Hardening Parts After Working The Metal

slickpuppy · October 23, 2001, 08:40 PM

Was wondering about some of the techniques you guys use after doing your tuneups with regards to hardening the parts to their previous hardness.

What thickness does the hardness go down to in the metal?

What do you use to re-harden the metal surfaces you just worked?

What temperature do you use to re-harden? Considering the metallurgy of the metal what is optimum temperature for typical carbon steel on the internal components of the firearm?

Or, do you just skip the step?

James K · October 23, 2001, 09:08 PM

Hi, slickpuppy,

Maybe George would be better on this, but I will try some quick answers, noting that whole books are devoted to the subject. The quick answer, as in most cases, is "it depends".

If the steel is already hardened high carbon steel to begin with, like a spring, I try to grind or polish it without getting it hot. If I am making a spring, I follow the tempering guide for the steel. Usually this involves heating cherry red to work it, then oil quenching, followed by reheating to a lower temperature to draw it.

For just hardening, if the steel is carbon steel, the above will work pretty well. But for sharp surfaces, like sears, I will use Casenit, which is a powder-like case hardening compound. You heat the part red hot and dip it in the Casenit. This is usually OK for most purposes. This type of hardening, and true factory case hardening (like S&W hammers and triggers), is very thin and can be cut through rather easily. Case hardening (colored or not) is usually used where it is desired to keep the parts soft inside to reduce breakage, but at the same time to make them wear resistant.

(Case hardening was used in the old days to harden frames (e.g. Colt) that were made of iron, not steel, and thus could not be heat treated.)

Carbon steel will harden all the way through if treated right, but the trick is to keep it from becoming brittle. Even hard steel is sometimes given an additional surface hardening for wear resistance. M1 rifles, for example, were made that way.

I don't think any gunsmith just "skips the step" unless dealing with a part that he knows is adequately hard all the way through.

Certainly in some cases it is essential; many trigger pull jobs will not last a box of ammo unless the parts are hardened.

Jim

slickpuppy · October 23, 2001, 09:48 PM

I appreciate the feedback Jim. Thanks for the information.

I had been perusing the Brownells catalog and saw some of their stuff in there and was curious about the techniques of metal hardening.

Years ago my great uncle used to make some of the most beautiful knives you ever saw and had his own technique for hardening the steel. He is long since passed 30 odd years ago and was always a wealth of information on working steel when I was but a young lad.

Keith J · October 24, 2001, 09:48 AM

Most actions are made from chrome moly and are through hardened. Only parts like sears and mating surfaces are case hardened medium to low carbon steels that usually do not respond to quenching. Typical uses of case hardened items are those requiring high hardness with great impact stress. Think hammers, firing pins, extractors and the like.

Higher carbon stuff like older actions etc can be quenched to the point of being brittle. Such is the case for knives (0.5-1.0 % carbon) and thus the requirement for tempering or drawing the steel. This is a sub-transformation temperature heat treatment at 400-900 F, followed by a prescribed cool-down.

I suppose the original thread was with respect to hammers. Its best to only polish the engagement surfaces. If the geometry is so out of spec that serious grinding is required, its best to seek a new part rather than grind away the case. No sense in making a silk purse out of a sows ear.

slickpuppy · October 24, 2001, 11:19 AM

Good info Keith. Thanks!

dZ · October 25, 2001, 10:19 AM

in a jewery class i had in college, we had a knife making assignment

the blade hardening was accomplished by timed heat applications in a kiln

the trick is hard edge / flexable spine

DFBonnett · October 25, 2001, 12:08 PM

I'm really a novice at metalworking but I've had reliable results surface hardening small parts such as firing pins using Kasenit I bought from Brownells.

October 23, 2001, 08:40 PM	#1
slickpuppy Senior Member Join Date: August 29, 1999 Posts: 928	Hardening Parts After Working The Metal Was wondering about some of the techniques you guys use after doing your tuneups with regards to hardening the parts to their previous hardness. What thickness does the hardness go down to in the metal? What do you use to re-harden the metal surfaces you just worked? What temperature do you use to re-harden? Considering the metallurgy of the metal what is optimum temperature for typical carbon steel on the internal components of the firearm? Or, do you just skip the step?

October 24, 2001, 09:48 AM	#4
Keith J Senior Member Join Date: December 15, 2000 Posts: 469	Know the steel Most actions are made from chrome moly and are through hardened. Only parts like sears and mating surfaces are case hardened medium to low carbon steels that usually do not respond to quenching. Typical uses of case hardened items are those requiring high hardness with great impact stress. Think hammers, firing pins, extractors and the like. Higher carbon stuff like older actions etc can be quenched to the point of being brittle. Such is the case for knives (0.5-1.0 % carbon) and thus the requirement for tempering or drawing the steel. This is a sub-transformation temperature heat treatment at 400-900 F, followed by a prescribed cool-down. I suppose the original thread was with respect to hammers. Its best to only polish the engagement surfaces. If the geometry is so out of spec that serious grinding is required, its best to seek a new part rather than grind away the case. No sense in making a silk purse out of a sows ear.

October 25, 2001, 10:19 AM	#6
dZ Senior Member Join Date: May 31, 1999 Location: Exiled, Fetid Swamp, DC Posts: 7,548	in a jewery class i had in college, we had a knife making assignment the blade hardening was accomplished by timed heat applications in a kiln the trick is hard edge / flexable spine __________________ "O tell the Lacedomecians to damn the torpedoes." BOTR, Chapter V: Some Monsters

October 23, 2001, 09:08 PM	#2
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Hi, slickpuppy, Maybe George would be better on this, but I will try some quick answers, noting that whole books are devoted to the subject. The quick answer, as in most cases, is "it depends". If the steel is already hardened high carbon steel to begin with, like a spring, I try to grind or polish it without getting it hot. If I am making a spring, I follow the tempering guide for the steel. Usually this involves heating cherry red to work it, then oil quenching, followed by reheating to a lower temperature to draw it. For just hardening, if the steel is carbon steel, the above will work pretty well. But for sharp surfaces, like sears, I will use Casenit, which is a powder-like case hardening compound. You heat the part red hot and dip it in the Casenit. This is usually OK for most purposes. This type of hardening, and true factory case hardening (like S&W hammers and triggers), is very thin and can be cut through rather easily. Case hardening (colored or not) is usually used where it is desired to keep the parts soft inside to reduce breakage, but at the same time to make them wear resistant. (Case hardening was used in the old days to harden frames (e.g. Colt) that were made of iron, not steel, and thus could not be heat treated.) Carbon steel will harden all the way through if treated right, but the trick is to keep it from becoming brittle. Even hard steel is sometimes given an additional surface hardening for wear resistance. M1 rifles, for example, were made that way. I don't think any gunsmith just "skips the step" unless dealing with a part that he knows is adequately hard all the way through. Certainly in some cases it is essential; many trigger pull jobs will not last a box of ammo unless the parts are hardened. Jim

October 23, 2001, 09:48 PM	#3
slickpuppy Senior Member Join Date: August 29, 1999 Posts: 928	I appreciate the feedback Jim. Thanks for the information. I had been perusing the Brownells catalog and saw some of their stuff in there and was curious about the techniques of metal hardening. Years ago my great uncle used to make some of the most beautiful knives you ever saw and had his own technique for hardening the steel. He is long since passed 30 odd years ago and was always a wealth of information on working steel when I was but a young lad.

October 24, 2001, 11:19 AM	#5
slickpuppy Senior Member Join Date: August 29, 1999 Posts: 928	Good info Keith. Thanks!

October 25, 2001, 12:08 PM	#7
DFBonnett Junior member Join Date: November 1, 1998 Posts: 109	I'm really a novice at metalworking but I've had reliable results surface hardening small parts such as firing pins using Kasenit I bought from Brownells.