冷却条件下两种成分X70管线钢的组织演变和力学性能。结果表明:随着冷却速度的增大,无Mo管线钢X70的组织构成为多边形铁素体+珠光体、多边形铁素体+针状铁素体、针状铁素体;含Mo管线钢X70的组织构成为多边形铁素体+针状铁素体、针状铁素体;Mo抑制了多边形铁素体和珠光体相变的发生。对于无Mo管线钢X70,层流冷却工艺所得到的组织有约40%的准多边形铁素体;超快冷工艺所得到的组织为针状铁素体,有利于提高X70管线钢的强韧性。超快冷工艺使晶界取向差大于15°的有效晶粒尺寸得到了细化,无Mo管线钢X70的强韧性略高于层流冷却条件下含Mo管线钢X70。超快冷条件下含Mo管线钢X70组织更细小,力学性能可满足X80管线钢的要求。

Dynamic phase transformation behavior and CCT curves of X70 pipeline steels containing and un-containing Mo were investigated by MMS-300 thermal/mechanical simulation tester. In virtue of rolling and cooling experiment, microstructure evolution and mechanical properties of the X70 pipeline steels with two different chemical composition were studied under the laminar cooling and ultra fast cooling conditions at laboratory. The results reveal that the mierostructure changes by sequence of polygonal ferrite and pearlite; polygonal ferrite and acieular ferrite; and acieular ferrite for non-Mo X70 pipeline steel, and of polygonal ferrite and acicular ferrite; aeilular ferrite for X70 pipeline steel eontaining-Mo with the increase of cooling rate. Mo restrains the polygonal ferrite and pearlite transformation. About 40% quasi polygonal ferrite can be obtained under the laminar cooling condition and aeicular ferrite is obtained under ultra fast cooling condition for non-Mo X70 pipeline steel. Acicular mierostructure is benefit for the increase of strength and toughness of X70 pipeline steel. Ultra fast cooling refines the effective grains, whose boundary misorientation is higher than 15%. The strength and toughness of the non-Mo X70 pipeline steel under ultra fast cooling is slightly higher than that of the XT0 pipeline steel containing-Mo under the condition of laminar cooling. Mierostructure is much finer under the condition of ultra fast cooling for Mocontaining X70 pipeline steel and the mechanical properties can satisfy the standard of X80 pipeline steel.