PSI - Issue 75

Jérémie BOUQUEREL et al. / Procedia Structural Integrity 75 (2025) 442–449 Author name / Structural Integrity Procedia (2025)

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1. Introduction While electrical vehicles are of interests at the beginning of the XXI st century, the largest share of the fleet (motorcycle + cars) is made up of thermal vehicles. Many countries have been optimizing the components of thermal engines for over a century, improving engine efficiency under complex local environmental conditions (temperature, pressure, fuel and exhaust media). Knowledge of the damage to the materials used can also be considered as avenues for optimization so as not to rely heavily on electrification. Among the main components of combustion engines, we distinguish the intake and exhaust valves. These latter play crucial roles, helping control the flow of air-fuel mixture and exhaust gases. Hence, they are also facing many possible degradations mechanisms (wear, thermal degradation, corrosion and oxidation, f atigue, creep…) Raghuwanshi et al. (2012). Various materials have been considered for such applications and the development of martensitic stainless steel after its discovery in 1915 was obviously very attractive for valve fabrication. In general, such kind of steels typically contain 12 – 17 wt% Cr, 0 – 4 wt% Ni and 0.1 – 1.2 wt% C. For the required properties, such as improved corrosion resistance, machinability, toughness., other alloying elements can be added, including Mo, V, Nb, Al or N. “Silchrome 1”, patented in 1919 belongs to this steel family and appears suitable for valve fabrication because they maintain their properties up to 600 – 650 °C under a high dynamic load (Petsov (1977). It has been employed for Harley-Davidson WLA/WLC World War II motorcycle exhaust valve. B y contrast to other valve’s materials, the literature on Silchrome 1 and its use, despite its long and very rich history, is sparse. However, focusing on the understanding of the microstructure resulting from heat treatment, chemical composition and the forming process allows for very high performance martensitic steels (Ruzicka et al. (2024)). The purpose of this study is to document an aspect of the degradation occurring in exhaust valve extracted from a Harley-Davidson WLC motorcycle of 1942. It takes into consideration that investigating historical samples might face problems linked to some level of inhomogeneity when comparing to modern materials (microstructure homogeneity, cleanliness (inclusions) …) . For such kind of investigation, a worn component has been compared with a replacement one produced at the same period. Figure 1 is a photograph of the two investigated valves. The as-new valve, referred to as HDEN1 (Harley-Davidson Exhaust New 1) comes from a surplus unused replacement kit (2 valve pieces), made in 1942 for a Harley-Davidson WLA/WLC motorcycle. The used counterpart (HDEU1) comes from a H-D 42WLC located in a private collection in the Czech Republic. The used valves are significantly shorter with a modified tip, despite service in the appropriate WLC engine. Various modifications at historical vehicles parts are common, especially when spare-parts are unavailable to the owner. The mileage of the used part remains unclear. Nevertheless, the valve has remained on the same vehicle from 1942 to 2021. In addition, the used valve has been refurbished as attested by the thickness of the valve margin, from which a range of use can be estimated. It can be expected that the motorcycle has a total mileage ranging from 150 000 km to 300 000 km. Hence, considering an average speed of 50-60 km/h, this corresponds to 3000-6000 hours of use. Considering also that the WLA/WLC engine max power is reach at 4600 rpm, this induces a number of cycles undergone by the valve ranging from 1.7 10 8 to 4.1 10 8 cycles per lifespan. 2.2. Structural observations The entire valves were cut along their axial direction. One of the valves halves was then cut into small pieces. The other valves half was mounted entirely into a polymer resin to examine the grain flow (flow lines). Vickers hardness profiles with as 5 mm step size, were done on the valves perpendicular cross section. Indents were placed at the center of the valve stem and valve disc to characterize the general hardness flow. The adopted metallographic preparation is the one commonly used for martensitic steels. 2. Materials and Methods 2.1. The investigated valves