Hardening And Tempering
WHAT ARE THE TREATMENTS?
Hardening and tempering of steels is performed to provide components with mechanical properties suitable for their intended service. Steels are heated to their appropriate hardening temperature (usually between 800-1050°C), held at that temperature, thereafter “quenched” (rapidly cooled at high tempertature), often in oil, water or air. This is followed by tempering (soaking at a lower temperature) which develops into final mechanical properties and relieves stress. The actual conditions used for all three steps are determined by steel composition, component size and the properties required.
Hardening and tempering are carried out in a protective environment (gaseous atmosphere) if a surface, free from scale and decarburization (carbon loss) is required (“neutral hardening”, also referred to as “clean hardening”) for the same.
WHAT ARE THE BENEFITS?
- Develops optimum combination of hardness, strength and toughness
- Savings in weight and material
- Components can be machined or formed in a soft state, then hardened and tempered to a high level of mechanical properties.
WHAT SORT OF STEELS CAN BE TREATED?
Almost all engineering steels containing over 0.3% carbon will respond to hardening and tempering. In addition to the above, bearing steel, fastener, nut, axle, machinery parts (or) moving parts made from 0.35 plain carbon steel to low alloy to high alloy medium to high carbon steel.
WHAT ARE THE LIMITATIONS?
The response of a steel component to hardening and tempering depends on steel composition, steel quality, component size and method of treatment.
Every steel has a “limiting” section size (“ruling section”) above which, full hardening cannot be achieved. A higher grade of steel will be required to ensure optimum properties are achieved in a larger section. It may be possible to harden larger components in lower-grade steels by using non-standard treatments such as faster quench rates or ‘water/brine’ or excessive hardening temperature. But it is to be noted that Ravi Metal Treatment does not use or operate under any non-standard methods.
Steels that are purchased after open treatments (e.g. `black bar`) are liable to lose some carbon from the surface layers (decarburization). Hence, decarburized layers must be fully removed via machining from all surfaces before any of the components are hardened, otherwise low hardness, excessive distortion or even cracking are highly likely to occur.
Steels that are purchased in cold-worked conditions, such as `bright bar` & machined parts, contain residual stresses. These stresses can contribute to distortion during hardening. It is recommended to get rough-machined blanks have these stresses removed, by normalizing or soft annealing before hardening, in order to reduce the risk of excessive distortion.
» Pit Type Gas Carburising Furnace.
» Shaker Hearth Furnace.
» Sealed Quench Furnace
» Pit Type Tempering Furnace
» Chamber Type Fac Tempering