Densification behaviour in forming of sintered iron–0.35% carbon powder metallurgy preform during cold upsetting

Plastic deformation is an important process to improve and obtain final product for sintered powder materials to compete with solid metal formed parts. The densification behaviour and forming limits of sintered iron–0.35% carbon steel preforms with different aspect ratios, during cold upsetting with two different lubricating constraints namely nil/no and graphite lubricant were investigated experimentally and is presented in this work. Powder preforms having initial theoretical density value of 84%, with two different aspect ratios were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press. Sintering operation was carried in an electric muffle furnace at the temperature of 1200 °C for a holding period of 1.5 h. Each sintered compact was subjected to incremental compressive loading of 0.05 MN under two different lubricant conditions till a visible crack appeared at the free surface. The densification mechanism is developed by studying the behaviour of densification against induced strain and Poisson’s ratio. Further, attained density is considered to establish flow stress and formability stress index behaviour. Increased frictional constraints produces high circumferential stress on the free surface due to barreling effect and hence inhibits forming limits. The present work provides a guideline for producing P/M components free from open surface pores.