Analysis of Mechanical Properties for the Heat Resistant Co-Modified 12 and 9% Cr Steels

An analysis of mechanical properties has been performed for 12% Cr and 9% Cr steels by means of tension tests at 20 and 650°C and yield tests at 650°C and applied stresses of 200–100 MPa with a step of 20 MPa. The yield strength and ultimate tensile strength of the 12% Cr steel are, correspondingly, 614 and 710 MPa at 20°С and 365 and 390 MPa at 650°C. At both temperatures, the strength properties of the 12% Cr steel under tension are better than for the 9% Cr steel due to higher values of contributions from solid-solution hardening (+30 MPa) and substructural hardening (+23 MPa) to the room-temperature yield strength. The analysis of creep properties shows that the time to fracture at high stresses for the 12% Cr steel is much longer than for the 9% Cr steel due to a more prolonged transient creep stage and, at low applied stresses, there is almost no difference in the creep behavior of the 12% Cr and 9% Cr steels. The 1% creep limit estimated from the empirical dependence between the stress and the time required to attain the strain with a degree of 1% for the 12% Cr steel is 82 MPa, being comparable with the 1% creep limit of the 9% Cr steel.