Heat Treating of Steels & Cast Irons for the Development of Microstructures and Mechanical Properties in Base Materials

30 June 2016

Fine manufacturing processes create sturdy cast iron items and robust steel-reinforced components that resonate with structural soundness, but such mechanical solidity doesn’t just happen, not without an incorporated processing stage that intelligently manipulates key metallic properties until they fit a specified application. The heat treating of steels & cast irons delivers finite mastery over these base mechanical attributes, thus altering the behavior of the metal, but why should we go through all of this trouble? Doesn’t iron come out of the ground hard and ready to serve numerous robust applications?

Organizing a Chaotic Microcrystalline Structure

Iron and its many alloy-rich familial members may look strong and feel dense, but looks can deceive because these apparently tough metals are relatively disordered at the granular level. The composition of the material is hard in some areas and possessed of localized brittleness in others. It needs to be homogenized and then toughened. Like a battalion of untrained soldiers, the microcrystalline structure must be tamed by heat and taught to assemble in an orderly manner.

The Trial by Fire Development of Heat-Tempered Properties

Of course, all of these processed alloys are bound for specific applications, so they also have to be modified to emphasize certain material characteristics while attenuating others, which means we’re talking about more than one structurally altering technique at this point. The process begins by normalizing the metal, by homogenizing the entire structure so that it can be declared uniformly treated. Hardening and ductility aren’t the goals here, but the elimination of localized mechanical irregularities is a definite objective.

The Refined Injection of Mechanical and Physical Attributes

The heat treating of steels & cast irons then moves on apace by imbuing the object with machined features, bent shapes and sectional cuts that bring the product ever closer to its final marketable form. Annealing is important during this fabrication stage because a slowly applied heating and cooling action relieve the metallic stress added by the machining work, thus making the part workable once more. Meanwhile, the trial by fire centers on a rigorous hardening phase, one that hardens the part by exposing it to extreme levels of heat and then immediately quenches the fire so that the required hardness rating is locked in place.

What’s been described here is a basic linear run, but the heat treating of steels & cast irons will typically use a cyclical chain, one that works with the machining phase to clarify a form-versus-function configuration. Form has been realized through tooling while material function has been established according to client specifications. And, finally, a necessary finishing stage adds polish and refinement to the overall form.

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