Development of an experimental-analytical method for obtaining optimal two-layer welding window of a Ni–Cr–Mo–V alloy steel

Abstract

This study investigates the feasibility of using two-layer tungsten inert gas (TIG) welding to repair damaged parts made of 3.5NiCrMoV low-alloy steel, which is widely used in various industries for complex and thick components. Experimental and analytical methods are used to determine the optimal heat input for the second layer of welding, which can eliminate the need for post weld heat treatment (PWHT). The first layer is welded with a heat input of 0.42 kJ/mm and the second layer is welded with heat inputs ranging from 0.59 to 0.92 kJ/mm. The effects of the second layer heat input on the microstructure, peak temperature profile, cooling rate, hardness, and impact energy of the welded alloy are evaluated. The optimal heat input for the second layer is found to be 0.76 kJ/mm, which is 1.8 times the heat input of the first layer. This heat input tempers the coarse-grained region in the heat affected zone (HAZ) caused by the first layer, maintains the hardness of the weld metal, and improves the impact energy of the welded alloy. This method is novel and useful because it can save time, money, and energy for repairing the damaged parts made of high strength low alloy steel. This method can also provide useful information for controlling the microstructure and mechanical properties of high strength low alloy steels during welding. Rosenthal's analytical models are used to simulate the temperature and cooling rate profiles of the welded metal and the HAZ, and the results are compared with the experimental data.