Weldability
Different product uses have different requirements for welding performance. Category I tableware generally does not require welding performance, even for some pot-type companies. But most products require raw materials with good welding performance, such as second-class tableware, thermos cups, steel pipes, water heaters, water dispensers, etc.
Corrosion resistance
Most stainless steel products require good corrosion resistance, such as Class I and II tableware, kitchen utensils, water heaters, drinking fountains, etc. Some foreign businessmen also conduct corrosion resistance tests on their products: heat NACL aqueous solution until it boils, and pour it after a period of time. Remove the solution, wash and dry, and weigh the weight loss to determine the degree of corrosion (Note: When polishing the product, the Fe component in the emery cloth or sandpaper will cause rust spots to appear on the surface during the test)
When the number of chromium atoms in the steel is not less than 12.5%, the electrode potential of the steel can suddenly change from negative potential to positive electrode potential. Prevent electrochemical corrosion.
Polishing performance
In today's society, stainless steel products generally go through the polishing process during production. Only a few products, such as water heaters and water dispenser linings, do not require polishing. Therefore, this requires the raw material to have good polishing performance. The factors that affect polishing performance mainly include the following points:
①Surface defects of raw materials. Such as scratches, pitting, pickling, etc.
② Raw material problem. If the hardness is too low, it will be difficult to polish during polishing (poor BQ properties). Moreover, if the hardness is too low, orange peel phenomenon will easily appear on the surface during deep drawing, thus affecting the BQ properties. BQ with high hardness is relatively good.
③For products that have undergone deep drawing, small black spots and RIDGING will appear on the surface in areas with great deformation, thus affecting BQ properties.
Heat resistance
Heat resistance refers to the ability of stainless steel to maintain its excellent physical and mechanical properties under high temperatures.
Effect of carbon: Carbon is an element that strongly forms and stabilizes austenite and expands the austenite zone in austenitic stainless steel. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is an interstitial element and can significantly improve the strength of austenitic stainless steel through solid solution strengthening. Carbon can also improve the stress-corrosion resistance of austenitic stainless steel in highly concentrated chlorides (such as 42% MgCl2 boiling solution).
However, in austenitic stainless steel, carbon is often regarded as a harmful element. This is mainly due to the fact that under some conditions in the corrosion-resistant use of stainless steel (such as welding or heating at 450~850°C), carbon can interact with the steel. Chromium forms high-chromium Cr23C6 carbon compounds, which leads to local depletion of chromium and reduces the corrosion resistance of steel, especially the resistance to intergranular corrosion. therefore. Most of the newly developed chromium-nickel austenitic stainless steels since the 1960s are ultra-low carbon types with a carbon content of less than 0.03% or 0.02%. It can be known that as the carbon content decreases, the intergranular corrosion sensitivity of the steel decreases. When the carbon content is lower than Only 0.02% has the most obvious effect. Some experiments also pointed out that carbon will also increase the tendency of pitting corrosion of chromium austenitic stainless steel. Due to the harmful effects of carbon, not only should the carbon content be controlled as low as possible during the smelting process of austenitic stainless steel, but also the surface carbonization of stainless steel and chromium carbides should be prevented during subsequent hot, cold working and heat treatment processes. Precipitate.
