Strain design based pipe line steel X70 and its manufacturing method

Abstract

The invention discloses strain design based pipe line steel X70 and its manufacturing method. the steel comprises the following ingredients of: by weight, 0.06-0.10% of C, 0.1-0.6% of Si, 1.0-2.5% of Mn, P being less than or equal to 0.015%, S being less than or equal to 0.003%, Cr being less than 0.1%, 0.05-0.35% of Mo, 0.01-0.15% of Nb, 0.005-0.03% of Ti, 0.01-0.06% of Al, one or two components selected from 0-0.5% of Cu and 0-0.5% of Ni, and the balance Fe and unavoidable microscale impurities. The manufacturing method is characterized in that slab heating temperature is 1050-1280 DEG C by a controlled rolling and controlled cooling method; the temperature for controlled rolling in a recrystallization zone is controlled within the range of 900-1250 DEG C; the temperature for controlled rolling in a non-recrystallization zone is controlled within the range of 700-950 DEG C; initial cooling temperature is 650-800 DEG C; finish cooling temperature is 100-500 DEG C; and cooling rate is 5-35 DEG C/s. According to the invention, elements of V, B and the like are not added, and the total amount of Mo, Cu, Cr and Ni is low. In addition, subsequent heat treatment is not required, the process is simple and requires low cost, and production efficiency is high.

Description

technical field [0001] The invention designs a steel for pipelines and a manufacturing method thereof, in particular relates to an X70 steel for pipelines based on strain design and a manufacturing method thereof. The pipeline steel prepared by applying the invention can be applied to pipeline pipes using X70 steel grade in polar regions, permafrost zones, seismic zones and deep seas, as well as welding steel materials for various pressure vessels and engineering machinery. Background technique [0002] In recent years, the change of energy structure and the growth of demand for energy have greatly promoted the exploration and exploitation of new oil and gas resources. Most of the large-reserve oil and gas fields discovered so far are located in areas with special geological conditions such as polar regions, permafrost zones, seismic zones, and deep seas. In the large-scale movement of strata or ocean currents in these areas, the pipeline steel must not only bear high inter...

AI Technical Summary

Problems solved by technology

However, the current X70 and X80 grade pipeline steels are typical less pearlite or acicular ferrite structures. The properties of steel plates corresponding to such structure types have good strength and toughness matching, but their plasticity is insufficient, and uniform deformation and extension The UEL rate is not more than 10%, and the yield strength ratio is mostly above 0.85, and some even reach 0.92

The pipeline steel produced by the traditional TMCP process cannot meet the material selection criteria based on the strain design method

[0005] At present, the research on pipeline steel based on strain design has been reported at home and abroad, but there are the following problems: For example, patents US5545270A, US5531842, US5755895A and CN101456034A provide the composition and manufacturing method of X80 and above duplex pipeline steel, and X70 Grade pipeline steel is not involved, and a large amount of high-priced metal elements Mo, Ni, Cr, etc. are added, which is not suitable for the production of cost-effective pipeline steel

In particular, the patents US5545270A, US5531842 and US5755895A propose to carry out three-stage rolling, which increases the temperature of the intermediate billet once and reduces the production efficiency; the final rolling needs to be carried out in the two-phase interval, because the rolling temperature is low and the rolling resistance is high. Mill demanding

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