Thermo mechanical treatment is the tmt full form. Thermo mechanical treatment is a process of heating an object or material to change its thermal properties. The most common example would be the expansion joint in your car’s suspension, which requires regular maintenance so that they don’t crack under pressure from driving over bumps on roads.
However, the most popular form of heat treatment is annealing. Annealing steel is used to increase ductility and reduce hardness in order to make it easier for manufacturers to machine rather than stamp or mill.
Depending on how high you go with the temperature of your annealing, you will get different results on your metal.
Normalizing: This process is used to restore pure and perfect crystals in the metal. The metal will be heated up to a very high temperature and then cooled down slowly. This will help in removing many of the impurities that would have been formed inside it since you last worked with the material.
Hardening: If you increase your annealing temperature even further than normalizing, you can get rid of all irregularities in the crystal structure and thus produce steel which has a uniform hardness throughout its body, no matter which area of it you use or cut into.
The only downside with this method is that once hardened, the steel can’t be softened again, so manufacturers tend to avoid this option if they don’t need something to be as hard as possible, like knife blades.
Stress Relieving: If you anneal at a temperature that is lower than the normalizing point but higher than the softening point then it can release any mechanical stress inside the steel that was caused by bending or hammering. This process also prevents cracking and thus makes your metal stronger.
You might have heard of something called “stress relief” before, which is used to reduce work-hardened stress in nonferrous metals such as aluminum, magnesium and copper alloys using heat up to 300 F which precludes strain ageing, recrystallization or changes in grain size so reducing internal stresses within the alloy. So basically it relieves them of any leftover tension caused by manufacturing.
The Difference Between Tempering and Annealing Steel – A Guide for Knife Makers
There is a rusty piece of metal on my knife and I am wondering if it can be removed or not?
The pitting seen in this knife blade is called “cold stain”. Cold stains are rust spots that have been etched into the surface of the steel through improper heat treatment. In most cases, these stains cannot be removed without destroying the aesthetic appeal of the knife as they will turn even more brown as the blade gets heated up from use. You can try to polish them out with a dremel tool but you would have to do it very carefully so as not to remove any metal from the blade.
Is this rust? If it is, and the metal has been heat treated (hardened), how do you get rid of it?
I have noticed some dark stains on the blade of my knives. It does not rub off or come off when I try to clean it with WD-40. Is this discoloration rust and will heating the steel remove it?
No, it’s not your typical rust on your knife that we all know about. This is actually called “stainless staining” which occurs during the process of stainless steels aging, namely from high chromium content and low carbon grades such as 440 A and 420 series SS. The stain is a product of corrosion and oxidation which is exhibited in the form of rust spots on the blade’s surface. It cannot be dissolved by any cleaners, but instead will need to be polished off with some time and effort.
Since it is a corrosion product, you would not want to put such knife through heat treatment (like heating up your blade with fire) as it would only make the staining worse over time. Just clean off your knife from grime and store them in a dry place so that they do not develop more stains later on.
I bought my friend a hunting knife and when I handed it over to him I noticed that there was green stuff near the end of the edge. When he told me that he has been using it for gutting deer, everything made sense. What causes this?
This discoloration happens to be one of the tell-tale signs of using carbon steel knives for field dressing your game, like it or not. The green stuff you noticed is actually oxidized iron that comes from blood stains when interacting with carbon steels which are prone to rusting.