【2026 Valve Material Selection】Valve material selection and heat treatment processes
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I. Common materials for valve bodies and applicable operating conditions The valve body is the main pressure-bearing component of a valve, and its material must meet the \"pressure-temperature class\" standards. The following are the nine major categories of commonly used valve body materials and their typical application areas:
II. Heat treatment process for valve body blanks Valve body blanks made of different materials (cast or forged) require appropriate heat treatment to eliminate internal stresses, refine the grain structure, and improve mechanical properties as well as workability. 1. Heat treatment of gray cast iron: Thermal aging (stress-relief annealing): This is a process that must be carried out on gray cast iron valve bodies in order to eliminate residual stresses from casting, thereby preventing dimensional deformation and cracking. High-temperature annealing: Used only when primary cementite (martensitic structure) is present in the cast structure, to eliminate free cementite and improve machinability. It can usually replace thermal aging.
2. Heat treatment of carbon cast steel: Cast steel parts suffer from significant casting stresses and coarse grains, requiring the following treatments: annealing or normalizing + tempering: to eliminate stresses, refine the microstructure, improve mechanical properties, and enhance machinability. The common processing method is: normalizing (air cooling at 850~900°C) + tempering (air cooling at 600~680°C).
3. Heat treatment of austenitic stainless steels. The main problem with austenitic stainless steels is their tendency to suffer from intergranular corrosion, which can be prevented through heat treatment: Solution treatment (quenching): The material is heated to 1050–1100°C and then rapidly cooled (by water quenching) to ensure that the carbides dissolve completely, thereby improving corrosion resistance. Stabilization treatment: For grades containing titanium or niobium (such as 321, 347), heating at 850–900°C after solution treatment allows titanium or niobium to combine preferentially with carbon, thereby preventing intergranular corrosion. Cryogenic treatment: Used in certain low-temperature applications to reduce residual austenite and improve dimensional stability.
4. Heat treatment of martensitic heat-resistant steels. Martensitic heat-resistant steels (such as 1Cr5Mo, WC6, etc.) have the property of air quenching; therefore, they must be annealed promptly after casting to prevent cracking, and the annealing holding time should be sufficient (4–8 hours). Purpose of annealing: to relieve stress, recrystallize, refine grains, reduce hardness, and improve workability. The final heat treatment involves normalizing plus tempering (e.g., normalizing at 950–1000°C with air cooling, and tempering at 700–750°C with air cooling).
5. Heat treatment of carbon forged steel: Taking a No. 35 forged steel valve body as an example: After forging: normalizing treatment is carried out to eliminate forging stresses and refine the grain structure. Final heat treatment: As specified in the valve technical documents, quenching and high-temperature tempering are usually carried out to achieve good overall mechanical properties (a balance between strength and toughness).
III. Material selection for other key components of valves 1. Material of the sealing surface: The sealing surface is the most critical working surface of a valve, and it must possess properties such as corrosion resistance, wear resistance, erosion resistance, and oxidation resistance.
2. Stem material: The stem is subjected to tension, compression, and torsion, and it comes into contact with the medium as well as experiences friction with the packing. It requires sufficient strength, toughness, corrosion resistance, and scratch resistance.
3. Material of the stem nut: The stem nut is in threaded engagement with the stem, and it is required to have a low friction coefficient, be rust-resistant, and resistant to seizure.
4. Packing material: The packing is used for sealing the valve stem to prevent leakage of the medium.
IV. Quick Reference: Relationship between Valve Material and Temperature