Case hardening vs. Induction hardening

What is the technological difference between Case Hardening and Induction Hardening?

Two methods have become established for hardening workpieces in mass production: case hardening and induction hardening. A comparison of these two methods shows their differences and the advantages of each.

Case Hardening vs. Induction Hardening – a Comparison

If one compares the two methods for hardening steel workpieces (for a general explanation of hardening see here: Hardening), then the first striking difference is the parts handling. While case hardening processes a large number of workpieces at the same time, induction hardening focuses on the individual workpiece. With induction hardening, components are hardened workpiece by workpiece. For case hardening, “batch by batch” would be a better description.

Of courses, this has an impact on the manufacturing. While case hardening relies on parts logistics to carry parts between the production line and hardening, induction hardening can be integrated directly in the production line with a suitable hardening machine (e.g. MIND series) and be part of the cycle.

Case hardening in detail

As mentioned above, case hardening is done in batches. As with induction hardening, the goal is to harden the outer layer of workpieces.

In case hardening the workpieces are hardened by carburization. The steel is heated to over 880 °C to become austenitic. Then coal is transferred into the part from a CO-emitting medium through the part’s surface. The diffusion causes the edge of the workpiece to receive more carbon, while the carbon density remains the same toward the center.

Hardening occurs after the application of carbon. Penetration of carbon is critical for the hardness and the depth hardness characteristic of the workpiece. The hardening, i.e. the hardness and the hardening depth, is defined by the carbonization depth, the receptiveness and thus the hardenability of the steel, and the quenching. The more carbon is inside an area of the workpiece, the more successful the hardening in that area.

After hardening, the workpieces are annealed (for more information about annealing please see here: Annealing) to restore some of their plasticity. The goal of any hardening process is to make the edge resistant to mechanical loads while giving the part enough elasticity to deflect external forces without damage.

There are two ways to influence the hardening depth in case hardening: One is to manipulate the heating of the workpiece, e.g. by application of special pastes that prevent heating in certain places. The other is by influencing the quenching process, e.g. by immersing only certain parts of the workpiece.  
With both methods, results are not particularly accurate and reproducible only within a relatively wide tolerance range. This is very different for induction hardening.

Induction hardening in detail

As mentioned above, each part is hardened separately with the induction hardening technology. Each part is heat treated, quenched, and annealed (if necessary) separately. (For a general description of induction hardening see here...)

In addition to integration in the production line, the great advantages of induction hardening are precise control and reproducibility of hardening results.
To achieve this, the entire hardening process from the inductor and the applied energy and frequency to quenching and annealing is specially adapted to the relevant workpiece. This yields excellent hardening results, even for workpieces with complex geometries.

Case hardening vs. Induction hardening

Which hardening method is the right one?

Which hardening process is suitable for an application depends on several factors. Both methods, case hardening and induction hardening, have advantages and downsides.

For the mass production of components in medium or large quantities however, induction hardening offers a range of benefits:

  1. With a suitable hardening machine, induction hardening can be fully integrated in the cycle of the production line and automated.
  2. Especially with induction hardening, results are reproducible, which contributes to a consistently high quality in production.
  3. This reduces unit costs considerably

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