Estimation of temperature in the lubricant film during cold forging of stainless steel based on studies of phase transformation in the films

摘要

Changes in friction during backward can extrusion of stainless steel was observed for four different lubricant systems. The observed changes in friction are believed to be caused by phase transitions in the lubricant. The lubricant systemsconsisted of two different carrier coatings (crystalline Zn{sub}3(PO{sub}4){sub}2·4H{sub}2O and amorphous Zn{sub}1.5Ca{sub}1.5(PO{sub}4){sub}2) lubricated with soap or MoS{sub}2. The temperature in the lubricant film during the process was estimated from changes in friction in correlation with observed phase transitions in the lubricant. Phase transitions in the carrier coatings as a function of pressure and temperature were investigated. Several previously unknown phase transitions were discovered. Fourdifferent crystal structures of Zn{sub}3(PO{sub}4){sub}2·xH{sub}2O were observed as a function of temperature. At 700-900℃ Zn{sub}3(PO{sub}4){sub}2 becomes amorphous (depending on the pressure). Amorphous Zn{sub}1.5Ca{sub}1.5(PO{sub}4){sub}2crystallises at 200-300℃ and a second phase transition is observed at 400-700℃ (depending on the pressure). It is estimated on the basis of the results from the backward can extrusion and analysis of the structure as a function of temperature that thetemperature may reach in the excess of 450℃ at a height/diameter ratio of two.