Stainless Steel World Magazine October 2024 | Page 34

[ Nickel Alloys ]

[ Nickel Alloys ]

Heat resistant alloys

Typically , when we think about nickel-containing alloys , we are considering their resistance to corrosive attack in an aqueous environment , such as seawater , food processing and production of chemicals . However , there is a group of alloys that are almost exclusively used at temperatures in the range of 540 – 1230 ° C ( 1000 – 2200 ° F ), which we generically describe as Heat Resistant Alloys ( HRA ).
By Geir Moe , Nickel Institute
There are two fundamental types of HRA , the ferritic and the austenitic . Austenitic are the most used because their microstructure provides ductility and high-temperature strength superior to carbon steel . These attributes are due to the presence of nickel , ranging from 8 to 75 %, which produces the austenitic microstructure . The table below shows some common HRA , the most well-known of which is Type 304 . At elevated temperatures , steel forms an oxide layer ( scale ) by reaction with oxygen , which causes metal loss . HRA possess high levels of
Ferrite Body centred cubic
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Austenite Face centred cubic
34 Stainless Steel World October 2024 www . stainless-steel-world . net