The research team of the University of Hong Kong has developed a "super steel" that can take into account the high strength, ductility and toughness of steel.
On May 12, Huang Mingxin, a professor of the Department of Mechanical Engineering of the University of Hong Kong, told the interface reporter at the press conference of the "Super Steel" research project that traditional scientific views believe that the three indicators of high strength, ductility and toughness required by high-end steel are difficult Both have achieved, but "Super Steel" has achieved a breakthrough, and is currently negotiating cooperation with some enterprises and applying for patents in multiple countries.
"Super Steel" is also called D & P (Deformed & Partitioned) steel.
Huang Mingxin told an interface reporter that a piece of "super steel" with a size of 1 square centimeter and a thickness of 1.5 millimeters can withstand a weight of 3 tons. This is equivalent to the weight of an adult Asian elephant.
"Super Steel" being tested. Image source: University of Hong Kong
The requirements of the automotive, aerospace and defense industries for metal materials not only require ultra-high strength to greatly improve the load-bearing and deformation resistance of the structure, but also hope that the material has good ductility and toughness, and it is not easy to break and fracture, so that the parts can be accurate Shape and prevent accidental failure of materials and components.
But for steel, high strength often means that it is not easy to stretch and break easily.
The traditional scientific view is that the three attributes of metal strength, ductility and toughness have a trade-off relationship, that is, when the function of one of the attributes is improved, the other one or two will be reduced accordingly, and the three will not have all.
In 2017, Huang Mingxin's team achieved a breakthrough in the combination of high strength and high ductility, and while maintaining the ultra-high strength of the steel, it could be accurately shaped.
This research paper was published in the "Science" journal.
But in the study of steel toughness, breakthrough is more difficult. Huang Mingxin said that increasing the strength of steel tends to reduce the toughness, resulting in increased brittleness of the material. The related research work is quite arduous. When the strength enters an ultra-high range, the difficulty of further improving the toughness of the material will double.
At present, the industrial steel used in bridge cables and armored vehicles has a very high yield strength, which can reach 1.7 GPa, that is, the structure has strong load-bearing and deformation resistance, but the highest toughness has not exceeded 65 MPam½, which is not ideal.
In 2019, Huang Mingxin's team collaborated with the University of California, Berkeley (UC Berkeley) National Laboratory. This year, they have made significant progress in improving the toughness of "Super Steel".
On May 8, the two sides cooperated to publish the latest research results in the journal Science. Science, which began in 1880, is an academic journal published by the American Association for the Advancement of Science and is one of the most authoritative academic journals in the world.
According to Huang Mingxin, his team found that D & P steel has a very unique fracture method, forming many tiny cracks under the main crack.
Huang Mingxin told the interface reporter that this latest scientific breakthrough can be understood as a "crack" that is criss-crossed on a piece of ordinary steel. The "crack" achieves toughness enhancement while ensuring strength.
"These tiny cracks can effectively absorb the energy caused by external forces, thereby greatly improving the fracture toughness of the steel, which is much higher than the steel materials currently used." Huang Mingxin said that this concept is called "grain boundary layering crack toughening" .
"Super Steel" unique lamellar structure. Image source: University of Hong Kong
According to Huang Mingxin, the yield strength and fracture toughness of "super steel" are higher than the maraging steel used in aerospace now, and the cost is only 1/5 of it.
The yield strength and fracture toughness of maraging steel are 1.8 GPa and 70 MPa m½, respectively, which are high yield strength and high fracture toughness, and the price is comparable to gold.
Can steel mills with blast furnace as the main process produce "super steel"?
Huang Mingxin told the interface news that this requires the steel mill to join the warm rolling process, which can be achieved by modifying the existing cold or hot rolling equipment. After the process modification, the possibility of mass production of "super steel" increased significantly.
Huang Mingxin predicts that the industry where "Super Steel" will be put into commercial use the fastest is military bulletproof.
