Characterization of Impact Toughness Properties of DIN39MnCrB6-2 Steel Grade

Boron added steels in quenched and tempered condition have been widely used in applications where good mechanical properties and low cost are required. In this study, impact resistance of DIN 39MnCrB6-2 steel grade was investigated due to its criticality in automotive components. Metastable phase diagrams were built to guide heat treatments. The influence heat treatment parameters and initial microstructure were evaluated. Impact toughness results showed low absorbed energy (<30J) for all tempering temperatures. CVN impact toughness was substantially increased in samples submitted to solution treatment. Microscopic observation showed coarse borocarbides in surface fracture of Q&T samples. It was concluded that the formation of borocarbides is inherent in boron steels and their coarse morphology should be avoided in order to reduce embrittlement.

经调质（quenched and tempered, Q&T）处理的含硼钢已广泛应用于兼具优异力学性能与低成本要求的工程场景。本研究针对汽车零部件中应用关键的DIN 39MnCrB6-2钢种，开展了其冲击性能的相关研究。研究构建了亚稳相图以指导热处理工艺制定，并评估了热处理参数与初始显微组织对材料性能的影响。冲击韧性测试结果显示，所有回火温度下的试样均表现出较低的冲击吸收功（<30J）。经固溶处理后的试样，其夏比V形缺口（Charpy V-notch, CVN）冲击韧性得到显著提升。显微观测发现，调质（Q&T）试样的断口表面存在粗大硼碳化物。研究得出结论：硼碳化物的形成是含硼钢的固有特性，为降低材料脆化风险，应避免其形成粗大形貌。