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The dissimilar welds between AISI 304L and Fe-15.6Cr-8.5Mn were investigated on oxidation at 700°C with the effects of dissolved nitrogen in the welds. This paper aims to clarify the oxidation behaviors to expand the range of application for Fe-Cr-Mn stainless steel.

Dissimilar welds between AISI 304L and Fe-15.6Cr-8.5Mn were fabricated using gas tungsten arc welding to investigate the oxidation behavior of the welds at 700°C. Pure Ar and Ar-4%N₂ shielding gases were used to evaluate the effects of nitrogen gas. The welds were introduced to the cyclic oxidation test. In each cycle, the furnace was heated up to 700°C, and the temperature was kept at 700°C for 8 h, then the mass gain because of oxidation was examined. The scales after oxidation test were investigated by using scanning electron microscopy with EDX and X-ray diffraction analysis.

Addition of 4 per cent nitrogen to Ar shielding gas reduced delta-ferrite content in the weld. Ar-4%N₂ shielding gas resulted in dissolved nitrogen which helped increase the diffusivities of chromium or oxygen vacancies in the oxide to facilitate the chromia formation at the inner part near the steel substrate. This protective layer can help reduce the Fe outward diffusion, thus reducing mass gain because of iron oxide formation.

The oxidation behavior of dissimilar welds between AISI 304L and Fe-15.6Cr-8.5Mn were investigated at 700°C. The evaluation is beneficial for expanding the range of application of Fe-Cr-Mn stainless steel at high temperature.

The purpose of this study is to investigate the aesthetic blackening coating formed by a hydrothermal process, focusing on the formation of magnetite and the oxide adhesion for improving the corrosion resistance of the steel.

The aesthetic black coating was applied on AISI 4140 steel using a hydrothermal process with a non-toxic solution consisted of ferrous sulphate hydrate (FeSO4·7H₂O), sodium hydroxide (NaOH) and hydrazine hydrate (N2H4·H₂O). Upon process parameters temperature and time, the morphology of the coatings and oxidation kinetics were investigated by using scanning electron microscopy and X-ray diffraction (XRD) analysis. Furthermore, the samples with coatings were subjected to the adhesion test using a tensile testing machine equipped with a charge-coupled device (CCD) camera.

From the formation parameters due to temperature and time for the conversion coatings, it was found that the oxidation kinetics had special characteristics which were in accordance with a linear rate law and Arrhenius relation. For the samples blackened, the XRD analysis results revealed that the magnetite was successfully formed on the surface of the steel. On the other hand, increasing the blackening temperature worsened the scale adhesion as observed by the lower strain provoking the first spallation and the higher sensitivity of the oxide to spall out with the imposed strain.

The effects of parameters of the formation of conversion coatings were investigated to understand the kinetics of the coatings. Furthermore, a tensile adhesion test using a CCD camera was applied to evaluate the adhesion between the native oxide formed by conversion coating.