There are nine common materials for valve body as follows:
1. grey cast iron, suitable for low pressure valves with working temperature between -15~+200℃ and nominal pressure PN≤1.6MPa.
2. black malleable cast iron, suitable for working temperature between -15 ~ +250 ℃, nominal pressure PN ≤ 2.5MPa low-pressure valves.
3. Ductile cast iron, suitable for working temperature between -30 ~ +350 ℃, nominal pressure PN ≤ 4.0MPa low-pressure valves.
4. Carbon steel (WCA, WCB, WCC), applicable to the operating temperature of -29 ~ +425 ℃ between the medium and high-pressure valves, of which 16Mn, 30Mn operating temperature of -40 ~ +450 ℃, often used in place of ASTMA105.
5. Low-temperature carbon steel (LCB), suitable for operating temperatures between -46 ~ +345 ℃ low-temperature valve valve.
6. Alloy steel (WC6, WC9), applicable to the operating temperature of -29 ~ +595 ℃ between the non-corrosive medium of high-temperature and high-pressure valves; WC5, WC12 applicable to the operating temperature of -29 ~ +650 ℃ between the corrosive medium of high-temperature and high-pressure valves.
7. Austenitic stainless steel, suitable for working temperature between -196 ~ +600 ℃ corrosive medium of the valve.
8. Monel alloy, mainly for valves containing hydrogen and fluorine media.
9. cast copper alloy, mainly applicable to the working temperature of -273 ~ +200 ℃ between the oxygen pipeline valve.
The above list is the valve body of commonly used materials in the broad categories, specific to each type of material, there are many different grades, a variety of different grades and apply to a variety of different pressure levels. Therefore, in the selection of valve body materials, should be based on different uses and different pressure levels, to determine the valve body materials suitable for the needs of the working conditions.
In addition, the valve body materials are titanium alloy (titanium valve), aluminium alloy (aluminium valve); plastic (plastic valve); ceramic (ceramic valve) and so on.
Valve body blank heat treatment process according to different materials are as follows:
1. grey cast iron heat treatment.
In order to achieve different purposes, grey cast iron after casting can be different heat treatment. Valve production of grey cast iron valve body and other parts in the casting of the heat treatment process is often used to eliminate casting stresses and eliminate the casting of hot aging and free carburite annealing at high temperatures. Thermal aging is a necessary process. High-temperature annealing only in the casting due to the chemical composition and casting cooling rate control is not appropriate, resulting in the presence of primary carburite in the casting organisation only when it is used instead of hot aging.
2. Carbon cast steel heat treatment.
Cast steel parts in the casting has a large casting residual stress, sometimes cast steel parts of the organisation of coarse, and even the emergence of superheated organisation. These affect the dimensional stability of cast steel parts, reduce the mechanical properties of steel and unfavourable to the cutting process. In order to eliminate casting stress, refinement of the organisation, improve mechanical properties and improve machinability, valve production of carbon steel valve body and other parts in the casting is often used after annealing or normalising + tempering.
3. Austenitic stainless acid-resistant steel heat treatment.
Austenitic stainless acid-resistant steel is the main defect is prone to intergranular corrosion, generally can be taken to apply a certain amount of heat treatment of steel to prevent measures. Valve production of austenitic stainless acid-resistant steel valve body and other parts are often selected heat treatment process: solution treatment (quenching), stabilisation and deep cold treatment.
4. martensitic heat-resistant steel heat treatment.
Martensitic heat-resistant steel in the casting should be annealed in a timely manner to prevent cracking, and annealing insulation time should be sufficient (generally 4 ~ 8 hours). Martensitic heat-resistant steel annealing is aimed at eliminating stress, recrystallisation, grain refinement, reduce hardness, improve cutting performance, and for the final heat treatment to make organisational preparations.
Martensitic heat-resistant steel final heat treatment using normalising + tempering.
5. Quality carbon steel heat treatment.
High-quality carbon steel heat treatment to 35 forged steel valve body as an example, 35 steel valve body forging to be normalised, and its final heat treatment according to the provisions of the valve manufacturing technology documents, generally to be tempered.