440A steel is a steel in the 440 family. The others include 440B, 440C, and the less common 440F. All the 440 steels are considered truly stainless, but 440A has the highest corrosion resistance of all because it contains the least amount of carbon.
How 440A Compares to Other Steels
Compared to other metals in the 440 family (ie. 440B and 440C), 440A has a slightly lower carbon content which makes it slightly softer. That means it can be sharpened easily and machined handily. Compared to other kinds of stainless steels, 440A is one of the most common for inexpensive knife blades as it is relatively cheap compared to higher quality steels. Many display only and replica weapons are made with 440A for this reason. Having said this, there are many higher-end knives that use 440A since it can be heated to a very high temperature to achieve very high hardness values.
There are 440A knives that are priced lower, but that is due in part to the quality of the other parts of the knife (handle, fasteners, etc.) and name brand power. So, in some cases, price and stain resistance are the high points of this metal. Besides being used for display knives and swords, it is also a preferred choice for diving knives. Salt water has little corrosive effect on it.
Downsides of 440A Steel
While good in terms of cost and stain resistance, 440A steel is not so stellar in wear resistance. Replica weapons don’t need to withstand use or force, so that is why it is a natural choice for those items. That being said, it’s still said to have enough wear resistance for mild day-to-day use.
You wouldn’t want to construct a survival knife or surgical scalpel out of it. Yet it does well in areas where rust resistance is the primary concern as mentioned regarding sea diving knives. Diving knives aren’t in continuous use, so the wear resistance isn’t an issue. However, those kinds of knives do need to be rust free in adverse conditions.
How 440A is Made
To anneal (heat and then let cool slowly) 440A, heat it to 850-900°C, and slowly cool it to about 600°C in the furnace. After that, air cool. Hardening is done at 1010-1065°C; quenching should be done in air or warmed oil. Right after hardening, it should be tempered at 150-370°C. Lower temperature in tempering yields a harder end product.
If you temper above 370°C, the impact resistance of the blade will be compromised. However, tempering in the range of 590-675°C gives a boost to the impact resistance. The offset is that you lose hardness.
Conclusion About 440A Steel
In short, 440A steel makes a good choice for applications where cost and stain resistance are foremost. If the ability to hold an edge or toughness is a bigger concern, choose another metal. If used as a display item or a light-duty tool, then it will serve well. Most likely, if you purchased a cheap kitchen knife from Walmart or the internet, it will be made of some type of 440 steel, but it’s very possible to get a higher-end version with great construction.