Quench and Temper Steel

Quenching and tempering strengthens iron-based alloys by heating and then rapidly cooling in water, oil, forced air or gases like nitrogen. The resulting hardness and toughness are important qualities in many applications, including file blades, tub grinder teeth and gear wheels.

But hardness alone can make steel too brittle for practical use. That’s why subsequent reheating at lower temperatures, known as tempering, is required.

Strength

Quenching and tempering are a series of heat treatments that change a steel’s internal microstructure to give it strength, toughness and hardness. To do this, the steel is subjected to extreme heat past its transformation range, then rapidly cooled (quenched) with water, oil or forced air. This is a highly precise process that involves very specific temperatures, cooling methods and substances.

Once quenched, the steel is very hard, but also brittle. It would break instantly if it were subjected to any sort of impact load. This is why the tempered process is done — it is necessary to add ductility, which is critical for certain applications.

Tempering is done by slowly heating the steel to a temperature that is lower than the quenching temperature. This allows the tetragonal martensite to diffuse out again, and the lattice distortion to partially recover [42].

In addition, tempering increases the dislocation density in both ferrite and martensite. This leads to an increase in the strength of ferrite and martensite, but decreases the hardness of tetragonal martensite. This allows for the spring steel strip steel to be able to bend or deform before it breaks, making it much more useful in a variety of applications.

Ductility

A metal’s ability to flex and bend before breaking is called ductility. It is measured by a simple test, in which the specimen is subjected to tensile stress and the moment it begins to distort or fracture is noted. The higher the ductility, the more it can be deformed before it breaks.

The quenching process improves ductility, but only up to a point. After the steel has been quenched, it needs to be tempered in order to improve its ductility further. The tempering process is carried out by heating the steel at a specific temperature for a specified period of time, before cooling it down in water, mineral oil or even forced air (primarily consisting of nitrogen).

Tempering also allows the atoms in the steel to rearrange themselves into new formations within the crystal structure, and these changes allow for slip planes to form, which means that areas packed with atoms can slide right past each other without colliding and forcing the material to fracture. This makes ductile materials much tougher and stronger than brittle ones, which can easily break under a single load.

The combination of quenching and tempering produces a metal with both high strength and ductility, ideal for applications such as gear wheels, cutting edges and earthmoving buckets, chutes and dump truck liners. Contact a Clifton specialist today to find out how this process could benefit your business.

Durability

The cooling process during quenching is highly regulated to ensure the steel reaches its desired hardness at the correct point. This is a complex and precise procedure, as it requires that the steel is heated to just below its critical temperature for a specific time and then rapidly cooled in water and force. During this period, various parameters such as heating duration, cooling method and cooling rate are monitored and measured.

As a result of the rapid cooling, the microstructure of the steel is changed and it becomes extremely hard with a high amount of martensite. A tempering process is then applied to the resulting hard and brittle steel to achieve a balance of ductility and strength. This is done by heating the steel to a specific temperature for a certain time period and then immediately cooling it again, in still air primarily consisting of Nitrogen.

This tempering process not only makes the steel less brittle, but it also increases its toughness and its ability to absorb impact energy. This makes quenched and tempered steel better able to resist stress, such as from repeated flexing of parts or impacts from heavy machinery.

Tempering also improves fatigue performance, which is a type of failure that occurs when a load is repeatedly applied and the material cannot recover from the strain. This is another reason why quenching and tempering steel is so valuable, especially for industrial applications that require a combination of hardness and ductility.

Flexibility

In some applications, the material Tinplate Sheet supplier needs to be able to bend before it fractures. This is why quenching and tempering steel provides flexibility. The high energy defects created during the process also increase the material’s hardness, which is directly related to strength.

During quenching, the steel is heated and then immediately cooled down by immersing it in water, oil or forced air (inert gas such as nitrogen). The temperature of the steel, the type of cooling medium used, and the cooling time need to be carefully monitored.

Rapid cooling prevents the microstructure from adjusting to thermodynamic equilibrium, leading to a highly stressed state of martensite. Unlike ductile austenite, pure martensite has no slip planes, making it extremely brittle.

During tempering, the defects are rearranged to relieve internal stresses and soften the steel. This process also improves the fatigue performance of the steel by reducing crack propagation, which is a common cause of failure in many industrial applications such as shafts and axles. This effect is primarily due to the fact that the rearranged defects absorb more energy and slow down the rate of crack growth during repeated stress loads. This is why the fatigue performance of quenched and tempered steel is often much higher than that of untreated materials.