Abstract
High current pulsed electron beam (HCPEB) has recently been developed as an effective technique of material surface modification. In this research, a self-developed HCPEB equipment (HOPE-I) was adopted to perform surface modification on quenched and tempered 40CrNiMo7 steel. A composite nanometer structure was formed on the modified surface layer, and the martensite transformation and the dissolution and fracture of cementite can be observed. After initial irradiation, the high cooling rate caused the formation of nanocrystalline on the surface. With continuous irradiation treatments, the cooling rate gradually reduced, while the carbon kept dissolving and ended with surface composition homogenization. Both competitive factors result in the evolution rule of nanometer dimensions of surface structure. After HCPEB treatment, the average size of austenite phase on the modified surface decreased from micron-sized to nanoscale. The corrosion rate decreased from 0.12 mm/a to 0.02 mm/a, showing remarkable improvement of corrosion resistance. The main factors of the improvements of corrosion resistance property are the flat, dense structured and preferred crystal orientation on the modification layer of the treated material surface.
Highlights
High-strength structural steels have been widely used in the manufacture of core mechanical components such as heavy loading shafts, large-section shafts, gas turbine cranks and gears, engines and various pump systems
After quenching and tempering heat treatment, the original microstructure of 40CrNiMo7 steel becomes tempered sorbite, and the composite microstructure of carbide pellet is generated in the matrix ferrite [7]
It can be seen from the figure that the high-temperature tempering martensite strips were generated, among which dispersedly distributed with cementite, carbide precipitate and a small amount of strip ferrite phase structure of different sizes
Summary
High-strength structural steels have been widely used in the manufacture of core mechanical components such as heavy loading shafts, large-section shafts, gas turbine cranks and gears, engines and various pump systems. As a typical low-alloy structural steel, 40CrNiMo7 steel is a kind of chrome-nickel-molybdenum steel, which has good performance and is widely used to withstand the impact load of parts and large section, high load shaft class. Though these types of structural steel can well meet the requirements of heavy load and frequent impact. It suffers from inherent shortcomings, such as relatively low hardness, soft dot. There have been few reports on Coatings 2020, 10, 311; doi:10.3390/coatings10040311 www.mdpi.com/journal/coatings
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
