Advanced high-strength steels (AHSS) are complex materials that are revolutionizing the auto industry. Each step of the process – the various microstructures and chemical compositions – are a result of a carefully controlled heating and cooling process. During the process, several strengthening mechanisms are employed to achieve a spectrum of toughness, strength, and fatigue tolerances.
All AHSS have one thing in common – they are all produced by controlling the chemistry and cooling rate from the austenite-ferrite phase, either during the hot rolled phase, or in the cooling section of the continuous annealing furnace. But what all is factored into the process?
Design for production
During the creation of an AHSS for mass-production, full-scale processing concerns are integrated into the design from day one. Different compositions are simulated, the results of which are later validated by observing actual production ingots.
Forgeability is measured by examining the fatigue, fracture toughness, and tensile strength properties of the newly created material.
The full extent of machining operations is evaluated for the prospective material, including milling, threading, boring, tapping, drilling, and turning. Everything from the feed speed to the optimal inserts and cutting tools are tested.
Prospective materials are then tested for the differences between their annealed and hardened state.
Combination of properties
The steel can be alloyed with materials such as cobalt, nickel, carbon, manganese, copper, chromium, and more. The different combinations of properties are tested to achieve the optimal properties.
Strength is a key factor in the design of AHSS materials. The ultimate tensile strength (UTS) is usually the end-all, be-all weight-limiting design factor, so this factor is among the most crucial in the creation of new AHSS steels.
Fracture toughness is an important consideration for advanced high-strength steels. This is the factor that measures the materials’ ability to resist fracturing under stress.
Different to fracture toughness, yield strength refers to the point at which the elastic properties turn into plastic properties as the fibers of the material begin to break down. Higher yield strength allows the material to endure more stress without becoming disfigured.
THE RENEWABILITY OF ADVANCED HIGH-STRENGTH STEEL
Once the material is created and tested for mass production, it begins its life as it is machined into a useable part for the automotive industry. What happens as it’s made, put out into the world, and comes to the end of its life cycle?
Efficient steel production
AHSS, while currently more expensive overall to produce than traditional steels, uses less materials in the manufacturing process. These steels are given their strength by the alloys, as described above. The reduced weight and higher strength is achieved in the manufacturing process, which leads to less material waste overall.
The material is further processed by a combination of casting, hot rolling, cooling, pickling, cold rolling, and then annealing.
Reusing materials during the process
Manufacturers will attempt to use residual materials that are generated during the manufacturing and recirculate it into the steel production process as a substitute for virgin raw materials. Not only is this more cost effective, but it also makes the material more renewable.
Resource-efficient product manufacture
AHSS are stronger standard steels, while also being lighter. This design philosophy extends to all stages of the product life cycle, including reducing emissions and increasing engine performance in automobiles. Some modern cars are made of more than 50% AHSS.
Recyclability of steel
Steel is the world’s most recycled industrial material and maintains its properties no matter how many times that it’s recycled, similar to aluminum. Products made from steel have a long useful life and can then be recycled indefinitely.
About National Material L.P. – Since its founding in 1964, National Material Limited Partnership has grown to over 30 business units and is now one of the largest suppliers of steel in America. The National Material group of industrial businesses consists of the Steel Group, Stainless and Alloys Group, Raw Material Trading Group, Aluminum Group, and Related Operations.
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