Page 22 - MetalForming December 2010

Tooling Technology
Stuart Keeler (Keeler Technologies LLC) is best known worldwide for his discovery of forming limit diagrams, development of circle grid analysis and implementation of other press shop analysis tools. Stuart’s sheetmetal forming experience includes 24 years at National Steel Corporation and
12 years at The Budd Company Technical Center, enabling him to bring a very diverse background to this column and the many seminars he teaches for PMA. His most recent project is technical editor of the AHSS Application Guidelines—Version 4.1, which now is available for downloading free from www.worldautosteel.org. Keeler Technologies LLC
P.O. Box 283
Grosse Ile, MI 48138
Fax: 734/671-2271
E-mail: keeltech@comcast.net
Stuart Keeler, Peter Ulintz and Ed Tarney will present the Deep Draw seminar on February 16 in Cleveland, OH. Check www.metalforming.com for this and other seminars.
Brad Kuvin’s editorial in the Sep- tember issue of MetalForming mag- azine highlighted the automotive industry’s increased use of higher strength steels, especially the dual-phase grades. Increased fuel-efficiency require- ments have dictated weight reductions achieved by higher strength and thinner gauges of steel components. To help meet these new requirements, the steel industry continues to explore new approaches to increase strength and reduce cost and welding problems.
The automotive industry tends to be a beta test site for many of these new steels because of the quantity of special steels utilized. Not a supplier to the automotive industry? These new steels could easily be the steels you will be using in the future. Learn about them now and you can be one-step ahead of your competition.
Many decades ago, higher strength steels were made by adding large amounts of carbon or by cold working the coils. While these were successful in achieving higher strengths at lower cost, the max- imum amount of stretchability was very limited. In the 1960s, metallurgists
began modifying the basic microstruc- ture of aluminum-killed draw-quality (AKDQ) steels. Grain size was reduced. Iron atoms in the unit cell were replaced with atoms of other elements that are larger or smaller than the iron atom (substitutional strengthening). Some atoms were inserted within the iron lattice iInterstitial strengthening).
Various combinations of these changes in microstructure are called thermal mechanical strengthening. These steels are the high-strength low- alloy (HSLA) steels. The yield strength of HSLA steels increases as more microstructural modifications are made. Initially their yield strengths were in the 35 to 50 KSI range. Today the most common yield strength upper limit is 80 KSI. However, one steel mill in Europe is providing HSLA type steels in the 100 to 110 KSI yield strength range.
In North America these higher strength steels were specified by yield strength. However, a special designa- tion also was assigned based on an arbi- trary range of yield and/or tensile strengths (Fig. 1). Using this typical chart to explain higher strength steels
30 Ksi 80 Ksi
Low Strength
AKDQ
HSLA
High Strength
Ultra-High Strength
Yield Strength
20 METALFORMING / DECEMBER 2010
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THE SCIENCE OF FORMING
Higher Strength Steel Options Keep Growing
Fig. 1—Schematic showing the terms used to define different levels of strength.
STUART KEELER
Formability