Metal Hardening, Metal Quenching, and Metal Tempering: What are the Differences?

24 October 2017

Certain questions always seem to return to torture novice engineers. No sooner has one problem been solved than the next comes careening down the track like a runaway train. It’s the different heat treatment terms that really create the deepest furrowed brows. Once and for all, we’re going to get rid of this tangle by injecting a heavy dose of clarity into metal transformation procedurals.

Abbreviating the Metal Hardening Process 

Furnace-hot temperatures send the metal workpiece towards its transformative thermal threshold. The microstructural components in that material change. They assume a special atomic relationship, which engineering types refer to as austenite. In this metal phase, the component is workable and corrosion resistant, but it’s hardly usable just yet because the metal is still red-hot. That’s why this is an ‘abbreviated’ description.’ Quenching, the next stage in the heat treatment process, rapidly cools the part, completes the treatment, and locks in the properties that were gained at the upper transformative temperature threshold. Metal hardening technology, therefore, injects the part with heat, whereas the metal quenching stage immediately removes that thermal load. In contemporary engineering methodologies, its water or oil that plays the part of the quenching agent.

Acquiring Metal Tempering Improvements 

There are misconceptions regarding the differences between metal tempering and metal quenching. That’s perhaps because of all the blacksmith scenes in old Hollywood movies. Viewers were told that the part was tempered when it was dropped in a wooden bucket of water, so they assumed the blade was now tougher and durable. In fact, the workpiece had been hardened. It was loaded with a martensitic grain, a form of steel that was brittle. The actual tempering operation was still waiting. Think of this as the process balancer, the heat treatment stage that removes brittleness but keeps the component hard enough to serve its purpose. This time the metal is heated to a lower temperature then allowed to cool until the ductility and workability ratio overwhelms the brittleness of the metal.

The tempered component is durable and corrosion resistant. Heat has been applied again, but it’s not the same near-melting hot thermal load that almost transformed the metal into a molten heap of smoking iron. Metal hardening is, therefore, an intensely hot, furnace-driven process. Metal tempering does again apply heat, but the thermal load is designed to transform the martensitic alloy, to cancel out the brittleness added during the hardening work. As for the metal quenching station, this is where the rapid cooling takes place, the immersion process that immediately removes the heat and locks in the desired mechanical properties.

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