The welding of experimental low-nickel Cr-Mn-N stainless steels containing copper

摘要

The rasceptibility of experimental low-nickel Cr-Mn-N stainless steels to hot cracking, sensitization, and pitting corrosion in the as-welded condition was investigated. These steels were developed for deep-drawing applications and are similar in composition to type 201 stainless steel. In order to obtain good formability, the rapid rate of work-hardening (characteristic of the 200-series stem) was decreased by the addition of copper. The behaviour of two sets of alloys during fusion welding was investigated: 17Cr-7Mn-4Ni-0.5Cu steels containing 0.001 to 0.27 per cent nitrogen, and 17Cr-7Mn-2Ni-0.1N steels with copper contents varying between 0.01 and 3.11 per cent. All the steels in these two sets initially solidify as 6-ferrite, which transforms partially to austenite daring cooling. As the nitrogen level increases, the microstructure of an autogenous-weld metal ranges from large amounts of 6-ferrite, martensite, and Widmanstatten austenite, to austenitic structures with small amounts of vermicular delta-ferrite. The formation of 6-ferrite during solidification and the presence of fertile retained in the weld metal indicate that the experimental alloys will not be susceptible to hot cracking during welding. Except for the alloy with 0.27 per cent nitrogen, the resistance to pitting corrosion of the experimental steels in the as-welded condition is inferior to that of type 304 stainless steel. None of the experimental steels is susceptible to intergranular attack in the as-welded condition. The alloys with 0.19 and 0.27 per cent nitrogen have properties (corrosion and microstructure) similar to those of typo 304 stainless steel in the as-welded condition.