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All about stainless steel
Source: | Author:Jasmine | Publish time: 2019-10-17 | 171 Views | Share:
It has excellent aesthetics and has multiple uses at low and high temperatures. As a metal, it has a passivation layer formed of oxide, which prevents any corrosion on the surface, making it a very durable product with a long life cycle. Not only is steel durable, but it can be recycled indefinitely without losing its integrity, so it has long-term value and sustainability.
Different product uses have different requirements for welding performance. A type of tableware usually does not require welding performance, and even includes some potware enterprises. However, most products require raw materials with good welding performance, such as second-class tableware, insulation cups, steel pipes, water heaters, water dispensers, etc.
Corrosion resistance
Most stainless steel products require good corrosion resistance, such as first- and second-class tableware, kitchenware, water heaters, water dispensers, etc. Some foreign traders also test the corrosion resistance of the product: use NACL aqueous solution to boil, then pour it into a period of time, remove the solution, wash and dry, and then weigh the weight to determine the degree of corrosion (note: due to emery cloth or The Fe component in the sandpaper, when polishing the product, will cause the surface to rust during the test)
Polishing performance
In today's society, stainless steel products are usually polished during the production process. Only need to polish some products, such as water heaters and water tanks. Therefore, this requires raw materials with good polishing performance. The factors affecting the polishing performance are as follows:
① Surface defects of raw materials. For example, scratches, pitting, pickling, etc.
②Material problem. If the hardness is too low, it is not easy to polish during polishing (BQ performance is not good), and if the hardness is too low, the orange peel phenomenon easily occurs on the surface during deep drawing, which affects the BQ performance. . High hardness BQ is relatively good.
③After deep-drawing the product, small black spots and bumps will appear on the surface of this area, and the deformation will be large, which will affect the BQ performance.
Heat resistance
Heat resistance means that stainless steel can maintain its excellent physical and mechanical properties at high temperatures.
The role of carbon: Carbon is firmly formed and stabilized in austenitic stainless steel. Elements that define austenite and extend the austenite region. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is an interstitial element, which can significantly increase the strength of austenitic stainless steel through solid solution strengthening. Carbon can also improve the stress resistance and corrosion resistance of austenitic stainless steel in high-concentration chloride (such as 42% MgCl2 boiling solution).
However, in austenitic stainless steels, carbon is generally considered a harmful element, mainly due to the corrosion resistance of stainless steel under certain conditions (such as welding or heating from 450 to 850 ° C), the carbon may be chromium . High-chromium Cr23C6 type carbon compounds will be formed, resulting in local consumption of chromium, which will reduce the corrosion resistance of steel, especially intergranular corrosion resistance. therefore. Since the 1960s, newly developed chromium-nickel austenitic stainless steels are mostly ultra-low carbon types with carbon content below 0.03% or 0.02%. It can be known that as the carbon content decreases, the intergranular corrosion sensitivity of steel decreases. Only 0.02% of the effect is the most obvious. Some experiments also show that carbon will also increase the pitting tendency of chromium austenitic stainless steel. Due to the harmful effects of carbon, not only should the carbon content be kept as low as possible during the austenite stainless steel smelting process, but also in the subsequent hot, cold working and heat treatment processes should be controlled at a low level to prevent the surface Add carbon and avoid chromium carbide precipitation.
Corrosion resistance
If the number of chromium atoms in the steel is 12.5% or more, the electrode potential of the steel can be changed suddenly from a negative potential to a positive potential. Prevent electrochemical corrosion.