No abstract

Duplex stainless steel (DSS) is an important material used for corrosion resistance in various harsh environment plants such as petrochemical, offshore subsea component, and other chemical industries. An approximately equal amount of austenite and ferrite (A/F) ratio grants good mechanical properties and rust protection on. The detrimental intermetallic phase frequently occurs due to an unbalanced A/F ratio caused by the welding’s thermal cycle. Backing gas is commonly applicable in the field combined Gas Tungsten Arc Welding (GTAW) process. However, the use of backing gas to complete a single weld from root to cap joint required huge additional costs for consumables. Maintaining the thermal cycle in the welding parameter and GTAW process with ER2209 filler metal for DSS below 10 mm thick can reduce the backing gas sequence. The research aims to efficiently substitute full backing gas consumption, which meets a desirable quality in terms of corrosion resistance. The effect of backing gas reduction was studied. All specimens were tested by visua Vickers microhardness, metallography, ferrite content measurement, and electrochemical corrosion test. The visual test shows no defects beyond the range of the ASME IX acceptance and criteria. The evaluation comes from the ferrite scope and electrochemical corrosion test. The backing gas on the root weld shows a balance A/F ratio of around 38% ferrite content accepted in various standards. The backing gas sequence on the root until filler-pass obtained 0.04 mm/year, which is the desirable corrosion resistance and met the requirement of ASTM A932.

Repeated welding caused by welding defects in the weld joint will result in changes in the mechanical properties of the weld joint, especially in the Heat Affected Zone (HAZ). Significant changes will occur when welding on steel materials that have undergone special treatment during the manufacturing process, such as quenched and tempered S690Q steel. S690Q steel is a structural steel with high yield strength with quenched and tempered conditions. The research was conducted by doing repeated welding as a simulation of the repair process using the GMAW process. Macro observations as well as tensile, bending, hardness, toughness tests were carried out on cross sections of welded joints. From the results of all the tests carried out the results meet the requirements of the BS EN ISO 15614-1 standard, but the results of the hardness test can identify significant changes in mechanical properties in the HAZ, especially in the bottom or root pass and hot pass areas. The average hardness value decreased from 334.07 HV at the top (face) to 209.55 HV and 198.88 HV at the bottom (hot pass and root pass) on the left side of the HAZ. While on the right side of the HAZ, the hardness value is 337.40 HV to 254.34 HV and 208.64 HV. Keywords: HAZ, S690Q, Structural Steel, Quenched and Tempered Steel

The aim of the study to investigate the effect of welding current on the microstructure and mechanical properties of gas tungsten arc welding (GTAW) for dissimilar austenite Stainless steel (AISI 309 and 201). Three models of welding currents have been used and their effect on microstructure and mechanical properties investigated. The results reveal that increase of welding currents improved the ultimate tensile strength (UTS) however, the hardness of the weld zone and Heat Affected Zone (HAZ) are similar. On the other hand, the microstructure of base metal AISI 309 and 201of austenite, ferrite structure, and ẟ ferrite of AISI 309 stainless steel were observed.