The Study And Control Of Metastable Phase In High Speed Steel As-Cast Strip

The twin-roll cast strip technology was considered as the newest one in the 21st century. It could change the melt metal into semi-finished or finished products directly, and had the obvious advantages in comparison with the traditional one. It was the trend of the thin steel production and the key technology to make the iron and steel enterprises modernized.The microstructure of the high speed steel (HSS for short) produced by the twin-roll caster with rapid solidification in lab was analysized. The laws that the effects aroused from the different heat-treatment were explored. The experiments of quantitative analysis and TEM showed that rapid solidification could refine the eutectic carbides in HSS, improve the distribution of the eutectic carbides. Heat-treatment could refine the carbides in HSS as-cast strip and improve the distribution of the eutectic carbides various degrees, and eliminate the eutectic carbides nets in HSS. At last the conclusion that the rational heat-treatment of HSS as-cast strip in lab was at 1200C, held time lh, was obtained.To speed up the course of industrialization of HSS in twin-roll cast strip technology, the heat-treatment and heat-deformation experiments were adopted based on the former work. The effects of heat-treatment and heat-deformation on the eutectic carbides in HSS as-cast strip in industrialization were studied. The experiments of quantitative analysis and TEM showed that the faster cooling rate was, the finer the carbides grain and space between two carbides were. The finer carbides decomposed more easily. Comparing the effects of the different heat-treatment and heat-deformation on the carbides showed the rational treatment of HSS as-cast strip in industrialization was at 1200C, held time 40min before carrying amount for 50% reduction heat-deformation. It could make the carbides decomposed greatly in heat-treatment and realize the carbides decomposed further in heat-deformation, get the best microstructure in as-cast strip.At last the effects of the treatment on the carbides in two different stages and studied the forming of metastable carbides in rapid solidification and its decomposing in heat-treatment were combined. The measures to prevent the new carbides fromabnormally growing up and spheroidizing were put forward.