W2

bluntcut said:
You are right, unlike cook book recipes, in ht we implicitly state ht temp in isothermal. Users have to tune them for their environment.

Please elaborate on why(s): Grain size is directly proportional to the hardenability? Also applicable to statement such as - W2 is more difficult to harden with each additional grain refinement thermal (beyond 2 cycles). Most obvious/well-stated reasons are being: higher recales intensity; more gb precip due to more gb interface volume; lower equillibrium aust temperature. On one hand, we want as fine grain as possible, otoh don't get too fine or you won't able to properly harden it <= woah, how's one determine the cross-over line? or is this line applicable to my(I meant, you - a particular ht) setting?
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From Verhoeven:

1) Effect of grain size on Hardenabiltiy It was pointed out above that the product constituents virtually always form on the austenite grain boundaries. The amount of grain boundary area depends on grain size. A larger grain size will reduce the amount of grain boundary area per unit volume, which will shift the start curves to longer times and improve hardenability. Hence, the position of the curves on IT diagrams depend on the austenite grain size. For this reason, as shown on Fig. 9.3, published IT diagrams always specify the grain size.
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Thank you Don and Stacy for bringing this up. I have some w2 and I am looking forward to working with it.

Don, is your ht routine much different when working with W1?
Thank you again.
Nathan
 
navin74 said:
Thank you Don and Stacy for bringing this up. I have some w2 and I am looking forward to working with it.

Don, is your ht routine much different when working with W1?
Thank you again.
Nathan
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Same HT for both, but this W2 I have will perform a bit better.
 
W1 coarse spheroidized

s2OzknF.jpg
 
Beautiful image Bluntcut!! Thank you

Looking at the picture it appears clearly that from that condition a simple go at austenitizing temperature without a significant soak it's not gonna move that carbon.
Do you also have a picture of the same steel after a normalization, with the same scale for comparing the carbide condition?
 
bluntcut said:
Please elaborate on why(s): Grain size is directly proportional to the hardenability?
Click to expand...

I'll try to explain it in simple terms, the way i figure myself what happens.
The pearlite will want to fill the grain starting at the grain boundary, preferring the nodes, toward the center. The pearlite plates will "grow" inward feeding on, depleting, the carbon in solution as it precipitates, leaving ferrite on their sides.
The smaller the grain the more start up places the pearlite plates have to begin their formation and the less open field they have to conquer to fill the whole grain...the less time they require at their target temperature range, where the "nose" is.
With larger grains, in the same frame time and in the same area there are less starting points and the carbon precipitation has just the time to happen at the grain boundaries but not enough to significantly penetrate the grain field.

With deeper hardening steels, alloy elements will get in between the plates path, interrupting their growing as obstacles, increasing thus hardenability, but the grain size will influence the hardenability as well for the same reasons.
 
Stefano, yes that soak is necessary to dissolve and diffuse the carbides to saturate the matrix .Unless that happens you never get the strength and hardness you should have !

The composition showing Copper as .16 is rather high and would expected to have some effect on hardenability and performance .

It goes back to - use W2 , find the composition of a supplier that's proper and stick with that supplier.

Comments on hardenability - We normalize three times .When you do more you end up in Kevin's situation of poor hardenability !!
 
I didn't find micrograph for normalized W1. However normalized W1/W2 looks similar to 1095;52100 normalized, except smaller grain.

FwIvdqg.jpg


stezann said:
Beautiful image Bluntcut!! Thank you

Looking at the picture it appears clearly that from that condition a simple go at austenitizing temperature without a significant soak it's not gonna move that carbon.
Do you also have a picture of the same steel after a normalization, with the same scale for comparing the carbide condition?
Click to expand...
 
:thumbup: Wow, fantastic explanation :thumbup:

However IMO - if aust configuration has 2-3x more gb and everything else stay the same, PN wouldn't change because pearlite driving force+time is independent of sites. How can a configuration with same deactivation/precip/diffuse energy get different result?

Or maybe structural can affect phase/chemistry. Does more GB structurally induce higher strain, thereby easier to deactivate (carbon diffuse out of aust)?

When there are competing and possibly contradictory reasons/conclusions deduced for a specific affect - it's healthy to ask and scrutinize.

I've encountered(since solved) hardening issues even with aust temp ~1475-1500F and Super Quench, therefore I am not convinced by narrowing PN reason.

stezann said:
I'll try to explain it in simple terms, the way i figure myself what happens.
The pearlite will want to fill the grain starting at the grain boundary, preferring the nodes, toward the center. The pearlite plates will "grow" inward feeding on, depleting, the carbon in solution as it precipitates, leaving ferrite on their sides.
The smaller the grain the more start up places the pearlite plates have to begin their formation and the less open field they have to conquer to fill the whole grain...the less time they require at their target temperature range, where the "nose" is.
With larger grains, in the same frame time and in the same area there are less starting points and the carbon precipitation has just the time to happen at the grain boundaries but not enough to significantly penetrate the grain field.

With deeper hardening steels, alloy elements will get in between the plates path, interrupting their growing as obstacles, increasing thus hardenability, but the grain size will influence the hardenability as well for the same reasons.
Click to expand...
 
Luong, thank you for the link to the image of the W1. I enjoyed reading thru that site yesterday. Interesting to me...comparing the W1 picture of spheroidized cementite to the 1095 pearlite. Note that the W1 image was etched to reveal, primarily, the cementite carbides, but some of the ferrite structure was revealed in that etch as well, a faint brownish color behind the cementite. However compare that image to the 1095 image. The 1095 image apparently was etched to only show the pearlite, but the carbide network is not discernible (as far as I can tell).
 
In figuring out hardenability issue - With aided of a microscope, I found (aka speculation/conjecture and it might be wrong - oh well):

~75%
GB is an element sink - pertain to hardening, more and more Carbon get locked/deposited there. So using same aust temp + time, aust matrix is carbon-lean. Solving this aspect by increase soak time to release more C and diffuse them away from GB. With perfect ht execution, grain size remain the same for subsequent hardening attempt (given enough C in solution via longer soak). Grain size ceiling/best is around 6-7um. Once approach the ceiling - grain isn't getting smaller & smaller with additional cycles. Poor execution will lead to fatter/thicker/well-defined-old GB and low RC <= time to normalize again :p

25% ...
 
i don't know.
since i don't have a metallurgical lab i am tempted to set up a simple test with NaCl and water.
2 equal solutions and one with just a cotton string hanging in and the other with 4 strings. i could let them cool for a while and then weight the chrystals that precipitated starting at my "grain boundaries" growing inside the beckers :)
 
Pearlite = ferrite intersecting/twine with cementite often referred as lamellar configuration/layout. Cementite mostly be fern/fuzzy-finger like thin membrance, thus easily dissolve due to higher surface per volume.

Fine pearlite has dark fuzz look, vs coarse where gaps/layer are visible between ferrite & cementite. Obviously fine pearlite easier to dissolve C.

This is my view anyway - hopefully someone with actual metallurgy background can add more clarity/coherent.

samuraistuart said:
Luong, thank you for the link to the image of the W1. I enjoyed reading thru that site yesterday. Interesting to me...comparing the W1 picture of spheroidized cementite to the 1095 pearlite. Note that the W1 image was etched to reveal, primarily, the cementite carbides, but some of the ferrite structure was revealed in that etch as well, a faint brownish color behind the cementite. However compare that image to the 1095 image. The 1095 image apparently was etched to only show the pearlite, but the carbide network is not discernible (as far as I can tell).
Click to expand...
 
I've determined, after working with W1 for about 15 years and W2 for 10, that it's all magic. I think the key, is making sure to hold your mouth just right.

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Nick, can you make a video of how to hold your mouth. Because those are the nicest hamons I've seen. You can get lost in those things.
 
Don, what difference did you find between the round bar and the square stuff? I still have a bunch of that along with a fair bit of round.
 
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