Biomedical Engineering Reference
In-Depth Information
Table 6.3
Results of microhardness and Young's modulus tests for
selected samples of Ni-free austenitic stainless steels and
316L stainless steel
Sample
HV
H
[MPa]
E
[GPa]
316L
276
2977
172
Fe
74
Cr
24
Mo
2
N
650
7014
201
Fe
54
Cr
24
Mn
21
Mo
1
N 542
5846
210
Fe
59
Cr
23
Mn
12
Mo
6
N 525
5663
213
Fe
64
Cr
24
Mn
10
Mo
2
N 469
5027
199
Young's modulus of obtained steels is about 210 GPa, which is
slightly higher than in conventional stainless steel 316L (~170 GPa)
and comparable with cobalt-chromium alloys (220-240 GPa) that
makes this material applicable for production of e.g. stents.
As one may expect, materials with high value of microhardness
(~500 HV) could show embrittlement. To exclude or endorse that
unwanted phenomenon, stress intensity factor —
K
IC
— should
be determined. It could be done by calculating
K
IC
from hardness,
diameter of indentation and length of Palmquist's cracks measured
directly in Vicker's method. Niihara's equation applies here [19].
Imprint of Vicker's indenter on polished surface of Ni-free
stainless steel with nanostructure (Fe
59
Cr
23
Mn
12
Mo
6
N) is shown on
the Fig 6.9. Load of 200 g, 500 g, 1 kg, 2 kg, 5 kg, 10 kg, and even
30 kg did not reveal any marks of Palmquist's cracks. It can be
concluded, that in case of Ni-free stainless steels obtained by
mechanical alloying high microhardness did not imply embrittlement
of the samples.
Figure 6.9
Imprint of Vicker's indenter (30 kg load) for Fe
59
Cr
23
Mn
12
Mo
6
N
sample [29].
