HEAT TREATING SERVICES
The mechanical properties (strength, toughness, and ductility) of steel and many other alloys are derived in part by their thermal history. Two steels with identical chemistry but different heat treatments can have radically different performance. At AIHT, we use the fundamentals of material science to tailor mechanical properties for specific customer applications through custom heat treatments.
AIHT HEAT TREATMENTS
INTEGRAL QUENCH (IQ) FURNACE
A high-temperature furnace with automated temperature and material handling control. fdfdf
• Working envelope: 44”L x 26” W x12”H
• Weight capacity: 800lbs per load
• Temperature range: Up to 1800F (980C)
• Quenching (Austenitizing)
• Quenching – Oil/Water
Two temper furnaces with industry-standard temperature control and monitoring capabilities.
– Working envelope: 57”L x 40”W x 30”H
– Temperature range: Up to 1350F (730C)
– Working envelope: 57”L x 26”W x 24”H
– Temperature range: Up to 1350F (730C)
• Water quench available
• Precipitation/ Age Hardening
• Bake Outs/ Stress Relief
• Working Envelope: 12”L x 12”W x 12”H
• Temperature Range: up to 2000°F (1090°C)
• Specialty alloy heat treatments such as tool steels (A2, D2, S7, O1, H13)
• Inert atmosphere heat treatments
Standard Heat Treatment Services
QUENCH AND TEMPER (Q&T)
Quench and Temper (Q&T) is a heat treatment method that can increase the strength and hardness of a material. The first step is to “reset” the microstructure by heating above a threshold temperature (also called austenitizing). Subsequent cooling from this threshold temperature transforms the microstructure of the material. The rate of cooling is directly related to the resulting strength and toughness properties. Rapid cooling or “quenching” is typically done in water or oil to achieve the high cooling rates for maximum hardness and strength or to harden thick sections. As-quenched steels have the highest strength but are also the most brittle. The extremely fast change in temperatures during quenching can cause distortion or cracking and is not recommended for finished parts or susceptible geometries.
Subsequent tempering can restore toughness and ductility to the as-quenched material. Tempering involves reheating the quenched microstructure to a temperature below the threshold for a length of time. Both the temperature and hold time determine the resulting toughness; however, the material experiences a corresponding drop in strength. Q&T steels are typically able to achieve an excellent combination of strength and toughness.
The Q&T process can be tailored to achieve a wide range of properties from a starting chemistry to meet specific design requirements. While most materials can be quenched and tempered to a degree, the starting chemistry dictates the range of achievable properties. Plain carbon steels like 1018 are not hardenable to the same extent as alloy steels such as 4140, 4145, or 4330V.“
PRECIPITATION HARDENING & SOLUTION ANNEALING
Some steels (such as 17-4 PH) become stronger after being held at a specific temperature for enough time to form secondary phases called “precipitates”. The rate at which precipitates form and grow can be adjusted with treatment temperature and holding time. This process of modifying the microstructure through precipitation treatment is called aging. If a material has been aged for too long (overaged), it’s microstructure must be “reset” by solution annealing. The balance of strength and ductility can be altered in these alloys to achieve a wide range of possible combinations.
In solution annealing, a component is heated to austenitizing temperatures and held there until all precipitates dissolve before quenching. This treatment erases all of the previous heat treatment history and uniformly distributes all alloying elements. Solution annealing is typically a precursor to a precipitation hardening. This treatment can cause distortion and is not recommended for finish parts.
Steels (and other iron alloys) can build up residual internal stresses following manufacturing processes like casting, forming, machining or welding. If the residual stress level is greater than the yield strength of the steel, it can cause permanent distortion during finish machining, especially on thin-walled components. Internal stresses can be relaxed by heating the component to elevated temperatures (typically in the range of 600-650°C) and holding for sufficient time followed by subsequent controlled cooling to prevent the formation of new residual stresses.
NORMALIZING & FULL ANNEALING
The mechanical properties of steel are in large part influenced by its thermal and processing history. Sometimes this can pose issues, and properties must be “reset” to allow for further processing. Normalizing resets and homogenizes a microstructure and composition, improving uniformity from previous treatments such as casting, rolling, or forging. Oftentimes normalizing is done as an intermediate processing step to improve the machinability before final heat treatment. The mechanical properties of normalized steels, in general, will fall between fully annealed (soft and ductile) and Q&T (balanced strength and toughness) treatment results.
Normalizing involves heating above the threshold transformation temperature (or austenitizing temperature), achieving a uniform temperature distribution through the material thickness, followed by cooling in still or forced air. The specific cooling rate for normalizing varies based on the chemistry and hardenability of the steel. Full annealing is a similar process but uses slower cooling rates (furnace cool) to create the softest, most ductile form of steel.
Components are heated in order to release hydrogen from the internal microstructure of the steel and decrease the risk of hydrogen-induced cracking.
This is commonly done prior to welding, particularly for components which have been in-service and have absorbed a significant amount of dissolved hydrogen.