1: Castability (castability): refers to the performance of metal materials that can obtain qualified castings by casting. Castability mainly includes fluidity, shrinkage and segregation. Fluidity refers to the ability of liquid metal to fill the mold. Shrinkage refers to the degree of volume shrinkage when the casting solidifies. Segregation refers to the non-uniformity of chemical composition and structure in the metal due to the difference of crystallization sequence during the cooling and solidification process.

2: Malleability: refers to the ability of metal materials to change shape without cracks during pressure processing. It includes hammer forging, rolling, stretching, extrusion and other processing in hot or cold state. The quality of malleability is mainly related to the chemical composition of metal materials.

3: Machinability (machinability, machinability): refers to the degree of difficulty for metal materials to become qualified workpieces after being cut by cutting tools. Machinability is usually measured by the surface roughness of the machined workpiece, the allowable cutting speed and the wear degree of the cutting tool. It is related to the chemical composition, mechanical properties, thermal conductivity and work hardening degree of metal materials. Generally, hardness and toughness are used to roughly judge the machinability. Generally speaking, the higher the hardness of metal materials, the more difficult it is to cut. Although the hardness is not high, the toughness is large, and cutting is also more difficult.

4: Weldability (weldability): refers to the adaptability of metal materials to welding processing. It mainly refers to the difficulty of obtaining excellent welded joints under certain welding process conditions. It includes two aspects: one is bonding performance, that is, the sensitivity of certain metal to form welding defects under certain welding process conditions; the other is service performance, that is, the applicability of certain metal welded joints to service requirements under certain welding process conditions.

5: Heat treatment

(1) Annealing: refers to the heat treatment process in which metal materials are heated to an appropriate temperature, maintained for a certain period of time, and then cooled slowly. Common annealing processes include recrystallization annealing, stress relief annealing, spheroidization annealing, complete annealing, etc. The purpose of annealing is mainly to reduce the hardness of metal materials, improve the plasticity, facilitate cutting or pressure processing, reduce residual stress, improve the homogenization of structure and composition, or prepare the structure for subsequent heat treatment.

(2) : normalizing: it refers to the heat treatment process of heating steel or steel parts to 30 ~ 50 ℃ above AC3 or ACM (upper critical point temperature of steel) and cooling them in still air after appropriate time. The purpose of normalizing is mainly to improve the mechanical properties of low carbon steel, improve machinability, refine grains, eliminate structural defects, and make structural preparations for subsequent heat treatment.

(3) : quenching: refers to the heat treatment process in which the steel parts are heated to a certain temperature above AC3 or AC1 (lower critical point temperature of steel), maintained for a certain time, and then the martensite (or bainite) structure is obtained at an appropriate cooling rate. Common quenching processes include salt bath quenching, martensite step quenching, bainite isothermal quenching, surface quenching and local quenching. The purpose of quenching is to make the steel parts obtain the required martensite structure, improve the hardness, strength and wear resistance of the workpiece, and prepare the structure for the subsequent heat treatment.

(4) Tempering: refers to the heat treatment process in which steel parts are hardened, heated to a certain temperature below AC1, held for a certain period of time, and then cooled to room temperature. Common tempering processes include low temperature tempering, medium temperature tempering, high temperature tempering and multiple tempering. Purpose of tempering: it is mainly to eliminate the stress generated during quenching of steel parts, so that the steel parts have high hardness and wear resistance, as well as the required plasticity and toughness.

(5) : quenching and tempering: refers to the composite heat treatment process of quenching and tempering steel or steel parts. The steel used for quenching and tempering treatment is called quenched and tempered steel. It generally refers to medium carbon structural steel and medium carbon alloy structural steel.

(6) : chemical heat treatment: refers to a heat treatment process in which metal or alloy workpiece is placed in an active medium at a certain temperature for heat preservation, so that one or several elements can penetrate into its surface layer to change its chemical composition, structure and performance. Common chemical heat treatment processes include carburizing, nitriding, carbonitriding, aluminizing, boriding, etc. The purpose of chemical heat treatment is mainly to improve the surface hardness, wear resistance, corrosion resistance, fatigue strength and oxidation resistance of steel parts.

(7) : solution treatment: refers to the heat treatment process of heating the alloy to the high-temperature single-phase zone and maintaining constant temperature, so that the excess phase is fully dissolved in the solid solution and then cooled rapidly to obtain the supersaturated solid solution. The purpose of solution treatment is mainly to improve the plasticity and toughness of steel and alloy and prepare for precipitation hardening treatment.

(8) Precipitation hardening (precipitation strengthening): refers to a heat treatment process in which the segregation zone of solute atoms in supersaturated solid solution and / or desolved particles are dispersed in the matrix, resulting in hardening. For example, austenitic precipitation stainless steel can obtain high strength by precipitation hardening at 400 ~ 500 ℃ or 700 ~ 800 ℃ after solution treatment or cold working.

(9) Aging treatment: refers to the heat treatment process in which the properties, shape and size of alloy workpiece change with time after solution treatment, cold plastic deformation or casting, and forging, and then placed at a higher temperature or maintained at room temperature. If the workpiece is heated to a higher temperature and aged for a long time, it is called artificial aging treatment. If the workpiece is stored at room temperature or under natural conditions for a long time, it is called natural aging treatment. The purpose of aging treatment is to eliminate the internal stress of the workpiece, stabilize the structure and size, and improve the mechanical properties.

(10) : hardenability: refers to the characteristics that determine the hardening depth and hardness distribution of steel under specified conditions. The hardenability of steel is good or bad, which is usually expressed by the depth of hardened layer. The greater the depth of the hardened layer, the better the hardenability of the steel. The hardenability of steel mainly depends on its chemical composition, especially the alloying elements and grain size that increase hardenability, heating temperature and holding time. The steel with good hardenability can obtain uniform mechanical properties for the whole section of steel parts, and the quenchant with small quenching stress can be selected to reduce deformation and cracking.

(11) : critical diameter (critical quenching diameter): the critical diameter refers to the maximum diameter when all martensite or 50% martensite structure is obtained in the center of the steel after quenching in a certain medium. The critical diameter of some steels can generally be obtained through the hardenability test in oil or water.

(12) : secondary hardening: some iron carbon alloys (such as high speed steel) must be tempered for many times before further improving their hardness. This hardening phenomenon, called secondary hardening, is caused by the precipitation of special carbides and / or the transformation of austenite into martensite or bainite.

(13) Tempering brittleness: refers to the brittleness of quenched steel tempered in some temperature range or cooled slowly from the tempering temperature through this temperature range. Tempering brittleness can be divided into the first type and the second type. The first type of tempering brittleness is also called irreversible tempering brittleness, which mainly occurs when the tempering temperature is 250 ~ 400 ℃. After the reheating brittleness disappears, the tempering in this range will be repeated and brittleness will no longer occur. The second type of tempering brittleness is also called reversible tempering brittleness, which occurs at the temperature of 400 ~ 650 ℃. When the reheating brittleness disappears, it should be cooled rapidly, and it should not stay for a long time or slow cooling in the range of 400 ~ 650 ℃, Otherwise, catalysis will occur again. The occurrence of temper brittleness is related to the alloy elements contained in the steel, such as manganese, chromium, silicon and nickel, which will produce temper brittleness, while molybdenum and tungsten have the tendency to weaken temper brittleness.

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