Alloy influence on the properties of tempered steels for casing pipes

The effect of alloying on the properties of high-tempered steels used for production of casing pipes is studied. The steels contained 0.25 %C, 0.9 %C and different amounts of Mo, V and Nb. It is shown that an increase in the molybdenum content from 0.15 to 0.53 % provides a noticeable increase in the mechanical characteristics of chromium-molybdenum steels after tempering at 600-690 °C. Vanadium and niobium addition (about 0.03 %) results in a further increase of strength properties. The highest hardening of steel with 0.32 % molybdenum in tempered state is provided by complex alloying with niobium and vanadium, which results in the same strength as that of 0.53 % Mo steel without additional alloying. V-notch impact toughness at -60 °C for all steels tempered at 660-690 °C is sufficiently high (150-280 J/cm2). The same is true for tempering at 600 °C with the exception of the vanadium-niobium steel.