This article aims to show the effects of the EDM process that influences the surface hardness by comparing the hardness values before and after the spark on the plastic mould steel AISI P20. Divided by the heat treatment, there were three different hardness levels: 1) the plastic mould steel AISI P20 through the process of quenching with the hardness value in the range of 690-710 HV; 2) the steel through the process of quenching and then annealing with the hardness value in the range of 470-490 HV; and 3) the non-heat treatment steel (raw material) with the hardness value in the range of 300-320 HV. The condition of EDM spark on the surface workpiece was 3 mm of depth and 10 mm of diameter copper electrode. The experiment was carried out under the cover of hydrocarbon, using dielectric cooling, and removing debris by the side flushing through the 6 mm of diameter pipe with the flow rate of 15 liters per minute. The experiment parameters included on-time duty factor variable, off-time duty factor variable, and current. Based on the experiment, it was found that when the duty factor increased, the hardened workpiece showed the less surface hardness value. At the same time, the annealed, and the non-heat treatment workpieces showed that the hardness values were proportional to the duty factor and the current of the EDM process.
The purpose of this research is to study the effect of heat input on microstructure and hardness of SKD 61 hot work tool steel by using Gas Metal Arc Welding (GMAW) process. The specimens made of SKD 61 steel plates were austenized and oil-quenched to room temperature, then they were double tempered. Base on identical welding specification procedure (WPS), the specimens were automatically welded by GMAW machine. The consumable copper coated-solid wire electrode was used for surfacing in the GMAW process. The microstructures at the HAZ of specimens for all conditions were composed mainly of martensite with some retained austenite in the dendritic segregation pattern. With the higher heat input resulted in increasing in hardness, which resulted from transformation of retained austenite to martensite.
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