Corrosion resistance of welded joints of 0Kh21N6M2T steel

Conclusions

• 1. Direct x-ray spectral microanalysis showed that the main alloyed elements are distributed between the α- and γ-phases in the heat affected zone of the weld and in the weld seams of Cl−Ni−Mo steel. A structurally selective corrosion in such metal occurs in some hot concentrated solutions of nonoxidizing acids.

• 2. Depending on the total nickel concentration in the steel, and consequently, on the relationship between the structural components, the amounts of nickel and molybdenum in the α- and γ-phases vary. This occurs in some aggressive media which dissolve either the austenite or the ferrite preferentially. The phase whose amount is smaller and which contains less nickel and molybdenum dissolves at a high rate.

• 3. The amount of ferrite increases in ferritic—austenitic steels subjected to the thermal cycles induced by welding. In spite of a certain decrease of interphase concentrational heterogeneity during this heating, the corrosion resistance of the metal decreases in aggressive media.

• 4. We determined the concentrations and the temperatures of sulfuric, phosphoric, and formic acids at which the corrosion resistance of welded 0Kh21N6M2T is satisfactory.