27MnCrV is a new type of steel used in the production of TP110T steel grade casing pipe
sleeves. The steel types used in conventional production of TP110T steel grade
oil pipe sleeves are 29CrMo44 and 26CrMo4. Compared with the latter two, 27MnCrV contains less Mo, which can greatly reduce production costs. However, after the 27MnCrV is produced by the normal austenitizing quenching process, there is obvious high temperature tempering brittleness, which results in low impact toughness and instability.
To solve such problems, two methods are usually used to deal with them. First, rapid cooling after tempering is used to avoid high temperature brittleness and obtain toughness. The second is the sub-temperature hardening method through the incomplete austenitization of steel to effectively improve harmful elements and impurities, and improve toughness. The first method has relatively strict requirements on heat treatment equipment and requires additional costs.
27MnCrV steel has AC1 = 736 ℃, AC3 = 810 ℃, and the heating temperature during sub-temperature quenching is selected between 740-810 ℃. For sub-temperature quenching, the heating temperature is 780 ° C, and the holding time for quenching and heating is 15min; after tempering, the temperature is 630 ° C, and the heating and holding time is 50min. Due to sub-temperature quenching in the two phases of α + γzone heating, quenching in the state where ferrite remains undissolved, while maintaining high strength, toughness is improved.
At the same time, the low-temperature quenching is lower than the conventional temperature, which reduces the quenching stress, thereby reducing the quenching deformation. This ensures the smooth operation of heat treatment production, and provides a good raw material for subsequent wire processing.
This process has been applied in the pipe processing plant of Tianjin Steel Pipe Group. The quality assurance data shows that the heat treated steel pipe has a yield strength Rt0.6 of 820-860MPa, a tensile strength Rm of 910-940MPa, and an impact toughness Akv of 65-85J. Destructive performance is 100% qualified. The data shows that 27MnCrV steel pipe is already a very good high-grade petroleum casing. On the other hand, it also shows that the sub-temperature quenching process is an excellent method to avoid high temperature brittleness in the production of steel products.