BEHAVIOR OF TRACE BISMUTH IN WELDED JOINT OF NODULAR CAST IRON AND DEVELOPMENT OF ZU238F COVERED ELECTRODE

The effect of trace bismuth in the weld and fusion zone of nodular cast iron on the nodulizing,graphitization and ferrite forming has been investigated.The results show that trace Bi increases strongly the number of graphite nodules and nodulizing stability,promotes the forming of ferrite,and effectively decreases or even eliminates the cementite in the weld and partial melting region.Therefore,the crack resistance and mechanical property are improved greatly in no-preheat welded joints.If the Bi content is 100~120 ppm,the no-preheat welds can attain a first or second grade of nodulizing,containing 80~95% ferrite but no cementite,with tensile strength-σ_b=540 MPa and elongation-δ=5.7%.As a result,a new type of covered electrode "ZU238F" containing Bi with high crack resistance and good mechanical property has been developed.This type of electrode has been satisfacto rily used in welding.