ASTM G133 Wear TEST prove 600 times wear reduction after EXPANITEPURELOW-T
Wear resistance test show improved on Austenitic stainless steel
Wear resistance, and wear related failure is one of the most common issues engineers encounter when selecting austenitic grades of stainless steel as a material for their design.
The trade-off between favorable manufacturing properties and hardness means that alloys like EN 1.4404 often require surface treatments like SuperExpanite®. However, in some cases, processes involving temperatures above stress relief (such as ExpaniteHigh-T) cannot be freely utilized due to the risk of losing high tolerances to distortion or due to cold worked condition that is crucial to mechnical performance of components. ExpanitePureLow-T aims at providing the same wear performance as SuperExpanite, without annealing of the microstructure – and does so in an remarkable way.
Ball-on-flat Sliding Wear Test (ASTM G133)
The test geometry of the ASTM G133 Standard wear resistance test method for linearly reciprocating ball-on-flat sliding wear includes a ball or semi-circular tip made of 100Cr6 alloy with hardness above 800HV. The flat counterpart with the tested treatment is placed in a setup, and the ball is slid against it in an oscillating manner with a frequency of 5Hz. The amplitude of 10mm and a total length of 100m are set as test parameters.
The force between the counterparts is constant throughout the test at 25N. The resulting scar – referred to as wear track is then measured with a profilometer and a cross-sectional area is integrated from the plot. In this test report three separate trials have been conducted on an ExpanitePureLow-T hardened EN 1.4404 block, and the results are compared to the results (presented earlier) from an untreated sample of the same alloy.
Figure 1.: Micrograph of diffusion layer with measured case depth (20µm) on EN 1.4404 treated with ExpanitePureLow-T. Magnification x40.
ExpanitePureLow-T – purely simple solution
Due to the lack of annealing step, the resulting surface hardness and case depth are strongly related to the initial microstructure and manufacturing history. The microstructure of the treated sample in the surface area, showing the diffusion layer is presented in Figure 1. A hardness profile measured on the test sample used in this test is shown in the graph in Figure 2. To minimise the influence of the subsurface damage layer, a few micrometres thick zone affected by the machining operations, an electropolishing step is conducted as a necessary pre-process
Analysing the results
Wear track number 2, with the highest wear rate, was used to obtain information on wear scar depth. The measured profile obtained from this scar is shown in the graph in Figure 3. The data presented has been filtered with a Gaussian filter at a cut-off length of 0.08mm, using a Python script. The profile of an untreated sample is also shown for comparison with a cut-off length of 0.25mm. The depth of the scar of 2µm was measured from the highest point on the scar’s banks to the lowest point on the filtered data.
Table 1.: Wear rates measured on wear tracks 1-6.
|
ExpanitePureLow-T Treated EN 1.4404 |
Track 1 |
Track 2 |
Track 3 |
Mean |
Standard deviation |
|
Wear rate (mm3/N.m) |
9.1·10-7 |
1.8·10-6
|
1.1·10-6
|
1.2·10-6
|
3.8·10-7
|
|
Untreated EN 1.4404 |
Track 4* |
Track 5* |
Track 6* |
Mean |
Standard deviation |
|
Wear rate (mm3/N.m) |
9.4·10-4 |
6.4·10-4 |
6.8·10-4 |
7.5·10-4 |
1.3·10-4 |
Figure 2.: Hardness profile of ExpanitePureLow-T treated sample manufactured in EN 1.4404. The raw stock material was a wrought and annealed bar.
Figure 3.: Comparison of wear scar profiles for untreated and ExpanitePureLow-T treated EN 1.4404 samples. (Smoothing: Gaussian filter, cut off 0.08 for the green trendline, cut off 0.025 for the blue trendline).
Almost 600 times lower wear rate
Analysing the results of the measured wear track depth and comparing them to the overall diffusion depth achieved with the treatment, we can conclude that such low amount of removed material is not detrimental to the material. The difference in depth of the scar between the treated and untreated samples was calculated at about 95 times.
Figure 4.: Photograph of the wear tracks. Scars 1-3 left to right.
Figure 5.: Micrograph of the wear scar number 2, roughly in the middle of the 10mm length. Many original features of surface topography can be seen connecting within the wear area. Magnification x2,5.
