Rolling method of X80 pipeline steel plate

Abstract

The invention discloses a rolling method of an X80 pipeline steel plate. Steel comprises the following chemical components including, by mass, 0.03%-0.08% of C, 1.40%-1.7% of Mn, less than or equal to0.001% of S, less than or equal to 0.01% of P, 0.015%-0.25% of Si, less than or equal to 0.1% of Nb, less than or equal to 0.04% of V, 0.015%-0.03% of Ti, 0.025%-0.06% of Alt, 0.6%-1.0% of Mo+Ni+Cu+Cr and the balance Fe and inevitable impurity elements. A key process comprises heating and rolling. According to the method, the chemical component design concept of compounding microalloy elements such as low carbon, low sulfur, low silicon, low phosphorus, Mo+Ni+Cu+Cr and the like is adopted, temperature gradient rolling is adopted for rough rolling, low-temperature high-pressure rolling is adopted for finish rolling, and a three-stage cooling manner is adopted for cooling after rolling, so that a pipeline steel plate which mainly comprises QF+BF and has a small amount of MA is produced. According to the pipeline steel plate, dispersed distribution is adopted, the grain size reaches 11 grades to 12 grades, the pipeline steel plate is of a microstructure with uniform structure sizes at different positions in the thickness direction, the yield strength is 500 Mpa-550 Mpa, the DWTT single value is larger than or equal to 70% at the experimental temperature of -20 DEG C, the average value is larger than or equal to 85%, the thickness is 38.5 mm, the width is 4336 mm, the steel grade is X80, and the low-temperature (-20 DEG C) crack arrest performance is excellent.

Description

technical field [0001] The invention belongs to the technical field of metallurgy, and relates to a rolling method of an X80 pipeline steel plate with large width and thickness and excellent low-temperature crack arrest performance. Background technique [0002] In the process of transporting a large amount of crude oil and natural gas through pipelines for long distances, in order to improve efficiency and reduce costs, one of the most commonly used methods in the world is to expand the diameter and wall thickness of steel pipes. For example, the first natural gas transmission pipeline built in China in 1958, the steel grade is Gr.B, the plate width is 500mm, the thickness is 7.8mm, and the transmission pressure is 4.8Mpa. After more than 60 years of development, the China-Russia East Line Heihe-Shanghai Natural Gas Transmission Pipeline Project under construction in China has a steel grade of X80, which is currently the highest steel grade for safe operation. Adopted for ...

AI Technical Summary

Problems solved by technology

[0008] 2270mm cross-section rolled steel plate with a width of 4336mm and a thickness of 38.5mm; the deformation is insufficient, especially in the unrecrystallized area of ​​the rough rolling stage, the deformation in the thickness direction of the steel plate is insufficient, and the original austenite grains are large, resulting in the internal deformation of the final steel plate. Severely uneven grain size

This rolling method is to roll directly to the thickness of the finished product after coming out of the heating furnace, without avoiding rolling in the part of the recrystallization zone, which is prone to mixed crystal structure, and at the same time, the surface temperature of the steel plate drops to 400~800°C during each rolling. When the austenite grains on the surface of the steel plate are very coarse before the first rolling pass, the ferrite phase transformation occurs, which is detrimental to the properties of the steel plate surface

However, in the case of many rolling passes, the grain size at different positions in the thickness direction will be fine, the phenomenon of mixed crystals is not obvious, and the impact on the crack arrest performance is not too great, and for the small effective compression ratio, the rolling If the number of passes is small, the mixed crystal structure will be serious, which will have a great impact on the crack arrest performance and lead to unstable performance. Therefore, this manufacturing method is suitable for thin steel plates with a thickness not greater than 30mm.

[0018] In short, judging from the technical review of existing invention patents, there is no record of rolling methods with excellent low-temperature crack arrest performance (-20°C DWTT performance) for the plate width 4336mm, thickness 38.5mmX80 pipeline steel

Images