热处理工艺对稀土微合金化1200MPa级高强钢性能的影响研究

Effect of heat treatment on properties of rare earth microalloyed 1200MPa high strength steel

摘要:

结合目前国内以2250mm热连轧生产机组为代表的先进控轧控冷工艺，开发了轧制结束利用加密层流冷却进行分段淬火-等温配分-低温卷取自回火的在线热处理工艺（DQ&P&T），与传统的离线调质热处理工艺（RQ&T）生产稀土微合金化高强钢（Rm≥1200MPa）进行对比研究分析。利用光学显微镜、扫描电子显微镜及配备的电子背散射衍射仪和拉伸试验机、冲击试验机、维氏硬度计，以及湿砂/橡胶轮磨损试验机分析检测手段，系统的分析了试验钢在两种热处理制度下组织转变形态和机械性能。研究表明:试验钢在两种热处理工艺，室温组织均由板条马氏体、贝氏体铁素体以及少量残余奥氏体组成。相比离线热处理（RQ&T），采用在线热处理（DQ&P&T）试验钢的板条马氏体含量降低，贝氏体铁素体含量增加。等温转变形成的贝氏体铁素体穿插分割形变过冷奥氏体，促进组织晶粒尺寸细化和大角度晶界比例增加，提高了材料的强韧性和耐磨性。但在产品厚度方向硬度的均匀性劣于经RQ&T工艺处理的。在线热处理相比离线热处理生产Rm≥1200MPa高强钢效率提高，制造成本降低，且产品各项性能满足标准要求，证明在线热处理工艺是可行的。

Abstract:

In this paper, combined with the advanced controlled rolling and cooling process represented by 2250mm hot continuous rolling production line in China, an on-line heat treatment process (DQ&P&T) is developed, which uses dense laminar flow cooling to conduct sectional quenching, isothermal distribution and low-temperature coil taking from tempering after rolling, and a comparative analysis were made with the traditional off-line quenching and tempering heat treatment process (RQ&T) to produce rare earth microalloyed ultra-high strength steel (Rm≥1200MPa). By means of optical microscope, scanning electron microscope, equipped with electron backscatter diffractometer, tensile testing machine, impact testing machine, Vickers and wet sand/rubber wheel wear testing machine, the microstructure transformation morphology and mechanical properties of the test steels under two heat treatment systems were systematically analyzed. The results show that the microstructure of the test steels at room temperature are composed of lath martensite, bainite ferrite and a small amount of residual austenite under the two heat treatment processes. Compared with off-line heat treatment (RQ&T), the lath martensite content of the steel tested by on-line heat treatment (DQ&P&T) is decreased and the bainite ferrite content is increased. The bainitic ferrite formed by isothermal transformation interposed and divided the deformed undercooled austenite, which promotes the refinement of the grain size and the increase of the proportion of large angle grain boundaries, and improves the strength, toughness and wear resistance of the material, however, the uniformity of hardness in the thickness direction of the product is inferior to that treated by RQ&T process. Relative to off-line heat treatment, the on-line heat treatment has higher efficiency and lower manufacturing cost in the production of high strength steel, and the performance of the product meets the standard requirements, which proves that online heat treatment process is feasible.