High-strength hot-galvanized dual-phase steel and preparation method thereof

Abstract

The invention relates to high-strength hot-galvanized dual-phase steel and a preparation method thereof, belonging to the field of metallurgy. Mainly aiming at the problems in a hot galvanizing technology for a cold-rolled high-strength steel plate and a direct hot galvanizing technology for a hot-rolled plate, the invention provides the high-strength dual-phase steel directly using hot-rolled strip steel as a raw material and the preparation method thereof. The method uses the hot-rolled strip steel as the raw material, the content of Si element (in percentage by mass) is not less than 0.5 percent, and the content of Mn element is not less than 3 percent; the method breaks through the limit of the galvanized steel plate on the range of additive amount of Si and Mn elements, meanwhile avoids adding Mo and Cr elements with high cost, and is beneficial to developing economical galvanized dual-phase steel. Moreover, the method carries out hydrogen reduction reaction in a continuous hot-galvanizing production line annealing furnace and then carries out direct hot galvanizing, so that the processes of acid picking and cold rolling are saved, the processes are reduce, the cost is reduced, and the environmental problem caused by acid picking is eliminated. Meanwhile, the defects of the prior art are overcome, and the additional facilities and inputs are not added. The method has the advantages of being less in investment, quick in taking effect and convenient to operate.

Description

technical field [0001] The invention belongs to the field of metallurgy, and in particular relates to a high-strength hot-dip galvanized dual-phase steel and a preparation method thereof. Background technique [0002] Reducing fuel consumption and improving the safety of the car body are the development trend of the automobile industry. Reducing the weight of the car is an effective way to reduce fuel consumption, which requires the use of thinner steel plates. However, thinner steel will inevitably lead to a decrease in the safety performance of the car body. To alleviate this The use of high-strength and ultra-high-strength steel plates is the only way for body design; dual-phase steel is a type of high-strength steel, which is generally obtained from low-carbon steel or low-alloy strength steel after critical zone heat treatment or controlled rolling. Its structure is ferrite (F) + a small amount (volume fraction less than 20%) martensite (M), with high tensile strength, ...

AI Technical Summary

Problems solved by technology

[0003] At present, the strength and other properties of the steel plate are mainly improved by adding alloying elements such as Si, Mn, etc., but a higher content of Si element is easy to oxidize on the metal surface to form oxides, which reduces the platability of the material; a higher content of Mn element will As a result, the hardenability of the steel is too high, which is not conducive to the fine control of the material structure; therefore, the content of Si and Mn elements is strictly limited when the conventional cold-rolled sheet is used for hot-dip galvanizing; such as the Chinese patent application number 2015102346487.8 In the application, Si≤0.3%, Mn≤1.5% (in terms of mass percentage), in the Chinese patent application with application number 20141033681.9, Si≤0.2%, Mn≤1.3%; according to different needs in use, V is also added to the steel plate , Ti, Cr, Mo, Nb and other elements, but the cost of these elements is relatively high

[0004] On the other hand, the corrosion resistance of automobiles has also become an increasing requirement for high-end automobiles. Usually, hot-dip galvanized steel sheets are thin steel sheets obtained by hot-rolling or cold-rolling steel billets as base materials. Recrystallization annealing and hot-dip galvanizing treatment are carried out in the annealing furnace of the type hot-dip galvanizing production line (abbreviated as CGL); the manufacture of alloyed hot-dip galvanized steel sheet is further alloyed after hot-dip galvanizing treatment; The manufacturing method of hot-dip steel plate with high-strength steel plate containing a large amount of Si and Mn as the base material, the process is generally continuous casting slab-hot rolling to obtain hot-rolled plate-cold rolling to obtain chilled steel strip-continuous hot-dip galvanizing ; Disclosed in the patent document Japanese Patent Application Publication No. 2009-287114 is the technology that cold-rolled dual-phase steel is annealed and coated at a recrystallization temperature of about 900° C.; The technology of annealing and plating at 900°C; the technology of annealing and plating at 800-850°C is disclosed in the patent document Japanese Patent Application Laid-Open No. 2010-150660; however, in the case of high-strength steel sheets containing a large amount of Si and Mn , when annealing at a high temperature exceeding 750 ° C, Si and Mn in the steel are selectively oxidized, and oxides are formed on the surface of the steel plate, so the adhesion of the coating will be deteriorated, and defects such as missing plating will occur; in the patent document Japan Japanese Patent Application Laid-Open No. 2004-323970 and Patent Document No. 2004-315960 disclose the technique of raising the dew point by specifying the heating temperature in the reduction furnace using an equation represented by the partial pressure of water vapor, thereby causing the iron-based surface layer to However, the region where the dew point is controlled is based on the premise of the entire furnace, so it is difficult to control the dew point and operate stably. In addition, when the alloyed hot-dip galvanized steel sheet is manufactured under unstable dew point control, it will form in the The distribution state of the internal oxides in the base steel sheet is uneven, and there is concern that defects such as coating wettability and alloying unevenness may occur in the longitudinal direction and width direction of the steel strip

[0005] In recent years, the method of direct hot-dip galvanized dual-phase steel has emerged, most of which use reducing atmosphere CO, H 2 The process of direct hot-dip galvanizing after oxidation and reduction with oxides, such as the patent application of Chinese application number 201310714802.4 "A method of hot-dip galvanizing for hot-rolled strip steel based on oxide scale reduction without pickling", provides a method based on oxidation Iron sheet reduction hot-rolled strip steel pickling-free hot-dip galvanizing method, by controlling the temperature rise to adjust the oxide scale structure of the hot-rolled strip steel, heating and reducing the hot-rolled strip steel after reduction annealing in a hydrogen atmosphere, and then performing hot-dip galvanizing, While reducing environmental pollution, it eliminates the corrosion of production equipment by pickling and reduces costs. The disadvantage is that after a short period of reduction under low-concentration hydrogen conditions, there are still some iron oxide scales that have not completely reacted, and the hot-rolled strip steel The content of Si and Mn elements is low, and the strength of the steel plate produced is not high; the Chinese application number is 201510277715.6 "A method for direct hot-dip galvanizing of hot-rolled thin strip based on CO reduction", which uses CO to reduce the surface of hot-rolled thin strip Iron oxide scale, the advantage is that the pickling and cold rolling processes are omitted, and CO gas is easy to obtain in the metallurgical industry, and the cost is low; the disadvantage is that the diffusion and transmission capacity of CO on the steel plate surface is weak, and the reaction rate is slow. The thickness is limited

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