# How hard is YOUR steel?

**URL:** <https://boards.straightdope.com/t/how-hard-is-your-steel/56765>\
**Category:** Factual Questions\
**Created:** [March 5, 2001, 1:25am UTC](https://boards.straightdope.com/t/how-hard-is-your-steel/56765 "2001-03-05T01:25:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mechmage](https://avatars.discourse-cdn.com/v4/letter/m/4bbf92/32.png) [@mechmage](https://boards.straightdope.com/u/mechmage)\
**Post date:** [March 5, 2001, 1:25am UTC](https://boards.straightdope.com/t/how-hard-is-your-steel/56765/1 "2001-03-05T01:25:12Z")

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Dear Millions,  
In many sources, I have seen the material knives are made out of called 420 stainless steel, or 440 steel? What does this mean?  
H. J.

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**Author:** ![Shiva](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@Shiva](https://boards.straightdope.com/u/Shiva)\
**Post date:** [March 5, 2001, 1:43am UTC](https://boards.straightdope.com/t/how-hard-is-your-steel/56765/2 "2001-03-05T01:43:37Z")

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Here’s a good site for finding out the properties of many nmetals: [http://www.principalmetals.com/properties/step1.asp](http://www.principalmetals.com/properties/step1.asp)

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**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\
**Post date:** [March 5, 2001, 3:16am UTC](https://boards.straightdope.com/t/how-hard-is-your-steel/56765/3 "2001-03-05T03:16:31Z")

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AISI 420 stainless steel has the following composition:

0.15% Carbon  
12.0 - 14.0% Chromium  
1.00% Manganese  
\<0.04% Phosphorus  
1.00% Silicon  
\<0.03% Sulfur

AISI 440 stainless steel is typically found in three grades: A, B, and, ironically, C, with the main difference being their carbon content:

440 A:

0.60-0.75% Carbon  
16.0 - 18.0% Chromium  
1.00% Manganese  
0.75% Molybdenum  
\<0.04% Phosphorus  
1.00% Silicon  
\<0.03% Sulfur

440 B:

0.75-0.95% Carbon  
16.0 - 18.0% Chromium  
1.00% Manganese  
0.75% Molybdenum  
\<0.04% Phosphorus  
1.00% Silicon  
\<0.03% Sulfur

440 C:

0.95-1.20% Carbon  
16.0 - 18.0% Chromium  
1.00% Manganese  
0.75% Molybdenum  
\<0.04% Phosphorus  
1.00% Silicon  
\<0.03% Sulfur

And from the [Steel FAQ](http://www.sff.net/people/pff/steel.txt):

> [@](#):
>
> “STAINLESS” Steels:  
> Remember that all steels can rust. But the following steels, by virtue of their \> 13% chromium, have much more rust resistance than the above steels. I should point out that there doesn’t appear to be consensus on what percent of chromium is needed for a steel to be considered stainless. In the cutlery industry, the de-facto standard is 13%, but the ASM Metals Handbooks says “greater than 10%”, and other books cite other numbers. In addition, the alloying elements have a strong influence on the amount of chromium needed; lower chromium with the right alloying elements can still have “stainless” performance.  
> 420  
> Lower carbon content (\<.5%) than the 440 series makes this steel extremely soft, and it doesn’t hold an edge well. It is used often for diving knives, as it is extremely stain resistant. Also used often for very inexpensive knives. Outside salt water use, it is too soft to be a good choice for a utility knife.
> 
> 440 A - 440 B - 440C  
> The carbon content (and hardenability) of this stainless steel goes up in order from A (.75%) to B (.9%) to C (1.2%). 440C is an excellent, high-end stainless steel, usually hardened to around 56-58 Rc. All three resist rust well, with 440A being the most rust resistant, and 440C the least. The SOG Seal 2000 is 440A, and Randall uses 440B for their stainless knives. 440C is fairly ubiquitous, and is generally considered the penultimate general-use stainless (with ATS-34 being the ultimate). If your knife is marked with just “440”, it is probably the less expensive 440A; if a manufacturer had used the more expensive 440C, he’d want to advertise that. The general feeling is that 440A (and similar steels, see below) is just good enough for everyday use, especially with a good heat treat (we’ve heard good reports on SOG’s 440A heat treat). 440-B is a very solid performer and 440-C is excellent.
> 
> 425M - 12C27  
> Both are very similar to 440A. 425M (.5% carbon) is used by Buck knives. 12C27 (.6% carbon) is a Scandanavian steel used often in Finish puukkos and Norwegian knives.