Heat-Treatment Process Optimization Using Dilatometry Technique and Simulation Tools

Any metal component undergoes various treatments to get desired shape and desired properties. Some of the important properties are strength, hardness, % elongation etc. which comes under mechanical properties. These properties can be easily achieved through heat-treatment process. Typical example of heat-treatment processes are hardening and tempering in case of steel and aging process in case of aluminium alloys. Some of the new emerging materials viz. micro alloy steel does not require any hardening and tempering if cooling rate is maintained. Heat-treatment cycle depends on material grade and its alloying elements. A heat-treatment cycle for any grade is generally fixed based on conventional methods but they are not optimized. The need of hour is to optimize the heat-treatment cycle to improve productivity and energy consumption. Dilatometer is used to optimize heat-treatment cycle on sample level whereas simulation tools can be used for component level.

This paper deals with effective use of heat-treatment simulation supported by Dilatometry technique to optimize heat-treatment cycle for automotive component. A case study of heat-treatment cycle optimization of a forged crankshaft is demonstrated in the paper. Existing heat-treatment cycle of crankshaft was studied and simulated during first phase of the project. The heat-treatment consists of hardening and tempering process. Dilatometry technique was used to optimize Continuous Cooling Transformation (CCT) and Temperature Time Transformation (TTT) curves as well the phase transformation temperatures like AC1 and AC3. To carry out simulation, required inputs were taken from dilatometry viz. temperature, soaking time, quenching time etc. Using these inputs, simulation setup and analysis was carried on crankshaft. Results of dilatometry at sample level were extrapolated to actual product level using simulation tools. Inferences were drawn from Heat-treatment simulation and the optimized heat-treatment cycle was finalized. Actual trials were conducted with optimized heat-treatment cycle. A comparison study in terms of Hardness, Microstructure etc. was carried out between physical testing and Simulation results and they are found in very good agreement. Methodology so developed helped in reducing heat-treatment cycle time significantly.