Some 4140 actions are heat treated and therefore harder. One is the M70. Most are not hardened as that warps the action. The old M70 was induction hardened at the front ring I think the Rule book says.

I've been wondering what kind of steel the CZ 550's are made out of. I emailed CZ's site but the guy didn't know.

mete,



I should have mentioned that the 8620 actions were hardened "carburized"(sp) I believe. This process from what I understand both hardens the outside of the action while adding carbon(?) yet maintains a soft inner core. The heat treatment and the addition of carbon increases the hardness of the outer surface considerably. The other steels I mentioned 4140 & 4340 made no mention of carburizing or case hardening. Perhaps they are through hardened...anyone know?



Regards,

Dave

DavidC,



SAE8620 is typically case carburized when used in firearms. Both SAE 4140 and SAE4340 are not carburizing grades as they both contain enough carbon to form martensite (that is the technical name for hardened steel). Your description of carburizing is adequate I feel. Basically, one is "baking" extra carbon into the steel so that when the steel is quenched it will form a hard martensitic surface case. That is what you said, if I understood your post correctly.



Not to bore you with great deals of technical mumbo jumbo, but if I were to rank the three steels you listed from BEST to WORSE and include another alternative I would do so as follows:



SAE8620 (case carburized)

SAE1340 (alternative through hardened and drawn back to HRC 30 to HRC 37)

SAE4340 (through hardened and drawn back to HRC 28 to HRC 35) and actually I would prefer a case carburized SAE4320.

SAE4140 (through hardened and drawn back to HRC 28 to HRC 34)



For the vast majority of the 20 century and the last few years of the 19th century "ordnance steel", at least in the United States, was a manganese steel alloy. Today it would be closest to SAE1330 or SAE1340. Manganese steels are characterized by there high impact strengths and ductility.



SAE4140 (chrome moly steel)is a " jack of all trades " alloy and is the largest alloy steel manufactured in the US (at least it was the last time I saw any data, which admittedly has been awhile) so it is CHEAP and will "get the job done". It is MOST DEFINITELY a " master of none " though. It has mediocre impact strength and ductility, particularly at hardness levels greater than HRC 20. Most firearms receivers made today are harder than HRC 20. It is easily machined though, something which cannot be said of high nickel alloys (manganese too for that matter). Both SAE4340 and SAE8620 are chrome moly nickel steels. The primary difference being that SAE4340 has more nickel in it, as well as more carbon (the last two digits in the alloy designation describe the percentage of carbon in the alloy i.e. SAE4340 is 0.4% carbon and SAE8620 is 0.2%).



You may find this interesting, and you don't have to take my word for it as it is listed in the ASM (American Society of Metals) handbook, but hardened SAE4140 has about 1/2 the fatigue life of hardened SAE1050. SAE1050 is a cheap PLAIN CARBON steel. This FACT is clearly published in the referenced handbook.



Finally for any given hardness, within the range of usefulness as a firearms receiver that is, the ultimate tensile strengths of SAE4140, SAE4340, SAE1340, and SAE8620 are all practically identical! The differences really come down to impact strength (notch sensitivity), fracture toughness (fatigue life), and ductility (stretch before fracture).



Quite frankly any of the material you listed can be used to manufacture a fine weapon. Some are just better than others. I would most definitely stay away from any SAE4140 receivers IF the hardness is greater than HRC 38 (HRC = Hardness Rockwell "C" scale).



ASS_CLOWN

Something that I have wondered about from time to time is the advisability of taking one of the current production, through hardened 4140 receivers, drawing it back to about HRC 28-30, squaring it up, polishing, etc., then having it nitrocarburized to acheive a hard, wear-resistant surface. Because of the subcritical temperature of the nitrocarburization process, that should result in minimal dimensional change. A cosmetic finish oxidizing step can also easily be added to the process to acheive the equivalent of "rust bluing."



It makes sense to me, but I'm no professional metallurgist or mechanical engineer, nor have I ever heard of this being done with firearms.

It has been used - the Tennifer coating used on Glocks is a gas carbonitriding process.....If you want to see an interesting KABOOM check http://www.bpcr.net/index-a.htm

AC,

Thanks for taking the time to give such a precise answer.

To Quote you....

Quote:

---

Finally for any given hardness, within the range of usefulness as a firearms receiver that is, the ultimate tensile strengths of SAE4140, SAE4340, SAE1340, and SAE8620 are all practically identical! The differences really come down to impact strength (notch sensitivity), fracture toughness (fatigue life), and ductility (stretch before fracture).

---

Would you mind comparing and contrasting the differences between the.......impact strength (notch sensitivity),
fracture toughness (fatigue life),and ductility (stretch before fracture) for all of the steel type you mentioned?
I am particularly interested in the quality and suitability/toughness of carburized 8620.

Regards,
Dave

The nickel in 4340 and 8620 provide higher toughness. When you carburize you get a surface that is harder ,stronger and more wear resistant with a core that is softer but tougher .

Hi
And how tough is stainless steel 416 compared to Cr-mo steels? many guns action are made from this steel. Are there any factory in USA making actions or other parts from 17-4 ph stainless steel?
best regards
danny

Danny,

Jarrett makes their Triple Lock action from 17-4 PH stainless.

jim

Not according to the Jarrett website:

Quote:

---

The receiver is the Jarrett Tri-lock, utilizing the three-lug principle to unilaterally support the case end in three locations. Built with a unique bolt bushing, it provides the ultimate in concentric alignment between the bolt and the bore at all times. What�s more, the extremely quick lock time in the Tri-lock minimizes the opportunity for aim drift during firing, while the 15-5 stainless steel housing is machined in a stress-free fashion on state-of-the-art CNC equipment in our factory.

---

15-5 PH minus 17-4 PH, well it was close anyway.

Thanks for catching that.

jim

Infosponge,



Make sure you polish the action before you nitride it. Also, nitriding will induce some distortion, but it is typically minute (< 0.002"). Nitriding the contacting surfaces should provide that slick feel that is achieved with a case carburized SAE8620 (or better yet case carburized SAE4320) action. Just remember nitriding is shallow, typically less than 0.005" thick.



ASS_CLOWN

Here you go:

4140

4340

8620

You may note that 8620 has the highest impact strength and the lowest tensile strength, while 4340 is just the opposite(lowest impact, highest tensile) 4140 falls in the middle of the road with respect to both qualities and seems to offer the best compromise.

Toolmaker

Toolmaker,

Nice imformation you posted. However, you interpretation is wrong. The hardnesses for the three alloys are NOT the same. Impact Strength and Tensile Strength are HARNDESS dependant. The hardnesses quoted in the links you provided are all much lower than what is typically used in a modern rifle action (BHN 217 for instance is HRC 17)

The following data is provided for reference at a Hardness of BHN 285 for all three steels. (BHN = Brinnel Hardness No )

SAE 8620 - 45.4 ft-lbs
SAE4340 - 25.5 ft-lbs
SAE4140 - 19.1 ft-lbs

SAE1340 - 37.6 lb-ft
SAE4320 - 34.9 lb-ft

Tensile strength
SAE8620 - 139,000 psi
SAE4340 - 145,000 psi
SAE4140 - 138,000 psi

SAE1340 - 137,000 psi
SAE4320 - 142,000 psi

The data is pulled from an ASM Handbook and/or from actual test specimens. The strengths are rounded to the nears 1000 psi.

The carburizing grades ie SAE 8620 and SAE 4320 allow for surface hardening to HRC 55+ which will provide a slick smooth feel, if properlly polished on the raceways. The other alloys will always feel a little "sticky" due to the fact that they must be finished at a softer temper (best to be less than HRC 37).

ASS_CLOWN