Abstract
Carbide-free bainitic steels are an example of high-strength steels that show an excellent combination of strength, ductility, toughness and rolling fatigue contact resistance and are progressively being introduced in the production of railways, crossings and automotive components. Although there are Mn-free approaches able to produce carbide-free bainitic steels, those based on the addition of Mn are less expensive. Therefore, it is important to fully understand the mechanical behavior of such materials to develop reliable engineering products. In this paper, three low-carbon bainitic steels, differing in Mn content, namely 0%, 2.3% and 3.2%, designated as steel A, B and C, respectively, were studied in a systematic manner. Low-cycle fatigue tests were conducted under symmetrical strain-controlled conditions for different strain amplitudes (0.6%, 0.7%, 0.8% and 1%). Independent of Mn content, a strong relationship between cumulative strain energy density and number of cycles to failure was found. Based on this relationship, a new predictive model, capable of estimating the fatigue lifetime, was developed. Predictions based on the new model were close to the experimental lives and were more accurate than those computed via the well-known Smith-Watson-Topper (SWT) and Liu criteria.
Highlights
Diminishing fuel consumptions and mandatory lower CO2 emissions are both pushing the automotive industry to weight reduction in the design of cars and increasing the use of railway transportation of goods and people
Fatigue life was evaluated by means of a cumulative strain energy density model and the predictions were compared to those obtained via the well-known SWT and Liu criteria
At a fixed value of strain amplitude, a close analysis of the results showed thatcontent plastic increased, strain energy energy density per cycle was higher for steel A and tended to diminish as Mn density per cycle was higher for steel and tended to diminish as
Summary
Diminishing fuel consumptions and mandatory lower CO2 emissions are both pushing the automotive industry to weight reduction in the design of cars and increasing the use of railway transportation of goods and people To achieve those goals, recently advanced high-strength steels are currently being used to reduce components’ thicknesses in the automotive industry and to produce improved railway rails and crossings. Concerning the loadings, automotive components and railway rails are being subjected to very complex and demanding loadings, requiring suitable bainitic steels with high yield strength to avoid severe plastic deformation, high toughness, strain hardening capability, and wear resistance, and improved RCF properties [7] in order to avoid, as much as possible, the nucleation and growth of fatigue cracks. Fatigue life was evaluated by means of a cumulative strain energy density model and the predictions were compared to those obtained via the well-known SWT and Liu criteria
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