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Galling on stainless stell is a pervasive problem \u2013 even on martensitic stainless steel treated with a standard vacuum hardening the challenges still exist<\/span><\/p>\n<\/div>\n Based on the results of standard ASTM G98 test for galling resistance of materials, the galling mitigation on the 1.4021 martensitic stainless steel achieved with the ExpaniteHigh-T surface hardening process are truly outstanding and show that Expanite\u00ae offers superior solutions to improve galling resistance.<\/a><\/p>\n<\/div>\n The ASTM G98 test geometry involves a cylindrical button which is rotated 360\u00b0 against a stationary block under increasing normal force. For the test conducted with samples manufactured in alloy 1.4021 and treated with ExpaniteHigh-T, the load was varied from 100psi to 30ksi (0.7 MPa to 207 MPa). In the test the load is gradually increased until galling is observed, thereby establishing the threshold galling stress. After the test the surfaces are visually inspected and a descriptive grade is given to characterise the mating pair\u2019s susceptibility to galling.<\/p>\n<\/div>\n Pressure (MPa)<\/span><\/strong><\/p>\n<\/td>\n Pressure (ksi)<\/span><\/strong><\/p>\n<\/td>\n Vacuum hardened surface<\/span><\/strong><\/p>\n<\/td>\n Expanite High-T treated surface<\/span><\/strong><\/p>\n<\/td>\n<\/tr>\n 3.4<\/p>\n<\/td>\n 0.5<\/p>\n<\/td>\n Major<\/p>\n<\/td>\n None<\/p>\n<\/td>\n<\/tr>\n 6.9<\/p>\n<\/td>\n 1<\/p>\n<\/td>\n Major<\/p>\n<\/td>\n None<\/p>\n<\/td>\n<\/tr>\n 34<\/p>\n<\/td>\n 5<\/p>\n<\/td>\n Major<\/p>\n<\/td>\n None<\/p>\n<\/td>\n<\/tr>\n 69<\/p>\n<\/td>\n 10<\/p>\n<\/td>\n n\/a<\/p>\n<\/td>\n None<\/p>\n<\/td>\n<\/tr>\n 103.5<\/p>\n<\/td>\n 15<\/p>\n<\/td>\n n\/a<\/p>\n<\/td>\n Major<\/p>\n<\/td>\n<\/tr>\n 138<\/p>\n<\/td>\n 20<\/p>\n<\/td>\n n\/a<\/p>\n<\/td>\n Major<\/p>\n<\/td>\n<\/tr>\n 207<\/p>\n<\/td>\n 30<\/p>\n<\/td>\n n\/a<\/p>\n<\/td>\n Major<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Expanite\u2019s solution heat treatment process for martensitic stainless steels such as EN 1.4021 or American standard AISI 420A used in this study, consists of three distinct steps.<\/p>\n First is high temperature solution nitriding of around 1mm depth, providing increased surface hardness (even 100 HV above core) and improved pitting resistance, owing to up to 1.0 wt% of diffused nitrogen.<\/p>\n Second step is a sub-zero deep cooling treatment, ensuring homogenous martensitic structure throughout the part. Lastly, low temperature tempering is conducted to improve core toughness. Such treatment provides excellent results in trials conducted under laboratory conditions such as ASTM G98 test, and can be readily applied to martensitic stainless steel parts to vastly improve their applicability.<\/p>\n<\/div>\n Standard Vacuum Hardening Against ExpaniteHigh-T<\/h2>\n \nThe results are summarised in Table 1. Two standard vacuum heat treated 1.4021 surfaces gall even under very low normal stresses of 0.7MPa (100psi). Galling threshold can be therefore defined below this contact pressure.<\/p>\n \nFigures 1 and 2 show severe galling of vacuum hardened surfaces that originated in ASTM G98 test under a contact pressure of 5ksi (34MPa). In a mating couple with two ExpaniteHigh-T-treated surfaces of martensitic stainless steel 1.4021 shown in Figures 3 and 4, galling is completely mitigated until very high loads are applied (even at 10ksi or 69MPa of contact pressure).<\/p>\n \nThe different shade of the circular mark on the flat counterpart can be attributed to surface polishing. The galling threshold has been crossed between the loads of 69MPa and 103MPa.<\/p>\n \nWhen comparing results on surfaces with and without ExpaniteHigh-T hardening treatement, a 150-fold increase of contact pressure is required to induce galling.<\/p><\/div>\n \n
\nASTM G98 Standard Test for Galling Resistance
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\n \n \n \n \n \n 0.67<\/td>\n 0.1<\/td>\n Minor<\/td>\n n\/a<\/td>\n<\/tr>\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\nHeat Treatment – the Expanite Way<\/h2>\n
\nTest Results, <\/p>\n
The test result shows a remarkable galling resistance afforded by ExpaniteHigh-T surface hardening.<\/p>\n\n
![\"ASTM](\"\/wp-content\/uploads\/2025\/05\/ASTMG98-Figure-1.png\")
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<\/p>\n<\/li>\n<\/ul>\nFigures 1 & 2: Surface of vacuum hardened mating couple after ASTM G98 test under the highest tested load of 5ksi (34 MPa). Severe galling can be seen on both flat (left) and rotating button (right).<\/h3>\n
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![\"ASTM](\"\/wp-content\/uploads\/2025\/05\/ASTMG98-Figure-3.png\")
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<\/p>\n<\/li>\n<\/ul>\nFigures 3 & 4: Surface of ExpaniteHigh-T hardened mating couple after ASTM G98 test under the highest test load below galling threshold at 10ksi (68 MPa). No galling can be seen on both flat (left) and rotating button (right).<\/h3>\n
Results with Expanite a case study<\/h2>\n
A valve manufacturing company aimed to replace conventional heat treatment for higher performance in their valve seat for gasoline high-pressure pump. The Expanite process increased corrosion and wear resistance and even simplified logistics since the Expanite hardening process was now made available in Europe, Asia and the US.<\/div>\n
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