METHOD FOR HARDENING OF INSIDE SURFACE OF STEEL PIPE BY PLASMA JET

摘要

PURPOSE:To obtain the inside surface of a steel pipe having constant hardness by injecting plasma jets generated under prescribed conditions and remelting the inside surface of the steel pipe successively. CONSTITUTION:Plasma jets 3 are generated from a jet torch 2 in the conditions of a shielding gas of Ar contg. 5-20% H2, a plasma gas of pure Ar, 1-2l/min. flow rate of gas, and 100-400A current. This torch 2 is disposed in a pipe and is moved in the axial direction of a revolving steel pipe 1, whereby the inside surface of the pipe 1 opposite to the jets 3 are remelted successively, and a molten layer having constant thickness by deep penetration is obtained. In this way, the hardenes of the surface of the pipe solidified after the melting is made constant.