轧后冷却路径对中碳钢扩孔性能的影响

EFFECT OF COOLING PATH ON THE HOLE-EXPANSION PROPERTY OF MEDIUM CARBON STEEL

利用超快速冷却技术,通过控制轧后冷却路径,调整不同的终轧温度和终冷温度,研究了冷却路径对热轧后经退火处理的中碳钢组织和扩孔性能的影响.结果表明,通过后续退火处理可以在铁素体基体上形成弥散分布的球化渗碳体组织;随着终轧温度和终冷温度的降低,退火处理后的渗碳体更加细小,且弥散程度提高,在扩孔实验中,当切向延伸率达到材料成形极限时,裂纹优先在冲孔的边缘出现,裂纹主要通过微孔集聚的方式形成;均匀细化的铁素体和球化的渗碳体组织能够明显提高实验钢的延伸率,有效阻止相邻微孔聚合,从而提高材料的扩孔性能.

In the present paper.ultra fast cooling（UFC） technology was applied in the cooling process to treat medium carbon steels after hot strip rolling,and the finish rolling temperature and UFC stop temperature are controlled as the important parameters.The effects of cooling path on the microstructure and hole-expansion property of annealing medium carbon steels were investigated. The results show that finely dispersed spherical cementite could be formed in ferrite matrix after annealing treatment.With decreasing the fininsh rolling temperature and UFC stop temperature,the spheroidized cementites after annealing were more homogeneous and dispersed finely.During holeexpansion test,cracks were observed to form usually in the edge region around the punched hole when the tangential elongation exceeded the forming limit,and cracks are mainly formed in the way of micro-voids coalescence.Fine and homogeneous microstructure comprised of ferrite and spheroidized cementite could improve the elongation of the experimental sheets,suppressing the coalescence of micro-voids,and improving the hole-expansion property.