Properties of relaxation-resistant steel Kh12VMBFR (EI 993)

1. Steel Kh12VMBFR may be utilized as rivet material for steam turbines with steam temperatures ranging from 565 to 580°. 2. Steel Kh12VMBFR possesses high resistance to relaxation and rupture strength over the 550–580° range and is not notch sensitive. The residual stress after 10, 000 hr testing of the ring samples made from this steel was 10–12 kg/mm2 at 565°, and 9 to 10 kg/mm2 at 580°. The rupture strength of steel Kh12VMBFR at 565° over 10, 000 hr is 26–28 kg/mm2. 3. The highest heat-resistant properties of steel Kh12VMBFR in terms of relaxation resistance and rupture strength may be produced by the following heat treatment method: oil-quenching from 1150° and tempering for 3 hr at 680–700°. 4. The manufacture of bolts and pins from steel KM12VMBFR may be recommended for the bracing of steam turbine and boiler parts made from steels of the ferritic and martensitic classes, if the linear expansion coefficients of these steels are closely similar.