O,N和Ni含量对0Cr25Ni7Mo4N双相不锈钢热轧塑性的影响

EFFECTS OF O,N AND Ni CONTENTS ON HOT PLASTICITY OF 0Cr25Ni7Mo4N DUPLEX STAINLESS STEEL

对不同O,N和Ni含量的0Cr25Ni7Mo4N双相不锈钢进行了1200℃,4道次热轧实验.利用OM,SEM和EBSD观察分析了实验钢的组织和夹杂物.结果表明,低O,N和Ni含量的实验钢热轧塑性良好.O含量为0.0059%的实验钢中夹杂物主要为Al2O3和MgO·Al2O3,分布于晶粒内部,未对热塑性造成不良影响.O含量为0.038%和0.046%的实验钢则发生了轧制边裂,开裂处为a/g相界,相界内的大颗粒Cr2O3和MnO2夹杂是造成开裂的主要原因.其中O含量较低(0.038%)的实验钢,由于N和Ni含量过高,使钢中g相体积分数在热轧状态时高达60%.过多的g相降低了g晶粒内部的总应变量,使其不足以发生再结晶软化,最终造成更严重的热轧开裂.

In order to identity the effect of narrow composition control on the hot plasticity of duplex stain- less steel, hot rolling test of OCr25Ni7Mo4N steels with various oxygen, nitrogen and nickel contents were per- formed at 1200 ℃ for 4 steps. The microstructures and inclusions were observed by OM, SEM and EBSD. The steels with the lowest oxygen, nitrogen and nickel contents showed excellent hot plasticity. The inclusions in the steel with 0.0059% oxygen were mainly Al2O3 and MgO Al2O3, which distributed in the grain interior and did no harm to the hot plasticity of the steel. The steels containing 0.038% and 0.046% oxygen actually cracked at the sheet edge during hot rolling, which resulted from the large inclusion particles of Al2O3 and MnO： at the a/y bound- ary. Furthermore, the reason for more serious cracking occurred in the steel containing 0.038% oxygen than that containing 0.046% oxygen was its relatively higher contents of nitrogen and nickel, making γ, volume fraction of the steel as high as 60% in the hot rolling state. Excessive γreduced its total strain, so that the inadequate stain did not induce the recrvstallization of γphase, which resulted in hot rolling cracking finally.