The focus of this study is to analyze hydrogen embrittlement susceptibility of a modified AISI 4130 steel by means of incremental step loading tests. Three different microstructures with a hardness ...of 40 HRC were analyzed: martensite with large and small prior austenite grains and dual-phase (martensite/ferrite). According to the results, the dual-phase microstructure presented the lowest hydrogen embrittlement susceptibility and martensite with large prior austenite grains, the highest. This behavior was attributed to the lower fraction of high-angle boundaries presented by the martensite with large prior austenite grains, which led to a higher diffusible hydrogen content. Moreover, the ferrite local deformation in the dual-phase microstructure enhanced its hydrogen embrittlement resistance by lowering the stress concentration. A synergic effect of decohesion and localized plasticity was identified on the hydrogen induced fracture of the tested microstructures leading to an intergranular + quasi-cleavage fracture in the martensite and quasi-cleavage in the dual-phase microstructure.
•Evaluation of the microstructure effect on hydrogen embrittlement by means of ISL test.•Hydrogen embrittlement analysis of martensitic and dual-phase microstructures.•Role of prior austenite grain size on hydrogen embrittlement susceptibility.•Effect of high-angle boundaries on hydrogen diffusion behavior.•Identification of hydrogen induced fracture micromechanisms through SEM and EBSD analysis.
Friction stir welding is a solid-state joining/processing technique that offers high strength and productivity, resulting in a microstructure similar to hot working cycles. However, high melting ...temperature metals such as steels cause excessive wear over welding tools, representing a significant economic issue. Most studies conducted in steels have used polycrystalline cubic boron nitride (PCBN) and W-Re composite tools, which offer a combination of high strength and hardness at high temperatures, along with high-temperature stability. However, even those tools are susceptible to tool wear. In the present study, experimental data was collected during friction stir processing of X70 grade pipeline steel plates, using W-Re and PCBN composite tools under well-controlled conditions. Profilometry and optical microscopy were used to quantify the volume loss at the welding tool due to the number of plunges and the welded distance. Torque and transverse force at the welding tool and the welded bead width were measured and related to the wear process. Tool contamination in boron-nitrogen particles and dissolved tungsten was identified at the stir and hard zones, more substantial at the latter.
The aim of this study was to characterize mechanical and microstructural characteristics of friction-stir-welded GL E36 shipbuilding steel. The tool rotational speed was kept constant at 500rpm and ...different welding speeds were used (1, 2 and 3mm/s) to achieve different heat inputs. Thermal cycles were monitored by thermocouples placed near the weld face. The welded joints showed a very good esthetics and homogeneous surface quality that indicate a stability of the considered process parameters. The welded joints properties were analyzed by metallography and mechanical tests such as microhardness, tensile and bending. Macrostructural observations were done at the beginning, middle and ending of the welded length. In addition, radiographic inspection was carried out. The pcBN tool exhibited good wear behavior even after welding around 8.5m where no apparent loss in dimensions and geometrical features of the probe and shoulder were found. The macrographs displayed different microstructural features and material flow pattern among the heat inputs achieved. A large microstructure gradient was observed, especially within the stirred zone. All the tensile samples broke at the base material showing that the joints achieved higher strength. Microhardness peaks of about 400HV were also encountered in all the joints. Finally, for welding speeds of 2–3mm/s the thermocouples presented the most uniform thermal profiles.
This study proposes the use of a loading profile based on a combination of the ISL technique and the continuous multicycle indentation. This combination in our study was named N-ISL loading profile. ...The N-ISL loading profile was used to evaluate the hydrogen effect on nanomechanical properties of a Ni-base superalloy single crystal. For this purpose, nanoindentations were performed on a single crystal Ni-base superalloy. Hydrogen charging was carried out by cathodic protection with the sample immersed in a NaCl 3.5 wt% aqueous solution under a current density of − 1 mA/cm
2
. The results showed that the modified N-ISL profile provided the required time for hydrogen accumulation under the indenter tip, enhancing the hydrogen effect. The load relief in the N-ISL profile was found to be the major indicator of plastic deformation event and consequently strong evidence of dislocation movement. The hydrogen charging accentuated the plastic deformation in all steps, indicating that the hydrogen affected the dislocation mobility.
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This study aims at evaluating the effect of test velocity associated with the Small Punch Test on the ultimate tensile strength. The velocity factor was investigated on two levels (1.0 μm/s and ...0.1 μm/s) based on a single factor design. This design was applied to three high strength steels (AISI 4130 M, 4137 M and 4140) widely used in the oil and gas offshore industry. The tests were performed in a cathodic protection environment, which consisted of a 3.5 wt% NaCl aqueous solution to simulate hydrogen embrittlement. For each material, one specimen in air at the conventional rate (0.02 mm/s) was also tested. An increasing trend was noted toward the susceptibility to hydrogen embrittlement when the test velocity was reduced from 1.0 μm/s to 0.1 μm/s. However, the Analysis of Variance showed that the test velocity factor caused statistically significant effects on the ultimate tensile strength only for 4137 M steel. The distinct behavior shown by the 4137 M, 4130 M and 4140 steels, under the experimental conditions investigated, was attributed to the combination of several factors: test velocity in the investigated H-charged environment; shape and volume fraction of non-metallic inclusion; calcium addition; tensile strength and hardness in air at the as-received condition.
•The test velocity effect of the Small Punch Test in a hydrogen environment was evaluated.•The susceptibility to hydrogen embrittlement of three high strength steels was investigated by means of SPT.•The test velocity reduction led to a decreasing trend on the ultimate tensile strength for the three high strength steels.•Several factors contributed to the distinct behavior of the three steels, such as inclusions, strength and hardness.
High-performance alloys such as super duplex stainless steels (SDSS) are of interest to the oil and gas industry, especially in deep and ultra-deep reservoirs where high pressures and highly ...corrosive environments are prevalent. SDSS have high nitrogen contents and pitting resistant equivalent number (PREN) values greater than 40, however, fusion welds of these alloys can exhibit unsuitable microstructures and defects that may result in failure during usage. Solid-state linear friction welding (LFW) offers an alternative for the effective joining of SDSS with a less detrimental effect on microstructure and properties. In this work, four LFW joints in UNS S32760 SDSS were produced and investigated by evaluating the process parameters required to achieve a high-quality joint with the desirable metallurgical, mechanical, and localized corrosion properties. These properties were assessed through metallography (optical microscopy and scanning electron microscopy), tensile and microhardness tests, and corrosion analysis according to the ASTM G48A standard. Results indicated that one specific combination of LFW parameters led to a defect-free joint, and that the mechanical properties of the weld in this case were comparable to those of the base material. Additionally, an adequate balance between ferrite and austenite phases was achieved throughout the microstructural gradients seen in the weld region. Microhardness values were below 350 HV, thus complying with the DNV–OS–F101 standard. Furthermore, no pitting corrosion was observed in this joint under the testing conditions suggested by ASTM G48A.
In the past few years, solid-state welding has been a great alternative in comparison to the conventional fusion welding technologies. Solid-state welds are usually processed in lower temperatures ...than the other common fusion joints, tending to avoid problems such as hydrogen embrittlement, brittle microstructures and porosity. Therefore, these advantages can be useful to industrial applications which do not allow fusion welding. Offshore mooring components, which are fabricated under restricted standard requirements to ensure the floating marine integrity, is one of these applications. Thus, defects in links of mooring chains cannot be repaired by traditional welding, resulting in high operational costs. In this context, this study aims to characterize the Friction Hydro-Pillar Processing (FHPP) application to a mooring chain steel IACS UR W22 grade R4. The main process parameter studied was an axial force ranging from 30 to 60kN. The welded joints were evaluated by metallography (macro and microstructure) and microhardness mapping. Furthermore, the toughness properties were assessed by Charpy and Crack Tip Opening Displacement (CTOD) tests, and the fractures were afterwards observed by scanning electron microscopy (SEM). The results showed that an increase in the axial force enhances the Charpy and CTOD values.
Repairing links of offshore mooring chains has presented a significant industry challenge, primarily arising from modifications in material properties, encompassing alterations in microstructure, ...hardness, and residual stress. In this context, the present work investigates the method of friction hydro-pillar processing (FHPP) applied to R4 grade mooring chain steel. Joints in as-repaired and post-weld heat treatment (PWHT) conditions were subjected to residual stress (RS) tests using the neutron diffraction technique, microhardness mapping, and microstructural evaluations. The process generated peaks of tensile and compressive stresses in different directions and hardness below that of the parent material in the softening zone. The friction zone promoted high hardness levels in the thermo-mechanically affected zone (TMAZ) with a maximum of 19% of the ultimate tensile strength of the parent material. As expected, the PWHT restored the RS and reduced the hardness; however, 4 h PWHT allowed the elimination of a hardness higher than that of the base material.
The objective of this work is the evaluation of hydrogen effects on the martensitic transformation and strain hardening in Duplex Stainless Steels (DSS) SAF 2205 (UNS S32205/S31803). DSS are ...two-phase alloys (austenite and ferrite), which are used for applications requiring high mechanical strength, in corrosive environments. Therefore, it is necessary a better understanding of the phenomena involved on the hydrogen embrittlement. For this, in situ measurements of X-ray diffraction were made during tensile test in H2 cathodically charging DSS 2205. The hydrogen charging reduces the stress relaxation, reducing the ductility and suppressing the hydrogen-induced austenitic to martensitic transformation. In addition, it also reduces the strain hardening (dislocation multiplication) in austenite. The strain hardening seems to have a higher influence than martensitic transformation on fracture process, even in absence of hydrogen.
The incremental step loading technique has been widely used for material hydrogen embrittlement characterization. However, due to numerous error sources that can affect the measurement results and to ...the current lack of standardization, users are facing difficulties in the evaluation of measurement uncertainty as well as in the metrological performance evaluation of incremental step loading equipment. The paper deals with evaluation of the metrological performance of equipment used to characterize the susceptibility of materials to hydrogen embrittlement through use of incremental step loading technique. Additionally, a procedure is developed to estimate the measurement uncertainty associated with the results obtained during the test. Two equipment configurations were verified. The first one, with a load cell of 20 kN, was used for test specimens with nominal dimensions of 30 mm, 30 mm and 200 mm in width, thickness and length, respectively; and the second, with a 1 kN load cell was used for test specimens with nominal dimensions of 10 mm × 10 mm × 60 mm. Three measurands were evaluated in each assemblage (force applied on the specimen, equipment arm positioning angle and stress). Several metrological parameters were estimated (bias, accuracy, expanded uncertainty, repeatability, maximum error, hysteresis and nonlinearity). The effectiveness of the proposed procedure for uncertainty assessment was tested by calculation of the uncertainty associated with lower value for fast fracture strength. From the obtained results, it was concluded that the two equipment configurations had excellent metrological properties, in both the loading and unloading phases. It was shown that the proposed procedure can properly estimate the uncertainty associated with measurement on incremental step loading testing. Considering the widely use of the incremental step loading technique, the results here presented can be particularly useful for ensuring the traceability of results to the International System of Units required by the ISO 17025 standard.
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