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    These problems must be paid attention to in the heat treatment of screw fasteners


      Most carbon steel screws require a heat treatmen […]


    Most carbon steel screws require a heat treatment process. After the heat treatment process, in addition to general quality inspection and control, there are some special quality inspections and controls. To build high-quality products, you need to master these points.

    First, decarburization and carburizing

    In the mass production process of heat treatment, whether it is the metallographic method or the microhardness method, it can only be a timed sampling test, because if all the measurements are taken, the time required is too long and the cost is high. Therefore, in order to judge the carbon control of the furnace, the heat treatment manufacturer can use spark detection and Rockwell hardness test as the preliminary judgment for decarburization and carburization. The spark detection is to quench the over-fired parts. On the grinder, gently grind from the surface and the inside to determine whether the surface and the core are the same. This requires the operation technician to have skilled experience and spark identification capabilities.

    The carbon steel screw also has a Rockwell hardness test on one side of the hexagonal bolt. Generally, a hexagonal plane of the quenched part is first lightly polished with a sandpaper to measure the first Rockwell hardness, and then Then grind this surface on the grinder to about 0.5MM. Rockwell hardness is measured again. If the hardness values ​​of the two are almost the same, it means that the screw fasteners are neither decarburized nor carburized. When the previous carbonity is lower than the subsequent carbon degree, the surface is off. Carbon, when the previous hardness is higher than the latter time, it indicates carburization, but in general, when the hardness difference is less than 5HRC, the decarburization or carburization of the parts is basically qualified when examined by metallographic method or microhardness method. Within the scope.