Quenched and Tempered Steel Strip

Quenched and tempered steel strip is stronger, tougher and more resistant to wear and abrasion than non-heat-treated carbon steel. It is also ductile and weldable.

The quenching and tempering process alters a metal’s internal grain structure, increasing its strength, hardness and ductility. Leeco stocks a number of grades of this heat-treated steel.

Hardness

Quenching and tempering transforms the brittleness of plain carbon steel strip into a hard, wear-resistant material. The strength of the steel is determined by its yield strength (the strength at which deformation becomes permanent), tensile strength and shear strength (resistance to transverse, or cutting forces). Its toughness is defined by its resistance to fracture.

To produce the desired mechanical properties, the steel undergoes a series of thermal treatments called quenching and tempering. During the quenching Quenched and tempered steel strip process, the material is rapidly cooled by immersing it in water or oil, which prevents oxidation, and forms a microstructure known as martensite that is responsible for the hardness of the steel.

The cooling rate determines the grain structure of the martensite, and therefore the hardness of the steel. A slow cooling produces a high percentage of austenitic structure, which provides a soft material with good ductility, while a very fast cooling results in a completely martensite structure that is very strong but not very ductile. Tempering reheats the martensite to lower temperatures, which reduces its hardness and restores ductility.

Strength

When equipment is subjected to severe impact and abrasion, it must be made from materials that are able to resist degradation. Quenched and tempered steel materials are able to stand up to such wear because they undergo heat treatment that alters their physical properties.

The process involves a series of heating and cooling steps that change a steel’s internal structure. It starts by heating the steel to a temperature that changes its molecular composition and ends by rapidly cooling it in water or oil.

This hardening process results in a martensite microstructure that increases strength, abrasion resistance and fatigue performance. However, this microstructure also makes the steel brittle. To improve the toughness of the material, it must be re-heated to a lower temperature and cooled slowly in air.

The result is a material that has high yield strength (the point at which deformation becomes permanent) and tensile strength, shear strength and compressive strength. This type of steel is often used in construction and manufacturing machinery and structures that are exposed to harsh environments. It is also widely used as a spring material.

Ductility

When equipment is used in harsh environments, it requires materials that are durable enough to withstand impact and stress without fracture. That is why many construction and manufacturing projects use Quenched and tempered (Q&T) steels. Tempering removes some of the brittleness that can result from heat treatment, enabling the material to absorb more damage before failure.

This is achieved by heating the material above its Hardened & Tempered Steel Strip Supplier critical point temperature and rapidly cooling it. This causes the austenite crystal structure to transform into martensite, which has a body-centered tetragonal microstructure. This distorted lattice significantly blocks dislocation movement, which improves hardness and strength but also reduces ductility.

However, the precise tempering temperatures and duration can be tuned to the specific needs of a project, creating a balance between hardness and toughness. This means that Q&T steel is ideal for a range of applications, including military, mining, quarrying and earthmoving machinery, as well as construction. It is also a common choice for equipment that has to withstand repeated impact, such as gear wheels and drill bits. The high toughness factor also makes it more resistant to wear and abrasion.

Weldability

When projects require equipment to be exposed to a lot of impact and abrasion, engineers often choose Quenched and Tempered (Q&T) steel materials. Q&T is a heat treatment process that alters the microstructure of metals and alloys by rapidly heating them to high temperatures, cooling them quickly (quenching), and then reheating them to lower temperatures before they cool again (tempering).

While steel is already strong to begin with, this heat-treating process gives it even more strength and toughness. When a steel is quenched, it’s at its hardest – but also most brittle – state.

To remedy this, a tempering process must occur. During the tempering stage, Eaton Steel thermally heats the quenched material to a temperature below its critical point for a short period of time. This produces a new microstructure known as martensite, which is both harder and softer than austenite. In fact, a recent study showed that Q&T weld joints prepared with both K-TIG and GMAW exhibited good ductility performance with no signs of hot cracking. This was demonstrated by studying the fracture surface of weld samples using FESEM imaging.

Flexibility

After the steel gets quenched to a hard state, it’s tempered to reduce some of its hardness and increase ductility. This process involves heating the metal for a set period of time at a temperature that falls between 400deg F and 1,105deg F. The metal then cools in still air rather than being quenched again.

Tempering also increases the flexibility of the steel, allowing it to bend more easily without cracking or breaking. The process is a combination of heating the strip to the right temperature for a specified length of time, then cooling it quickly in still air.

Quenching involves heating the steel, followed by immediate cooling in water comma oil and forced air (primarily composed of nitrogen). These factors get monitored during the quenching process to ensure the desired hardness results.