Through hardening, also known as neutral hardening, is a procedure that can increase a metal alloy’s hardness and tensile strength. It is a way to make a steel alloy stronger by rapidly quenching it to increase the hardness of the material uniformly.
If you need to get the specified degree of hardness, the iron mix must have a proportion of carbon. A high amount of carbon is added to the iron mixture by through-hardening. In through hardening procedure, the carbon is spread uniformly across the steel.
Through hardening describes the result of the component being toughened during the heat treatment from the surface to the core.
Components made of through-hardened steel are relatively brittle. So, they have the potential to crack or shatter if they are subjected to stress loads or impacts.
Standard Temperatures – Heating Time Required for Through Hardening
Standard operating standards suggest you choose the alloy that provides the most value for money while consistently delivering the essential characteristics.
| Thickness (inch) | Thickness (mm) | Time in Furnace (min) |
|---|---|---|
| 1/4 | 6.35 | 2 |
| 1/2 | 12.70 | 3 |
| 3/4 | 19.05 | 4 |
| 1 | 25.40 | 5 |
| 2 | 50.80 | 8 |
| 3 | 76.20 | 12 |
| 4 | 101.60 | 15 |
| 5 | 127.00 | 18 |
| 6 | 152.40 | 21 |
| 7 | 177.80 | 20 |
| 8 | 203.20 | 24 |
| 9 | 228.60 | 26 |
| 10 | 254.00 | 30 |
Steps in Through Hardening
Thorough hardening happens during the heat treatment of the steel workpiece.
STEP 1: Heating of an alloy
The steel is initially heated in ovens above its critical temperature to modify its structural characteristics. The temperature varies depending on the alloy.
STEP 2: Rapid quenching
In the second step, the material is rapidly cooled by soaking it in oil or water.
STEP 3: Reheating/ tempering
After quenching, tempering, or annealing can reduce the remaining brittleness to remove its excessive brittleness.
Through Hardening by Induction
When hardening materials with induction, it is preferable to use low power so that there is no considerable temperature difference between the inside and outside.
And then, you need to consider the power to loss ratio, which is that the total amount of power given to the task is slightly more significant than the radiation losses at the specified temperature.
It is possible to reduce the amount of electricity required to heat each workpiece by connecting a number of applicator coils to one another. The amount of power given to the task decreases as the distance between the workpiece and the applicator coil increases.
Material Selection for Through Hardening
If the steel has a significant amount of carbon, its surface can be heated, quenched, and tempered in the same way that it would be to harden the steel. Through-hardening is an excellent choice for hardening thin sections of carbon steel. But as section sizes rise, alloy steels with more significant hardening potential are required.
However, choosing an alloy that is bigger than what is necessary is not the best choice. because it enhances the alloy’s characteristics and may raise the danger of quenchable cracks.
When applied to stressed areas, martensitic structural hardening followed by sufficient tempering provides the finest possible combination of ductility and strength.
Advantages and Disadvantages of Through Hardening
- Through hardening procedures can make it difficult to achieve uniform hardness across the whole inside of a large object.
- Machine parts such as gears and cams are far better when using case hardening than through hardening. Because thermal energy distortion is reduced and the strong core of ductile material is better equipped to absorb impact energy.
- Surface hardening requires far more high-frequency currents than induction hardening.
Applications
- Thorough hardening can be used when the material requires the highest strength, durability, and hardness.
- It’s used to make gears and cams (but case hardening is a better method).
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