Analysis and development of heat treatment strategies for a modern manufacturing process using coupled thermo-mechanical simulation

Abstract

The metal forming technologies is advancing in order to offer the best production of metal characteristics based on different desirable requirements and applications. This thesis is an analysis and development project of heat treatment strategies for a modern manufacturing process using coupled thermos-mechanical simulation (Simufact Forming). In order to inspect phase transformation, the work piece was originally heated locally by a furnace then formed into a flange shape before undergoing two stages of cooling (the first one is the CCS and the second is the CAC stage). The CCS was performed at different cooling temperatures and different contact time while the CAC was fixed at 20 minutes cooling time and at a room temperature of 20 degrees Celsius. All of these simulations were performed in order to inspect the change in the microstructure in the whole forming process and to inspect the effect of increasing the contact time and contact temperature on the microstructural change. It was found that this forming process transformed the Ferritic-Bainitic original microstructure of the 34Cr4-TA850-ASTM75-HT steel alloy into a microstructure consisting mostly of Martensite and Bainite. As expected, the lower cooling temperature along with the higher contact cooling time gave the highest percentage of Martensite of around 97% at the core and surface of the flange and by decreasing the CCT and increasing the cooling temperature, the martensitic percentage will decrease along with an increase in the Bainitic percentage across the formed flange. One thing that didn’t give the expected result is the hardness, because in order to increase the hardness of any metal a phase transformation process should occur. The problem is that the unheated part was found to have an equal hardness as the part that was heated and then was subject to the transformation process which is not possible cause the high increase in hardness should come from the martensitic transformation and the unheated part is still consisting of a ferritic-pearlitic microstructure.