What happens to the hardness of seamless steel pipes after annealing? Increase or decrease?

Most of the seamless steel pipes are produced by cold-drawing and hot-rolling processes. Cold-drawn seamless steel pipes are mostly produced by the combined process of cold-drawing and cold-rolling. Cold-drawn steel pipes are more accurate in size and smoother than hot-rolled steel pipes. For parts, some cold-drawn steel pipes require annealing treatment before leaving the factory, and some do not. So what is the change in the hardness of seamless steel pipes after annealing, is it greater than the hardness of unannealed steel pipes?

First of all, let's understand what the role of annealing of seamless steel pipes is. The main function of annealing is to soften the metal and strengthen its toughness, which is applied to various metal processing; Then slowly cool to obtain a heat treatment process close to the equilibrium structure. The purpose of annealing is to homogenize chemical composition, improve mechanical properties and process performance, eliminate or reduce internal stress and prepare the structure for final heat treatment of parts. After annealing the blanks of most machine parts, tools and molds, the internal stress and compositional inhomogeneity of castings, forgings and weldments can be eliminated; the mechanical properties of steel can be improved and adjusted, and the organization can be prepared for the next process. .

From the above analysis, we can see that the chemical composition of the seamless steel pipe is uniform after annealing, the metal structure is softened, and the toughness is strengthened. , but will decrease. No. 20 45#Q345B is a commonly used steel grade in seamless steel pipes. The hardness of 45# seamless steel pipes is higher, and annealing treatment is required when used as mechanical parts.