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

Reduction factor
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 100 200 300 400 500 600 700 800 900
Temperature [C]
Steady-state tests, Base mat. Transient state tests, Base mat.
Steady-state tests, RHS-tubes Transient state tests, RHS-tubes
Figure 36. Reduction factors of the yield strength of austenitic stainless steel EN 1.4301,
comparing the results of different methods used to test virgin sheet and cold-formed material
(Ala-Outinen & Oksanen, 1997).
The strength of a material increases due to cold working during the fabrication process.
The remains of this increased strength at elevated temperatures can be seen in Figure
36. The increased strength due to the cold-forming process remains more or less
constant up to 600 °C but beyond this point strength begins to decrease and the
influence of cold-forming totally disappears at 900 °C.
Since the various stainless steel types behave differently, it is reasonable to determine
the specific reduction factors separately for each type of stainless steel. Furthermore,
both tensile strength and elastic modulus behave similarly to proof strength at elevated
temperatures. However, determining the modulus of elasticity based on the slope of the
stress-strain curve is very inaccurate, as the proportional limit of austenitic stainless
steel is very low. The least inaccuracy in the measured curves has a very significant
influence on the calculated modulus of elasticity and the unreliability of modulus-ofelasticity
values determined in this way is thus quite remarkable.
Table 13 shows the reduction factors of yield strength in relation to 0.2 % proof strain
for various stainless steel grades and various delivery conditions. Further data on the
fire properties of the various stainless steel grades and forms are given by Ala-Outinen
(1996), Ala-Outinen et al. (2003), Outinen & Mäkeläinen (1997) and Baddoo & Burgan
(2008).
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