The atmosphere that causes decarburization on the surface of Q345B seamless steel tubes
is mainly oxidizing gases such as oxygen, water vapor and carbon dioxide. When these oxidizing gases come into contact with the surface of the heated steel wire, oxidation and decarburization occur at the same time; due to the greater affinity of the solid solution carbon in the iron with these gases, the carbon on the surface of the Q345B seamless steel pipe is first removed.
The above-mentioned gases are generally taken in from outside the furnace; scales, rust on the surface of Q345B seamless steel pipe and residues on the surface of the steel wire after cold drawing will also decompose after heating in the furnace and react to generate some oxidizing gas.
We can purposely control the atmosphere in the furnace to make it in a reducing state, which can effectively avoid the decarburization of the surface of Q345B seamless steel pipe. For example, controlling the ratio of carbon dioxide to carbon monoxide in the furnace, neither oxidizing nor decarburizing at the equilibrium point; oxidizing and decarbonizing when the ratio of carbon dioxide exceeds the equilibrium point; oxidizing and decarbonizing when it is below the equilibrium point . The specific value of the equilibrium point should be calculated according to the carbon content and temperature of iron. The key to solving the problem of decarburization on the surface of Q345B seamless steel pipe is the heat treatment process.