The results show that the banded ferrite structure,widmanstatten structure,dendritical microstructure and nonmetallic inclusion which decreasing the toughness of the steel cause the brittle fracture.

• 结果表明,宏观断口为脆性断裂,金相组织不仅有回火索氏体,还包含不应有的带状铁素体、魏氏体组织及明显的枝状晶和非金属夹杂物,从而导致钢的韧性降低。