Materials Engineering Department
BS in Materials Engineering
The purpose of this project was to qualify welding procedure specifications for the Las Positas College welding program using A36 steel in accordance with American Welding Society (AWS) D1.1, B4.0, and B2.1. Qualification was to be performed using both 1G (flat) and 3G (vertical) positions for Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) processes. Required qualification procedures included two face and two root bend tests coupled with a visual inspection for cracks within the weld region greater than ⅛” long, along with two reduced section tensile tests to ensure the tensile strength exceeded 58 ksi if the sample broke within the weld region or 55.1 ksi if the sample broke outside of the weld region. Tests were standardized by using American Society for Testing and Materials (ASTM) standards. Cracks greater than 1/8” were found in the weld region of bend tested samples in each process except for the 3G GTAW, disqualifying them. The failed samples were broken open at the crack and examined using optical microscopy in conjunction with polarized light as well as stereo microscopy to determine the inclusion and porosity content of the base and weld metal. The microscopic examination revealed a high degree of porosity and a lack of fusion in a 1G GTAW root bent sample as indicated by the presence of back gouging marks found in the areas of the weld having lack of fusion. This was the result of improper back gouging procedures. Microscopic examinations of GMAW fracture surfaces showed signs of heavy oxidation and inclusion content within the weld metal as well as a lack of fusion between the weld passes. Both 3G GTAW samples passed tensile tests with tensile strengths greater than 64 ksi, and the 3G GTAW process was therefore qualified.