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O/T - BTU's required to melt 17-4 ss?

Terry Keeley

Titanium
Joined
Oct 18, 2005
Location
Toronto, Canada eh!
I'm going to cast some small parts in 17-4 and need to melt about 2 oz. of material in 30 sec. or less.

Doing some research I'm leaning towards a Victor 100 handle with a propane rosebud nozzle (propane for less carbon in the melt and higher heat):

1 Welding Handle | Gas Equipment | Products & Solutions | ESAB

Victor 324-118 8-MFN-1 Propane Heating Nozzle Rosebud 1FC [Misc.] - Gas Welding Accessories - Amazon.com

There are bigger handles but I also need regulators and want to make sure I go big enough without too much overkill.

Is there a way to figure the heat required?
 
I'm going to cast some small parts in 17-4 and need to melt about 2 oz. of material in 30 sec. or less.

Doing some research I'm leaning towards a Victor 100 handle with a propane rosebud nozzle (propane for less carbon in the melt and higher heat):

1 Welding Handle | Gas Equipment | Products & Solutions | ESAB

Victor 324-118 8-MFN-1 Propane Heating Nozzle Rosebud 1FC [Misc.] - Gas Welding Accessories - Amazon.com

There are bigger handles but I also need regulators and want to make sure I go big enough without too much overkill.

Is there a way to figure the heat required?
.
.
vast majority of heat is wasted. in general when you use 2x fuel flow rate it takes 1/4 time to melt. flame too small you can be hours to melt anything. obviously if you can better insulate around flame stuff melts faster
.
melt in 30 seconds or less ? most metal needs time to warm up. thicker it is longer to melt. i cannot see melting in 30 seconds unless you had a electric arc of over 500 amps or about 15,000 watts. by the way that much electrical power arc is very loud
.
by the way if you preheat fuel and air flame can get hot enough to melt a crucible especially where flame touches it. and you can melt the refractory lining of a furnace
 
Just as a frame of reference using a torch.

Every time I run into stainless (when scrapping), you'll get to orange heat (ready to hit the oxygen)
and then you will form an oxide insulating layer, and every thing stops at that point.
 
You need two properties of the steel of interest.
Specific heat for 17-4 it is .11 BTU/lb-F
and
Heat of fusion. Looking up this value is left as an exercise to the reader.

total BTU is Mass of sample *.11*(melting temp of steel-room temp) + Heat of fusion* mass of sample.

That is the heat required inside the sample. You also have to heat up the crucible Using properties of it and first equation.
Then there is the inefficiencies of all the heat that does not go into the sample.

Gut feel. two ounces in 30 seconds= big a$$ torch.
 
DMF_TomB and digger doug seem to have experience in this.

Here's some theory. You've got a chunk of 17-4 at room temperature and you want to melt it. First you need to heat it to raise it's temperature. The energy required for this is called the sensible heat change. As in you you can sense the temperature change going from room temperature to the melting point. Then, if you keep adding heat, the stuff starts to melt. As it melts, it absorbs energy. This energy is called the latent heat of fusion. After its melted, you want to raise the temperature of the melt slightly above the melting/freezing point to ensure that it doesn't start solidifying too easily. More sensible heat. You can calculate the theoretical heat values required pretty exactly.

That theoretical number is interesting but useless. As DMF_TomB points out, much of the heat involved in heating a crucible is wasted. You have to heat the crucible and the furnace lining, and heat leaks out through the insulation and escapes with any exhaust gas. If you are just using a rosebud heater, and no furnace (that is, you've no insulation) I see no way to melt what you want in any practical way. Further, when the metal becomes liquid and you keep it hot with a rosebud, there is ample opportunity for the melt to react with air. So you want a furnace with a controlled atmosphere to melt this, not a rosebud hooked to an LP tank.

You;ll also want to post cast homogenize. Here's some aspects of 17-4ph casting from eng-tips.com

EdStainless (Materials) 14 Feb 07 09:02 I have never seen cooling too fast being an issue metallurgically. I have seen it cause excessive distortion. I don't like quenching other than forced air unless there is no other way to get the part cool in 30 min.
Have you talked with the casting house? They may be able to put the hot castings into a holding funace and carry out the homogenize step right then.

Some points.
- The higher temp homogenize is important. Your casting will have significant segregation.
- Atmospher control will be critical. You can't do the high temp steps in air. Oxidation will kill you. Surface damage, alloy depleation and such.
- If low temp toughness is your goal then you are going to need a higher aging temp (lower strength). The 925F condition is not known for beign forgiving.
- The aging should be 4 hours. You adjust the temp, not the time. Playing with time can give you unstable or unrepeatable results. = = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

israelkk (Aerospace) 14 Feb 07 09:37 Here is a quote from MIL-HDBK-5J regarding 17-4PH castings "Alloy 17-4PH castings are produced in sand molds, investment molds, and by centrifugal casting.
While 17-4PH has good castability, it is subject to hot-tearing, so heavy X or T sections, sharp corners, and
abrupt changes in section size should be avoided. Alloy 17-4PH castings are susceptible to microshrinkage
which will decrease the ductility but have no effect on the yield or ultimate strength. During heat treatment,
care must be exercised to avoid carbon or nitrogen contamination from furnace atmospheres. Combusted
hydrocarbon and dissociated ammonia atmospheres have been sources of contamination. Air is commonly used
and both vacuum and dry argon are effective for minimizing scaling. Oxides formed during solution treating
in air may be removed by grit blasting or abrasive tumbling. Alloy 17-4PH can be heat treated to develop a wide range of properties. Heat treatment procedures
are specified in applicable material specifications and MIL-H-6875."

As to hardness correlation to yield/tensile strength, there is no direct and exact correlation. For the same yield/tensile strength there may be up to 10Rc hardness variations. Therefore, if hardness is required, for each batch you will need to test heat treatment parameters which is not practical and you may end up with non standard heat treatments.

If this part is for aerospace/military use you probably do not have the freedom to use non standard heat treatments but only those allowed by MIL-H-6875. Therefore, hardness can not be defined but only yield and tensile strength.
 
With a big ass tip in an oxyacetylene outfit, you can barely get a pinpoint hot enough to start cutting in 30 seconds, let alone a half of a cubic inch of material melted. And that is with the hottest part of a very hot flame tickling the surface.

You'd need something on the order of plasma hot to do this, maybe melting a feeding wire with a plasma metallizing torch. Actually a MIG on a high setting (spray transfer mode) could maybe crank out that much molten material, if you had a preheated crucible in an inert atmosphere ready to accept it. What are you going to do with this glob of metal anyways? You've got almost zero time to work with it.
 
You need two properties of the steel of interest.
Specific heat for 17-4 it is .11 BTU/lb-F
and
Heat of fusion. Looking up this value is left as an exercise to the reader.

total BTU is Mass of sample *.11*(melting temp of steel-room temp) + Heat of fusion* mass of sample.

That is the heat required inside the sample. You also have to heat up the crucible Using properties of it and first equation.
Then there is the inefficiencies of all the heat that does not go into the sample.

Gut feel. two ounces in 30 seconds= big a$$ torch.



I don't quite get your equation, is it:


mass of sample X specific heat X heat of fusion + BTU's req'd?

You have mass of sample in there twice plus an extra "+" sign.


Here's what I'm trying to do:


Poking around the jewelry casting forums they do Platinum this way all the time and it melts at 3200F vs 2600 for my 17-4.
 
The problem with doing it the jewellery casting way is not the temperature, its the basic fact that molten stainless reacts really badly with air, in a way platinum, gold and sliver just don't. All the common jewellery metals melt and don't oxidize readily with air even at that temp. By the time any stainless melts the iron will burn well enough to make a mess in ambient air.

Now thats not to say you can't lost wax cast stainless and other iron bearing alloys, you can, but you have to do it in a inert environment to get anything out that does not resemble a aero bar. Lots of places offer this service and its surprisingly cheap compared to what i was expecting too at least in my experience.
 
The problem with doing it the jewellery casting way is not the temperature, its the basic fact that molten stainless reacts really badly with air, in a way platinum, gold and sliver just don't. All the common jewellery metals melt and don't oxidize readily with air even at that temp. By the time any stainless melts the iron will burn well enough to make a mess in ambient air.

Now thats not to say you can't lost wax cast stainless and other iron bearing alloys, you can, but you have to do it in a inert environment to get anything out that does not resemble a aero bar. Lots of places offer this service and its surprisingly cheap compared to what i was expecting too at least in my experience.


I found lots of places that pour 17-4 but none that did small dental or jewelry size stuff by investment or lost wax, hence trying to do it on my own...
 
Poking around the jewelry casting forums they do Platinum this way all the time and it melts at 3200F vs 2600 for my 17-4.

Well, in your video example more than half the nearly 5min presentation was heating the melt. 30 seconds seems pretty fast!

I have some stuff from Harris called 'SolarFlux B" that prevents oxidation on the backside of SS sheet when you can't backpurge. I wonder if it might 'float' over your melt and prevent oxidation? Maybe someone here has tried that. It would be cheaper than rigging an inert atmosphere but you'd have to spin out of a bottom hole to keep the flux out of your casting.
 
Well, in your video example more than half the nearly 5min presentation was heating the melt. 30 seconds seems pretty fast!

I have some stuff from Harris called 'SolarFlux B" that prevents oxidation on the backside of SS sheet when you can't backpurge. I wonder if it might 'float' over your melt and prevent oxidation? Maybe someone here has tried that. It would be cheaper than rigging an inert atmosphere but you'd have to spin out of a bottom hole to keep the flux out of your casting.


See that, not sure what he's casting but came across this post that suggests the faster the melt the less "carbon pickup" that happens, also the reason for using propane vs acetylene:



As an example if you were going to cast an ounce of platinum,
you need to melt it in about 12 to 30 seconds to avoid exessive
carbon pick up. Your torch will eventually melt the metal but it
will take 30 minutes to do so. In order to achive such a fast
melt your torch has to be several 1000 degrees above the melting
point and this can only be achived by compressed systems. I use
65 lbs. oxygen and 5 lbs of propane to achive tempretures hot
enough to melt the platinum in 12 seconds to do my casting.
Platinum solidifies in 3 seconds after the heat is removed so
speed is crucial to get a complete casting.


I know jewelers use borax powder as a flux, could that be to prevent oxidation?
 
Trying to edit my post but I get "403 Forbidden".

Is the equation:

mass of sample X specific heat X heat of fusion = BTU's req'd?

He wrote:

BTU is Mass of sample *.11*(melting temp of steel-room temp) + Heat of fusion* mass of sample.

Which I interpret as:

BTU = Mass x Specific Heat x Temp Rise + Heat of Fusion x Mass

or you could write it as:

BTU = Mass x ( Specific Heat x Temp Rise + Heat of Fusion)
 
Is the equation:

mass of sample X specific heat X heat of fusion = BTU's req'd?

Mass of metal * (specific sensible heat change to warm up to melting + latent heat of fusion + sensible heat change to overheat past melting temp) + HEAT LOST TO ENVIRONMENT

That last term will get ya. And as other have pointed out, molten stainless interacts with the atmosphere.
 
Why 30 seconds form room temp to molten? If you double that time you almost halve the torch size needed. I am not sure if you will have a gas supply capable of that rate unless your shop has some big gas supplies. I wonder about inductive heating in an inert atmosphere. If the atmosphere is controlled oxidation is not an issue.
Bill D
 
You can't cast with a flux, well thats not true, you can if you want a casting thats part flux part metal.

As to solidification times, all depends on what you preheat the investment upto prior to moulding, most people that i know that do it do it with the investment mould pretty near the melting point. Its why in that video the moulds only added at the last minute, because its kinda std practice to have it sitting in a nice warm kiln right upto the last possible go point.

Also worth adding most people that cast alloy steel parts don't melt the exact casting alloy, you use additions because a differing percentage of different things will get burnt off. Thats were the skill comes in if you want a exact material output.
 
I have a suggestion that might be useful... or not.

You could pack it in clay = zero atmosphere.
Then heat with whatever equipment, however slow, and when you crack the clay the molten metal comes out.

Since the quantity is small, even an electric induction oven could be used, for the full thing or perhaps to preheat it.
You would then need vastly less thermal energy to do the final melt.

You could experiment with any blower + heat source, they easily get hot enough to do cast iron.
Videos on youtube.

I have no idea how to crack the clay sensibly, if it is full of molten metal.
But it might be as easy as simply having the clay tube over a funnel, crack it and watch the metal flow into place.

Perhaps a grid to screen for clay particles .. no real experience.

You could experiment with lead or tin, perhaps, and the same should work for steel, I think.

It might be a fired clay funnel, cast from a suitable ceramic, would be the ticket, and easy to make, or have anyone doing pottery do for you for a few minutes/bucks.

Or get a volcanic stone molcahete, drill a hole in the bottom with a masonry bit.

Probably best to test carefully, and preheat the vessels you use - I have no idea about inclusions or moisture in same, leading to learning opportunities of spectacular nature.

What You probably don´t want is molten steel splattering from the vessel.
Easy enough e.g. to use some form of shield.
 
Thanks for the suggestions gang, guess I'll just find out what the guys casting Platinum are using and go with that.

I did come across someone using a Tig setup to do the melt, do they not use argon gas to shield the molten stainless?
 
Terry,

If you want to go ahead and try this, explore away. But if you read some of the expert comments, you should be seeing stuff like "You can't do the high temp steps in air. Oxidation will kill you. Surface damage, alloy depleation and such." If you were able to do the melt and spin in argon, or under vacuum, maybe you'd be safe. Otherwise, even if you can melt the stuff, you're not going to end up with 17-4ph after some of the components are oxidized. You're going to end up with some modified alloy that will not have the strength, hardness, ability to HT, etc. of 17-4ph.

Folks do this with gold and platinum and are successful because these are noble metals and don't easily react with oxygen. 17-4PH is a stainless steel, and doesn't oxidize much are room and even some elevated temperatures. But if you get it to melting temperature, its components will react.

If you want to continue to try this, I do wish you good luck. But you should expect that your result will not be 17-4PH.

I believe that 17-4PH is cast (using investment casting for pump impellers, for example), but I assume its done in a vacuum furnace or under argon. I think sometimes 17-4PH stuff is made using sintering as well.

But "Man's reach should exceed his grasp, or what's a heaven for?". Good luck!
 








 
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