Effect of welding procedure on wear behaviour of a modified martensitic tool steel hardfacing deposit

摘要

In the last years hardfacing became an issue of intense development related to wear resistant applications. Welding deposits can functionalize surfaces and reclaim components extending their service life. Tool steels are widely used in hardfacing deposits to provide improved wear properties. Nevertheless systematic studies of wear behaviour of new alloys deposited by hardfacing, under different service conditions are scarce. In this work the effects of shielding gas, heat input and post-weld heat treatment on the microstructural evolution and wear resistance of a modified AISI H13 martensitic tool steel deposited by semi-automatic gas shielded arc welding process using a tubular metal-cored wire, were studied. Four coupons were welded with different welding parameters. The shielding gases used were Ar-2% CO_2 and Ar-20% CO_2 mixtures and two levels of heat input were selected: 2 and 3 kJ/mm. The as welded and 550 ℃-2 h post-weld heat treated conditions were considered. From these coupons, samples were extracted for testing metal-metal wear under condition of pure sliding with a load of 500 N. Chemical compositions were determined; microstructure and microhardness were assessed. It was found that content of retained austenite in the microstructure varied with the welding condition and that heat-treated samples showed secondary hardening, associated with precipitation phenomena. Nevertheless, as welded samples showed higher wear resistance than heat treated specimens. Under these test conditions post-weld heat treatment led to a reduction in wear resistance. The best wear behaviour was observed in samples welded with low heat input and under the lowest oxygen potential shielding gas used here, in the as welded condition. The intervening mechanism was mild oxidative. These results were explained in terms of the relative oxidation resistance stemming from different welding conditions.