The influence of the arc plasma treatment on the structure and microhardness C120U carbon tool steel

The examination of the structure and microhardness of surface layer of C120 U carbon tool steel after arc treatment are presented in the paper. They are compared with the properties obtained after conventional hardening. The GTAW (Gas Tungsten Arc Welding) method was used. The remelted zone consists of dendritic cells and columnar crystals. Inside the columnar crystals dependent to current arc plasma intensity the martensite or lower bainite was observed. The cooling rate of the remelted zone is similar to the cooling rate obtained in the classical heat treatment. The maximum hardness 650 HV0,1 was measured in material after treatment with a smaller current intensity of arc plasma – 60A. Increases of the current intensity of arc plasma from 60 A to 110 A (for fixed speed rate of source) lead to increases the depth of the remelted zone from 1,2 to 3,1 mm. Thickness of the heat affected zone in the all specimens was similar (1,9 to 2,1 mm).