Harry.C

Different types of stainless

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What is the difference between ferritic, austenitic and martensitic stainless steels?

I've not done much metalwork and I'm looking to get some stainless steel to experiment with.

Harry

 

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There are four major groups of stainless steel defined according to the crystal structure of the steel: austenitic, ferritic, martensitic and duplex. This microstructure of these alloys depends on the alloying elements present in them;  these alloys have different alloying elements as well.

Ferritic steels are high chromium, magnetic stainless steels that have a low carbon content. Known for good ductility, resistance to corrosion and stress corrosion cracking, ferritic steels are commonly used in automotive applications, kitchenware, and industrial equipment. An example is most 400 series

Austenitic steels are non-magnetic stainless steels that contain high levels of chromium and nickel and low levels of carbon. Known for their formability and resistance to corrosion, austenitic steels are the most widely used grade of stainless steel. Example is the 300 series

Martensitic stainless steels are a group of chromium steels ordinarily containing no nickel developed to provide steel grades that are both corrosion resistant and hardenable via heat treating to a wide range of hardness and strength levels. 431 and 440 are examples. 

Duplex and Super Duplex Stainless Steel Duplex stainless steels have a two-phase microstructure that consists of grains of 50% austenitic and 50% ferritic stainless steel. This type of steel has a selection of benefits, and it is often chosen over regular ferritic or austenitic stainless steels due to its increased strength - it is about twice as strong as these metals. Examples are 2205 and 32750

None of these make a good starting point for learning how to forge

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I have a 7 foot SS hex shaft about 2.5 inches across that looks to have been used as a drive shaft for some kind of machinery, probably from the tuna packing plant here, that broke and was found in the local scrap yard. It is non magnetic and i have not tested it yet for hardenability, but will cut off a piece and see how it works as a dive knife. Are there any field tests beyond the magnet and hardenabilty to try to ID SS series?

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If it is nonmagnetic I wouldn't even waste my time trying to harden it. You can probably work harden it, but not with heat.  SS will work harden enough to stop a HSS drill from drilling it.

SS is also not an easy metal to forge - tough. I would think of some other use for that hex you have.

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