New Sharps Relia-Bolt design using S7 tool steel.

[BufordTJustice]

Companies that heat treat have programs to tell them the temp and time depending on the type of steel, hardness and depth required. All heat treat processes are alloy specific.

That's good to know. Do these calculations typically take into account the dimensions of the part, overall mass, etc. so that the process can be controlled in the metal itself?

[constructor]

That's good to know. Do these calculations typically take into account the dimensions of the part, overall mass, etc. so that the process can be controlled in the metal itself?

They do. Hopefully the tech has enough sense to measure the thin areas and knows what areas take the load. Bolts with all of the holes that pass through have very thin areas.

[BufordTJustice]

They do. Hopefully the tech has enough sense to measure the thin areas and knows what areas take the load. Bolts with all of the holes that pass through have very thin areas.

Outstanding info. Also, how much of a role does shot-peening play in am S7 type alloy if the heat treat is done properly?

[constructor]

Outstanding info. Also, how much of a role does shot-peening play in am S7 type alloy if the heat treat is done properly?

5.56 bolts don't break that often. Barrel extension lugs compress more than bolts break. By the time the bolt breaks the barrel and barrel extension are poor shape and both should be replaced. Already using s7 or even 9310 I don't think shot peening will add much. If an unpeened bolt doesn't break then does it being a unbroken shot peened bolt add anything? All I can say is shot peening is used very very little in common applications. The aircraft industry uses it more than any because if there is a failure it could mean many lives lost.

"Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. Its main application is to avoid the propagation of microcracks from a surface. Such cracks do not propagate in a material that is under a compressive stress; shot peening can create such a stress in the surface.[3]

Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, shot coverage, shot peening can increase fatigue life up to 1000%.[2]

Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion.[1] The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior."

[BufordTJustice]

5.56 bolts don't break that often. Barrel extension lugs compress more than bolts break. By the time the bolt breaks the barrel and barrel extension are poor shape and both should be replaced. Already using s7 or even 9310 I don't think shot peening will add much. If an unpeened bolt doesn't break then does it being a unbroken shot peened bolt add anything? All I can say is shot peening is used very very little in common applications. The aircraft industry uses it more than any because if there is a failure it could mean many lives lost.

"Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. Its main application is to avoid the propagation of microcracks from a surface. Such cracks do not propagate in a material that is under a compressive stress; shot peening can create such a stress in the surface.[3]

Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, shot coverage, shot peening can increase fatigue life up to 1000%.[2]

Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion.[1] The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior."

That post ALONE should be a sticky. Thank you.

Sent from my SPH-D710 using Tapatalk

[constructor]

That post ALONE should be a sticky. Thank you.

Sent from my SPH-D710 using Tapatalk

It is...a wiki stiki

[Ned Christiansen]

I've used tons of S7. No really, I mean tons.... OK one ton at least, in 20-plus years making plastic injection molds and some additional years having them built to my design or to a design overseen or influenced by me. S7 got drafted into the mold making biz in the late '70's (before my time) for its toughness. So we used a lot of it and H13. S7 definitely made the grade as a mold steel but honestly I would not say that that application tested it in the same way a bolt does. It was darn good stuff, harder and tougher than H13, although H13 had some advantages that don't apply here and nothing about H13 would make it a better bolt choice. We always heat treated S7 to the high end of its range as it was toolmaker lore that it was tougher at say 56 than it was at 50.... whether or not a Carpenter metallurgist would agree I don't know ......but it seemed borne out by decades and decades of combined experience among the many toolmakers I worked with.

Whether or not S7 or anything else is a good bolt material will best be determined not by the Carpenter book but by round-pounding..... I'll be interested in anyone's results but it's gotta come with good (high) round counts and other data.....

[BufordTJustice]

I've used tons of S7. No really, I mean tons.... OK one ton at least, in 20-plus years making plastic injection molds and some additional years having them built to my design or to a design overseen or influenced by me. S7 got drafted into the mold making biz in the late '70's (before my time) for its toughness. So we used a lot of it and H13. S7 definitely made the grade as a mold steel but honestly I would not say that that application tested it in the same way a bolt does. It was darn good stuff, harder and tougher than H13, although H13 had some advantages that don't apply here and nothing about H13 would make it a better bolt choice. We always heat treated S7 to the high end of its range as it was toolmaker lore that it was tougher at say 56 than it was at 50.... whether or not a Carpenter metallurgist would agree I don't know ......but it seemed borne out by decades and decades of combined experience among the many toolmakers I worked with.

Whether or not S7 or anything else is a good bolt material will best be determined not by the Carpenter book but by round-pounding..... I'll be interested in anyone's results but it's gotta come with good (high) round counts and other data.....

Thank for adding that, Ned. What makes the bolt's application so difficult to find a suitable material aside from C158? Is it the combination of all the different elements (i.e. temp cycling, exposure to combustion byproducts, shock loading, etc.) that makes this task so difficult?

[Ned Christiansen]

Thank for adding that, Ned. What makes the bolt's application so difficult to find a suitable material aside from C158? Is it the combination of all the different elements (i.e. temp cycling, exposure to combustion byproducts, shock loading, etc.) that makes this task so difficult?

I don't think the hottest bolt on the hottest day in the hottest land after the longest fire fight is hot enough to affect the steel. It's the goin' on 4 tons of bolt thrust over and over, thousands of times. I can't equate that to a tooling application in a mold, stamping die, or the like. Somewhere there is a tooling scenario where something similar exists but I don't believe anything I've done was it. I'd love to get the job of building the tooling to approximate bolt loading when firing...... then run it at 800 cycles a minute.... that's 48000 simulated rounds an hour..... we could find some things out in short order! But that'd be a pretty sophisticated design.... it might actually be cheaper to just buy the guns and ammo!

[Ned Christiansen]

I just checked it out on their site, kinda rad and kinda impressive if it proves out. The strength numbers are hard to argue with, I'm not going to bother digging out my Carpenter book, which doesn't list 158 anyway, but as those numbers are easily checked I doubt they'd fib on that.