Blown temper, how hot is too hot

[superbleu]

I have a Boker red injun that someone rounded off. The razor takes a beautiful edge, except the last 1/8-3/8th of an inch where someone ground off the point. I am assuming this is because it got too hot and ruined the tempering of the blade there.
My question is how hot does the blade need to get to ruin it's temper?
I would imagine during the grinding process of making these blades they would get pretty warm as well.

[Bruce]

Most razor steels are drawn to about 400 F. If the tip was ground and got hotter than that, it should be softer than the rest of the blade.

[superbleu]

Thanks for the post Bruce. So if it get's too hot, the metal will become too soft and not take an edge? I thought if it got too hot the metal would become too hard to take an edge. Shows how little I know about metallurgy.

[cutalot]

it should take a edge just not hold it. a good rule when gringing any hardened steel be it knifes or razors is if you cant do it under water hold the blade as close to the area being grown as possible when it starts to get warm not hot , dunk it and continue. if you see blue you just ruined it

[Joed]

This is a perfect example of why I will not purchase any razors that appear to have been restored, unless it has been restored by someone I know and trust. With the explosion in straight razor sales people are trying to make a buck on them and know that the shiny ones sell for more, so they try their hand at restorations. If they anneal the steel they just buff the blue away and it's nice and shiny again. I'd rather do the work myself and know what I have when I'm done.

[Bruce]

The blue hue indicates the steel got to about 700 F or more, spring temper, definitely not what the shaver is looking for in his favorite razor.

[JoshEarl]

it should take a edge just not hold it. a good rule when gringing any hardened steel be it knifes or razors is if you cant do it under water hold the blade as close to the area being grown as possible when it starts to get warm not hot , dunk it and continue. if you see blue you just ruined it

Actually, there's a range of colors that you might see, starting with a light golden, then dark brown, then blue and blue/purple, then black. Dark brown is usually where the trouble starts.

Another good tip is to grind hardened blades while holding them in your bare hands, preferably with your fingertips close to the area being ground. If it gets too hot to hold, dunk it in some water. With thin sections on full hollows, though, you can get to dark blue in half a second if you're not careful.

[superbleu]

This is a perfect example of why I will not purchase any razors that appear to have been restored, unless it has been restored by someone I know and trust. With the explosion in straight razor sales people are trying to make a buck on them and know that the shiny ones sell for more, so they try their hand at restorations. If they anneal the steel they just buff the blue away and it's nice and shiny again. I'd rather do the work myself and know what I have when I'm done.

Not to worry Joe, I didn't pay a lot for this razor, actually I got it in a lot sale of razors I found on the local CL, the wonderedge alone was worth more than I paid, the other 8 razors were just gravy on on top.

[gssixgun]

Another good tip is to grind hardened blades while holding them in your bare hands, preferably with your fingertips close to the area being ground. If it gets too hot to hold, dunk it in some water. With thin sections on full hollows, though, you can get to dark blue in half a second if you're not careful.

+1 with this on using buffers too,, Greaseless and polishing compounds will heat a blade very quickly....

I pretty much have made a habit of resting the side of my finger along the blade face on the oppisite side of where I am buffing this keeps my skin away from the edge should the spine catch a wheel and allows me to keep a constant tell on the temperature of the steel... The added benefit is it does NOT allow you to use much pressure at all while buffing...

[Bruce]

Thanks for the post Bruce. So if it get's too hot, the metal will become too soft and not take an edge? I thought if it got too hot the metal would become too hard to take an edge. Shows how little I know about metallurgy.

super,

Simplisticly, taking the blade into the mild incandescent range, about a maraschino cherry red and then quickly quenching it will get the blade about as hard as it will get. At this point it's also as brittle as it will get. To get it to a point where it will do a razor's work without the edge chipping, it needs to be tempered or softened very slightly, and that's done by heating the blade to much lower temperatures than are needed for hardening: harden about 1400 F and temper about 400 F.