Main characteristics of stainless steel products

 

Weldability
Different product uses have different requirements for welding performance. Class I tableware generally does not require welding performance, even including some pot companies. However, most products require good welding performance of raw materials, such as Class II 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 Class II tableware, kitchen utensils, water heaters, water dispensers, etc. Some foreign merchants also conduct corrosion resistance tests on their products: use NACL aqueous solution to heat to boiling, pour out the solution after a period of time, wash and dry, and weigh the weight loss to determine the degree of corrosion (Note: When polishing the product, because the sandpaper or sandpaper contains Fe, it will cause rust spots 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 be suddenly changed 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 tanks do not need polishing. Therefore, this requires that the raw material has good polishing performance. The factors that affect polishing performance are mainly the following:
①Surface defects of raw materials. Such as scratches, pitting, over-pickling, etc.
②Raw material problems. If the hardness is too low, it is not easy to polish (poor BQ performance), and if the hardness is too low, the surface is prone to orange peel during deep drawing, which affects BQ performance. BQ performance with high hardness is relatively good.
③For products that have undergone deep drawing, small black spots and RIDGING will also appear on the surface of the area with extremely large deformation, which affects BQ performance.
Heat resistance
Heat resistance refers to the ability of stainless steel to maintain its excellent physical and mechanical properties at high temperatures.
The influence 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, which 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 high-concentration chloride (such as 42% MgCl2 boiling solution). However, in austenitic stainless steel, carbon is often regarded as a harmful element. This is mainly because under some conditions in the corrosion resistance of stainless steel (such as welding or heating at 450~850℃), carbon can form high-chromium Cr23C6 carbon compounds with chromium in steel, resulting in local chromium depletion, which reduces the corrosion resistance of steel, especially the intergranular corrosion resistance. Therefore. Since the 1960s, the newly developed chromium-nickel austenitic stainless steels are mostly ultra-low carbon types with a carbon content of less than 0.03% or 0.02%. It can be seen that as the carbon content decreases, the intergranular corrosion sensitivity of steel decreases. When the carbon content is less than 0.02%, it has the most obvious effect. Some experiments also point out that carbon will 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 in the subsequent hot, cold working and heat treatment processes, carbon increase on the stainless steel surface should be prevented to avoid the precipitation of chromium carbides.