Production method of polyphase structure high tenacity ship plate steel EH40

Abstract

The present invention discloses a production method of polyphase structure high tenacity ship plate steel EH40. The steel includes the following chemical compositions by weight percentage: carbon=0.04-0.08, silicon 0.15-0.35, manganese=1.50-1.60, phosphorus less than and equal to 0.015, sulfur less than and equal to 0.005, niobium less than and equal to 0.02-0.03, titanium less than and equal to 0.008-0.02, aluminum=0.015-0.05, nickel=0.30-0.40, and the remaining of Fe and inevitable impurities. The process steps include smelting, continuous casting, rolling, relaxation and cooling. The methodof the present invention breaks through the limitation of compression ratio for rolling continuously cast bloom by the traditional TMCP process without additional thermal treatment process; high tenacity steel plate with a low temperature impact requirement of below -40 DEG C is produced, the maximum thickness may reach 100 mm, and the product can be widely applied to manufacturing of thick plates in various fields such as shipbuilding, maritime work, wind power, bridge, architecture and engineering machinery; and the method of the present invention can be realized by using the current equipment and process condition of a steel mill, which does not increase investment and equipment upgrading, and further improve the production efficiency and realizes energy conservation and consumption reduction.

Description

technical field [0001] The invention belongs to the technical field of metallurgy, and relates to a production method of ship plate steel EH40 with multiphase structure and high toughness. technical background [0002] When continuous casting slabs are used to produce medium and heavy plate products with high toughness requirements, the traditional rolling method can only produce ferritic pearlite structure or Only the bainite structure has good strength and toughness, so the traditional TMCP process can generally only be used for rolling thin plates below 50mm. For thick plates over 50mm, due to the limitation of the compression ratio, the original austenite grains cannot be fully recrystallized and refined during the rolling process, the structure is generally coarse, and the toughness deteriorates. Usually, an additional heat treatment process is required. Only in this way can the strength and toughness of the thick plate be matched, which not only increases the producti...

AI Technical Summary

Problems solved by technology

For thick plates over 50mm, due to the limitation of the compression ratio, the original austenite grains cannot be fully recrystallized and refined during the rolling process, the structure is generally coarse, and the toughness deteriorates. Usually, an additional heat treatment process is required. In order to ensure the strength and toughness matching of the thick plate, this not only increases the production cost, but also prolongs the production cycle

In addition, the medium and heavy plate products produced by the TMCP process in the world are generally single-phase matrix structures of pure ferrite or pure bainite. Although by controlling the rolling parameters, sometimes a mixed structure of ferrite and bainite can be obtained. Or multi-phase structure, but generally it is a grain structure with relatively coarse grains. Although the strength is improved, the plasticity and toughness are deteriorated.

[0003] Chinese patent 200680039706.2 discloses a "method for manufacturing hot-rolled strip with multi-phase structure", a method for producing TRIP steel (transformation-induced plasticity steel) through hot rolling process, which adds higher carbon, and there is no requirement for the content of Ni, this composition system is only suitable for the production of strips or coils with a thickness of ≤16mm in hot continuous rolling or cold rolling, and is not applicable to single rolled medium and heavy plates

Chinese patent 201180011390.7 discloses a "Multiphase structure stainless steel plate and steel strip and their manufacturing method", through off-line multiphase annealing of cold-rolled stainless steel plate or steel strip to form a multiphase of ferrite and martensite Organization, there is obvious difference with the online rolling of the present invention

Chinese patent 201410791739.9 discloses "A X90 grade multi-phase pipeline steel plate for longitudinal seam welded pipe and its manufacturing method". The chemical composition of the content of the invention is different from that of the present invention. Significantly improve the strength of the steel plate, but it will inhibit the aggregation and diffusion of carbides, thereby inhibiting the generation of ferrite and promoting the formation of granular bainite. Unfavorable, so it is only suitable for pipeline steel products with a thickness below 30mm, not for thick gauge steel plates above 50mm

At the same time, the post-rolling cooling rate in the production process reaches 25-35°C / s. At present, the post-rolling cooling equipment capacity of wide and thick plate manufacturers is not enough, especially for steel plates with a thickness greater than 50mm, it is difficult to achieve such a large cooling rate.

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