The Influence of Steel Composition on the Formation and Effectiveness of Anti-wear Films in Tribological Contacts

Abstract

The effectiveness of antiwear additives in laboratory tests is commonly evaluated using specimens made of AISI 52100 through-hardened bearing steel. However, many lubricated machine components are made of steels with significantly different material compositions, which raises an important practical question of whether the performance of antiwear additives with these other steel types is different from that established with AISI 52100. To help answer this question, this paper investigates the influence of steel composition on the formation and effectiveness of antiwear films. Four steels that are commonly used in tribological applications, namely AISI 52100 through-hardened bearing steel, 16MnCr5 case-carburised gear steel, M2 high speed steel and 440C stainless steel are tested in rolling-sliding, ball-on-disc contacts lubricated with three custom-made oils, one containing ZDDP and two containing different types of ashless antiwear additives. The relative effectiveness of their boundary films was assessed by measuring their thickness and associated wear and friction over 12 h of rubbing at two specimen roughness levels. For ZDDP it was found that the formation of antiwear film was not significantly influenced by steel composition or specimen surface roughness. A similar tribofilm thickness, final tribofilm roughness and friction was observed with all four steels. No measurable wear was observed. By contrast, for the ashless antiwear additives the thickness and effectiveness of their tribofilms was strongly influenced by steel composition, particularly at higher roughness levels. The exact trends in film thickness vs steel relationship depended on the specific chemistry of the ashless additive (ester-based or acid-based) but in general, relative to AISI 52100 steel, M2 steel promoted ashless tribofilm formation whilst 440C retarded ashless tribofilm formation. This behaviour is attributed to the presence of different alloying elements and the ability of the additives to extract metal cations from the rubbing surfaces to support the growth of a tribofilm. In all cases ZDDP films were thicker and rougher, and produced higher friction than those formed by the ashless additives. However, unlike ZDDP, ashless blends generally produced significant wear, particularly with 16MnCr5 and M2 steels. The results indicate that to ensure reliable performance of a given machine component, the chemistry of an ashless antiwear additive should be matched with the types of steel present in the lubricated machine.

In-Situ Observation of the Effect of the Tribofilm Growth on Scuffing in Rolling-Sliding Contact

“…Interestingly, up to the 3 m/s test stage, DDP and TPP formed relatively thin tribofilms of less than 10 nm, but their film thicknesses then grew to more than 20 nm above this sliding speed stage. It has been shown that these ashless P-S additives form films more slowly that ZDDPs [32]. MoDTC formed a thick tribofilm of around 10 nm to 15 nm quite early in the test sequence and this remained stable up to 6 m/s.…”

Structural characterisation of iron sulfide tribofilms formed on carbon and stainless steels

“…5,6,11 Thus, recent studies have focused on the influence of metallic and nonmetallic substrates in the tribochemical reactions of MoDTC [12][13][14] and ZDDP. [15][16][17] Chlorine-containing EP additives are commonly used in the cold-working processes of steel because of their cost effectiveness and high lubricity along with high corrosion resistance. 3 However, their application is limited owing to environmental and public health hazards such as carcinogenicity.…”

“…In particular, MoDTC reduces friction by forming a MoS 2 tribofilm on the contact area, 7–10 whereas ZDDP prevents wear by forming an amorphous tribofilm with multilayered structures 5,6,11 . Thus, recent studies have focused on the influence of metallic and nonmetallic substrates in the tribochemical reactions of MoDTC 12–14 and ZDDP 15–17 …”

Tribological responses of steels to different surface films generated in oil lubricants

“…In addition, it was recently reported that the tribofilm formation kinematics could be affected by the steel composition depending on the lubrication additives. Pagkalis et al found that the boundary lubrication effectiveness of ashless anti-wear additives on 100Cr6, M2, 16MnCr5 and 440C steels was significantly different, while the ZDDP tribofilm was little influenced by the steel composition (Pagkalis et al , 2021).…”

“…In tribological contacts, surface films are sometimes generated on the worn surface that significantly influence the tribological behaviors of steels and other metals. Typical examples include tribofilms generated by oil additives on surfaces of engine steels (Gellman and Spencer, 2002;Spikes, 2004) and oxide film spontaneously formed on surfaces of passive metals (Feyzi et al, 2022;Sun and Bailey, 2023;Toh et al, 2018). However, depending on their nature, the generated surface films affect the friction and wear behaviors of metals in various manners (Cao et al, 2016;Carrington et al, 2021;Luiz and Spikes, 2020;Mittal et al, 2022;Topolovec-Miklozic et al, 2008).…”