Mechanical Properties and Microstructures of Warm-Extruded Carbon Steels

The main advantages of warm forging have been thought to be in that products are worked more precisely by warm forging than by hot forging, under a lower deformation pressure than by cold forging. However, little attention has been given to the mechanical properties of warm-forged products. It is necessary to have a fuller understanding of the effects of the working conditions on the mechanical properties of warm-forged products for applications of warm forging, because warm-forged products have various mechanical properties according to the working conditions. Therefore plain carbon steels containing 0.20% C to 0.53% C have been extruded in the temperature range from 300°C to 900°C with reductions of 40, 60 and 80% in cross-sectional in order to investigate the effects of working temperature, reduction of area and carbon content on the mechanical properties and microstructures of the products.The results obtained were as follows:(1) Tensile strength, elongation and hardness of products varied rather regularly with carbon content and working temperature. But they were not greatly influenced by the reduction of area.(2) The impact values varied in a complex manner with the combination of carbon content, working temperature and reduction of area. The impact values of products extruded with high sectional reductions in area increased remarkably even at lower working temperatures.(3) The increase in impact values of warm-extruded low carbon steels seems to be due to the recovery and recrystallization of ferrite, while medium carbon steels seems to increase their impact values due to the fibrous pearlite formed by extrusion in addition to the recovery and recrystallization of ferrite.