Hydrogen‐induced stress corrosion cracking studied by the novel tuning‐fork test method

Abstract

A novel tuning-fork test method was developed to study hydrogen-induced stress corrosion cracking of high-strength steels. Special tuning-fork specimens are designed to enable accurate stress adjustment via constant displacement under cathodic hydrogen charging conditions. In this study, the testing method is further developed, making the potentiostatic hydrogen charging possible through the modifications of the corrosion cell. Different direct-quenched, lowand medium-carbon steel grades, with a hardness range of 300-550 HBW, are investigated with both galvanostatic and potentiostatic hydrogen charging techniques. For each steel grade, the lowest fracture stress and highest nofracture stress are determined. Both hydrogen charging techniques produce similar results, and it is observed that the fracture stress decreases with the increase in hardness. However, the potentiostatic technique produces larger differences between the lowest fracture stress results, thus having a better resolution.

Hydrogen-Induced Cracking of 500 HBW Steels Studied Using a Novel Tuning-Fork Test with Integrated Loadcell System

“…This study presents the latest developments of the Tuning-Fork Test (TFT) 20,21 with modifications on the corrosion cell, the addition of the loadcell clamping system, and special software for the data analysis. The loadcell clamp together with the developed software allows monitoring of the crack initiation, propagation, and time-to-fracture of individual tests.…”

“…The novel tuning-fork specimens (Figure 2a) are utilized in this study 20,21 . The specimens were wire electrical discharge machined (WEDM) from 5 mm thick machined sheets and oriented so that the expected crack growth plane is either in the longitudinal or transverse direction in terms of rolling direction.…”

“…The distribution of the compressive stress is not relevant in the crack initiation and therefore it is not displayed in Figure 3. Stress distribution in the tuning-fork specimens during compression was analyzed with FEM software Abaqus 21 for each steel grade. Compressed specimen arm distance applied during the tests was calculated using this data.…”

“…A novel constant-displacement testing method for evaluating the HE susceptibility of martensitic high-strength steels has been developed 20,21 . Initially, tuning-fork tests (TFT) were conducted under galvanostatic 20 or potentiostatic 21 hydrogen charging conditions and used for ranking of high-strength steels by the determination of σth. The testing method is here developed further by adding a loadcell clamping system, which improves loading accuracy and eliminates unpredictable testing time issues with relatively short testing times.…”

“…Variability of the data is small, and the tests have good repeatability. In addition to time-to-fracture, trustworthy threshold stress level can be determined with a longer testing period 21 by applying the binary search procedure according to SFS-EN ISO 7539-1 22 .…”