Effect of Heat Treatment Temperature on Hardness and Micro Structure Change of Assab 705 Steel as a Die Mould Material

Abstract

The mould is most imfortance tools for large production for example in automotive industry. The cost of mould is highly dependant on part geometrical complexity and material selection. Steel has long been used as a material for making moulds, although new materials such as plastics and composites have been discovered. However, steel maintains its position above material selection because of its mechanical properties. This research uses Assab 705 steel, because Assab 705 steel is classified as medium carbon steel (carbon content of 0.38-0.43%) and has the ability to be hardened through a heat treatment process. Application of Assab 705 steel is widely used for making bolts, tools and various kinds of moulds. The heat treatment process carried out in this study is by heating the steel sample with a temperature variation of 750, 800, 850 and 900°C and continued with the quenching process using Olie SAE 90 as cooling media. Steel samples that had been heat treated were tested by Rockwell hardness and micro structur changes were analyzed using optical microscope. Based on the results of rockwell hardness testing that the highest hardness value was achieved at 54.5 HRC in samples that have been heat treated at 900°C, which when compared to hardness samples without heat treatment, there has been an increase of 60.30%. The microstructure of the Assab 705 steel sample changed after the heat treatment process, which formed a martensite phase and tended to increase with increasing heat treatment temperatures.