How to modify the hardness on a workpiece?

The required hardness of a workpiece could be defined by its functionality. If a harder or softer hardness on the workpiece is required, heat treatment will be helpful for modifying its specification. Typically, we use several different heat treatments below to meet the requirements:

1.) quenching

The way to increase the hardness of workpiece made of carbon steel or alloy steel is generally performed by quenching, which heats the workpiece above its critical temperature and holds it there for a period of time. After that, the workpiece has to be rapidly cooled in water, oil, or air to complete the quenching process. In that way, quenching can increase the hardness but decreases the ductility of the workpiece.

2.) tempering

Tempering is used to increase the toughness of the tooling or spring made of carbon steel or alloy steel. For parts with excess hardness or that become too hard or brittle after quenching, a subsequent tempering process can reduce the hardness and increase ductility by heating the workpiece to a temperature below its critical point and then steadily cooling it to a lower temperature

3.) annealing

Annealing is similar to tempering, which is also capable of altering the properties of a workpiece to reduce its hardness and increase its ductility. Under a proper heating temperature, the freely moving atoms of the metal workpiece can reach a more stable equilibrium state. After the heating stage, the workpiece is usually left in the oven for steadily cooling while recrystallization and grain growth are happening. For parts made of carbon steel or alloy steel, if it is a terminal or connector spare part for crimping, an annealing heat treatment might be required.

4.) case hardening

There are a lot of heat treatment methods to partially harden the workpiece. Case hardening is capable of increasing the stiffness of the outer case of carbon steel or alloy steel while keeping its core soft as before for better ductility. The hardened outer case of the workpiece can be much more durable and wear resistant. However, the hardened surface will no longer be suitable for machining. Therefore, case hardening is generally applied once the workpiece has been completed in the CNC machining process.

Vickers: F ≥ 98 N, diamond pyramid (HV)
Brinell: F = 29.421 N, ball ø 10 mm (HB)
Rockwell: F = 1,471 N, diamond cone (HRC)

1 MPa = 1 N/mm²

Vickers: F ≥ 98 N, diamond pyramid (HV)
Brinell: F = 29.421 N, ball ø 10 mm (HB)
Rockwell: F = 980 N, ball 1/16" (HRB)

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