Heat Treating Steel
Steel can be heat treated to create a variety of excellent properties and microstructures; and generally, the process of heat treating steel makes use of phase transformation during the cooling and heating stage to alter the microstructure into a solid-state.
The method of heat treating steel involves the utilization of chilling or heating (usually to extreme temperature) to attain the desired result like softening or hardening a material.
The heat treatment method includes case hardening, tempering, annealing, precipitation strengthening, quenching, and normalizing.
Steel needs heat treatment to acquire better mechanical properties like increasing elements such as strength and hardness. The hardening process is made from heat treating steel above the critical temperature, keeping this for an hour per inch of thickness.
After this, cooling is necessary and it should be fast enough to allow the material to readily transform into a stronger and harder structure before the process of tempering is done.
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Steel is generally known as an alloy of carbon and iron while other types of steel alloys feature different types of metal elements in their solution.
When heating the material higher than the necessary critical temperature, it will cause carbon, as well as other elements to get into a solid solution.
The process of quenching will freeze the microstructure, so parts are tempered to alter the microstructure to achieve the necessary hardness while simultaneously eliminating unnecessary stress.
The term hardened steel is commonly utilized for medium or high carbon steel that has undergone the process of heat treating steel before quenching and tempering.
Quenching results in the composition of metastable martensite, the fraction that is decreased to reach the desired amount during the process of tempering.
This is a common state for finished items such as machine parts and tools; in contrast, the same composition of steel in the annealed state is much softer which is greatly necessary for machining and forming.
The hardness and stability of steel are determined by the content of carbon that is present. Without carbon, the steel will not be hardened.
Heat Treatment Process
The two main processes of tempering and hardening can be divided into four main steps; a piece of carbon steel will be gradually heated until it reaches a specific temperature level which is higher than the critical temperature of the alloy.
The next step will be quenching steel which is usually done in oil or water. The quenchant depends on the kind of steel used and in general, severe quenching can eventually cause cracks on the steel; overheating before quenching may also have the same effect.
By this time, the steel has acquired the given alloy’s maximum hardness but despite this, it is also brittle. At this point, the process of tempering is commonly done to reach a more efficient balance of toughness and hardness.
The steel will then be gradually heated until the required colors appear; this is usually lower compared to the alloy’s critical point. After, the steel is re-quenched to establish the temper at the required level.
To harden steel, it should be heated until it reaches a shade of medium red or until it reaches a point where it becomes non-magnetic. The steel will then be quenched in oil, air, or water, depending on the kind of steel used.
Since the steel will be brittle, it will be tempered to lessen the brittleness and heating will be between 350°F and 1350°F. Most kinds of steel need to be tempered at a temperature of 450°F to achieve a maximum hardness that is useful.
Advantages of Heat Treating Steel
Steel parts usually require some type of heat treatment to be able to achieve the increased hardness and acquire maximum durability and strength. Through the numerous heat treatment processes, the properties of steel are altered through mechanical and physical channels.
Additionally, heat treatment can also help in the manufacturing process. When it comes to mechanical properties, this refers to the toughness and tensile strength of steel.
For extremely hardened steel like the 1095 carbon steel, this is commonly utilized in various applications such as cutting tools where extremely defined and sharp edges are maintained.
Heat treating these kinds of steel is a very critical and tedious operation to acquire the perfect performance and job that is necessary.
For those that feature hard surfaces that also have a ductile base material, these can be developed and improved also via heat treatment.
The possible uses and applications for the process of heat treatment of steel seem to be endless, and this also goes for its endless advantages.
If the increase in wear resistance and material strength is necessary, then it only means that the process of heat treating steel should be done since this is also one of the best ways to acquire maximum performance and usage out of the material.
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