Method for producing ultra-fine grains on surface layer of thick/ultra-thick low-alloy steel plate

Abstract

The invention relates to a method for manufacturing a low-alloy steel plate, and particularly discloses a method for producing ultra-fine grains on the surface layer of a thick / ultra-thick low-alloy steel plate. The method specifically comprises the following steps of 1, uniformly heating a plate blank for 30 to 60 minutes, and taking the plate blank out of a furnace; 2, reducing the temperature of the surface layer of an intermediate blank to 350 to 550 DEG C at speed of more than or equal to 10 DEG C per second, and waiting for temperature rise; 3, when the temperature of the surface layer of the intermediate blank returns to 850 to 960 DEG C, and performing multi-pass rolling, wherein the temperature of the surface layer of the plate blank is reduced to be lower than Ar1 at speed of 10 to 80 DEG C per second between every two rolling passes, the rolling of the next pass is started after the temperature rise, and the final rolling temperature is 780 to 850 DEG C; 4, cooling the plate blank after the plate blank is rolled, namely quickly cooling the blank plate at speed of 1 to 20 DEG C per second, air-cooling the blank plate to 250 to 400 DEG C after the temperature rise, and performing stack cooling. According to the method, energy accumulatively stored on the middle part of the thick steel plate is fully used for performing controlled rolling and controlled cooling for multiple times to refine austenite grains on the surface layer on the premise of no remarkable increase of load of a conventional rolling mill.

Description

technical field [0001] The invention relates to a method for manufacturing a low-alloy steel plate, in particular to a method for manufacturing ultra-fine crystals on the surface of a low-alloy steel thick plate / extra-thick plate. Background technique [0002] Steel structure refinement is an important method to ensure high strength and high toughness of steel plate; structure refinement: on the one hand, the austenite grains are refined, which provides more places for subsequent ferrite nucleation, so that ferrite On the other hand, rolling is carried out in a temperature region close to the two-phase region, so that the structure undergoes deformation and induces ferrite phase transformation, thereby refining the ferrite structure; in the production of steel plates, controlled rolling and controlled rolling are generally used. The cold method refines the microstructure of steel. However, for thick plates / extra-thick plates, due to their own thickness effects and production...

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Problems solved by technology

[0002]Steel structure refinement is an important method to ensure high strength and high toughness of steel plate; The ferrite nucleation provides more places, so that the ferrite grains are refined. On the other hand, rolling is carried out in a temperature region close to the two-phase region, so that the structure is deformed and the ferrite phase transformation is induced, so that the ferrite Microstructure refinement; In the production of steel plates, controlled rolling and controlled cooling methods are generally used to refine the microstructure of steel products. However, for thick plates / extra thick plates, due to their own thickness effects and production process characteristics, it is difficult to meet large deformation and Due to the high cooling rate and other conditions, it is difficult to achieve full-thickness microstructure refinement; therefore, it is feasible to only superfine microstructure on the surface of the steel plate and rationally refine microstructure in the center of the steel plate; The super-thick plate with crystal can hinder the crack propagation, has good surface toughness at low temperature, crack resistance and fatigue resistance, and has a good application prospect; search and find, patent publication number: CN101906519A "Low yield is lower than the surface ultrafine grain The manufacturing method of the carbon steel thick plate "and the patent publication number: CN102828116A " based on the TMCP process superfine grain high-strength steel plate and its manufacturing method" The patent discloses the superfine grain manufacturing method of the surface layer, all adopt the cooling after the rough rolling mill The device quickly cools the intermediate billet + warms up the process to achieve the refinement of the surface structure; this method has a certain effect on the refinement of the surface structure of the steel plate, but the refinement effect is not very obvious; especially for the steel plate with a finished thickness ≥ 40mm , because the middle billet is thicker and has a lot of heat in the core, it is difficult to achieve ultra-fine surface structure by a water spray cooling + reheating process for the middle billet

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