Defects and Prevention of Brazing Cemented Carbide
1) Causes of Cemented Carbide Brazing Cracks
There are many factors that cause cracks in carbide brazed workpieces, such as groove design, brazing process, heating process, and sharpening.
I． Some cemented carbides with high hardness and low strength, such as YT60, YT30, YG2 and YG3X, are prone to brazing cracks. Especially when the brazing area of these grades of cemented carbide is relatively large, it should be paid more attention to.
II． The closed or semi-closed groove is an important reason for increasing the brazing stress and causing cracks. The brazing area should be reduced as much as possible to reduce brazing stress while meeting the strength requirements of Hanfeng.
III． If the welding heating speed is too fast, the cooling speed after welding will cause uneven heat distribution, resulting in transient stress and cracks. During rapid heating, the outer layer of cemented carbide is under compressive stress and the middle is under tensile stress. When the allowable heating rate is exceeded, visible cracks and invisible cracks may occur inside. During rapid cooling after brazing, tensile stress develops on the outer layer, causing cracks in the alloy. Avoid placing the workpiece on wet floors or in wet lime troughs, which can cause cracks in the cemented carbide due to quenching.
IV. The cemented carbide itself has defects, which were not found during the pre-welding inspection, resulting in cracks after brazing. For large-area or special-shaped cemented carbide, strict inspection must be carried out block by block before brazing. Defects of cemented carbide in the sintering process, such as small cracks, chipping, looseness, etc., may expand to form large cracks after heating and brazing.
V. Improper sharpening after brazing will also cause cracks. For example, the material, hardness and particle size of the grinding wheel are not properly selected. Water cooling during grinding, excessive grinding allowance, and improper grinding process are also easy to cause cracks.
2) Measures to reduce brazing cracks in cemented carbide
I. Adding compensating gaskets in the weld is one of the effective measures to reduce the stress of the weld. There are many ways to add compensating gaskets in welds, such as using barbed wire, punching fillers, nickel-iron alloy gaskets, and electroplating pure iron on cemented carbide. Since the melting point of these compensators is more than 200°C higher than the melting point of the solder, the gasket is not melted during brazing and is sandwiched in the middle of the weld. When the weld is cooled, the layers of the weld between the cemented carbide and the base metal have sufficient plastic deformation, so that each part of the weld can shrink relatively freely, reducing the brazing stress. However, the addition of compensating gaskets will lead to a substantial decrease in the strength of the weld. In production practice, using low carbon steel sheet or nickel-plated iron sheet with thickness of 0.4~0.5mm as compensation gasket can achieve good results.
II. The use of double-layer cemented carbide brazing is an effective measure to prevent cracks. This method does not require special materials and is easy to popularize and use. It can eliminate brazing cracks of high hardness cemented carbide such as YT30, YT60, YG2, YG3X. It is to weld the high-strength YG8 cemented carbide as a gasket and the base, and then weld the cemented carbide with low strength and high hardness on it. The advantage is that the brazing stress is concentrated on the high-strength cemented carbide as a gasket, and the cemented carbide that is prone to cracks is welded together with YG8, and the coefficient of linear expansion is relatively close, so the stress after brazing is small, and it will not. Cracks occur. Since two layers of cemented carbide are welded together, the overall compressive strength of the cemented carbide is improved, and the service life of the tool is prolonged.
III. When using the red copper sheet as compensation gasket, although it can effectively reduce brazing stress and prevent cracks, it is necessary to use solder with a melting point lower than 850 ° C, such as L-Ag-49 silver solder, otherwise, during brazing It is easy to melt the copper sheet and lose its function. Copper itself is relatively soft and is not suitable for use under shock or heavy load and high temperature.
IV. When brazing a long and narrow carbide workpiece, in order to reduce brazing stress and prevent cracks, double-layer carbide brazing can be used, and the lower layer is made of small pieces of carbide to become Prefabricated "cracked" forms. This method is particularly effective in eliminating cracks and can be used on large carbide tools and special carbide molds.
Brazing Quality Inspection
Mainly check the quality of the brazed joint between cemented carbide and steel and whether there is crack in the cemented carbide. The normal weld should be uniform without black spots, the weld that is not filled with solder is not more than 10% of the total length of the weld, and the width of the weld should be less than 0.15mm. The brazing of the blade is skewed, and those that do not meet the requirements of the drawing should be re-soldered. The crack tendency of cemented carbide inserts can be checked by the following methods.
After the knives are sandblasted, they are first cleaned with kerosene, and then observed with the naked eye or a magnifying glass. When there is a crack on the blade, a noticeable black line will appear on the surface.
Make a solution with 65% kerosene, 30% transformer oil and 5% turpentine, add a small amount of Sudan red, soak the pre-inspection tool in the solution for about 10~15min, take it out and wash it with clean water, apply a Layer kaolin, check the surface after drying, if there are cracks on the tool, the color of the solution will be displayed on the white clay, which can be clearly seen with the naked eye.
( The above content is translated from the Chinese website Taodocs.com )
Below are a few carbide brazing products that we manufactured. We can also provide custom service according to your requirements.
Carbide Brazed Scraper Blades Carbide Brazed Tile Molds Carbide Chute Liner Plates
