Bolt heat treatment method

Bolt processing technology: hot-rolled rod – (cold dial) – ball (softening) annealing – mechanical descaling – pickling – cold dial – cold forging – thread processing – heat treatment – a test, the design of steel fasteners Manufacturing, the correct choice of fastener material is an important part, because the performance of fasteners and materials are closely related. Such as improper selection of materials or incorrect, may result in performance requirements, shortened life expectancy, or even accidents or processing difficulties, high manufacturing costs, the choice of fastener materials is a very important part. Cold heading steel is the use of cold heading forming process of high interchangeability of fasteners steel. Because it is the use of metal plastic processing molding at room temperature, the deformation of each part is large, the deformation rate is also high, therefore, the performance of cold heading steel material requirements are very strict. On the basis of long-term production practice and user research, combined with GB / T6478-2001 Technical Requirements for Steel for Cold Heading and Cold Extrusion GB / T699-1999 “High-quality Carbon Structural Steel” and Target JISG3507-1991 “Cold Heading Steel with carbon steel wire rod “feature to 8.8, 9.8 bolt material requirements, for example, the determination of various chemical elements. C content is too high, cold forming properties will be reduced; too low can not meet the mechanical properties of parts requirements, it is set at 0.25% -0.55%. Mn can improve the permeability of steel, but adding too much will strengthen the matrix structure and affect the cold formability; when the parts are quenched and austenite grain growth tend to promote, it is appropriate to increase on an international basis, set 0.45% -0.80%. Si can strengthen the ferrite, promote cold formability, and decrease the elongation of the material to Si of 0.30% or less. S.P. as impurity elements, their existence will segregate along grain boundaries, resulting in grain boundary embrittlement, impairing the mechanical properties of steel, should be reduced as much as possible, P less than or equal to 0.030%, S less than equal to 0.035%. B. The maximum boron content is 0.005%, because boron has a significant effect on the permeability of steel, but at the same time it can increase the brittleness of steel. Boron content is too high, the bolts, screws and studs such as the need for good overall mechanical properties of the workpiece is very unfavorable.

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