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When is it necessary to harden steel?

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Greetings everyone, 

I am currently testing different types of steel (mainly steels of grades 200s and 300s) for work, some of which have been hardened before to improve their mechanical properties. 

But before I'm starting my project, I was wondering if anyone has a handy spreadsheet or something which says when steel starts to corrode, show signs of wear or which temperatures are critical for the material. And by that I of course mean untreated steels i.e. steels that have not been heat treated or anything. Then, I will compare these results to the steels that have been hardened. Of course I could find out by myself, but it's much easier to run these tests knowing under which conditions you're supposed to test them under. 

Thanks for any helpful answers in advance! I know it's a long shot, but yeah. Worth a try, ye?

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What specification are you referring to for your 200 and 300 series materials?

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2 hours ago, Supe said:

What specification are you referring to for your 200 and 300 series materials?

I'm thinking it's in reference to OU812.

  • Haha 1

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I don't think you're going to find much tabular information relative to any of the three traits you list, because they are very much temperature and service dependent.  That said, I'd go look at the literature available from Outokumpu, Rolled Alloys, and AK Steel as a starting point.  You may find some information relative to cold work properties on grades like the 301 where that sort of thing is common.  

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Those information are quite hard to find, I'm afraid. I have found some info on 202 and the 300 grades here. It's in relation to corrosion but I am not sure how reliable these numbers are. What are the hardening processes you're going to test by the way? There are a lot and they all promise improvement on different mechanical properties (although most are centered on improving hardness). For example boronizing promises a hardness of up to 2800HV (source). I'd be interested to see if they can keep their promise. So if you happen to check that one out, lemme know the results.

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Hardening has little to no effect on corrosion resistance.

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Thru-hardened steels are stronger, and the UTS is tabulated vs hardness value (link, see p. 2). Surface hardening (i.e. carburizing, nitriding, cyaniding, etc.) are often used for gears to increase contact stress resistance, while maintaining a softer core for resistance to shock, but hard enough to resist the bending stresses.

In practice, for a thru-hardened steel (e.g. for a transmission jack shaft), a nominal stress is calculated, and a necessary safety factor is needed, so the strength of the material is defined, leading to the hardness specification on the drawing.

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Here is some insight on 304 steel properties. Hardened steel is resistant to corrosive chemical environments, potable water and atmospheric corrosion. Hardened steel is applied with corrosion-resistant coating to further enhance its resistive properties. To find out specific details, you should probably ask any of steel manufacturers for steel properties and certain metal application.

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