Abstract: The controlled rolling and cooling test was conducted on V-N-Cr microalloyed low carbon steel. There are three cooling mode, including cooling with furnace, cooling with insulation quilt, and air cooling, and the microstructure, mechanical properties and fracture morphology of three kinds of cooling system were analyzed. The results that show the fine polygonal ferrite and acicular ferrite multiphase structure were obtained in air cooling steel plate. The grain size of ferrite is 5 to 8 pim. Acicular ferrite consists of interwoven laths with width of 1 to 3μm. The tempering occurred in polygonal ferrite and acicular ferrite, and small dispersed carbides were precipitated due to the slow cooling rate in cooling with furnace and cooling with insulation quilt. Under three kinds of cooling conditions, the yield strength ≥585 MPa, tensile strength ≥ 694 MPa, elongation ≥ 27% , and 1/2 sample impact toughness at -60 °C ≥36 J are obtained. The comprehensive mechanical properties is better than GB requirements of Q550F grade. Fine grain strengthening, precipitation strengthening, and microstructural strengthening were the main ways to strengthen the steel. The impact fracture are composed of dimples, exhibiting toughness fracture mode. The grain refinement and acicular ferrite formation caused by controlled rolling and cooling effectively resist the propagation of cleavage cracks, enhancing the low temperature toughness.

Key words:  , V-N-Cr Microalloying, Controled Rolling and Cooling, Q550E, Acicular Ferrite, Strength and Toughness

摘要： 对低碳V-N-Cr微合金化钢进行了控轧控冷实验,终冷后采用了随炉冷、保温毡缓冷、空冷3种冷却制度,并对3种不同冷却制度钢板进行了显微组织、综合力学性能和断口形貌的分析。研究表明,空冷钢板显微组织为细小多边形铁素体及针状铁素体复相组织,铁素体晶粒尺寸5～8μm,针状铁素体由交织的板条组成,宽度1～3μm。在随炉冷及保温毡缓冷时,由于冷却速率缓慢,多边形铁素体及针状铁素体发生了回火,并析出细小弥散的碳化物。3种冷却条件下,屈服强度均≥585 MPa,抗拉强度≥694 MPa,延伸率≥27%,而且1/2试样-60℃冲击功≥36 J,综合力学性能优于Q550F级国标要求。细晶强化、析出强化、组织强化为本钢种的主要强化方式,冲击断口均由韧窝组成,呈现韧性断裂模式,控轧控冷引起的晶粒细化及针状铁素体的形成有效阻碍解理裂纹的扩展,从而增强低温韧性。