Abstract
PH13-8Mo is a precipitation hardened martensitic stainless steel, known for its high strength but also for its high sensitivity to hydrogen embrittlement. Small punch test, SPT (also referred to as the ball punch test, BPT), is a relatively simple and new technique to assess the mechanical properties of samples under biaxial loading conditions. The current study utilizes the unique loading conditions of SPT to investigate the mechanical behavior and fracture prior to and after the hydrogen charging of PH13-8Mo steel. The mechanical characteristics were investigated at different metallurgical conditions: solution and quenched (SQ); fully-aged (550 °C for 4 h) and over-aged (600 °C for 4 h). Samples were cathodically hydrogen charged in a 1 M H2SO4 solution containing NaAsO2 (0.125 mg/L) at 50 mA/cm2 for different durations of 0.5 h, 2 h, and 19 h, and compared to the as-heat-treated condition. A fractographic examination was performed following the SPT measurements by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses were used as complementary characterization tools. It is shown that upon hydrogen charging, the SPT fracture mode changes from ductile to completely brittle with a transition of mixed mode cracking also affecting the SPT load-displacement curve.
Highlights
Precipitation hardened martensitic stainless steels (PHMSS) are an important sub-class of theFe-Cr-Ni type alloys, which are widely utilized in the aerospace and petrochemical industries due to their optimized combination of high strength, toughness, and good corrosion resistance [1,2]
The current research studies the effects of various metallurgical conditions of the solution and quenching and subsequent aging treatments, prior and following hydrogen charging, of PH13-8Mo maraging stainless steel on the mechanical properties evaluated by the small punch testing (SPT)
For 0.5, 2, and 19 h, was used to introduce high fugacity hydrogen following over-aging at 600 ◦ C for 4 h, where the relative amount and size of the γ-FCC reverted the austenite phase, reaching ~10% and ~450 × 450 nm2, respectively, were significant
Summary
Precipitation hardened martensitic stainless steels (PHMSS) are an important sub-class of the. In a recent study by Garcia et al [32], different empirical correlation functions and data analysis approaches to the SPT curve were assessed This was used to analyze SPT’s conducted on a variety of metallic alloys, including different types of steels having a wide range of mechanical properties, where all specimens had a thickness of 500 μm. It was concluded by Garcia et al [32] that the best estimation for the yield stress, σys , of a metallic specimen can be obtained by utilizing Equation (1) based on the Py_t/10 method shown in his work. An SPT’s relative simplicity, and the fact that charging conditions can be controlled (small thin samples), sample dimension and loading conditions possibly create better sensitivity to the hydrogen-rich layer in electrochemically charged samples
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