Abstract:
Effects of five welding variables including welding speed, power input, weld geometry, welding process and types of electrode on the microstructural and mechanical properties of Type 304L austenitic stainless steel Heat-Affected Zone (HAZ) were investigated in this study. To this end, chemical analysis of the as-received 304L austenitic stainless steel was carried out to determine its chemical composition using AR4 30 metal analyser. Thereafter, the as-received 304L austenitic stainless steel plate was cut with hacksaw into sample of dimensions 70 mm length, 45 mm breadth and 8 mm thickness, thirty samples were produced in all, they were then classified into A, B and C with each having equal number of ten samples. The classified samples were further cut into two equal halves with hacksaw and welded under a range welding variables to produce butt joint HAZ samples. The obtained HAZ samples and as-received sample were machined to shapes to produce hardness, tensile, and impact test specimens. Hardness, tensile and impact measurements were made using standard approaches. Instron universal testing machine of model -3369, Rockwell hardness (HRA) and Charpy –V impact testers were used for the tensile, hardness and impact toughness respectively. Specimens for microscopy studies were prepared from the (HAZ and as-received) samples by machining to appropriate dimensions, they were then etched in a solution of 1ml HCl + 3ml HNO3 + 1ml glycerol and the microstructures were examined using metallurgical microscope - Model AXIA 1m with camera attached at a magnification of 400xx. Results obtained from the HAZ micrographs showed that mechanical properties (tensile, hardness and impact) of the HAZ were influenced in varying degrees by all the variables investigated. Microstructure of the HAZ that was mixture of austenite and ferrite was observed with variation in volume fraction and grain size of the phases. In addition, chromium carbide formation and precipitation due to sensitization was observed at the grain boundaries. Optimum mechanical properties were obtained as follows: best tensile properties (UTS, YS) was achieved with square geometry using GTA welding process and 308L electrode at moderate welding speed and 9.2KW power input, hardness with single V geometry sample produced by SMA welding process and 312L electrode at fast welding speed and 12.00KW power input, and impact toughness with double V geometry welded by GTA process and 316L electrode at slow welding speed and12.00KW power input
