Steel may be a common alloy but what happens when researchers attempt to turn it into super steel?
Developing ultra-high-strength alloys is a challenging task as it often ends up exposing weaknesses in other areas. Creating super steel requires a fine balance between all the different properties and a breakthrough has emerged, defying convention.
Engineers have developed a stronger and tougher super steel that defies the trade-off, staying strong while resisting fractures. It was made possible by something called ‘grain-boundary delamination. As a result of the characteristics, this alloy is ideal for use in aerospace engineering, bulletproof vests and bridge cables among others. Let’s take a closer look at this incredible breakthrough study.
Exploring The Super Steel Project
Professor Huang Mingxin in the Department of Mechanical Engineering at the University of Hong Kong (HKU) led the Super Steel project. In collaboration with the Lawrence Berkeley National Lab (LBNL), they made an important breakthrough in its new super D&P steel.
D&P refers to steel produced using a new deformed and partitioned method. This greatly enhances its fracture resistance while maintaining superior strength for advanced industrial applications. The super steel gets its toughness from a unique design feature that allows tiny, multiple cracks to form below the surface when a fracture appears.
That’s where the magic happens as these micro-cracks absorb energy from external forces, preventing the main fracture from spreading too fast. Developing ductile, fracture-resistant, and cost-effective ultra-high-strength steels is an attractive option for so many applications.
Developing Super Strong, Tough and Economical Engineering Materials
For ductile materials, like metal, toughness is typically proportional to the fracture stress, strain and the gauge length of the crack. Delamination toughening with intensive but controlled cracking at Mn-enriched prior-austenite grain boundaries normal to the primary fracture surface drastically improves the overall fracture resistance.
This results in fractures under plane-strain conditions to automatically transform into a series of fracture processes in “parallel” stress conditions through the thickness. The current “high-strength induced multi-delamination” strategy is a different approach to develop super strong, tough and economical engineering materials.
This super steel breakthrough study shows that by activating delamination toughening, along with transformation induced plasticity, you can achieve improved fracture resistance in steel with a yield strength of nearly 2GPa.
Finding The Right Balance
When it comes to steel, three main properties need to be balanced, i.e. strength, toughness and ductility.
Strength is measured in Pascals of pressure which describes the load a material can take before it deforms or fails. At the same time, toughness measures the amount of energy it takes to fracture the material.
Finally, we look at ductility which is a measurement of how easy it is to extend or elongate a material into different shapes. A good reference point is glass as it’s relatively strong but it lacks in toughness. While glass can certainly support quite a bit of weight, it doesn’t take much energy to break it.
While previous attempts resulted in strengthening one aspect while weakening another, this breakthrough has resulted in researchers finding the right balance. This super steel has high-performance levels in all three properties – strength, toughness and ductility.
Super Steel Applications
The new super steel has a yield strength resistance against deformation of around 2 GigaPascals, fracture toughness of 102 MPa-m½, and uniform elongation of 19%. According to the research team, these numbers indicate that the super steel is stronger and tougher than the Grade 300 maraging steel used in aerospace engineering.
An added benefit is that the new super steel only costs around 20% of the price to manufacture. Among others, the most common applications of the new super steel include the following:
- high-strength bridge cables
- bullet-proof vests
- car springs
- lightweight automobile and military vehicles
- aerospace engineering
- high strength bolts and nuts in the construction industry
Material scientists and engineers are always looking to develop new steel materials with advanced features and characteristics. Their primary goal is to develop a material that has better ductility, strength and toughness while remaining lightweight and with lower production costs.
According to Professor Huang Mingxin, they have made significant strides toward industrialising this novel super steel as it demonstrates great potential across various applications. This breakthrough has also changed the conventional thinking that improving strength will result in deteriorating toughness or ductility. For a more detailed look at the research study, you can find it in the journal Science.
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