What is secondary quenching and why should it be tempered after quenching

For carburized parts, carburizing is followed by a process of slowly cooling to room temperature and then quenching twice. The purpose of the first quenching is to refine the core grains and eliminate the surface reticulated cementite. The quenching temperature should be higher than the core AC3 temperature.

This heating temperature is much higher than the normal quenching heating temperature of the surface layer, so the surface grain is coarse. In order to refine the grains, a second quenching is required, and the quenching temperature is above the AC1 of the surface layer, and this heating temperature does not affect the grain size of the core. The disadvantages of this method are that the process is complex, the production cycle is long, the parts are easy to deform, and the oxidation and decarburization tendency is large.

There is usually a high-temperature tempering between quenching, which is often the case in high-alloy carburized steels. There are similar quenching methods in other steels (tool steel), the purpose is to eliminate and improve the structural defects of the material, so that the material can obtain better mechanical properties (especially toughness).

Quenching: It is a process method of heating steel to a suitable temperature, keeping warm, and then cooling rapidly (usually cooling in water, oil or air) to transform supercooled austenite into martensite and bainite structure. It is generally used to improve the hardness and strength of parts, or to change their physical and chemical properties.

Secondary quenching: There is more residual austenite after quenching in steels with more carbon and alloying elements (except CO and AL), and in high-alloy steels, for example, the residual austenite after quenching of high-speed steel is as high as 25% 30%. In general alloy steels, the residual austenite is converted into f and carbide in 200 300 tempering.

However, in the quenched high-alloy steel at 500 600, it leads to the precipitation of carbides in A, which reduces the content of alloying elements in A, and raises the transition temperature from A to M above room temperature, so that A is transformed into M after cooling, thereby improving the hardness of steel. In high-alloy steels, the phenomenon of residual austenite turning into m when tempered and cooled is called secondary quenching. In high-speed steel and high-chromium steel, there is often a secondary tempering phenomenon.

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Some alloy steels due to the alloying elements reduce the MS point, so there are often more residues in the quenching structure of high-alloy steel, carbide precipitation during high temperature tempering, reducing the content of alloying elements and carbon in this residue, so that the MS point increases, so that the poored Remnants are transformed into martensite when tempered and cooled, often called secondary martensite, this martensite is similar to the martensite formed by supercooled austenite quenching, but its alloying element content and carbon content are lower than the martensite directly formed when supercooled austenite quenching. Due to the formation of secondary martensitic, the hardness of steel parts is increased, so it is often called the secondary quenching hardening mechanism. View the original post

Grinding high temperature, due to untimely cooling, the ferrule grinding surface is instantly heated to above the quenching temperature of the product, and then cooled rapidly, causing cracks on the surface of the product, which is different from the first normal quenching heat treatment, and the quenching generated during grinding is called the second quenching burn. View the original post

There is also an explanation that alloying elements also have an effect on the decomposition of residual austenite when there is residual austenite in the quenched steel. Sometimes, residual austenite can even be converted to pearlite or bainite when tempered. If the residual austenite does not decompose during tempering, it is likely to undergo a martensite transition due to catalytic (de-stabilization) during subsequent cooling, a phenomenon known as secondary quenching.

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The second heating quenching mainly refers to the carburizing product, which is relative to the carburizing direct quenching, carburizing a heating quenching, the first quenching after infiltration is used to eliminate the seepage layer network carbide and refine the core structure, which is higher than the second temperature (850-870 degrees), and the second quenching (810-830 degrees) is mainly to improve the seepage structure, but the core performance requirements are higher should be quenched above AC3. View the original post

Reply 1 The landlord's question is more general, and there are many kinds of secondary quenching. As we mentioned, carburizing secondary quenching, refined grain secondary quenching, and rework secondary quenching. Attention should be paid to the secondary quenching to eliminate the stress of the first quenching and prevent the occurrence of secondary quenching cracks. View the original post

Heating quenching in heating secondary quenching.

After quenching, it is necessary to temper, the purpose of which is:

1. Eliminate the residual stress generated during the quenching of the workpiece to prevent deformation and cracking;

2. Adjust the hardness, strength, plasticity and toughness of the workpiece to meet the performance requirements;

3. Stabilize the structure and size to ensure accuracy;

4. Improve and enhance processing performance.

Therefore, tempering is the last important step in the process of obtaining the required performance of the workpiece. Through the combination of quenching and tempering, the required mechanical properties can be obtained.

According to the tempering temperature range, tempering can be divided into low temperature tempering, medium temperature tempering and high temperature tempering. Will be quenched into martensite.

The steel is heated to a critical point.

A heat treatment process that is kept at a temperature below a1, kept warm for an appropriate time, and then cooled to room temperature.

The purpose of tempering is to eliminate the quenching stress and transform the microstructure of the steel into a relatively stable state. Improve the plasticity and toughness of the steel without reducing or appropriately reducing the hardness and strength of the steel to obtain the desired properties.

It is a heat treatment process in which the steel is heated to a temperature above the critical temperature AC3 (sub-eutectic steel) or AC1 (super-eutectic steel), held for a period of time to make it fully or partially austenitic, and then cooled to below ms (or isothermal near ms) at a cooling rate greater than the critical cooling rate for martensite (or bainite) transformation.

The purpose of quenching is to make the supercooled austenite undergo martensite or bainite transformation to obtain martensite or bainite structure, and then cooperate with tempering at different temperatures to greatly improve the rigidity, hardness, wear resistance, fatigue strength and toughness of steel, so as to meet the different requirements of various mechanical parts and tools. It can also meet the special physical and chemical properties of some special steels such as ferromagnetism and corrosion resistance through quenching.

When the steel is heated to a certain temperature, the internal structure of the steel is rapidly cooled to obtain a more rigid form.

In the past, when striking iron, the iron was burned red (900 or so) and inserted into the pool to cool, and then the process (forging, quenching) was repeated, as if the red iron was "dipped in" in water, so the word in the industry was pronounced as dipping fire.

What does normalizing, annealing, quenching, and tempering mean? Have you figured it all out?

Quenching is a heat treatment process that heats the steel to a certain temperature, so that the internal structure of the steel is quickly cooled to obtain a more hardness form When the iron is struck before, the iron is burned red (up and down 900) and inserted into the pool for cooling, and then the process is repeated (forging, quenching), just like the red iron is "dipped in" in water, so the word industry is pronounced as dipping fire.

Quenching, a heat treatment process for metal and glass. The quenching of steel is a heat treatment process in which the steel is heated to a temperature above the critical temperature AC3 (sub-eutectic steel) or AC1 (super-eutectic steel), kept warm for a period of time to make all or part of the austenite 1, and then cooled to below ms (or isothermal near ms) at a cooling rate greater than the critical cooling rate for martensite (or bainite) transformation.

Solution treatment of materials such as aluminum alloys, copper alloys, titanium alloys, tempered glass, etc., or heat treatment processes with a rapid cooling process are usually referred to as quenching.

Quenching is a heat treatment process method that heats the steel above the critical temperature, keeps it warm for a certain time, and then cools it at a temperature greater than the critical cooling rate, so as to obtain an unbalanced structure dominated by martensite (bainite or single-phase austenite is also obtained as needed). Quenching is the most widely used process method in steel heat treatment process.

There are four basic processes for steel heat treatment: annealing, normalizing, quenching and tempering.

Annealing heats the workpiece to the appropriate temperature, adopts different holding times according to the material and the size of the workpiece, and then undergoes slow cooling (the slowest cooling rate) in order to make the internal structure of the metal reach or close to equilibrium, obtain good process properties and usability, or prepare the structure for further quenching.

Normalizing heats the workpiece to a suitable temperature and then cools it in the air, the effect of normalizing is similar to annealing, but the resulting structure is finer, often used to improve the cutting performance of the material, and sometimes used for some parts with low requirements as the final heat treatment.

In order to reduce the brittleness of the steel, the quenched steel is kept warm for a long time at an appropriate temperature higher than room temperature and lower than 710, and then cooled, which is called tempering.

A heat treatment process in which quenched workpieces are heated to austenitization and then cooled in an appropriate way to obtain a martensitic or bainite structure. The most common ones are water-cooled quenching, oil-cooled quenching, air-cooled quenching, etc.

Annealing, normalizing, quenching and tempering are the "four fires" in the overall heat treatment, in which quenching and tempering are closely related, often used together, and one is indispensable.

Quenching and tempering are both heat treatment processes, their roles are different, and their principles are more professional, in popular language, that is: quenching is to make the workpiece hard, annealing is to make the workpiece soft, and tempering is to make the workpiece soft and hard.

The above inaccuracies are only approximate meanings, and are actually much more complicated, and are only for the sake of a simple explanation.

Quenching is to burn the iron with rigidity red, and then quench it with oil (generally waste engine oil) or water to make it harder, and tempering is also called annealing, that is, the hard steel parts are burned with fire and buried in quicklime, which is annealing!

Some friends with strong hands-on ability are interested in steel, but we often hear some very professional terms when buying or using steel. For example, what is the difference between quenching and tempering? In fact, quenching and tempering are two steps in the forging process of steel, generally speaking, it is first quenched and then tempered, quenching is to heat the steel to above the critical temperature, and then cool rapidly, which can effectively increase the hardness of the steel.

And this makes the steel too brittle, so there is tempering, that is, heating the steel again to about 200 degrees to make it flexible.

What does normalizing, annealing, quenching, and tempering mean? Have you figured it all out?

Secondary quenching: refers to the fact that there is more residual austenite after quenching in steel with more carbon alloying elements (except CO and AL), and in high-alloy steel, for example, the residual austenite after quenching of high-speed steel is as high as 25% to 30%. In general alloy steels, residual austenite is converted into f (ferrite) and carbide in 200 300 tempering.

In addition, the essence of the secondary quenching is that the residual austenite is not decomposed into pearlite or bainite after tempering and martensite transformation, because the residual austenite content is usually not high, so it will not significantly increase the hardness of the material, but will greatly increase the brittleness of the material, and should be followed by a tempering to reduce the brittleness.