Double phase stainless steel gland head casting

Taxonomy:Medium temperature wax silica sol precision casting
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Date of release:2019/02/28
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Stainless steel castings is a general term for steel castings made of various stainless steel materials.

As early as 1910, it was found that steel with Cr content of more than 12% had good corrosion and oxidation resistance.A typical stainless steel contains one or more other alloying elements, such as Ni, Mo, Cu, Nb, Ti and N2, in addition to more than 12% cr.

According to the classification of chemical composition of stainless steel Cr stainless steel and Cr, Ni stainless steel two categories.The main influence on the corrosion performance of stainless steel is the C content and precipitated carbide, so the lower the C content of corrosion resistant stainless steel, the better, usually C 0.08%, but the high temperature mechanical properties of heat resistant steel is determined by the stable carbide precipitated phase in the structure, so the C content of heat resistant steel is high, generally the carbon content in more than 0.20%.

According to the classification of metallographic structure, stainless steels are divided into ferritic stainless steels, martensitic stainless steels, austenitic stainless steels and duplex (ferritic in the austenitic matrix) stainless steels:

(1) ferritic stainless steel

With chromium as the main alloy element, Cr content is generally between 13% and 30%.It has good corrosion resistance to oxidizing medium and air oxidation resistance at high temperature. It can also be used as heat-resistant steel.This kind of steel has poor weldability.Chromium is more than 16%, the as-cast organization bulky, in 400-525 ℃ and between 550-700 ℃ heat preservation for a long time, there will be a "475 ℃" brittle phase and the sigma phase, make steel brittle.475 ℃ brittleness associated with ordering containing Cr ferritic phenomenon.475 ℃ brittle phase and the sigma phase brittleness, can be heated to above 475 ℃ and then quickly to improve the cold.Room temperature brittleness and post-weld heat affected zone brittleness are also basic problems of ferrite stainless steels, which can be improved by vacuum refining, adding trace elements (such as boron, rare earth and calcium) or austenitic forming elements (such as Ni, Mu, N, Cu, etc.).In order to improve the mechanical properties of the weld zone and the heat-affected zone, a small amount of Ti and Nb is usually added to prevent the grain growth in the heat-affected zone.The commonly used ferrite steels are ZGCr17 and ZGCr28.This type of steel has low impact toughness and has been replaced in many cases by austenitic stainless steel with high nickel content.Ferrite steels with a Ni content of more than 2% and N content of more than 0.15% have good impact properties.

(2) martensitic stainless steel

Martensitic stainless steels include martensitic stainless steels and precipitation hardened stainless steels.In engineering application, mechanical properties are the main purpose.Although this kind of steel in atmospheric corrosion and more moderate corrosion medium (such as water and some organic media) has a good ability to resist corrosion, but its corrosion performance is often not as a test item.Its chemical composition range is: Cr13%-17%, Ni2%-6%, C 0.06%.The microstructure is mainly low carbon strip martensite, therefore, has excellent mechanical properties, the strength index is more than two times of the austenitic stainless steel, and has good process properties, especially welding properties.Therefore, it occupies a very important position in important engineering applications and is an important branch in the field of casting stainless steel.

(3) austenitic stainless steel

Austenitic stainless steel can be divided into four groups as Cr‐Ni series;Cr‐Ni‐Mo, Cr‐Ni‐Cu or Cr‐Ni‐Mo‐Cu systems;Cr‐Mn‐N series and Cr‐Ni‐Mn‐N series.The Cr‐Ni series is represented by the famous "18-8".Cr‐Ni‐Mo, Cr‐Ni‐Cu, Cr‐Ni‐Mo‐Cu system on the basis of Cr‐Ni system to add 2%-3% of molybdenum and copper (or both at the same time), in order to improve the corrosion resistance of sulfuric acid, but molybdenum is ferrite forming elements, in order to ensure the austenitization, after adding molybdenum Ni content to increase appropriately.Cr‐Mn‐N series are Ni - saving alloys.When the Cr content is more than 15%, the ideal austenite tissue cannot be obtained by adding fierce alone, and 0.2-0.3% nitrogen must be added, and more than 0.35% nitrogen must be added to obtain a single austenite.Cr‐Ni‐Mn‐N series can be obtained by adding an appropriate amount of N and a small amount of Ni.Of course, to obtain the austenite and ferrite complex phase structure, it is not necessary to add more N and Ni.

(4) austenitic ferrite duplex stainless steel

The metallographic structure of multiphase steel usually contains 5%-40% ferrite to improve the weldability, strength and stress corrosion resistance of the alloy.For example, Cr28%-Ni10%-C0.30% high - carbon and high - chromium alloy steel, has a good ability to sulfuric acid corrosion, can be used to make castings.On this basis, the controllable ferritic steel is developed, which has high strength and good stress corrosion resistance in sulfates.