Choosing Steel

[Steve Sells]

Choosing a simple steel for blade making.


Choosing the correct steel is the first step in making any blade. There are exceptions to everything I state here, as Metallurgy is a complex field, but I will try to present this information in an easy to understand way, so we can use this information to decide what steels to use for making our blades.

Also most steels manufacturing specifications will not have an exact amount of an added element but a range declared, because of many factors that can happen in the manufacturing process. All steels contain a low level of impurity elements that result from the steel making process. These impurity elements can be eliminated from laboratory prepared steels where cost is not a problem. However, steel is an industrial metal produced in mega-tonnage quantities, and economic production processes result in a low level of certain impurity elements present in steel.

Steel is a mix of iron and carbon. When added in amounts of >2% the mix is referred to as Cast Iron, and in most cases this high of content is not good in a blade steel. Most blade steels are in the range of .50 to 1.0% carbon.

Steels containing a higher amount of carbon in this range are vary good for smaller blades. While steels with a carbon content in the lower range are often used for larger blades, and even swords, This is not a hard and fast rule, as there are makers such as Howard Clark, that do use steels such as AISI number 1086. And there are people using Rail Road spikes, even tho these are 0.30 carbon at best and will never give a great edge, they are a fun novelty.

Today Manganese(Mn) is present in all steels to overcome problems with sulfur embrittlement causing hot shortness. This element also aids in the hardening process, and would be added in the amounts of 0.35% to 0.75% in most of the steels we will have access to. The lower levels of this addition are better for the formation of a Hamon, also incorrectly known as a temper line, because of this aid to hardening. Higher additions make a steel stronger. These steel are often referred to as 10XX series steels, the 10 meaning simple carbon steel with a small amount of MN added, the XX will be numbers stating the carbon content in parts per thousand. But in practice, the content can have a small variance. As an example the carbon content of 1086 should be 0.86 but it will actually be between 0.83 and 0.9 or so. Which explains why two different batches of the same grade of steel can work and harden differently. While it is common for some to use a Rail Road spike for knife making, the "HC" or “high carbon” type are equivalent to 1035 at best, and will not usually give a lasting edge when hardened. 1050 through 1095 are very common blade choices from this group.

Another common addition to a steel is a carbide former known as Chromium(Cr) this addition in small amounts makes our steel deep hardening. Normally about 0.8% is added. At higher levels other things can happen, and when there is more than 12% free chrome in the mix, its referred to as a stainless steel. 5160 is a very common choice from the low Chrome group. Which is basically 1060 with the addition of 0.8% chrome, and D-2 has 12% total, but since this has a lot bound up in carbide, is not classified as a stainless, nor is this a beginners steel.

Molybdenum(Mo) aka Molly is another carbide forming addition used in small amounts around 0.10 to 0.4 A little goes a long way in steel, High additions are hard to work even when glowing a yellow heat.

Nickel(Ni) is not a carbide former, but is added to many times assist other elements such as Chrome in grain refinement. It is used in high amounts in some Stainless steels. In amounts of up to 2% is may be in simple steels such as L-6 or 15N20. A Nickel bearing steel is a common choice for the bright layers in a pattern welded blade as well.

Silicon(Si) is also used for additions to blade steels, many times added in amount from .3 to 2% to aid in toughness. In higher amounts it increases the conductivity and is used in the electrical field. 9260 is a good large blade steel at 2% silicon.

Vanadium(V) and/or Tungsten(W) also called Wolfram, can also be added to retard grain growth of the steels, these assist in keeping smaller grains in a finished blade, and can also raise the tempering temperature. Usually added in the amount of 0.1 to 0.35, higher additions cause the steel to be very hard to move under the hammer, Most the properties of these two elements are very similar when used in knife steels so I address them together here. W-series and F-series steels make very good blades. The F series and WHC are sadly no longer being produced, but W-1 and W-2 are common, and give good Hamon as well.

This is only a start, and is not complete, but only an over view to assist in sorting out the mis-mash of some common steel alloy elements. I hope this simple explanation will help you understand what some of the steel have to offer for your blades.

References:
Prof. J.Verhoeven, Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel

Metals Handbook, Vol. 1, 10th Edition, Properties and Selection: Irons, Steels, and High Performance Alloys,
p.141, Classification and Designation of Carbon and Low Alloy Steels, ASM International, (1990).

[Glenn]

Metallurgy of Steel for Bladesmiths Edited April 24, 2009 by steve sells
url correction

[UncleBobsWorkshop]

Newbie question:  I thought O-1 was a good material for blades or other cutters.  What Steve refers to here sounds like a whole different system.  How do they compare?

thanks,

Uncle Bob

[Frosty]

Welcome aboard Uncle Bob, glad to have you. In that reply Steve was answering a different kind of question. He was pointing out how many different steels can be used to make blades and many are for specific uses so care needs be used to select for specific blade/tool use.

You're question is too general for anybody with the knowledge to say, "yes or no."  

If you want a meaningful answers you need to provide more information: 

First, it REALLY helps to do some reading so you have a handle on a craft, ANY craft. It really helps you ask good questions and understand the answers without us having to first grill you on what you are actually asking and then explain the terms and usages in the answer. 

Second: What kind of knife and what use? A punch dagger and a filet knife are two entirely different knives requiring different steels, production techniques, heat treats, etc. How about a Dive knife? Now that's a different world of blade making, they just look like a common utility knife but WAY different. Make sense?

Steve's reply above applies directly to your question, the specific answer is on the list. We just can't tell which one it is. 

I'm  not being snarky or trying to discourage you. This is just how it is breaking into a new craft, you have to build a base of knowledge and have a handle on at least the trade jargon. We WANT you to be a successful blade smith, honest we LOVE pics of eye candy blades and I'd love a glimpse of what your eye sees.

Frosty The Lucky.

[ThomasPowers]

There are hundred if not thousands of pages written on this; stop by and I'll let you read my ASM handbooks.

One of the pluses for O1 for beginner knifemaking is ease of heat treat, (pretty low cost and availability are two others).

Now if you want to know how to map the names from one naming system to another; again thats a lot of pages, especially if you include the european naming systems. You generally have to get the elemental analysis and start comparing it to names in other systems.

AISI / ASTM A681 O1 tool steel

 

[Steve Sells]

I was mainly using the SAE system of steel naming for this, there is also AISI and other conventions for naming steels.  The  O series, L series H series etc.  I did not, and I could not cover them all.

The point was to explain what the alloy additions did for the steel to assist a person in deciding what to use.