Techalloy 420 description: Techalloy 420 is used to weld stainless steels of similar chemical composition. It has higher carbon and chromium content which leads to higher hardness levels that with Techalloy 410. The higher hardness imparts greater wear resistance. A 600°F preheat is required prior to welding, 350°F inter-pass temperature and PWHT in accordance with final strength and harness requirements.