Coatings - avoiding hydrogen embrittlement

moose2367 · Mar 13, 2020

I make broadheads, don't make a living out of it, but enjoy it and as most here, try to improve the process.

They are made from 1055, stamped out in an incline press, heat treated in house by me, and sharpened on a pretty big surface grinder. Theya re 1.2mm thick, and a couple of different shapes, 75mm long and 28mm wide and the other about 50mm long and 28m wide, with cutouts on the centre for the ferrule.

I heat treat about 2000 blades at a time, in racks and then put them in a cement mixer to descale before tempering in 2 cycles in clamps, ending up at 52-54rc.

I have for the past few years since i bought the business just had the bare steel finish, sprayed with a product called dry coat, a water soluble rust preventative.

I've always hated the visual look and have looked at various coatings, even went and bought all the gear to cerakote them in house, but the prep work was too time consuming, having to bead blast every blade with those thick gloves was a knightmare.

I decided on black oxide a few weeks ago and asked if he has any issues with hydrogen embrittlement and was told no. Although i didn't specifically ask what he prepped them with.

I have just had a few snap in the jigs on the grinder and a few snap while re-sharpening on a stone.

I have since found out the prep is hydrochloric acid at 33%, then black oxide coated, the hydrochloric is the issue i think, as they aren't baked afterwards.

Bearing in mind i have to courier them a couple of hours each way to get them done, and sent down about 35kg(77 lbs) of blades to be done at once.

Anyone else get bulk flat parts prepped good enough for coating without using acid?

Only thing i can think of is a rotary sandblaster, but don't know of anyone that does it.

I'm in Australia too.

FredC · Mar 13, 2020

I am not an expert on hydrogen embrittlement. I had some heat treated parts plated and the plater was adamant that post plating baking was necessary very quickly done after plating.

"I have since found out the prep is hydrochloric acid at 33%, then black oxide coated, the hydrochloric is the issue i think, as they aren't baked afterwards."

I am with you most likely culprit.

pcm81 · Mar 14, 2020

moose2367 said:
I make broadheads, don't make a living out of it, but enjoy it and as most here, try to improve the process.

They are made from 1055, stamped out in an incline press, heat treated in house by me, and sharpened on a pretty big surface grinder. Theya re 1.2mm thick, and a couple of different shapes, 75mm long and 28mm wide and the other about 50mm long and 28m wide, with cutouts on the centre for the ferrule.

I heat treat about 2000 blades at a time, in racks and then put them in a cement mixer to descale before tempering in 2 cycles in clamps, ending up at 52-54rc.

I have for the past few years since i bought the business just had the bare steel finish, sprayed with a product called dry coat, a water soluble rust preventative.

I've always hated the visual look and have looked at various coatings, even went and bought all the gear to cerakote them in house, but the prep work was too time consuming, having to bead blast every blade with those thick gloves was a knightmare.

I decided on black oxide a few weeks ago and asked if he has any issues with hydrogen embrittlement and was told no. Although i didn't specifically ask what he prepped them with.

I have just had a few snap in the jigs on the grinder and a few snap while re-sharpening on a stone.

I have since found out the prep is hydrochloric acid at 33%, then black oxide coated, the hydrochloric is the issue i think, as they aren't baked afterwards.

Bearing in mind i have to courier them a couple of hours each way to get them done, and sent down about 35kg(77 lbs) of blades to be done at once.

Anyone else get bulk flat parts prepped good enough for coating without using acid?

Only thing i can think of is a rotary sandblaster, but don't know of anyone that does it.

I'm in Australia too.

Any time you have iron in any type of acid, the H+ from acid will get into the metal and stay there to cause Hydrogen embrittlement. Usually you have to bake parts within 2ish hours to remove H from metal. You can't bake say next day, because H will combine into H2 and won't be removed by baking. Often the plating shops will completely ignore the H embrittlement issue since most of their work is not "mission critical" hence cracking to H embrittlement is not an issue.

Rickyb · Mar 14, 2020

A couple of hours at about 300 degrees F is what I remember. Op does not define temper temperature but from final hardness I'm guessing 6-700 F maybe a bit more. As long as the bake temp is significantly lower than the temper there will be no appreciable drop in hardness. Never understood why, just know it is true.

moose2367 · Mar 14, 2020

My temper temperature is 265c and 250c, first one is with the clamps finger tight, second is with them tightened as tight as possible.

Had a thought, what if i get them coated straight after heat treating, but before tempering, then temper and baking the hydrogen out at the same time?

The coating should be able to handle 265c? I will have to ring and ask them.

I would just have to be there to pick them up and drive directly back to get them in the kiln within a few hours preferably.

TDegenhart · Mar 14, 2020

Not a good idea to harden, then coat, and finally temper and bake. Proper procedure is harden, temper coat and bake. The purpose of the temper is to relieve the internal stresses caused by the quench. By allowing those stresses to remain while immersing in acid aggravates the problem.

I have had some people say the baking must be done immediately after coating, others have said it doesn't make a different so long as it done. I would say bake as quickly as possible.

To the kinds of hardness from a 1055 steel says that you are water quenching which adds a lot stress.

I am afraid I don't know what a broadhead is so I cannot suggest an alternate method of manufacture.

Tom

akajun · Mar 14, 2020

As a bow hunter I would say ditch the black oxide and go for a tool coating like TIN,PVD,or even Melonite. You’ll have a tougher edge, and better corrosion resistance.

moose2367 · Mar 14, 2020

TDegenhart said:
Not a good idea to harden, then coat, and finally temper and bake. Proper procedure is harden, temper coat and bake. The purpose of the temper is to relieve the internal stresses caused by the quench. By allowing those stresses to remain while immersing in acid aggravates the problem.

I have had some people say the baking must be done immediately after coating, others have said it doesn't make a different so long as it done. I would say bake as quickly as possible.

To the kinds of hardness from a 1055 steel says that you are water quenching which adds a lot stress.

I am afraid I don't know what a broadhead is so I cannot suggest an alternate method of manufacture.

Tom

I am quenching in castrol quenching oil.

Heating 250 blades to 850c for 7 mins then quench.

moose2367 · Mar 14, 2020

akajun said:
As a bow hunter I would say ditch the black oxide and go for a tool coating like TIN,PVD,or even Melonite. You’ll have a tougher edge, and better corrosion resistance.

It's not the coating i am worried about, any type of coating requires some prep work, it's usually an acid that causes an isssue, or i go to the extremely laborious task of sandblasting.

One thing i haven't tried yet is ultrasonic cleaning, we have a couple of big ultrasonics here that we do sets of dis-assembled diesel injectors in.

Might try a few blades and see what happens

pcm81 · Mar 14, 2020

Plethora of coating options exist and many you can do at home if you don't mind messing with chemicals. 2lb of sodium hydroxide and 5lb of sodium nitrate per gallon of water is your DIY black oxide. Add water to keep solution boiling between 270F and 290F. Nasty stuff though. I usually wear full protective gear when i do it at home. If it gets in your eye, you will go blind. Don't let it go over 300F. Parkerizing bath runs at lower temperature but requires more chemistry monitoring. If you are doing it at home you save driving time and can bake the parts within reasonable amount of time to relieve hydrogen embitterment. Coatings like TiN are nicer but cost more and you can't do at home. Electroless nickel will be the most expansive one that you can do at home, but it looks nicer and cleaner than oxide of phosphate. The 2hr time after acid for baking to relieve H embitterment matches what i remember. Your coating provider may have a kiln available to baking to relieve H embrittlement.

moose2367 · Mar 14, 2020

I will call him in the morning ans see if he has a kiln or oven to bake them as well.

Before i went to the hot black oxide i did a couple of different cold black oxide, caswell and jane kits, both were ordinary at best, the coating looked ok, but the black smutt constantly comes of on your hands and it cost more to trial them than getting 100 times the amount hot black oxided outside.

I didn't want to have to have the hot black oxide chemicals here, haven't got the room and having the acid here is a no go.

Just having a tub of it when i did the cold oxiding did damage to other surfaces from the fumes. One lathe bed got surface rust, so did my big surface grinder and various tooling.

akajun · Mar 15, 2020

moose2367 said:
It's not the coating i am worried about, any type of coating requires some prep work, it's usually an acid that causes an isssue, or i go to the extremely laborious task of sandblasting.

One thing i haven't tried yet is ultrasonic cleaning, we have a couple of big ultrasonics here that we do sets of dis-assembled diesel injectors in.

Might try a few blades and see what happens

Your missing the point, the other coatings I recommended do not go through a process that risks hydrogen embrittlement, they make your cutting surface tougher, and melonite for example increases lubricity and prevents rust way better than any black oxide or hot blue.
If you insist on using black oxide you can use what gunsmiths use to clean before a hot blue which is a key solution and or boiling.

pcm81 · Mar 15, 2020

akajun said:
Your missing the point, the other coatings I recommended do not go through a process that risks hydrogen embrittlement, they make your cutting surface tougher, and melonite for example increases lubricity and prevents rust way better than any black oxide or hot blue.
If you insist on using black oxide you can use what gunsmiths use to clean before a hot blue which is a key solution and or boiling.

Also, it should be noted that black oxide or even parkerizing are not rust preventive coatings on their own. You have to apply oil to these porous coatings and it is the oil that does rust prevention. Since broadheads are usually used for hunting, the application of oil may be a no-no for some users...

Rickyb · Mar 15, 2020

moose2367 said:
My temper temperature is 265c and 250c, first one is with the clamps finger tight, second is with them tightened as tight as possible.

Had a thought, what if i get them coated straight after heat treating, but before tempering, then temper and baking the hydrogen out at the same time?

The coating should be able to handle 265c? I will have to ring and ask them.

I would just have to be there to pick them up and drive directly back to get them in the kiln within a few hours preferably.

Interesting isea to black oxide after quench. Adding a stress riser to an already highly stressed metal matrix.
If you are not experiencing quench cracking now your part geometry is robust and your idea is worth a try. Fe3O4 is a very stable compound and should withstand you temper temp.

moose2367 · Mar 15, 2020

akajun said:
Your missing the point, the other coatings I recommended do not go through a process that risks hydrogen embrittlement, they make your cutting surface tougher, and melonite for example increases lubricity and prevents rust way better than any black oxide or hot blue.
If you insist on using black oxide you can use what gunsmiths use to clean before a hot blue which is a key solution and or boiling.

With all due respect, how am i missing the point? I am guessing with the small googling i have done on melonite coating and the others, that some sort of prep work is still going to be needed, correct?
Melanite is also called salt bath nitriding, from the process i have just looked at, the material need to be heated to 700-8--f or 375c, which will ruin my temper. Is there something i am missing?

Rickyb said:
Interesting isea to black oxide after quench. Adding a stress riser to an already highly stressed metal matrix.
If you are not experiencing quench cracking now your part geometry is robust and your idea is worth a try. Fe3O4 is a very stable compound and should withstand you temper temp.

Whether it would work i don't know, they are just flat blades, zero stress until the 2nd temper cycle, where i clamp them all together flat, the first temper just reduce their stress enough to not break, as they do if i tighten too much the first temper, hence finger tight only.

akajun · Mar 16, 2020

moose2367 said:
With all due respect, how am i missing the point? I am guessing with the small googling i have done on melonite coating and the others, that some sort of prep work is still going to be needed, correct?

Whether it would work i don't know, they are just flat blades, zero stress until the 2nd temper cycle, where i clamp them all together flat, the first temper just reduce their stress enough to not break, as they do if i tighten too much the first temper, hence finger tight only.

Melanite actually creates a surface hardness and corrosion protective layer. Its commonly used on heat treated gun parts mostly made of 4140 and 416 stainless hardened to 28-32rc and does not affect the temper. I don't believe they use an acid prep, they do an Electro polishing to clean it but I may be wrong. A few custom knife makers are using this process too and seems to work well.
The point I was trying to make is that as a hunter, and a bowhunter, black oxide and Hot blue finishes plain suck. Yes they look pretty but offer little to none of corrosion protection. Here in South Louisiana, its not uncommon to get rained on hunting or be exposed to brackish water. Switching to a tool coating like Tin, PVD, or Melanite would give you the toughness and corrosion resistance you want.
Back before the days of Mechanical Broadheads, I started hunting with the old Bear fixed broadhead with the "bleeder blade". These were painted carbon steel and while you could replace the bleeder blade, the fixed blade requires a yearly cleaning, sharpening, and oiling. When Companies like Swifter and Muzzy came out with allow bodies with replaceable stainless tips and blades that was the answer to my prayers. It sounds like what your making is similar to the old Bear Broadhead.

TDegenhart · Mar 16, 2020

Make them out of 400 series stainless, then there is no need to coatings.

Tom

Rickyb · Mar 16, 2020

moose2367 said:
With all due respect, how am i missing the point? I am guessing with the small googling i have done on melonite coating and the others, that some sort of prep work is still going to be needed, correct?
Melanite is also called salt bath nitriding, from the process i hauve just looked at, the material need to be heated to 700-8--f or 375c, which will ruin my temper. Is there something i am missing?

Whether it would work i don't know, they are just flat blades, zero stress until the 2nd temper cycle, where i clamp them all together flat, the first temper just reduce their stress enough to not break, as they do if i tighten too much the first temper, hence finger tight only.

The high stresses are formed in the steel matrix when austenite is quenched and forms untempered martensite. You experience the results of this in your stacking process. The internal stresses are so high from quenching that a minor bend causes fracture.

Differential stress near corners and holes can get high enough for parts to fracture in the quench water, long before you stack them. If you are not losing parts to cracking in the quench you have a shot at the black oxide process before temper. They may fracture more readily in your stacking process. Hey, it might work.

moose2367 · Mar 17, 2020

TDegenhart said:
Make them out of 400 series stainless, then there is no need to coatings.

Tom

Wish it was as easy as that, weight would then be different for the same thickness, as i have ferrules with slots already for that thickness blade.
I could change that when i get my swiss lathe sorted i guess, but the actual weights might not be where i need them to be.

pcm81 · Mar 17, 2020

moose2367 said:
Wish it was as easy as that, weight would then be different for the same thickness, as i have ferrules with slots already for that thickness blade.
I could change that when i get my swiss lathe sorted i guess, but the actual weights might not be where i need them to be.

Keep thickness the same, but change size to match weight.

Coatings - avoiding hydrogen embrittlement

Plastic

Diamond

Cast Iron

Cast Iron

Plastic

Diamond

Stainless

Plastic

Plastic

Cast Iron

Plastic

Stainless

Cast Iron

Cast Iron

Plastic

Stainless

Diamond

Cast Iron

Plastic

Cast Iron

Similar threads