O1 tool steel is a cold work steel and is one of the most forgiving for making knife blades. It’s known as a low alloy steel due to the fact that it contains eight additives.  The largest additive is Manganese at just 1.2%. The other minerals added are Carbon at 0.95%, Silicon at 0.4%, Chromium at 0.5%, Tungsten at 0.5%, Vanadium at 0.2%, Phosphorus at 0.3%, and Sulfur at 0.03%. In reference to the listed additives, O1 steel is in compliance with SAE J437 and J438, ASTM A681, and DIN 1.2510.

Chemical Composition

O1 tool steel is a cold work steel and is one of the most forgiving for making knife blades. It’s known as low alloy steel due to the fact that it contains eight additives. 

Element	%
Carbon	0.95
Silicon	0.4
Chromium	0.5
Tungsten	0.5
Vanadium	0.2
Phosphorus	0.3
Sulfur	0.03

 In reference to the listed additives, O1 steel is in compliance with SAE J437 and J438, ASTM A681, and DIN 1.2510.

O1 Tool Steel Properties

Hardness

O1 tool steel specification and instructions specify that this steel hardens and tempers to a Rockwell hardness of 57-58HRC. This is a considerably high hardness level and provides a perfect balance between toughness, wear resistance, and great edge retention.

You do not have to worry about the surface of your O1 steel getting destroyed or chipped away easily.

Toughness

A tough steel blade resists chipping and complete breakdown when subjected to impact, beating, twisting, and torsion. Tough blades are perfect for camping and outdoor use in the wild. Where a normal steel blade might chip or even break down, tougher steel blades are able to withstand that and much more such as batoning sessions, steel strapping, and much more!

The O1 tool makes considerably tough knives. The O1’s steel chipping resistance is quite high compared to other steel knives which have the same Rockwell hardness. The steel provides high toughness levels for knife-making.

Some people might argue that the O1 steel is not the toughest steel available, but we cannot ignore that that it manages to provide a decent amount of toughness for knives while at the same time maintaining high hardness, wear resistance, and grindability.

You can put your full trust in your O1 steel knife to last a good period of time with decent maintenance and without showing any signs of chipping or cracking under stress.

Edge retention

The edge retention is the knife’s ability to hold its sharpness while in use. Whether it is cutting up nylon ropes, cutting fresh meat, sharpening wood, or cutting up cardboard boxes, no one wants to deal with a dull knife. The performance you can observe during cut tests is quite remarkable when you compare high-end steels to lower-end ones.

Edge retention and hardness typically go hand in hand. The O1 steel is mainly used for cutting other knives and blades which means that it delivers decent edge retention.

After sharpening your O1 knife steel, you can be sure as hell that it will retain its sharpness for a really long period of time. This is a great factor as this will lead you to decrease the frequency of sharpening your steel, and subsequently, preserve the steel’s quality.

Corrosion resistance

Are you someone who tends to venture out into the wild, salty, wet, and humid environments? Do you often use your knife for prepping meals with acidic ingredients such as tomatoes or lemon? 

Certain steels are pretty good at resisting rust and corrosion and can be left uncleaned for hours without any complications or ill effects. Carbon steel knives will easily pit and rust in wet, humid environments if not looked after properly. Usually, knives with a low corrosion resistance can be protected with a thin layer of mineral oil.

As we already know, Chromium is the essential factor for controlling corrosion resistance in a steel alloy, besides additional chemical elements like Nitrogen and Molybdenum. Keeping that in mind, the amount of Chromium is quite low – as much as 0.6% – which results in overall average corrosion resistance. 

Ease of sharpening

Usually, the most overlooked aspect of blade steel is its sharpenability and sharpness. Touching up or sharpening certain steels with a sharpening stone can be quite a simple, easy, and relaxing process whereas harder steels can make the process much tougher, tedious, and not so relaxing. 

Achieving the right amount of sharpness can be a life-or-death matter when you are out in the wild, as it determines your ability to cut up and cook food as well as other tasks. It is crucial to keep in mind that an easy to sharpen knife usually indicates low edge retention.

For steel that exhibits such sort of hardness and wears resistance, one would expect it to be equally hard to sharpen. But surprisingly, O1 steel is quite easy to sharpen and does not require you to break your back over it.

Heat Treatment of O1 Tool Steel

Annealing

Strengthening should be performed after hot working and before re-solidifying. 

Warmth at a rate not surpassing 222°C each hour to 802-816°C, and hold at temperature for 1 hour for every inch (25.4mm) of most extreme thickness; 2 hours least. Then, at that point cool gradually with the heater at a rate not surpassing 28°C per hourto 538°C. Keep cooling to surrounding temperature in the heater or in air. The resultant hardness ought to be a limit of 212 HBW. 

Stress Relief of Unhardened Material 

Heat it up gradually to 1250° F. Splash for two hours for every inch of thickness at heat. Moderate cool (heater cool if conceivable) to room temperature. 

Solidifying 

Preheat: Heat marginally prior to dashing into the preheated furnace which ought to be working at about 1100°-1200°F. 

Solidifying: Heat to 1475 to 1500° F. Douse at heat for 30 minutes for each inch of thickness. 

Extinguish: Quench O1 steel in warm oil and permit to cool in the oil until a temperature of 125°-150°F has been reached, or to where the part can be held in the exposed hand, and temper right away. 

Temper: Normally oil solidifying preparations should be single tempered as it were. Notwithstanding, twofold hardening some of the time may be liked. Douse at heat for 2 hours for every inch of thickness for each temper. Air cool to room temperature between tempers. The typical hardening range for this evaluation is 300 to 450° F. 

Stress Relief Temper 

A pressure alleviation temper for solidified material is firmly suggested after huge granulating, or welding, or EDM. Select a temperature that is 25 or 50° F lower than the last treating temperature utilized.

Applications for O1 Steel

O1 tool steel is used for applications requiring tough, rugged parts including punches, knock-out pins, cams, and of course, knife blades. Some old time knife makers have alleged that an expertly made blade of O1 will outperform a blade made of Damascus steel. Some balisong knives use 01 in their latches.

O1 Steel for Knives

O1 steel can be used to make knives because of how easy it is to work with. It is easy to form as well as sharpen. The steel produces a very good edge that won’t dull easily as well. However, O1 steel can rust and care should be taken to prevent rust. Drying and oiling the knife after use is usually sufficient. Some high-end mass produced knives use O1 steel.

Samurai Katana by Swords of Northshire

O1 steel vs. Other steels

O1 vs. 1095

Properties	O1	1095
Toughness	8/10	7/10
Edge retention	6/10	5/10
Corrosion Resistance	3/10	2/10
Ease of sharpening	5/10	7/10

From the above table, it is fair to say that O1 tool steel provides improved toughness, edge retention, and corrosion resistance. 1095 steel provides improved ease of sharpening.

O1 vs. A2

Properties	O1	A2
Toughness	8/10	8/10
Edge retention	6/10	6/10
Corrosion resistance	3/10	5/10
Ease of sharpening	5/10	4/10

From the above table, it is fair to say that the O1 tool steel provides improved ease of sharpening and the A2 steel provides improved corrosion resistance. Both the steels rank equally in terms of toughness and edge retention.

O1 vs. D2

Properties	O1	D2
Toughness	8/10	6/10
Edge retention	6/10	7/10
Corrosion resistance	3/10	4/10
Ease of sharpening	5/10	3/10

From the above table, it is fair to say that the O1 tool steel provides improved toughness and ease of sharpening whereas the D2 steel provides improved edge retention and corrosion resistance.

O1 vs. H1

Properties	O1	H1
Toughness	8/10	7/10
Edge retention	6/10	2/10
Corrosion resistance	3/10	10/10
Ease of sharpening	5/10	8/10

From the above table, it is fair to say that the O1 tool steel provides improved toughness and edge retention whereas the H1 steel provides improved corrosion resistance and ease of sharpening.

Conclusion

In conclusion, O1 steel is one of the most versatile oil quenched, tool steels and makes for a tough, serviceable knife blade. Its toughness slows the machining process, and that makes it excellent for beginners as it takes longer to make a mistake. Thus they are often caught before they become irrecoverable. Also, because it’s so tough, once tempered, it holds an edge and resists wear extremely well. Read our machete review.