What’s up guys?!?!?! It’s Michael with Michael Talks Metal and we’re back for the 140th time and our topic today is the basics of the ferritic types of stainless steels.
When enough Chromium is added to iron it creates a stainless steel. If no other alloying element is added, its metallurgical structure is “ferritic” at all temperatures it would encounter in fabrication and use. Ferritic types are magnetic at temperatures below the Curie point and are used in some applications where magnetic properties come into play.
Very simply, the amount of Chromium determines the degree of general corrosion resistance. More Chromium is more corrosion and oxidation resistant, but would also be more costly. As Chromium increases, ductility and toughness decrease, particularly at low temperature. For these reasons, applications specify the lowest Chromium containing alloy with adequate performance. Ferritic grades are relatively low strength among the stainless steels and are not as easily welded or formed as the Austenitic types.
Some examples help illustrate the kinds of applications where the Ferritic types are most commonly found.
Type 409 at 10.5 -11.75% CR is used in applications like automotive exhaust systems where appearance is not important. Corrosion / oxidation will be visually apparent but not to a degree that would affect lifetime performance. Modern automotive exhaust and pollution control equipment typically require corrosion resistance exhibited by grades of this level of Chromium content.
Type 430 at 16-18 % Chromium is used for automotive and appliance appearance applications in normal environmental conditions or when the environment is a bit more corrosive than acceptable for the lower Chromium grades described above. Free machining grade 430 F……..F designation used here for Free machining using sulfer as the additive ….. and 430F Se (using Selenium as the adder) are more costly but are specified when the lower machining costs provide the benefit that outweighs a loss of some toughness and corrosion performance. Selenium is used when the ductility loss needs to be minimized. Types 434 and 436 have .75 -1.25 %Molybdenum added to increase corrosion performance as compared to 430.
Type 442 at 18-23 % chromium and Type 446 at 23-27 % chromium have the additional oxidation resistance required at even higher temperatures for applications like industrial pollution control exhaust systems.
Specifications and part requirements can alter what we have shown you today, so for the 140th time….
So this is Michael with Michael Talks Metal thanks for watching. For more on any ferritic stainless steels or other metals, visit our website www.michlinmetals.com. Missed last weeks’ video, click here. Still here and haven’t subscribed, condiser doing so now, please. See you next week, same time, same pleace. 10am YT Thursday. I’m out!We’re back for the 140th time and our topic today is the basics of the ferritic types of stainless steels.