On the effects of heat and surface treatment on the fatigue performance of high-strength leaf springs

Abstract

Leaf springs constitute the most effective suspension way of commercial vehicle axles from the cost and maintainability point of view. Especially in case of front axles, they overtake both the guidance and suspension functions, which consequently designates them as safety components, whose pre-mature failure is explicitly prohibited. The present paper deals with the fatigue performance of downsized parabolic leaf specimens made of the high-strength spring steel 51CrV4 under serial manufacturing conditions. It focuses on the influence of the major manufacturing steps, i.e. the heat treatment and the subsequently applied stress shot peening. The effectiveness of the applied heat treatment on the microstructure transformation and the extent of surface decarburization is determined by means of optical microscopy and corresponding microstructural analyses. Comprehensive series of constant amplitude fatigue tests are executed before and after the applied stress shot peening to quantify its effectiveness on the fatigue performance. The tests cover two characteristic stress ratios of operational significance with the complete range of interest being experimentally investigated. Additionally, surface residual stresses measurements together with micro- and macro-hardness and roughness values before and after stress shot peening are executed to expose the influence of each individual technological effect on the overall fatigue performance.

Fatigue Crack Propagation of 51CrV4 Steels for Leaf Spring Suspensions of Railway Freight Wagons

“…Figure 11 illustrates the regression obtained from Equation(8) and the respective propagation threshold points previously obtained. Comparing the experimental γ with the one obtained via Equation(5), which resulted in γ = 0.5941 for σ uts = 1438.35 MPa, it was verified that the value of 0.5767 determined from Equation (8) was in satisfactory agreement.Once γ was determined, the Walker model written in Equation (4) resulted via the least-squares method in a coefficient C w,I I = 3.47 × 10 −8 and an exponent m w,I I = 2.16, with a coefficient of determination R 2 = 0.89, as shown in Figure12. Figure12shows a greater scatter in the data obtained for ratios of 0.5 and 0.7; however, all points were contained in the grey area (illustrated in darker blue in Figure12), corresponding to the prediction curves for one standard deviation of the propagation rate, σ da/dN , with regards to the average value, µ da/dN .…”

“…Figure11illustrates the regression obtained from the equation (8) and the respective 358 propagation threshold points obtained previously. Comparing the experimental γ with 359 the one obtained via equation(5), which results in a value of γ = 0.5941 for σ uts = 1438.35 360 MPa, it is verified that the value determined from equation (8) of 0.5767 is in satisfactory 361 agreement.362…”

“…The chromium-vanadium alloyed steel, 51CrV4 steel grade, has been used for the design of industry machinery components and suspension elements of road and rail vehicles [1][2][3]. In the rail freight sector, 51CrV4 steel grade is usually found in leaf springs due to its high mechanical strength to static and fatigue loadings [4,5].…”

Analysis of Experimental Results Regarding the Selection of Spring Elements in the Front Suspension of a Four-Axle Truck

“…The material from which the springs were made is 51 CrV4 steel. Data to develop a fatigue curve were selected based on papers [1,21,23] and the results of tests carried out on leaf springs. Figure 11 shows the fatigue curves for 51 CrV4 steel with different values of the exponent k depending on the state of the material after the spring manufacturing process at R = 0.…”