The main characteristics of stainless steel

Weldability

The requirements for welding performance vary depending on the purpose of the product. A type of tableware generally does not require welding performance, and even includes some pot enterprises. But the vast majority of products require good welding performance of raw materials, such as second-class tableware, insulated cups, steel pipes, water heaters, water dispensers, etc.

Corrosion resistance

The vast majority of stainless steel products require good corrosion resistance, such as Class I and II tableware, kitchenware, water heaters, water dispensers, etc. Some foreign merchants also conduct corrosion resistance tests on the products: heating NACL aqueous solution to boiling, pouring out the solution after a period of time, washing and drying, weighing the weight loss, to determine the degree of corrosion (note: during product polishing, rust spots may appear on the surface during testing due to the presence of Fe in sandcloth or sandpaper)

When the number of chromium atoms in steel is not less than 12.5%, it can cause a sudden change in the electrode potential of the steel, rising from negative potential to positive electrode potential. Prevent electrochemical corrosion.

Polishing performance

In today's society, stainless steel products are generally polished during production, and only a few products such as water heaters, water dispenser liners, etc. do not require polishing. Therefore, this requires good polishing performance of the raw materials. The factors that affect polishing performance mainly include the following:

① Surface defects of raw materials. Such as scratches, pitting, acid washing, etc.

② Material issues with raw materials. 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 phenomenon during deep stretching, which affects BQ performance. High hardness BQ is relatively good.

③ Products that have undergone deep stretching will also have small black spots and RIDGING on the surface of areas with significant deformation, thereby affecting their BQ properties.

Heat resistance performance

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 a interstitial element, and solid solution strengthening can significantly improve the strength of austenitic stainless steel. Carbon can also improve the stress and corrosion resistance of austenitic stainless steel in highly concentrated chlorides (such as 42% MgCl2 boiling solution).

However, in austenitic stainless steel, carbon is often considered a harmful element, mainly due to certain conditions in the corrosion resistance of stainless steel (such as welding or heating at 450-850 ℃), where carbon can form high chromium Cr23C6 type carbon compounds with chromium in the steel, leading to local chromium depletion and a decrease in the corrosion resistance of the steel, especially intergranular corrosion resistance. Therefore. Since the 1960s, most newly developed chromium nickel austenitic stainless steels have a carbon content of less than 0.03% or 0.02% ultra-low carbon type. It can be known that as the carbon content decreases, the sensitivity of steel to intergranular corrosion decreases. The most significant effect is only when the carbon content is less than 0.02%. Some experiments also indicate that carbon can increase the tendency of chromium austenitic stainless steels to pitting corrosion. Due to the harmful effects of carbon, it is not only necessary to control the carbon content as low as possible during the smelting process of austenitic stainless steel, but also to prevent surface carbonization and the precipitation of chromium carbides in subsequent hot, cold work, and heat treatment processes.