Thixoforming technology of high carbon X210CrW12 steel

Abstract

Several samples were cast using thixoforming method. The feedstock used was a hot rolled commercial bar of the steel X210CrW12 with the following chemical composition: 2,11%C, 10,5%Cr, 0,7%W, 0,4%Si. An apparatus was constructed allowing the thixoforming of steel parts in a protective argon atmosphere and at a high piston velocity powered by a high pressure air. It was designed and built in such a way to allow first pumping air out and argon in, fast heating of a feedstock using high frequency generator, stamping of semi liquid sample at a high piston rate of a few m/s with in earlier resistance heated mould and simultaneous control of sample and mould temperature to ±1°C. The liquid fraction was determined using Differential Scanning Calorimetry (DSC). Observation of the microstructure was performed using optical and transmission electron microscopy. It showed a globular structure in the material, when pre-heated to the temperature of 1230°C at a liquid fraction of 30%. After several experiments with various sample and mould temperatures, a desired globular microstructure after a thixoforming process was obtained. Basic technological parameters which permit the complete filling of the die and a useful microstructure, such as piston velocity, temperature of the die, were elaborated. The microstructure after the thixoforming process showed globular structures with a size of 50 to 200 µm of the oval particles of the austenite within an eutectic matrix. The crystal structure of globules was mainly austenite and that of the eutectic ferrite and M7C3 carbide.