Mechanical property requirements for subway bolts:

The impact test temperature is -50°C, with an absorbed energy of KV, min ≥ 27J. The above low-temperature impact energy requirement is primarily to meet the usage requirements of high-speed EMUs (Electric Multiple Units) in cold winter conditions.

2. For bolts, screws, and studs with "H (High) Risk Level" as specified in TB/T 3246.1-2010 for M16 and above sizes (Grade 10.9 and above), impact tests are conducted on the specified sizes and lengths of bolts, screws, and studs as required by GB/T 3098.1-2010.

The mechanical properties of bolts, screws, and studs after quenching and tempering should comply with the requirements of GB/T 3098.1-2010, specifically Grade 8.8, Grade 10.9, and Grade 12.9 bolts.

Manufacturing Requirements for Subway Bolts:

The bolts, screws, and studs for the subway have been heat treated, with the core microstructure consisting of at least 90% martensite, and neither spheroidite nor lath-shaped ferrite nor network ferrite is permitted.

2. Metro bolts, screws, and studs are cold rolled once after final heat treatment; the scale formed on the support surfaces, shanks, transition arcs of the shanks, and the blank diameters of the threads during the heat treatment process must be removed prior to the thread rolling.

3. The heads of subway bolts and screws should be formed by upsetting.

4. Surface of subway bolts, screws, and studs shall not have an accumulation layer of white phosphatizing compounds detectable by metallographic analysis; the removal of the phosphatizing accumulation layer should be done prior to heat treatment.