This work considers the influences of various types of die surface treatment, lubricants and temperature on friction for hot forging process of brass. Well-known ring compression test were carried out to evaluate friction coefficient for various conditions. Tool material was hot work tool steel H13 and workpiece material was brass C3771. Tool surface condition selected were normal hardening, treated by hard chrome, plasma nitriding and vacuum nitriding. Tests were conducted with and without lubricants at elevated temperature between 400–600°C. The results of experiments without lubricant show that friction coefficient is reduced when using die with treated surface regardless of working temperature. The influences of surface treated on die are not significant when forming under lubricated condition. In other word, lubricant has minor effect to reduce friction when the treated tools are employed. However, graphite in water was found to be almost compatible lubricant to graphite in oil when forming by tool which is treated by vacuum nitriding. The hardness and roughness of tool surfaces are found no relevance to friction coefficient in this work.

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