Carbide vacuum brazing

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For the development and application of cemented carbide, quality is becoming more and more important, but in the process of vacuum welding in some manufacturers, some problems often occur, such as cracks. The root cause of vacuum brazing cracks is that the tensile stress generated during the vacuum brazing process exceeds the tensile strength of the cemented carbide, and sometimes also occurs in the matrix. We can find that there are five ways to generate tensile stress: tool structure, thermal stress, difference in mechanical properties, subsequent processing and so on.

1.Cracks caused by tool structure

The additional tensile stress caused by the unreasonable structural design of the tool is an important factor causing cracks. Among them, the closed or semi-closed brazing seam is the main reason for increasing the brazing stress and causing cracks. Designers should master the following principles: that is, under the premise of satisfying the strength of the brazing seam required for use, the brazing surface and brazing area should be reduced as much as possible. When designers design tools, the first thing to check is the strength of the brazing seam. In order to improve the connection strength, the brazing surface or brazing area is often simply increased, and the brazing stress caused by increasing the brazing area is ignored, resulting in the root cause of the crack is not in the vacuum brazing process, and it is difficult to rely on the vacuum brazing process to avoid such Cracks occur.

2.Cracks caused by thermal stress

The main cause of cemented carbide cracks caused by thermal stress is too fast heating rate of vacuum brazing or severe cooling after vacuum brazing. Brazing processes such as flame brazing, resistance brazing, and high-frequency induction welding can easily lead to excessive heating and rapid heating of brazing. When the oxygen acetylene flame is heated, the high temperature zone of the flame can reach 3000 ° C. When the flame directly burns the cemented carbide, the surface or local temperature of the cemented carbide is heated too fast, and sometimes even the corners of the cemented carbide are burned, and the hard alloy is heated. Cracks will be induced when the alloy size is large. During high-frequency brazing, the sharp angle effect, skin effect and hoop effect of the induced current cause the local heating of the cemented carbide to be too fast and too high to cause cracks. After brazing, cracks are caused by severe cold in the following situations: After brazing, put the tool on the wet ground or in a wet lime tank, after brazing, the tool is blown by cold air; after brazing , because the tool needs to be quenched and the severe cooling occurs. In general, for YT30, YT15 and large-area brazed cemented carbide tools, it is not suitable to perform overall quenching after brazing. Grasp the appropriate method to use the BYAT automatic induction brazing method to avoid cracks.

3.Cracking caused by differences in mechanical properties

Cemented carbides of YT60, YT30, YW2, YG2, YG3X and other grades are prone to cracks during brazing due to poor impact toughness. Cemented carbides with larger geometries are more prone to cracking during brazing due to stress build-up. The defects of the cemented carbide itself during the sintering process, such as internal cracks, chipping, looseness, etc., will expand after heating and brazing to form large cracks. In general, the cemented carbide must be strictly inspected batch by batch before brazing. Cemented carbides with poor impact toughness should be heated and cooled slowly.

Equipment selection: The RHVB-H vacuum brazing furnace provided by SIMUWU is an excellent product for handling this kind of process. It has the characteristics of good temperature uniformity and high temperature control accuracy. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process and are committed to giving customers the most convenient and efficient experience.