Effect of Secondary cooling on microstructures in a rapidly solidified high Cr stainless steel strip

The rapid solidification process, which omits the hot rolling stage, was employed for the production of a thin strip made of materials which typically have poor workability. The process required the solidified strip to be cooled carefully so that embrittlement or recrystalization did not occur: 30Cr-14Ni stainless steel, solidified to a thin strip by a twin roll easter, was subjected to another cooling (secondary cooling) before coiling. The transition of strip temperatures during the cooling was estimated both by measurement and by calculation. From the experimentally observed relationship between the heat treatment and embrittlement. the optimum condition for the secondary cooling was obtained. Experiments showed that the strip became embrittled when it was subjected to 930 K for 5 min. Therefore the cast strip was passed through the secondary cooling zone of water jets. The coiling temperature was kept below 700 K and no embrittlement was observed. As a result, a strip was delivered as an overlay welding material on a semi-commercial basis.