Hardening 4140 - 4150 steel and Phase II hardness tester?

[spope14]

I have in my school shop, a heat treat furnace that has two temperatures - off and hot as heck. I am not as knowledgable about hardening as I would like, so I am asking questions here.

I have had my students make parallels out of 4140 and 4150 steel. Would use A2 or something if it were as affordable, but alas, cost is an issue (maybe, unless i find different). I have had them heat them to a dull to medium red and soak heat for a few minutes, maybe 30 (furnace on and off, watch the color action, keep at medium red), then quench in clean hydraulic oil (gallon bucket), and let cool.

Am I on the right track? Hardness tester shows hardening occurs, no cracking, but would like to know if there are some better specifics I can teach.

Have also wondered about "Case hardening" these items.

Speaking of hardening, I have one of those "Phase II hardeness testers that is all but impossible to figure out, and the instructions were best written for someone who was on site while they were written - they say squat. Anyone have one of these and can share some light? I am using it at best wrong, but with at least some idea ofthe theory, so i have at least some show and tell.

[Gizmo]

Since you don't have any decent responses yet (that means NONE) I will give it a shot to get you started. I don't know 4150, but have a little experience with 4140, and it has plenty of the right alloys to harden.
The easiest way to get it full hard is take it up to non-magnetic(which is a yellow-orange, much hotter than red) then quench straight down and wiggle it around in the oil so it doesn't create a hot spot. This is dead hard, and quite brittle, so generally things need to be drawn back a bit to be useful. So you polish the piece back up, and play a flame until the surface oxide turns color. Pale straw color is around 460 if memory serves, through gold, then brown, finally blue then purple up around 570. The hotter, the softer. Once it starts showing colors it goes fast! Quench in oil same as before, and then the part is drawn back to a more useable hardness. If you have a toaster oven that goes to 550 or so, you can bury the part in clean sand just leaving a little bit showing, and watch the color. Then it goes slower with better control. If it goes from purple to grey it's about as soft as when you started out, and you need to start over. The older shop manuals had all this 'by eye' stuff, and charts for the type of tool and recommended draw (anneal) temps.
Your dull red color is giving you some hardness? Kids happy and not hurting themselves? Then you have a winning ticket. Drop a full hard piece of steel and sometimes the shrapnel goes off like a Corelle plate, you know, the unbreakable dishware. They aren't going to sit still for the metallurgy anyway. It is cool the first time you see a piece of steel go non-magnetic, though.
Case hardening is generally used on mild steel to give it some toughness it cannot attain on its own, no matter how much you heat it. Your alloys can get hard on their own, and don't need the extra carborizing surface treatment. If a miracle happens I'll drag some books out and get more technical. NAH. I'll bet at least 20 of these guys carry this stuff in their heads, so better answers coming! But that's the jist of it...

[Thrud]

You can buy temperature crayons that indicate the temperature range you require fairly cheaply. They are handy for a non-temperature controlled oven.

Dimensionally speaking A2 keeps its shape better (less distortion, more money, more hassles) than the 41xx alloys. I would use 4130 or whatever you have on hand - they may distort a little but that is what surface grinders are for. Go for it. Agitate the oil with air or a pump to reduce hot spots - just enough to get the oil moving a little makes a big difference.

Can't help you on the hardness tester - get in touch with Phase II and ask them. www.phase2plus.com

Dave

[SGW]

Dusting off my engineering lab experiences of 30+ years ago.....

The theory is, you apply a defined weight to a particular testing point (steel ball of a given diameter, diamond, or whatever it is depending on which Rockwell or Brinnell scale you're using) and measure the amount of penetration by the testing point into the piece being tested.

To do this, you put the point on what you're testing and set a slight preload on the point until the tester's dial reads 0. Then trip the lever to apply full test weight. The amount of penetration should read on the tester dial as a hardness number.

[hms50]

Did you ever attend the summer institute at KSC?? I met a teacher there with the same last name. How would you like all the o1. a2 and other tool steel you could carry free? Feel free to email me and I'll let you in on a little secret!

Goog luck
hms50

[BrianH]

....I'll throw in some change....

One thing I don't think I saw in the thread was that, hardness-wise, you will get two VERY different results from 4140 and A2. A2 will get harder than holy hell. (62+ RC if you give it a chance) And 4140 prob. won't get much above 35 RC or so. That's perfect for parallels. When the kids hit them with a cutter, you won't blow the cutter all to crap.

The Phase II hardness tester is the same one sold under many names from many sources. It's Taiwanese, I believe, and we got the one sold from McMaster-Carr a couple years ago. It's a very good tester for the money (around $800-900), whereas the next step up in testers will run over $2,000.

[spope14]

HMS50 - Emailed you, did keene, really enjoyed it.

Hope to hear back.

Scott.

[cannons]

I had several things to say but Thrud took the words out of my mouth.I worked in heat treat for 10 yrs dont remember everything but I believe 1550 or 1575 Deg F is the temp you want then quench. If you can locate some quench oil it would be safer because of the higher flash temp.Put a screen in the middle of oil container so the part is suspened. After harding ck hardness then temper one at 800F for 45min reck hardness when you find what works your in biz. Im not sure what your tester is Ill see if theres any info at work.

[BrianH]

Actually, I think the soak temp is more around 1650 to 1750 for 4140; and make sure
when you dunk in the oil you swirl like hell and don't stop until its cool. When the part hits the oil, the oil closest to the metal wants to turn to gas, and that creates a vapor pocket around the part, and that screws up the quenching.