Pre-hard machinable steel with highest compressive yield strength

Hi everyone,
Can anyone please tell me what machinable pre-hard steel has the highest compressive yield strength ? I'm guessing it would be a pre-
hard 4000 series, perhaps 4340 or a bearing steel or pre-hard tool steel.
I'm looking for the highest yield strength I can find in a steel that is still machinable, i.e., not so hard that it can't really be machined effectively. Depending on how the part is machined, I would need a thickness of around 1.338" or 1.585".
Thanks John
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John2005 wrote:

NAK 55
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John R. Carroll
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John R. Carroll wrote:

DH2F
Viscount 44
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Black Dragon wrote:

44 is a pain. It's nothng more than H-13 without the Tungsten. It also isn't pre hardened. You have to do that yourself.
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John R. Carroll wrote:

John, Viscount (pronounced vi-count) 44 is Rockwell C 42/46 off the shelf. The only heat treatment I've ever seen done to it is nitriding for wear resistance. It's more difficult to drill than NAK 55 and DH2F but other than that it's not a bad material to work with.
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Thanks for the feedback guys,
After reading your replies, I searched online for NAK55 and DH2F. I will also check into the Viscount.
I read something about one of the grades in a "hi hard" condition of 45/48 RC, which would probably have a high compressive yield strength in that hardness. At about what point in general would a pre-hard steel be too hard to really machine effectively ?
Can you recommend any online sources or books that have compressive yield strengths for these materials in their pre-hard state ? So far, I have not found much. Can you recommend any sources of supply for small prototype quantities ?
Thanks again guys, John
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John2005 wrote:

Without knowing what the application is, it's difficult to recommend the best material.
These guys sell DH2F and Viscount 44, don't know about NAK 55.
http://sturdell.com
The online sources for the specs would be the manufactures of the steels. The names mentioned are trade names specific to a particular manufacturer. If not available online, it's certainly available from a supplier.
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John2005 wrote:

NAK has a grade this hard but you might also be refering to something known as Super P-20. Thyssen makes it.

Tooling for hard milling has come a long way over the years. People are machining 60 RC D-2 these days from the start.
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Black Dragon wrote:

I built seat belt cover molds out of it in the 70's for Allied Chemical. They tried to save a buck by having me requote the tools in Viscount instead of the S-7 I'd originally wanted to use. When that little window shut off in the center where the little latch release mechanism ( the thingy with GM on it ) would start to flash a lot they had to be welded. Guess what happened to those little cavities when we put enough heat into them to get a good weld? LOL We converted a lot of cavities in the end to S-7 so I guess you're right. It's not bad material at all <EG>
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John R. Carroll wrote:

Recently used some Viscount 44 for slides and cores in radiator tank molds for Modine. H13 is the preferred material for tank molds as it can be heat treated to a few points higher hardness (typically RC 46/50), but it takes two days to treat (double temper) and lead times are tight so Viscount 44 is an excellent substitute. Carburetor molds for Rochester Products were made from it too. We use it quite often for cores, turns and drills much nicer than thru hardened H13 core pins.
Yep. Viscount 44 is a terrible steel alright. I'd much rather machine DH2F, it's a wee bit more forgiving. <g>
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Black Dragon wrote:

Well, we hated the stuff but to each his own.

What is that anyway? D-2?
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Tool steel at RC 60 would be plenty strong. What type of cutter and feed rates are needed to machine tool steel this hard ? I didn't think anything would really cut tool steel that hard, let alone do it cost effectively. EDM may be a way to go as well, but I'm not sure expensive it is for two prototype pieces to test.
I think most tool steel at around 52-55 RC would have a yield around 300,000 PSI which would be plenty strong (280,000 PSI compressive yield strength would be enough for me) . A2 or S7 would probably be ideal, but I don't know if their available in pre-hard, or at these hardness levels. Generally I had thought that anything at these hardness levels pretty much had to be ground.
I've drilled and countersunk pre-hard 4140 (I think it was 27-32 RC). I just used a new HSS bit and I was surprised how easy it cut but I had always thought machining tool steel in the 55-60 RC range was out of the question.
John
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John2005 wrote:

http://www.moldmakingtechnology.com/inmotion/greenleaf1 /
MMT inMotion Multimedia Presentation
The Benefits & Techniques Of Hard Milling With Ceramics
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John R. Carroll wrote:

http://www.creat.com/videos.shtml
See the hard milling and rib milling videos.
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Thanks for the additional feedback and links guys, I will check into this a little further.
The shop I'm having machine the parts has no in house heat treating. I was trying to avoid having to fool with machining a few thousandths over size, heat treating, and griding to final size. From an accuracy standpoint, it's also best to machine this in one setup.
I might be able to get close to what I need or perhaps I will have to heat treat and grind. Perhaps I will test some pre-hard and see how it does first. I will also check out the links John gave regarding hard milling, that sounds interesting.
Thanks again and take care guys, John
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John2005 wrote:

Again. What's the application? What tolerances do you need to hold? Why do you need pre-hard material, are you trying to avoid the cost of heat treat you may be able to do yourself if you select the proper material?

A2 and S7 are typically very stable in heat treat when done by commercial heat treaters that service the mold industry. You can expect growth of approx .0008" per inch after heat treat and very minimal warpage and distortion. S7 is tough steel which will bend before it breaks and can be hardened up to approx RC 57. A2 steel is used in wear applications and can be hardened up to approx RC 62. I've never seen those materials purchased in a pre-hard condition. Also, S7 machines much better than A2 at the same hardness, any steel designed for wear resistance is going to be more difficult to machine.
Once again, without knowing what your application is it is difficult to recommend the best material.
Anything to around RC 55ish is readily machinable (mill or turn, forget drilling at that hardness, if you have to thread - mill bore with an endmill then thread mill) with good TIALN coated carbide and a rigid spindle. If you're thinking about machining stuff like this in a Bridgeport you're destined for a colossal headache.

The Viscount 44 I mentioned is RC 42/46 and it can be drilled and tapped with HSS tools.
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John R. Carroll wrote:

It is another pre-hard to around RC 40ish H13 type steel.
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On Sat, 31 May 2008 14:52:44 -0700 (PDT), John2005
<snip>

<snip> =========Depending on how many you have to do, consider EDM. Hardness is no problem.
FWIW -- iron is a minority ingredient in some of the "super steels," and while ther performance is "out of this world," so is the price.
for some additional info click on http://www.brownmac.com/pdf/BrownMcFarlaneHSSSP.pdf http://en.wikipedia.org/wiki/Maraging_steel http://www.matweb.com/search/GetMatlsByManufacturer.aspx?navletter=L&manID94&manname=Latrobe+Steel http://www.thomasnet.com/northern-new-jersey/aircraft-steel-79790408-1.html http://www.allvac.com/allvac/pages/PDF/tech/vascomaxt.pdf
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
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