抄録
Microstructure and tempering behavior of rapidly solidified layer formed by laser surface melting has been investigated in high C-high alloy tool steels SKH51 and SKD11, and medium C-medium alloy tool steel SKD62.
In SKH51 and SKD11 which contain a large amount of primary carbides even after conventional quenching, solution of alloying elements is promoted by rapid solidification. This results in formation of supersaturated martensite in SKH51 and meta-stable austenite in SKD11.
Subsequent heat treatment at 550°C of rapidly solidified layer leads to extremely high secondary hardening to HV 1100 in SKH51, probably because of the increase of the amount of carbides precipitation.
Heat treatment of rapidly solidified SKD11 at 600°C also leads to hardening from HV500 to HV750 because of decomposition of meta-stable austenite to ferrite+carbide phase and martensite.
In SKD62 in which carbides are almost dissolved in matrix even in conventional quenching, substructure and tempering behavior of rapidly solidified layer is similar to conventionally quenched one.
