海豚音（Dolphin sound）

海豚音（Dolphin sound） 海豚音(Dolphin sound) 1. explain the following nouns: Work hardening, reversion, recrystallization, hot working, cold working. Answer: work hardening: with the increase of plastic deformation, the strength and hardness of metal increase rapidly, and the plasticity and toughness decrease rapidly. In order to eliminate the work hardening of metal, the deformed metal is heated to a certain temperature to change its microstructure and properties. When the heating temperature is low, the activity is not atomic, then no obvious change in the metal grain size and shape, just point defects in the crystal in the disappearance of dislocation and migration changes, therefore, when the strength of the metal, the hardness and plastic mechanical properties have changed little, but the internal stress and the electrical resistivity of performance decreased significantly. This stage is the recovery stage. Recrystallization: when heated to a higher temperature, the atom also has a greater activity, so that the shape of the grain begins to change. From broken and elongated grains into new equiaxed grains. Similar to the grain shape before deformation, the lattice type is the same, and this stage is called recrystallization". Thermal processing: the metal is heated to recrystallization temperature above a certain temperature for pressure processing. Cold work: a process of pressing below the recrystallization temperature. 2. what is the cause of the work hardening? What are the advantages and disadvantages of working hardening in metal processing? Answer: with the increase of deformation, the grain is stretched gradually, until broken, sub grain so that the grains are broken into fine, deformation, grain fragmentation degree is bigger, so that the dislocation density increased significantly; at the same time with the sub grain fine grain stretched and stretched. Therefore, with the increase of deformation due to the increase of dislocation density and grain crushing, plastic deformation resistance of metal will increase rapidly, the strength and hardness increased significantly, while the plasticity and toughness of the so-called "hardening" phenomenon. The metal's work hardening phenomenon will bring difficulties to the further processing of metal, such as the steel plate will be rolled harder in the cold rolling process, so that the final rolling can not be moved. On the other hand, people can improve the strength and hardness of metals by using the work hardening phenomenon, such as cold drawn high strength steel wire, which is used to improve the strength of steel wire by the work hardening caused by cold working deformation. Work hardening is also an important factor in the realization of certain pressure processing techniques. If a cold drawn steel wire pulls through the die hole, because of the work hardening, it will not continue to deform and transfer the deformation to the part that has not been drawn through the die hole so that the steel wire can continue to form through the die hole. 3. what are the main conditions for dividing cold and hot working? Answer: mainly recrystallization temperature. In the recrystallization temperature of the following pressure processing for cold processing, resulting in work hardening phenomenon; the other is hot processing, resulting in the work hardening phenomenon is eliminated by recrystallization. 4. compared with cold processing, what are the benefits of hot metal parts? Answer: (1) through thermal processing, can make the weld metal in the casting hole state, so that the density can be improved. (2) by thermal processing, the dendrite and columnar crystal of the cast metal can be broken, thus the grain is refined and the mechanical performance is improved. (3) by thermal processing, can be cast in metal dendrite segregation and non-metallic inclusions distribution changes, making them fine along the deformation direction of elongated, heat of formation pressure processing "(streamline), fibrous tissue" the longitudinal strength, plasticity and toughness was significantly greater than the horizontal. If the hot working flow line is properly utilized, the maximum tensile stress of the flow line and the part of the workpiece can be consistent as much as possible, and the service life of the component can be improved when the flow is perpendicular to the applied shear stress or impact force. 5., why is fine grained steel high strength, plasticity and toughness? Answer: the grain boundary is hindering the movement of dislocation, and the different grain orientation, mutual restraint, also hinder the grain deformation. Therefore, the finer the grain of the metal, the greater the total area of the grain boundary, the more the number of grains of different orientations around each grain, and the greater the resistance to plastic deformation. Therefore, the finer the grain of metal, the higher the strength. At the same time, the finer the grain, the more the grain per unit volume of metal, During deformation, the same amount of deformation can be dispersed in more grains, resulting in a more uniform deformation, without causing local stress concentration, resulting in premature crack initiation and development. Therefore, plasticity, toughness and the better. 6. what is the change in the structure and properties of the metal after cold plastic deformation? Answer: the grains elongated along the deformation direction, the performance tends to be anisotropic, such as longitudinal strength and plasticity is far greater than the horizontal; the grain crushing, the dislocation density increases, hardening, namely with the increase of deformation, strength and hardness increased significantly, while the plasticity and toughness decreased; the texture of the phenomenon that is, along with the deformation of grain, not only in metal will be broken and the lattice orientation of elongated, each grain will be along the direction of deformation and rotation, rotation results in metal lattice orientation of each crystallite tends to be roughly the same, produce the phenomenon of texture; cold stress in the process due to the uneven deformation of each part the material is not uniform or grain in each part and each crystal, metal can form inside the residual stress, which is disadvantageous in general, will cause the spare parts Dimensional instability. 7. analysis the strengthening effect of work hardening on metal material A: with the development of plastic deformation, the dislocation density is increasing, so that the dislocations are moving in each other, and the dislocation entanglement is increasing, which leads to the increase of the resistance of dislocation movement and the increase of deformation resistance. In this way, the plastic deformation of the metal becomes difficult. If it continues to deform, the external force must be increased so that the strength of the metal is increased. The 8. known metal tungsten, iron, lead and tin melting point were 3380 C and 1538 C, 327 C and 232 C, calculate the minimum recrystallization temperature of these metals, and analysis of tungsten and iron at 1100 DEG C, processing of lead and tin at room temperature (20 DEG C) under various kinds of machining processing why? Answer: T =0.4T T =[0.4* melt; tungsten (3380+273)]-273=1188.2 C; iron T =[0.4* (1538+273)]-273=451.4 C T =[0.4*; Pb (327+273)]-273=-33 C; tin T =[0.4* (232+273)]-273=-71 C. T to 1188.2 DEG C for W > 1100 DEG C, so it belongs to heat processing; iron T to 451.4 degrees less than 1100 degrees Celsius, so it belongs to cold processing; lead T -33 degree less than 20 degrees Celsius, is cold processing; tin T again for -71 less than 20 degrees Celsius, which belongs to the cold processing. 9., in the manufacture of gears, sometimes by shot peening method (the upcoming metal pellet sprayed on the surface of the parts), so that the tooth surface to be strengthened. Try to analyze the reasons for strengthening. A: the high-speed metal pellet is sprayed onto the surface of the part, causing the plastic deformation of the surface layer of the workpiece, forming a work hardening layer with a certain thickness, and increasing the strength and hardness of the tooth surface. The third chapter is the alloy structure and the two state diagram 1. explain the following nouns: Alloy, composition, phase, phase diagram, solid solution, intermetallic compound, mechanical mixture, dendrite segregation, specific gravity segregation, solid solution strengthening, dispersion strengthening. Answer: Alloy: a new substance with metallic properties, called alloy, formed by melting, sintering, or other methods by combining a metal element with one or several other elements. A basic, independent substance that forms an alloy, called a constituent. Phase: in metals or alloys, homogeneous components, which are of the same composition, of the same structure, and separate from those of other parts, are called phases. Phase diagram: a concise graphical representation of the crystallization process of each alloy in an alloy. Solid solution: the alloy components are mixed in different proportions, and the lattice structure of the solid phase formed by mixing is the same as that of a component of the alloy, which is a solid solution. Intermetallic compound: a new phase in which metal elements interact to form a new phase, called intermetallic. Its crystal structure is different from that of any component, and its composition is expressed by molecular formula. Mechanical mixture: the structure of an alloy consists of different phases, mechanically mixed together in different proportions, called a mechanical mixture. Dendrite segregation: in practical production, alloy cooling rate is fast and atomic diffusion is not enough, so that the solid solution alloy which is first crystallized contains more high melting point component, and later crystallization contains lower melting point component The phenomenon of inhomogeneous chemical composition in the grain is called dendrite segregation. Gravity segregation: gravity segregation is caused by the difference in density between composition and solution. If between the eutectic phase and solution density difference, is solidified under slow cooling condition, the eutectic phase will float or sink in the liquid, resulting in crystallization on the casting part of the chemical composition is not the same, produce gravity segregation. Solution strengthening: the phenomenon of increasing the strength and hardness of a metal by dissolving a solute element into a solid solution is called solid solution strengthening. Dispersion strengthening: the solid solution is the main component in the alloy, and the dispersion of intermetallic compound will improve the strength, hardness and wear resistance of the alloy. This strengthening mode is dispersion strengthening. 2. point out the main differences between the following nouns: 1) displacement solid solution and interstitial solid solution; Answer: replacement solid solution: solute atoms instead of solvent, part of the atoms on the lattice node of the solid solution is called substitutional solid solution. Interstitial solid solution: a solid solution formed by the solute atoms filled in the gap of the solvent lattice, i.e., the interstitial solid solution. 2) phase composition and tissue composition; Phase composition: the basic composition of an alloy. An independent component in the microstructure of an alloy. 3. which solid solutions do the following elements form in alpha -Fe? Si, C, N, Cr, Mn Answer: Si, Cr and Mn form substitutional solid solutions; C and N form interstitial solid solutions. 4. the strengthening principle of solid solution strengthening, processing strengthening and dispersion strengthening are expounded, and the differences between the three are explained Answer: solid solution intensification: when the solute atoms are dissolved, they cause the lattice distortion of the solvent metal, and then the resistance increases when the dislocation moves. Dispersion strengthened metal compounds have very high hardness of the alloy in order to solid solution matrix have amount of intermetallic compounds were uniformly dispersed and small, can improve the strength, hardness and wear resistance of the alloy. The strengthening of alloys by intermetallic compounds is strengthened by diffusion. Processing: by strengthening the plastic deformation to increase the dislocation density, thereby increasing the turning motion resistance, caused by the increase of plastic deformation resistance, improve the strength and hardness of alloy. Difference: solid solution strengthening and dispersion strengthening use alloy composition to strengthen alloy. Solid solution strengthening is to make dislocation movement by producing lattice distortion