Effects of alloying elements on transformation behaviour for synthetic weld heat-affected zone of steels (II)

Effect of Si on SH-CCT diagram for Welding

Abstract

The effect of Si on transformation behaviour in synthetic weld heat-affected zone of steel was investi-gated using simplified steels made of pure metals and graphite.
Si element did not almost influence ferrite transformation region in SH-CCT diagram for welding, and displaced slightly pearlite transformation region to a longer time and to a higher reaction temperature. Zw (Zwischenstufengefüge) rmat transformationregion was present on the side of very short time regardless of Si content, and existed to longer time in case of higher Si content. Cz' which is critical cooling time to obtain from SH-CCT diagram for welding could not measure because Cz' was too small. Cf' was a little influenced by Si, and it was small. Cp' and Ce' increased with Si content.
In the region of middle cooling time (cooling time from A₃ to 500°C; 6-60 sec), massive ferrite grew slightly large, and Zw precipitated easily with Si content. Morphology of Zw appeared that austenite between both ferrite sideplates or both rodlike ferrites decomposed to ferrite and relative large cementite. In the region of shorter cooling time (cooling time from A₃ to 500°C; under 6 sec), ferrite grew to long ferrite sideplate and long needlelike ferrite by Si content, and morphology of pearlite was influenced by Si, too. Degenerate pearlite formation was difficult with Si, and the volume of pearlite was decreased by Si content increased.
The hardness of martensite was not so influenced by Si. The hardenability curves in synthetic weld affected zone of steels raised with Si content, but Si above 1.0% did not influenced to the hardenability curves. heat-Though Si diplaced slightly longer the cooling time which hardness was rapidly decrease, it seems that Si dose not strongly influence to hardenability of weld heat-affected zone of steels.