Page 20 - MetalForming May 2013

Automotive Steels
Miles per gallon equivalent 70
Obama Administration Standards
X
60 50 40 30 20 10
0
1975 1980
54.5 mpge Fleetwide Average in 2025
Passenger Cars
Light Trucks
1985 1990 1995
2000 2005 Model Year
2010 2015
2020 2025
Fig. 3—NHTSA’s call to increase CAFE standards for cars and light trucks by 2025 will continue to fuel the growing use of AHSS.
processes used to make aircraft parts, such as vacuum arc remelting and forg- ing, are not typical automotive processes, automotive steels are indeed approach- ing that amazing 2000-MPa threshold.
Developing the Third Generation of AHSS
The quest for lighter automotive parts and higher standards for vehicle structure and safety continue to inspire research and development of future steels. The Auto/Steel Partnership (A/SP), composed of several automo- tive steel producers and automakers, together with five universities, two engineering companies and Pacific Northwest National Labs was recently awarded a $6 million research grant along with the United States Automo- tive Materials Partnership. The grant will support the study and modeling of the metallurgical characteristics of a new generation of AHSS grades, a third generation that will have high giga- pascal strength levels and exceptional formability.
The objective is to move high-ten- sile-strength steels into uncharted ter- ritory, so more of them can be cold stamped economically into very light- weight parts. The science that will be employed in this 4-yr. study is called integrated computational materials science. It makes use of the amazing rise in computer-based analysis involv- ing materials models essentially span- ning the scales from atomic/nano microstructures all the way to assem- bled vehicle structures.
As new metallurgical steel grades are discovered through such research, more studies dealing with formability, fracture and joining of the new steels will certainly follow. The A/SP is study- ing these enabling technologies.
So, the answer to the question of how high is high for AHSS: The highest strengths we will see in future vehicles is limited only by the creativity of the engineers and scientists doing the research needed to unlock the seem- ingly unlimited potential of steel, to satisfy the ever-increasing demands of automotive customers. MF
100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0
􏰀 ULSAB
􏰀 ULSAB-AVC
􏰀 FSV
50.7
22.5
4.3
20.9 12.1
4.8
9.2
1.4
16.4 5.7
22.0 17.8
Tensile Strength (MPa)
Fig .4—With the advent of the FSV project, we’re well on our way to use of AHSS grades in excess of 1500-MPA tensile strength.
Fig. 5—This 2014 Mazda CX-5 bumper assembly features a hot-stamped beam of 1800- MPa steel.
Steel Grade: MnB1800
Length = 1138mm Mass = 8.01 kg
of ULSAB-AVC technology is enhanced in FSV, and there is a noticeable shift to higher tensile-strength steels (Fig. 4). The AHSS grades are considerably stronger and more formable—five dif- ferent grades of AHSS exceed the 1000- MPa level.
Today we see the trend of introduc- ing steel grades with increased tensile
strength continuing. For example, an 1800-MPa tensile-strength bumper recently was developed for the Mazda CX-5 bumper (Fig. 5). This represents the highest production tensile-strength automotive part to date. Tensile strengths exceeding 2000 MPa are familiar in parts like aircraft landing gear, but not automobiles. While the
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1000 1200 1470 1500 1520
Body Structure MAss (kg)