Microstructural Characterization of the Heat Affected Zone of HSLA (High Strength Low Alloy)-100 Steel GMA (Gas Metal Arc)-Weldment

摘要

A high strength low alloy steel, HSLA-100, is under developement by the U.S. Navy. The research presented in this thesis evaluated the effects of cooling rate on the heat affected zone (HAZ) of Gas Metal Arc Weldments (GMAW). The cooling rate at 540 C after gas metal arc welding was varied from 22 C/second to 42 C/second by using different plate thickness, different preheat and interpass temperatures as well as different heat inputs. Mechanical property data is reported elsewhere but summarized in this thesis. All welds met required strength and toughness. However, for all but the fastest cooling rate, the tensile test transverse to the weld failed in the weld metal rather than in the base metal as would be expected with HY-100 steel. No failures occurred in the HAZ which indicates that the strength of the HAZ is not a strength limiting factor. The HAZ microstructure was characterized by optical metallography, scanning and transmission electron microscopy. These microstructures were correlated with microhardness and the mechanical properties. Microconstituents of the coarse grain HAZ for all the weldments were predominately a mixture of low carbon, higher bainite and martensite.