Is this grain coarse?

P

PMQ

Joined
Feb 17, 2020
Messages
176
I recently got this SUP9 steel, it's a Japanese spring steel equivalent to 5160. I'm planning on making it a competition chopper. I had a piece of it quenched at 1500C for 15min, no temper, break it to check the grain size:

https://imgur.com/REj4mJ8

Do you think that this is too coarse? I know that a few cycles of grain refinement should do some good but I have a small workshop with no forge so I don't want to go through the whole process if I don't have to. Thanks.
 
PMQ said:
I recently got this SUP9 steel, it's a Japanese spring steel equivalent to 5160. I'm planning on making it a competition chopper. I had a piece of it quenched at 1500C for 15min, no temper, break it to check the grain size:

https://imgur.com/REj4mJ8

Do you think that this is too coarse? I know that a few cycles of grain refinement should do some good but I have a small workshop with no forge so I don't want to go through the whole process if I don't have to. Thanks.
Click to expand...
1500 Celsius?

Hoss
 
DevinT said:
1500 Celsius?

Hoss
Click to expand...
Oops, that's F, not C, 1500C would melt the steel.
DevinT said:
Too coarse

Hoss
Click to expand...
Thank for your input,
weo said:
If you don't care about making the highest quality tool you can, you don't have to.
But if you are, then listen to Hoss.
Click to expand...
If this were to be a gardening tool, I wouldn't bother to check the grain size, but since it'll be a competition chopper, it'll need to be the best quality. Thanks.
 
If you want to make a competition chopper you have to take the time to do the required HT needed to make it a good competitor.
The other folks in the competition will certainly do all the steps needed to make their blades have the best possible edge.

You should be using a proper HT oven and all the metallurgical procedures necessary to get the exact results you want. If your shop does not have them try and find someone who does to do the HT.

If the knife is just a chopper style knife for your own use and fun, then that is not as important, but for competition you need the very best knife you can make.
 
I should look almost like clay if you're working with it and find what it likes. I haven't used 5160, but the micrographs of it look very fine.

I have a suggestion, though - get an offcut of 5160 and heat it past critical, quickly, and then quench it right away. let it cool and then snap it. You should be aiming to end up with finer grain with whatever you develop, or at least not more coarse.

The first samples I snapped always got worse the more I did with them, but over time, I managed to find something the two steels that I use like (O1 and 26c3).

As an example, here's 26c3 just heated and quenched. It's about as fine as an old file (probably similar steel).

https://imgur.com/30zf4tY

Without doing anything special, this actually performed OK (I make chisels, not knives - tracking edge damage makes it easy to see what's better - and quickly)

I came up with a light shaping (heating and hammering, not full forging) and thermal cycle, and this is the result:

https://imgur.com/Vb6A2qB

Sorry about the light and dark - these finished their quench in the freezer and when I pull them out and snap them, condensation often forms since they're cold.

In my opinion, there's no real better way to learn than making mistakes on your own time and dime. keep all of your small offcuts and get a hand held microscope for about $20 on ebay - one of the USB types, and take pictures of what you get. Write down and record what you did, as I've found out pretty starkly that what one relatively plain steel likes, another (or others) may not.

One other aside, if you any old dull files around - they break easily, are high carbon and will have a slightly more coarse grain structure than you're looking for - so they're a good bar to get past early if you're using something that's fine grained.

if you're working with a forge, testing the small offcuts as much as you can is ideal because they're quick to do and if you have a little free time between other things, you can just walk to the forge with a few free minutes and do a sample or four, or intentionally do three or four different things to samples and compare each one to see which worked better.
 
  • Like
Reactions: PMQ
If you can find an old file, OR take a drill bit and break that. Look at the grain - that's what you're looking for. Hold the sample and broken drill bit side by side and compare. You should be able to get a good indication of desired grain size, and how close your sample is. Here's a decent photo I found somewhere to illustrate grain.
grain-structure.jpg
 
Last edited:
Ken H> said:
If you can find an old file, OR take a drill bit and break that. Look at the grain - that's what you're looking for. Hold the sample and broken drill bit side by side and compare. You should be able to get a good indication of desired grain size, and how close your sample is. Here's a decent photo I found somewhere to illustrate grain.
grain-structure.jpg
Click to expand...

that's a good picture. It's possible to come back from normalizations and shrink grain, though I'm sure there are other problems with too much forge time other than grain size, but it's something observable.

I'd suggest to the OP that if the forge HT is going to go further than just a couple of things, this small experimenting is worth the time - not all at once, but like something every week or two. When I first started, I broke a file and keeping the grain small seemed very difficult. Over time, I was examining results of performance with chisels made of file steel and when I was done, circled back and thermally cycled a file and shrunk the grain smaller than factory by heating only to just prior to magnetic repeatedly and quenching to partially cool in oil.

I think there's a notion that quick critical quenches will shrink grain in hypereutectoid steels, but any time I've tried that, the grain has gotten more coarse with visibly shiny carbides - not so good.
 
You said you heated it to 1500F and quenched. Do you have an oven? Unless you are forging, you only need to normalize once and harden. 10 minutes at 1650F, cool in still air, 1500F for 10 minutes and quench in warm oil, temper twice at 400F for 2hrs each cycle. That is a basic heat treatment protocol... of course there are variations.
 
Ken H> said:
If you can find an old file, OR take a drill bit and break that. Look at the grain - that's what you're looking for. Hold the sample and broken drill bit side by side and compare. You should be able to get a good indication of desired grain size, and how close your sample is. Here's a decent photo I found somewhere to illustrate grain.
grain-structure.jpg
Click to expand...

What do you think the sparkles are in the middle of that file on the bottom? At lunch today, I went out and put up on my comment above on a new nicholson file (as in recent make). It has nice grain, and I think after a thermal cycle and fast hot quench (as in, no soaking, just run it a little past where it should go if it were soaked and then quench quickly), the grain is about identical in size, but in my re-done sample, the sparkles in the center of the file are gone. I'm assuming they are carbides, but wonder why they're in the middle there but the results at the edges on the factory HT are pretty divine. Something in the process of heat treat must've not gotten all the way to the center - it could even be on purpose if it's quench related - as in, if the file is slightly less hard in the center.
 
Rick Marchand said:
You said you heated it to 1500F and quenched. Do you have an oven? Unless you are forging, you only need to normalize once and harden. 10 minutes at 1650F, cool in still air, 1500F for 10 minutes and quench in warm oil, temper twice at 400F for 2hrs each cycle. That is a basic heat treatment protocol... of course there are variations.
Click to expand...
No I don't have an HT oven, I have a small stock removal workshop, the biggest problem for me is that there isn't a lot of HT service where I live, and they usually do industrial parts that HT for hours, not minutes in blade making. I haven't check their normalizing service though, but does normalizing time matters? What happens if we normalize at 1650F for 1 hour and air cool, will it help or just worsen the problem, because I know that overheating when austenizing cause grain growth.
 
if you're going without a furnace, you'll have to snap samples yourself with your setup - there's just no other substitute for it that I can think of. Any good HT service should be able to do 1084, 5160, O1, etc - most of the industrial users (tooling/machinist shops) that I've heard from here are making single or low use dies with O1 or A2 and doing the HT in house, so the services you're mentioning are probably tied up with more difficult and lucrative work.

but solving the grain size issue first with a method that you can repeat is job 1 - the rest is after unless you outsource HT. Less heat or high heat less time for small grain, and if you're not getting good hardness, then you have to start working up from there.

you can do crude tests for toughness later by making same sized samples and putting them in a strong vise and hitting them with a hammer to see how resistant they are to breaking, but there's no sense doing those while the results are making coarse grain.
 
PMQ said:
No I don't have an HT oven, I have a small stock removal workshop, the biggest problem for me is that there isn't a lot of HT service where I live, and they usually do industrial parts that HT for hours, not minutes in blade making. I haven't check their normalizing service though, but does normalizing time matters? What happens if we normalize at 1650F for 1 hour and air cool, will it help or just worsen the problem, because I know that overheating when austenizing cause grain growth.
Click to expand...
Short answer... You need to send this to a heat treating service provider that specializes in knives.
 
You must log in or register to reply here.
Back
Top