Doesn t cementite participate in the reaction when austenite is converted to martensite?

Mild steels are involved, in which the carbon is solidified in the flat octahedral martensite to cause solution strengthening.

Austenite is a kind of interstitial solid solution formed by carbon dissolving in iron, which is generally a structure at high temperatures, and its existence has a certain range of temperatures and compositions. Some quenched steels retain some of the austenite until room temperature, and this austenite is called residual austenite. In addition to carbon, other alloying elements in alloy steels can also be dissolved in austenite, and the temperature and composition range of the austenite stabilization zone can be expanded or reduced.

For example, the addition of manganese and nickel reduces the critical transition temperature of austenite below room temperature, allowing the steel to maintain its austenitic structure at room temperature, the so-called austenitic steel.

Ferrite is formed by pre-eutectic precipitation of austenite of sub-eutectic components. Ferrite is also the matrix of pearlitic tissue.

Cementite is a Fe3C type carbide precipitated by iron-carbon alloy during solidification and cooling transition according to a substable equilibrium system, which is divided into primary cementite (precipitated from the liquid phase), secondary cementite (precipitated from austenite) and tertiary cementite (precipitated from ferrite).

Pearlite is a eutectic of ferrite and cementite formed by the eutectic transformation of austenite (austenite is a gap solid solution in which carbon is dissolved in Fe). It gets its name from its pearl-like luster. Its form is a layered complex with alternating layers of ferrite and cementite layers, also known as flake pearlite.

Martensite is the product of the non-diffusion colattice shear phase transition of supercooled austenite, i.e., martensite transformation.

Soxatenite, a mechanical mixture of ferrite and cementite obtained by normalizing or isothermal transformation of steel. Sostenite structure belongs to the pearlite type of tissue, but its structure is finer than the pearlite structure, its essence is a kind of pearlite, is the high-temperature transformation product of steel, is a duplex mixed structure of ferrite and cementite in the sheet, the spacing between the layers is small (30 80nm), the carbon has no supersaturation in the ferrite, is a balanced structure.

Drystingite, also known as torsite, is an extremely diffuse mixture of ferrite and cementite obtained by the austenite isothermal transition. It is the finest type of pearlite type of tissue, and its structure is thinner than that of sostenite tissue. The quenching of steel at 300 450 tempering obtained is called tempered quenched quench.

Bainite, the metastable structure formed by ferrite and the diffuse carbides distributed in it, the complex structure of -Fe and Fe3C, is transformed into a metastable structure formed by ferrite and diffuse carbides distributed in it after austenitization.

During the heating of the metallic material, the original austenite structure undergoes a phase transformation into other microstructures, such as ferrite or pearlite. Reheating is a commonly used method in which the temperature and holding time are controlled to bring the material to the austenitizing temperature again, so that it can be re-austenitic in the austenitic structure.

The principle of the reheating method is based on phase change dynamics. When the material returns to near the austenitization temperature, the phase change dynamics promotes the reformation of the original austenite in the material. In the carburizing method, by controlling the diffusion of carbon during the heating process, the necessary carburizing layer can be formed and the hardness can be improved.

In the ferrite method, the ferrite phase in the material can be changed to austenite through a heating and rapid cooling process.

The advantage of the reheating method is that it can repair the microstructure of the material and restore its original properties. For example, during the quenching process, the material may be overcooled or form an undesirable structure, which can be corrected by reheating. In addition, the reheating method can also change the phase content and grain size of the material, thereby adjusting its mechanical properties and other properties.

In summary, the reheating method uses phase change kinetics to bring the material to the austenitization temperature again, so as to realize the formation of the original Okushishite structure, repair and adjust the properties of the material.

Ferrite is -Fe and the solid solution based on it, with a body-centered cubic lattice. The austenite of the sub-eutectic component is precipitated by pre-eutectic to form ferrite. This part of the ferrite is called pre-eutectic ferrite or tissue-free ferrite.

With different formation conditions, pre-eutectic ferrite has different morphologies, such as equiaxed, along crystalline, spindle-shaped, zigzag-shaped, and needle-like. Ferrite is also the matrix of pearlitic tissue. In the hot-rolled (normalized) and annealed microstructures of carbon steel and low-alloy steel, ferrite is the main constituent phase; The composition and structure of ferrite have an important impact on the process properties of the steel, and in some cases, also on the performance of the steel.

Introduction to austenite English name: austenite

Crystal structure: face-centered cubic (fcc).

Letter code: a,

Definition: A solid solution formed in Fe by carbon and various chemical elements.

Naming: Named in honor of the contribution of British metallurgist Roberts-Austin (1843 1902) to metal science.

Microscopic expression: Fe is a face-centered cubic crystal, its maximum void is, slightly less than the radius of carbon atoms, so its carbon dissolving capacity is greater than Fe, at 1148, the maximum amount of Fe dissolved carbon is, with the decrease of temperature, the carbon dissolving capacity gradually decreases, at 727 its dissolved carbon capacity is.

Performance characteristics: austenite is a solid solution with good plasticity and low strength, and has a certain toughness. It is not ferromagnetic. Therefore, one of the ways to distinguish austenitic stainless steel tools (common 18 8 type stainless steel) is to use a magnet to see if the tool is magnetic.

Cementite - Fe3C-type carbide precipitated by the solidification and cooling transition of iron-carbon alloys according to a sub-stable equilibrium system.

It is divided into primary cementite (precipitated from the liquid phase), secondary cementite (precipitated from austenite) and tertiary cementite (precipitated from ferrite).

Cementite: The crystal lattice is an orthogonal lattice, and the chemical formula is similar to that of triferrocarbide.

Tempered structure Tempered structure refers to the tempered martensite, tempered dronsterite, tempered sostenite, granular pearlite and other structures formed after tempering at the same temperature. (1) When tempering at low temperature below 250, the structure formed is called tempered martensite. The characteristics of martensitic needle-like crystals on its structure are still preserved, and the precipitated carbide has a Fe2 component called -carbide, and the composition of this carbide changes due to the different tempering temperatures, and finally transforms into cementite, which is generally called transition carbide.

The tempered martensite is deeper than the quenched martensite after corrosion by 4 nitric acid alcohol solution, and under the light microscope, the morphology is similar to that of bainite, and the -carbides precipitated in the martensite are irregularly distributed. (2) After the steel is quenched, the extremely corrosive structure formed when tempered at about 400 is called drosting, and some literature calls it tortosite. The BCT structure (body-centered cube) formed during quenching is transformed into a BCC structure with little distortion, and as a result, the acicular martensitic crystal disintegrates and transforms into an equiaxed ferrite structure through recrystallization, and the precipitated carbides are small and difficult to distinguish under the optical microscope. (3) The structure formed when the quenched steel is tempered above 600 is called söxtenite, which is characterized by the distribution of fine spherical cementite in the fully developed equiaxed ferrite.