ACHIEVING ARMOR STEEL QUALIFICATION ON 4K3014AM AND 4K3014BM STEEL THROUGH QUENCHING TEMPERING HEAT TREATMENT WITH AUSTENITISATION TEMPERATURE AND SOAKING TIME VARIATIONS

• Main Author: AUDI PAHLEVI (NIM : 12514057), GILANG
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/27521
• Institution: Institut Teknologi Bandung

Armor steel, as one of the main component in arms manufacturing process, has not been produced by Indonesia until now. PT. Krakatau Steel already tried to produce this steel, but has not achieve the required qualifications. Armor steel is a kind of steel which has good combination between high strength, hardness and toughness to withstand ballistic attack. Armor steel must fulfill sort of performance standard which in this case is MIL-DTL-46100E. That standard requires armor steel to have hardness between 477-534 HB and 16,2 J of toughness in -40 oC. Then, armor steel must have martensite microstructure that inherit high hardness and strength. To develop this microstructure, quenching and tempering heat treatment was done. A lot of factors that influenced quenching and tempering process, one of them is austenitisation. Austenitisation is a process of heating steel above critical Ac3 temperature for certain time period before the steel is quenched. So, it is necessary to conduct a research of austenitisation process parameter that can produce armor steel that fulfill MIL-DTL-46100E standard. <br /> <br /> In this research, two armor steel prototypes 4K3014AM (steel A) and 4K3014BM (steel B) from PT. Krakatau Steel was used. These two armor steels undergone full annealing process first to make machining easier. Test samples then experienced heat treatment process with austenitisation temperature variations of 825, 850, 875, 900 and 925oC in soaking time of 10, 20, 30 and 40 minutes. After quenching, samples were tempered in 200oC for 20 minutes. Samples are tested using Vickers Hardness, Charpy V-Notch Impact Test and tension test. Samples then were characterized using optical microscope to observe microstructure and fractography using Scanning Electron Microscopy (SEM) to investigate type of fracture that occured. <br /> <br /> Quenching and tempering process showed fully martensite microstructure. Highest hardness value was achieved in austenitisation temperature of 825oC in 20 minutes for steel A and 850oC for 20 minutes for steel B, with each hardness value were 541.5 HB and 539.7 HB. Highest toughness value for both of the steels was achieved in austenitisation temperature of 900oC in 20 minutes with toughness value of 27,364 J. Highest UTS value was achieved in austenitisation temperature of 825oC in 20 minutes for steel A and 900oC for 20 minutes for steel B, with each UTS value were 1781.03 MPa and 1937.41 MPa. Fracture which occurred in Charpy Impact samples was ductile fracture.