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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.<\/p>\n<\/div>\n
The trade-off between favorable manufacturing properties and hardness means that alloys like EN 1.4404 often require surface treatments like SuperExpanite\u00ae. 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<\/a> 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 \u2013 and does so in an remarkable way.<\/p>\n<\/div>\n 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.<\/p>\n The force between the counterparts is constant throughout the test at 25N. The resulting scar \u2013 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.<\/p>\n<\/div>\n \n 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<\/p><\/div>\n \n 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 2\u00b5m was measured from the highest point on the scar\u2019s banks to the lowest point on the filtered data. <\/p><\/div>\n ExpanitePureLow-T Track 1<\/span><\/strong><\/p>\n<\/td>\n Track 2<\/span><\/strong><\/p>\n<\/td>\n Track 3<\/span><\/strong><\/p>\n<\/td>\n Mean<\/span><\/strong><\/p>\n<\/td>\n Standard deviation<\/span><\/strong><\/p>\n<\/td>\n<\/tr>\n Wear rate (mm3<\/sup>\/N.m)<\/p>\n<\/td>\n 9.1\u00b710-7<\/sup><\/p>\n<\/td>\n Untreated EN 1.4404<\/span><\/strong><\/p>\n<\/td>\n Track 4*<\/span><\/strong><\/p>\n<\/td>\n Track 5*<\/span><\/strong><\/p>\n<\/td>\n Track 6*<\/span><\/strong><\/p>\n<\/td>\n Mean<\/span><\/strong><\/p>\n<\/td>\n Standard deviation<\/span><\/strong><\/p>\n<\/td>\n<\/tr>\n Wear rate (mm3<\/sup>\/N.m)<\/p>\n<\/td>\n 9.4\u00b710-4<\/sup><\/p>\n<\/td>\n 6.4\u00b710-4<\/sup><\/p>\n<\/td>\n 6.8\u00b710-4<\/sup><\/p>\n<\/td>\n 7.5\u00b710-4<\/sup><\/p>\n<\/td>\n 1.3\u00b710-4<\/sup><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \nAnalysing 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.\n<\/p><\/div>\n
\nBall-on-flat Sliding Wear Test (ASTM G133)<\/h2>\n
\n\n![\"Wear](\"\/wp-content\/uploads\/2025\/06\/Wear_disc_x40-1.jpg\")
<\/p>\nFigure 1.: Micrograph of diffusion layer with measured case depth (20\u00b5m) on EN 1.4404 treated with ExpanitePureLow-T. Magnification x40.<\/h3>\n<\/div>\n
ExpanitePureLow-T – purely simple solution<\/h2>\n
Utilising the same technology as our ExpaniteLow-T step of the SuperExpanite product, ExpanitePureLow-T provides an increase in surface hardness of austenitic EN 1.4404 alloy. The thermo-chemical conversion of the surface creates a layer of expanded austenite with surface hardness above 900HV. The increase in hardness is achieved thanks to diffusion of large amounts of nitrogen and carbon into interstitial sites (specifically, octahedral holes in the FCC lattice). The achieved thickness of the diffusion zone is 20\u00b5m \u00b1 5\u00b5m. <\/p>\n
\nAnalysing the results<\/h2>\n
All three of the wear scars have been measured with a profilometer, and the cross-sectional area of the track was measured using a Python script. The measured profiles had an original length of 1.5mm and were levelled based on average height in specified non-zero ranges from both ends of the profile. The measured area is multiplied by the test amplitude and normalised by the test parameters to achieve a wear rate. In Table 1, a summary of calculated wear rates for both ExpanitePureLow-T treated as well as untreated EN 1.4404 blocs is presented. <\/p>\n\n\n
\n \n
\nTreated EN 1.4404
\n<\/span><\/strong><\/p>\n<\/td>\n\n \n \n \n \n \n \n \n 1.8\u00b710-6<\/sup><\/td>\n 1.1\u00b710-6<\/sup><\/td>\n 1.2\u00b710-6<\/sup><\/td>\n 3.8\u00b710-7<\/sup><\/td>\n<\/tr>\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
![\"Wear](\"\/wp-content\/uploads\/2025\/06\/PLT_hardness_profile-1.png\")
<\/p>\nFigure 2.: Hardness profile of ExpanitePureLow-T treated sample manufactured in EN 1.4404. The raw stock material was a wrought and annealed bar.<\/h3>\n<\/li>\n
![\"Wear](\"\/wp-content\/uploads\/2025\/06\/ASTM-G133-test-wear-scar-profiles.png\")
<\/p>\nFigure 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).<\/h3>\n<\/li>\n<\/ul>\n
Almost 600 times lower wear rate<\/h2>\n
With such low wear rates, as presented in the table above for the treated sample, the measurement of the scars is not an easy task. The overview photograph of the three wear tracks is shown in Figure 4. When observing the scars under high magnification (Figure 5), the original grind lines are still visible in all three scars. This means that the scar depths are within the original surface finish of the block. The wear rate reduction calculated as a proportion of average wear rates is over 592 times. <\/p>\n\n
![\"wear](\"\/wp-content\/uploads\/2025\/06\/Wear_scars_photo.jpg\")
<\/p>\nFigure 4.: Photograph of the wear tracks. Scars 1-3 left to right.<\/h3>\n<\/li>\n
![\"Micrograph](\"\/wp-content\/uploads\/2025\/06\/Scar_2_x25.jpg\")
<\/p>\nFigure 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.<\/h3>\n<\/li>\n<\/ul>\n
![\"Surface](\"\/wp-content\/uploads\/2025\/05\/RUS1.jpg\")
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