Stainless Steel Allen Head Screws

The manufacturing process of Stainless Steel Allen Head Screws has a decisive impact on its performance consistency. The internal hexagonal groove of the head is usually formed by precision cold heading rather than cutting. The cold heading process keeps the metal streamlines on the edge of the groove continuous and avoids micro-cracks and stress concentration points that may be caused by cutting. According to ISO 898-1 regulations on fastener head strength, M8 hexagonal socket head screws must withstand a torque of no less than 28 Nm in the breaking torque test without notch cracking or head breakage. This value is verified through the batch sampling breaking torque test, and 95% of the batch average is used as the lower limit for factory qualification. At the same time, the grain refinement of the head material during the cold heading forming process increases the hardness. According to the ASTM E18 Rockwell hardness test, the hardness of the screw head is about HRB 95 to 105, which is about 10% higher than the screw area. This provides a material basis for the notch to maintain geometric integrity under high torque.

The attenuation or enhancement of the mechanical properties of stainless steel hexagon socket screws in extreme high or low temperature environments must be considered during the design stage. According to the ASTM E21 high-temperature tensile test method, the tensile strength of A2-70 grade stainless steel at 300 degrees Celsius is approximately 78% of the room temperature value, which is approximately 550 MPa, while the specified non-proportional extension strength is reduced to approximately 400 MPa, a decrease of approximately 25%. Therefore, when used in high-temperature drying tunnels or thermal pipe supports, the pre-tightening force needs to be reduced and corrected based on the actual operating temperature. Under working conditions from low temperatures to minus 60 degrees Celsius, according to the ASTM E23 Charpy impact test, the impact absorbed energy of austenitic stainless steel remains basically unchanged as the temperature decreases, remaining above 80 joules, and no ductile-brittle transition occurs, ensuring the connection integrity of hexagon socket screws in polar equipment or cold storage facilities. During installation, because stainless steel threads are prone to cold welding seizure when screwed in at high speed, according to the friction coefficient regulations of DIN 267 Part 27, it is recommended to apply an anti-seize agent containing copper or graphite to the threaded parts before assembly to stabilize the friction coefficient in the range of 0.10 to 0.15, thereby achieving accurate conversion of torque and preload force.

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