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Daniel Cauble

My initial journey into crucible steels.

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When I have looked at grain boundaries, it has been in easy things like this:

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I generally wet grind up to 1200 grit, then polish on felt with 1 micron followed by whatever I have that is less than 1 micron, sometimes 0.50 or 0.25 micron, sometimes 0.05 micron.  I then etch by rubbing the surface with a "lint free Q-Tip" dipped in etchant as long as it takes to go cloudy; typically about 30 seconds.  Rinse with water, blow dryer until dry, check on microscope.  Re-etch as necessary, typically in 5-10 second intervals (don't re-polish unless you've over-etched).  

If you can, definitely add scale bars to all your images.  ImageJ is freeware that is quite powerful for these kinds of things.  All you need otherwise is an appropriate sized scale bar to take a picture of, then make sure you don't change camera settings.  

Edited by Jerrod Miller
Edited to add: Not sure why that image has to be downloaded. Because it is a tif?
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Here is is a a jpeg.  

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Thank you Jerrod. I am not classically trained in microscopy so it's a learning curve. Looking at yours and looking at mine, I would say mine looks almost over etched. Idk. 

My left eyepiece has a faint scale bar across the middle but I never use it to take pictures because it has a crack in it.

I also remembered I have .25 micron diamond paste.

Edited by Daniel Cauble

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You can't use one built into an eyepiece nearly as easily as one you look at as if it were a sample.  If you want to give it a shot I can get you more info and/or PM me your number and we can discuss it over the phone, possibly while you're looking at it in the microscope or at a PC.  

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13 hours ago, Jerrod Miller said:

You can't use one built into an eyepiece nearly as easily as one you look at as if it were a sample.  If you want to give it a shot I can get you more info and/or PM me your number and we can discuss it over the phone, possibly while you're looking at it in the microscope or at a PC.  

That would be great. As much info as I can get.

I currently have the book "Optical Microscopy of Carbon Steels" by L.E. Samuels, for reference. 

I will also try a shorter etch this next time to see if it helps.

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400x + camera optical zoom. Nital 3.6% (my exact concentration), 12 second etch. Getting better!!

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Ok, some updates here. I recently built a new, more durable melting furnace able to withstand 3300F using 94% alumina castable.This new furnace I am using a 1.5" blown propane burner I made for it.

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 The first puck made in the furnace didnt turn out the way I had hoped, so I remelted it again with some more, higher carbon material (my oroshigane). This bumped it up to the 1.3-1.4% C range.

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I have been making 1.6-2.5% C crucible steel in the past, so this lower carbon content was a little new to me.

I also purchased an electric kiln to do an initial roast of the puck.

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Now I have roasted the puck for 22 hours and am ready to forge this evening.

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What is most peculiar is without even forging, there are latitudal lines already bunched up it appears seperate from the grain boundary cementite. These last photos are 40x10 mag, dirty belt finish, longer than normal etch in 3% nital.

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Looking good, making the mechanics of smelting an easier process is a good idea, I am working on that as well ...interesting structures...thanks for posting.

Edited by Jan Ysselstein

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6 hours ago, Daniel Cauble said:

What is most peculiar is without even forging, there are latitudal lines already bunched up it appears seperate from the grain boundary cementite. These last photos are 40x10 mag, dirty belt finish, l

Cool looking progress Daniel. When I read the words above, and looked at the photo, my first impression was belt grinder marks, but there seem to be very evenly spaced striations within the steel. Some sort of lamellar structure.

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23 minutes ago, Joshua States said:

Cool looking progress Daniel. When I read the words above, and looked at the photo, my first impression was belt grinder marks, but there seem to be very evenly spaced striations within the steel. Some sort of lamellar structure.

It's probably cementite bands. Which is weird because they usually dont start showing up until forging.

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Ran into some frustration because I felt like I was not seeing enough cementite spheroidizing. I figured I would see more for 1.3-1.4%. I nearly gave up on this bar.

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Them I forged it some more and gave it literally one last etch before chucking it to the side.

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I havent posted my previous puck's forgings, but it was pretty massive and forged out real nicely but found a void, so it ceased. It was an experiment with Manganese, but decided I'm not going to use Mn any more as it hurts the patterning.

 

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After that fail I set it aside and did some of my oroshigane japanese blade work. Well i answered a few questions there, ironed out a few questions only gleaned from doing it...and am back go crucible again.

 

I'm avoiding Mn. No Mn addition except for the W2 I am spiking the oroshigane with to add Vanadium which will give detectable Mn in a beneficial range rather than for any depth of hardening.

 

I made a pulverizer to break up my oroshigane. My oroshigane or hearth steel is made a little differently than commonly seen. My way coarsens the grain structure at creation thus making it friable. The oroshigane for this melt is all in 1.5%-3.3% range. Mostly steel under 2.1% with some white cast and bits of gray cast that was made in the hearth.

 

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Now I can fit 4-5 pounds in the crucible comfortably and hopefully speed up the melt.

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OKAY.

 

Like puck number 12 or 13 on the books. Melting went great. Carbon calculation based on my experiences with hearth steel seems to be yet again spot on. The top of the puck seems to be around 1.5% C with very thick GBC and below that are sheets of dendrites that i would suspect are in thr 1.7-1.8% range. After some heat treatment carbon should even out across the board. I'll know more after and look at with the scope but I would bet it's probably going to fall around 1.7ish.

 

Pics are crappy ferric etch and cellphone. Have to prepare more nital.

 

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Totally gutted on this puck. My electric kiln I use for REM had something go haywire, and the crucible I reseal my pucks in to bake bled some and as it touched the soft firebrick, it undermined the crucibles plinth inside and the cruciblr tilted and overheated to the point of remelting and pouring out into the kiln. Lol.

 

Needless to say I lost half a pound of steel, need to remelt it. I'm going to add a half pound of W2 to bring the carbon down a tic, and buy new elements for the kiln.

 

Plan to remelt this Friday.

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Ok let's do this again. I had lost weight before from the mishap so I added a pound or so of W2. Calculating the estimated carbon of the puck and the new steel addition, the carbon was estimated to lower to a more workable 1.7ish.

 

The new puck is 5 pounds. The surface I dendritic in places and the dirty ferric etch shows grain boundary cementite in most areas with pockets of heavier dendrites.

 

I'm estimating carbon at 1.6-1.7% currently. It may change when I mix up some Nital again.

 

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Posted (edited)

I'm revising carbon prediction to 1.5-1.6. The grain boundary cementite is thick, but looks less dense than I'm used to seeing once things cross over into 1.6% territory. Of course things will change when I move the concentrations of cementite around, so they will thicken, and I know this based on the thick pockets of dendrites.

Edited by Daniel Cauble

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