Decarburization?

[MetalMuncher]

Greetings everyone. Just a quick question: How long can a blade be in the fire, say at forging temp? Lets say I have a spring and hot cut it, uncurled it, flattened it, forged the point, put the bevels on and drew out the tang. Forging time about 5 hours(possibly less). Is that enough to decarb it totally? Or will it still harden properly? I never forge past a dark yellow heat .Thanks guys, this one has really been bugging me. I dont want to destroy a knife. Have a good one!

[Quenchcrack]

Carbon diffuses out of steel at about .010"-.015" per hour at 1750F. It moves faster at higher temperatures. After 5 hours, I would guess you might get .075"-.100" of decarb but the effects of forging might affect that number. This is why the old saying is "If a worthy edge you'd win, forge it thick and grind it thin". Of course, if you are using a gasser, the number might be more and if you use coal, and keep it in the neutral zone, it might be less.

[MetalMuncher]

I use charcoal and have no idea where the neutral zone is. Thats why I have been having issues with forge welding. That sounds like an awful lot of decarb....if using 5160, I'd probably wind up with almost no carbon to speak of...bummer. Thats why I really want to buy some bars, ready for foring the point and the bevels. But I mean, like, for sure you can use old springs right? Or do I take too long to forge 'em? Thanks Quenchcrack!

[Rich Hale]

I have played this old song for a lot of years. but will ick it up at the chorus once again....If you become proficient at forgeing before making blades everything will go better for you. WE need to develop mental and motor skills to the point tahtWhen yo p ut steel in the fire youi have a plan mentally and the ability physically to pull the steel out when ready and do exactly what needs done in a timely manner. You get the muscle memory by putting in the hours at the forge. Find out what each part of the anvil does to the bottom of the steel and what each type of hammer you have does to the top part of the steel. Learn to make steel longer and shorter, wider and thinner and how to hold the steel to make a tpaer in the piece. Another big thing is learning when you are done forgeing. And of course what to do after the forging is done. Methinks you are trying to ride a bike before you have learned to crawl. Body mechanics are best helped by someone else. If you can get a smith to watch you forge it will be a great leap ahead in what you do. How you stand at the anvil, how you move, how you work with tools, all are important. The learning curve can be shortened alot by using proven methods to build a base to work from. Join an area group and get involved however you can. REading or watching videos is good but you only see someone else doing the work. If you wish, make a video of yourself forgeing that I or anyone else can see and I for one will give you my thoughts. And have fun.

[patrick]

With respect to decarb, in the heavey forgings we make, we assume 3/16" total decarb from the starting stock size through heat treated part. So, when we measure hardness, we grind at least 3/16" deep before checking hardness. Keep in mind that between heat for forging, and heat treating you could have well over 30 hours above the austenitizing temp. I think that scaling will be more of a factor than decarb. Above about 1500 F, scale developement is quite rapid, so if you are constantly breaking off scale, you probably have fairly thin decarb. Once you get the point of little deformation, then you will begin to develop deeper regions of decarb, but still not too significant if you are working efficiently.

Patrick

[dablacksmith]

is it really takeing you 5 hours of forgeing to get a blade?? if it is then ya decarburizeing is a problem... are you uncoiling a coil spring and forgeing it into a bowie ? or sword? try something easyer like starting with a leaf spring cut it close then forge it to shape .. shouldnt take more than 45 minutes to forge to rough shape...dont go any thinner than 1/16th thick max . normalize (heat to where a magnet wont atract to the steel then let cool slowly) you might do that a few times if you have a lot of grain growth. harden and temper should work fine.

[MetalMuncher]

I think five hours might have been an exageration, but by the time I have un curled, flattened and forged the bevels some considerable time has passed. I have watched many videos, and have studied TarAlderions tutorial closely. I can forge fine, I think I have the technique down pretty good. I have made BBQ forks, spoons and a bunch of knives. But when I spark tested a file and then tested my own forged piece, the difference was ridiculous(in terms of sparks) Of corse my piece was normalized,not tempered. I think that makes a difference in sparks. But thanks for you help guys!!! I will work on my technique. Have a good one!!!!