Yearning for stronger, more durable metals, researchers continuously explore innovative techniques. One such endeavor, delving into the world of metallurgy, revolves around the quest to enhance the properties of steel, a material central to our modern infrastructure. From towering skyscrapers to vital machinery, steel’s role is ubiquitous, making its strength and resilience a subject of paramount importance. This pursuit of advancing steel treatment is a testament to the unyielding human spirit to push the boundaries of material science, striving for advancements that echo through various industries and applications.

The study, led by Professor Toshihiko Yoshimura and his colleagues Dr. Shintaro Yamamoto and Hayato Watanabe from Sanyo-Onoda City University, Japan, represents a significant leap in the field of metal processing. Published in the journal “Results in Materials,” this research introduces an innovative metalworking technique, Positron and Laser Assisted Magnetic Energy Intensive Multifunction Cavitation (PLMEI-MFC), significantly advancing the treatment of SCM440 Cr–Mo steel.

The method uses a narrow nozzle to create water jet cavitation bubbles, followed by ultrasonication in a magnetic field. These cavitation clouds are then irradiated with laser beams, including ultraviolet light, enhancing their impact on the steel. The integration of positron irradiation into this process is a game-changer, as it greatly enhances the steel’s surface strength.

Dr. Yoshimura’s team found that the small WJC bubbles produced by the narrow nozzle were key to achieving high compressive residual stress and significant hardness in the steel. “The use of a narrow nozzle in the process creates small WJC bubbles, which are critical in achieving high compressive residual stress and significant hardness in the metal,” explained Dr. Yoshimura.

The positron irradiation in this process played a pivotal role in altering the steel’s properties. “Incorporating positron irradiation significantly increased the compressive residual stress by 1160 MPa, effectively converting tensile residual stress into compressive residual stress,” said Dr. Yoshimura. This conversion is essential in improving the metal’s resistance to fatigue and cracking, thereby extending its usable life.

The research team’s approach was meticulous. They first subjected the steel specimens to multifunction cavitation processes. They then measured residual stress using a portable X-ray device, which allowed for precise determination of the changes brought about by the treatment. The surface morphologies and roughness were then evaluated using three-dimensional laser microscopy, providing a clear picture of the enhancements on the steel’s surface. Finally, Micro-Vickers hardness measurements were performed to quantify the improvement in hardness, a critical factor in determining the steel’s suitability for various applications.

This study’s findings are not just a step forward in material science; they represent a leap. The methodology developed by Dr. Yoshimura and his team opens new avenues in metal treatment, offering a way to significantly increase the strength and durability of steel without compromising its surface quality. The potential applications of this research are vast, ranging from automotive and aerospace industries to construction and machinery, where the strength, longevity, and reliability of metal components are crucial.

In conclusion, the research by Professor Yoshimura and his team at Sanyo-Onoda City University has paved the way for new, innovative approaches to metal processing. Their work is a testament to the power of scientific inquiry and its ability to drive technological advancement.

Journal Reference

Yoshimura, T., Yamamoto, S., Watanabe, H., “Precise peening of Cr–Mo steel using energy-intensive multifunction cavitation in conjunction with a narrow nozzle and positron irradiation,” Results in Materials 20 (2023) 100463. DOI:

About the Author

Toshihiko Yoshimura

Sanyo-Onoda City University, Japan

He got Engineering Doctor’s degree at Tokyo Institute of Technology in 1995. Specialist in materials engineering, he got the paper awards from The Vacuum Society of Japan, The Water Jet Technology Society of Japan, and Technology Creation Award from The Japan Society of Mechanical Engineers.