I'm also curious about this. I noticed on the ASM International guide for 5160 for example, it says do not forge above 2200F.

I can assume that there would be some burning of the alloys if forged above that, but can't be sure. I've held off on trying my hand at Damascus for this reason.

So long as forging is occurring it is a matter of rate of deformation vs. temperature. If you overheat parts that are not being worked then you will need some cycles to bring it back in line. Sparklers is definitely a dividing line, if you get that, you have permanently damaged the steel. Grain growth is not the issue many believe in the chaos of forging. Excessive heat without deformation will allow the grains to grow, but deformation at temperature drives dynamic recrystallization. This is why steel has those recommended forging temperatures, heat properly matched to the rate of deformation keeps things balanced. But hand forging is going to result in all kinds of inhomogeneity anyhow since we can’t hammer as evenly as say a rolling mill could deform steel, and this is why normalizing is so useful; enlarged grain, uneven grain etc… it can all be fixed with a couple of controlled cycles… unless you burn it. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//sad.gi f' class='bbc_emoticon' alt=':(' />

Awesome. Thanks Kevin. That gives me some peace of mind.

A note on "burning". For years I have heard folks refer to it as "burning the carbon out" but this is not an accurate description at all, it is much more complex and serious than that. What burning actually is is very aggressive and destructive oxidation that eats its way into the steel at the grain boundaries, compromising them so that the integrity of the steel is also compromised. This is why the steel often crumbles or comes apart on the anvil, there is little left holding it together. You may be able to hammer the steel back to shape if you only had a little sparking but under the microscope it really looks cruddy and is not the same.

Coal forges make the best sparkler displays but the sparking is your friend because it tells you the steel is burnt. Often the atmosphere in the gas forge will not give you the sparks and it is much worse when there is no sparks and the steel just crumbles without warning. In light of this I would say that it is never a good idea to take a high carbon steel to "white" hot. But then I don't know why that would be necessary. Even when making damascus a light yellow should be more than enough. The greater the carbon content, the lower the melting temperature of the steel and the easier it is to harm it with high temperatures. This is where it can be a problem getting bladesmithing advice from a blacksmith that has never worked with high carbon steel, understandably many of their working temperatures could be higher.

Burning is just the extreme end of overheating, other consequences from working things unnecessarily hot are more decarburization and heavy scaling which makes mess of your forging as well as robbing you of material. I try to do most of my forging around the 1,800F range, and work my way down in temperature as the forging nears completion to avoid overheating parts that are done.

This also begs the question, how cold is too cold?

As always; temp plus time. When just chunking a blade into a oven or forge; how long was the tip at temp before the rest came up to temp? Not a lot of room for decarb or grain growth at the tiny end of the blade.

A blade's geometry requires that the smith have control of the heat. That is the evenness and intensity. The more intense the heat, the more that timing is critical.

Thank you for the information Kevin and Lin. This has been eye opening. Any tips on forge welding mild steel to carbon steel given their different carbon content?

I would suggest using a simple carbon steel when welding to mild steel. The 10** series. I've had more success with forge welds using them.

Thank you. I've got some 1045 and some 1060 plating I've been meaning to get rid of. Not particularly knife steel, but not bad for other things such as hammers, hawks, etc.

In the case of welding mild to higher carbon steel you can replace the higher temp with time do a slightly longer soak at a lower temp and then weld as normal. It quickly evens out in carbon content anyway.