Steel used for Cr micro-alloyed oil casings and preparation method of steel

Abstract

The invention discloses steel used for Cr micro-alloyed oil castings. The steel used for the Cr micro-alloyed oil castings comprises, by mass, 0.25-0.30% of C, 0.25-0.40% of Si, 1.45-1.55% of Mn, 0.020-0.055% of Alt, not larger than 0.015% of Sn, 0.40-0.50% of Cr, not larger than 0.015% of P, not larger than 0.008% of S and the balance the iron element and inevitable impurity elements. The invention further discloses a preparation method of the steel mentioned above. The steel used for the oil castings has the beneficial effects that good comprehensive mechanical performance is achieved and the strength surplus amount is high, and can be suitable for deeper wells; and according to the steel and the method, by adding a certain amount of Cr, for example, 0.40-0.50% of Cr, the requirement forthe steel pipe strength is met and corrosion resistance of the steel is increased to a certain degree.

Description

technical field [0001] The invention relates to the field of steel for oil casing, in particular to a low-carbon steel for oil casing which is micro-alloyed with a small amount of Cr and has good comprehensive mechanical properties. Background technique [0002] Petroleum casing is used in deep wells and complex formation conditions that require stringent casing performance. Therefore, it is required to have good comprehensive performance, that is, high tensile and connection strength, excellent anti-collapse performance, that is, sealing performance, so higher quality requirements are put forward for the tube blank steel used for oil casing. [0003] The Chinese patent application with the application number CN201210007350.1 discloses a high-expansion oil casing steel, which includes C 0.03-0.25%, SI 0.3-2.5%, Mn 0.5-4.0%, Cr 0 -0.5%, S≤0.02, P≤0.02, the balance is iron, and one or more of Nb, Ti and V can be selectively added for strengthening. The metallographic phase o...

AI Technical Summary

Problems solved by technology

However, the yield strength of seamless steel pipes prepared by this method is not high

When no other strengthening elements are added, the yield strength of the pipes in this application only reaches 380MPa. Higher strength pipes need to be strengthened by adding other elements, and the introduction of other alloying elements will not only increase the cost, And it will lead to fluctuations in product performance. For example, the yield strength of the pipe is 360-450MPa, and the steel with higher yield strength needs to add more elements such as Mn and Si. However, too much Si will reduce the plasticity and flexibility of the steel. Toughness, too much manganese will increase the tendency of steel grain coarsening and temper brittleness sensitivity, too high C will reduce the corrosion resistance of steel

[0004] Therefore, the existing steel for oil casing still has the defects of higher cost and lower performance to be overcome

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