TEMPERING

[Flagg]

I agree with everything . But I never see purple color on blade tempering at 2 x 2 hour on 400f ....NEVER ??

Our kitchen oven is is 2 years old and gives a higher temperature reading than my new gauge I hang in said oven and I set my 400 degrees by it
I have just filed blade edge again to check and file skates over it'

I have put edge on blade and it passes the paper test, I have shaved wood with it and it is OK but how long will sharpness last?
There is not much I can do now but finish it.

I will start another one in the next few days and -
put heat sink in oven and let it reach 400 degrees prior to putting blade in oven
for 2x1 hour cycles or 1x2 hours cycle????????????, I will not take it out until it has had the time irrespective of colours..

Flagg

 

[NickBoyle]

If this is your first knife, which sounds like it is, this knife is perfect to test! You wanna know how long the sharpness lasts you say? Then start cutting stuff! Cut rope and cardboard and anything else you can get your hands on. Do this before you start your next knife. If it isn’t staying as sharp as you think it should then temper your next knife at 325-350 and test it! I always start low and walk in my final hardness with my tempers. On carbon steels anyway.

 

[HSC ///]

Reason to do that ?

the reason to do this is to have a clean surface to evaluate the color for the second or subsequent temper.
I did this last night with 6 slipjoint 1095 springs.
flame torch temper, cool in water, sand the color off, repeat.

 

[Natlek]

The reason to sand off the color is because the colors build upon each other each cycle, that was mentioned above.

I don think that this is correct ? And it is not color....color come for light reflection try that oxide layer ....and probably thickness of that layer dictate which color from spectrum will pass...

I believe that this quote is correct . What I m not sure is does oxide layer thickness increases only with temperature or with time on temperature too ...?

EDIT to add .... The layer will also increase in thickness as time passes, which is another reason overheating and immediate cooling is used. Steel in a tempering oven, held at 205 °C (401 °F) for a long time, will begin to turn brown, purple or blue, even though the temperature did not exceed that needed to produce a light-straw color.

If steel has been freshly ground, sanded, or polished, it will form an oxide layer on its surface when heated. As the temperature of the steel is increased, the thickness of the iron oxide will also increase. Although iron oxide is not normally transparent, such thin layers do allow light to pass through, reflecting off both the upper and lower surfaces of the layer. This causes a phenomenon called thin-film-interference , which produces colors on the surface. As the thickness of this layer increases with temperature, it causes the colors to change from a very light yellow, to brown, then purple, then blue. These colors appear at very precise temperatures, and provide the blacksmith with a very accurate gauge for measuring the temperature.

 

[Natlek]

the reason to do this is to have a clean surface to evaluate the color for the second or subsequent temper.
I did this last night with 6 slipjoint 1095 springs.
flame torch temper, cool in water, sand the color off, repeat.

I never do that and I have same color/ a bit more pronounced / after second temper ?

 

[Flagg]

I have learned one thing for certain from this forum, there are some experts here.

In the UK the 'knife' interest of individuals is harshly suppressed by government with police backing.
Basically, carrying a folding blade not longer than 3 inches is all we can have in public and they want a good reason for that if they find one one you.

We have knife culture here with a certain element of people who seem to like stabbing others.
I will not elaborate.
Our gun laws are really tight, take a look on Google.The decent people are bunched together with the evil bxxxxxxx



Thank you/

Flagg

 

[Stacy E. Apelt - Bladesmith]

It is two temper cycles, with cooling to room temperature between them. You can do them for one or two hours each. One hour is sufficient for your 1080 blades.

 

[Pendexter]

If you screw up your temper by heating to 500 for two hours, for example, is there any way to save the blade? Could you reharden to nonmagnetic and then temper again?

 

[Natlek]

If you screw up your temper by heating to 500 for two hours, for example, is there any way to save the blade? Could you reharden to nonmagnetic and then temper again?

Of course , you can heat treat it again . I don t understand your last question... Reharden to nonmagnetic? If you think .... to heat blade to nonmagnetic temp, and then quench ...and then temper on right temp ,yes .

 

[Pendexter]

Of course , you can heat treat it again . I don t understand your last question... Reharden to nonmagnetic? If you think .... to heat blade to nonmagnetic temp, and then quench ...and then temper on right temp ,yes .

I misspoke, you are correct. I meant taking a blade that was messed up by tempering at too high a temperature, heating it in a forge to about 1500 degrees (non-magnetic for the 10xx steel) and quenching in oil to get the hardness up. Then tempering at 400 degrees again.

Thank you. That makes me feel a little better that it's not a one shot deal.

 

[Stacy E. Apelt - Bladesmith]

500F didn't ruin anything. In 1084 it will be around Rc 59-60 (assuming you fully hardened it in the quench).

 

[Pendexter]

Thanks Stacy, I've still got a lot to learn, but loving every minute of it. For anyone interested, I got the following info from USAKnifeMaker.com:

1095:

• 450F yields approximately 62RC
• 500F yields approximately 59-60RC which is where most will want this steel.
• 600F yields approximately 58RC

1080/1084:

• 400F yields approximately 62RC
• 500F yields approximately 59-60RC which is where most will want this steel.
• 600F yields approximately 57RC

On the other hand, Per Kevin Cashen (ABS Certified Master Bladesmith) at cashenblades.com:

1080/1084:
350f: 63-64
400f: 60-61
450f: 57-58
500f: 55-56
550f: 53-56

1095:
350f: 63-64
400f: 62-63
450f: 61-62
500f: 59-60
550f: 57-58

There are many BF threads on this topic, so it's time for me to get some snacks and a soda and dive in

My plan for my first blade is probably going to be 375 x 2, use the blade and see if it chips, then raise it 25 degrees, retest, and go up until it doesn't chip anymore.

 

[Stacy E. Apelt - Bladesmith]

In reply to Natlek's question about time/temperature:
Tempering is a matter of both time and temperature. However, temperature far more affects hardness than time (over 10X). If you tempered for one hour at 400 compared to ten hours at 400, you would get nearly the same hardness. If you tempered one hour at 400 compared to one hour at 410 for an hour, you would see a drop in hardness over the 400 results.

As to colors, those charts are not related to oven tempering over time. They are for flame and heat hardening steel while you watch the colors form and walk.
The colors from tempering blades in an oven for an hour or two mean absolutely nothing. They are the result of the oils and other contaminants on the surface. You might see a bronze color, a rusty brown, or a peacock cloud of magenta and purple .... they are both no indication of hardness ot oven temperature.

 

[Natlek]

This blade is from very old 4.5mm Nicholson file after first temper /one hour / on 250 celsius .....

 

[Pendexter]

Here's 1095 after (2) 2 hr cycles at "400 degrees."

I put a bar of metal in the toaster oven with the blade to try to regulate the temperature a little bit, but I didn't have a thermometer, so I'm not sure what the exact temperature was.

The blade is not too soft. If anything, it may be harder than optimal. No chips or rolls after some light batoning and aggressive whittling to test it out. Sharpens like the RC is in the high 50's or low 60's. Harder than GEC's 1095.

Color does not indicate temp. I have seen the rainbow and am now a true believer.

 

[Stacy E. Apelt - Bladesmith]

Now finish sanding it and put on a handle.

 

[Flagg]

Here's 1095 after (2) 2 hr cycles at "400 degrees."


After 2 x1 hours at a checked 400 degrees in a toaster oven with heat sinks my last knife has a very similar appearance to this one of yours.

I put a bar of metal in the toaster oven with the blade to try to regulate the temperature a little bit, but I didn't have a thermometer, so I'm not sure what the exact temperature was.

The blade is not too soft. If anything, it may be harder than optimal. No chips or rolls after some light batoning and aggressive whittling to test it out. Sharpens like the RC is in the high 50's or low 60's. Harder than GEC's 1095.

Color does not indicate temp. I have seen the rainbow and am now a true believer.

Here's 1095 after (2) 2 hr cycles at "400 degrees."

I put a bar of metal in the toaster oven with the blade to try to regulate the temperature a little bit, but I didn't have a thermometer, so I'm not sure what the exact temperature was.

The blade is not too soft. If anything, it may be harder than optimal. No chips or rolls after some light batoning and aggressive whittling to test it out. Sharpens like the RC is in the high 50's or low 60's. Harder than GEC's 1095.

Color does not indicate temp. I have seen the rainbow and am now a true believer.

 

[Pendexter]

Now finish sanding it and put on a handle.

Finished it last weekend. I posted pics in the Kephart thread in the general section, here's the link.

https://bladeforums.com/threads/kepharts-they-just-work.1627840/page-16#post-18726232

4.5" blade, 4.5" handle, 1/8"x1", 5.5oz, convex with walnut handles and brass pins. First knife I've ever made. I want to say that I purposely kept it rustic because it's a Kephart but it's actually because I am still learning how to grind properly.

And here are some photos of it from today. I made a makeshift sheath out of cardboard, zip ties, and duct tape so that I could take it on a hike with my family.

 

[Stacy E. Apelt - Bladesmith]

Congratulations for finishing your first knife.


It suffers from BHS - blocky handle syndrome. On the next one ( or on this one) round the handle more at the corners so the cross section is more oval.
Also, those little tits of wood going down at the ricasso may snap off in use. Best to avoid sudden downturns against the grain.

 

[Flagg]

This is the knife I am working on, my latest temper which scares me. .

I