硅酸盐夹杂在集装箱底侧梁脆性开裂过程中的作用

Role of silicate inclusion in brittle cracking process of bottom side rail of container

某集装箱底侧梁在正常使用过程中发生开裂,事故发生时箱内载重未超过箱体允许的承重极限。通过对开裂的底侧梁进行化学成分光谱分析、拉伸及冲击性能测试、梁正常部位及断口毗邻区域金相检验、断口分析以及夹杂物综合分析等,分析了底侧梁开裂的原因,研究并解释了夹杂物在开裂过程中所起的作用。检验及分析结果表明,底侧梁钢板强韧性低下,且表面脱碳,存在表面强度进一步低于基体的现象,在服役过程中导致裂纹易于在表面萌生。酸溶铝(Als)含量极低,这也导致钢板存在较高的韧脆转变温度,服役过程中存在较大的安全隐患。同时钢板内存在大量大尺寸的MnO-SiO2-Al2O3系和CaO-SiO2-Al2O3系硅酸盐塑性夹杂,该夹杂在热加工过程中被严重拉长,分布于晶界和晶内,严重破坏了钢材基体连续性,导致其强韧性低下并促进了裂纹的扩展。服役过程中底侧梁R角处作为应力集中部位首先发生开裂,进而裂纹以沿晶+穿晶解理的方式快速扩展,最终脆性开裂。

The bottom side rail of one container was cracked in normal service condition.The load in container did not exceed the allowable weight limit when the accident occurred.The cracked bottom side rail was characterized by chemical composition spectral analysis,tensile and impact property test,metallographic examination of normal position and fracture-adjacent region,fracture analysis and comprehensive analysis of inclusions.The cracking reasons of bottom side rail analyzed.The role of inclusions in cracking process was studied and explained.The examination and analysis results showed that the obdurability of bottom side rail steel sheet was low.Moreover,the surface decarburization was observed.The surface strength was further lower than that of matrix.As a result,the cracks were easily initiated on surface in the course of service.The content of acid soluble aluminum(Als)was very low,leading to high ductile-brittle transition temperature of steel sheet.Therefore,great safety risk existed in the course of service.Meanwhile,there were a lot of large-size MnO-SiO2-Al2O3 and CaO-SiO2-Al2O3 plastic silicate inclusions in steel sheet.These inclusions were severely stretched in hot-working process and distributed in grain boundary and grains,which seriously destroyed the continuity of steel matrix,leading to the low obdurability and the expansion of cracks.The R angle was the stress concentration position of bottom side rail in the course of service and firstly cracked.Then the cracks were rapidly extended in the mode of intergranular fracture and transgranular cleavage,and finally causing brittle cracking.