The Influence of Heat Input to Mechanical Properties and Microstructures of API 5L-X65 Steel Using Submerged Arc Welding Process

API 5L-X65 steel is the type of high strength low alloy (HSLA) steel, widely used in the manufacture of pipe. Submerged arc welding (SAW) is widely used for the fabrication of the pipe, the extent of use submerged arc welding caused it could be done automatically and high reliability. The results of the welding process will lead to differences and changes in the microstructure in heat affected zone (HAZ) and weld metal that will affect the mechanical properties of the output, so as to obtain good welding results required the selection of welding parameters accordingly. As the use of the heat input during welding is very important influence on the mechanical properties and microstructure of the weld. The purpose of this study to determine the effect of heat input on the microstructure, hardness and toughness of welds in submerged arc welding. Welding currents used were 200, 300, 400 and 500 Ampere with a voltage were used 25, 27 and 30 Volt. The results showed that the higher heat input will result in a growing area of HAZ region width and grain size increased. Highest hardness values are the results of the weld heat input with a low of 244.69 HVN caused by the rapid cooling rate of the weld area. The highest toughness values are the results of the highest heat input that was dominated by acicular ferrite phase.