Effects of Alloying Elements on Transformation Behaviour for Synthetic Weld Heat-Affected Zone of Steels (IV)

Effect of Cr on SH-CCT diagram for welding

Abstract

The effect of Cr on transformation behaviour in synthetic weld heat-affected zone of steel was investigated using simplified steels made of pure metals and graphite. Cr element displaced ferrite and pearlite transformation regions to a longer time, and extended Zwischenstufengefüge (Zw) transformation region to a longer time in the SH-CCT diagram for welding. Each critical cooling time Cf', Cp' and Ce' increased with Cr content. Cz' was very small value.
Morphologies of ferrite, pearlite and Zw were strongly influenced by Cr. In the region of longer cooling time (cooling time from A₃ to 500°C; above 60 sec), the growth of massive ferrite and ferrite sawteeth were controlled by the addition of Cr. Rodlike ferrite did not precipitate in austenite grain at 0.09%C-3.86%Cr steel which was most amount of Cr in this study. According to the addition of Cr, degenerate pearlite and fine colony pearlite precipitated more easily than lamellar pearlite. In the region of middle and shorter cooling time (cooling time; under 60 see), ferrite sideplate and rodlike ferrite or needlelike ferrite were more liable to develop with Cr than massive ferrite and ferrite sawteeth, and fine colony pearlite formed more easily than other pearlite. Zw accompanied with fine carbide precipitated easily in these region of cooling time by the addition of Cr.
Cr element raised the hardenability curves in synthetic weld heat-affected zone of steels. It seems that the hardness is influenced considerably by the morphological change of microstracture. The effect of Cr on the hardness of martensite was a little.