Quality characteristics of stainless steel

Thickness tolerance

Generally speaking, different stainless steel products require different thickness tolerances of raw materials, such as second-class tableware and thermostat cup, thickness tolerances are generally higher, for - 3-5%, and a kind of tableware thickness tolerances are generally - 5%, steel pipe requirements - 10%, Hotel refrigerators thickness tolerances are - 8%, dealers on thickness tolerances The difference is usually between -4%~6%. At the same time, the difference in product export will lead to different requirements for the thickness tolerance of raw materials. Generally, the thickness tolerance of export customers is higher, while the thickness tolerance of domestic enterprises is relatively low (mostly for cost considerations), and some customers even require - 15%.

Weldability

The different uses of products have different requirements for welding performance. One kind of tableware does not normally require welding performance, and even includes some pot enterprises. But most products need good welding properties of raw materials, such as second-class tableware, insulation cup, steel pipe, water heater, water dispenser and so on.

Corrosion resistance

Most stainless steel products require good corrosion resistance, such as first and second class tableware, kitchenware, water heater, water dispenser, etc. Some foreign businessmen also do corrosion resistance tests on the products: heating to boiling with NACL aqueous solution, pouring out the solution after a period of time, washing and drying, weighing the weight loss, to determine the degree of corrosion. Meaning: When the product is polished, rust spots will appear on the surface of the test due to the Fe content in the abrasive cloth or sandpaper.


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Polishing performance

In today's society, stainless steel products are generally polished in the production process, only a small number of products such as water heater, drinking machine liner, etc. do not need polishing. Therefore, the polishing performance of raw materials is very good. The main factors that affect the polishing performance are as follows:

1. surface defects of raw materials. Such as scratches, pock marks, pickling and so on.

2. raw material quality. Too low hardness, polishing is not easy to polish (BQ is not good), and the hardness is too low, in deep drawing surface prone to orange peel phenomenon, thus affecting the BQ. BQ with high hardness is relatively good.

3. After deep drawing, small black spots and RIDGING will appear on the surface of the area with great deformation, which will affect the BQ property.

Heat resistance

Heat resistance refers to high temperature.

Effect of Carbon: Carbon is an element that strongly forms and stabilizes austenite and enlarges the austenitic zone in austenitic stainless steels. 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 improved by solution strengthening. Carbon also improves the stress corrosion resistance of austenitic stainless steels in highly concentrated chlorides (such as 42% MgCl2 boiling solution).

However, in austenitic stainless steels, carbon is often regarded as a harmful element, mainly due to the formation of chromium-rich Cr23C6-type carbons between carbon and chromium in steels under certain conditions in stainless steels and corrosion-resistant applications (e.g. welding or heating at 450-850 C), resulting in local chromium depletion and corrosion resistance of steels, in particular crystalline resistance. The corrosion resistance decreased. So. Most of the newly developed Cr-Ni austenitic stainless steels since the 1960s are of ultra-low carbon type with carbon content less than 0.03% or 0.02%. It is known that with the decrease of carbon content, the susceptibility to intergranular corrosion of the steels decreases. When the carbon content is less than 0.02%, the most obvious effect is achieved. Some experiments also indicate that carbon can increase the chromium austenitic stainless steel. Point corrosion tendency. Because of the harmful effect of carbon, not only in the smelting of austenitic stainless steel and medium should be controlled as low as possible according to the requirements of carbon content, but also in the subsequent hot, cold processing and heat treatment process to prevent stainless steel surface carburization, and chromium-free carbide precipitation.

Corrosion resistance

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