ANALYSIS OF MICROSTRUCTURE AND MECHANICAL PROPERTIES API5LX65MO HOT ROLLED COIL STEEL WITH DUAL PHASE MICROSTRUCTURE THROUGH INTERCRITICAL ANNEALING AND QUENCHING PROCESS

• Main Author: (NIM : 12509007), STEVEN
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/24393
• Institution: Institut Teknologi Bandung

Nowadays, the need for high strength steel with good formability in automotive applications is increasing. To meet this demand, the steel with those criterias is needed, one of them is dual phase steel with excellent combination of strength and drawability as a result of its microstructure consists of soft ferrite and hard martensite. <br /> <br /> <br /> <br /> Dual phase steels can be obtained by heat treatment of HSLA steels. HSLA steels have high strength through the mechanism of grain refinement and precipitation hardening. Then, martensitic hardening can be given to HSLA steels in addition to the previous mechanisms through heat treatment at intrercritical annealing region. <br /> <br /> <br /> <br /> In this research, API5LX65MO hot rolled steels were used to produce dual phase steel. Those steels were heated on intercritical annealing regional at the temperatures of 740oC, 765oC, 790oC, and 815oC and were retained at holding times of 5, 10, 15, and 20 minutes. Once heated, the steels were quickly cooled (quenched) in water coolant. Tensile test, hardness test, and bending test were done to measure the mechanical properties of the dual phase steels. Microstructures were observed using optical microscope. <br /> <br /> <br /> <br /> From the result, it was found that the most optimal heating temperature was at 815oC with the holding time of 20 minutes. The tensile strength was observed to be at 699 N/mm2 (increased by 19.31% of the initial material). Hardness value was 302 HVN (increased by 46% of the initial material). Elongation dropped from 46% to 26%. The martensite volume fraction was 17,19%, while the result of bending tests did not reveal any cracks on the surface of the materials.