A question about steel heat treatment

[Gordon Bartlett]

6150 tool steel is usually hardened in one of two ways:

1) Conventional hardening, in which the entire piece is heated, quenched, and tempered. This is usually used to get the piece up to maybe 54 or 56 Rockwell C, at least in my experience.
OR
2) It is flame hardened, a type of case hardening accomplished by heating the surface with a torch head that immediately quenches the surface with water. This leaves the surface very hard, and leaves the interior of the block, and all untreated surfaces, dead soft.

So here's my question:
Can a block of 6150 be conventionally hardened to, say, 48- 52 Rockwell C, and then flame hardened on critical surfaces to get those to a much harder condition suitable for a heavy wear surface? This could be very useful for me. Does anybody here know?

[oznabrag]

6150 tool steel is usually hardened in one of two ways:

1) Conventional hardening, in which the entire piece is heated, quenched, and tempered. This is usually used to get the piece up to maybe 54 or 56 Rockwell C, at least in my experience.
OR
2) It is flame hardened, a type of case hardening accomplished by heating the surface with a torch head that immediately quenches the surface with water. This leaves the surface very hard, and leaves the interior of the block, and all untreated surfaces, dead soft.

So here's my question:
Can a block of 6150 be conventionally hardened to, say, 48- 52 Rockwell C, and then flame hardened on critical surfaces to get those to a much harder condition suitable for a heavy wear surface? This could be very useful for me. Does anybody here know?

I would say no.

As I understand it, a piece of steel can get only so hard.

If it is 'conventionally hardened', it's as hard as it's going to get, so flame hardening can't take it any further.

Case hardening on the other hand . . .

Anyway, I've already told you more than I know about it.



What is the project?

[oznabrag]

http://www.astmsteel.com/product/aisi-6150-steel/

[Jimmy W]

I likely know less than Oz about it, but case hardening might do what you want.

[robm]

Thing is though, the tempering reduces the hardness of the steel. It may be possible to then add a harder layer with the flame trick, which is just quenched, not tempered. The piece of steel would have to be quite thick so the bulk of it is not affected by the flame.

I wonder if a case hardening process involving carbon would work better: First case harden, then harden conventionally. The higher-carbon skin would wind up harder than the core.

[Gordon Bartlett]

robm has it right in saying the tempering brings the hardness well down from its as-hardened state. I usually have it brought down to around 48-52 Rockwell C.
A million years ago, during my apprenticeship, I seem to recall being told that the flame hardener used a yellow "carburizing" flame on his torch which imparted extra carbon into the work piece's surface, enabling a higher maximum hardness at the surface.
In any case, flame hardening certainly works in providing a good, hard wear surface. I have just never seen it combined with a conventionally hardened - and - tempered core. I'm using it in die design for cams drivers, and such.

[oznabrag]

robm has it right in saying the tempering brings the hardness well down from its as-hardened state. I usually have it brought down to around 48-52 Rockwell C.
A million years ago, during my apprenticeship, I seem to recall being told that the flame hardener used a yellow "carburizing" flame on his torch which imparted extra carbon into the work piece's surface, enabling a higher maximum hardness at the surface.
In any case, flame hardening certainly works in providing a good, hard wear surface. I have just never seen it combined with a conventionally hardened - and - tempered core. I'm using it in die design for cams drivers, and such.

So it's a method of case hardening.

PaulF is the accomplished blacksmith around here (no offense to others' abilities).

Maybe he'll chime in on this.

It is my impression that adding a certain range of percentages of Carbon to pure Iron results in steel, but that is a VERY primitive understanding of metallurgy.

Modern steels are pretty complicated, and simply adding Carbon may or may not be the path to your desired result.

On a semi-related note, I spoke with a machinist one afternoon, and he was involved with turning a new driveshaft for a machine that pulped pine logs for paper.

It was the third one he had made in as many weeks, but after the second one snapped he had a long, heart-to-heart with his customer and discovered that the 8" diameter shafts were snapping off right where they entered the acid bath.

What the customer had failed to mention was the specification of the steel needed to resist embrittlement in an acid bath.

All the best!

John T

[Tom from Rubicon]

Nitriding.

[Paul Pless]

In any case, flame hardening certainly works in providing a good, hard wear surface. I have just never seen it combined with a conventionally hardened - and - tempered core. I'm using it in die design for cams drivers, and such.

Modern steels are pretty complicated, and simply adding Carbon may or may not be the path to your desired result.

simpler processes may be better in this application

ie, choose another steel that will give you the necessary end properties with one heat treat cycle. . .

[oznabrag]

simpler processes may be better in this application

ie, choose another steel that will give you the necessary end properties with one heat treat cycle. . .

That's the ticket.

There's thousands of precisely-formulated steels out there tailored to thousands of specific applications.

I was told that some folks actually get a sheepskin for putting big chunks of that sort of info under a mortar-board, but I'm juss a country boy and I'm sure I'm leaving something out of that picture.

[paulf]

CASE HARDENING OF STEEL COMPONENTS & STRAIGHTENING
30% carbon or any alloy steel which has a carbon above . 30% and additional alloys of chromium, nickel, molybdenum, etc. (4140, 4150, 6150, 1060, etc.). These are not carburizing grades and they are not recommended for case hardening.

What Oz and PaulP said. Its tough stuff, but if you have a special need for deferential hardening, bite the bullet and find a better fit. Also if this is a new thing to you read up on the techniques. It's easy to make some freshman errors when doing this at first.

It can be done, but with out firm control on the process things can and will go sideways. There is a top when it comes to hardness, stress relief is necessary, quench control is also necessary.

The amount of carbon is the deciding factor, try to stay within the manufacturers recommendations they know the product. Also make sure!! what the steel really is,if you got it from a junk yard and not a mill you don't know if there are stress failures within the block.

Whatcha makin??

[paulf]

There is a lot of information out there on the web, some of it very good, some not so good.

Play around with some junk steel and get a feel for how it responds. Having the tools to really test the results is a leg up!

Knife makers and tool makers (amateurs) have a lot of information.

[Canoeyawl]

simpler processes may be better in this application

ie, choose another steel that will give you the necessary end properties with one heat treat cycle. . .

see: A11
http://cintool.com/documents/powdered_Metal/A11PM.pdf

[Gordon Bartlett]

choose another steel that will give you the necessary end properties with one heat treat cycle. . .

That's a great idea, but I've been in the automotive tooling business since 1972 and I've never heard of a steel like that, which is why I'm asking the question. 6150 gets hard enough on its surface,when flame hardened, to be used as a high-pressure wear surface. It is also brutally strong and tough when hardened into a mid-hardness range, meaning it won't break easily when used and abused, as is always the case in automotive stamping dies. This mid-hardness also keeps it from getting easily damaged during casual handling and assembly, where even the slightest dents or dings create cratered-up points that can throw parts of the assembly out of alignment. It also prevents holes from becoming worn or wobbled out of round or bell-mouthed.
So anyway, I'm trying to find a way to make a cam or a driver that has glass-hard, non-galling surfaces where I need them, and also has moderately hard, but not brittle surfaces elsewhere, along with a strong, tough, interior.
If you know of a steel that offers that, I'm all ears.
I appreciate the thoughts so far.

[Paul Pless]

So anyway, I'm trying to find a way to make a cam or a driver that has glass-hard, non-galling surfaces where I need them, and also has moderately hard, but not brittle surfaces elsewhere, along with a strong, tough, interior.

how big is this part? how is it machined?

i read an interesting thing about top fuel crankshafts and cams recently, the engines accelerate so violently to 10,000+rpm that cranks and cams were being twisted enough to break them; yet they seek a surface hardness (cams moreso than cranks need surface hardness) in the region that you seem to be looking for

this led to a search for a new steel for their applications

competition cams is using 8620 and 9310; lunati is using st4 tool steel for these

these are all pretty exotic alloys and priced accordingly

[paulf]

I thought you were just a guy poking around in your shop, you have access to better info than here after almost 40 years in the business.

[Gordon Bartlett]

how big is this part? how is it machined?...
these are all pretty exotic alloys and priced accordingly

I wasn't asking about one particular part, but rather about cams and drivers in general. I'm not talking about cam shafts and valve-lifting cams. I'm talking about slide cams in stamping dies, used to change the direction of motion from the press's vertical travel to horizontal travel or some angle in between (or even beyond). Cams like this will usually weigh from, say, five pounds to a few hundred pounds. The bigger ones are usually cast iron, so that's a whole different thing, but lots of smaller ones up to maybe a hundred pounds are steel and are made by milling, drilling, and surface grinding.
Your last point about the cost of exotic materials is a lot more important than you may realize. Die shop owners are really reluctant to spend more than necessary on materials for obvious reasons. Conventional die steels such as D2, O-1, A2, S7, 6150, 4150 P.H., etc. are familiar and comfortable to them. And their price is what is factored into the quoting process. Bringing expensive, exotic stuff into the picture during the design process is really frowned upon.

I thought you were just a guy poking around in your shop, you have access to better info than here after almost 40 years in the business.

Paul, while I've been in the die business for that long (actually that's almost fifty years), I really don't have much hands-on experience with the various heat-treat processes. Every die shop I have ever worked in , including my own, has sent the heat treat work out to dedicated heat treat companies. I've played with it a few times on non-critical things, but not in any serious way.

And now the big news: Just before typing this post I had a wild and crazy idea. I called a major Detroit-area flame hardening company on the phone and asked him the same question I asked you guys. He pretty much shot down the whole idea. He said 6150, already hardened, would almost certainly crack when flame hardened. 4150 P.H. would have a slightly better chance, but not much. He said I might possibly get away with doing that to a piece of 1060, but really discouraged it. So I guess I'll keep muddling my way through the whole steel selection process like I always have, and rely on hardened or bronze inserts where appropriate.
Once again I'd like to thank you guys for the thoughts.

[paulf]

It is an interesting problem.
These guys used FLAME Spray.

https://www.researchgate.net/publica...e_applications

Hope something helpful, let us know how you proceed, interesting!

[Canoeyawl]

Ah-ha! cams...

[Bob (oh, THAT Bob)]

It is an interesting problem.
These guys used FLAME Spray.

https://www.researchgate.net/publica...e_applications

Hope something helpful, let us know how you proceed, interesting!

Ford motor is, or will be, using plasma-sprayed cast iron onto aluminum cylinder walls; Should be lighter than typical cast iron liners, more durable than Nikasil, and from what I read, rebuildable, can be reapplied and re-bored during engine rebuild instead of just scrapping the block. Of course, the days of the internal combustion engine are limited, but they'll be around awhile, and there are wider implications for this process.

[Ross M]

I worked for a company that made C-130 Main Landing Gear ball-screws out of 6150. Unusually, the aircraft weight is borne by these ballscrew assemblies, and sometimes only 1 out of the 4 screws is in play, and thus required 160,000 lb. capacity. We core hardened these (1.5" pitch diameter) to 36-39 Rc, and then induction hardened the ogive threads to 58-62 Rc (from memory) with a very light tempering. Each one was magnafluxed and we never experienced any cracking, even after straightening. Load testing to failure - accompanied by a 1/2 dozen Lockheed engineers - was interesting.

[Gordon Bartlett]

I'd like to have seen that test. What was the failure? Did the whole thing just buckle?

[rregge]

First of all 6150 is a medium carbon low alloy steel...not a tool steel.

It is a chrome vanadium grade of steel and according to my copy of Metals Handbook Desktop edition (0.8-1.10 chrome, >or equal to 0.15% vanadium, 0.48-0.53% carbon and 0.7-0.9% manganese) and often used to make springs.

When you talk about hardening a block of steel what size block are you talking about?

The maximum potential hardness for low alloy steel (as hardened) is a function of the carbon content (more carbon from 0% up to around 1% the harder the steel can potentially get) (Above a certain point you will begin to form carbides which are great for wear resistance)

The size of the block (and the alloy content) determine if you will be able to cool the block fast enough to reach (or come close to reaching) the maximum hardness based on the carbon content. The larger the block the slower the cooling, the need for more alloys.

If your block is too large to get hard for the alloy (6150 in this case) than yes you COULD case or surface harden it. The issue is how to get a uniform hardness with a torch/flame so that when you quench it you get uniform hardness and it doesn't crack. The higher the carbon content the more likely you are to develop cracks (it has to do with volumetric growth going from austenite (the phase structure when heated above the critical temp prior to quenching) to martensite (the phase structure you are trying to get when quenching.

Not sure why you would do both.

Regarding trying to get the max hardness by not tempering...DANGER WILL ROBINSON. Untempered martensite is very brittle and is subjected to catastrophic failure without warning. Also if you have retained austenite after quenching (much more likely with high carbon steel)and do not temper the steel and the sample gets cold...think outside in the winter...the retained austenite in the steel can transform to martensite...and it will crack at that point.

Yes you will lose a couple of points of hardness by tempering, but you will have a much better and more reliable piece after tempering.

If you wonder...yes I am a metallurgist.

[oznabrag]

. . .Cams like this will usually weigh from, say, five pounds to a few hundred pounds. . . .

. . .

When you talk about hardening a block of steel what size block are you talking about?

. . .

If you wonder...yes I am a metallurgist.

OK!

You are now on the permanent record as being a metallurgist, so don't be surprised when you are summoned to enlighten the rest of us in the future!

!

[rregge]

I am always happy to help.

[oznabrag]

I am always happy to help.

How difficult would it be to harden and temper a cam weighing 300 pounds?

Would a hand-held propane torch and a garden hose do the trick?

[rregge]

How difficult would it be to harden and temper a cam weighing 300 pounds?

Would a hand-held propane torch and a garden hose do the trick?

Are you serious? I think/hope not

First off this is a 300 pound 6150 cam is that correct?

If this is this for an industrial application with potential liability issues...hell no.

If this is back yard tinkering...hell no.

1. No way to through harden a piece that size with a torch and a garden hose. (never use water... use an oil quench). You could never get it to a uniform temp above critical...so you will end up with cracks, soft spots and warping. But then again it is so massive it will never cool fast enough to form martinsite (at least not uniformly)

2. If you want to flame/case harden it again how are you going to get a uniform temperature with something that massive. If you get it hot enough the core could act as a heat since and self quench it...but you will almost surely end up with soft spots, cracks and warping.

Send it to a professional heat treater, and I suspect they will turn you down.

[oznabrag]

Easy, tiger.

It was just a mild troll is all.

When serious questions come up, we'll know who to ask.

Thanks!

[paulf]

Easy, tiger.

It was just a mild troll is all.

When serious questions come up, we'll know who to ask.

Thanks!

I'll bet a cord of wood, a big fire , a leaf blower and a stock/cattle water tank (full of light tempering oil) and it might work!

[Ross M]

I'd like to have seen that test. What was the failure? Did the whole thing just buckle?

These ballscrews are loaded in tension - the failure occurred at (from memory) somewhere near 195,000 lbs. The screw did not fail, the nut did. a semi-spiral failure running from the first of three independent ball circuits (2.5 turns per circuit) to a neck adjacent to the spherical loading point (maybe 3" in diameter). Ended with a sudden big bang. Instrumentation on the machine was not really capable of capturing elongation data, so no one really knew exactly when to expect the failure.

The test machine was an enormous (and ancient) Baldwin Locomotive Works hydraulic piece that spent most of its days crushing concrete test samples for the FL DOT. Locomotive black, of course. Tampa has some interesting things here and there...

[Bob (oh, THAT Bob)]

The size of the block (and the alloy content) determine if you will be able to cool the block fast enough to reach (or come close to reaching) the maximum hardness based on the carbon content. The larger the block the slower the cooling, the need for more alloys.

(As a metallurgist, I know you know this, I'm just clarifying for others): (bold) Increasing the alloy content increase "hardenability", the ease with which it hardens; You don't need to quench the steel as fast. "Stainless" (corrosion resistant) steels have enough alloy content that they easily harden just from air cooling. Many of you have experienced this, you're drilling through a piece of stainless, get it just a bit too hot, and a couple seconds later, it's hard as glass and the drill you were using just bounces off the surface. To anneal, you need to heat it to the annealing temperature and then cool it very slowly.

[rregge]

I'll bet a cord of wood, a big fire , a leaf blower and a stock/cattle water tank (full of light tempering oil) and it might work!

no problems.

I knew the question was either a troll, a test or someone was way out there.

[rregge]

(As a metallurgist, I know you know this, I'm just clarifying for others): (bold) Increasing the alloy content increase "hardenability", the ease with which it hardens; You don't need to quench the steel as fast. "Stainless" (corrosion resistant) steels have enough alloy content that they easily harden just from air cooling. Many of you have experienced this, you're drilling through a piece of stainless, get it just a bit too hot, and a couple seconds later, it's hard as glass and the drill you were using just bounces off the surface. To anneal, you need to heat it to the annealing temperature and then cool it very slowly.

Nice to know I am not alone, and with really high carbon steels (.8%C and above) that cooling time for annealing could take a day (think 52100 bearing steel and a sherodize anneal)

[Canoeyawl]

For small hardened parts that you want to anneal and rework, heated dull red and quenched/submerged in a bucket of lime for 24 hours will keep it warm at least overnight.
Hardening and tempering again is more far more complicated

I do have a big container of Kasenit: https://www.travers.com/1lbcan-1-sur.../p/81-003-001/

[Tom from Rubicon]

Disregard #8, might not work. No data. OP stated block of 6150 tool steel which is a chrome Vanadium spring steel and at 52C Rockwell is pretty darn tough. Not file hard but in its applications the chromium allows under pressure to work harden. and continue to work hardening through the service life of heat treated 6150 part. Pretty respectable knife steel though it will tarnish and rust.
6150 HR Annealed |Chrome Vanadium Steel | Alro Steel
AISI 6150 Steel | 1.8159 | 51CrV4 | Sup10 Spring Steel - Otai Special Steel (astmsteel.