Expansion and performance of surface treatment steel plate application field

by:ChangZeng     2021-02-23
Expansion and performance of the application field of surface treatment steel sheet (1) Expansion and performance of the application field of surface treatment steel sheet The majority of surface treatment steel sheets are Zn-plated steel sheets. In 2008, Japan's Zn-coated steel production was 15 million tons, of which 77% was hot-dip Zn steel. Zn-plated steel sheets are used in automobiles, construction, electrical appliances and other aspects, half of which are used in automobiles. Since the 1980s, 55% Al-Zn hot-dipped steel sheets have been widely used in Japan. In coastal areas where sea salt has a great influence, pitting corrosion occurs in Al-plated steel sheets, and the corrosion resistance decreases. The results of long-term exposure to corrosion show that Zn-coated steel sheets produce red embroidery due to Zn consumption, while 5% Al and 55% Al-Zn coated steel sheets maintain corrosion resistance and substitute corrosion protection functions. The metal structure of the 55% Al-Zn coating is a Zn-rich phase containing b-Zn between the primary crystallized Al-rich phase grains. Townsend pointed out that in the early stage of exposure corrosion, the Zn-rich phase first dissolves and exhibits an alternative corrosion protection effect; in the later stage of exposure corrosion, the Al-rich phase plays a role in corrosion resistance. This anti-corrosion mechanism is also reflected in the end face corrosion of Zn-coated steel sheet and 55% Al-Zn-coated steel sheet. The research data pointed out that in the long-term exposure experiment, the corrosion rate of the coating expansion (linear corrosion) of the 55% Al-Zn coated steel sheet from the end surface of the sample at the initial stage of exposure is relatively large, and the coating expansion of the Zn-coated steel sheet in the later period of exposure The corrosion rate is relatively high. At the initial stage of exposure, the Zn-rich phase of the 55% Al-Zn coated steel sheet dissolves at the interface between the coating and the coating. Therefore, the corrosion proceeds rapidly from the end surface of the sample to the inside. When the corrosion proceeds to a certain distance, the distance from the cathode increases. The corrosion rate is reduced. After the corrosion of Zn-plated steel sheet occurs, since there is no Al-rich phase, the area of u200bu200bthe cathode increases, and the corrosion continues. In order to improve the corrosion resistance of 5% Al-Zn coated steel sheet, a series of 6%-11% Al-3%Mg-Zn alloy coated steel products sheets with 3% Mg added are developed. The addition of Mg to 6% Al-Zn prolonged the time of red rust, and the effect of Mg on improving corrosion resistance was also confirmed in the air-exposed samples. No ZnO was found in the corrosion products generated by the exposure experiment of the coated steel plates in the coastal area. The corrosion products generated and accumulated by exposure corrosion greatly inhibit the cathodic reaction. The ZnO in the corrosion product of Zn-plated steel sheet has semiconductor properties and cannot inhibit the cathodic reaction of redox. No ZnO was detected in the corrosion products of the 3% Mg coated steel sheet, which is consistent with the above experimental results. Since the 1980s, the fingerprint-resistant steel sheet and lubricated steel sheet coated with about 1% of organic film on the chromate film, and the steel sheet coated with about 20% of organic film, have realized the realization of pre-coated steel sheets without the coating process. Commercialized and widely used. After that, the RoHS (Regulations Regarding the Restriction of the Use of Certain Hazardous Substances) banning the use of P, Cr6+ and Cd6+ in electrical and electronic equipment came into effect in 2006, advancing the process of Cr-free treatment. The performance characteristics of pre-coated steel sheet are corrosion resistance, high processability, surface defect resistance, anti-fouling, antibacterial, heat absorption, heat dissipation, etc. These properties are mainly determined by the characteristics of the coating film. (2) Cr-free treatment process In recent years, the concept of protecting the global environment, preventing pollution, and building a recycling-oriented society has been strengthened, and the requirements for materials to reduce the environmental load have become higher and higher. In Europe, the RoHS decree for electrical and electronic equipment stipulates the maximum allowable value of P, Hg, Cr6+ and Cd6+ and two organic substances in the form of EU law as 1000 ppm. Products exceeding this value are prohibited from being sold in the EU. The ELV decree on automobile scrapping prohibits the use of P, Hg, Cr6+ and Cd6+. According to the chromate treatment process, Japan has begun to explore alternatives to chromate treatment technology since the chromate treatment process will produce harmful Cr6+. Since no effective method has been found, the chromate treatment process is still in use. However, after the promulgation of the above-mentioned laws and regulations, the study of corresponding measures was accelerated. On the day when the laws and regulations took effect, Japan's Cr-free treatment technology has been fully developed. The Cr-free treatment process should still maintain the barrier function and self-repair function of the chromate treatment film. The mechanism of Cr-free treatment is to use organic resin film less than a few microns to ensure barrier function, use inhibitor to ensure corrosion resistance, and add silane coupling agent to improve the adhesion of organic resin film to metal oxide layer and coating . The corrosion resistance of the high-functional Cr-free organic composite coated steel plate is basically comparable to that of the chromate-treated steel plate. At present, the chemical conversion treatment of Japanese steel plants has basically achieved Cr-free treatment. In the future, a film with better self-repairing and corrosion resistance should be further developed. Araki's method of chemically modifying alkanethiol self-organized monomolecular film with silane compounds to form a binary polymer can obtain high corrosion resistance with a few nanometers thick film, which is a method worthy of attention. (3) Surface treatment steel plates and automobiles Since the 1970s, the goal of surface treatment steel plates for automobiles has been set as the body corrosion protection. Since then, with the gradual increase of the target value, electro-galvanized steel sheets, Zn alloy coated steel sheets, alloyed hot-dip galvanized steel sheets, organic thin film coated Zn-coated steel sheets, etc. have been developed, and the proportion of steel sheets used for automotive surface treatment has been increasing. Recently, in order to reduce fuel consumption, reduce CO2 emissions, and meet the requirements of the ELV Act to reduce environmental load and improve safety, the development of automotive surface treatment steel products sheets is aimed at reducing the weight of the body, non-Cr treatment, and improving collision safety. jobs.
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