Insulation furnace preparation of high melting point alloy semi-solid melt

A key issue in the semi-solid forming of high melting point metals is the preparation of semi-solid melts. For a long time, the preparation of semi-solid melt by electromagnetic stirring method has dominated the actual metal semi-solid forming application, but its process is complicated, equipment investment is large, efficiency is low, and cost is high. The near liquidus insulation method is a simple, feasible and low cost method. The aluminum alloy is cast in the vicinity of the liquidus for 30 minutes and then cast to obtain the ideal semi-solid billet 11~51. The outstanding disadvantage of this method is long holding time and low production efficiency.

For the first time, the liquid phase insulation method was applied to the preparation of semi-solid melt of cast steel. The water-quenched structure and air-cooled structure of ZG25MnCNMo low alloy steel melt under different holding temperature and different holding time in medium frequency induction furnace were studied. The results show that the method is simple and feasible, and the effect in the near liquidus insulation is remarkable. However, the influence law of the holding time is different, and the short-term (5 min) heat preservation can obtain better effects, so that the problem of low production efficiency can be solved.

1 Test process The test material is ZG25MnCNMo, which is the main type of low-alloy cast steel for rolling stock. The material can reach the mechanical properties of C grade steel and E grade steel in the American AAR cast steel standard by normalizing + tempering and quenching + tempering heat treatment respectively. The chemical composition is shown in the table: 1. The liquidus temperature of the material is determined by differential thermal analysis (DTA) to be 1510 ° C. The test uses an alkaline medium frequency induction furnace to oxidize the charge without oxidation. Using the bare head platinum iridium 30 platinum 铑6 thermocouple directly continuous temperature measurement 61, the thermal balance error is 0.36, the temperature response time is less than 01s temperature measurement principle, the self-developed temperature control cabinet can control heating, cooling and heat preservation according to preset parameters, temperature control Accuracy is ±1 ° C. Sampling is performed with a quartz tube aspirator.

The remaining amount (a) thermocouple installation partial top view (b) temperature measurement node enlarged view temperature measurement. Temperature measuring hole 2 Temperature measuring end Heat transfer section 3坩埚4 Filling material 5 Temperature display instrument 6. Thermocouple wire 7. Inductive line 8 Thermocouple temperature measuring node 5201535°C respectively keep warm, change the holding temperature, to eliminate the last insulation The effect is to first heat the molten steel to 1600 ° C and then cool to the next holding temperature. Two samples were taken in sequence at 1, 515, 3050 min during the heat preservation process, one water quenching and the other air cooling. In addition, water quenching and air cooling were also sampled after holding at 1580 ° C for 30 min at ordinary casting temperature.

All samples were coarsely ground, finely ground, and polished, and etched with a 2% by volume nitric acid solution, observed on an XXI optical microscope, and photographed with a metallographic photograph.

Fund Project: Major Project of the “10th Five-Year Plan” of Northern Jiaotong University (230-12) First: Zhang Lizhong, male, born in 1961, Ph.D., Associate Professor, School of Mechanical and Electronic Control Engineering, Beijing Jiaotong University, Beijing (1(1)044), telephone E-maU1 Zhang Zhenshan, Chai Tianyou. Secondary cooling control of Fugang steel alloy billet continuous casting machine. Control Theory and 2 Guo Yi, Qiao Junfei, Wang Wei. A cascade control method for the continuous casting process. China Nonferrous Metals 3 Chen Qinghai. Numerical simulation of the solidification process of castings. Chongqing: Chongqing University Press, 19914 Li Donghui, Bai Jinlan, Qiu Yiqing, et al. Research on on-line control method of billet continuous casting secondary cold water based on heat transfer theory. Special casting and non-ferrous alloy, 2 (1) 525 (2) 92955 Liu Qing. On-line control of secondary cooling of rectangular billet continuous casting machine. Metallurgical Automation, 1997 (Editor: Zhang Zhenghe) 2 Test results 1 The different crystallizing temperature of the tissue nCNMo solidification occurs when the peritectic reaction, the liquid phase first precipitated e, further cooling, the melt reached the peritectic reaction temperature, rape and part of the residual The liquid phase undergoes a peritectic reaction to transform into austenite. Cooling continues and the remaining liquid phase is also transformed into austenite. Both the water quenching and air cooling samples undergo the above process, except that the cooling strength is different. After the two samples are transformed into austenite, they are transformed into different tissues at different cooling rates. It can be seen from the continuous cooling transition curve of ZG23MnCNMo that the water quenching sample enters the martensite transformation zone after undergoing a bainite transformation zone, that is, the martensite transformation occurs after the austenite transforms a small amount of bainite along the grain boundary. Under the optical microscope, the water-quenched structure is a small amount of white bainite surrounding the black block-like lath martensite, and the white bainite can be regarded as the prior austenite grain boundary. The austenite in the air-cooled sample first precipitates ferrite along the grain boundary and then undergoes eutectoid pearlite transformation. Under the optical microscope, the structure is white ferrite surrounding the black pearlite.

Sample tissue. The ferrite in the sample is in the form of coarse clusters and coarse needles. It is a typical Wei's body structure. The pearlite is surrounded by ferrite, and many needle-like ferrites protrude into the pearlite. The morphology of the ferrite and pearlite of the two samples is not much different, but the air-cooled structure of the ferrite and the beads at the different holding temperature of the sample after 1 508 °C is the water-quenched structure after being kept at 14951508152015351580C for 30 min. The equivalent average grain diameters at different temperatures were 143, 85156 171, 244/% i. Due to the different cooling rates, two different water quenching structures were formed. The water-quenched structure below 1 530C has bainite surrounding the martensite in a line shape, and the prior austenite grain boundary is clear. The closer the holding temperature is to the liquidus, the smaller the crystallites and the more uniform (see ab, c). After quenching at 1530C or above, the water-quenched structure is bainite distributed around the martensite, and the prior austenite grain boundaries are not clear. The higher the holding temperature, the larger the austenite grain size and the more uneven it is. (The water-quenched structure of d temperature is significantly different from the water-quenched structure after heat preservation. The former has an equivalent grain diameter of 253/%!, while the latter After 1~50 min of heat preservation, it is not more than 120 Zm, and its grain size and morphology change are not large. The effects of short-time heat preservation and long-term heat preservation are equivalent.

3 Analysis and discussion 1 Heterogeneous nucleation and transient nucleation In the actual liquid alloy, due to the presence of metal or non-metallic impurity atoms, the probability of aggregation of homogeneous or heterogeneous atoms is increased, and there is a sharper than pure liquid metal. More structural fluctuations and energy fluctuations. When the size of the heterogeneous body is between 1 and 0 nm, stable atomic clusters are formed in the alloy melt, which are called quasi-solid phase clusters, which have similar spatial lattice structure to the crystal nucleus and are close to solid state in physical properties. The crystal, when below the liquidus temperature, acts as a solid phase substrate for the heterogeneous nucleation.

The nucleus is in a transient under a small subcooling slightly below the liquidus temperature

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Rotary Rings

Rotary Rings are a type of rotating seal widely used in various rotating equipment, such as rotary joints, rotary couplings, rotary connectors, etc. Its main function is to prevent liquid or gas leakage and maintain the normal operation of the equipment. In different applications, the material, structure, sealing method, size, etc. of Rotary Rings vary to adapt to different working conditions.