DefinePK

Abstract

Hot Roll Quench Tempered Steel (QTS) is term of hot roll steel which produced by PT. Krakatau Steel with carbon content 0.29 %C that given by martempering treatment. Martempering treatment meant to increase the steel hardness for about 500 BHN, thus it cannot be penetrated by bullet. QTS designed as alternative material for industrial supporting of military tactical vehicles. Martempering treatment has been changed metal microstructure from tough ferrite-pearlite to the hard martensite. The weakness of martensite structure in welding field is low weldability and prone to the delay cracking for post welding. Delay cracking also resulted in defect or initial crack which occur by the rapid cooling in the post welding and the dissolved of inclusion and gas in the welding area during solidification in weld metal. In many researches, high circulation rate of weld pool could improve weld metal structure and HAZ, decrease welding defect and improve the other properties. Circulation rate of weld pool can be increased by enlarging electromagnetic force or Lorenz force (FL). Electromagnetic force can be enlarged by increasing welding current density (J) or increasing magnetic flux (B) as with the equation FL = J x B. In this research, it was conducted by QTS plate welding used MIG welding with gas protector CO2. Welding electric current 140 A was flowed to the electrode wire AWS ER 70-S6 with the average welding speed 15 cm/minute. Magnetic flux was added from outside during the welding by flowing DC current to the solenoid 100 x 100 x 10 mm. The DC current that flowed to solenoid was 0, 3, 6, 9, 12 and 15 Ampere. Those current variations resulted in magnetic flux for 0 mT, 2,4 mT; 3,4 mT; 4,43 mT; 6,43 mT and 9,03 mT. Thermocouple of K type was carbon welded in the distance of 10 mm from welding core to measure HAZ temperature. The result was peak temperature in the distance of 10 mm from welding core getting lower because of outside magnetic flux addition from 0 mT to the 9.03 mT. By taking temperature range of post welding comparison from 400°C to 200°C, it was known that without magnetic flux addition which results the highest post welding cooling rate and getting lower to the magnetic flux addition of 9.03 mT. From the radiography test, it was known that magnetic flux addition could decrease welding defect percentage. The bigger magnetic flux addition resulted in smaller welding defect percentage. The bigger magnetic flux addition also resulted in bigger impact strength of welding area with more ductile fracture.