Acid washing-free direct hot galvanizing method of hot-rolled strip steel

Abstract

The invention relates to an acid washing-free direct hot galvanizing method of hot-rolled strip steel, and belongs to the technical field of metallurgy; mainly aiming at the problems of weak hot galvanizing effect and low oxide scale reduction efficiency in a traditional galvanizing technology, the invention provides a method for improving a hot-rolled strip steel oxide scale reduction ratio; the oxide scale thickness and structure of the hot-rolled strip steel are adjusted in the hot rolling process: the hot-rolled strip steel is straightened in a straightener after being wound; after the surface of the strip is suffered from the bending stress, the strip is repeatedly bent and stretched; the huge difference of iron basal body and oxide scale covering layer material performances is used; the iron basal body is stressed to generate a certain plastic deformation; because of weaker plasticity and low breaking strength, a surface oxide scale layer cannot adapt to the deformation of the iron basal body to cause the internal stress to be higher than the breaking strength so as to finally generate different forms of scale cracks or stripping; the heating reduction is performed in a hydrogen atmosphere to improve the reduction efficiency; and then, the hot galvanizing is performed to obtain a more excellent acid washing-free reduction hot galvanizing effect.

Description

technical field [0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for direct hot-dip galvanizing of hot-rolled strip steel without pickling. Background technique [0002] Galvanizing is the most common anti-corrosion method for metal surfaces. Hot-dip galvanizing is one of the main methods used for galvanizing the surface of steel sheets. The hot-dip galvanizing process has been developed on a large scale along with the rapid development of cold-rolled strip steel. In recent years, due to its increasingly mature technology, stable coating performance, long service life and economic benefits, it has been widely used in many fields such as construction, household appliances, electromechanical industries, and automobile manufacturing. [0003] The substrate used for traditional hot-dip galvanizing on the surface of the steel plate is a cold-rolled substrate. The cold-rolled substrate is obtained by rolling the hot-rolled st...

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Problems solved by technology

[0003] The substrate used for traditional hot-dip galvanizing on the surface of the steel plate is a cold-rolled substrate. The cold-rolled substrate is obtained by rolling the hot-rolled steel strip after cooling. Oxidation occurs in contact with oxygen, and a layer of iron oxide scale is formed on the surface of the steel plate. The existence of the iron oxide scale greatly reduces the galvanizing performance of the steel plate and reduces the performance stability of the obtained galvanized layer; Pickling can obtain good steel surface quality, but it also brings a series of negative effects: the cost of pickling process is relatively high, and the pickling process will inevitably bring some pollution to the environment, and the recovery of waste acid And the regeneration process is complicated, and the cost increases significantly

[0004] Due to the large negative impact of pickling, people began to study the way of cleaning and treating the scale on the surface of the steel plate. At present, the treatment methods mainly focus on three aspects: (1) Scale structure control technology in the hot rolling process: Magazine "Rolling Steel" , the article "Current Situation and Development Trend of Scale Control Technology for Hot-rolled Strip Steel" reported in Volume 29, Issue 4 in August 2012, disclosed that the process parameters such as optimizing phosphorus removal process, hot rolling temperature, and coiling temperature can be eliminated. Red iron sheet, producing pickling-free direct hot-dip galvanized coils; the advantage of this method is that it can reduce pickling operations, but the disadvantage is that the process parameters are not easy to control, and defects such as iron oxide sheet pressing caused by improper control seriously hinder the product grade (2) Acid-free mechanical dephosphorization technology: such as Chinese application number 200610086831.0 "Cold-rolled strip steel Acid-free descaling process and production device” patent application provides a process and production device for acid-free descaling of cold-rolled strip steel, mainly through a multi-roller toothed descaling machine to break the oxide scale on the surface of the strip steel , the remaining scales are removed by the steel brush machine, and then the strip is washed with wet sand with a water content of 5% by high-pressure water in the descaling box, and rinsed with clean water after descaling; the advantage of this method is that the production Hot-rolled sheets can be used as raw materials for post-cold-rolling processes, or directly used for deep drawing or other deformation treatments. The disadvantages are that the equipment is cumbersome and the operation procedures are complicated; (3) using reducing atmosphere CO, H 2 The technology of heating and reducing reaction with oxides, such as the patent application of Chinese application number 201310714802.4 "A method of hot-rolled strip steel pickling-free hot-dip galvanizing based on oxide scale reduction", provides a hot-rolled steel strip based on oxide scale reduction. Pickling-free hot-dip galvanizing method for strip steel. By controlling the temperature rise to adjust the oxide scale structure of the hot-rolled strip steel, the reduction-annealed hot-rolled strip steel is heated and reduced in a hydrogen atmosphere, and then hot-dip galvanized. While reducing environmental pollution , eliminates the corrosion of production equipment by pickling, and reduces the cost. The disadvantage is that after a short period of reduction under low-concentration hydrogen conditions, the reduction efficiency is low; Hot-dip galvanizing method "provides a method that does not require pickling and cold rolling before galvanizing, and uses CO to reduce the oxide scale on the surface of hot-rolled thin strip steel. The advantage is that the pickling and cold-rolling processes are omitted, and CO gas is The metallurgical industry is easy to obtain and the cost is low; the disadvantage is that the diffusion and transmission ability of CO on the surface of the steel plate is weak, the reaction rate is slow, and there are requirements for the thickness of the hot-rolled steel plate, and the application range is limited

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