What type of valve internals are generally used in valves made of stainless steel 321?

For 321, the corresponding forged material is A182Gr.F321; this material can be used for the valve internals. For cast parts, A351Gr.CF8C is used, so it is preferable to use 347 for the valve internals. For some of the overseas projects we have worked on, process packages are used, and for the forgings, castings, and internal components, 347 material is employed.

We have used 321 for the valve internals of our A351Gr.CF8C valves； Actually, it’s best to use the same material.

The material of the valve internals shall be no lower than that of the valve body; the valve body is made of 321 material, while the internals use an even higher-grade material

This post was last edited by Liu Jiajia on 2017-2-13 at 17:07. It seems that material 321 is not used for castings; generally, A351Gr.CF8C is used for castings. Is material 321 or 347 typically used for valve internals? 1. Regarding the casting issues of 321: There is a reason why 321 does not have a casting grade in American standards: ① 321 contains titanium, and titanium is highly susceptible to oxidation; generally, foundries lack the appropriate measures to prevent titanium from oxidizing during casting. ② The poor castability of 321 is also due to the tendency of titanium to form titanium carbide sulfide inclusions, which reduces the steel’s plasticity and impact toughness, and can also lead to edge corrosion. ③ The United States is a country with limited titanium resources, yet it is also a major titanium producer (titanium alloys are lightweight, strong, resistant to high temperatures and corrosion, and thus are widely used in industry). Therefore, for its stable-cast stainless/heat-resistant steels, the United States uses only the more abundant alloying element niobium, namely CF8C. China is a country poor in niobium but rich in titanium; since the price of niobium is higher than that of titanium, niobium-containing stainless and heat-resistant steels in China are mainly used to manufacture welding electrodes for stainless/heat-resistant steels. ① ② Technically speaking, 321 castings are not easy to obtain. ③ It is from an economic perspective. For these three reasons, no casting grade for 321 material is specified in the American standards. 2. Comparison of 321 and 347: Both 321, which contains titanium, and 347, which contains niobium, are used to stabilize carbon, thereby reducing the reaction between carbon and chromium that leads to the formation of Cr23C6. They also help to refine the grain structure and reduce harmful impurities and gases in the steel. However, the strength of 347 is slightly higher than that of 321; this is also reflected in its greater pressure resistance, as stated in ASME B16.34 (you can also compare the temperature and pressure values for flanges with the allowable stresses of pipes). The relevant excerpt is as follows: 3. Should valve internals be made of 321 or 347? Generally, the principle is: ① Use 321 for forged valves and 347 for cast valves. ② If the valve body is made of 321, then the internal components should also be made of 321; if the valve body is made of 347, then the internal components should be made of 347 as well.

What the hell is this? That’s what it looks like after editing; I’ve tried many times, but it still doesn’t work. Never mind, I’ll just make do and look at it.

Thank you to those who replied above; it seems everyone is in agreement – use 321 for forgings and 347 for castings

Where can I obtain this material data? Thank you!

Are you referring to the data in those two charts? I already mentioned the source of the data in the reply; it’s in ASME B16.34.

The purpose of 321 and 347 is to prevent intergranular corrosion; 321 contains titanium, while 347 contains niobium. 347 is more expensive than 321, so generally 321 is used for the internal components and 347 for the valve bodies – this combination is the most cost-effective. However, 321 has weaker resistance to intergranular corrosion than 347; if money allows, 347 should be used for the internal components