Heat treatment common concepts and structures

Common concepts

1. Metal: material with opaque, good metallic luster, thermal and electrical conductivity, and its electrical conductivity decreases with the increase of temperature, which is rich in ductility and ductility. A solid (that is, a crystal) in which the atoms of a metal are regularly arranged.

2. Alloy: material having metallic properties consisting of two or more metals or metals and nonmetals.

3. Phase: the component of the alloy with the same composition, structure and performance.

4. Solid solution: the atoms (compounds) of one (or several) component dissolve into the lattice of another component, while remaining the solid metal crystal of the lattice type of the other component.

5, solid solution strengthening: because solute atoms enter the gap or node of the solvent lattice, the lattice distortion, the hardness and strength of the solid solution increased, this phenomenon is called solid solution strengthening.

6. Compound: alloy components combine to form a new crystalline solid structure with metal properties.

7. Mechanical mixture: an alloy composed of two crystal structures. Although it is a two-sided crystal, it is a component with independent mechanical properties.

Common organizations

1. Ferrite: ferrite is soft and tough, and the interstitial solid solution of carbon in a-fe (iron with body centered cubic structure); In alloy steel, it is the solid solution of carbon and alloying elements in a-fe.

The solubility of carbon in a-fe is very low, and the maximum solubility of carbon at Ac1 temperature is 0.0218%. With the increase of carbon content in steel, the amount of ferrite decreases relatively, and the pearling volume increases. At this time, ferrite is like a network and a crescent.

2. Austenite: the interstitial solid solution of carbon in -fe (face-centered cubic iron). It is a high-temperature phase, which is transformed into other phases during cooling in carbon or alloy structural steels. Only after high carbon steel is quenched at high temperature can the austenite remain in the martensite gap.

3. Cementite: a stable compound (Fe3C) formed by carbon and iron, with a carbon content of 6.69%. The cementite is hard and brittle with a hardness of about 800HB. In steel, it is often distributed as network, semi - net, sheet, needle - sheet and granular.

4. Pearlite: a mechanical mixture composed of ferrite and cementite (F+Fe3C containing 0.8% carbon), which is the eutectoid transformation product of steel, and its form is that ferrite and cementite alternate with each other like fingerprints and are arranged in layers.

5. Martensite: the supersaturated solid solution of carbon (alloying element) dissolved in a-fe. It is the product of the fast cooling of the supercooled austenite in the shear mode between the Ms and Mf points.

At this time, the carbon (alloying element) has no time to spread, but just changes from the lattice (face center) of work-fe to the lattice (body center) of work-fe, and the solid solution (austenitic) of carbon in work-fe to the solid solution of carbon in -fe, so the martensitic transformation is "non-diffusion".