Rolling method for large-wall-thickness pipeline steel

Abstract

The invention discloses a method for rolling pipeline steel with large wall thickness, which includes the following process steps: (1) Heating: the continuous casting slab is heated by a walking beam heating furnace, and the preheating section is from room temperature at a rate of 4 to 5 min / cm heating speed, the temperature is controlled at 800~900°C; the heating speed of the heating section is controlled at 6~8min / cm, the temperature is controlled at 1160~1180°C; the temperature of the soaking section is controlled at 1160±20°C, and the holding time is 120~160 minutes; (2) Rolling: rough rolling, finish rolling temperature ≥ 980 ℃, middle billet thickness range 80~90mm, adopt large reduction system at the same time, after widening, there are 2 consecutive passes with reduction rate ≥ 25%; finish rolling, start rolling The temperature is 830°C, the final rolling is 720~740°C, and the rolling is two passes; cooling, the starting cooling temperature is 690~710°C, the cooling speed is 15~18°C / S, and the final cooling is 380~420°C. A pipeline steel with a large wall thickness of 30.8mm, a pipe diameter of 1422mm, and a steel grade of X80 with excellent crack arrest performance was produced by using a billet with a cross-sectional size of 260mm×2280mm. Compared with the TMCP+OLT process, the manufacturing cost is reduced, that is, the online tempering cost is saved.

Description

Technical field [0001] The invention belongs to the technical field of steelmaking and is a rolling method for large-wall thick pipeline steel. Background technique [0002] In the process of long-distance transportation of large amounts of crude oil and natural gas through pipelines, in order to improve efficiency and reduce costs, one of the more commonly used methods in the world is to expand the pipe diameter and increase the wall thickness of steel pipes, such as the Sino-Russian oil and gas transmission east line ( For the Heihe-Changling project, the designed transmission pipe diameter is 1422mm and the pipe wall thickness is 30.8mm. Among the various technical indicators of steel for long-distance oil and gas transportation pipelines, the required steel's crack arrest performance ("DWTT" for short, drop hammer tear test, is an experimental method mainly used to evaluate brittle fracture arrest performance) is One of the key indicators. If the steel has poor crack arrest...

AI Technical Summary

Problems solved by technology

The crack arrest performance of the steel plate produced by this TMCP+OLT process is good, but the cost of online tempering is high, especially it consumes a lot of electric energy, so the TMCP process is used for rolling, especially for small size (300mm×2300mm section) slabs. The DWTT performance of the steel plate is extremely unsatisfactory for the X80 high-grade large-wall pipeline steel with a pipe diameter of 1422 mm and a wall thickness of 30.8 mm.

[0004] The large-wall pipeline steel plate produced by the traditional TMCP process using the slab section size of 260mm×2280mm, the main defect is that the structure of the steel plate is not uniform throughout the thickness direction, and the MAO island (referred to as "MA") is flake and unevenly dispersed. In addition, during the experiment, the hammering force was extremely large, and the stress concentration was serious, resulting in a large percentage of the fracture brittle area of ​​the sample, and the brittleness of the through rod appeared.

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