Reasons Why Steel is Tempered after Being Hardened

27 September 2018

Here’s a case study where a steel workpiece was hardened in a cutting-edge furnace. The process is locked in, and it has been exhaustively tested, so the repeatability factor is indisputable. The internal structure of the alloy workpiece has transformed. It’s mechanically harder, more durable and rigid than before the heat treatment action. However, at this juncture anyway, hardness isn’t enough, not if the part brittle.

Post-Quench Tempering

The heat treatment work has plainly created a hardened product, and the quenching phase has essentially set that phase change in stone. Sinking into the quench medium, the rapid cooling effect discharged a huge cloud of steam. Everything sizzled for one long minute until the hardened steel was returned to room temperature. In all honesty, that workpiece can’t just leave the facility, not yet, not until it’s tempered. Imagine the steel installed and put under load. It’s hard, but it shatters because brittleness is part of the hardening process. Therefore, right after the quenching station, the process turns to the tempering stage.

Injecting Tempering Strength

Thanks to semantic subtleties, the general populace has somehow mixed up certain words and their meanings. A hard material, for instance, resists abrasion and friction, but it can still fracture and even break apart. Tensile strength is the goal, then, with the tempering stage relieving the steel part’s quench-trapped brittleness state. The goal is not only to remove this mechanically undesirable feature, but to also add tensile strength, toughness, and an ingrained quantity of deformability.

A Stress Removing Technique

Alongside the annealing work, we temper steel as a stress elimination technique. The alloy becomes more stable and dimensionally consistent when the low-temperature tempering operation is properly conducted. Inside that crystalline structure, the carbon atoms of the steel alloy are on the move. They’re forming steel carbides and other deformation-facilitating particles inside the workpiece’s Martensite form. It’s still incredibly hard, but that feature has been offset by brittleness and stress relieving tensile strength. Pressed into service, that newly tempered steel part is as tough as it is hard, all thanks to the precision-managed application of a low-temp environment.

In olden times, Samurai swords were rolled and folded, then they were hardened by that same flame and quenched in water. But they weren’t taken into battle, not right then and there, not until they were tempered. To do otherwise would be to see the blade shatter as soon as the sword crossed paths with another weapon. No, the tempering stage, carried out by a seasoned blacksmith, made the sword tough. In heat treatment technology, the exact same principle applies, only its structural loads, not weapon edges that require the extra strength.

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