FATIGUE CHARACTERISATION OF DISSIMILAR WELDS

Abstract

Fatigue crack growth rate and Low cycle fatigue were studied of dissimilar weld joint. Dissimilar joints are extensively utilized in energy conversion system. The parts of the boilers that are subjected to lower temperature are made of low alloy steel for economic reason. The other parts operating at higher temperature are constructed with austenitic stainless steel. A low alloy steel and austenitic stainless steel (AISI 304) were joined by gas tungsten arc weld (GTAW) process using an austenitic stainless steel (AISI 308) filler metal. The fatigue crack growth rate test is conducted at stress ratio 0.1 and frequency 4 Hz The crack growth rate is higher in austenitic stainless steel (AISI 304) base metal compare to low alloy steel base metal and austenitic stainless steel (AISI 308) weld metal. Fully reversed total axial strain controlled low cycle fatigue tests were carried out on all weld metal and base metal samples. The fatigue tests were conducted at room temperature employing strain amplitude in the range of ± 1% at a constant strain rate and 0.03 Hz. Base metal samples exhibited an initial hardening followed by continuous softening regime that ends with stress saturation prior to failure, but weld metal samples does not show initial hardening. However austenitic stainless steel (AISI 308) weld metal and low alloy steel base metal have better fatigue life than austenitic stainless steel (AISI 304) base metal. Mechanical and metallographic properties of the specimens were obtained by means of microhardness testing, tensile testing, charpy impact testing, light optical and scanning electron microscopy. Scanning electron microscope was used to observe the fracture surfaces of fatigue crack growth rate, low cycle fatigue and charpy impact test specimens.