Changing the properties of metals by processes involves heating. It is used to harden, soften, or modify other properties of materials that have different structures at low and high temperatures.
The type of transformation depends on the temperature that the material is heated to, how fast it is heated, how long it is kept heated, what temperature it is first cooled to, and how fast it is cooled. (Hardened and quenched)
Followed by a secondary heating stage of a much lower temperature and a length of time it is held. (Tempering)
Every heat treatable material has specific temperature ranges for hardening and quenching mediums long with tempering temperatures to produce the mechanical properties or hardness’s required for the application it has been chosen.
Hardening and Tempering develops the optimum combination of hardness, strength and toughness in engineering steels. Components can be machined from soft material then hardened and tempered to achieve mechanical properties.
Most Engineering or Tool steels up to High Speed Steels and Spring Steels can be treated to deliver mechanical properties they have been chosen for. There are several differing process methods available utilizing differing furnace and techniques.
Prior to any manufacture contact your heat treater to discuss you requirement and the right process for the application.
Different grades of material utilize different heating and cooling techniques along with the size and shape of items that can be processed depends on the type of equipment operated by the heat treater. For large items, check the availability of suitably-sized facilities at an early stage.
Distortion
Distortion of hardened and tempered tools and dies can arise from a variety of factors. Many of these are outside the control of the heat treater who cannot therefore accept responsibility for its prediction or it consequences.
Complex shapes and sharp changes in section will generate stress, and hence distortion, during rapid cooling for hardening. If it is impossible to avoid such stress-raisers, select high-hardenability steel so that slower cooling rates can be utilized. The possibility of distortion can also be reduced by specifying stress relieving prior to final machining.
Cracking
Cracking usually results from factor such as:
- Poor Quality of Steels
- Defects in steel
- Decarburization – usually because of insufficient or unequal metal removal during initial machining or “black” billet.
- Poor design and material selection
- Poor post-heat-treatment practice, such as incorrect grinding or EDM
All of the following information should be included if possible. If uncertain, ask your heat treater before producing a specification:
- The process: Harden and Temper ( Double or Triple Temper )
- Material: type, grade, and the standard from which it is drawn, with drawing, composition and mill certificate where available.
- Any general standards applicable (national, international or company) that contain relevant details which must be adhered to.
- Existing condition; e.g. details of any prior heat treatment, such as hardening and tempering, solution treatment and ageing, intended to establish mechanical or other properties.
- The level of mechanical properties required. Generally a hardness range . A maximum hardness level is often requested.
- The type(s) of testing required; e.g. hardness (Vickers, Brinell), tensile etc. and any special locations for testing or the removal of samples for test pieces.
- Requirements for any special certificates or data to be provided by your heat treater.
Guidance and information is always available from our experience heat treatment professionals.
Our procedures and work instructions are fully documented under our AS 9100 and ISO 9001 quality management systems.