Fe-16Cr-3Ni-9Mn-0.5Si-xN and Fe-13.2Cr-0.5Mn-0.5Si-0.1C-xN stainless steel alloys were cast in stainless steel mold and water-cooled Cu mold with different nitrogen content from 0.15 to 0.26wt% in case of 16Cr-3Ni-9Mn-0.5Si-xN and from 0.059 to 0.12wt% in case of 13.2Cr-0.5Mn-0.1C-xN.
The effects of nitrogen content and cooling rate on the formation of nitrogen gas pore during solidification of stainless steel solidifying primary δ ferrite were investigated. The amount of nitrogen gas pore increased with increasing initial nitrogen contents of castings. Increasing cooling rate almost did not affect the formation of nitrogen gas pore.
The critical initial nitrogen content for the formation of nitrogen gas pore was experimentally investigated. The critical nitrogen content was about 0.19wt% for Fe-16Cr-3Ni-9Mn-0.5Si-xN and about 0.066wt% for Fe-13.2Cr-0.5Mn-0.5Si-0.1C-xN.
Fe-16Cr-3Ni-11Mn-0.5Si-xN and Fe-13.2Cr-0.5Mn-0.5Si-0.1C-xN stainless steel alloys were also cast to examine the effect of Mn content for the formation of nitrogen gas pore. Increasing Mn content decreased the amount of nitrogen gas pore.
The segregation of nitrogen and alloying elements were calculated with Thermo-Calc. for equilibrium and Scheil solidification. The calculated data and the experimental results were compared to estimate the critical nitrogen partial pressure in the residual melt for the formation of gas pores.
The critical nitrogen partial pressure of 16Cr-3Ni stainless steel was 1.27atm and 1.23atm for equilibrium and Scheil solidification respectively. The critical nitrogen partial pressure of 13.2Cr nickel free stainless steel was 1.24atm and 2.27atm for equilibrium and Scheil solidification respectively.
