回火温度对高强海洋平台钢组织和性能的影响

Effect of tempering temperature on microstructure and properties of high-strength offshore platform steel

对自制的高强海洋平台用合金钢850℃油淬后进行200~650℃×2 h回火处理,研究了回火温度对试验钢显微组织和力学性能的影响。结果表明：随回火温度的升高,试验钢的淬火组织逐渐转变为回火马氏体、回火屈氏体和回火索氏体;强度和硬度逐渐下降,但与抗拉强度相比,上屈服强度下降得更慢些,塑性总体呈现升高趋势。600℃回火试样拉伸过程中出现屈服平台,继续提高回火温度,屈服现象更明显。冲击性能随回火温度的升高先下降后上升,在300~500℃范围内出现明显的回火脆性。当回火温度为600℃时强韧性匹配最好,抗拉强度840 MPa,上屈服强度760 MPa,断后伸长率17%,-40℃冲击吸收能量175 J。

The effect of tempering temperature on microstructure and properties of selfmade high-strength offshore platform alloy steel was studied. All samples were austenitized at 850 ℃ for 30 min followed by oil quenching,and then tempered at different temperatures ranging from 200 ℃ to 650 ℃ for 2 h,respectively. The results show that with the tempering temperature increasing,the as-quenched microstructure of the tested steel transforms to tempered martensite,tempered troostite and tempered sorbite in turn. The strength and hardness gradually decrease,but the upper yield strength decreases at a lower rate compared with that for the ultimate tensile strength,and the ductility shows a mainly increasing tendency. Yield point elongation begins to appear for the testing steel tempered at 600 ℃ during tensile test,and this phenomenon is more obvious by increasing the tempering temperature continually. The impact property initially decreases and then increases with the tempering temperature increasing,and obvious temper brittleness appears at 300-500 ℃. The best strength and toughness are achieved when the tempering temperature is 600 ℃,the tensile strength and upper yield strength reach 840 MPa and 760 MPa,respectively,the elongation reaches 17%,and the impact absorbed energy at-40 ℃ reaches 175 J.