热处理工艺对高强度含铜9Ni钢组织和性能的影响

来源期刊：钢铁2011年第7期

论文作者：张怀征 刘东升

文章页码：79 - 85

关键词：含铜9Ni钢； QLT处理； 显微组织； 高强度； 深冷韧性

Key words：copper containing 9Ni steel； QLT heat treatment； microstructure； high strength； cryogenic toughness

摘    要：随着液化天然气(LNG)储罐朝着大型化发展,在不增加容器壁厚的情况下,必须提高钢板强度。在传统9Ni钢中添加Cu,通过析出强化,使其强度水平得到显著提高。提出一种新型含1.25%Cu(质量分数)9Ni钢。试验钢经过控轧直接淬火(DQ);研究了DQ材料分别经过1)QLT(奥氏体(γ)单相区淬火(Q)+两相区(α+γ)淬火(L)+回火(T))和2)DQ-LT(直接两相区淬火+回火)热处理时的显微组织和性能;考察了QLT处理试验钢在单道和双道次焊接条件下粗晶热影响区(CGHAZ)的性能和断口形貌。采用光镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和XRD鉴定了材料的组织特征。测试了室温拉伸性能和深冷条件下(-196℃)夏比冲击吸收能量(AKV)。试验钢经QLT(t_L=635℃)处理,奥氏体体积分数为13.5%,屈服强度R_p0.2=718 MPa,总延伸率23%,-196℃下AKV为130 J;CGHAZ在-196℃时的AKV达到66J。

Abstract: The increase in the size of LNG-tanks leads to mandatory requirement of strengthening of 9Ni steel plates which enables the thickness of the wall without being increased.The strength of the 9Ni steel is markedly increased by the Cu addition due to precipitation of finely dispersed Cu particles.A 9Ni steel with 1.25 pct(mass fraction) copper addition was proposed.The experimental steel plates were processed by controlled-rolling and direct-quenching(DQ).The DQ treated plates were further heat treated,respectively,by 1) QLT,i.e.,quenching from austenite(γ) single phase(Q) followed by reheating and quenching from two phase(α+γ) region(L) and tempering(T),and 2) DQ-LT,i.e.,quenching from α+γ region and tempering after the controlled rolling.The thermal conditions of the CGHAZ in the QLT treated samples were simulated.The mechanical properties of the CGHAZ and fractographs were examined.The microstructures were analyzed employing optical microscope(OM),scanning electronic microscope(SEM) and transmission electronic microscope(TEM).The volume fraction of austenite was detected by XRD technique.Tensile properties were tested at room temperature while the Charpy V notch impact energy(AKV) was measured at a cryogenic condition of -196 ℃.The volume fraction of austenite in the QLT(t_L=635℃) treated steel was 13.5%.The yield strength(R_p0.2) reached 718 MPa,the AKV was 130 J.Sufficient cryogenic toughness(AKV at 66 J) was achieved in the CGHAZ by double-pass welding operations.