Stainless steel casting is a general term for steel castings made of various stainless steel materials. It is mainly used under various medium corrosion conditions, such as marine castings. As early as 1910, it was found that when the Cr content in steel exceeds 12%, it has good corrosion resistance and oxidation resistance. Typical stainless steels contain one or more other alloying elements, such as Ni, Mo, Cu, Nb, Ti and N2, in addition to Cr12%.

Stainless steel refers to the steel resistant to weak corrosive media such as air, steam and water and chemical corrosive media such as acid, alkali and salt, also known as stainless and acid resistant steel. In practical application, the steel resistant to weak corrosion medium is often called stainless steel, while the steel resistant to chemical medium is called acid resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to chemical medium corrosion, while the latter is generally rust resistant. The corrosion resistance of stainless steel depends on the alloy elements contained in the steel.

Main characteristics of stainless steel:

1. Weldability

The requirements for welding performance are different for different product uses. This type of tableware generally does not require welding performance, and even includes some pot enterprises. However, most products require raw materials with good welding performance, such as class II tableware, thermos cup, steel pipe, water heater, water dispenser, etc.

2. Corrosion resistance

The vast majority of stainless steel products require good corrosion resistance, such as class I and II tableware, kitchenware, water heater, water dispenser, etc. some foreign businessmen also conduct corrosion resistance tests on the products: heat the products with NaCl aqueous solution 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, due to the composition of Fe in the abrasive cloth or abrasive paper, rust spots will appear on the surface during the test).

3. Polishing performance

In today's society, stainless steel products are generally polished during production. Only a few products, such as water heaters and water dispensers, do not need polishing. Therefore, it requires good polishing performance of raw materials. The main factors affecting polishing performance are as follows:

① Surface defects of raw materials. Such as scratches, pockmarks, acid pickling, etc.

② Raw material material problem. If the hardness is too low, it is not easy to polish (BQ property is not good), and if the hardness is too low, orange peel is easy to appear on the surface during deep drawing, thus affecting BQ property. The BQ property with high hardness is relatively good.

③ After deep drawing, small black spots and riding will appear on the surface of the area with great deformation, thus affecting the BQ property.

4. Heat resistance

Heat resistance means that stainless steel can still maintain its excellent physical and mechanical properties under high temperature.

Effect of carbon: carbon is strongly formed and stable in austenitic stainless steel. An element that fixes austenite and enlarges the austenite zone. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is a kind of interstitial element, and the strength of austenitic stainless steel can be significantly improved by solid solution strengthening. Carbon can also improve the stress and 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 (such as welding or heating at 450 ~ 850 ℃) in the corrosion-resistant application of stainless steel, carbon can form Cr23C6 type carbon compound with high chromium with chromium in the steel, which leads to the depletion of local chromium and the deterioration of the corrosion resistance of the steel, especially the intergranular corrosion resistance. Therefore. Most of the chromium nickel austenitic stainless steels newly developed since the 1960s are of ultra-low carbon type with carbon content less than 0.03% or 0.02%. It can be known that with the decrease of carbon content, the susceptibility of steel to intergranular corrosion will decrease. When the carbon content is less than 0.02%, it will have obvious effect. Some experiments also pointed out that carbon will increase the tendency of pitting corrosion of chromium austenitic stainless steels. Due to the harmful effect of carbon, not only the carbon content should be controlled as low as possible in the process of austenitic stainless steel smelting, but also the carburization of stainless steel surface and the precipitation of chromium carbide should be prevented in the subsequent heat, cold processing and heat treatment.

5. Corrosion resistance

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.