THIXOFORMING TECHNOLOGY OF HIGH CARBON X210CrW12 STEEL

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 degrees 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 degrees 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 mu m 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.