Combination of hexagon socket flat head screws with spring washers and standard flat washers

　　Strength: 10.9 Material: carbon steel, alloy steel

　　Material: medium carbon steel

　　Material description: Chemical composition C (carbon): 0.18-0.23; Si (silicon): ≤ 0.10; Mn (manganese): 0.70-1.00; P (phosphorus): ≤ 0.030; S (sulfur): ≤ 0.035; B (boron): ≥ 0.0005

　　Surface treatment: Blackening (quenching)

　　Surface treatment content: Blackening is a common method of metal heat treatment, which is to create a layer of oxide film on the metal surface to isolate air and achieve the purpose of rust prevention. When the appearance requirements are not high, blackening treatment can be used, and the surface of steel parts can be blackened, also known as bluing.

　　Risk reminder: Products with fastener performance level ≥ 10.9 may have a risk of hydrogen embrittlement during electroplating