120 Steels: Metallurgy and Applications,, ,, ,, ,
Process Development
Materials' Design [ - '?_ i- ~!
I '~ _ .su~.',c~st.,s , >i
i - T, Rl~'Stee~, ~,
I .High'Strength IFiSteols R.m > ~ M.Pn' ~>
I Bake-Her(ler~ing-$teeis Re z, 180...300 MPa>
[ - , ..... "-Dual' , F;hase-'Steels' _
[. Rephosphodzed S!eols R, ,~ 2'20...~X) ,, MPa'
[Mlcroalloy~lSteels I~"~ 280':..420 MPa' ' ilsotrop,r Steels R. ~250 MP~:~a~
t r.~i...~,ed Sic*,. ~, ._., _.(^1975) , 19~10 , ' 1985 " '- , , 1990 ' ' '1995 ,, 2000
Figure 1.119 The development of high-strength, cold-rolled steels for auto-body appli-
cations. The time axis reflects the approximate first industrial usage, from a European
perspective, in the automotive industry (After Bleck 94)
Table 1.14 Progress of the ULSAB project at the end of phase 1
Representative Performance Achieved
figure post-2000 target figure
Mass 250 kg 200 kg 205 kg
Static torsional rigidity 13 000 Nm/deg. > 13 000 Nm/deg. 19 056 Nm/deg.
Static bending rigidity 12 200 N/ram > 12 200 N/ram 12 529 N/mm
First BIW mode 40 Hz >40 Hz 51 Hz
account of different vehicle size. The main performance features being considered
are the static torsional rigidity, the static bending rigidity and the first B IW mode.
The latter is the resonant frequency for vibration of the body and should be as
high as possible for passenger comfort. Table 1.14 gives the properties expected
to be representative of a typical mid-size body in the post-2000 time period, after
reasonable further improvements to existing types of design have been made. It
compares them with the targets for the ULSAB design and the figures that have
been achieved. It is seen that the main objective was to give a 20% reduction in
weight from 250 to 200 kg while maintaining or improving the body performance.
It is evident that the performance objectives have been achieved comfortably but
that the weight reduction target has not been quite achieved.
The approach to the design has been a holistic one. Thus, parts of the body
have been increased in weight to be able to make greater reductions elsewhere.
Hydroforming is to be used to make the roof-rail sections, which could not
easily be made using conventional forming techniques. Some parts are made by
roll forming and some are made from sound deadened steel as described below.
The torsional and bending rigidities of the structure have been improved by weld
bonding, but a number of continuous joints have also been achieved using laser
welding. The complexity of the structure has been reduced by the use of laser-
welded blanks thus obviating the need for additional strengthening members.
The estimated cost of production has been given as $154, less than for a typical