Structural changes and corrosion resistance of [17% Cr, 2% Ni] steel Kh17N2

Conclusions

• 1. Heating of steel Kh17N2 to 1000–1300°C for 1 to 5 mins followed by air cooling results in a martensitic structure with a 545–649 kg/sq. mm microhardness, which reduces the impact toughness of the metal to 0.36–0.60 kgm/sq.cm.

• 2. Tempering in the 300–600°C range causes a precipitation of fine Cr carbides from the martensite and depletion in chromium of the martensite substance. The tempered martensite has a low corrosion resistance.

• 3. After tempering at 400–650°C the character of the corrosion changes to structurally-selective and intercrystalline: the areas of tempered martensite are corroded, those of chromium ferrite are not.

• 4. Tempering of steel Kh17N2 at 680–700 C/1 hr results in a complete decomposition of martensite into a ferrite-carbide mixture, this resulting in a relief of the residual stresses and a formation of stable chromium carbides at the grain boundaries.

• 5. Heating of the quenched steel at 750, 800, 850, 900–1300°C/30 mins causes intercrystalline corrosion in tests on specimens in an aqueous solution of copper sulfate and sulphuric acid. Heating above 800°C followed by a relatively rapid cooling produces susceptibility to intercrystalline corrosion.

• 6. Weldments on this steel performed with austenitic electrodes are prone to structurally-selective and intercrystalline corrosion in the HAZ after multi-layer arc welding or welding with pre-welding. To prevent this, it is necessary to temper the welded parts at 680–700°C/1 hr.