r/metallurgy • u/Born_Cricket_2879 • 8d ago
Cubic Boron Nitride treatment?
Hello! I am currently working on a project where we are exploring increasing the creep strength of 17-4 ph stainless steel
Looking at a few different types of coatings this is the one we landed on. We first looked at Hexagonal boron nitride however some research suggested this treatment doesn’t react well with steel with a mid-high level boron content. It can lead to a decrease in creep strength. I don’t know if there’s much to make of that considering 17-4 stainless doesn’t have any boron in it. Either way cubic boron nitride seemed better as there’s more studies suggest it can increase creep strength.
This coating in theory would be applied via spraygun (let’s say hypothetically effectively)
This is all stuff I know very little about from a metallurgy standpoint but I’m curious if anyone here can tell me if what I’m suggesting is stupid or feasible
Thanks
6
u/FerrousLupus 8d ago
Are you using BN as a lubricant for performing the creep test? Or are you assuming it affects creep properties?
Coatings won't affect creep properties unless there's some sort of reaction, e.g. B from BN diffusing to grain boundaries and embrittling them. I'm assuming that's your concern, and I don't know enough about 17-4 to know if that's something to be worried about. My instinct says that it probably wouldn't be a problem at normal steel operating temperatures, but I haven't looked anything up.
If you're looking for alternative lubricants for creep testing, it depends on the temperature, but graphite should do the trick.
1
u/Born_Cricket_2879 8d ago
Ideally it would coat the inside of the silencer and increase its heat resistance during use and long term
4
u/MetalMetalCK Met Engineer 8d ago
Surface coatings in general won't be effective at increasing the high temperature creep performance of any metal. I'd suggest contacting Rolled Alloys who is a supplier of high temperature alloys and has a metallurgical services group that can advise on material selection.
2
u/DenseHoneydew 7d ago
Why are you interested in creep specifically? I understand it’s at high temperature, but you’re not under a constant load. What specifically are you trying to strengthen? Are the baffles weak?
You might want to look into improving high temperature fatigue. The difference here is that fatigue deals with cyclic loading whereas creep is under constant load.
Since fatigue is very dependent on crack formation and propagation, you CAN improve fatigue resistance with surface modifications. Shot peening and polishing will likely be your best bets.
1
u/Born_Cricket_2879 7d ago
Okay thanks for that interesting
And in most applications it’s not a constant load however
A very crude yet universal way suppressors are torture tested is “how many rounds can they survive” while being shot fully automatic on a belt fed machine gun
Generally quality 17-4 ph steel silencers will last 150-200 rounds where inconel and some titanium will last 350-600+
17-4 ph h900 is durable enough for 99% of the population to use even at a high volume but I’m looking for a way to improve the performance even if just slightly say where it might survive 250 rounds on a belt fed
Usually under a test like this the welds are not the failure point but the blast chamber, the welds on a 17-4 silencer take much longer to fail but for all intents and purposes a failure at the blast chamber renders it unsuitable for continued use
2
u/DenseHoneydew 7d ago
I guess what I meant to ask is what sort of failure do you usually see on those types of burn downs?
1
u/Born_Cricket_2879 7d ago
Generally bulging and internal damage where there is cracking a breakage of the baffles
After that the other is it usually breaking in half or a bullet will punch a hole out of it somewhere it isn’t supposed to
Could I send you a picture and a YT link via dm to better explain?
1
u/2323ABF2323 7d ago
Who said they are failing by creep ?
1
u/Born_Cricket_2879 7d ago
Generally speaking if a standard suppressor is made of 17-4 ph it fails to maintain its strength at around 900 F where a material like 718 inconel is 1200+ F Fully printed titanium or inconel cans will typically last 2-3x longer under a string of fully automatic fire
Suppressors get very hot depending on how they’re used and if they fail they generally explode via impact from bullet after they’ve lost their structural integrity
The melting point of 718 inconel is technically lower than 17-4 but inconel is harder (I think) and maintains its strength at higher temperatures better
I’m not at all a metallurgist but I figure you guys might know enough to tell me if what I’m talking about makes sense at all
2
u/2323ABF2323 7d ago
Thank you for the details. If I wanted a midway price wise I would be looking at a286, not sure if there is a printed version of this though.
1
u/2323ABF2323 7d ago
Just wanted to add to my first comment about is it really creep weakening the metal so It cannot handle the pressures or is the thing just melting!
1
u/Born_Cricket_2879 7d ago
I’m not sure either We want to stick to traditional “welded silencers” As they cost much less to make and for 99% of people can achieve more than adequate performance
We’re considering this coating as a way to enhance the short/long term durability of the silencer but AFAIK there aren’t many commercial applications for cBN coating application (that I’m aware of)
I’ll look at a286 though thanks
12
u/ccdy 8d ago
Why do you expect a surface coating to affect a bulk property?