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heat treat questions


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By way of introduction, I'll just say that I am a student and I am here because I have some heat treat questions that I hope somebody can point me in the right direction...

I am currently taking a materials technology class.  For a lab, we were given 5 steel specimens of various shapes: 1” round, 1” hex, ¾” hex, 1” square, and 13/16” square.  Each sample was about 1/3” thick.  We were told that each shape corresponds to one of the following steels: 1018, 1045, 4140, 1215, and 8620.  

For the lab we were supposed to test the hardness of each specimen, then heat treat them, then test the hardness again.  Finally, we are supposed to match each shape to the appropriate steel type.  

The heat treat process consisted of being inside the heat treat furnace at 780°C for 20 minutes followed by an immediate quench in room temperature oil.

For hardness, here is what we measured.  The first number is pre-heat treat.  The second number is post heat treat.
1” round – 93 HRB then 87 HRB (marginally softer)
1” hex – 26 HRC then 35 HRC (harder)
¾” hex – 93 HRB then 76 HRB (much softer)
1” square – 17 HRC then 51 HRC (much harder)
13/16” square – 88 HRB to 44 HRC (much harder)


I am having difficulties matching up the results for each steel type.  Here is what I have concluded so far:
1” square – 4140
13/16” square – 1045
1” round – 1018?  (Didn’t respond to heat treat process; too low of carbon.)

After that, I am stuck.  I have done a bit of research but can’t figure out how the 1215 and 8620 would respond to the heat treat process we put them through.  The instructor won’t tell us the condition of the samples when we received them so we don’t know if they were hot rolled, cold-worked, annealed, cased hardened, etc.  All he said was to look up how they are normally purchased and that might give us some ideas.

I know 8620 is commonly used in case hardening applications.  I’m wondering if this sample would be the one that became much softer after our heat treat process?

Any suggestions would be helpful!

 

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Have you referred to the product data sheets provided by the steel manufacturers? This sounds more like a half to a whole hour's worth of research than a lab to me. You have the test #s now is a matter of interpretation and that's what the reference books on the shelf are for. I believe HRA would be a better indicator for the 8620 but I could be wrong, I haven't actually read the materials data documents offered online.

I can't tell you how happy I did do a little memory refreshing before hitting "Submit" though or I was about to make a real idiot of myself. There's a lesson for you, don't offer an opinion without double checking.

Of course the instructor isn't telling, what fun is that?  ;)

Frosty The Lucky.

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10 hours ago, BIGGUNDOCTOR said:

Why did you choose the matches of the ones you have figured out?

Look up heat treat ranges. When I sent die sets out I didn't specify one hardness number, I had to pick a range that would work. 

 

I matched the 4140 and 1045 because I know that those are both capable of direct hardening.

I know 1018 doesn't have enough carbon to direct harden although it can be case hardened.  I also know 8620 is often case hardened.  I know 1215 is a free-machining steel steel that is resulfurized and rephosphorized.  My problem is I can't seem to find details on how the 1018, 8620, and 1215 would respond to the heat treatment described above.  

Can you give me an idea of where to look for heat treat ranges and what to look for?  I have a book from the engineering library at work, "Engineering Properties of Steel."   For the 8620, I see that the ranges for forging, annealing, normalizing, carburizing, and reheating are all above the 1436°F that the instructor set the oven for.  I'm thinking this would mean the hardness would be little changed after we heated and quenched it? 

 

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I just realized I forgot to Welcome you aboard, glad to have you. If you'll put your general location in the header you might be surprised how many of the IFI gang live within visiting distance. You might be surprised how many of the IFI gang are professional materials engineers and more.

The materials data sheets I browsed online showed a pretty wide range of effects of heat treatment on virtually any alloy produced.

I think your main problem here is not knowing what questions to ask and where to find the answers. There is no ONE book and sometimes the biggest challenge is figuring out what to ask. I've spent most of my "educatable brain cells" on developing a handle on subjects. By handle I mean just enough to ask good questions and find the answers. A warning though, doing it this way means you'll never be able to look up just the word you want you keep getting lost reading the rest of the page.

Frosty The Lucky.

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If you go to the McMaster Carr catalogue and search for tool steels there is a link to a basic heat treating guide for the different tool steels they sell. I think it has good information but maybe one of our members with more experience with steel hardening could take a look at it for any discrepancies.

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1 hour ago, bonehead-student said:

Thanks Frosty. Can you tell me what site you were looking at data sheets on?  I think you are probably right that I don't know what questions to ask and where to go for answers.

Using Yahoo I searched 8620 data sheets. That didn't tell me much with a quick skim of links. Next I searched "Heat treat charts." A skim of the links provided everything I needed for this thread. Represented were charts from: metal suppliers, specific and general. There were specific alloy charts. Charts from furnace manufacturers and various types of furnace  and heat supply. That's: coke, oil, coal, nat gas, through arc, resistance and induction.

There are charts re. quenchants, tempering and methods.

 Heck there are charts for converting various hardness tests, scales and methods with the disclaimer there are no really reliable conversion calculations, those illustrated should be used is initiation points and proven by testing.

Like I said I just skimmed the links before opening any. My advantage over you is I know a LITTLE about what I was looking for making my search shorter. I used my handle and it got a little firmer in the process. It's what I like about handles, I start out knowing I don't really KNOW what I'm after so I'm primed to learn more and side tracks on wrong subjects / answers refines my handle and often gives me more.

Yahoo for "Heat Treat Charts" will open up hours of skimming, then you get to do the reading and that's just for a set of general handles on the real subjects. Liking the learning curve yet? I love the learning curve but I'm kind of strange that way.

Frosty The Lucky.

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