Method for producing superfine integrated ferrite grain and steel of retained austenite

Abstract

A low-alloy steel containing superfine complete ferrite crystal grains and residual austenite is prepared through smelting in vacuum furnace, casting, heating, cogging rolling, final rolling, water cooling, winding, holding temp and cooling in air. It features that the fast multi-pass rolling with short intervals is performed to ensure superfine crystal grains, use proper amount Si and higher temp for final rolling can ensure complete ferrite, and lower-temp winding can result in residual austenite.

Description

[technical field] [0001] The invention relates to a production method of superfine complete ferrite grains and residual austenite steel, which belongs to the field of low alloy steel manufacturing. The so-called "complete" grains here generally refer to grains with fewer defects in the grains such as dislocations, less heterogeneous atoms such as C atoms in the grains, or relatively pure grains. Grains with fewer defects not only have high strength, but also have low ductile-brittle transition temperature. The presence of retained austenite can inhibit the initiation and propagation of cracks in the steel and significantly improve the plasticity of the steel. [Background technique] [0002] Before the present invention, there were papers such as Seung Chui BAIK of South Korea Puxiang Iron and Steel Co., Ltd. Seung Chui BAIK, etc. disclosed in the document ISIJ Int., Vol.41 (2001), No.3, pp.290-297, "Alloying Elements on Cold-rolled TRIP Steel The influence of mechanical pr...

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Problems solved by technology

[0002] Before the present invention, there were papers such as Seung Chui BAIK of South Korea Puxiang Iron and Steel Co., Ltd. Seung Chui BAIK, etc. disclosed in the document ISIJ Int., Vol.41 (2001), No.3, pp.290-297, "Alloying Elements on Cold-rolled TRIP Steel The influence of mechanical properties and phase transformation", the disadvantage of the steel containing retained austenite is that the microalloying element Nb is added to the steel, which brings certain difficulties to the smelting and rolling process of the steel; at the same time, The cold rolling and annealing process is used, and the production cost is relatively high for hot-rolled steel sheets; in addition, the grain size of the microstructure has not reached the level of ultrafineness below 5 μm, and the ferrite grains do not have the requirement of integrity

Another example is the paper "Retained austenite characteristics of TRIP type bainite steel and Tensile properties", the disadvantage is that the production process has also gone through cold rolling and annealing processes, and the ferrite grain size and shape have not reached the level of ultra-fine and complete

[0003] In addition to the deficiencies in factors such as cost, process and equipment, the steel grades produced under the existing process conditions simply have a certain amount of retained austenite or ultra-fine grains, but do not have retained austenite at the same time. and ultra-fine grains, and even the microstructure characteristics of complete ferrite grains