How hard is YOUR steel?

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.

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

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: