Microstructure and mechanical properties of 1000 MPa grade deposit metals under different welding methods

Abstract

The 1,000 MPa grade Ni-Cr-Mo deposited metal was prepared by metal active-gas welding and tungsten inert gas welding respectively. Optical microscope (OM), scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM), were used to characterize the microstructure of the deposited metal. The mechanical properties of the deposited metal were evaluated through tensile testing, instrumented charpy impact testing, and hardness testing to investigate the influence of welding methods on the strength and toughness of 1 000 MPa-grade Ni-Cr-Mo deposited metal. The results show that the final weld microstructure of the deposited metal prepared by different welding methods consists of lath martensite, lath bainite, Granular bainite and retained austenite. TIG deposited metal is mainly lath martensite, MAG deposited metal is mainly bainite-like microstructure. The width of columnar crystals in MAG deposited metal is larger than that in TIG deposited metal, and the number and density of non-metallic inclusions in MAG deposited metal are larger than those in TIG deposited metal; The different microstructure led to significant differences in mechanical properties, both tensile strength reached 1 080 MPa, their yield strengths differed substantially: where TIG 1,008 MPa, MAG 829 MPa; AKV (−50 ℃) difference is obvious: TIG 95 J, MAG 51 J, TIG deposited metal strength and toughness match better.

Keywords

• welding method
• 1000 mpa grade ni-cr-mo deposited metal
• microstructure
• strengthening and toughening mechanism