Common heat-resistant steel
According to the different use characteristics, heat resistant steel is divided into antioxidant steel with oxidation resistance as the main use characteristics and heat strength steel with high temperature strength as the main use characteristics.
① Resistance oxide steel resistance oxide steel is mostly in the carbon quality fraction of high Cr steel, high Cr Ni steel or high Cr-Mn steel based on the appropriate amount of Si or Al preparation, mainly ferric type and austenitic type two categories. Fertin type antioxidant steel, such as 1Crl3SiAl, its highest use temperature is 900℃, commonly used as nozzle, aling stove hood, etc. Austenitic type antioxidant steel, such as 2Cr20Mn9Ni2Si2N and 3Crl8Mnl2Si2N steel has good oxidation resistance (maximum use temperature up to 1000℃, sulfur corrosion resistance and carburization resistance, and has good casting performance, so it is often used to manufacture castings, but also shear, hot and cold stamping and welding.
Antioxide steel is mainly used for long-term work at high temperature, but the mechanical properties (strength, etc.) requirements are not high parts, such as gas turbine combustion chamber, roller, furnace tube, heat exchanger, etc.
② Thermal strength steel can be divided into three categories: ferrite one bead light body thermal strength steel, martensitic thermal strength steel, austenitic thermal strength steel.
A. The composition characteristics of hot-strong steel are: low carbon, WC <0.2%; Cr and Si improve the oxidation resistance of steel; Cr, Mo (W) are soluble in ferrite and enhance the recrystallization temperature, thus increasing the creep limit of the matrix; Cr, Mo, V (Ti) strengthen the dispersion.
The heat treatment features: normal ignition (950~1050℃) and then 100℃ (i. e. 600~750℃). The normal tissue is fertin + pearlet, and the subsequent high temperature tempering is designed to increase tissue stability (due to carbon dispersion precipitation) to improve creep resistance.
The common steel numbers are 15 CrMo, 12Cr1MoV, 25Cr2MoVA, etc., which belong to low-carbon alloy steel. Its small expansion coefficient, good thermal conductivity, has good cold, thermoplastic processing performance and welding performance, the working temperature in 450~550℃, has a high thermal strength. This kind of steel is mainly used for manufacturing parts on the power plant with small load, such as boilers and pipes with operating temperature less than 600℃, other pipes, pressure vessels, steam turbine rotor, etc.
B. The characteristics of martentic thermal strength steel are: low (medium) carbon, WC=0.1%~0.4%; in the alloy elements contained, high Cr is used to improve the oxidation resistance of steel; Cr, w, Mo, V, (Ti, Nb) and other elements enhance solid dissolution and dispersion; W, Mo can also reduce the tempering fragility.
The characteristics of heat treatment are: quality conditioning treatment + high temperature tempering of 100℃ above the use temperature, and the tissue in its use state is tempering iron body, so as to ensure the stability of the tissue and performance at the use temperature.
The commonly used steel number is 1Crl3, 2Cr13,1CrllMoV, 1Crl2w.MoV, and 4Cr9Si2,4Crl0Si2Mo and other high alloy steel. This kind of steel quenching ability is good, air cooling can get martensite. Its working temperature can be between 550 and 600℃, and the thermal intensity is higher than that of the bead light body hot steel. LCrl 3,2 Crl 3,1CrllMoV and 1Crl2wMoV have high creep resistance and excellent vibration elimination below 500℃, which are suitable for the manufacture of steam turbine blades, so it is also called blade steel.4Cr9Si2,4Crl0Si2Mo are mainly used for the manufacture of engine exhaust valves with a temperature lower than 750℃, so it is also called air valve steel.
C. Austenitic thermal strength steel is characterized by low (medium) carbon, WC=0.1%~0.4%; and contains high Cr, Ni alloy elements. Cr and Ni improve oxidation resistance and improve thermal strength; Cr, W, Mo; Cr, W, Mo and Ti.
The characteristics of heat treatment are: solid solution treatment (heating to more than 1000℃ after oil cooling or water cooling) + 60~100℃ higher than one or two aging treatment, precipitation out of the reinforcing phase, stabilize the steel organization, and further improve the thermal strength of steel. Use state tissue is austenitic (1 Cr14Nil4W2Mo steel) or austenitic plus diffusion precipitated alloy carbide (4Cr14Nil4W2Mo steel).
The common brand number is 1Crl8Ni9Ti and 4Crl4Nil4w2Mo, and the use temperature is from 600 to 700℃. This kind of steel is added on the basis of austenitic stainless steel W, Mo, V, Tl, Ni, Al and other elements, used to strengthen austenite, forming stable carbide and metal compounds, in order to improve the high temperature strength of steel. Because the austenite lattice density is larger than the ferrite, the atomic binding force is large, the diffusion of alloy elements in austenite is slow, so this kind of steel not only high thermal strength, but also high plasticity, toughness, good weldability, cold formability, coupled with a single-phase austenitic organization, and has excellent corrosion resistance.
The antioxidant working temperature of 1Crl8Ni9Ti steel can reach 700~900℃, and it has enough thermal strength at about 600℃, which can be used to manufacture the boiler superheater pipe and main steam pipe below 610℃.4Crl4Nil4w2Mo steel has higher thermal strength and organizational stability. It is commonly used as ultra-high parameter boiler below 650℃, superheater pipe of steam turbine, main steam pipe, and internal combustion engine exhaust valve, steam or gas pipe with working temperature within the range of 650~750℃.
