| With the formation and development of heavy machinery industry, large forgings emerged. It occupies a crucial position in people's daily lives. The quality of large forgings, not only affect the quality of the entire facility, but also is a concentrated expression of comprehensive level of national and regional heavy machinery industry, and heat treatment as a process of large forgings is very important,, plays an important and direct role in the final quality of large forgings. Therefore, it is very urgent to study distribution of temperature field of the large forging in heat treatment process and to reveal the evolution and distribution of internal microstructure in the different regions, so that formulate a reasonable production process to exert the performance perfectly of raw materials and obtain artifacts that is meet the actual for production requirements.In this paper, the typical size of the low-pressure rotor 30Cr2Ni4 MoV steel as research subjects, research and conclusions obtained mainly are as follows:(1) Using resistance furnace at a certain speed to set the small samples were heated to a temperature and heat preservation(0.5 h, 1 h, 2 h, 4 h, 7 h, 10 h, 15 h,20 h) to set a time after the water cooled quickly after quenching to room temperature. Though analyzing the experimental data, this is what can be obtained: If other conditions are consistent except the holding time, which is the single variable, the austenite grain size of the material become larger in the way of similar parabola with the increasing time. When other conditions are consistent except the holding temperature, which become the single variable, the austenite grain size become larger in the way of index with the increasing temperature. Temperature in the heating process on the austenite grain size effect than the holdtime, play a leading role; Austenite grain established under isothermal and non-isothermal conditions grew up model.(2) Take 30Cr2Ni4 MoV steel of low pressure rotor that its size is typical types as object by using DEFORM-HT.Then study its temperature field and thermal stress generated inside of steel in the heating process, then obtained actual temperature rising curve and thermal stress curve at several key sectionalpositions of typical types low pressure rotor. The results are summarized that heating rate and holding time have an effect on the temperature discrepancy and the thermal stress. Analog Conclusion: The stepwise heating can effectively suppress the large rotor temperature difference on the surface of the core department continue to expand; The rotor thermal stress caused by temperature difference between surface and center is far less than the allowable workpiece deformation and fracture stress, so it has little effect on the quality of the rotor.(3)According to temperature field results of large-scale rotor simulated by DEFORM, obtained the actual heating process from the surface to axis at different positions through linear fit of the Origin software. Then according to the actual heating process in different locations, made experiments of small samples, that is physical simulation, obtained the distribution and evolution of the microstructure in different positions. Research and analysis obtained was:average size of austenite grain of large rotor forgings at edge is larger than the other parts of the rotor, so it can be left out of allowance. To ensure the overall rotor crystal grain uniform as much as possible, removed coarse grains area at both ends edge of the rotor after heat treatment. Despite the large temperature discrepancy of the rotor surface and the axis of the rotor was large, and overall average size of austenite grain was not large. Austenite grains of the whole rotor are within the range of 4 to Level 5.The results showed that: though slow heating speed and long incubation had less effect on the temperature discrepancy of the rotor surface and the axis, it can make austenite grains of the whole large rotors more uniform to avoid mixed crystal. |
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