To start this off, I feel that a short dissertation on steel and steel testing is in order. Some of you, no doubt, are familiar with this, but I would like to cover as much of the interested audience as possible. Please bear with me. I don't wish to come off preachy, etc. I just want to get the information out there so everyone is on the same page.

Steel Basics:

What is steel? Steel is the solid mixture of elemental iron and elemental carbon. Without carbon, you don’t have steel, and you don’t get all of the engineering possibilities that steel has. Carbon is the foundation for all alloying strategies. The carbon content dictates the achievable strength (this is a Key Concept). Low carbon, low strength, high carbon, high strength. From the the base of iron and carbon, we mix and match different alloys to meet a need. We also mix and match different processing to meet a need.

A Few Definitions and Explanations:

Alloy – any element that is mixed into the steel to enhance or change the behavior or properties of the steel. Carbon (most important element), manganese, nickel, chrome, vanadium, titanium, silicon, phosphorous, sulfur, nitrogen, niobium, tungsten, cobalt, and molybdenum are commonly used. Each alloy imparts some characteristic that the engineer wishes to harness.

Hardenability - This term describes how easy a steel is to heat treat. It is usually used in an abstract sense. Like "this steel has high hardenability". There are equations that directly compare one alloy to another. Generally speaking, the more alloy you add the higher the hardenability. This term also tells you if a steel will reach full hardness at depth as well as at the surface. If you have a 1 inch thick bar of low hardenability steel, only the surface or near surface will harden. The same size bar of high hardenability steel will harden all the way through. The thickness of the part is critical in choosing the alloy if the part is to be heat treated.

Hardness – A measure of the steels resistance to indentation. An indenter is forced into the surface of the steel part and the depth of the indentation is measured. Obviously, a soft steel will indent deeply compared to a hard steel. Hardness can be used to approximate the tensile strength of a material. It is also a good comparative test. There are several hardness tests out there. Rockwell, Knoop, Vickers, and Brinnell are the most common. Rockwell has several scales used, and needs to be carefully chosen based on the material being tested. The other 3 use one scale, and are adequate for most any material.

Keep in mind that a hardness test indents the surface of the material. This plays a part in the information the test gives you. Rockwell C is the common scale used in heat treating. This test measures both the surface and the core because it is designed to indent deeply. It can give you all of the information that you need, but you should understand it. This test will give you the same reading under different circumstances. If the case layer of a case hardened part is thin, but very hard, it will yield the same Rockwell C value as a a part with a case layer that is thicker, but softer. It gives you a composite value. A better method is to check with the Rockwell C test, then check on the Rockwell D scale as well. The D scale was intended for use on case hardened materials. It uses the same indenter as the C scale with a lower load. This means that it measures the case more than the base metal, and gives you more information about the case hardness. The combination can give you the case hardness, and maybe some information of the case depth. However, the only way to positively determine case depth is destructive testing.

That said, both situations would likely be safe in a firearm receiver. The purpose of the case hardened layer is only partially to hold the pressure back. It is this layer coupled with the size of the lug and the strength of the steel beneath the case that hold back the pressure. There is a caveat to this. The case layer should be thick enough to be durable over time, but it cannot be too hard. If it is too hard it will crack, or chip under impact.

Yield Strength – the force is takes to permanently deform a material. Usually denoted as pounds per square inch, or megapascals.

Tensile Strength – the force it takes to tear a material apart. Usually denoted as pounds per square inch, or megapascals. If this is exceeded, the receiver will be torn to pieces. Simple as that.

Elongation – How far a material stretches before is breaks. Denoted as a percentage.

Steel will yield at the yield strength, elongate some amount, then fracture at the tensile strength. This is what happens when receiver lugs set back. The force on the lugs has exceeded the yield strength and they are deformed. In case hardened receivers, the core material has a large gap between the yield and tensile strength. For a 1030 steel, the yield will be around 60,000 psi, and the tensile will be around 80,000 psi. It will have an elongation of something around 20%. This is good, because the receiver will tell you when you have gone too far without it turning into a grenade. The lugs set back, the bolt sticks, and you should stop shooting.

In an alloy steel receiver that is fully heat treated, the yield will be much closer to the tensile strength, but they will both be very high. For 4130, the yield will be something like 145,000 psi, and the tensile will be something like 150,000 psi. With and elongation of only 5%. In this case, the lugs would not set back, they would probably just shear off. However, it would take an impossibly overloaded cartridge to do it since the strength of the steel is so high. Maybe a 30-06 full of Blue Dot?

This is why the bottom receiver lug in a Ruger or Savage is half the size of the lug in a military Mauser. Ruger and Savage use alloy steels that are fully heat treated and rely on the strength from heat treating. The Mauser design relies of the size of the lug.

Toughness – This described how a material behaves under impact loading. A low toughness material shatters under impact, where a high toughness material takes the impact without deformation. Glass is an example of a low toughness material. A steel ball peen hammer head is an example of a high toughness material. This is a critical property. As quenched steel parts have low toughness, and must be tempered. More on this later.

Different Steel Classes:

Plain Carbon Steel – This is your basic steel made with limited alloying. These are typically alloyed with carbon, manganese, silicon, phosphorous, sulfur, and/or very small amounts of niobium, titanium, and vanadium. This group is also referred to as carbon/manganese steel. Carbon steel is divided into three groups: low carbon, medium carbon, and high carbon. Low carbon contains less than 0.25% carbon. Medium sits in the 0.25% to 0.40% carbon range. High carbon contains 0.40% up to 2.00% carbon. Once you add more than 2% carbon it is called Cast Iron, and this material is a completely different animal not suitable for much in a firearm.

Alloy Steel – Carbon steel has limitations in its application, so other alloy elements are added to enhance it. The most common of these steels will contain some combination of manganese, nickel, chrome, molybdenum, and vanadium. The most common that I have seen in the firearms industry are 4130, 4140, 4340, and 8620. There are many other alloy steels that are proprietary to a manufacturer. I have seen this with barrel makers.

The alloys added to this group are there for 2 primary reasons: increase hardenability, and inprove wear resistance. Nickel, manganese, molybdenum, vanadium, and chrome all increase hardenability. Adding these alloys allows the part to achieve full hardness all the way through on thicker and thicker sections. The other aspect is wear resistance. Chrome is the main alloy to improve wear resistance. It creates fine carbides within the steel that resist abrasion. Many knife makers use very high chrome alloys (52100 is common) to make them as wear resistant as possible. The same goes for ball bearings.

Stainless Steel – This group is alloyed primarily with chrome and nickel to achieve better corrosion resistance. The best corrosion resistance is achieved by adding 18% chrome and 8 % nickel. This makes 304 stainless used for things like kitchen sinks. However, adding too much chrome or nickel prevents the material from heat treating, so for firearms typically only chrome is used. The most common alloy is 440. There are 3 flavors of this alloy: 440A, 440B, and 440C. The difference is mainly in the carbon content. Nominally, A has 0.7% carbon, B has 0.9% carbon, and C has 1.10% carbon. So 440A won’t be as hard as, B or C, but it will be a tougher alloy. From a heat treating standpoint, these stainless alloys behave similarly to the Alloy Steels. Because only chrome is used, and because chrome forms carbides, 440 is not corrosion proof. It will rust, just not as fast as plain carbon steel, or alloy steel.

Steel Alloy Designations:

Steels have a standard system of alloy designations for commercially available alloys. This makes it easy for buyers to get the same steel from multiple sources.

The designation is broken down as follows: first two digits denote the alloy family, and the third and fourth digits denote carbon content in tenths of a percent.

So a 1040 steel is in the 10 family (plain carbon, or carbon manganese), has no additional special alloy additions, and contains 0.40% carbon.

4340 steel is in the 43 alloy family so it contains molybdenum, chrome and nickel. The last two digits say that it has nominally 0.40% carbon.

Stainless is designated a little differently, and the name only denotes which alloy family it is in. There is no information on carbon content. Common families for stainless are 300 and 400.

Design engineers will use alloys with whatever combination to achieve their desired end use. Large parts will have a lot of nickel and molybdenum in them. Wear resistant parts will have a lot of chrome in them. Corrosion resistant parts will have a lot of chrome and or a lot of nickel.

I hope that this is useful to you. The next installment will cover heat treating and carburizing.

Jeremy

I hope the guys read this stuff !

I'm reading, I'm reading!

You define alloy as "any element that is mixed into the steel to ehance or change the behavior or properties of the steel."

I always thought that an alloy was the result of the element(s) added to the steel.

Yes, both definitions are used. Most metallurgists (the ones I work with) separate the two, and use alloy for the element added, and grade to describe the end result.

This is because the grade, say 4140, contains alloys to make it what it is.

It is a matter of perspective I suppose.

Farbedo,

This is a good report on steel as most people have very little knowledge. Gunsmithing school at TSJC required all students to have at least one semister of metallurgy in the old days. Later it was dropped. We also got to go to Pueblo, Co. for a tour of the steel plant and watch as they made steel.

Brownells sold Mark X Mauser actions years ago and these actions were made of a high alloy. I don't have the spec's, but people should not get them mixed up with the military Mausers.

I have searched for info on the Martini small actions (12-15) made by BSA. I haven't found any one that knows the steel used on these small actions. We ran a Rockwell C test in the a Mod. 15 and it was soft before heating and quinching in Oil. I would like to know more about these actions if anyone has this info.

I don't know about the composition but all Cadets I've smithed have had soft receivers and case-hardened internal lock parts. The surfaces of the breech blocks were quite hard but the case was only on the surface, therefore I 'assume' that they are made of low-carbon steel with minimal alloying. Same for the Francotte Cadets and BTW the parts will interchange nicely between the late 1930s BSAs and the early 1880s Francotte Cadets.

Makes one wonder just exactly WHO made the actions.......
Regards, Joe

This will be one of those threads that I'll print and keep in a notebook.

Keep it coming....

Too many people watch the History channel and get it wrong. Iron has more carbon than steel. About 2%. When the carbon content is lowered to about .5% you have steel.

Good read.

Add to the definition of hardness.
Resistance to not only deformation but scratching. Harder metal is usually more difficult to remove than soft metal. Ask an engraver.

This is great. It's been 39 years since I took some metallurgy courses in college, and since it's been almost 30 years since putting any of that knowledge to use, I welcome this refresher course. I too shall save this.

Excellent - extremely well written and informative. Thanks so much. Looking forward to future installments!

This should be made into a STICKY.

Jeremy - interesting and well written - thank you!

friar

p.s. welcome to AR! It's nice to be able to read something that is more than a couple of people pissin' in the wind.

It's worth noting that 400 series stainless steels are magnetic while 300 series are not. You can tell them apart with a magnet.

No sharpshooting in class today Craig.

Interesting read. I will print this of along with that glorious thread with Tom Burgess, D'Arcy Echols and (IIRC) Jim Wisner all contributing. It is in the pinned information collection at the top of this page.

LD

PS "Alloy" is like my (even) padded rear end and the assistant principal's aerated model paddle while I was in parochial school - inseparable.

LesBrooks, I find it odd and sad that they don't require a basic metallurgy course. I am sure that the instructor retired and they dropped it. Maybe the powers that be, figure the firearms manufacturers did the metallurgy for you. BUT, if you need to make a part, that no longer holds true.

I will also make sure to draw a hard line between pre WWII firearms, and post. With a distinction for military actions. You bring up a good point in that Mark X, and other flavors of post war Mauser clones need to be in a separate category.

Leo, That is also a good catch. I am trying to condense so much, and have missed a few details. Maybe at least I hit the high points.

Thanks for the feed back everyone.

Jeremy

When I attended gunsmithing school ,CST, they wouldn't permit me in the class !!

We always shorten things in our language . Properly an 'alloying element' is an element added to a metal to change properties. The combination is an alloy.

srose, you're talking about "cast iron" an iron carbon mix formed by casting.

quote:

Originally posted by farbedo:
LesBrooks, I find it odd and sad that they don't require a basic metallurgy course. I am sure that the instructor retired and they dropped it. Jeremy

Odd and sad indeed. It never even OCCURRED to me that a smithing school wouldn't automatically require a metallurgy class as SOP.

Of course it also never occurred to me that they wouldn't require the students to actually make their own tools, either. At TSJC in the '60s we were required to make chisels, punches and screwdrivers as a basis, then more various elective tools and fixtures until the overall requirement was met.

Back then we didn't have the emphasis on plastic stocks and paramilitary superrepeaters, though. Guess the Powers That Be (the EDUCATORS) figure that today's students don't need to know that basic stuff any more.

Bah to the 'educators'.
Regards, Joe

farbedo ;Very good article . Now for those who don't own a Engineers Metallurgical handbook may also find the Timken site useful.



http://www.timken.com/en-us/kn...284023%29-sept06.pdf

Hardbound Book :

http://www.amazon.com/Handbook...eering/dp/0824741064

An for those who prefer free downloads might try the below posted link :

http://www.ebookfree-download....stm-handbook-pdf.php

Farbedo, that was well done. It is very accurate, but written so a layman can follow it. I've learned much of this in the fastener industry over the past 20+ yrs, but do not have the engineering knowledge to use it in the firearm end of things. Thanks for taking the time to do this - looking forward to the balance.
Ron

quote:

Originally posted by srose:
Too many people watch the History channel and get it wrong. Iron has more carbon than steel. About 2%. When the carbon content is lowered to about .5% you have steel.

srose
I have to point this out because you are passing along bad information. "Iron" has no carbon because "iron" is an element. Steel is mixture of iron and carbon(<2%).

As was stated in the original post: "Once you add more than 2% carbon it is called Cast Iron".

Jason,

You are correct and I stand corrected. I should have said CAST IRON or wrought iron. I'm sorry for the confusion.

Sam

I started life at Timken and have the early copies of "practical Data for Metallurgists ". It's a very usefull book.

quote:

mete

Were you a bearing or race ?

Timken also has a steel mill making large amounts of alloy steel .That's where I worked .
The bearing factory always sent broken bearing for investigation so we looked at them and told them how they screwed up !