Effect of Temperature and Strain Rate on Deformation Behavior of Invar 36 Alloy

Since the thermal expansion coefficient of Invar 36 alloy is so low that it matches the composite materials well. It is very suitable as the material of composite material forming mould. Invar 36 alloy mould surface is usually produced by hot pressing technology. The hot pressing temperature and strain rate severely affect the quality of mould surface. In this work, the mechanical properties of Invar 36 alloy were studied in the temperature range from room temperature to 900. under different initial strain rates (8x10(-5), 8x10(-4) and 8x10(-3) s(-1)) by using uniaxial tensile tests. The effect of temperature on the springback trend of thick Invar 36 alloy sheet by three-point bending tests at room temperature, 600. and 800. was investigated. The results indicate that the yield strength and ultimate tensile strength of Invar 36 alloy significantly decrease with increasing temperature. Meanwhile, the elongation firstly increases and then decreases with the increase of temperature. It reaches a peak value of 69.2% at 600. and increases by 55% than that at ambient temperature, which mainly results from the plasticity improvement by dynamic recrystallization. Invar 36 alloy at lower temperature (room temperature and 500 degrees C.) shows insensitive to the strain rate. Nevertheless, the strength and plasticity at 800 degrees C. substantially decrease with decreasing strain rate. When the strain rate decreases from 8x10(-3)s(-1) to 8x10(-5)s(-1), the yield strength, ultimate tensile strength and elongation reduce by 38%, 47% and 50%, respectively. The three-point bending springback value decreases by 87.0% when the tested temperature increases from room temperature to 800 degrees C.