High carbon steel is no longer relevant. Now, the physical properties of steel have evolved thanks to research carried out by an international team led by Hao Chen of Tsinghua University. The researchers used chemical engineering of the limits or CBE to make the steel lighter, more flexible, and yet ultra resistant.
Lighter but stronger steel, what for?
Steel has many uses, but it is mainly used in the field of construction and transportation. The consumption of this material is constantly increasing: according to the latest figures reported by the WSA (World Steel Association), its production reached 1.87 billion tonnes for the year 2019.
Today we are in the presence of solid steel, but which remains very expensive because of its high carbon content and other doping elements. However, the group of international researchers was able to find another alternative: the use of chemical engineering can produce steels that are both flexible, ultra-resistant, without carbon content and therefore less expensive.
What is chemical engineering?
Always looking for a more robust, more flexible and less expensive steel structure, the use of grain boundary engineering has become widespread. It seemed indeed the best approach when it came to the mechanism of metallic materials. This method consists in creating defects, the plane discontinuities in metallic crystals, in the microstructure of steel to arrive at a very solid and less expensive form. Although excellent, this approach is still limited, since the grains are quite unstable in terms of heat and mobility. Researchers have noticed that the grains grow larger as soon as they are exposed to heat.
The improvement of this engineering technique of grain boundaries impossible, the researchers used another approach which is the method CBE (Chemical Boundary Engineering). The CBE method is an approach by which planar defects in the microstructure of steel lead to the formation of a very clear chemical discontinuity. This method makes it possible to create a finer, more ductile or flexible (> 20%), ultra-resistant structure which can reach up to 2.0 GPa (gigapascal) and which is above all inexpensive. The microstructure thus becomes heterogeneous and does not fear heat, even very high.
How did the researchers do it?
As steel is one of the most used metallic materials, the researchers conducted their research on it. A low carbon steel having a poor composition is then selected. It is then subjected to cold rolling followed by a standard austenite overhaul treatment (ART) at 600 ° for two hours. After that, it is heated quickly with a temperature increase rate of 100 ° C per second in a single-phase austenite region, then immediately cooled to room temperature to be able to reach its final state.
After tests and comparisons with the standard technique, the researchers found that the material became more resistant and flexible at the same time. This is a real revolution, all the more since the CBE method does not only concern steels. The researchers concluded that it could also be applied to other metallic systems and used as a surface treatment. Research continues in this direction.