TY - THES

T1 - Influence of explosive depth hardening on the formation of craze cracks in Hadfield steels

AU - Rockenschaub, Martin

N1 - embargoed until 12-10-2026

PY - 2021

Y1 - 2021

N2 - Work hardening is an effective and commonly used strategy to increase the wear resistance and the lifetime of Hadfield steel railway crossings. A widely used technique for obtaining such a work hardened microstructure is explosive depth hardening (EDH). In this work it will be investigated if and how EDH affects the craze cracking of railway crossings. Craze cracking is a phenomenon where a fine and branched network of several millimeter deep cracks on the surface of railway crossings is formed. Therefore, several samples from crossings received from voestalpine Railway Systems MFA SASU in France and voestalpine Railway Systems Nortrak (Inc.) in the US were investigated. The crossing from voestalpine Railway Systems Nortrak (Inc.) thereby tend to develop craze cracks very frequently while this specific quality issue is absent in crossing from voestalpine Railway Systems MFA SASU. The microstructure and microhardness of both crossings was examined, the chemical composition was analyzed and the Charpy notched impact energy was tested. Furthermore, the prepared microstructural cross sections and the existing craze crack surfaces were analyzed in the light microscope as well as in the scanning electron microscope to deepen the understanding of the formation of craze cracks in Hadfield steel railway crossings during EDH. It was found that craze cracking is an intercrystalline grain boundary fracture and additionally, no grain boundary precipitates were detected. However, the major difference was a significantly coarser grain size and a lower Charpy notched impact energy in crossings from voestalpine Railway Systems Nortrak (Inc) which developed craze cracks. Due to these facts, it can be concluded that the presence of craze cracks is directly related to the coarse grain structure which predominates the surface of voestalpine Railway Systems Nortrak (Inc.) railway crossings.

AB - Work hardening is an effective and commonly used strategy to increase the wear resistance and the lifetime of Hadfield steel railway crossings. A widely used technique for obtaining such a work hardened microstructure is explosive depth hardening (EDH). In this work it will be investigated if and how EDH affects the craze cracking of railway crossings. Craze cracking is a phenomenon where a fine and branched network of several millimeter deep cracks on the surface of railway crossings is formed. Therefore, several samples from crossings received from voestalpine Railway Systems MFA SASU in France and voestalpine Railway Systems Nortrak (Inc.) in the US were investigated. The crossing from voestalpine Railway Systems Nortrak (Inc.) thereby tend to develop craze cracks very frequently while this specific quality issue is absent in crossing from voestalpine Railway Systems MFA SASU. The microstructure and microhardness of both crossings was examined, the chemical composition was analyzed and the Charpy notched impact energy was tested. Furthermore, the prepared microstructural cross sections and the existing craze crack surfaces were analyzed in the light microscope as well as in the scanning electron microscope to deepen the understanding of the formation of craze cracks in Hadfield steel railway crossings during EDH. It was found that craze cracking is an intercrystalline grain boundary fracture and additionally, no grain boundary precipitates were detected. However, the major difference was a significantly coarser grain size and a lower Charpy notched impact energy in crossings from voestalpine Railway Systems Nortrak (Inc) which developed craze cracks. Due to these facts, it can be concluded that the presence of craze cracks is directly related to the coarse grain structure which predominates the surface of voestalpine Railway Systems Nortrak (Inc.) railway crossings.

KW - EDH

KW - explosive depth hardening

KW - craze cracks

KW - Hadfield steel

KW - railway crossing

KW - EDH

KW - explosive depth hardening

KW - craze cracks

KW - Hadfield steel

KW - railway crossing

M3 - Master's Thesis

ER -