Q420qD桥梁板冲击性能不合原因分析及改进措施

Cause analysis of unqualified impact performance of Q420qD bridge plate and its countermeasures

针对河北普阳钢铁有限公司3 500 mm产线生产的25 mm厚Q420qD桥梁板低温冲击性能不合的问题,通过对钢板化学成分、轧制工艺和金相组织的分析,发现精轧终轧温度过低,进入两相区轧制而形成沿晶界连续分布的铁素体网及混晶组织是导致钢板冲击不合的主要原因。通过降低Q420qD板坯出炉温度,以细化板坯的原始奥氏体晶粒,并提高精轧终轧温度到Ar;温度以上,避开两相区轧制,改善了钢板组织形态,使桥梁板低温冲击性能得到明显提高,满足标准要求。

To the problem of unqualified low temperature impact performance of Q420 qD bridge plate with thickness of 25 mm produced in 3 500 mm production line in Hebei Puyang Iron and Steel Co., Ltd., the chemical composition, rolling process and metallographic microstructure of plate were analyzed. The results show that the final rolling temperature of finishing rolling is too low, and the ferrite network continuously distributed along the grain boundary and the mixed crystal structure formed by rolling into the two-phase zone are the main reasons of the unqualified impact performance of the plate. By reducing the tapping temperature of Q420 qD slabs, the original austenite grains of the slab are refined, and the final temperature of the finishing rolling is increased to above the Ar;temperature to avoid rolling in the two-phase zone, the microstructure of the plate are improved, so that the low temperature impact performance of the bridge plate has been significantly improved to meet the standard requirements.