Properties of heat-resistant steel

 Properties of heat-resistant steel

Commonly used heat-resistant steels are divided into pearlitic heat-resistant steels, martensitic heat-resistant steels, ferritic heat-resistant steels and austenitic heat-resistant steels.

1. Pearlitic heat-resistant steel

The carbon content is 0.1-0.4%, adding Cr, Mo, W, V, etc. is mainly to strengthen the ferrite, prevent the spheroidization and graphitization of flake Fe3C at high temperature, and improve the high temperature strength of the steel. Typical grades: 12CrMo, 15CrMoV, 25Cr2MoVA, etc.

The microstructure of this type of steel in the normalized state is P+F. Due to the low carbon content and low content of alloy elements (no more than 3-5%), the thermal expansion coefficient is small, the thermal conductivity is good, and it has good cold and hot processing properties. It is widely used in the manufacture of boilers and pipes, pressure vessels, steam turbine rotors, etc. with an operating temperature of 350-600 °C.

2. Ferritic heat-resistant steel

This type of steel has strong oxidation resistance, but low high temperature strength, high brittleness and poor weldability, and is mostly used for heating furnace parts with little stress.

Composition and performance characteristics On the basis of ferritic heat-resistant steel, alloying elements such as Si and Al are added to improve its oxidation resistance.

Typical grades 1Cr13Si3, 1Cr13SiAl, 1Cr18Si2, etc.

3. Martensitic heat-resistant steel

This type of steel has good hardenability, martensite can be obtained by air cooling, and it is used in the range of less than 620 °C. Commonly used steel grades 1Cr13, 2Cr13 and 1Cr11Mo, 1Cr12WmoV developed on the basis of them (it has good creep resistance and excellent shock absorption below 500 °C, and is most suitable for manufacturing steam turbine blades, so it is also called blade steel.)

4. Austenitic heat-resistant steel

On the basis of austenitic stainless steel, W, Mo, V, Ti, Nb, Al and other elements are added to strengthen austenite, form stable carbon compounds and intermetallic compounds, and improve the high temperature strength of steel. Not only has high oxidation resistance (700-900°C), but also has sufficient strength at 600°C. This type of steel is generally used in the range of 600-700 °C.

Commonly used steel grades are 1Cr18Ni9Ti (18-8 type steel), 4Cr14Ni14W2Mo steel (14-14-2 type steel), etc.

5. New ferritic heat-resistant steel

⑴, T91/P91 steel

The new ferritic heat-resistant steel T91/P91 steel is a new generation of medium-alloy heat-resistant steel developed on the basis of 9Cr1Mo steel, using purification, fine-grained metallurgical technology, and micro-alloying, controlled rolling, and controlled cooling. hot steel.

⑵, T122/P122 steel

Ferritic heat-resistant steel T122/P122 (HCM12A) is an improved 12Cr steel, adding 2% Nb and 1% Cu, the effects of solid solution strengthening and precipitation strengthening are greatly increased, and the allowable stress at 600 and 650 ° C are respectively It is 113% and 168% higher than X20CrMoV121, and has higher heat strength and corrosion resistance.

⑶, T23 (HCM2S), T24 steel

It is improved by absorbing the advantages of steel 102 on the basis of T22 (2.25Cr-1Mo) steel. Its strength at 600°C is 93% higher than T22 and comparable to steel 102. However, due to the reduction of C content, the processing performance and welding performance are better than steel 102. In some cases, it can not be preheated before welding; when the wall thickness is less than or equal to 8mm, it can not be heat treated after welding.

6. High temperature mechanical properties of heat-resistant steel

Under the conditions of high temperature, high pressure, high speed and long-term working in corrosive media, heat-resistant steel will undergo changes in organizational structure and mechanical properties, as well as surface wear and corrosion, resulting in failure of parts and accidents. Therefore, it is necessary to understand the high-temperature mechanical properties and corrosion resistance of steel for high-temperature and high-pressure equipment.