高强高韧异质结构温轧TWIP钢

Strong and Tough Heterogeneous TWIP Steel Fabricated by Warm Rolling

通过简单的温轧工艺,制备出高屈服强度(1250 MPa)、高延伸率(24%)和高断裂韧性(K_(JIC)为125 MPa·m^(1/2))的部分再结晶TWIP钢。相比于热轧和冷轧钢,温轧TWIP钢的微观组织具有异质结构特征,即包含高密度位错和孪晶的形变粗晶晶粒以及几乎无缺陷的再结晶细晶。形变粗晶提供高屈服强度,再结晶晶粒提供大的塑性变形能力,从而在拉伸实验中具有优异的加工硬化率。与此同时,在断裂韧性测试中的裂纹扩展过程中,再结晶晶粒能使裂纹尖端钝化和裂纹偏折,提高其断裂韧性。这种温轧产生的异质结构TWIP钢同时取得了高屈服强度和高韧性的优异性能组合。

Twinning-induced plasticity(TWIP) steel has received significant research attention because of its superior mechanical properties,including uniform elongation,ultimate tensile strength,and fracture toughness.However,it has a relatively low yield stress,which limits its industrial application.Increasing the dislocation density has been proved to be an effective method for enhancing the yield stress.In this work,a simple warm rolling(WR) route was applied at 700℃ to manufacture partially recrystallized TWIP steel with a high yield stress(1250 MPa),good total elongation(24%),and exceptional fracture toughness(K_(JIC) of approximately 125 MPa·m^(1/2)).The steel manufactured using WR was characterized using SEM,EBSD,and TEM at different length scales.Compared to the steel microstructure obtained after hot rolling or cold rolling(CR),this WR TWIP steel exhibits a distinct heterogeneous structure.The matrix has numerous dislocations with twinned coarse grains(approximately 75%) and nearly defect-free recrystallized fine grains(approximately 25%),which form during the reheating period of the WR process.The in situ tensile tests of the WR and CR steels show that the deformed coarse grains provide high yield stress with negligible deformation,whereas the recrystallized fine grains can undergo considerable plastic deformation,which results in a good work hardening capacity during tensile deformation.The fracture toughness tests of the compact tension(C(T)) samples indicate that the recrystallized grains in the WR steel can enhance the crack tip blunting and deflect cracks,which enhance the crack-growth resistance.Alternatively,these toughening mechanisms are not observed in the homogeneous CR steel.Therefore,this heterogeneous structure,which is induced by the high temperature WR process,provides the TWIP steel with excellent strength and toughness.