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Deformation strengthening (or strain strengthening, work hardening) China auto parts suppliers Manufacturer
01 Definition
After the material yields, with the increase of the degree of deformation, the strength and hardness of the material increase, and the plasticity and toughness decrease, which is called deformation strengthening or work hardening.
02Mechanism
With the progress of plastic deformation, the density of dislocations increases continuously, so the mutual exchange of dislocations in motion is intensified. As a result, obstacles such as fixed cut orders and dislocation entanglements are generated, which increases the resistance of dislocation motion and causes deformation. The increase in resistance makes it difficult to continue plastic deformation, thereby increasing the strength of the metal
Law: The degree of deformation increases, the strength and hardness of the material increase, the plasticity and toughness decrease, and the dislocation density increases continuously. The larger the vector b is, the more significant the strengthening effect is. China auto parts suppliers Manufacturer
03 Method
Cold deformation, such as cold pressing, rolling, shot peening, etc.
04 Examples
Cold drawn wire doubles its strength.
05The practical significance of deformation strengthening (pros and cons)
(1) Profits:
① Deformation strengthening is an effective method for strengthening metals. For some materials that cannot be strengthened by heat treatment, the strength of the material can be increased by means of deformation strengthening, which can double the strength.
② It is an important factor for the processing and forming of some workpieces or semi-finished products, which makes the metal deform uniformly and makes the forming of workpieces or semi-finished products possible, such as cold-drawn steel wires and stamping of parts. China auto parts suppliers Manufacturer
③ Deformation strengthening can also improve the safety of parts or components during use. When stress concentration or overload occurs in some parts of the parts, plastic deformation occurs there, and the deformation of the overloaded parts is stopped due to work hardening, thereby improving safety. sex.
(2) Disadvantages:
① Deformation strengthening also brings troubles to the production and use of materials. Deformation increases the strength and reduces the plasticity. Continuing the deformation brings difficulties and requires more power consumption. China auto parts suppliers Manufacturer
② In order to allow the material to continue to deform, recrystallization annealing is required in the middle, so that the material can continue to deform without cracking, which increases the production cost.
- Solid solution strengthening
01 Definition
As the content of solute atoms increases, the strength and hardness of the solid solution increase, while the ductility and toughness decrease, which is called solid solution strengthening.
02Mechanism
(1) The dissolution of solute atoms distorts the lattice of the solid solution and hinders the dislocations moving on the slip plane.
(2) The Coriolis air mass formed by the segregated solute atoms on the dislocation line can pin the dislocation and increase the resistance of the dislocation movement.
(3) The segregation of solute atoms in the stacking fault region hinders the movement of extended dislocations. All factors that hinder dislocation movement and increase the resistance of dislocation movement can increase the strength. China auto parts suppliers Manufacturer
03 Rules
①In the range of solid solution solubility, the greater the mass fraction of alloying elements, the greater the strengthening effect
② The larger the size difference between the solute atoms and the solvent atoms, the more significant the strengthening effect.
③ The strengthening effect of solute elements that form interstitial solid solutions is greater than that of elements that form substitutional solid solutions
④ The greater the difference in the number of valence electrons between the solute atom and the solvent atom, the greater the strengthening effect.
04 Method
Alloying means adding alloying elements.
05 Examples
The strength of copper-nickel alloys is greater than that of copper and nickel pure metals. China auto parts suppliers Manufacturer
- Fine grain strengthening
01 Definition
As the grain size decreases, the strength and hardness of the material increase, and the ductility and toughness are also improved. This phenomenon is called fine-grain strengthening.
02 Mechanism
The principle lies in the retardation effect of grain boundaries on dislocation slip. For polycrystals, the movement of dislocations must overcome the resistance of grain boundaries. This is because the orientations of dislocations on both sides of the grain boundaries are different, so in a certain grain, the slipping dislocations cannot directly pass through the grain boundaries and enter the adjacent ones. The movement of existing dislocations in adjacent grains can be stimulated to generate slip only when a large number of dislocations are packed at the grain boundaries and the stress concentration is caused. So the finer the grains, the higher the strength of the material.
03 Rules
The finer the grain, the larger the grain boundary area. According to the Hall-Page formula picture, the smaller the average diameter d of the grain, the higher the yield strength σs of the material.
04Methods of grain refinement
①In the crystallization process, the grains can be refined by increasing the degree of subcooling, metamorphism, vibration and stirring to increase the nucleation rate; China auto parts suppliers Manufacturer
②For cold-deformed metals, the grains can be refined by controlling the degree of deformation and annealing temperature;
③ The grains can be refined by the heat treatment method of normalizing and annealing;
④ Alloying elements can be added to the steel to form a new phase to inhibit grain growth.
Fourth, the second phase strengthening
01 Definition
One or more other phases are also present in the metal matrix, and the presence of these phases increases the strength of the metal. Due to the different processes for obtaining the second phase, the second phase strengthening is divided into: ① Precipitation strengthening: the second phase is obtained by phase transformation heat treatment ② Dispersion strengthening: the second phase is obtained by powder sintering or internal oxidation.
02 Mechanism
The dislocation encounters the second phase during the movement, and needs to bypass or cut through the second phase, so the second phase hinders the movement of the dislocation and improves the strength of the material.
03 Examples
The presence of cementite in the steel increases the strength of the steel. China auto parts suppliers Manufacturer
