High-strength high-ductility X70 thick-wall seamless pipeline steel and manufacturing method

Abstract

The invention provides a high-intensity and high-toughness X70 thick-walled seamless pipeline steel. The steel comprises the following elements, in weight percentage: 0.04 to 0.12 percent of C, 0.17 to 0.35 percent of Si, 1.20 to 1.60 percent of Mn, 0.015 percent or less than 0.015 percent of P, 0.010 percent or less than 0.010 percent of S, 0.10 to 0.30 percent or less than 0.10 to 0.30 percent of Mo, 0.005 to 0.045 percent of Al, 0.02 to 0.06 percent of Nb, 0.02 to 0.10 percent of V, 0.10 to 0.25 percent of Cu, 0.10 to 0.30 percent of Ni, 0.010 to 0.030 percent of Ti, 0.20 percent or less than 0.20 percent of Cr, 0.43 percent or less than 0.43 percent of CE, 0.22 percent or less than 0.22 percent of Pcm, balance iron and trace impurity element. The invention also provides a seamless pipeline steel rolling and manufacturing method. The invention has the advantages that micro-alloy steel is adopted, the seamless pipeline steel is suitable for the production of the thick-walled pipeline with the wall thickness of less than 36 mm, the overall structure of the pipe adopts an even Bainite structure, the carbon equivalent is low, the welding performance is good, the impact performance at low temperature is good, the requirements of the thick-walled pipeline used in deep sea and under other cold weather are satisfied, the mechanical property of the pipeline is enhanced, the steel hardness penetration when in water quenching is improved, and the difficult problem of thick-walled pipe machining by a chamfering machine is solved.

Description

technical field [0001] The invention belongs to the manufacturing technology of seamless steel pipes in the metallurgical industry, and relates to a X70 thick-wall seamless pipeline steel suitable for high strength and high toughness and a manufacturing method thereof. Background technique [0002] With the development of offshore and deep-sea oilfields, the demand for large-scale and thick-walled pipelines is gradually increasing. In order to transport farther and deeper oil and gas to the coast, the corresponding pipelines require longer lengths and thicker walls. Therefore, pipelines not only require good welding performance, high strength and high toughness, but also high anti-collapse performance. To achieve high anti-collapse performance requirements, on the one hand, it can be improved by increasing the steel grade, and the other way is to increase the wall thickness. For pipelines, increasing the steel grade not only involves crack propagation, but also involves The...

AI Technical Summary

Problems solved by technology

[0003] At present, there are X52, X60, X65, X70, X80, X100 and other steel grades patents for the design and manufacture of API 5L pipelines, but these patents are basically for thin-walled pipelines with a wall thickness less than 20mm, and for wall thickness Patents for thick-walled seamless pipelines greater than 20mm and steel grades higher than X60 have not yet been seen

The progress of metallurgical technology and the development of micro-alloyed pipeline steel make it possible to produce thick-walled pipeline steel with high strength, high toughness and good weldability. more difficult

If quenching and tempering treatment is used, due to the limitation of the carbon equivalent of pipeline steel and the wall thickness exceeding 20mm, generally speaking, pipeline steel with a wall thickness greater than 20mm is called a thick-walled pipeline. The cooling capacity during quenching is limited, and it is difficult to ensure The internal structure is consistent with the outer surface, which leads to many problems such as inconsistent performance, poor impact performance and poor welding performance. In addition, since thick-walled pipelines are mostly large outer diameters, continuous casting and rolling processes are relatively difficult.

And for thick-walled pipelines, since the weight of a single pipe often exceeds the design range of the chamfering machine, bevel processing has always been an important problem that is difficult to solve

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