Shandong Jiugang Tisco Steel Co., Ltd.
compared to carbon steel
1. Density
The density of carbon steel is slightly higher than that of ferritic and martensitic stainless steel, but slightly lower than that of austenitic stainless steel;
2. Resistivity
Resistivity increases in order of carbon steel, ferritic, martensitic and austenitic stainless steel;
3. The order of linear expansion coefficient is also similar, austenitic stainless steel is the highest and carbon steel is the smallest;
4. Carbon steel, ferritic and martensitic stainless steel are magnetic, and austenitic stainless steel is non-magnetic, but it will produce magnetism when it is cold-work hardened to form martensitic phase transformation, and heat treatment can be used to eliminate this martensite tissue to restore its non-magnetic properties.
Compared with carbon steel, austenitic stainless steel has the following characteristics:
1) High resistivity, about 5 times that of carbon steel.
2) Large linear expansion coefficient, which is 40% larger than that of carbon steel, and as the temperature increases, the value of the linear expansion coefficient increases accordingly.
3) Low thermal conductivity, about 1/3 of carbon steel.
Weldability
Different product uses have different requirements for welding performance. Class I tableware generally does not require welding performance, even some pot companies. However, most products require good welding performance of raw materials, such as second-class tableware, thermos cups, steel pipes, water heaters, water dispensers, etc.
Corrosion resistance
The vast majority of stainless steel products require good corrosion resistance, such as first and second-class tableware, kitchen utensils, water heaters, water dispensers, etc. Some foreign businessmen also conduct corrosion resistance tests on products: heat up to boiling with NACL aqueous solution, and pour it after a period of time. Remove the solution, wash and dry, and weigh the weight loss to determine the degree of corrosion (Note: when the product is polished, because the abrasive cloth or sandpaper contains Fe, it will cause rust spots on the surface during the test)
Polishing performance
In today’s society, stainless steel products generally go through the polishing process during production, and only a few products such as water heaters, water dispenser inner tanks, etc. do not need polishing. Therefore, this requires the polishing performance of the raw material to be very good. The main factors affecting the polishing performance are as follows:
① surface defects of raw materials. Such as scratches, pitting, pickling, etc.
② The problem of raw materials. If the hardness is too low, it will not be easy to polish when polishing (the BQ property is not good), and if the hardness is too low, the orange peel phenomenon will easily appear on the surface during deep drawing, thus affecting the BQ property. BQ properties with high hardness are relatively good.
③For deep-drawn products, small black spots and RIDGING will appear on the surface of the area with a large amount of deformation, which will affect the BQ performance.
Heat resistance
Heat resistance means that stainless steel can still maintain its excellent physical and mechanical properties at high temperatures.
Influence of Carbon: Carbon is an element that strongly forms and stabilizes austenite and expands the austenite zone in austenitic stainless steels. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is an interstitial element that can significantly increase the strength of austenitic stainless steel through solid solution strengthening. Carbon can also improve the stress 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, mainly because carbon can interact with Chromium forms high-chromium Cr23C6 carbon compounds, which leads to the depletion of local chromium, which reduces the corrosion resistance of steel, especially the resistance to intergranular corrosion. therefore. Most of the newly developed chromium-nickel austenitic stainless steels since the 1960s are ultra-low carbon types with a carbon content of less than 0.03% or 0.02%. It can be known that as the carbon content decreases, the intergranular corrosion sensitivity of the steel decreases. Only 0.02% has the most obvious effect. Some experiments also pointed out that carbon will also increase the tendency of pitting corrosion of chromium austenitic stainless steel. Due to the harmful effect of carbon, not only in the smelting process of austenitic stainless steel, the carbon content should be controlled as low as possible, but also in the subsequent heat, cold processing and heat treatment processes to prevent carbonization on the surface of stainless steel and avoid chromium carbides Precipitate.
