Manufacturing method for low-compression ratio hot-rolled 9Ni steel thick plate

Abstract

The invention discloses a low-compression-ratio hot-rolled 9Ni steel thick plate and a manufacturing method thereof. The composition mass percentages of the steel thick plate are: C0.035-0.075%, Si0.15-0.25%, Mn0.50-0.80% , S≤0.006%, P≤0.008%, Ni8.9~9.5%, Alt0.020-0.045%, the balance is Fe and impurities. The manufacturing steps are: converter smelting, LF+RH refining, continuous casting into a 150mm thick slab, rolling in two stages, the rolled piece is cooled by laminar flow, and heat treated by off-line quenching and tempering process. The invention has the advantages of simple alloy composition and low cost; the steel plate with a thickness of more than 35mm is rolled with a low compression ratio, the plate shape is good, the transverse impact energy at -196°C after heat treatment is ≥160J, and the steel plate has good strength and toughness matching.

Description

technical field [0001] The invention relates to a steel rolling process, in particular to a low compression ratio hot-rolled 9Ni steel thick plate and a manufacturing method thereof. Background technique [0002] The demand for LNG in my country is maintaining a strong growth trend. More than 10 LNG receiving bases have been built along the coast of my country. At present, the volume of such land LNG storage tanks does not exceed 160,000 m3, and the thickness specification for 9Ni steel does not exceed 30mm. The 9Ni steel with specifications below 30mm has been produced on an industrial scale in my country. [0003] Usually, the transportation between LNG land tanks and large transport ships, as well as the transportation of offshore and inland rivers, requires small LNG ships. Such small LNG ships or larger volumes, such as land storage tanks of more than 200,000 m3, need to use 9Ni steel plates with a thickness of 50 mm. For example, a 27,000m3 double C-type tank LNG ship...

AI Technical Summary

Problems solved by technology

[0005] Chinese patent CN 101215668 discloses a method for manufacturing 9Ni steel with a carbon content of 0.02-0.04%. The preparation process mainly simulates the continuous casting and rolling process. Thereby shortening the production process, which is difficult to achieve in industrial production

Laminar cooling to below 200°C after hot rolling, in this process, due to the existence of residual deformation stress, thermal stress and phase transformation stress, and the distribution uniformity is difficult to ensure, it will make it difficult to control the shape of the plate after cooling

In addition, its main feature is to carry out heat preservation and quenching in the two-phase zone. The yield strength of the steel plate is as high as 710MPa or more, but the impact energy at -196°C can only guarantee 120J

[0007] Chinese patent CN 102586683 discloses a method for manufacturing 9Ni steel thick plates with a thickness of up to 50 mm. Cu, Ti and Mo elements are added to the alloying design of the steel plate composition , the comprehensive mechanical properties can be improved after the critical quenching process, but it will obviously increase the cost of the alloy

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