How does Tianjin Yuantai square tube control the decarbonization of square tube products during production?

The most effective measure currently adopted to prevent decarburization of square tube products is the addition of alloy elements. Generally, adding Sb and Sn to suppress quenching decarburization.

The same chemical composition, one of which is steel with added Sb and Sn (SbSn added steel), and the other is steel without added Sb and Sn (without SbSn steel). The surface carbon concentration of steel without SbSn is about 0.2% and the decarburization depth is about 0.3mm, while the surface carbon concentration of steel with SbSn addition is about 0.45% and the decarburization depth is about 0.1mm. The inhibitory effect of Sb and Sn on decarbonization has been confirmed, as the addition of SbSn reduces the diffusion coefficient of C and inhibits decarbonization.

Steel with added Sb and Sn increases residual stress after shot peening. To improve the fatigue characteristics of spiral springs, shot peening treatment is generally required. However, due to a significant decrease in the yield strength of the decarburized layer, the residual stress imposed on the spring by shot peening treatment is significantly reduced. The compressive residual stress in the maximum principal stress direction from the surface to a depth of 0.2mm for SbSn added steel is -600MPa to -800MPa, while the value for steel without SbSn is -300MPa to -400MPa. The compressive residual stress of SbSn added steel is about 300MPa higher than that of current spring steel. The reason is that the addition of SbSn inhibits decarbonization.