Hot Crack Susceptibility Studies on High-Nitrogen Stainless Steel

Conventional fusion welding of high-nitrogen stainless steel (HNSS) can lead to a number of potential defects, such as nitrogen porosity, weld metal subjected to solidification cracking, heat-affected zones (HAZ) subjected to liquation cracking, lowering of dissolved nitrogen content, and formation of nitride precipitates in the HAZ. Among these, solidification cracking in the weld zone and liquation cracking in the HAZ are the most serious ones. Susceptibility of materials to hot cracking is an important factor to be considered while combining the materials, particularly in HAZ. Thermo-mechanical history of the weld can be simulated by applying a strain to induce cracking and measuring the material's response to cracking. To assess the hot strength and ductility of the material and its susceptibility to hot cracking, a series of hot tensile tests were conducted at temperatures below the solidus temperature using Gleeble thermo-mechanical simulator. Based on the results obtained from the series of tensile tests, it was noticed that for temperatures above 1250 degrees C, liquid film formation was more pronounced. During heating, nil ductility was observed above 1357 degrees C. On the other hand, during cooling a significant recovery in ductility (45%) and a ratio of ductility recovery of 53.85% during the thermal cycle were observed. Thus, it can be concluded that the hot cracking tendency in the heat-affected zone of HNSS is very low.