Air from our environment has various elements that can easily react with metals and cause undesirable results. Under room temperature, the moisture, oxygen, carbon dioxide, and hydrogen that are present in the atmosphere can each cause small but varying reactions with metals. Most of the time, however, these reactions can accelerate drastically if the metals are exposed to heat or a hot environment.
One instance where metals would be subjected under heat would be their fabrication process. The colour of a polished metal that is held over a heat source can ultimately turn to blue or black as it reacts to the elements present in the atmosphere. Without any intervening processes, some types of metals would truly have worse reactions and severe property changes than the mentioned example.
Basic Principles of Vacuum Heat Treatment
Fortunately, more and more metal fabrication companies have been applying the processes of vacuum heat treatment for their works. Vacuum heat treatment is comprised of a series of processes that can prevent metals from interacting directly with reactive elements. Some of the undesirable results that vacuum heat treatment can avoid include discolouration, scale, and contamination.
To effectively remove the reactive elements, the metal product is placed in a tightly sealed heat-treating chamber. The vacuum pumping system on this chamber is guaranteed to remove most of the air that would affect the overall quality and integrity of the metal material. At the same time, in this very same chamber, the metal is heated to a suitable temperature for it to possess the desired properties. Inert gases are then used for the cooling process of the processed metal material.
Advantages of Vacuum Heat Treatment
The advantages brought by vacuum heat treatment are abundant. One great advantage of this process is that it ensures the absence of oxidation, decarbonisation, and other presence of carbon inside the metal material. The absence of these processes and elements will then allow the workpiece to be formed without unnecessary scaling or discolouration. Additionally, the very same workpiece would emerge ready for further processing and forming, all without the need to clean it again.
As for the properties of the metal material, vacuum heat treatment can significantly improve its plasticity, toughness, and fatigue strength. Improvements over the thermal efficiency of metal materials are likewise expected right after all necessary vacuum heat treatment processes are done.
Common Vacuum Heat Treating Services
Some of the most common services that are conducted for vacuum heat treatment are the following:
Other vacuum heat treating services that can be used for metal materials are normalising, solution heat treatment, and aging treatment.
Metals typically undergo various heat treatment processes to alter their overall properties and characteristics. Generally, heat treatment is a group of industrial, thermal, or metalworking processes that are utilised to change the physical or chemical properties of a material. Aside from metals, other materials like glass can also maximise the benefits of different heat treatment processes.
There are a lot of processes that are under heat treatment. Some of these processes include annealing, case hardening, carburising, precipitation, strengthening, tempering, and quenching. A wide variety of properties, such as ductility and toughness, that is found on a specific material can be easily modified by one or more of the mentioned heat treatment processes.
Heat Treatment Processes for Metals
Metals such as steels and other alloys are hugely utilised in the manufacturing industry. Their versatility, durability, and longevity have encouraged a lot of manufacturers to maximise them and fabricate them into different equipment, appliances, devices, and other products.
The fabrication of metals has been carried out through different heat treatment processes. One of the most common heat treatment processes for metals is annealing. This heat treatment process heats and slowly cools metal to eradicate stress and makes it softer. Annealing likewise modifies the structure and ductility of the metal. Precipitation hardening, on the other hand, subjects the metal at elevated temperatures to increase its yield or even high-temperature strength.
Carburising is another heat treatment process that adds carbon to the surface of the metal by heating it below the melting point and exposing it with carbon-rich elements. This process helps the metal gain a harder surface and withstand abrasion. Quenching, alternatively, is a heat treatment process that cools the metal by immersing it into water or oil. This is done to fix the whole metal structure in a solidified state.
Protective Atmosphere Normalising
Another heat treatment process or technique that can be utilised by manufacturers would be a protective atmosphere normalising. The purpose of undergoing this heat treatment process is to refine the grain size of the metal and subsequently improve the uniformity of its microstructure. This process can also enhance the overall machinability of the metal.
Protective atmosphere normalising is carried out by heating the metal under suitable temperature and subsequently still-air cooling it to eliminate the heat or thermal influence from hot rolling or forging. The metals under this process are typically heated about 37°C above the upper critical temperature, which is around 900°C. They are then held at the given temperature so that all their parts are evenly heated before cooling them in air.
Cold worked metals are expected to soften when normalised, while metals that have undergone annealing will become reinforced when subjected under this heat treatment process. The microstructure that is produced by this heat treatment process can be pearlite, pearlite in a ferrite matrix, or pearlite in a commentate matrix.
Materials that have been welded, segregated in castings, and forged can all utilise the refinements of protective atmosphere normalising, especially when it comes to their microstructure and grain size.