Factors that limit hardness of stainless steel

[StringJunky]

Why can't you get SS as hard as tool steel?

[studiot]

Hardness is basically a function of carbon content.

Hard steels, like tool steels are basically those with a carbon content of around 4% or greater.

Most stainless steels are austenitic with a much lower carbon content.

This leads to a more ductile steel.

 

It is possible to increase the hardness of stainless - so called surgical steel is stainless and hard enough.

I don't know what level are hardness you are seeking.

 

Here are some actual results from a paper I wrote years ago, following a materials failure investigation.

The (just under) 0.4% carbon stainless steel achieved around 575 Vickers. Pretty hard by most counts an about in the middle of the tool steel range which goes up to about 750 Vickers.

However if you note the fracture toughness of this steel (it was martensitic) it was hopelessly low - equivalent to a pure aluminium can. Thus the steel was well hard enough but cracks could (and did) propagate due to the flow fracture toughness. The steel was too brittle.

Edited August 2, 2018 by studiot

[StringJunky]

Thanks for the info so far. My current mini-project is researching all things scissors and the hardest-edged scissors are white paper steel, blue paper steel and Damascus steel, which are all 59+ Rockwell C (Don't know Vickers scale).  The trouble is they can go rusty and this led me onto wondering why SS scissors can't be as hard. The scissors I mentioned  are laminated with a softer steel; only the edge steel face  is really hard.

Yes, I can see from your table that fracture toughness and hardness go in opposite directions; you can have one or the other but not both as you head in either direction.

 

Edited August 2, 2018 by StringJunky

[studiot]

Sorry one small booboo.

The Kreutz stainless was 0.4% carbon (now corrected on the last post)

[John Cuthber]

Faraday did some research on stainless steels containing platinum which is hard and rustproof.

How good is your research budget?

[Sensei]

8 hours ago, studiot said:

Hard steels, like tool steels are basically those with a carbon content of around 4% or greater.

It's important how uniformly contamination is mixed with base material. Local less, or local more, is weakening that region of material.