The development of power generation technology requires large capacity and high parameter thermal power units to be used in recent years, and now super (super) critical units have become the main models in the power industry. The boiler is one of the three main engines in a thermal power plant. It has the largest volume, the heaviest weight, the highest internal temperature and the most complex system. It converts the chemical energy of fuel into the heat energy of water steam. One of the most effective ways to improve the efficiency of thermal power plants is to improve the boiler steam temperature, pressure and other parameters, and metal materials restrict this problem. At present, the boiler steel mainly includes:
|ASME||Carbon steel||SA-106B, SA-106C, SA-210C|
|Alloy steel||SA213, T2, T11, T12, T22, T23, T91, T92, SA335 P11, P12, P22, P23, P91, P92|
|Stainless steel||SA213 TP304H, TP347H, TP347HFG, TP310HCbN(HR3C), S30432(SUPER304H)|
|Alloy steel||10CrMo9-10, X10CrMoVNb9-1|
SA-210C: Low carbon steel, has good plasticity, good toughness, weldability, has enough strength below 450℃, has satisfactory oxidation resistance below 530℃, but long-term use above 450℃ will occur pearlite spheroidization and graphite, reduce the creep limit and durable strength, cause burst. 210C steel tubing is used for low and medium pressure boiler (the working pressure is generally not greater than 5.88mpa, the working temperature is below 450℃) heating surface tube; high-pressure boiler (the working pressure is generally above 9.8mpa, the working temperature is between 450℃ ~ 650℃) heating surface pipe, economizer, superheater, reheater, petrochemical industry pipe, etc.
T11, T12, P11, P12: The addition of chromium improves the stability of the carbide, which effectively prevents the tendency of graphitization, but the pearlite spherospherification and alloying element redistribution will lead to the decrease of the thermal strength of the material. When the temperature exceeds 550℃, the thermal strength decreases significantly and the oxidation resistance deteriorates.
T22, P22: They have high thermal strength and durable plasticity, 580℃ surface formation of dense oxide protective film, enough oxidation resistance, good weldability, the long-term operation will appear pearlite spheroidization and alloying element redistribution phenomenon, reduce the thermal strength.
T23: It is reducing the content of C and adds W, V, Nb, B on the basis of T22, and obtain low carbon, multiple, high strength, high toughness bainite type heat resistant steels. At 600℃, its strength is 93% higher than T22, and its weldability and workability are better.
T91: is an improved 9Cr-1Mo high strength martensite heat resistant steel, the steel by reducing the carbon content, adding alloy elements V and Nb, control the content of N and Al, so that the steel has high impact toughness, thermal strength and corrosion resistance. The steel has a small linear expansion coefficient and good thermal conductivity. It is mainly used in the collection box and steam pipe of the boiler with subcritical parameter and supercritical parameter whose wall temperature is less than 600℃.
T92: a new 9%Cr martensite heat resistant steel is obtained by reducing the content of Mo, increasing the content of W and controlling the content of based on T91 steel. The mechanical properties are similar to T91 but the weldability is improved. The creep strength is greatly improved at 600 ~ 650℃. The allowable stress is 34% higher than T91, and the strength is 1.12 times that of TP347H.
T122: T122 is a 12%Cr Martensite heat resistant steel by adding 2% W, 0.07%Nb and 1% Cu, the steel has higher thermal strength and corrosion resistance, carbon content is reduced, welding performance is further improved, mainly used in the manufacture of main steam pipe below 620℃.
SUPER304H: It is an improved type of TP304H with 3% Cu and 0.4% Nb added. Due to fine grain structure and precipitation strengthening of fine copper phase, it has extremely high creep strength, and the allowable stress at 600 ~ 650℃ is 30% higher than THAT of TP304H. It has excellent mechanical properties, steam oxidation resistance and thermal corrosion resistance at high temperature. It can run for a long time below 650℃. It is the preferred material for super (super) critical boiler superheater and reheater.
TP347HFG: It can be said to be a special TP347H stainless steel after specific hot working and heat treatment process. The grain is refined more than 8 times and the allowable stress is increased by more than 20%. It also greatly improves the ability of the material to resist steam oxidation.
HR3C steel (25Cr-20Ni-NB-N steel): A new stainless steel developed in Japan. By limiting the content of C, adding 0.20%-0.60% Nb and 0.15%-0.35% N, and using the dispersed strengthening phase, the material has excellent high temperature strength and high-temperature steam oxidation resistance and is one of the main heat resistant steel pipes for the final superheater and reheater of 650℃ supercritical power plant boiler.