Effect of strip entry temperature on the formation of interfacial layer during hot-dip galvanizing of press-hardened steel
Abstract
Strip entry temperature is one of the important factors that affect alloying reactions at the steel/coating interface. This study focuses on the influence of strip entry temperature on phase formation at the press-hardened steel (PH) substrate/coating interface in zinc baths with 0.12 wt.% and 0.2 wt.% Al content respectively. The microstructure of the interfacial layer was characterized by Scanning Electron Microscope (SEM) and Glow Discharge Optical Emission Spectrometer (GDOES). It was determined that the microstructure components of steel/coating interface are significantly influenced by the strip entry temperature within 440–480 °C. In the zinc bath with 0.12 wt.% Al, the interfacial layer consists of mainly ζ phase (FeZn13), and the size of the ζ phase increases with the strip temperature. However, the amount of ζ phases and the Al content of the interfacial layer decreases with the strip temperature. Meanwhile, in the zinc bath with 0.2 wt.% Al, a continuous inhibition layer Fe2Al5 was formed on the steel surface. The Al enrichment at the interfacial layer increased with increasing strip temperature, accompanied with which is the coarser inhibition layer morphology.
Keywords
Hot-dip galvanizing; Interface layer; Hot stamping; Press-hardened steel
High speed ball nose end milling of hardened AISI A2 tool steel with PCBN and coated carbide tools
Abstract
High speed machining (HSM) of tool steels in their hardened state is emerging as an attractive approach for the mold and die industry due to its potential for significant cost savings and productivity improvement. An experimental study was conducted to investigate the tool wear mechanism and surface integrity in high speed ball nose end milling of hardened AISI A2 tool steel using coated tungsten carbide and polycrystalline cubic boron nitride (PCBN) tools. It is found that coated carbide tools can only be used at low speed (120 m/min) while high content PCBN tools are suitable for HSM range (470 m/min). PCBN tools produce a damage free workpiece with better surface finish and less work hardening. Despite the higher tool cost, HSM with PCBN tools lead to reduction in both total cost and production time per part.
Keywords
High speed machining (HSM); PCBN; Ball nose end milling; Hardened steel;
Surface integrity; Die/mold