Common Materials of Valve Body and Their Heat Treatment
2016-11-20
Many kinds of valve body materials for different applications. Following are 9 different common materials:
1. Gray cast iron, suitable for working temperature between -15 ~ +200 ℃, nominal pressure PN ≤ 1.6MPa low-pressure valve.
2. Blackheart malleable cast iron, suitable for the low and middle pressure valve whose working temperature between -15 ~ +250 ℃, nominal pressure PN ≤ 2.5MPa.
3. Ductile iron, suitable for the low-pressure valve whose working temperature between -30 ~ +350 ℃, nominal pressure PN ≤ 4.0MPa.
4. Carbon steel (WCA, WCB, WCC), suitable for working temperature between -29 ~ +425 ℃ the middle and high pressure valves, among them, the material 16Mn, 30Mn with working temperature of -40 ~ +450 ℃, generally used to Instead of ASTMA105.
5. Low-temperature carbon steel (LCB), suitable for the LCB valves whose working temperature in -46 ~ +345 ℃ .
6. Alloy steel(WC6, WC9), suitable for high temperature and high pressure valves whose working temperature between -29 ~ +595 ℃ with non-corrosive medium; WC5, WC12 used as body material of high temperature and high pressure valves, suitable for corrosive medium with temperature ranges from -29 to +650 ℃
7. Austenitic stainless steel, selected as body material of valves used for working temperature between -196 ~ +600 ℃ with the corrosive media valves.
8. Monel alloy, mainly used as body of valves whose have hydrogen fluoride medium.
9. Cast copper alloy, this kind of valve body mainly applicable to the working temperature of -273 ~ +200 ℃ used in the oxygen pipeline.
The materials listed above are broad categories of commonly used body materials, there are many different material grades in each specific category, every grade applies to a variety of different pressure levels. Therefore, in the selection of the valve body material, should be based on different uses and different pressure levels, to determine the valve material to meet requirements of different applications
In addition, the valve body materials also includes titanium (titanium valve), aluminum (aluminum valve); plastic (plastic valve); ceramic (ceramic valve) and so on.
The heat treatment technology of valve body rough can be classified following according to different materials:
1. Grey cast iron heat treatment
In order to achieve different purposes, gray cast iron has varied heat treatment after finishing process of casting. In valve production, for the gray cast iron valve and other parts, frequent selected heat treatment are: thermal aging which remove casting stress and high temperature annealing that removes free cementite.
Thermal aging is the necessary procedure,while high temperature annealing, it only happens to replace thermal aging when some primary cementite remain in organization due to the poor operation for process of chemical component and cooling velocity.
2. Carbon steel heat treatment
There are much residual stress after casting process for cast steel, sometimes coarse structure even appearing overheat structure.These will have influence on casting dimensional stability,lower mechanical properties and bad for machining.In order to remove stress,refine microstructure,improve mechanical properties and easy machining,in valve production, general choose annealing or normalizing + tempering as the heat treatment way for the castings..
3. Austenitic stainless steel heat treatment
It generally take precautionary measures to (heat treatment) to avoid the flaws- intergranular corrosion appeared in austenitic cast process.For the valve parts, often heat treatment adopted are:solution treatment(quenching), stabilizing treatment and subzero treatment.
4. Martensitic heat-resistant steel
Timely annealing should be taken after cast process to avoid generating crack,the annealing duration should be enough (4 ~ 8 hours).The purpose of annealing is removing stress, recrystallization, structural grain refining,lower hardness,improve machining properties, creating good preparation for the final heat treatment : normalizing + tempering.
5. High-quality carbon steel heat treatment
General heat treatment is normalizing, the final heat treat will be performed according to the manufacturing technical specifications, such as thermal refining.