Transformation process of weld heat-affected zone in solution-strengthened ferritic ductile cast iron

Abstract

The purpose of this study was to examine the weldability of Si-solution-strengthened ferritic ductile cast iron (SSFDI: ENGJS-500-14) compared with a traditional ferrite-pearlite type ductile cast iron of similar strength (JIS-FCD500-7). The a þgraphite!g reverse transformation characteristics on heating process and the transformation characteristics on cooling were investigated by the synthetic weld thermal cycle method. Heating SSFDI at 300°C s-1 (200-800°C), the reverse transformation started at 8378C and finished at 1149°C. The austenite arose around graphite nodules and the fraction in the matrix moderately increased to 100% as the temperature became higher. In the ferrite-pearlite type ductile cast iron FCD500 with 2.27%Si, the reverse transformation occurred in the temperature range from 7638C to 11058C. The pearlite rapidly transformed to austenite and then the ferrite moderately transformed. The austenitization rate of SSFDI was also lower than the ferrite-pearlite type ductile cast iron at 1000°C. In the case of the cooling parameter t8/5 ¼ 25 s, the martensite area fraction increased as the maximum temperature rose. Less martensite appears in SSFDI, indicating arc welding would give rise to less brittle heat-affected zone un SSFDI.