Effect of water contamination on the diffused content of hydrogen under stress in AISI-52100 bearing steel

Abstract: Popular Abstract in Swedish Abstract Hydrogen embrittlement is a degradation process of mechanical/tribological properties (toughness, wear etc.) of mating steel surfaces. This is caused by the presence and interaction of hydrogen with applied stresses. Therefore, it is important to quantify the hydrogen content which could be dissolved under applied stresses in steel. Water contamination of lubricants is often considered as a reason of hydrogen embrittlement of rolling bearings. Thus the effect of water and %RH (relative humidity) on the hydrogenation/dehydrogenation of steel was studied experimentally under different operating conditions. Two types of steels were used, that are silver steel and AISI-52100 ball bearing steel. The testing conditions used in various tests, were percent relative humidity (%RH), temperature, rotating bending stresses, uni-axial tensile stress, rolling and sliding in combination with rotating bending stresses. As a first task, the hydrogen content was quantified in as-received specimens of bearing steel. The spread of hydrogen content was measured in radial and axial directions of the as-received bearing steel bars. This was done to show the importance of the internal hydrogen embrittlement effects of the initial hydrogen content. Sample melting technique (SMT) was used to quantitatively analyze the total content of hydrogen in all specimens using a hydrogen analyzer. In addition to this, Elastic Recoil Detection Technique (ERDT) was employed to qualitatively analyze the local hydrogen content distribution in soft and hard AISI-52100 bearing steel. Secondly, the influence of applied stresses on the absorption of hydrogen content into respective steel specimens was studied. A rotating bending set up was used through a lathe machine. Water was used as a source of hydrogen charging of the testing samples in all rotating bending tests. The influence of rotating bending stresses on the absorption of hydrogen was studied in silver steel and in bearing steel bar samples. Further, a universal fatigue testing machine was used to study the effect of cyclic released uni-axial tension on the absorption of hydrogen in the bearing steel. Similarly, the influence of Sliding and Rolling on the absorption/desorption of hydrogen content was studied in combination of rotating bending stresses using the same lathe machine. Mild and water quenched silver steel bar specimens were used to study the influence of quenching and applied stresses on the absorption of hydrogen. Finally, the experiments were conducted on SKF-624 deep groove ball bearing (DGBB) under isolated operating environment. Non water absorbing grease was used as lubricant. Tests were run for 10% of L10 life of deep groove ball bearing. Two different amplitudes of pure radial loading were selected for testing under high and low relative humidity of the operating environment. Total content of hydrogen was measured in the inner ring, outer ring and 7-balls of DGBB (deep groove ball bearing) using the hydrogen analyzer. Results are presented for total dissolved (or absorbed) hydrogen content in various components as a function of bearing shaft revolutions and operating conditions. Results obtained revealed a dependence of total content of hydrogen on the number of inner ring shaft revolutions. Hydrogen seems to accumulate in the specimens with the increase of number of stress cycles or shaft revolutions.