Development of Cast-iron/Steel Composite by Fusion Welding

Cast iron with nodular graphite was surface welded on 12mm thick,150mm and 350mm wide,and 600mm long SS400 plates,by self-shielded gas arc welding method. Instead of ordinary preheating,the heat-flows from multiple weld beads were accumulated to raise the temperature of welding zone. For the purpose,the parallel beads were laterally reciprocated at a small bead pitch of 3mm. The effect of welding heat-cycle on the microstructure and mechanical properties of the deposited metal was investigated,changing the reciprocating length, 110mm and 310mm. Main results obtained were as follows;(1) The influence of the heat-flows from preceding and following weld beads on the structure of deposited metals were composed of two major parts. They were the influence of slow cooling,and that of annealing effect on the rapidly-cooled deposited metal. (2) With the short welding heat cycle on the 150mm wide specimen,the molten metal was kept in a temperature range higher than 1500K with a small fluctuation,and cooled slowly resulting bull's-eyes structure with small amount of cementite. (3) With the long heat cycle on the 350mm wide specimen, the deposited metal was rapidly cooled. Following rapid cooling, the temperature of the deposited metal was sharply fluctuated with lower end below 1200K,as the subsequent beads approached and departed,resulting many small graphite nodules in the ferrite matrix. (4) Except the 1st bead, low dilutions resulted from the small bead pitch.