Chemical Composition, Microstructure, and Mechanical Properties of Steel Rails Produced by China Hanyang Iron Works

The history of steel rail manufacturing at the Hanyang Iron Works in China is briefly summarized first in this paper. The chemical composition, microstructure, inclusions, and mechanical properties of the manufactured rails were then systematically analyzed. The progress of manufacturing process evolution and the enhancement of product quality are elucidated through this study. The chemical composition of steel rails produced by Hanyang Iron Works in its initial stage (before 1904) was characterized by low carbon content (0.13–0.22 wt.%) and high phosphorus levels (P ≥ 0.15 wt.%). Inclusions were primarily identified as sulfides (MnS) and composite inclusions of sulfides and silicates (MnS·SiO2). The microstructure consisted of a large amount of ferrite and pearlite. Following the technical transformation from 1905 to 1908, dephosphorization was achieved and the composition control of the steel rails was optimized. The carbon content of the rails was increased to above 0.48 wt.%, while the phosphorus content was significantly reduced (P ≤ 0.10 wt.%). The inclusions were identified as sulfides (MnS) and composite inclusions consisting of sulfides and aluminum oxides (MnS·Al2O3). The microstructure was transformed into a combination of a small amount of proeutectoid network ferrite and pearlite. The mechanical performance of the steel rails was substantially improved via the implementation of technological upgrades at the Hanyang Iron Works. A tensile strength of 800 MPa grade was achieved in some rails, which constitutes a 200 MPa increment over the strength of rails from the early production period. A transition in the fracture morphology of tensile specimens was observed, shifting from large and shallow dimples with a small amount of cleavage fracture to small, shallow dimples combined with predominant cleavage fracture.