The transformation from austenite to martensite is accompanied by a change of the magnetic 
properties: austenite is antiferromagnetic, martensite is ferromagnetic. Therefore, the amount of Aire 
martensite generated during tribological stressing was measured by an eddy current method used for [= 
measurements of magnetic properties e.g. for measurements of ferrite contents in welds of . 
austenitic steels. The measurements were carried out across as well as along the wear tracks. J 
In order not to disturb the measurements the counterbody material was carefully chosen to avoid ro. 
any transfer of magnetic material onto the sample surface during the friction process. Preliminary e 
experiments showed that the best results could be obtained with balls of htc-Al,O3 (99,7%). > 
Results AH 
Austenite/Martensite Transformation E 
The tribologically induced transformation behaviour is illustrated by the results of magnetic ir 
measurements. 
Fig. 1: Steel 1.4301. Friction induced martensite; 
5. temperature dependence (Fy=5 N, vs=0,2 ms”) 
8 A RT/Air 
ON 77KILN2 Results of the temperature dependence of the 
3 ~ 30Kite transformation are shown in fig. 1 for the metastable 
4,2 WLHe oo 
ua steel 1.4301. Martensite is formed already at room 
temperature. With decreasing working temperature 
1 the amount of martensite increases. However, this 
- 0 lo. tendency turns back beneath a certain temperature. 
0 3 : gy i2 16 This is caused by changes of the magnetic properties 
Measuring distance across the wear at the Néel temperature [ 3, 4]. 
track (mm) 
5,0 - 0,5 
N a) steel 1.4301 N b) steel 1.4439 
240 A Api ow An AA X04. 
2,0 4 = ) 1 0,2 A 
5 —4A--- measured j a op an a af 
ä 1,0 | —— seers VET AGE A 0.1 a 
0,0 ‘- - 0 lmwnmw ZEMENT EEE seam 
0 20 180 270 360 0 90 180 270 360 
Circular segment of the wear track (°) Circular segment of the wear track (°) 
Fig. 2: Martensite along the circular wear track of steel 1.4301 (a) and steel 1.4439 (b); experimental conditions 
as fig. 1; T = 20 K/in Hegas (note the different scales of the ordinates) 
The distribution of martensite along the wear track of steel 1.4301 is rather homogeneous (fig 2a). 
Against that, the same tribological conditions do not cause transformations at room temperature in 
the wear tracks of the „stable“ steels 1.4439 and 1.4958. At low temperatures (fig. 2b) also in these | 
materials martensite transformation takes place; however, only at some places. Further decrease of 
the working temperatures results in an increase of the content of martensite without any general Ast 
change in the distribution [ 5]. On material 1.4591 in any case no martensite could detected. ge on 
374