Korelasi Kuat Arus Laser Welding Terhadap Sifat Mekanik dan Struktur Mikro Baja NAK 80

Abstract

The shortcomings of GMAW welding are still found distortion defects, and HAZ is too wide, so Nd: YAG laser welding is one of the solutions to repair injection moulds. The purpose of this study was to determine the correlation of variations in laser welding current strength to the mechanical properties and microstructure of NAK 80 steel used in injection moulds. The research was conducted using experimental method. The tool used was Nd:YAG laser welding with model HT-WY180-Mk. The materials used were NAK 80 steel and NAK 80 filler with a diameter of 0.4 mm, while the current strengths used were 225 A, 250 A and 275 A. The test results show a correlation of variations in current strength to the mechanical properties and microstructure of NAK 80 steel. At a current strength of 275 A, the hardness of the base metal area is 399.8288 VHN, weld metal 485.5191 VHN, and HAZ 521.4778 VHN. At a current strength of 250 A, the hardness of the base metal area is 392.0443 VHN, weld metal 478.6415 VHN, and HAZ 510.111 VHN. At a current strength of 225 A, the hardness of the base metal area is 382.9029 VHN, weld metal 457.295 VHN, and HAZ 502.5802 VHN. Significant microstructure changes occur at a current strength of 275 A in the HAZ area, namely with the appearance of cementite and bainite phases, while the lower the current strength the phases are dominated by cementite and pearlite. The reason is because the laser welding process has the characteristics of high heat energy intensity in a small area and short time.  The higher the heat input or current strength used will affect changes in hardness values and changes in microstructure until the appearance of cementite and bainite phases