热处理工艺及Nb微合金化对9Ni钢组织性能的影响

Effect of Heat-treatment Process and Nb Microalloying on Microstructure and Properties of 9Ni Steel

为了适应LNG燃料罐、储罐使用需要,对9Ni钢进行冶炼、轧制关键工艺控制,研究两相区热处理工艺及Nb微合金化对组织性能的影响。结果表明,随着亚温淬火温度的升高,屈服强度、抗拉强度、屈强比先降低后升高。随着回火温度的升高,屈服强度与抗拉强度逐渐降低,伸长率升高;当回火温度为600℃时,屈服强度与抗拉强度达到最低值,伸长率达到最高值。亚温淬火态组织呈现大、小晶粒并存状态,有助于降低钢板屈强比。Nb微合金化9Ni钢板成品组织主要为回火索氏体组织及3%~8%残余奥氏体。0.015%Nb的加入使9Ni钢平均屈服强度提高约50 MPa,抗拉强度提高约40 MPa,-196℃横向夏比V型冲击吸收能提高约40 J。

To meet the use needs of LNG fuel tanks and storage tanks,the key process control of steel-making and rolling of 9Ni steel were carried,and the influence of two-phase area heat-treatment processes and Nb microalloying on microstructure and properties of 9Ni steel was studied.The results show that with the increase of intercritical quenching(IQ)temperature,the Yield stress(YS),tensile strength(TS)and the ratio between YS and TS(Y/T)decreases firstly,then increases.Subsequently as the tempering temperature increases,the YS and TS gradually decrease,while the elongation increases;When the tempering temperature is 600℃,the YS and TS reach their lowest values,and the elongation(EL)reaches its peak.The microstructure after intercritical quenching presents distribution of large and small grains,which contributes to the reduction of Y/T ratio of steel plate.The microstructure of Nb micro-alloyed 9Ni steel plate is mainly composed of tempered sorbite structure and 3%-8%reverse austenite.The addition of 0.015%Nb increases the average YS and TS of 9Ni steel by about 50 MPa and 40 MPa,respectively.The impact absorption energy increases by about 40 J tested at-196℃.