Wear, 25 (1973) 271-279 0 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands zyxwvutsrqponmlkjihgfedcbaZYXWVUT 271 FACTORS AFFECTING DIE WEAR* A. K. SINGH zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Tata Iron and Steel Co. Ltd., Jamshedpur (India) B. W. ROOKS and S. A. TOBIAS Department of Mechanical Engineering, University of Birmingham (Gt. Britain) (Received March 5, 1973; in final form April 10, 1973) SUMMARY Simple upsetting tests were used to assess the wear of hot forging dies. The influence of forging variables such as die-billet contact time and lubrication is described. A “white” layer is formed at the surface of lubricated dies when die-billet contact times exceed 5 ms. This layer was identified as martensite of increased wear resistance. Lubrication affects the frictional condition at the die-billet interface thus facilitating the relative movement of the billet material over the die surface resulting in the increased wear of flat dies. INTRODUCTION It is generally recognised that damage of hot forging dies can be traced four basic phenomena, each of which can cause eventual die failure. These are: (i) Erosion of the working surfaces (ii) Plastic deformation of protrusions (iii) Thermal fatigue on areas subject to rapid heating and cooling (iv) Mechanical fatigue at fillets, deep recesses and other stress raisers. - to Of these phenomena the first three are a result of high die temperatures during the hot forging process and sliding speed which is influenced by the lubricant. In a forging operation a lubricant is applied to prevent seizure of the die and deforming metal and to provide a low shear strength film to reduce the coefficient of friction between tool and work-piece. Interfacial frictional conditions influence the plastic flow pattern of the deformed billet and, therefore, control the relative sliding motion between billet and die’,‘. These factors may affect the wear of dies to a considerable extent. The effect of temperatures may be reflected in changes in the physical and metallurgical properties of the dies at and near their working surfaces. Reduced hardness and severe temperature gradients may be accompanied by structural changes resulting in reduced resistance to erosive wear and thermal fatigue. * Paper presented at the First World Conference on Industrial Tribology, New Delhi, December, 1972.