Formation and characteristics of white etching layers on austenitic steels
Publicerad
Författare
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Transport by train for passengers and for industrial logistics require advancements
on the maintenance and demand a deeper understanding of the damages that influence
the railway system. Railways experience significant mechanical and thermal
loads at the wheel and rail interface, which demand materials with high durability
and to prevent failure mechanisms. While fine pearlitic steel (R260) is the predominant
material used in Europe, certain areas such as switches and crossings S&C
employ alternative materials like Mn13, Hadfield steel, or bainitic steel to withstand
high dynamic impact.
By examining the microstructural changes and hardness variations in these railway
steels, this study contributes to a deeper understanding of the effects of mechanical
deformation and thermal exposure in the wheel and rail interface. These findings
can provide information to improve maintenance strategies aimed at preventing failures
and increasing the lifetime of railway systems.
This project aims to characterise the microstructural changes and evaluate the hardness
properties of two railway steels, R260 and Mn13, in the heat-affected region. By
subjecting the materials to mechanical deformation and thermal pulses, this study
seeks to gain insights into the damage interactions that may occur at the wheel and
rail interface.
The result confirms that R260 steel transforms to martensite, forming a thin layer
known as a white etching layer (WEL) at the surface after thermal pulses. The rolled
austenitic manganese steel instead remelts and forms a layer with a combination of
dendrite and columnar structure, similar to cast or welded Mn13. Notable observations
include the increased presence of segregated carbides along the heat-affected
zone, grain boundaries, and solute accumulation in between the dendrites.
Microhardness and microstructural evaluations were conducted on both untreated
bulk materials and those subjected to deformation and thermal exposure. In the
thermally exposed region, the R260 steel shows an increase in hardness, while the
hardness instead decreases in Mn13. Insights into what affects the hardness and
why the microstructure changes are presented in the report.
Beskrivning
Ämne/nyckelord
White etching layers WEL, austenitic manganese steel, Mn13, phase transformation, railway steel, microstructure, hardness