QUENCHING BERTINGKAT PADA PROSES HARDENING TERHADAP SIFAT MEKANIK DAN STRUKTUR MIKRO BAJA AISI 4140

Abstrak

Quenching on steel is one of several heat treatment processes which aims to increase the strength and hardness ofthe steel by heating the metal at a certain temperature, usually between 845 - 870 OC, then cooled rapidly on the coolingmedium to obtain the martensite structure. The purpose of this study is to improve the mechanical properties of AISI4140 steel through a multilevel process quenching. The cooling medium used is oil and water. The research methodused is AISI 4140 material made specimen of hardness test, impact test, and micro structure observation. Initial tests onAISI 4140 materials are tensile, hardness, impact strength, and microstructure tests. The process of heating the specimenat a temperature of 850 OC for 60 minutes with a holding time of 240 minutes, then the material in quenching into theoil and water by comparison; 0: 100, 10:90, 20:80, 30:70, 40:60, and 50:50. Result of data analysis of test result anddiscussion in this research, can be concluded: 1). The AISI-4140 Steel Tensile Strength is 1034.4 N / mm2 and anextension of 9.2%. This indicates that AISI 4140 Steel includes medium carbon steel with high strength, 2). The AISI-4140 steel hardness prior to the heat treatment process is 32.54 HRC. This indicates that AISI 4140 Steel includes alloycarbon steel with high hardness, 3). The highest hardness in AISI-4140 Steel after diquenching using stratified coolingmedium (oil and water) was 61.10 HRC in oil and water ratio 10:90 and lowest hardness 43.36 HRC in oil and waterratio 50:50, 4). The hardness value of AISI-4140 steel decreases with the increase of oil volume, but on the contrarythere is an increase in impact strength as the cooling oil volume increases, 5). The fracture properties in AISI 4140 steelafter diquenchig with stratified refrigerant media are hard and tough (tough) so no more tempering process is required,6). The best quenching oil voleme percentage to get the hardness level and the optimum impact strength is 32%.