Edge Retention/Rolling Test Stand

[KnifeGrinders]

Don't even know how should I put this...
I don't know a single sharpener who would be sharpening an unhardened steel.
As a minimum it will clog your stones, and deburring will probably be a pain.

[EOU]

"I don't know a single sharpener who would be sharpening an unhardened steel."

Well now you know one KG...us, (although we really don't regard ourselves as "sharpeners"). Agreed, the burr removal process is likely to be a pain. We got the cold rolled steel into the 200's though so hope to do at least as well with the A2. It's also possible that we will be able to do more complete burr removal after it's hardened.  Its also possible that we're smoking dope and that the edges will come back to us from heat treat totally messed up. Don't know, we'll just have to see. It's like buying stocks on the stock market KG; if your stock goes up you're a financial genius and if it goes down you're an idiot.

[Jan]

Brief comment from the metallurgical point of view.

During quenching martensite is formed. Because martensite has lower density than the austenite it expands during the rapid cooling. Martensite is highly stressed and strained arrangement of iron and carbon atoms. Martensite is full of defects, mainly dislocations, which paradoxically cause its strength.

Jan

[EOU]

"During quenching martensite is formed. Because martensite has lower density than the austenite it expands during the rapid cooling. Martensite is highly stressed and strained arrangement of iron and carbon atoms. Martensite is full of defects, mainly dislocations, which paradoxically cause its strength."

Thanks Jan. We know that you don't post information to the Exchange unless you have something in mind so how would you apply the above quoted statement specifically to what we are doing now? 

Here's a little update. We think that monday or tuesday everything will be ready to send off for heat-treat. In case you're curious, here's a couple of pictures of the test A2 in the mill. Front and side.

                                                              

The mill head is set at a 15° angle and the A2 piece is vertical. We made one pass per side and set the feed rate really, really slow. 15 minutes to cut one 6" long side.

Here's a couple of micro pics of what the bevel and edge looked like. The first is right off the mill and the second is after some deburring on leather.

                                                      

Ever wonder how sharp a deburred edge is after coming off a mill? We never wondered either but since we had the opportunity, we measured it.

                                                      

Now we're going to see how sharp we can get these uncooked babies using a Kally and Mr. Greppers super extra special angle guide and rest!

[Jan]

EOU, martensite formation during quenching is de-facto rebirth of a new material. Martensite formation always produce a shear deformation in the crystals of the steel grains. For this reason I think it is understandable that the final edge sharpening is done after the heat treatment.

Jan

[Mark Reich]

Don't even know how should I put this...
I don't know a single sharpener who would be sharpening an unhardened steel.
As a minimum it will clog your stones, and deburring will probably be a pain.

I totally agree. This is not standard proceedure.

I know volume of martensite is greater, but I don't know how much.

I was thinking the edge would have to get wider through transformation.

Normally, A2 heated to 1500°F would have a significant layer of scale (oxidized steel), which would certainly have impact.

Brad's fancy kilns use inert gas shielding, so oxidation is impossible, but there has still been a very thin, very stubborn layer of... something like scale, on the blades he's done for me, but that's S35VN and CPM M4. Much different than A2.

It's very surprising that he is ok with apex thickness less than .010", and expects the edges to be unaffected.

Brad may not realize the level of precision you're able to quantify, Mike.

[Mike Brubacher]

Thanks Jan and Mark. I get it now Jan. Yes, I'm a little concerned but hopeful of the sharpness levels coming back. What makes me hopeful is that Brad seems to place a fair amount of faith in the predicted outcome due to the fact that this is a air-hardened steel. We sharpened one of these Saturday and got it down to 275 without a whole lot of effort. We'll try to do better. 275 doesn't give us a whole lot of fudge factor. I don't mind if we send them in at 225 and they come back 300. We have data on 300 edges so can still make good comparisons. As a fall-back, and assuming the edges come back higher (duller), we're hopeful that stropping on leather might improve it (surface crap-ola). If the edge swells during heat treat though, that is unlikely to help us significantly. This experiment is a big deal to us though because it represents the very clear opportunity to see if sharpening, in and of itself, somehow significantly affects the yield strength characteristics of the steel. If it doesn't, we move on. If it does we then can investigate if this is true of all sharpening methods or just some and to what degree.

[Jan]

Thanks Jan and Mark. I get it now Jan. Yes, I'm a little concerned but hopeful of the sharpness levels coming back. What makes me hopeful is that Brad seems to place a fair amount of faith in the predicted outcome due to the fact that this is a air-hardened steel. We sharpened one of these Saturday and got it down to 275 without a whole lot of effort. We'll try to do better. 275 doesn't give us a whole lot of fudge factor. I don't mind if we send them in at 225 and they come back 300. We have data on 300 edges so can still make good comparisons. As a fall-back, and assuming the edges come back higher (duller), we're hopeful that stropping on leather might improve it (surface crap-ola). If the edge swells during heat treat though, that is unlikely to help us significantly. This experiment is a big deal to us though because it represents the very clear opportunity to see if sharpening, in and of itself, somehow significantly affects the yield strength characteristics of the steel. If it doesn't, we move on. If it does we then can investigate if this is true of all sharpening methods or just some and to what degree.

OK Mike, I am really eager to know the impact of quenching on the edge sharpness.  I have not gathered enough own results yet.

Mr. Mark you are correct, the volume of martensite is larger, but this impact on the edge thickness will be small.  
What I am wondering about is not only the edge thickness increase caused by formation of different surface layers, but also the misalignment of grains in the edge vicinity.


Introductory reading about quenching and martensite formation is of course the book by prof. Verhoeven. As complementary (apparently more popular) reading I have found a paper by prof. Helmut Foell from Uni in Kiel, Germany.

Jan

[EOU]

We're sharpening now non-hardened A2 now. Looks to us like 260-275 is going to be the number. Lower numbers can be squeezed out but not on a consistent level throughout the edge. Don't know what the 30° chisels are going to turn out to be yet because we haven't tried them yet. To the right is a micro pic of a sharpened and deburred edge. We've done the minimum amount of grinding here. The bevel is 15° and all we've done is created a 19° micro-bevel on the edge.

                                                        

We did run another test prior to shipping these off. We ran a roll test on this now sharpened but non-hardened A2 steel. As you may recall we did something similar with a piece of cold rolled sheet goods that was .050 thick a few weeks ago. That non-hardened material was sharpened to 275 and then placed in the SET for rolling...and roll it did, all the way to 818 (one series of five back and forths). This as compared to hardened steels that roll in the 200 - 250 point range (ending sharpness level minus beginning sharpness level). The non-hardened A2 began at 259 and ended at 720 so it seems that hardening must have some considerable and beneficial effect with regard to rolling of edges. We're sure that this revelation comes as quite a surprise to Mark Reich but as we said in an earlier post (remark) about Mark. Even an old dog can learn new tricks.

Of course we have just presented strong evidence of something we had all suspected was true so "why do it?" We are about to harden A2 steel at different levels and then measure the effect of these various hardness levels on edge rolling. Now we have established the far end of the hardening spectrum as well... no hardening at all.  Our conclusion is that "non-hardened steels roll a lot and now we know, fairly precisely, how much "a lot" is. "

[grepper]

test post - please ignore