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Nickel :

  • Does not harden austenitic stainless steel

  • Ease the tempering of martensitic stainless steel

  • Harden maraging steel by forming precipitates

I also read people saying that it harden ferritic steel. Is it true ?

The chemicals reasons behind all of this are quite unclear for me. Could you explain how it works?

Thanks

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  • $\begingroup$ Hardness is hardly a chemical property. $\endgroup$ – Ivan Neretin Sep 27 '18 at 21:06
  • $\begingroup$ @IvanNeretin - Hardness is a characteristic of chemical compounds. It is used extensively in mineral identification. // The gist is that think of different alloys as different chemical compounds. The how and why that creates hardness in compounds is the subject for a book. $\endgroup$ – MaxW Sep 27 '18 at 23:54
  • $\begingroup$ Unless we want to salami slice part of Chemistry.SE into a MaterialSci.SE, we are going to have to accept materials questions. $\endgroup$ – A.K. Sep 29 '18 at 18:04
  • $\begingroup$ Material science is both part of the program of chemistry and mechanical engineering courses. But while mechanical engineers only know what is happening, chemists know why is it happening. This is why I would rather ask this type of question in the chemistry forum $\endgroup$ – user6131 Sep 30 '18 at 2:34
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I have the following comments about nickel steels:

  • Tensile strength is different than hardness. I assume you are specifically asking about hardness, not strength.

  • Hardness has two different aspects: resisting wear and machinability. Different steels will exhibit different degrees of the two aspects. Ideally, you want a steel that is hard wearing, yet highly machinable.

  • There are different alloys involving nickel, notably the nickel alloys and chromium-nickel alloys. These two types of steel are different.

  • Different alloys have very different hardening characteristics. Even very minor changes to the amount of carbon or nickel in an alloy can have dramatic effects on its hardening characteristics.

  • The main effect of nickel when present in a ferritic or pearlite matrix is to increase the fineness of the grain structure.

  • Nickel slows the growth in size of ferritic/pearlite grains. This makes it easier to obtain a consistent carburization on the surface of a workpiece. For this reason, small amounts of nickel are valuable in alloys which will be case hardened.

  • Nickel preferentially dissolves into the ferritic crystals of certain steel phases, therefore it can potentially increase the hardness of a steel without harming its ductility.

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Metals are hardened by changing the grain structure to make it more difficult for crystals to move. Adding a substance that precipitates or forms a solid solution, e.g. nickel, and locks crystals in place, makes the metal harder but more brittle.

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