High-toughness medium-carbon quenched and tempered round steel of grade 120 KSI and manufacturing method thereof

Abstract

The invention discloses high-toughness medium-carbon quenched and tempered round steel of the grade 120 KSI. The high-toughness medium-carbon quenched and tempered round steel of the grade 120 KSI comprises, by mass, 0.35%-0.50% of C, 0.15%-0.40% of Si, 0.60%-1.30% of Mn, equal to or less than 0.015% of P, equal to or less than 0.040% of S, 0.75%-1.30% of Cr, 0.15%-0.35% of Mo, equal to or less than 0.25% of Ni, equal to or less than 0.25% of Cu, 0.015%-0.040% of Alt, equal to or less than 0.10% of V, equal to or less than 0.10% of Nb, equal to or less than 0.05% of Ti, equal to or less than 0.008% of N, equal to or less than 0.0010% of B and the balance Fe and unavoidable impurity elements, wherein the content of V, the content of Nb and the content of Ti are not equal to or less than 0.010% at the same time. The round steel with the maximum specification reaching 260 mm is manufactured through Kanbara reactor (KR) pretreatment, basic oxygen furnace (BOF) smelting, ladle furnace (LF) refining, Ruhrstahl Heraeus (RH) vacuum degassing, continuous casting, heating, continuous rolling, and hardening and tempering, so that the requirements for high specifications and toughness are met.

Description

technical field [0001] The present invention relates to 120KSI steel grade round steel and its manufacturing method, in particular to a quenched and tempered round steel produced by continuous casting and rolling process, which still has relatively high plasticity and normal temperature and low temperature impact toughness when the yield strength reaches 120KSI steel grade and methods of manufacture thereof. Background technique [0002] 4140, 4137, 4145 and other medium carbon quenched and tempered steels have high hardenability, good comprehensive mechanical properties such as strength, plasticity and toughness, and are widely used in oil fields, wind power, machinery and other fields. However, with the development of various industries, customers have higher and higher requirements for materials, and it is difficult for these steel products produced by traditional methods to meet the requirements for use. For example, the quenched and tempered steel used in oil well dril...

AI Technical Summary

Problems solved by technology

On this basis, the yield strength index was further improved, and the 1 / 2 radius hardness and -20°C low-temperature impact requirements were added. It can be seen that the larger the bar size, the higher the requirements for the hardenability of raw materials and equipment. The more difficult it is, the current domestic steel mills and heat treatment manufacturers cannot guarantee such high performance requirements

[0006] The invention patent with the publication number CN102330027 discloses a 120KSI steel grade primary sulfur-resistant drill pipe and its preparation method. The minimum content of precious metal Mo in the steel is 0.5%, and it is 0.6% in the example. The cost of raw materials is very high, and the content of C is between 0.24%~0.30%, the hardenability is poor, and it is difficult to meet the heat treatment needs of large-diameter bars or thick-walled pipes (such as drill collars). And the cost of heat treatment is very high, the patent does not specify the maximum supply specification and mechanical performance sampling depth

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