From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: Beretta 92F Stainless Availability
Organization: Lawrence Berkeley Laboratory

In article <40167@mimsy.umd.edu> thi@mips2.ma30.bull.com 
(Saigon Smuggler) writes:
#In article <40093@mimsy.umd.edu> boyd@mailer.cc.fsu.edu 
(Mickey Boyd) writes:

##A small caveat:  Stainless steel is softer than carbon steel.  I am unsure
##what the price difference is for the stainless model, but if it is more than
##$80 or so, you could buy a black one and have it hard chromed for about the
##same price (and end up with a much more durable and rust resistant gun).
##Another nice thing about hard chrome is that it will not pick up tiny
##scratches like stainless will (just from wiping it off!).

#Hmm.. From what I have heard and read, stainless steel is harder than carbon
#steel.  This is the reason why some stainless steel guns are rougher than
#their carbon steel counterparts from the same manufacturers.  Because of its
#hardness, stainless steel is more difficult to machine and polish.

There are hundreds of types of steels in all.  There are various categories of 
non-stainless steels such as carbon steels (with many sub-categories), alloy 
steels, superalloys, low alloy steels, and high strength low alloy steels to 
name a few; then there are stainless steels such as austenitic, martensitic, 
ferritic, and age-hardening to name a few more.  Each of these categories 
has dozens of members.  Most all of these categories are used to some degree 
by some manufacturers.

In the old days, guns were all made of soft, lower carbon, easy to machine 
steels; these would have an Rc under 20.  Many manufacturers use better 
steels these days: In the non-stainless steels, the wrought low alloy steels, 
4130, 4140, and 4340 are fairly cheap and easy to machine and so are common.  
These will have a hardness from Rc 15 (BH 202) up to Rc 57 (BH 578) according   
to how the part is tempered.  The hardest tempers are not often used since  
impact strength suffers so badly.  These steels can be tempered for a tensile  
strength of anywhere from 100,000 psi up to almost 300,000 psi.  For these 
steels, tensile strength is equal to about 500 times the Brinell hardness.
One should temper parts serving different purposes to different strengths.

In stainless steel, I rather like 17-4 PH since it's not too horrible to 
machine, has excellent tensile strength, and fairly good impact strength.  Its 
hardness varies from maybe Rc 30 up to Rc 45.  Its strength varies from 150,000 
psi to 200,000 psi over this same range.  A number of manufacturers use 17-7 PH
for its superior tensile strength, I suppose, but its impact strength is pretty 
low, so I don't think I would consider it.  Incidentally, PH means "precip-
itation hardening"; after you machine it, you warm it up a little to say 900 to 
1200 F and some components of the alloy precipitate out of the solution and 
cause the strength to go up due to "pinning" and other metallurgical phenomena.
There are much better stainless steels around; these are kind of middle-of-
the-road type alloys in price and performance.

How nicely a part is machined is basically related to the machinability of the
material and the amount of time the manufacturer is willing to spend in
machining a part.  Any of the steels I've mentioned above can be made to have
a gorgeous finish if the manufacturer will take his time.  To take specific
examples, the 17-4 isn't as machinable as the 4130.  It would take quite a
bit more time to machine.  Most manufacturers won't spend the time, so the 
stainless parts look worse.  

There are a lot of tricks which can be used to raise the machinability of a
steel.  A couple of them are "re-sulphurization" and "leading"; adding sulphur
or lead makes a vast improvement in machinability but materials so treated
can't be welded properly.  Where machinability is really important is in barrel
steels.  Barrel steels are made to give extraordinarily good finishes with
normal rifling methods. 

I know the above doesn't answer your question but the fact is that there is no 
answer.  You have to ask which stainless alloy and which steel alloy were used 
and how they were tempered before you can say how hard they are unless you 
have access to a hardness testing machine.

         JHBercovitz@lbl.gov    (John Bercovitz)

From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: Beretta 92F Stainless Availability
Organization: Lawrence Berkeley Laboratory

#I am of the opinion that stainless is softer (on the Rockwell C scale) 
#than comparable carbon steel. 

As explained in a lengthy earlier post, which is harder very much depends on
which particular stainless and carbon steel alloys are being compared and what 
hardnesses they are tempered to.  Without this data, there is _no_answer_ to
this question of which is harder or stronger or tougher.  The only things
we know when you say "stainless" is that the alloy is corrosion resistant
and that as a very general rule with plenty of exceptions, the stainless
has to be machined more slowly to achieve an equally good finish.

#Why? I recall from class that stainless is fundamentally carbon plus additives.

This is basically correct although, of course, carbon is not a required
constituent of stainless; many stainlesses don't have carbon in them at all.
Most stainlesses have around 0.1% carbon.

One of the primary additives to this unrequired carbon is iron.  Iron is
usually found at the 80% or greater level.  8-)

The component which defines stainless as stainless is chromium.  If the 
percentage of chromium in a chromium-iron alloy exceeds 11%, that alloy
is called stainless steel (unless it's muffler stainless which has as
little as possible of chromium in it due to chromium's cost).  Once you 
reach the 11% chromium level in an alloy, the chromium oxide skin that 
forms on the surface of a part protects the part from most further corrosion.
This is akin to the protective aluminum oxide skin which forms on bare aluminum.

#These additions do not strengthen the steel.

Well, actually they do.  Carbon is of course one way to strengthen an alloy
but other additives can do similar jobs.  But I will agree that the primary
purposes of other additives are usually things like increased toughness and
increased strength at high temperature.

A later poster suggested that nickel was the thing that made an alloy stainless;
around 5% nickel is often found in stainless alloys put it isn't what makes
an alloy stainless, it's what raises its high temperature strength.  Perhaps
the poster was thinking of alloys which have as the primary constituent nickel.
These alloys are extremely expensive but mimic stainless alloys only at very
high temperatures.  The Incoloy, Hastelloy, Monel, and Waspalloy groups may
ring a bell with that poster.  

#Regret that I am doing this "off the top of my head" and do 
#not have my technical books handy at this location.

Hey!  That's my excuse!

      JHBercovitz@lbl.gov    (John Bercovitz)

From: arno@nitro.pp.utu.fi (Arno Hahma)
Newsgroups: rec.guns
Subject: Re: What are the advantages and drawbacks of stainless?
Date: 22 Mar 1997 15:12:30 -0500

Advantages:

- corrosion resistant
- easier to clean
- easier to polish/finish

Disadvantages:

- wears faster
- higher friction against itself, tends to cold weld -> needs
  larger tolerances
- low thermal conductivity (this is why full or even
  semi-autos are not made of stainless and this also affects accuracy)
- higher thermal expansion coefficient (lowers accuracy)
- weaker, especially the fatigue resistance and heat 
  resistance
- more expensive
- more expensive to machine

Coating is not a problem, both materials can be blackened
with a manganese phospatizing method or black chrome plating.
Blueing is possible for rusting steel only, but then again,
it is not a good corrosion protection anyway; I'd rather
use something else.

For a bright finish, nickel or chromium plating will make
both materials look the same.

ArNO
    2

From: "Julius Chang" <p00302@psilink.com>
Subject: Re: glock finish
Organization: PSI Public Usenet Link

#DATE:   20 Jul 93 22:43:04 GMT
#FROM:   Josh A Grossman <jagst18+@pitt.edu>
#
##From _Glock, The New Wave in Combat Handguns_ by Peter Alan Kasler page 136-7.
#
#	"Tenifer is applied in a 500 degree C (932 degree F) nitrate bath
#	to give the coated parts a skin hardness of 69 Rockwell Cone (RC).

		The correct terminology is HRC, which represents
		Hardness Rockwell C.  The C scale means that a
		Brale diamond cone indenter was used and the major
		indentation load was 150 Kg.  There is no such
		thing as a "Rockwell Cone" measurement.

#	This is extremely hard, by comparison, a metal file's hardness is
#	only 62 to 65 RC, and the hardness of an industrial diamond is 70
#	RC.

		A Rockwell hardness test on diamond is meaningless.
		The Rockwell test depends upon permanent deformation
		(an indentation) of the material.  Valid test
		materials include steels, cast irons, copper alloys,
		aluminum alloys, and bronzes.

		A diamond-on-diamond indentation test doesn't make
		a lot of sense since both test material and indenter
		are made of the same material and have the same
		hardness.  More importantly, diamond isn't going to
		plastically deform anyway.  So how can diamond even be
		tested on the HRC scale?  Kind of like doing an
		indentation hardness test on glass.

		Finally, each unit of HRC represents 0.002 mm of
		penetration.  The difference between 62 HRC and
		69 HRC is 0.014 mm depth of penetration.  HRC
		maxes out at 100.  Since it is a linear scale,
		69 HRC is only about 7/62 = 11% harder than 62 HRC.
 		This hardly merits calling a metal file's hardness
		"only" 62-65 HRC.


#		Glock's Tenifer coating penetrates the metal so that
#	coated parts have a hardness of 55 to 60 RC at a depth of .02mm
#	(.05 inch) below the surface. From 20 to 30 percent deeper, the
        ^^^^^^^^^^

		0.02mm is not 0.05 inch.

		0.02mm * (1cm/10mm) * (1 inch/2.54cm) = 0.0008 inch

		Rule of thumb:

		Unless the thickness of the surrounding material is
		more than ten times the thickness of the depth of
		the indentation, an accurate HRC is not possible.

		69 HRC gives a penetration depth from minor to major
		load of (100 - 69) * 0.002mm = 0.062mm.  Unfortunately,
		the Tenifer layer is only 0.02mm thick.

		Bottom line: the hardness data on Tenifer is invalid.

		-Julius

From: "Julius Chang" <p00302@psilink.com>
Subject: Re: glock finish
Organization: PSI Public Usenet Link

Sorry to stub toes.  I personally like Glock's and think that
they are a great piece of machinery.  Please correct my errors
from my previous post.  All I have to go on is the piece from
your book that was posted.

I have no doubt that carbonitriding using a liquid cyanide process
can achieve HRC of 69.  But the data from the posting did not
support that.  Until I saw that Tenifer was liquid carbonitriding,
how am I supposed to divine what kind of coating/process Tenifer is?  It
could stand for teflon (te), nickel (Ni), iron (Fe), with the
letter "r" appended to create a pronounceable word.

As for there being better people than I employed by competitors
and gov'ts, that is true for anyone.  There is always someone
better/smarter/faster/stronger.  So what?

Provide a correction to my errors so that I can learn something.
I'll admit I'm wrong at that point.

Until then, it is hard for me to understand what your problem is.

First, the Tenifer film was stated to be 0.02 mm thick or 0.05 inches.
That is clearly wrong.  0.02 mm does not equal 0.05 inches.  It
equals 0.0008 inches.

Second, at an HRC of 69, the minimum thickness for a valid HRC
test is 0.022 inches.  Since 0.02 mm = 0.0008 inches, one cannot
conduct a valid HRC test on such a thin case hardening.  You are
sampling some of the mechanical properties of the substrate
material below.  No doubt that one can achieve HRC 69, but it
is unclear if Tenifer has HRC 69 based on the data from the original
post.  The 10:1 rule of thumb I presented is experimentally valid.
Since it is only a rule of thumb, anything close is probably good
enough.  But a 1:30 ratio isn't even close.  See "The Making, Shaping
and Treating of Steel" for a brief discussion of the Rockwell test.

Third, as for the HRC of diamond being 70, the CRC Handbook of Chem and
Physics lists the Knoop hardness at 7000.  For a Knoop hardness
of about 900, the equivalent HRC is about 68-69 (see any published
hardness conversion table).

Fourth, Rockwell C hardness is denoted as HRC, not Rockwell Cone.
That is well-documented terminology (see for example Metals
Handbook, American Society for Metals).

Last, I have no axe to grind against Glock.  I think that they make
excellent guns.  I see no defamation on my part and intend
none.

-Julius