Weldability

 

The requirements for weldability vary with the use of the product. A kind of tableware generally does not require welding performance, and even includes some pot enterprises. But most products need good welding performance of raw materials, such as second-class tableware, insulating cup, steel pipe, water heater, water dispenser and so on.

 

Corrosion resistance

 

Most stainless steel products require good corrosion resistance, such as tableware, kitchenware, water heater, water dispenser, etc. Some foreign businessmen also do corrosion resistance tests on products: use NACL water solution to heat up to boiling, pour out the solution after a period of time, wash and dry, weigh weight loss, to determine the degree of corrosion (note: when polishing products, due to sand cloth or sand paper contains). The composition of Fe will lead to rust stains on the surface during testing.

 

Polishing performance

 

In today's society, stainless steel products are usually polished in production. Only a few products, such as water heaters and inner liners of drinking machines, do not need polishing. Therefore, the polishing performance of raw materials is required to be very good. The main factors affecting polishing performance are as follows:

 

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

 

(2) Material quality of raw materials. When the hardness is too low, it is not easy to polish (BQ is not good), and the hardness is too low, the surface of orange peel is prone to appear when deep drawing, which affects BQ. BQ with high hardness is relatively good.

 

(3) After deep stretching, small black spots and RIDGING will appear on the surface of the area with large deformation, which will affect the BQ property.

 

Heat resistance

 

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

 

Effect of Carbon: Carbon is strongly formed and stabilized in austenitic stainless steel. Elements that fix austenite and expand austenite zone. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is a kind of interstitial element. The strength of austenitic stainless steel can be significantly increased by 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 due to the formation of chromium-rich Cr23C6-type carbon compounds with chromium in the steel under some conditions (such as welding or heating at 450-850 C) during the corrosion resistance of stainless steel, which leads to the depletion of local chromium, and the corrosion resistance of the steel, especially the intergranular corrosion resistance, decreases. Therefore. Most newly developed chromium-nickel austenitic stainless steels 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 sensitivity of intergranular corrosion of steels decreases. Only when the carbon content is less than 0.02%, can the most obvious effect be achieved. Some experiments also point out that carbon will increase the pitting corrosion tendency of chromium-austenitic stainless steels. Because of the harmful effect of carbon, not only should the carbon content be controlled as low as possible in the smelting process of austenitic stainless steel as required, but also the surface of stainless steel should be prevented from carburizing and chromium carbide precipitation in subsequent hot, cold and heat treatment processes.

 

Corrosion resistance

 

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