OFCC University - Metallurgy 101 (Steel)

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OFCC University - Metallurgy 101 (Steel)

Postby Morne » Fri Dec 19, 2008 10:45 am

Using the topics prompted by Mr. Glock:

1. Gun Steel: What is it? What are the different kinds +/-? Old days vs current times.


First, let us discuss what STEEL is, exactly.

If you look at the periodic table of the elements:
Image
http://www.webelements.com/
You don't see anything called STEEL. That is because STEEL is not an elemental metal - it is an ALLOY of IRON (symbol Fe, atomic number 26) and CARBON (symbol C, atomic number 6). Sometimes other elements are added as well - they can include:

MOLYBDENUM
MANGANESE
COPPER
NICKEL
CHROMIUM
SILICON
VANADIUM
COBALT
COLUMBIUM (AKA NIOBIUM)
TANTALUM
ALUMINUM
TITANIUM
SULPHUR
LEAD
BORON
NITROGEN
TUNGSTEN
PHOSPHORUS

But what is an ALLOY? An ALLOY is a solid solution of two or more elements where at least one is a metal (in the case of STEEL that element is IRON). A solid solution is much like a liquid solution such as salt water except that the matrix is a solid, not a liquid. Just as salt dissolves in water you can dissolve certain elements into iron. Kind of cool, huh?

Certain alloying elements are very important. CARBON is the most critical alloying element in STEEL. Generally speaking, more carbon content equals harder steel. Thus, all things being equal a STEEL with 0.50% C will be harder than a STEEL with 0.40% C. CHROMIUM is what makes a stainless steel "stainless", provided that there is at least 12% of it in the STEEL. SULPHUR and LEAD are nice for machinists because they make cutting chips break off easier and thus extend tool life. The detrimental things they do to STEEL on a microstructural level, though, are horrendous.

There is a whole convention for naming/numbering STEEL. It is known as the AISI (American Institute of Steel & Iron) system and it consists of a 4-digit designator, sometimes with some letters tossed in. The first two numbers determine which alloy family the STEEL belongs to:

Carbon steels
10xx Plain carbon (Mn 1.00 max)
11xx Resulfurized
12xx Resulfurized and rephosphorized
15xx Plain carbon (max Mn range: 1.00-1.65)
Manganese steels
13xx Mn 1.75
Nickel steels
23xx Ni 3.50
25xx Ni 5.00
Nickel-chromium steels
31xx Ni 1.25; Cr 0.65 and 0.80
32xx Ni 1.75; Cr 1.07
33xx Ni 3.50; Cr 1.50 and 1.57
34xx Ni 3.00; Cr 0.77
Molybdenum steels
40xx Mo 0.20 and 0.25
44xx Mo 0.40 and 0.52
Chromium-molybdenum steels
41xx Cr 0.50, 0.80, and 0.95; Mo 0.12, 0.20, 0.25, and 0.30
Nickel-chromium-molybdenum steels
43xx Ni 1.82; Cr 0.50 and 0.80; Mo 0.25
43BVxx Ni 1.82; Cr 0.50; Mo 0.12 and 0.25; V 0.03 min
47xx Ni 1.05; Cr 0.45; Mo 0.20 and 0.35
81xx Ni 0.30; Cr 0.40; Mo 0.12
86xx Ni 0.55; Cr 0.50; Mo 0.20
87xx Ni 0.55; Cr 0.50; Mo 0.25
88xx Ni 0.55; Cr 0.50; Mo 0.35
93xx Ni 3.25; Cr 1.20; Mo 0.12
94xx Ni 0.45; Cr 0.40; Mo 0.12
97xx Ni 0.55; Cr 0.20; Mo 0.20
98xx Ni 1.00; Cr 0.80; Mo 0.25
Nickel-molybdenum steels
46xx Ni 0.85 and 1.82; Mo 0.20 and 0.25
48xx Ni 3.50; Mo 0.25
Chromium steels
50xx Cr 0.27, 0.40, 0.50, and 0.65
51xx Cr 0.80, 0.87, 0.92, 0.95, 1.00, and 1.05
50xxx Cr 0.50; C 1.00 min
51xxx Cr 1.02; C 1.00 min
52xxx Cr 1.45; C 1.00 min
Chromium-vanadium steels
61xx Cr 0.60, 0.80, and 0.95; V 0.10 and 0.15 min
Tungsten-chromium steel
72xx W 1.75; Cr 0.75
Silicon-manganese steels
92xx Si 1.40 and 2.00; Mn 0.65, 0.82, and 0.85; Cr 0 and 0.65
Boron steels
xxBxx B denotes boron steel
Leaded steels
xxLxx L denotes leaded steel
Vanadium steels
xxVxx V denotes vanadium steel

The last two digits indicate the decimal percent carbon content. Thus, a 1040, 4140 and an 8740 all have 0.40% carbon content.

In STAINLESS STEELS you have the following families:
300-series are called AUSTENITIC STAINLESS STEELS and have the best overall corrosion resistance.
400-series are called MARTENSITIC STAINLESS STEELS and can have both good hardness and some corrosion resistance.
PH-series are called PRECIPITATION HARDENING STEELS and can be "aged" to a moderate hardness with good corrosion resistance.

Of all of these STEELS, relatively few are used in firearms. 4140, 41V45 and 4150 are the well-known ordnance grades specified by the US Military for things like barrels. Some companies, like Olympic Arms, have been known to use 416 STAINLESS STEEL for barrels. Still others use 17-4 PH STAINLESS STEEL for barrels.

But just having STEEL isn't enough. There is a reason that STEEL is so useful - that is its ability to be either soft or hard depending upon its HEAT TREATMENT. What governs this ability is the capacity of STEEL to change its crystalline structure (yes, metals are crystalline). There are three crystal structures to know with regards to STEEL:

Body-Centered Cubic (BCC) or Ferrite
Image

Face-Centered Cubic (FCC) or Austenite
Image

Body-Centered Tetragonal (BCT) or Martensite
Image

Generally speaking, BCC is soft and BCT is hard. FCC is a kind of transition structure during heat treatment (when the steel is orange-red hot around 1350-1900 F). Basically, you start with a BCC structure and then when you heat it up to orange-red hot it changes to FCC. Then, when you quench it (usually into oil) the FCC changes to BCT. The reaons why it changes structure are kind of complicated but if you really wanna know I can explain that, too.

After you quench the steel and make it BCT you need to TEMPER it. This is a moderate heat operation (anywhere from 350-1100 F) that reduces the strength of the BCT structure but allows it to regain ductility and toughness (as-quenched BCT is almost as brittle as glass). The higher the tempering temperature the softer it gets. You usually pick a tempering temperature in order to hit a certain hardness range (such as HRC 33-36 for a barrel). And before you go saying that you want it to be as hard as possible you should remember two things:

1 - The machinist who is going to cut the rifling in the barrel will use the whole book of swear words on you and then write a new chapter.
2 - While a low tempering temperature might get you really high hardness that won't last after your first 30-round mag-dump. When you exceed the tempering temperature in service the STEEL will soften, possibly causing distortion as well. The last thing you want when holding off the zombie horde is a wet-noodle for a barrel.

WAY BACK IN THE BAD OLD DAYS STEEL was much harder to come by. It wasn't until the mid 19th century that blast furnaces made steel making an industrial production. Before that it was the province of skilled artisans who closely guarded their secrets. Regardless, you needed three things to make STEEL:

Iron Ore
Limestone
Charcoal

Combining these things with a LOT of heat (be it in a crucible or forge) resulted in a simple and dirty kind of plain carbon STEEL. The STEEL would then be forged into whatever forms were needed (hoes, ploughs, swords, whatever). Damascus STEEL was a kind of pattern-welded (welded on the forge) STEEL that allowed for some early control over impurity and carbon levels. For making gun barrels the steel was drawn into wires or cords and then twisted around a mandrel and forge-welded in that twisted pattern. Because the forge-welding technique depends greatly upon the skill of the blacksmith you should NEVER consider a damascus STEEL gun barrel to be safe to use.

In modern times, we use blast furnaces (though the 3 basic ingredients remain) to make our basic (or ladel) STEEL. We then use something called a Basic Oxygen Furnace (BOF) to "burn-down" the carbon content until it reaches the desired range. With this process we can make steel with very well-controlled carbon levels, down to a hundredth of a percent accuracy (0.01%).

STEEL is sometimes re-melted in a controlled fashion to eliminate some impurities and refine the crystal grain structure (fine grain is desirable for lots of reasons). Some of these methods include Electro-Slag Remelting (ESR), Vacuum Induction Melting (VIM) and Vacuum Arc Melting (VAR). While this remelting adds cost it is desirable for safety critical applications.

I'll get to the other proposed topics as time permits, but feel free to post any questions for more detail about the chemistry of steel or its heat treatment in this thread.
Last edited by Morne on Mon Dec 22, 2008 9:02 pm, edited 1 time in total.
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Re: OFCC University - Metallurgy 101

Postby usmcbeck » Fri Dec 19, 2008 11:06 am

Ok you win, do you work at a smelting plant by chance?
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Re: OFCC University - Metallurgy 101

Postby gabe » Fri Dec 19, 2008 11:12 am

great info, and once I get the question formed in my head correctly I have a couple of questions concerning how mauser actions were heat treated back in the day.

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Re: OFCC University - Metallurgy 101

Postby Morne » Fri Dec 19, 2008 11:15 am

usmcbeck wrote:Ok you win, do you work at a smelting plant by chance?

Nope - not even a Metallurgist by education (I got my degree in Chemical Engineering). But I worked with a BUSHEL of Metallurgists for many years and learned all I could. By the time I left I was being requested, both from within the company and outside, to teach Basic Metallurgy courses. I figure the most important thing I learned in college was HOW TO LEARN, apply that to the situation you find yourself in and you can be an expert in anything you apply yourself to.
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Re: OFCC University - Metallurgy 101

Postby carmen fovozzo » Fri Dec 19, 2008 11:26 am

ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ. Sorry
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Re: OFCC University - Metallurgy 101

Postby 1911nut » Fri Dec 19, 2008 12:33 pm

Very informative, I think. :| This reminds me of when I ask my dd a siple "how does this network work vs that network, he's a networking guy by trade, and he gives me a very long over informitive answer. One of my favorite things, he could just say this will be faster than that. I love learning things I don't know, I will be studig this thread at legth when I can prit it out and pay atention.

Great info.
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Re: OFCC University - Metallurgy 101

Postby willbird » Fri Dec 19, 2008 1:37 pm

I think you forgot 8620 as a common gun steel, used in M1 Garand and M14 receivers. It offers the benefit of allowing "soft core" heat treating, it is carburised and hardened for a hard outer shell and a softer tougher more ductile core.

416 stainless is one of the most common "firearms" stainless steels, it was used in rifle barrels before Olympic arms existed maybe :-). it will and does rust because it actually has iron in it. There is actually a grade called 416R which is specifically used for rifle barrels, it has added sulfur for enhanced machining properties. 416 BTW cuts like butter. Lothar Walther uses a different stainless for rifle barrels, it does NOT cut like butter, these barrels were electropolished internally and sold under the Blackstar name. This steel is said to be more resistant to erosion from hot powder gasses, and longeraccurate barrel life is said to be the result.

http://www.blackstar-barrels.com/body_g ... %20(082204).html

Most of our stainless steel guns are 416 stainless.

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Re: OFCC University - Metallurgy 101

Postby curmudgeon3 » Fri Dec 19, 2008 2:11 pm

It would be nice if someone could now post a treatise on the chemical structure and content of plastic/polymers so the Glock worshippers don't feel slighted.
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Re: OFCC University - Metallurgy 101

Postby Morne » Fri Dec 19, 2008 2:11 pm

carmen fovozzo wrote:ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ. Sorry

No apology necessary. I fell asleep in every class I ever took in college.

willbird wrote:I think you forgot 8620 as a common gun steel, used in M1 Garand and M14 receivers. It offers the benefit of allowing "soft core" heat treating, it is carburised and hardened for a hard outer shell and a softer tougher more ductile core.


I didn't know about 8620 being used in the past for steel receivers - thanks for cluing me in! :D I intended to cover case hardening heat treatments in the section on "external coatings" since so many people want to know about stuff like Melonite (which is a case hardening treatment as well).

416 stainless is one of the most common "firearms" stainless steels, it was used in rifle barrels before Olympic arms existed maybe :-). it will and does rust because it actually has iron in it.


ALL stainless steels have iron in them. In fact, iron is the most abundant element in any stainless steel. Notice I said that the 400-series of stainless had "some corrosion resistance" - it is clearly not the best available. But it is still, technically, stainless. As you obviously know - stainless does not equal rustproof. A lot of folks put additional coatings on 400-series stainless steels, like Olympic Arms phosphating their 416 barrels, to help compensate for the non-optimal corrosion resistance. Where I used to work any 400-series stainless got a nickel flash and then cadmium plating on top of that.
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Re: OFCC University - Metallurgy 101

Postby willbird » Fri Dec 19, 2008 2:30 pm

Morne wrote:
carmen fovozzo wrote:ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ. Sorry

No apology necessary. I fell asleep in every class I ever took in college.

willbird wrote:I think you forgot 8620 as a common gun steel, used in M1 Garand and M14 receivers. It offers the benefit of allowing "soft core" heat treating, it is carburised and hardened for a hard outer shell and a softer tougher more ductile core.


I didn't know about 8620 being used in the past for steel receivers - thanks for cluing me in! :D I intended to cover case hardening heat treatments in the section on "external coatings" since so many people want to know about stuff like Melonite (which is a case hardening treatment as well).

416 stainless is one of the most common "firearms" stainless steels, it was used in rifle barrels before Olympic arms existed maybe :-). it will and does rust because it actually has iron in it.


ALL stainless steels have iron in them. In fact, iron is the most abundant element in any stainless steel. Notice I said that the 400-series of stainless had "some corrosion resistance" - it is clearly not the best available. But it is still, technically, stainless. As you obviously know - stainless does not equal rustproof. A lot of folks put additional coatings on 400-series stainless steels, like Olympic Arms phosphating their 416 barrels, to help compensate for the non-optimal corrosion resistance. Where I used to work any 400-series stainless got a nickel flash and then cadmium plating on top of that.


The "non magnetic" stainless steels have iron in them ??

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Re: OFCC University - Metallurgy 101

Postby Morne » Fri Dec 19, 2008 2:47 pm

willbird wrote:The "non magnetic" stainless steels have iron in them ??

Yeppity skippity.

The 300-series of "Austenitic" stainless steels are the famed "non-magnetic" stainless steels - at least when they are ANNEALED (in their softest condition). These have been so heavily alloyed with other stuff that they are actually in the FCC (austenite - and hence the name) crystalline structure AT ROOM TEMPERATURE. These steels cannot thus be heat treated in the conventional sense but instead can be work-hardened (usually on rolling mills) to achieve higher strength. That same work-hardening phenomenon can be a real headache to machinists, too.

Iron is only magnetic when it is in a body-centered crystal structure - either cubic or tetragonal. That's actually one way to test the effectiveness of quench oil - take a steel sphere suspended from a steel wire (all at about 1600 F) and dump it into a cup of quench oil with a strong electromagnet at one side. You measure the time from immersion until you hear the "TINK" indicating that the sphere has finally been swung over to hit the cup wall. Weird, huh?
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Re: OFCC University - Metallurgy 101

Postby GWC » Fri Dec 19, 2008 3:30 pm

Thanks Morne,

I eagerly await the next lesson.
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Re: OFCC University - Metallurgy 101

Postby Javelin Man » Fri Dec 19, 2008 3:40 pm

Morne,

How about some real detail into your lesson? I learned all of this in eighth grade science class, both years! :P
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Re: OFCC University - Metallurgy 101

Postby color of law » Fri Dec 19, 2008 3:55 pm

expert - An X is a has been and a spurt is a drip under pressure.
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Re: OFCC University - Metallurgy 101

Postby Mr. Glock » Fri Dec 19, 2008 4:52 pm

Cool...good work...some follow up from the class on Lesson 1.

1. Late 1800's Blackpowder Rifles (like the early Winchester lever actions)..what type of steel in the barrel?

2. When smokeless powder came out, Winchester went to Nickel Steel (as marked on the barrel) to differentiate from the older guns...which is that one(s) on your chart?

3. Ruger Hammer-Forges barrels around a mandrel to create rifling (as opposed to gun drilling them), does this process impact the type of steel used?
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