Why Are Stainless Steel Pipes Prone To Breakage When The Carbon Content Is High
Why is Stainless Steel Weld Fitting easy to break when the carbon content is high? For example, a shaft made of 45# steel will break after not being used for a long time. Taking samples from fractured thick parts and conducting metallographic analysis often cannot find the cause. Even if some reasons are barely found, they are not the actual causes.
In order to ensure higher strength, some stainless steel raw materials must add carbon to the stainless steel, and then iron carbides will precipitate. From an electrochemical point of view, iron carbide plays the role of a cathode and accelerates the anodic dissolution reaction around the matrix. The increase in the iron carbide fraction within the microstructure is also attributed to the low hydrogen overvoltage properties of the carbides.
The surface of steel is easy to generate and adsorb hydrogen. When hydrogen atoms penetrate into the interior of the steel, the volume fraction of hydrogen may increase, significantly reducing the hydrogen embrittlement resistance of the material.
The higher the carbon content, the hydrogen diffusion coefficient decreases and the hydrogen solubility increases. Various lattice defects such as precipitates (as trap sites for hydrogen atoms), potential, and pores are directly proportional to the carbon content. As the carbon content increases, hydrogen diffusion will be inhibited, so the hydrogen diffusion coefficient is also lower.
Since the carbon content is directly proportional to the hydrogen solubility, the greater the volume fraction of carbides as hydrogen atom traps, the smaller the hydrogen diffusion coefficient inside the steel, and the hydrogen solubility increases. The hydrogen solubility also contains information about diffusible hydrogen. Therefore, Hydrogen embrittlement susceptibility. As the carbon content increases, the diffusion coefficient of hydrogen atoms decreases and the surface hydrogen concentration increases. This is due to the decrease in hydrogen overvoltage on the steel surface.
