Limits of Contact Stress Allowable on Rollers Made of Carbon and Alloy Steels (160〜130 HB) and Changes in Contact Surface

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Rolling contact fatigue tests were conducted under pure rolling conditions using carbon steel and alloy steel rollers. Hardnesses of pitting rollers were in the range 160 〜 100 HB (mating roller hardness was 420 HB in the case of unequal hardness combination). The results obtained are as follows : (1) Theoretical limits of contact stress p_max allowable on the steel rollers are in the range 0.31 〜 0.52 HB (kg/mm^2) when they are calculated under assumption that pitting does not occur until the reversed shear stress τ_2max in rolling contact reaches the endurance limit τ_w in reversed twisting. (2) In the cases of unequal hardness combination, pitting occurred at Hertzian stresses less than 0.3 HB when the roughness R_max2 of harder roller was greater than the theoretical oil film thickness h_min. For instance, many pits occurred at a Hertzian stres of 50 kg/mm^2 = 0.17 HB when a 300 HB roller with a roughness of 1μm R_max was combined with a 420 HB roller with a roughness of 3 μm R_max. (3) However, no pitting occurred at Hertzian stresses greater than the upper limit of theoretical pitting limit p_max = 0.52 HB when R_max2 < h_min. For instance, no pitting occurred until 10^7 rotations even when loads corresponding to Hertzian stresses of 113 (=0.71 HB), 140 (=0.61 HB) and 165 (=0.55 HB) kg/mm^2 were applied on 160,230 and 300 HB steel rollers respectively. (4) Appreciable increases in hardness were observed at the subsurface of pitting rollers when the rollers were rotated at Hertzian stresses greater than the theoretical pitting limit 0.52 HB (kg/mm^2).
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Limits of Contact Stress Allowable on Rollers Made of Carbon and Alloy Steels (160〜130 HB) and Changes in Contact Surface

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