Influence of chemical charging parameters on Hydrogen intake on pearlitic steel wires

Abstract: Hydrogen Embrittlement (HE) in steels occurs by hydrogen absorption, leading to a delay or sudden reduction in ductility or maximum load capability. This can happen either during fabrication or in service operations and will mainly depend on the exposure media and the type of steel. The media can be further divided into chemical, electrochemical or gas and material based on the composition, type of phases and microstructure characteristics. The HE behavior of ferritic and austenitic steels has been deeply studied in literature, and it is generally accepted that the higher the Ultimate Tensile Strength (UTS) of steel, the higher the sensitivity to HE. On the other hand, little attention has been paid in the literature to the effect of HE on pearlitic steel wires with mechanical strength above 2 GPa. Therefore, the present study aims to clarify the effect of electrochemical hydrogen charging on HE behavior of drawn pearlite steel wires.

The materials to be studied are fully pearlitic steel wires with carbon equivalent varied from 0.87 to 0.97 with initial, intermediate and final diameters of 5.5, 2.3 and 1.5 mm. For the charging experiments several factors were varied as pH, hydrogen recombination poison, voltage and charging time. Total and diffusible hydrogen were measured in G8 Galileo via the Impulse and Infrared Furnace and Mass Spectrometer. The HE behavior was evaluated by means of mechanical testing in Zwick Tensile machine with a maximum load capacity of 100 kN at a constant cross speed. The initial microstructure and after fracture were examined by Optical and Scanning Electron Microscopy.

The experimental results are evaluated and discussed as a function of relevant factors for the Hydrogen absorption, critical hydrogen amount, pearlitic morphology of steel, fractography and HE.

Keywords: hydrogen embrittlement, pearlitic steel, hydrogen charging, microstructure.