超高强韧油井管合金设计与高强韧机制

 为了揭示1 000 MPa级低碳加铌钒钛微合金钢的高强韧机制,研究了S1(w(C)=0.09%)与S2(w(C)=0.17%)两种合金成分的油井管钢成分-工艺-组织-性能关系。试验表明,两种成分试验钢经水淬后的组织分别为板条贝氏体加少量马氏体和马氏体加少量贝氏体的复相组织。两种成分钢经过450~600 ℃、30 min的中温回火后,组织中均出现碳化物析出,且S1试验钢回火后的屈服强度基本不变,抗拉强度下降了约70 MPa,S2试验钢回火后的屈服强度与抗拉强度迅速升高170 MPa左右。溶度积公式的计算结果表明,两种钢的水淬组织中铌、钛元素析出彻底且析出物的体积分数都很小,因此回火铁素体基体中的VC析出强化对S1试验钢回火后屈服强度保持不变以及S2试验钢回火后屈服、抗拉强度提高起到重要作用。

Metallurgical design and high strength-toughness mechanism of ultrahigh strength-toughness oil pipeline steel

To reveal the high strength-toughness mechanism of 1 000 MPa low carbon plus Nb,V,Ti oil pipeline steel,the relationship between chemical composition-process-microstructure and performance of two carbon content (S1(w(C)=0.09%) and S2(w(C)=0.17%)) oil pipeline steel was studied. Experiments showed that microstructure of S1 and S2 steel after water quenched were a mixture of lath bainite with a little martensite and martensite with a little lath bainite respectively. After tempered at 450-600 ℃ for 30 min,carbides precipitated in the microstructure of both steels. The yield strength of S1 steel after tempered remain unchanged and tensile strength declined slightly for about 70 MPa. Both the yield strength and tensile strength of S2 steel after tempered increased for 170 MPa. The calculation using solubility product formula showed that alloy elements Nb and Ti were completely precipitated in both steels after quenching,and the volume percent of Nb and Ti precipitations were very low. Therefore precipitation strengthening of VC in ferrite matrix after tempering played an important role in the maintaining of yield strength for S1 steel and the increasing of yield strength and tensile strength for S2 steel.