STRUCTURE EVOLUTION DURING HEAT-TREATMENTS OF 12-PERCENT CR MARTENSITIC STEEL FOR NET

The structure evolution of martensitic 12% Cr steel has been followed in the range from room temperature up to 600°C by means of X-ray diffraction with analyses of the grain textures and of the diffraction line profiles, together with observations in optical and scanning electron microscopy and with hardness measurements. The behavior of hardness appears referable to two stages in the transformation of martensite to ferrite, involving subsequent disappearance of martensite laths of different thickness and characterized by specific texture variations. Carbide precipitation in the ferritic volumes appears determining for the hardness change above 400°C, with concomitant effects on the hardness drop above 500°C depending on internal stress dislocation density decreases. Some effects referable to elements with large diffusivities are also indicated.