Study On Influencing Factors And Evaluation Methods Of Fish-scaling Resistance Of Enamel Steel

Enamel product is a kind of composite material composed of enamel and metal steel plate,which is widely used for its beauty,sanitation and corrosion resistance.But enamel products have defects,and fish-scaling is the most dangerous one.Because the occurrence of fish-scaling is not regular,it may occur within 3 days after coating or several months later,which will bring serious security risks and economic losses to enterprises and users.Studies have shown that scale explosion has a great relationship with the steel plate’s resistance to fish-scaling.Therefore,predicting the fish-scaling resistance of the enamel steel is the key to effectively reduce the rate of enamel products waste.At present,there are three main standards for evaluating the fish-scaling resistance of enamel steels,namely the international standard ISO17081:2008,the European standard EN10209:2013,and the Chinese national standard GB/T29515:2013.Among them,EN10209:2013 has high detection accuracy and good data stability,so it is widely recognized by domestic and foreign companies,and it is often used as the basis for the inspection of import and export of enamel steel.However,the electrolytic solution used in this standard contains highly toxic reagents Hg Cl₂ and As₂O₃,so there are potential safety hazards and environmental pollution problems during use,which should not be extended to the production site.Secondly,the study found that the fish-scaling resistance of enamel steel is closely related to the precipitation phase.The more the precipitation phase,the better the fish-scaling resistance of the steel plate.By studying the coiling temperature of the steel plate and the precipitation rules of the precipitation phase on the matrix orientation,the precipitation of the precipitation phase can be effectively controlled,thereby improving its fish-scaling resistance.Based on the above reasons,this article first carried out a new non-toxic evaluation method for enamel steels,which was used to replace the Hg Cl₂ and As₂O₃ highly toxic reagents in EN10209:2013.Secondly,the effect of coiling temperature on the fish-scaling resistance of hot-rolled enamel steel was carried out.Third,the EBSD and EDS experimental methods were used to study the precipitation rules of different precipitate phases in different matrix orientations.The conclusion is as follows:1)Hydrogen permeation experiments on 0.6 mm thick 1#steel plates in non-toxic reagents containing sodium thiosulfate pentahydrate and European standard.The TH values of five concentrations of sodium thiosulfate pentahydrate in A,B,C,D and E were studied（In view of the confidentiality requirements of enterprises,the specific concentration of sodium thiosulfate pentahydrate is indicated by letters.）.Comparative experimental results found:The TH value data measured by a non-toxic reagent containing 0.5 ml C concentration sodium thiosulfate pentahydrate solution is the most stable.Although it is different from the European standard TH value,the data has the highest reliability and repeatability.Although there are several data of TH values measured at other concentrations that are close to the TH values of European standards,the upper and lower deviations of the data are large and the stability is not high.Therefore,it was determined that the C concentration of sodium thiosulfate pentahydrate solution+100 ml of 6%sulfuric acid solution was a non-toxic electrolyte formula.2)The TH value of 2#enamel steel with thicknesses of 0.6 mm,0.8 mm,1.0 mm,1.2mm,1.5 mm,and 1.8 mm was tested using a non-toxic reagent containing sodium thiosulfate pentahydrate in C concentration.Compared with the test results of European standard,it is found that the applicable range of the thickness of the non-toxic agent evaluation method is 1 mm to 1.5 mm.Two methods were used to test the TH values of 11different components and different thickness steel plates,and the results were found to be very close,indicating that non-toxic reagents can replace the highly toxic reagents to test the anti-scaling performance of steel plates.In the 14 sets of data,the TH value of 12 groups of non-toxic reagents was greater than the TH value measured by European standards,and the absolute value of the maximum difference was 2.02.Therefore,the critical value of anti-scaling performance of non-toxic reagents was set to 8.7.3)The microstructure and hydrogen permeability of hot-rolled enamel steel plates at three coiling temperatures of 550℃,600℃and 640℃were studied.It was found that the grain structure of the steel sheet was recrystallized during coiling at 600℃,the grain structure was the most uniform,the number of precipitated phases per unit volume was the largest,the hydrogen penetration time was the longest,and the fish-scaling resistance was the best.4)The precipitated phase has a matrix orientation which is easy to precipitate.According to EBSD analysis,it is found that there are three grain orientations of（001）,（111）and（101）in the steel substrate for enamel.By means of EDS surface scanning,it is found that there are precipitates such as tis,tic and tin in the sample.It is found by calculation that the number of precipitates per unit area is the most in（001）orientation,and each precipitate is such a distribution rule,so（001）grain orientation is compatible and easy to precipitate.