Investigation of Austempering Effect on Fatigue Crack Growth of AISI 4140 Steel

Abstract:

The compact tension (CT) and tensile specimens of the AISI 4140 steel in cold rolling condition (untreated steel) were austempered by immersing it into the salt bath at 362°C for 60 minutes. The tensile strength properties and the fatigue crack growth (FCG) resistance were performed to investigate the effect of the austempering process in AISI 4140 steel. A significant increase in the yield strength for austempered steel is about 8.7 % and the elastic strain energy increases by 55.7 %. Austempered steel's fatigue crack cycle is longer than that of untreated steel. Data of stress intensity factor range (ΔK, MPa.m^1/2) and FCG rate (da/dN, m/cycle) was constructed in double log plot x-y axes for determining the materials constants m and C according to Paris’s law equation using a linear regression method. From the curve of ΔK versus da/dN, the constant m value for austempered steel (m = 3.45) shows better resistance than untreated steel (m = 3.77). On the other hand, the constant C value of 1.409×10^-12 for austempered steel is one order magnitude higher than that of untreated steel (C = 4.151×10^-13). The resistance of austempered steel against fatigue crack growth can be attributed to the formation of a bainite structure.

• Periodical: Defect and Diffusion Forum (Volume 431)
• Pages: 115-120
• DOI: https://doi.org/10.4028/p-5jJqQO
• Online since: February 2024
• Authors: Mohammad Badaruddin*, Reza Annisa Ainnayah, Rizqy Nurully Wijaya, Slamet Sumardi
• Keywords: AISI 4140 Steel, Austempering, Bainite, Fatigue Crack Growth, Intensity Stress Factor

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