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can't get 4140 hard

4140 hardening

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#21 nonjic

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Posted 01 September 2011 - 03:58 PM

Can decarb very deep, and I think the austentising temp might be very high (900c ish)? magnet and a very deep file test are your friends :D

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#22 gearhartironwerks

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Posted 01 September 2011 - 08:45 PM

For a while now I am trying to harden 4140 for use under the power hammer. I use 3/4 x 3 x 8 blanks that I bought for a blacksmith magician. I forge them to shape, soak them in my propane forge (with a little excess propane to not produce scale) for an hour, quench and then temper. For quenching I tried old motor oil first and for tempering my wife's kitchen range (400 F). The resulting tool did not hold an edge for butchering one tenon and the end mushroomed. I later heard that motor oil is no good and changed to 3 gallons of canola oil: Same result. Then I added 1 third Diesel fuel to my canola oil to reduce viscosity: still not hard. Finally I thought, even if it cracks: lets water quench. It did not crack, but the resulting tool was very soft again (for tempering this time used a knife makers kiln at 400 F. My tool, a feather swage for power hammer use had lost its nice surface after one leaf.


Imho, 4140 only gets hard when quenched in water, and needs tempering at 325 deg for an hr per inch of thickness. That's not what the specs say, but that's what I've found works. Hammer heads, dies, whatever... Oil will not get it hard. Tempering beyond 325 deg will soften it beyond use. Rob Gunther says it can be hardened in super quench. I don't know as I haven't tried it. 4140 seems to me to be one of those border line materials that depending upon how you want to use/abuse it, there is a lot of latitude in processing. For most, it's a pretty forgiving material. I like it.

JE

#23 Jura T

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Posted 02 September 2011 - 12:50 AM

Imho, 4140 only gets hard when quenched in water



According to this data sheet
www.fordtoolsteels.com/pdf/LSS_4140-4142HT.pdf
you can use oil for quenching.

The quenching temperature for 4140 is quite a bit higher than the Curie (non-magnetic) point, so using a magnet for detemining the quench temperature does not work.

#24 Nakedanvil - Grant Sarver

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Posted 02 September 2011 - 01:31 AM

Sorry John, not my experience at all. Most references warn "NEVER water quench 4140". Water quenching is usually avoided in sections smaller that 2". In tools up to 1 to 1-1/2" I've never had trouble getting low to mid 50's Rc as-quenched and 46-48 Rc after 400 draw.
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#25 MattBower

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Posted 02 September 2011 - 12:12 PM

I don't have much experience with 4140, but I did do a hammer head out of the stuff. Hardened fine in oil. The point of all that chrome and moly is to make it deep hardening -- and deep hardening allows for slower quenchants.

#26 gearhartironwerks

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Posted 24 September 2011 - 12:24 AM

Sorry John, not my experience at all. Most references warn "NEVER water quench 4140". Water quenching is usually avoided in sections smaller that 2". In tools up to 1 to 1-1/2" I've never had trouble getting low to mid 50's Rc as-quenched and 46-48 Rc after 400 draw.

Grant


Grant,
I'll be happy to send you some "beater" hammer 4140 heads that did not harden in oil despite being heated to 1550 deg in a heat treat oven and quenched in 150 deg oil. Water is where it's at if you want to get 4140 hard. I don't care what most references say. I'm going with reality.
I made a number of hammer heads using the "referenced" method, only to find they were soft. As a last resort, I went to a water quench, and 4140 finally got hard...w/no cracks.
I feel that one has to go with what works for you. I'll take h2o.

JE

#27 forgemaster

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Posted 25 September 2011 - 05:46 AM

Just as a comparison we harden tons and I mean tons of 4140 over 3" thickness in water from about 870 deg C and retemper to 575 deg C and can always reliably get a hardness of 302 hardness brinell. I reckon it's not 4140. For the app you describe I would tend to find 4140 a little soft, I'd use 5160 (spring) harden from 850 deg C in oil, temper by heating till the oil from quenching flashes into flame.

Phil

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#28 Nakedanvil - Grant Sarver

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Posted 25 September 2011 - 01:05 PM

Over 2", I agree completely with water. Even then it won't get very hard in the center.

As I was trying to tell John, I agree oil won't do it when you get above 1-1/2 or 2 inch. Which I believe is right where he's at unless he's making awful small hammers. Plus austenizing at 1600º as Phil is doing in important too.

I've made thousands and thousands of tools from 4140 and never have trouble getting full hardness in oil. But just like the original question in this thread I'm talking less than 1" thickness.
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but then there are others who, with the help of their art and their intelligence,
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#29 forgemaster

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Posted 28 September 2011 - 08:56 PM

Yeh I agree for 2" thickness or less I would recomend oil. Years ago I spent ages on making some fully forged axe heads from 4140, had a bright idea to harden them in water, still got 25 axe heads here years later, all with cracks running all over the blades. xxxx. I'll find a use for them one day. We also make a forged ring from 4140 normally 60 off at a time 185mm od x 120mm id x 75mm thick (or long depend on how you want to call it) gives about a 32.5mm wall thickness, we always harden them in oil from 870 deg C and temper to 580 deg C holding for a couple of hours, I can almost guarantee to get a minimum of 277HB every time.

Those who live by the sword normally end up getting shot by those who don't.

 


#30 HWooldridge

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Posted 28 September 2011 - 09:36 PM

Try the salt based "superquench" formula. Even mild steel (A36) will get in the 35-40 range with a fast quench.

 


#31 Awalker

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Posted 01 October 2011 - 07:58 PM

I don't think it would matter if it was decarb steel, as he has heated it and forged it, hence you have reworked the surface and likely lost the decarb layer. I think he just doesn't have 4140, just mild steel. Also, there is no need at all to soak a 3/4" thick piece of steel in the forge at that high a temperature. Here is the data for that material.

Thermal Treatments. Annealing: 1550F (840C), hold 2 hours, slow cool 50F(30C)/hr. max. to 1200F (650C), then air or furnace cool. Hardness BHN 185/200.

Stress Relieving:

Annealed Material: 1100-1300F (595-740C), hold 2 hrs, air cool.

Hardened Material: 50-100F (30-55C) below last tempering temperature, hold 2 hrs, air cool.

Straightening: Best done warm 400-800F (205-425C)

Hardening: (Atmosphere or Vacuum Furnace)

Preheat: 1250-1300F (675-705C), equalize

High Heat: 1550-1600F (840-870C), soak 10 to 30 minutes. For vacuum hardening, use the high side of the high heat range and soak times.

Quench: Oil quench to hand warm, 150F (650C). Temper immediately. Water quenching from 1550F (840C) may be used for simple shapes and larger sections. Note vacuum furnaces must have oil quench capability to achieve comparable results.

Temper: Tempering at 400-1200F (205-650C) for 1 hour per inch (25mm) of thickness at temperature is recommended (2 hrs min). Air cool to room temperature.
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#32 LongShadows

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Posted 04 October 2011 - 04:03 AM

There are already many good responses to your original question, but I thought I'd share an URL that is loaded with good info about many steels, including heat treat procedures.

www.suppliersonline.com

www.miblacksmith.org





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