Since self-tapping locking screws are required to have […]
Since self-tapping locking screws are required to have the performance of self-tapping low-carbon steel plates, they require high-hardness surfaces to achieve cutting and extrusion capabilities. At the same time, there must be sufficient heart strength and toughness to prevent distortion or twisting during work. The carburizing of this type of screw belongs to shallow carburizing. Therefore, mesh belt furnaces or continuous production lines of shaking hearth furnaces are mostly used at home and abroad.
Self-tapping locking screws, whether low-carbon steel, medium-carbon steel, or medium-carbon alloy steel, must be carburized, quenched and tempered. If the depth of the hardened layer is too shallow, the surface hardness and torsion strength are insufficient. When screwing in, the thread may deform or slip; on the contrary, if the hardened layer is too deep, it is easy to become brittle, either turning around or breaking. The sensitivity to hydrogen embrittlement is also high, and this trend is closely related to the tempering conditions and materials. The self-tapping screw has a wide range of carburizing effective hardened layer depth specified in the standard. The purpose, size, material and tempering conditions of the self-tapping screw should be considered, and the target value should be appropriately increased or decreased within the specified range.