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What is the fatigue strength of the bimetal liner?

High temperature fatigue refers to the process of bimetallic liner plate damage to the plate fracture due to the effect of cyclic and repeatedly changing stress under high temperature. Thermal fatigue refers to that when the temperature of bimetal composite liner changes and is constrained by external forces during heating and cooling, the internal expansion and contraction deformation of the liner corresponding to itself will produce stress and damage the Jiangsu bimetal liner. When heating and cooling repeatedly and rapidly, the stress will have impact, and the stress generated will be greater than that under normal conditions. At this time, some bimetal lining plates will be brittle. This phenomenon is called thermal shock. Thermal fatigue is similar to thermal shock, but the former is mainly accompanied by large plastic strain, while the latter is mainly brittle failure. The composition and heat treatment conditions of bimetal composite liner plate have influence on high temperature fatigue strength. Especially when the carbon content increases, the high temperature fatigue strength is obviously improved, and the solution heat treatment temperature also has a significant impact. Generally speaking, ferritic bimetallic liner has good thermal fatigue performance. In the austenitic Jiangsu bimetallic liner, the grades with high silicon and good extensibility at high temperatures have good thermal fatigue properties. The smaller the thermal expansion coefficient, the smaller the strain under the same thermal cycle, the smaller the deformation resistance and the higher the fracture strength, the longer the service life. It can be said that the fatigue life of martensitic bimetallic liner 1Cr17 is longer, while the fatigue life of austenitic liner plates such as 0Cr19Ni9, 0Cr23Ni13 and 2Cr25Ni20 is shorter. In addition, castings are more likely to be damaged due to thermal fatigue than forgings. At room temperature, the 107 times fatigue strength is 1/2 of the tensile strength. Compared with the fatigue strength at high temperature, there is not much difference in the fatigue strength from room temperature to high temperature.

2021/09

What should be paid attention to when the bimetal backing plate is welded through?

The temperature control of bimetal liner involves many parameters. The excitation frequency is inversely proportional to the square root of capacitance and inductance in the excitation circuit, or is proportional to the square root of voltage and current. The excitation frequency can be changed by changing the capacitance, inductance or voltage and current in the circuit. So as to control the welding temperature. Why should the cooling process of welded junction be good? Because of the milling of the welding end face of the bimetal backing plate, how to keep the end face clean, and the cooling process and time of the weld junction, these problems may not be shown from the weld junction. However, the inherent performance of the welded junction cannot be guaranteed. Therefore, the correct and effective implementation of welding procedures and operating procedures is crucial, and is closely related to the stability of welding equipment performance and the sense of responsibility of operators. In terms of electric fusion connection, it is not enough to ensure the stability of the transmission and discharge voltage of the electric fusion plate and the accuracy of the welding time, but the preparation work before welding, such as whether the end face of the bimetal composite liner plate to be welded is clean, if there are impurities, the welding effect must be affected. If the oxide layer is scraped, not scraped or not scraped enough, it is likely to cause the failure of welding. For low carbon steel, the welding temperature shall be controlled at 1250~1480 ℃, which can meet the requirements of 3~5mm plate wall thickness penetration. In addition, the welding temperature can also be realized by adjusting the welding speed. When the input heat is insufficient, the heated weld edge cannot reach the welding temperature, and the metal structure remains solid, forming incomplete fusion or incomplete penetration; When the input heat is insufficient, the heated weld edge exceeds the welding temperature, resulting in overburning or droplet, which causes the weld to form a cavity. After the two edges of the bimetal composite liner slab are heated to the welding temperature, the common metal grains are formed under the extrusion of the extrusion roller to penetrate and crystallize each other, resulting in a solid weld. If the extrusion force is too small, the number of common crystals formed will be small. The strength of weld metal decreases and cracks will occur after being stressed; If the extrusion force is too large, the molten metal will be extruded from the weld, which will not only reduce the strength of the weld, but also produce a large number of internal and external burrs, and even cause defects such as weld overlap. Whether the assembly of the electric fusion plate and the bimetal backing plate to be welded is correct will also affect the welding quality. In addition, whether the storage conditions of the electrofusion plate before welding meet the standards and whether the cooling process after welding is proper are all factors affecting the welding quality of the bimetal backing plate.

2021/09

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