Elements affecting the performance of stainless steel seamless pipes

The quality and performance of stainless steel seamless pipes are determined according to needs. According to different needs, different element contents and types must be matched.

(1) The meaning of carbon in stainless steel and its distribution form largely affect the performance and structure of stainless steel: on the one hand, carbon is a stabilizing austenite element and its effect is very large, about 30 times that of nickel. Times, stainless steel with high carbon content (for example: martensite) can fully accept quenching strengthening, which can greatly improve its strength in terms of mechanical properties; the higher the carbon content, the higher the hardness of the steel, but its The plasticity and toughness are worse.

(2) Phosphorus can significantly reduce the plasticity and toughness of steel, especially at low temperatures. This phenomenon is called cold brittleness. Steel with a high sulfur content is prone to brittleness when subjected to pressure processing at high temperatures, which is usually called hot brittleness. Sulfur and phosphorus must be strictly controlled in stainless steel seamless pipes. But on the other hand, low carbon steel contains high levels of sulfur and phosphorus, which can make it easy to break when cutting. It is beneficial to improve the machinability of steel, but it will reduce toughness and corrosion resistance.

(3) Manganese and nitrogen have similar effects to nickel in stainless steel. The role of manganese in stabilizing austenite is 1/2 that of nickel, that is, 2% manganese can replace 1% of nickel, and the role of nitrogen is about 40 times greater than that of nickel. Therefore, manganese and nitrogen can replace nickel to obtain a single austenite. organize. Manganese content below 2% does not have a significant impact on the performance of stainless steel. However, too high manganese will reduce the corrosion resistance of stainless steel with low chromium content. At the same time, high manganese austenitic steel is difficult to process. Therefore, manganese is not used alone in stainless steel seamless pipe products, and nickel is only partially replaced. Manganese can increase the strength of steel, weaken and eliminate the influence of sulfur, and improve the hardenability of steel. High-alloy steel (high manganese steel) with a high manganese content has good wear resistance and other physical properties. .

(4) Nickel: To obtain a pure austenite structure for low carbon nickel steel, the nickel content needs to reach 24%; to significantly change the corrosion resistance of steel in certain media, the nickel content needs to be above 27%, so , Nickel alone cannot constitute stainless steel. Nickel is an element that protects the large austenite zone, but the role of nickel can only be exerted when combined with chromium. Adding nickel to high-chromium stainless steel can cause obvious changes in the structure. For example, after adding 2% nickel to Cr17 steel, the single ferrite structure will transition to a two-phase state, which can partially undergo quenching strengthening and obtain high mechanical properties. When the nickel content of high-chromium stainless steel is increased to 8%, the martensitic transformation point (M8) of the steel can be dropped below room temperature, allowing it to have an austenite structure at room temperature. This is the widely used 18-8 chromium-nickel austenite. For stainless steel, increasing the nickel content can improve the strength and toughness of the steel and improve the hardenability. When the content is high, it can significantly change some physical properties of steel and alloys and improve the corrosion resistance of stainless steel seamless pipes.

(5) Boron: When steel contains trace amounts (0.001-0.005%) of boron, the hardenability of the steel can be doubled.

(6) Silicon: It can increase the hardness of steel, but the plasticity and toughness are reduced. Electrical steel contains a certain amount of silicon, which can improve the soft magnetic properties.

(7) Vanadium: It can refine the grain structure of steel and improve the strength, toughness and wear resistance of steel. When it melts into austenite at high temperature, it can increase the hardenability of steel; conversely, when it is carbonized When the physical form exists, it will reduce its hardenability.

(8) Chromium: In oxidizing media, chromium can quickly form a layer of chromium-rich oxide film Cr2O3 on the surface of stainless steel seamless pipes that cannot be penetrated and insoluble by corrosive media. This oxide film is very dense and is incompatible with The metal matrix is very firmly combined, which can improve the hardenability and wear resistance of the steel, and improve the corrosion resistance and oxidation resistance of the steel.

(9) Titanium: It can refine the grain structure of steel, thereby improving the strength and toughness of steel. In stainless steel, titanium can eliminate or reduce the intergranular corrosion phenomenon of steel.

(10) Aluminum: It can refine the grain structure of steel, inhibit the aging of low carbon steel, improve the toughness of steel at low temperatures, improve the oxidation resistance of steel, and improve the wear resistance and fatigue strength of steel.

(11) Molybdenum: It can significantly improve the hardenability and thermal strength of steel, prevent temper brittleness, and improve remanence and coercivity. Stainless steel seamless pipes contain molybdenum and low carbon content, which greatly improves their resistance to pitting corrosion in marine and chemical industrial environments.

(12) Copper: Its prominent role is to improve the atmospheric corrosion resistance of ordinary low alloy steel, especially when used in conjunction with phosphorus.

(13) Tungsten: It can improve the red hardness and thermal strength of steel, and can improve the wear resistance of steel.

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