The removal of the surface oxide of stainless steel plate is to soak the material in alkaline molten salt or solution, which is called alkaline leaching, and alkali leaching is divided into two types: molten salt and solution alkali leaching.
The molten salt is made up of alkali metal or alkaline earth metal hydroxide or carbonate and oxidant, commonly used antioxidants including sodium peroxide, nitrate, potassium permanganate, borax and dichromate, etc.
Molten salt leaching process is to put the stainless steel plate is placed in an alkaline solution of molten corresponding time rapid quenching after soaking in water, the action principle of this method is mainly have two aspects, one is stainless steel plate expansion coefficient of metal oxide coating and the magnesium substrate have distinction, scale of plasticity is lower, stainless steel plate in the quenching water will cause the scale burst or fall off; The second is that some components of the oxide skin, such as MoO3, SiO2, Al2O3 and TiO2, will be dissolved in alkaline solution, and Cr2O3 will also act with molten salt to form high price chromate.
As part of the skin of the stainless steel plate is dissolved and the high price of chromium salt is produced, it will loosen the skin and be easily dissected in the subsequent pickling. Molten salt to remove oxide skin has the advantage of not etching stainless steel substrate, nor cause acid hydrogen embrittlement, due to the strong alkali molten salt oxidizing, alkali leaching can skim and remove the stainless steel panel black ash, moreover the alkali leaching as long as according to the proportion of added regularly molten salt, alkali leaching processing can continue.
But need to pay attention to in alkali leaching operation into the base groove stainless steel plate must be kept dry, can not with water, or it will lead to explosion, stainless steel plate also must be completely immersed in the molten salt, alkali leaching after rapid quenching water quenching is completed in a timely manner to clean water, remove residual alkali on the surface of the stainless steel plate, avoid stainless steel plate by alkali corrosion. Molten alkali trough in the application after a period of time, the bottom of the channel will deposit base mud, stainless steel plate in the alkaline mud not by alkaline process, will form in the pickling local scale couldn’t remove defects, so be sure to get rid of precipitation alkaline mud on a regular basis.
In alkali leaching operation, need to pay attention to some stainless steel materials, such as precipitation hardening stainless steel and high chromium iron ferrite stainless steel, during 450-600 ℃ for alkali Baptist abate material of plastic, need to strictly control the temperature and time.
Principle and molten salt leaching solution of alkali leaching, alkaline leaching and acid pickling solution, can significantly reduce the time to remove the oxide of the stainless steel plate, the technological process is acid, water washing, alkali leaching solution, water washing and three pickling.
Source: China Stainless Steel Plate Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)