#bainite

Researchers create 'smart steel,' 30% stronger

Researchers from South Ural State University are working on producing an innovative, super-light, and super-strong kind of steel called bainite. This new material has potential applications in the aviation industry, mechanical engineering and the defence industry.

The developments have been published in Physics of Metals and Metallography. The authors of the article are Doctor of Sciences (Physics and Mathematics), Professor Djalal Mirzayev and Associate Professor of the Department of Optoinformatics of the SUSU Institute of Natural Sciences and Mathematics Ivan Buldashev.

Highly Strong and Malleable Steel

Steel is an alloy of iron and carbon, but depending on the temperature the iron is heated to, it is possible to obtain different steel structures. This is because within the interval of zero to 911 degrees Celsius, the properties of iron change completely. At a temperature lower than 911 degrees Celsius, austenite enters a more malleable and soft phase called ferrite, which is formed with slow cooling. In manufacturing, ferrite is used for machining. However, with shock cooling, austenite forms a superhard phase called martensite.

The automotive industry's demand for high-performance alloys known as advanced high-strength (AHS) steels has increased in recent years owing to increasingly tough passenger safety, vehicle performance and fuel economy requirements.

Characterized by improved formability and collision resilience compared to conventional steel grades, high-strength steels have been used in critical safety locations in car body structures to absorb energy from impacts. However, some of these high-strength alloys tend to become brittle as a result of welding and may break when submitted to the hot stamping and forming required by many manufacturing processes.

"This problem makes it impossible to use AHS steel not only in the automotive industry but also in other industries such as aerospace," said Milton Sergio Fernandes de Lima, a researcher at the Brazilian Air Force Command's Institute for Advanced Studies (IEAv). To address this issue, Lima has developed an innovative method of high-temperature laser welding for AHS steel appropriate for aerospace applications.

The results, obtained while Lima was a visiting fellow at the Colorado School of Mines in the United States with support from the Sao Paulo Research Foundation, have now been published in the Welding Journal.

Carbon Steel Microstructures: Bainite

Formed when steels are cooled quickly - but not so quickly as to create martensite - bainite ( 1 , 2 , 3 ) is a microstructure that consists of a combination of ferrite and cementite. While it exists in carbon steels, it is more commonly found in alloy steels. Bainite increases the hardness of the material, but the many dislocations present in the ferrite still allows for some ductility.