Innovative Stainless Steel Applications in transport ... - Euro Inox

4. Manufacturing issues in lightweight structures
The manufacturing of any structure obviously requires several steps and techniques that
are at least partially common engineering knowledge. However, there are certain
methods worth a closer look, due to the different behaviour of, specifically, austeniticstainless
and mild or low-alloyed steels. Regarding forming, anisotropy in cold formed
austenitic stainless steel material requires particular attention, as explained in Chapter
2.3. Further information on the formability of stainless steels is given by Van Hecke
(2006).
4.1 Bending of high strength stainless steel sheets
With conventional carbon steels, bending is usually carried out according to the data in
DIN 6935 “Cold bending of flat rolled steels” (1975). This standard prescribes the
minimum bending radii for a wide variety of steels. Austenitic stainless steels in general
and especially the unstable grade 1.4318 exhibit higher strength than ferritic carbon
steels and have different forming behaviour.
DIN 6935 ranks the available steel grades according to ultimate tensile strength, in three
categories: Rm < 390 N/mm 2 , 390 < Rm < 490 N/mm 2 and 490 < Rm < 640 N/mm 2 . A
minimum bending radius is given for each category. The ultimate tensile strengths, as
measured by a quasi-static tensile test using a single crosshead speed of 2.7 mm/min,
and the corresponding minimum bending radii of the project materials, are given (where
possible) in Table 19.
Table 19. Ultimate tensile strength and minimum bending radius according to DIN 6935 (1975).
Material t
(mm)
Rm
(N/mm 2 )
90 °
73
Rm
(N/mm 2 )
90 °
rmin
(mm)
0 °
rmin
(mm)
90 °
1.4318 2H/C1000 (301LN) 1.9 1119 1129 NA (4*) NA (4*)
1.4318 2H/C850 (301LN) 1 961 947 NA (1.6*) NA (1.6*)
1.4301SP 2B (304SP) 1 755 755 1.6 1.6
1.4318 2H/C1000 (301LN) 1.2 1070 1073 NA (2.5*) NA (2.5*)
1.4318 2H/C850 (301LN) 1.5 1055 1049 NA (2.5*) NA (2.5*)
*values in brackets are those of the highest strength category of DIN 6935
As can be seen from Table 19, the ultimate tensile strengths of most of the DOLTRAC
materials are too high for the highest categories mentioned in DIN 6935. This standard
is therefore not suitable for determining the minimum bending radius of the ultra highstrength
grades investigated in this project. Rules of thumb for minimum bending radii
of high-strength austenitic stainless steels are however given by Ordenbach (1989). The