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 systems consisted of two different carrier Ε½ Ε½ . Ε½ .. coatings crystalline Zn PO P 4H O and amorphous Zn Ca PO lubricated with soap or MoS . The temperature in the lubricant 3 4 2 2 1 . 5 1 . 5 4 2 2 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 Ε½ . transitions were discovered. Four different crystal structures of Zn PO P x H O were observed as a function of temperature. At 3 4 2 2 Ε½ . Ε½ . Ε½ . 700-9008C Zn PO becomes amorphous depending on the pressure . Amorphous Zn Ca PO crystallises at 200-3008C and a 3 4 2 1.5 1.5 4 2
Ε½ . second phase transition is observed at 400-7008C 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 the temperature may reach in the excess of 4508C at a heightrdiameter ratio of two.