October 30, 2023
1. Castability (castability)
Refers to the performance of metal materials that can be cast to obtain qualified castings. Castability mainly includes fluidity, shrinkage and segregation. Fluidity refers to the ability of liquid metal to fill the casting mold. Shrinkage refers to the degree of volume shrinkage of the casting when it solidifies. Segregation refers to the inhomogeneity of the chemical composition and structure within the metal due to differences in the crystallization sequence during the cooling and solidification process of the metal.
Refers to the ability of metal materials to change shape without causing cracks during pressure processing. It includes hammer forging, rolling, drawing, extrusion and other processing in hot or cold state. The quality of forgeability is mainly related to the chemical composition of the metal material.
3. Cutting processability (machinability, machinability)
Refers to the difficulty of metal materials being cut and processed by tools to become qualified workpieces. The quality of cutting processability is often measured by the surface roughness of the workpiece after processing, the allowable cutting speed and the degree of tool wear. It is related to many factors such as the chemical composition, mechanical properties, thermal conductivity and work hardening degree of metal materials. Hardness and toughness are usually used to roughly judge the quality of cutting processability. Generally speaking, the higher the hardness of a metal material, the more difficult it is to cut. Although the hardness is not high, it has high toughness and is more difficult to cut.
4. Weldability (solderability)
Refers to the adaptability of metal materials to welding processing. Mainly refers to the difficulty of obtaining high-quality welded joints under certain welding process conditions. It includes two aspects: one is the combination performance, that is, under certain welding process conditions, a certain metal is susceptible to welding defects; the other is the use performance, that is, under certain welding process conditions, a certain metal is welded Suitability of the joint to the requirements of use.
5. Heat treatment
(1) Annealing: refers to a heat treatment process in which metal materials are heated to an appropriate temperature, maintained for a certain period of time, and then slowly cooled. Common annealing processes include: recrystallization annealing, stress relief annealing, spheroidizing annealing, complete annealing, etc. The purpose of annealing: mainly to reduce the hardness of metal materials, improve plasticity, to facilitate cutting or pressure processing, reduce residual stress, improve the uniformity of the structure and composition, or prepare the structure for subsequent heat treatment, etc.
(2) Normalizing: refers to a heat treatment process in which steel or steel parts are heated to 30 to 50°C above Ac3 or Acm (the upper critical point temperature of steel), maintained for an appropriate period of time, and then cooled in still air. The purpose of normalizing: mainly to improve the mechanical properties of low carbon steel, improve the machinability, refine the grains, eliminate structural defects, and prepare the structure for subsequent heat treatment.
(3) Quenching: refers to heating steel parts to a temperature above Ac3 or Ac1 (the lower critical point temperature of steel), maintaining it for a certain period of time, and then using an appropriate cooling rate to obtain a martensite (or bainite) structure. heat treatment process. Common quenching processes include salt bath quenching, martensitic graded quenching, bainite isothermal quenching, surface quenching and partial quenching. The purpose of quenching is to obtain the required martensitic structure of the steel parts, improve the hardness, strength and wear resistance of the workpiece, and prepare the structure for subsequent heat treatment.
(4) Tempering: refers to the heat treatment process in which steel parts are hardened, then heated to a temperature below Ac1, kept 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. The purpose of tempering: mainly to eliminate the stress generated by the steel parts during quenching, 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. 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 workpieces are placed in an active medium at a certain temperature for insulation, so that one or several elements can penetrate into its surface to change its chemical composition, structure and properties. Common chemical heat treatment processes include: carburizing, nitriding, carbonitriding, aluminizing, boronizing, etc. The purpose of chemical heat treatment: mainly to improve the hardness, wear resistance, corrosion resistance, fatigue strength and oxidation resistance of the steel surface.
(7) Solid solution treatment: refers to a heat treatment process in which the alloy is heated to a high temperature and maintained at a constant temperature in the single-phase region, so that the excess phase is fully dissolved into the solid solution and then rapidly cooled to obtain a supersaturated solid solution. The purpose of solid solution treatment: mainly to improve the plasticity and toughness of steel and alloys, to prepare for precipitation hardening treatment, etc.
(8) Precipitation hardening (precipitation strengthening): refers to a heat treatment process in which metal hardens due to the segregation of solute atoms in the supersaturated solid solution and/or the dispersion of dissolution particles in the matrix. For example, after solution treatment or cold working, austenitic precipitation stainless steel is subjected to precipitation hardening treatment at 400~500℃ or 700~800℃ to obtain high strength.
(9) Aging treatment: refers to a heat treatment process in which the alloy workpiece is placed at a higher temperature or maintained at room temperature after solid solution treatment, cold plastic deformation or casting, forging, and its properties, shape, and size change with time. If the workpiece is added the aging treatment process that heats to a higher temperature and performs aging treatment for a longer period of time is called artificial aging treatment. The aging phenomenon that occurs when the workpiece is placed at room temperature or under natural conditions for a long time 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. Good or poor hardenability of steel is often expressed by the depth of the hardenable 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 alloy elements that increase the hardenability and the grain size, heating temperature and holding time. Steel with good hardenability can achieve uniform mechanical properties across the entire cross-section of the steel, and a quenching agent with a small quenching stress on the steel can be used to reduce deformation and cracking.
(11) Critical diameter (critical quenching diameter): the critical diameter refers to the maximum diameter when the core of the steel obtains all martensite or 50% martensite structure after quenching in a certain medium. The critical diameter of some steels It can generally be obtained through hardenability tests in oil or water.
(12) Secondary hardening: Some iron-carbon alloys (such as high-speed steel) must be tempered multiple times before their hardness is further increased. This hardening phenomenon, called secondary hardening, is caused by the precipitation of special carbides and/or by participation in the transformation of austenite into martensite or bainite.
(13) Temper brittleness: refers to the embrittlement phenomenon of quenched steel that is tempered in certain temperature ranges or slowly cooled from the tempering temperature through this temperature range. Temper brittleness can be divided into the first type of temper brittleness and the second type of temper brittleness. The first type of temper brittleness is also called irreversible temper brittleness. It mainly occurs when the tempering temperature is 250 to 400°C. After the reheating brittleness disappears, repeated tempering in this range will no longer cause brittleness. The second type of tempering brittleness will no longer occur. Brittleness is also called reversible temper brittleness. It occurs at a temperature of 400 to 650°C. When the brittleness disappears after reheating, it should be cooled quickly. It cannot stay for a long time or cool slowly in the range of 400 to 650°C, otherwise the catalytic phenomenon 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 tend to produce temper brittleness, while molybdenum and tungsten tend to weaken temper brittleness.