Cold and hot deformation and densification studies on sintered Fe-C-Cr-Ni low alloy P/M steels

Abstract

The present research work pertains to the study of the densification behaviour of sintered low alloy P/M steels with Ni and Cr during cold and hot deformation processing. Elemental powders of atomized iron, graphite, chromium and nickel were mixed in suitable proportions using a ball mill, compacted and sintered in order to yield the following alloy compositions: Fe-0.2% C, Fe-0.2% C-1% Cr, Fe-0.2% C-2% Cr and Fe-0.2% C-1% Cr-2% Ni. The compaction was performed in a 1000 kN hydraulic press using suitable cylindrical die-punch combination. Sintering of the ceramic-coated cylindrical preforms was carried out at 1000 ± 10°C in a muffle furnace for a period of 180 minutes. Cold and hot upsetting studies on the sintered preforms were undertaken in order to study the densification and plastic deformation behaviour of the low alloy P/M preforms under various applied loads. Further, microstructural analysis was done on the cold and hot worked alloy preforms in order to correlate the deformation behaviour with the metallurgical structure of the alloys. Among the various alloys under consideration, the plain carbon steel preforms exhibit better densification and deformation behaviour under hot upsetting. The addition of Ni and Cr as alloying elements to the plain carbon steel preforms promotes better densification characteristics during cold upsetting. However, the deformation of the alloy preforms with Ni and Cr is found to be sluggish compared to that of the plain carbon steel preforms. So, it is contended that the presence of carbide phase in the case of alloy steel preforms containing Ni and Cr additions strongly influences the deformation behaviour of alloy preforms.