Bent Furnace Tube,Ethylene Cracking Tube,Centrifugal Casting Tube,Radiant Section Furnace Tube Tuopu Industry(Jiangsu) Co., Ltd. , https://www.tuopu-industry.com
The influence of metal journals has been extensively studied by researchers. However, research on the continuous cooling phase transition behavior of gear steel after austenite deformation is rarely done to ensure that the hot-rolled gear steel tube is suitable for cutting. Microstructure and hardness, study of continuous cooling phase transformation behavior and microstructure change of deformed austenite in gear steel have important practical significance. This paper studies the continuous cooling phase transition behavior and microstructure of a gear 炯 after deformation at different temperatures in the austenite recrystallization zone. The change can provide theoretical basis for the controlled rolling and controlled cooling process on site. The experimental material is gear steel, which is smelted by super-commercial electric furnace external refining vacuum degassing process. The rectangular ingot is cast, and the average size of the section is steel ingot. On the initial rolling mill, the diameter of the blank tube blank is sampled and processed on the tube blank to form a thermal simulation sample of the diameter of the knife. The main chemical composition mass fraction is the uniaxial compression experiment using the thermal simulation test machine. To, heat, and then to cool, according to the strain rate of a 'deformation, the true strain pot is heated to the deformation process sample , heat preservation, deformation at this temperature, deformation and strain rate and deformation process, the deformation of the two processes, the sample is rapidly cooled to, and then cooled to room temperature to test the deformation of austenite structure and state.
Corrosion of metallographic structure of nitric acid in the continuous cooling phase transformation of the metallurgical journal of the Journal of Metals, the addition of a grain boundary ferrite in vitro, the presence of intragranular ferrite in the austenite grains simultaneously There is a very small amount of pearlite and the medium temperature phase transition product is acicular ferrite instead of bainite. The structure is as shown in the figure, and the pro-eutectoid ferrite, pearlite and acicular ferrite appear. When the cooling rate is greatly increased, the structure of the structure is the same as that of the cooling rate. As shown in the figure, compared with the gear steel when deformed, the amount of pro-eutectoid ferrite and pearlite in the structure at this time. Significantly increased, while the medium temperature phase change product, that is, the amount of acicular ferrite is greatly reduced. When the cooling rate is high, the structure is composed of fine pro-eutectoid ferrite pearlite, as shown in the figure. The cooling rate of the ferrite-like pearlite structure is larger than that of the gear steel when it is deformed. The critical cooling rate is one. In addition, the phase transformation structure under the two deformation conditions is different from the above, the martensite in the structure. The distribution, shape, size and quantity of austenitic islands also exist The difference is that in the tissue eroded with nitric acid alcohol solution, the island is gray, as shown in the figure, the gray block phase is the island. However, in the figure, it is difficult to distinguish its shape in order to clearly show the islands in the tissue under two deformation conditions. The morphology, distribution, etc., the sample is etched with reagents. The structure is as shown in the figure. Austenite and martensite are white and bright, ferrite is gray, and pearlite is black. After the steel is deformed, the island is distributed intermittently between the bainitic ferrite slabs, as shown in the figure, or distributed in a small block between the acicular ferrite sheets. As shown in the figure, the number is small, the size is small, and the gear steel is deformed. Except that a small number of islands are distributed in small pieces between the acicular ferrite sheets, the island is basically a large block. Distributed between the pro-eutectoid ferrites, as shown in the figure, the number is larger and the size is larger. In addition, it can be seen from the figure that the gear steel is deformed, at medium cooling rate, in the tissue. The finest structure of the island is shown in the figure. As you can see, the island contains More twinned martensite indicates that the retained austenite has a higher carbon concentration after the acicular ferrite phase transition ends because the higher the carbon concentration, the lower the martensite transformation start temperature is. When the retained austenite is cooled to room temperature, when the martensite transformation occurs, the twinning is more likely to occur, and the island will contain more twinned martensites. The fully dynamic recrystallized austenite grain size decreases with the decrease of deformation temperature and the deformation rate, but it is independent of the original grain size. Therefore, the austenite grain of the gear steel during deformation is more deformed. Therefore, the austenite grain boundary area which can be used as the preferential nucleation point of the pro-eutectoid ferrite is large, and the gear steel exhibits a large flow stress when deformed.
In the acicular ferrite phase transition, the deformed austenite exhibits mechanical definiteness. The phase transformation reduces the gear steel after deformation, the austenite contains more dislocations, and the mechanical stability of austenite is also better. Therefore, due to the above reasons, after the gear steel is deformed, in the middle temperature phase transition zone, the acicular ferrite phase transition end temperature and the number of transitions are reduced, a large amount of austenite is retained, and then cooled to room temperature. During the process, part of the martensite transformation occurs to form a large number of islands with larger blocks, which are distributed between the pro-eutectoid ferrites. In addition, the number of islands in the phase-change structure of the gear steel is also fixed when the cooling rate is deformed. The influence of the cold speed is large, for example, the degree of supercooling is large, the driving force of austenite to acicular ferrite transformation is large, and the amount of austenite transformation is large, then the number of islands is small when the cooling rate When the temperature is small, the degree of subcooling is small. At this time, the austenite stays in the high temperature zone for a long time, and the carbon has sufficient time for high temperature diffusion. The precipitation of the proeutectoid ferrite and the pearlite increases. After the change, the amount of retained austenite is significantly reduced, so the final room temperature tissue The number of islands is also small. Only when the cooling rate is appropriate, for example, the number of islands is the most. Conclusion By continuous cooling phase transformation behavior and phase transformation microstructure of a gear steel after deformation at different temperatures in the austenite recrystallization zone It is found that as the deformation temperature decreases, the temperature of the phase transition of the polygonal ferrite increases, and the phase change zone shifts to the left. The critical cold velocity of the complete polygonal ferrite plus pearlite mixed structure is increased in the intermediate temperature phase transition zone. There is a mutual competition mechanism between bainite and acicular ferrite. With the decrease of deformation temperature and cooling rate, a large amount of inert grain boundary crystal ferrite is precipitated on the austenite grain boundary, occupying the austenite. The body grain boundary inhibits the formation of bainite, which is beneficial to the acicular ferrite transformation. With the decrease of deformation temperature, austenite grain boundary and crystal precipitate a large amount of pro-eutectoid ferrite, austenite Carbon enrichment reduces the driving force of acicular ferrite nucleation and growth. At the same time, intragranular ferrite introduces more dislocations due to the collision of low temperature deformation of acicular iron body. Austenitic machinery Increased stability, acicular ferrite phase transition end temperature