dissertation global and local fracture properties of metal matrix ...

Section 5
5. The relation between the inclusion size and the local fracture properties
in a mild steel
The knowledge of the maximum particle stresses or the maximum decohesion stresses at the
moment of void initiation would be interesting for other materials, too. To check whether our
procedure can be used to more generally used engineering materials, it shall be applied in this
section for MnS-inclusions in a mild steel St37.
5.1. Material and mechanical properties
5.1.1 Materials characterization
The chemical composition of the St37 is given in Table 5.1. Test pieces were cut transverse to
the rolling direction. They were austenized at 870°C for 45 minutes and quenched in salt
water to achieve a uniform distribution of the carbon content. Then they were tempered at
700°C for 4 hours and furnace cooled down to 500°C at a rate of 2° per min. to spheroidize
the iron carbides.
The resulting microstructure after heat treatment consist of large MnS-inclusions with a
Table 5.1. Chemical composition of the mild steel St37.
C Mn Si Ni Mo P S Cr Cu As
0.17 0.54 0.01 0.04 0.01 0.019 0.018 0.01 0.01 0.002
00 µm
Fig. 5.1. The microstructure of the mild steel St37.
69
50 µm