Surface Processing Technology in Improving Operational Properties of Hot-Work Tool Steel

The present study is devoted to the surface processing technology of 3Х2В8Ф hot-work tool steel and the effect on its operational properties. The surface processing included thermal-chemical treatment (TCT) and surface finishing. Boroaluminizing (joint diffusion with boron and aluminum) was chosen as a TCT method. Steel samples were covered by a treatment paste, containing boron carbide, aluminum and sodium fluoride powders. The exposure time was 2 hours and the treatment temperature 950°C and 1050°C. The surface finishing was carried out by an elbor grinding tool to coordinate grinding on a vertical milling machine. The diffusion layers with a composite structure were formed on top of the steel as a result of TCT at 1050°C. Processing at 950°C resulted in a diffusion layer formation with layered structure. The surface roughness after boroaluminizing have increased from initial Ra 1.5 μm to Ra 4 μm after 950°C TCT and to Ra 7.7 μm after 1050°C TCT. The roughness increase was due to surface reactions with air components, such as oxygen and nitrogen, as well as their penetration to the upper zones. Applying surface finishing as a final mechanical operation (FMO) resulted in roughness reduction from the above mentioned values to Ra 0.09 μm to Ra 0.43 μm, respectively. In addition, the upper redundant zone of the layer was removed with no damage done to the inner zones by means of FMO. The provided surface quality ensures sufficient operational properties of the machine parts and details made of this particular steel. Keywords— thermal-chemical treatment, boroaluminizing, composite structure, roughness, surface finishing