Laser welding of new austenitic cryogenic corrosion-resistant steels alloyed with nitrogen

Abstract

There were studied structures and properties of welded joints of laboratory melted austenitic steels: Fe-0.04C-18Cr-9Ni-0.2N and new-developed Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu. Correct choice of composition and deformation-heat treatment leads the new-developed steels are high-strength corrosion-resistant ones with stable austenite. Computer simulation shows that enough quality of welded seam can be provided by laser welding of plates of up to 4 mm in thick at the room temperature. For bigger thicknesses preliminary heating is necessary. Microstructure, phase compositions, lattice periods, X-ray diffraction peak broadening, microhardness, bending strength and ductility, resistance against intercrystalline, pitting and total corrosion was studied for bulk metal and laser welded joints of high-temperature thermomechanically treated hot-rolled plates, including tests after 1000 thermal cycles in range –163…+20 °C were investigated. It was shown that welded seams are 300…1000 μm in wide and have no porosity and no thermal affected zone. The welded seam strength is the same as for bulk metal, 180° bend test shows no cracks in the seam. The resistances of welded seam and bulk of Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu steels against total corrosion in the sea water (3 % NaCl) and in acid environment (0,5M H2SO4, including additional blowdown by H2S), pitting and intercrystalline corrosion in standard environments are practically equal. The structures, phase compositions, hardnesses and corrosion resistances of welded joints of both new-developed steels are constant after the thermocycling.