Some Metallurgical Observations on Heating of Explosive Austenitic Stainless Clad Steel

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Metallurgical aspects of a problem on explosive 18Cr-8Ni stainless clad steel heated at high temperatures have been investigated by means of microhardness test, microscopic examination, electron-microprobe technique and X-ray diffraction analysis. The main results are as follows : Heating to above 500℃ for long time causes a diffusion of carbon atoms from mild steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. At about 600° to 700℃, chromium carbides, mainly Cr_7C_3, precipitate very closely in the carburized layer with remarkable hardening. As the temperature increases up to 900℃, Cr_<23>C_6 and σ-phase appear besides Cr_7C_3 and they disperse into stainless steel followed by a decrease in hardness. Also, another thin layer of lower chromium and nickel contents than the original composition of stainless steel forms with no precipitates at bond interface since both chromium and nickel atoms diffuse from stainless steel into mild steel. All the precipitates dissolve fully in austenite at 1100℃. Short-time spot smelting by TIG arc causes a little diffusion of carbon and precipitaion of carbides in the bonded zone, and it develops a layer of α-γ phases in the heat affected stainless steel of clad metal.
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