What’s the material that is on the forefront of innovation in the automobile industry? If you guessed aluminum or composite steels, you guessed wrong. When it comes to increasing fuel efficiency, quality, affordability, and durability, no material has made more of a difference than Advanced High-Strength Steel (AHSS) and Ultra High Strength Steel (UHSS).
In this and future communications we will begin sharing information about these products.
Advanced High-Strength Steel refers to a new generation of steel that provides high-strength (up to 2,000 MPa) and durability while maintaining formability that is crucial to the manufacturing process.
The primary AHSS grades are produced on high tech Continuous Annealing Lines that provide very high heat followed by a rapid controlled cooling rate of the austenite phase. Further controlled heating and cooling can take place depending on the desired properties.
The difference is this production process and finished microstructure of the steel. Where conventional Low Carbon thru HSLA steel grades exhibit a nearly 100% Ferrite microstructure, AHSS / UHSS steels will exhibit a variety of different microstructures depending on the grade.
The primary types of materials being utilized are Dual Phase, Complex Phase/Multi Phase, Trip, Martensite and Press Hardenable Steel.
Dual Phase Steel
Ferrite-Martensite dual-phase steel is a low-to-medium carbon material with between 5-50% volume fractional martensite islands that are dispersed in a soft ferrite matrix. In addition to martensite, bainite and retained austenite components can also exist; these are normally produced when improved edge stretch formability is desired.
These variations in microstructure give dual-phase steels a wide spectrum of strength and ductility. DP steels are known to be capable of absorbing large amounts of energy. Combined with a low cost of production, these properties make DP steels highly desirable for automotive applications.
Dual-phase steels can be produced as both hot rolled and cold rolled based material. When Hot Rolled, the rolling temperature and cooling process on the Hot Strip Mill is carefully controlled to produce the ferrite-martensite structure from austenite. When Cold Rolled, the properties are developed on Continuous Annealing lines where there is even greater control over thermal treatment.
Automotive parts that currently use DP steels including but not limited to Crossmembers, Pillars, Roof Rails, Frame Extensions, Shock Towers, Crush Cans and Wheels.
Complex Phase steels gain their strength through extremely fine grain size and micro structure containing small amounts of martensite, pearlite and retained austenite embedded in a ferrite-bainite matrix. High grain refinement is achieved by precipitation of micro alloying elements such as Nb, Ti or V or retarded recrystallization.
CP steels have a higher minimum yield strength in comparison with dual phase steels of identical tensile strengths of 800 Mpa and greater. When compared to DP steels, CP steels have a much higher yield strength to tensile strength ratio.
Complex Phase steel is being produced as both hot-rolled and cold-rolled which can be hot dipped galvanized for corrosion protection. Hot-rolled products are available in the higher thickness ranges needed to produce structural type parts.
As the technology continues to develop, the applications for AHSS in automobiles continue to expand. Crash safety with advanced high-strength steels continues to increase; as well as fuel economy, increased engine performance, and top speeds, which are a result of the reduced weight. Additionally, its cost effectiveness makes it an attractive material for structure parts, as well as bumper systems, seating, doors, and other safety parts.
Beyond the automotive industry, the following industries also stand to benefit with the development of advanced high-strength steels.
National Material recently upgraded their facilities with a Red Bud 72” (1830mm) wide slitting line with in-line leveling that has a thickness range of .012” – .250” and is capable of slitting grades up to 250,000 psi (1725 MPa) – an upgrade that was made with servicing the advanced high-strength steel market in mind.
About National Material L.P. – With more than 3,000 employees from a multinational portfolio of companies, NMLP provides engineered metal products, which include aluminum extrusion and stainless steel rolled product companies, to automotive, aerospace, construction, defense, electrical, and industrial markets.
National Material of Mexico, a subsidiary of National Material L.P., one of the largest automotive-focused flat rolled processors and distributors in Mexico, is expanding its Monterrey facility by 82,000 sq. ft. (7,700 sq. meters) to add capability for processing Advanced High Strength Steels, increase its railcar receiving capabilities, and to create a new headquarters office building.
NMM will host an Open House on November 28th, 2017 to show customers, suppliers, and leaders of government the outcome of their latest project that is expected to create 50 jobs. According to Carl Grobien, Vice President and General Manager, “To meet the demands of customers’ requiring advanced high strength steels, we needed to make this investment. We decided to increase slitting capacity and improve our process for unloading and handling shipments to become more efficient and responsive to our customers’ needs. To make room for the slitter we moved our existing office space to a brand new modern office building. These are very exciting times for our company that will benefit our customers.”
The new Red Bud 72ʺ (1830mm) wide slitting line with in-line leveling has a thickness range of .012” – .250” is capable of slitting grades up to 250,000 psi (1725 MPa), mainly used in mass reduction engineering designs for parts used in cars and trucks. National Material of Mexico, with its network of seven plants (including joint ventures), has a combined slitting capacity of > 1 million tons and a configured blanking capacity of 300,000 tons.
About National Material L.P. Elk Grove Village, IL – With more than 3,000 employees from a multinational portfolio of companies, NMLP provides engineered metal products, which includes aluminum extrusion and stainless steel rolled product companies, to automotive, aerospace, construction, defense, electrical, and industrial markets.