The full transcript for the video can be found below. In this video we are trying to answer the following questions: What makes stainless steel stainless? What is ferritic stainless steel? Can ferritic stainless steels be heat treated? What’s the difference between austenitic and ferritic stainless steels? What grades of stainless steel are ferritic?
So we know that the element Chromium added to iron is what makes a stainless stainless. If no other alloying element is added its metallurgical structure it’s “ferritic” at all temperatures it would encounter in fabrication and use. Other types of similar Chromium levels typically have advantages over the Ferritic types, but at higher cost. 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. Typical applications specify the lowest Chromium containing alloy with adequate performance. Best value for a given application strikes the balance of all the requirements. Ferritic grades are relatively low strength among the stainless steels and are not as easily welded or formed as the Austenitic types.
The majority of applications using ferritic grades are at the original equipment manufacturer level, otherwise known as “OEMs”, where the design requirements can be well identified and substantial volumes of metal used. Metal producers have been able to create non- standard compositions in addition to the generic standard grades we are describing in this video.
Standard grades offer examples of the kinds of applications that the Ferritic types are used for.
Of the standard commercial alloys, 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 pollution control equipment typically require corrosion resistance exhibited by grades of this Chromium level.
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.
434 and 436 have .75 -1.25 % Molybdenum to increase corrosion performance as compared to 430.
Going a step higher in chromium in the ferritic series….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.
Next in this series will be the Martensitic stainless steels. So stay tuned. If you need a refresh on Austinitic stainless steels check here, and don’t forget to like the video and subscribe here. Thank you for watching, stay healthy and have a great day. This is Michael Michlin Metals, OUT.