Upsetting method: For grade 1 bolts and screws, it can be produced by cold heading or hot forging process, and the option of cold heading or hot forging is used in the manufacturer.
For bolts and screws of class 2, 5, 5.2, 8 and 8.2 with a nominal diameter â‰¤ 3/4 in and a length â‰¤ 6 in., the screws and screws shall be produced by cold heading process, unless special agreement is made to produce by hot forging. For products with a larger nominal diameter and longer length, the choice of hot forging or cold heading is up to the manufacturer. The 5.1-stage combination screw should be produced by the cold heading process.
Thread processing methods: bolts, screws with a nominal diameter of â‰¤ 3/4 in and lengths of 2 in 5, 5.2, 8 and 8.2, and combination screws of type 5.1 shall be threaded. For bolts, screws and bolts, screws and bolts of the above grades with nominal diameter >3/4in and length >6in, the thread can be twisted, cut and ground for the thread. By.
Heat treatment and thread decarburization: Bolts, screws and studs of grades 1 and 2 do not require heat treatment. However, the 1st and 2nd grade bolts and screws produced by the cold heading process should be tempered at a temperature not lower than 470 Â°C to eliminate the stress caused by cold work hardening. The grade 4 and 8.1 studs can be machined after heat treatment, and the finished fasteners do not need to be heat treated. Bolts, screws, and screws of grade 5 and above shall be heat treated, ie quenched and tempered. The 5.1-stage combination screw should be oil quenched with a minimum tempering temperature of 340 Â°C. The minimum tempering temperature for the 5th, 5.1th bolts, screws and studs is 425 Â°C. The 8th grade bolts, screws and studs must also be oil quenched. The minimum tempering temperature is also 425 Â°C. Bolts and screws of class 8.2 shall be fully austenitized, oil quenched or water quenched, and the minimum tempering temperature is 340 Â°C.
The decarburization requirements for bolts, screws, and studs of Class 5, Class 5.1, and Class 5.2 shall comply with Class 1 of ASTM F2328 (equivalent to the requirements of Class 8.8 of ISO898-1). The decarburization requirements for Class 8, 8.1 and 8.2 shall be in accordance with Level 2 of ASTM F2328 (equivalent to the requirements of Class 10.9 in ISO 898-1).
Surface defects: For bolts, screws and studs with a nominal diameter â‰¤ 1 in, a length â‰¤ 6 in, and a performance class above 5, the surface defects shall comply with ASTM F788M. Although not mentioned in the standard, for bolts, screws and screws with a nominal diameter of >1 in and a length of >6 in, surface defects shall also be in accordance with ASTM F788/F788M. The degree of defects specified in the surface defect standard is the minimum requirement, and the actual use shall be subject to customer requirements.
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