Thermal Treatments

Thermal Treatments

Hi fellow Bladesmiths, and greetings from the Blade show!

This years Blade show was certainly a tremendous event. I had the opportunity to socialize and talk shop with the worlds top bladesmiths as well as some of the production and factory knife people, keep your eyes and ears peeled for new and innovative concepts in cutlery in the near future!

My last couple of newsletters have been dealing with various aspects of Damascus bladesmithing. this week we'll go into that most important topic of thermal treatments.

This topic as far as I can tell has more misinformation surrounding it than just about any other topic one might discuss. I will only talk about the things that I personally have tested and verify to be sound information.

There are certain concerns that are more or less particular to the bladesmith forging pattern welded steels. First let's talk about what happens to the pattern welded billet during the process of fabrication. During the the process the billet has been subjected to extremely high heats for prolonged periods of time. This has several effects on the steel, not all of them good.

Firstly there is a certain amount of decarburization of steel due to exposure to O2 at high temps. This to an extent cannot be helped, but it can be kept to a minimum by properly adjusting your fire to maintain a reducing atmosphere. If the fire is properly maintained, our carbon losses are minimal, if not, the damaging effects upon the steel may be all but irreversible, so keep close watch on that fire , it's your primary and most important tool in this entire process.

The second important thing that must be considered is grain growth. When steel is subjected to high temps for extended periods of time, the grain boundaries of the steel expand making the steel weak and useless.

Before committing the steel we've just made to being forged into usable objects, we must THERMAL CYCLE it. This is a procedure by which prescribed courses of thermal treatments undo the damage of prolonged heating. My method of accomplishing this is to do my final shaping of the billet at progressively lower heats. I start by doing my final shaping of the billet at normal forging range ( 1800-2000F)and continuing down to a temp just below the austenizing temp(!455F) and allowing the billet to cool slowly in still air. I will do this a minimum of three times. I will add a final time as a longer cooling phase that will happen over several hours.

I do this final phase by allowing the billet to slowly cool in the forge after shutting it down while quite hot and closing the openings of the forge with insulating material(firebrick). this will let the billet cool slowly and so doing allow the grain structure of the steel to assume a uniformly small and fine structure.

As well, the steel will be at it's softest so all cold working operations will be rendered easy. In this condition the steel will be easily workable with files and any and all cutting tools. Bear in mind that once a tool is forged from this steel, the thermal cycling should be done again to insure steel that will achieve its maximum potential in the three important areas of hardness, strength, and toughness. After all, extreme performance is what we do.