What are the main types of high alloy steel? What are their characteristics?

High alloy steels are divided into austenite type, ferrite type, Martensite type, austenite ferrite type and precipitate hardening type, but currently used for pressure vessels, mainly for austenite type [such as S30408(0Cr19Ni9)] and ferrite type [S11306(0Cr13)]. Martensite is only used in bolts [S42020(2Cr13)]. Iron grain size materials with 475 ℃ brittleness, mouth, brittleness resulting from phase precipitation and grain growth tendency, cold formability, also is not very good, in addition, preheating before welding, must carry on the heat treatment after welding, the main welding difficulty is joint embrittlement, if the joint rigidity, after welding will produce crack, these reasons have limited the iron grain size materials (0 cr13) use; Martensite material has high carbon content, high strength, high hardness, strong tendency of hardening, poor weldability, so it is not used as pressure vessel compression parts; Austenite size high alloy steel toughness, plasticity and good process performance, so it is widely used in pressure vessel, the average austenite size high alloy steel without stabilizing element, stay within the range of 450 ~ 850 ℃ will produce intercrystalline corrosion tendency, when in contact with the corrosive medium due to intergranular corrosion damage, high alloy steel austenite size can also be used for low temperature; The precipitate hardening material belongs to the Cr-Ni high alloy steel strengthened by heat treatment. After heat treatment, there are many kinds of microstructure types。