A TEM Investigation of Crack Formation Mechanism on Chrome–Molybdenum Steel Tested under Real Driving Conditions

Figures & data

Fig. 1 Examples of typical surfaces of tested transmission components (color figure available online).

Fig. 2 Sections A and B (circled) were cut out for TEM samples using the FIB technique.

Table 1 Test Parameters

Item	Parameter
Test running time	400 h
Rotation of the engine side pulley	6,200 rpm
Velocity of the CVT belt	21 m/s
Belt clamping force by the wheel side pulleys (pressure to the element of the belt)	20 kN (41.6 MPa)
Test oil temperature	353 K

Table 2 Mechanical Properties of the Specimens

Item	Parameter
Tensile strength	More than 785 MPa
Elongation	More than 14%
Yield strength	More than 932 MPa
Retained austenite	About 20%

Fig. 3 Dark-field images and the corresponding ED patterns of the crystal structure below the sliding surface.

Fig. 4 Analysis of ED of Fig. 3D (color figure available online).

Fig. 5 Analysis of ED of Fig. 3B (color figure available online).

Fig. 6 Analysis of ED of Fig. 3A (color figure available online).

Fig. 7 Cross-sectional TEM image just under the sliding surface of section B of Fig. 2 (color figure available online).

Fig. 8 Temperature change in the isochronal annealing and TEM observations.

Fig. 9 Annealing of microstructure near the sliding surface.

Fig. 10 ED analysis.

Fig. 11 TEM image of isochronal annealing at 873 K.