![]() It was a topic in our Materials Science course in mechanical engineering. It's pretty neat, but a lot is involved at the molecular level. ![]() Quenching typically hardens because it maintains the crystalline properties of the steel which are lost if the steel is cooled slowly, which would make the steel take on more ductile properties. It rushes the material through its various phases, from partially liquid to mostly hard, which gives the steel a different molecular structure than if it were cooled slowly. It's called quenching, which is a technique to manipulate the properties of various iron alloys, including steel. So what happens when you quench something? Well, the atoms do not have time to rearrange themselves so they undergo a rapid shear transformation AND the carbon does not have time to diffuse and so is "frozen" in place, forming Martensite.Įdit: just found a slightly longer but easy to understand article on heat treatments of steel: Place the blade bar in the forge at the most convenient position for extraction and quick placement on the jig. Place the counter-bending jig in the hardy hole or vise. The cementite transforms last and uses up remaining the carbon that has been rejected from the growing ferrite regions. Bending With The Railroad Spike Counter-Bending Jig. If done slowly this forms regions of ferrite with low carbon concentrations and regions of high carbon cementite. So in order to transition from Austenite to ferrite not only must the atoms rearrange themselves but they must also reject the dissolved carbon. At lower temperature the atoms prefer to rearrange themselves into a body centered cubic configuration called alpha-ferrite which can not dissolve much carbon (see the phase diagram posted by Underbear below). If you want an explanation - at high temperatures steel prefers to be in a face centred cubic configuration, called Austenite, which is relatively soft and can dissolve a lot of carbon. Yes the rapid temperature change forms martensite, which is much harder and alpha ferrite.
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