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How does this grain structure look?


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I made a hunting knife for my cousin out of 80CrV2. I had a piece about 2.5"-3" long left over so I thought I would test my heat treat program for it. Here is how I did it.

 

1. Put in cold oven and took it to 1600° and held for 2 minutes and removed to cool in still air until no red color at all showing in the dark. Then back into oven.

2. Held it at 1500° for 5 minutes, then cooled in still air, then back in oven.

3. Held at 1425° for 5 minutes, then cooled again and returned to oven.

4. Held at 1325° for 5 minutes, cooled and returned to oven.

5. Held at 1100° for 5 minutes and then left to cool to room temp. Then I heated back to 1600° and soaked for 5 minutes and quenched in Canola oil.

 

After it came to room temp, I clamped it into a vice to hit it with a hammed and break it. I whacked it 20 or so times pretty damn hard and couldn't break it. So I pulled out my phone and videoed me beating on it some more and the video shows what happened. LMAO! It's pretty damn funny! Anyway, the piece of steel never did break. It didn't even bend. I ended up clamping it in another heavier duty vice, between three pins, and proceeded to clamp away and when I got to about the point where I couldn't turn the handle anymore, the steel exploded. Here is a picture of the grain. What do you think? It looks pretty good to me, but I'm no expert in examining grain structures.

MC001.jpg

MC002.jpg

Edited by Paul Carter
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To start off with Im no expert either so I'm sure the more experience will show up and correct me later. 

 

Generally what you are looking for in the grain structure when you do these break tests is how fine the grain is, how consistent it is, and really if anything jumps out like the outer layer is a different colour from the inner layer. You can get more detailed and accurate info from the grain structure with a microscope so there is a diminishing return on using your eye. Unless you got super vision or are really good at seeing the subtle differences once it gets to a certain level of fine you wont see a change if it gets finer without assistance.

 

To me it looks like a shear split not a break but that might just be my eyes at 2AM looking at silver on a silver background. So if it is grainy that is a fine grain and is the basics of what you are looking for. I mean just the effort you put into it to perform the grain exam should tell you how well your HT process is.

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That looks like a pretty thick piece you tested.  That's probably why you had so much trouble breaking it.  

Here's my (almost) standard response to the 'how's my grain structure' question: (hard to tell with out of focus pics)

grain structure.jpg

 

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Billy's picture is a great example.  Note that the 3x Normalization is after the bad heat control.  So if you never let your grains get that bad to begin with, then 3x normalization will get you even closer to the last sample.  And your sample looks to be pretty fine, though as Billy mentions, it looks pretty thick.  Untempered steel is extremely strong, it just doesn't take kindly to bending.  So to get it to bend, and subsequently break) thinner is easier.  It is also ideal if your test coupon has a cross-section similar to the blades you make (so add the bevel first).  Overall, good work!  

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The test piece was .169" thick. I keep hearing people mention the grain should look like talcum powder. Well, that's about the best way I can describe this grain structure. Thanks guys!

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