低合金高强度钢板坯窄面微裂纹产生机理分析和工艺改进

Analysis on Forming Mechanism of Fine Cracks at Narrow Faces of Slab of HSLA Steel and Process Improvement

采用金相分析方法对低合金高强度钢(/%:0.16~0.18C,0.20~0.40Si,1.42~1.55Mn,≤0.025P,≤0.012S,0.015~0.025Nb,0.100~0.115V,0.010 0~0.015 0N)连铸板坯窄面微裂纹的产生机理进行了分析研究。结果表明:板坯窄面表层显微组织不合理如奥氏体晶粒粗大、奥氏体晶界处先共析铁素体膜的形成以及第二相质点在奥氏体晶界处的偏析等是微裂纹产生的机理。通过优化连铸板坯窄面冷却工艺,将窄面冷却水量增加35%;细化了晶粒,抑制了铁素体膜的产生,改变了第二相质点析出,改善了铸坯表层组织,消除了铸坯窄面微裂纹缺陷。

The mechanism of fine crack at narrow faces of slab of HSLA steel(/%:0.16~0.18 C,0.20~0.40 Si,1.42~1.55 Mn,≤0.025 P,≤0.012 S,0.015~0.025 Nb,0.100~0.115 V,0.010~0.015 ON)was analyzed and researched by the means of metallographic analysis.The results show that the mechanism of fine crack is unreasonable microstructure of surface of slab narrow faces,such as coarse austenite grain,as well as formation of pre-eutetoid ferrite film and segregation of the second phase particle at the austenite grain boundaries.By optimization of cooling process i.e.increasing narrow face cooling water rate by 35%,the austenite grains are fine,the formation of ferrite film is suppressed and the participation of second phase particle is changed as well as the surface structure of slab is improved,the defect of fine crack at narrow faces of slab is eliminated.