Creep Limit and Structural Stability of the Parent Metal and Weld Joints made from Improved Low-Alloy Heat-Resisting Steel 12MKh and 12Kh1MF,

The steels 12MKh and 12Kh1MF are widely used to fabricate equipment and pipe operating at temperatures of up to 540 and 560 degrees centigrade, respectively. Preliminary tests of these steels established that the optimal regime of improving their qualities and welding such as would assure a welded joint of the same strength as the base metal at normal and elevated temperatures during short-time tests is as follows for 12MKh steel water quenching from 930 degrees centigrade tempering at 680 degrees centigrade for 2 hr running energy of welding 2500-4500 calcm for 12Kh1MF steel, water quenching from 980 degrees centigrade tempering at 750 degrees centigrade for 3 hr running energy of welding 4000-6000 calcm. 12MKh steel is best postheated at 630 degrees centigrade and 12Kh1MF steel, at 700 degrees centigrade. The high temperature strength of these steels and of their welded joints, as determined by tensile stress-rupture tests was found to be greater for the steels in improved state. However, in time the effect produced by this improvement gradually diminishes and on extrapolation to 100,000 hr of normal operation this effect completely disappears. On the other hand, if the steels are tested at approximately 520 degrees centigrade this beneficial effect of heat treatment persists. Author