High strength seamless steel pipe with excellent low temperature toughness and manufacturing method thereof

Abstract

The invention provides a high strength seamless steel pipe with excellent low temperature toughness and manufacturing method thereof. The steel pipe comprises 0.15%-0.20% of C, 0.20%-0.30% of Si, 0.2%-0.5% of Mn, no more than 0.010% of P, no more than 0.003% of S, 0.6%-0.8% of Cr, 0.4%-0.7% of Mo, 1.0%-1.4% of Ni, 0.01%-0.035% of Nb, 0.01-0.05% of Als and the balance of Fe. The method comprises steps of: (1) smelting: pretreated molten iron with sulfur no more than 0.005%; and after smelting: P<=0.010%, S<=0.003%, O<=0.002%, N<=0.006% and H<=0.0002%; (2) manufacturing of round billet: degree of superheat of continuous casting superheat of square billet less than 30 DEG C, casting speed fluctuation less than 0.05m / min, straightening temperature higher than 950 DEG C and square billet heating temperature of 1300-1340DEG C; (3) steel pipe molding: billet heating temperature of 1250-1300 DEG C, piercing temperature higher than 1200 DEG C, continuous rolling temperature higher than 1050 DEG C, and sizing and reducing temperature higher than 800DEG C; and (4) heat treatment: quenching temperature of 900-920 DEG C, tempering temperature of 500-600 DEG C and tempering time longer than 60 min. The product provided by the invention has yield strength of 125ksi, and -60DEG C impact energy greater than 40J.

Description

technical field [0001] The invention belongs to the field of low-alloy steel manufacturing, and in particular relates to a low-alloy seamless steel pipe with a yield strength of 125ksi (862MPa) and excellent low-temperature impact toughness and a manufacturing method thereof. Background technique [0002] With the development of industrialization, the world's energy is becoming increasingly tense. People begin to consider obtaining energy from cold land and seabeds. High-strength steel with excellent low-temperature impact toughness is urgently needed for mechanical equipment construction, oil drilling, and transportation in cold environments. Most of the existing low-carbon and medium-carbon high-strength steels on the market have low toughness when the strength is high. For example, the Q125 steel grade oil well pipe in API Spec 5CT, although the strength can reach 125ksi, the toughness index can only reach 0. ℃ is 20J in the transverse direction and 41J in the longitudina...

AI Technical Summary

Problems solved by technology

[0004] 1) The patent whose publication number is CN 1098359C, the Japanese patent whose publication number is JP1985121219(A), and the Chinese patent whose publication number is CN 1986861A, the strength of steel cannot reach more than 100ksi under the condition of obtaining better low temperature toughness

Moreover, the invention product is a welded pipe, and the quality of the weld and the fluctuation of the structure and performance of the welding heat-affected zone always exist as a risk factor

[0005] 2) Patents with publication numbers CN 1087356C and CN 1087357C and patents with publication numbers CN1146784A, CN 1148416A and CN 101548026A claim to be able to obtain steel plates with both high height and excellent low-temperature toughness, but the control of the product manufacturing process is difficult, and the industrial The stability of product quality and performance under production conditions is not easy to achieve

Moreover, the invention product is a welded pipe, and the quality of the weld seam and the fluctuation of the structure and performance of the welding heat-affected zone are another potential risk factor

[0006] 3) The Chinese patent with the publication number CN 101343715A discloses a seamless steel pipe with excellent low-temperature toughness and its manufacturing method, which avoids the influence of welding on the performance and quality uniformity of the steel pipe, but it is only used when the yield strength is below 70ksi

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