316L奥氏体不锈钢厚板焊接工艺及接头性能研究

根据316L奥氏体不锈钢的焊接性,制定了316L厚板的焊接工艺,采用钨极氩弧焊和焊条电弧焊的组合焊接工艺对316L厚板进行了焊接,并对焊接接头进行了力学性能、金相检测和晶间腐蚀试验。结果表明,所获得的焊接接头无缺陷,力学性能合格,焊缝组织为奥氏体和少量δ铁素体,焊接接头无晶间腐蚀倾向。焊接工艺合理,满足316L奥氏体不锈钢厚板焊接生产要求。     

Additively manufactured 316L stainless steel: An efficient electrocatalyst

In the quest of finding an economical, yet efficient material, the idea of fabricating 316L stainless steel using additive manufacturing technology was explored to produce material with refined sub-granular structure. The surface of the stainless steel was further chemically treated with an etching solution to expose the grain boundaries. The grain boundary enriched surface resulted in more active sites for the oxygen evolution reaction (OER) in additively manufactured treated (AM-T) 316L stainless steel. AM-T sample manifests enhanced catalytic activity for OER with an overpotential of 310 mV to draw a 10 mA/cm² current density, along with a lower Tafel slope of 42 mV/dec compared to AM and wrought samples. These features were validated from the increased double-layer capacitance of AM-T and approximately 1.5 times larger electrochemically effective surface area of AM-T due to etching treatment compared to the wrought sample. Furthermore, AM-T also possesses stable activity retention for 100 h at a current density of 10 mA/cm².     

Thermal creep properties of alloy D9 stainless steel and 316 stainless steel fuel clad tubes

Uniaxial thermal creep rupture properties of 20% cold worked alloy D9 stainless steel (alloy D9 SS) fuel clad tubes for fast breeder reactors have been evaluated at 973 K in the stress range 125–250 MPa. The rupture lives were in the range 90–8100 h. The results are compared with the properties of 20% cold worked type 316 stainless steel (316 SS) clad tubes. Alloy D9 SS were found to have higher creep rupture strengths, lower creep rates and lower rupture ductility than 316 SS. The deformation and damage processes were related through Monkman Grant relationship and modified Monkman Grant relationship. The creep damage tolerance parameter indicates that creep fracture takes place by intergranular cavitation. Precipitation of titanium carbides in the matrix and chromium carbides on the grain boundaries, dislocation substructure and twins were observed in transmission electron microscopic investigations of alloy D9 SS. The improvement in strength is attributed to the precipitation of fine titanium carbides in the matrix which prevents the recovery and recrystallisation of the cold worked microstructure.     

Static and impact crack properties of a high-strength steel welded joint

In order to gain the benefits of weldable high-strength steels in pressurized equipment applications, satisfactory toughness and crack properties of the welded joint, both in the weld metal and the heat-affected –zone (HAZ), are required. Experimental investigations of toughness and crack resistance parameters through static and impact tests of a high-strength, low-alloy steel (HSLA) with a nominal yield strength of 700 MPa and its welded joint, were performed on Charpy-sized specimens, V-notched and pre-cracked, of the parent metal, weld metal and HAZ. The selected electrode produced slight undermatching and enabled the welded joints to be manufactured without cold cracks. The impact energy and its parts responsible for crack initiation and propagation were determined by toughness evaluation. Crack sensitivity, defined as the ratio of the impact energy for V-notched and for pre-cracked specimens, enabled a comparison of the homogeneous microstructure of the parent metal and the weld metal, and of the heterogeneous microstructure of the heat-affected-zone (HAZ), which indicated a better crack toughness behaviour of the HAZ. The results obtained showed that the toughness and crack resistance of the weld metal were significantly lower than those of the parent metal and the HAZ. The fracture mechanics parameters, J_Ic integral, and plane strain fracture toughness, K_Ic, as well as J resistance curves expressed the degradation less.     

Effects of hydrogen on tensile properties and fracture surface morphologies of Type 316L stainless steel

The effects of hydrogen on the tensile properties and fracture surface morphologies of Type 316L stainless steel were investigated using virgin and prestrained specimens. Hydrogen gas exposure at 10 MPa and 250 °C for 192 h resulted in its uniform distribution in the specimens. Such internal hydrogen degraded the tensile ductility of the specimens. Cup–cone fracture occurred in the non-, Ar-, and H-exposed specimens. The fracture surfaces were covered with large and small dimples. The H-exposed specimens exhibited larger small-dimple areas than the non- and Ar-exposed ones. The diameter of the large dimples decreased with increasing small-dimple area. Three-dimensional analysis of the dimples showed that the small-dimple regions were void sheets produced by local shear strain. Hydrogen accelerated nucleation of voids and formation of the void sheets by enhancing localization of shear deformation, thereby reducing the average size of the dimples.     

Neutron diffraction residual stress measurements in a 316L stainless steel bead-on-plate weld specimen

The distribution of residual stress in three orthogonal directions has been measured within a Type 316L austenitic stainless steel bead-on-plate weld specimen. Neutron diffraction was employed using the ENGIN-X instrument, located at the ISIS spallation facility of the Rutherford Appleton Laboratory, UK. A stress-free lattice parameter reference value was determined from a small cube, extracted from a far corner of the plate. A high magnitude of tensile residual stress was found along the weld bead in the longitudinal and transverse directions. The distributions of stress along through-thickness lines at the weld bead nominal start and stop locations and at the mid-length position showed an almost identical stress variation. However, a map of measured residual strain in the transverse direction beneath the weld bead revealed a concentration of strain located several millimetres before the nominal weld stop position where through-wall stress profiles were measured.     

Plasma-nitrided austenitic stainless steel 316L as bipolar plate for PEMFC

Stainless steel bipolar plates for the polymer electrolyte membrane (PEM) fuel cell offer many advantages over conventional machined graphite. Austenitic stainless steel 316L is a traditional candidate for metal bipolar plates. However, the interfacial ohmic loss across the metallic bipolar plate and membrane electrode assembly due to corrosion increases the overall power output of PEMFC. Plasma nitriding was applied to improve the surface performance of 316L bipolar plates. A dense _γN${\gamma }_{\mathrm{N}}$ phase layer was formed on the surface. Polarization curves in the solution simulating PEMFC environment and interfacial contact resistance were measured. The results show that the corrosion resistance is improved and the interfacial contact resistance (ICR) is decreased after plasma nitriding. In comparison with the untreated 316L, the ICR between the carbon paper and passive film for the plasma-nitrided 316L decreases at the same condition and lowers with increasing pH value.     

TP316L不锈钢管在以中水作为循环水补水的凝汽器中的应用

中水对凝汽器铜管腐蚀性强,导致凝汽器频繁发生泄漏。通过采用TP316L不锈钢管替代铜管,并做好不锈钢管的安装及运行维护工作,解决了中水对凝汽器管的腐蚀问题,保证了凝汽器安全运行。     

Corrosion resistance of chromized 316L stainless steel for PEMFC bipolar plates

Corrosion resistance of the chromized 316L stainless steel was studied in a proton exchange membrane fuel cell (PEMFC) operating condition. Cr-rich surface layer was formed by pack cementation technique and electrochemical properties of the chromized surface were examined by potentiodynamic and potentiostatic tests. Results showed that the Cr-rich layers underneath the free surface passivated the surface and protect the surface from corrosion in 0.5 M H₂SO₄ solution at 80 °C. However, the Cr-rich layers showed columnar grains with voids when the stainless steel was pack cemented for an extended period of time, resulting in drastic degradation of corrosion resistance. The optimum condition for the best corrosion resistance in the PEMFC operating condition was obtained without sacrificing the interfacial contact resistance.     

Anticorrosion properties of Ta-coated 316L stainless steel as bipolar plate material in proton exchange membrane fuel cells

In order to reduce the cost, volume and weight of the bipolar plates used in the proton exchange membrane fuel cells (PEMFC), more attention is being paid to metallic materials, among which 316L stainless steel (SS316L) is quite attractive. In this study, metallic Ta is deposited on SS316L using physical vapor deposition (PVD) to enhance the corrosion resistance of the bipolar plates. Simulative working environment of PEMFC is applied for testing the corrosion property of uncoated and Ta-coated SS316L. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods (potentiodynamic and potentiostatic polarization) are also used for analyzing characteristics of uncoated and Ta-coated SS316L. Results show that, Ta-coated SS316L has significantly better anticorrosion property than that of uncoated SS316L, with corrosion current densities of uncoated SS316L being 44.61 μA cm⁻² versus 9.25 μA cm⁻² for Ta-coated SS316L, a decrease of about 5 times. Moreover, corrosion current densities of Ta-coated SS316L in both simulative anode (purged with H₂) and cathode (purged with air) conditions are smaller than those of uncoated SS316L.     

Tearing–fatigue interactions in 316L(N) austenitic stainless steel

This paper presents the results from a programme of tearing, fatigue and tearing–fatigue tests performed on specimens from a 316L(N) stainless steel plate. All tests were carried out at ambient temperature. The experimental results have been compared with assessments performed using current guidance within the R6 defect assessment method. The work has shown that there is some evidence that fatigue cycling modifies the JR-curve behaviour of this material. In most cases, the data lie approximately 20–30% above the base-line JR-curve. However, whilst there may be a modest influence of fatigue crack growth on the ductile tearing characteristics, it is difficult to separate this from experimental scatter. In tearing–fatigue tests performed at a stress ratio, R=0.2, ductile tearing reduces the fatigue crack growth rates by up to 50%. This is likely to result from the presence of a residual compressive zone at the crack-tip, and increased crack closure due to the irregular and non-matching fracture surfaces generated by the ductile crack growth mechanisms. For R=0.1 tearing–fatigue tests, fatigue crack growth rates are apparently enhanced by a factor up to of 10, particularly during the latter stages of the tests when ΔK>60 MPam. This is likely to result from: (i) loading being in the elastic–plastic regime where the J-integral (rather than K) characterises the crack-tip fields, (ii) increments of ductile tearing which may occur during each fatigue cycle, and (iii) crack blunting which reduces crack closure effects. For the R=0.2 tearing–fatigue tests, the linear summation approach described in R6 provides a consistently conservative prediction of ductile, fatigue and total crack growth during the tests. However, for the R=0.1 tearing–fatigue tests, the Paris law under-predicts fatigue crack growth rates. This may be corrected by using the Kaiser equation, which acknowledges loading in the elastic–plastic regime and incorporates incremental growth due to tearing as well as fatigue. R6 provides conservative predictions of instability for the CT specimen geometry tested in the current programme, both in terms of the critical crack growth and load required for instability to occur.     

Influence of macro segregation on hydrogen environment embrittlement of SUS 316L stainless steel

The objective of this work is to identify microstructural variables that lead to the large scatter of the relative resistance of 316 grade stainless steels to hydrogen environment embrittlement. In slow displacement rate tensile testing, two almost identical (by nominal chemical composition) heats of SUS 316L austenitic stainless steel showed significantly different susceptibilities to HEE cracking. Upon straining, drawn bar showed a string-like duplex microstructure consisting of α′-martensite and γ-austenite, whereas rolled plate exhibited a highly regular layered α′-γ structure caused by measured gradients in local Ni content (9.5–13 wt%). Both martensite and austenite are intrinsically susceptible to HEE. However, due to Ni macro segregation and microstructural heterogeneity, fast H-diffusion in martensite layers supported a 10 times faster H-enhanced crack growth rate and thus reduced tensile reduction in area. Nickel segregation is thus a primary cause of the high degree of variability in H₂ cracking resistance for different product forms of 316 stainless steel.     

Thermal ratchetting deformation of a 316L stainless steel cylindrical structure under an axial moving temperature distribution

A study of progressive inelastic deformation under a moving temperature distribution was carried out for a 316L stainless steel cylinder by a structural test and corresponding analysis. This structural test intends to simulate the thermal ratchetting behavior occurring at the thermal liner of a liquid metal reactor as a free surface of a hot sodium pool moves up and down under plant heat-up, cool down conditions and other thermal transients. The thermal ratchetting load of heating the test cylinder up to 550 °C was applied nine times and deformation was measured with one laser displacement sensor and two LVDTs. The temperature distribution of the test cylinder in the axial direction was measured and this was used for the ratchetting analysis. The thermal ratchet deformations were analyzed with the constitutive equation of the non-linear combined hardening model, which was implemented into ABAQUS by means of a UMAT subroutine and the analysis results were compared with those of the test. The residual displacement after nine cycles of the thermal load was measured to be 1.79 mm. The ratchetting deformations obtained by the analysis with the combined hardening model were in reasonable agreement with those of the structural tests. In addition, a case study of the effect of variations of load conditions and geometry conditions on the thermal ratchet was carried out.     

Ductility and fatigue properties of low nickel content type 316L austenitic stainless steel after gaseous thermal pre-charging with hydrogen

The susceptibility of low nickel content type 316L austenitic stainless steel to hydrogen was quantified using low strain rate tensile tests and strain-controlled low-cycle fatigue life measurements. Both tests were performed under air condition after charging with high-pressure 10-MPa hydrogen gas at 300 °C for eight days. No significant influence of hydrogen was recognized in 0.2% proof stress, but the strain at fracture and reduction area was decreased significantly in both hydrogen pre-charged and in gaseous hydrogen conditions compared to companion tests conducted in air. The decrease of fatigue life in the high strain amplitude region was related to a significant decrease in the plastic component while the effect of hydrogen on the elastic component was negligible. Highly localized deformation and a pronounced martensite transformation occurred near the site of the fracture surface in the high strain amplitude regime, resulting in the early formation of abundant micro-surface cracks in this regime of the hydrogen pre-charged samples.     

Effect of hold-time on low cycle fatigue behaviour of nitrogen bearing 316L stainless steel

Axial strain controlled low cycle fatigue (LCF) behaviour and creep–fatigue interaction behaviour of 316L(N) stainless steel (SS) in solution annealed condition has been investigated at various strain amplitudes. Creep–fatigue interaction behaviour of the material has been evaluated by employing tension and compression holds at peak strain. Tension holds up to 90 min were studied. Under all the testing conditions, the material showed initial hardening followed by stress saturation. Hold-time conditions generally showed lower cyclic stress response compared to continuous cycling. The decrease in cyclic stress response with hold-time is attributed to enhanced recovery of the substructure and increase in the grain boundary damage accumulated during the stress relaxation period. The fatigue life is observed to be lower in tensile-hold conditions and the endurance decreased with increase in the duration of the hold. The factors that contribute to the decrease in fatigue life with hold-time have been identified from metallographic studies as the development of creep cracks and cavities and crack initiation and propagation assisted by oxidation. Creep–fatigue damage values based on the damage summation rule have been computed and compared with the RCC-MR bi-linear creep–fatigue interaction diagram suggested for nitrogen alloyed 316L SS at 600°C.     

Comparative study on corrosion characteristics of Al2O3/316L and TiO2/316L stainless steel in supercritical water

Al₂O₃ and TiO₂ coatings were fabricated on 316L stainless steel by atmospheric plasma spraying to improve the corrosion resistance of 316L stainless steel in supercritical water. The corrosion characteristics of the samples were evaluated in a batch reactor at 500 °C and 25 MPa with an oxygen concentration of 1000 mg/L for 80 h. The adhesive strengths of the coated samples were tested, and the weight changes, morphologies and elements distributions of the fresh and corroded samples were analyzed. Results showed that the bond strength of TiO₂/316L was 1.5 times than that of Al₂O₃/316L (26.639 N/mm²). The surface morphology of Al₂O₃/316L showed gully erosion with much pores and cracks after exposed in SCW, which provided channels for oxygen and SCW to get into the substrate and also the elements in substrate to diffuse to the surface of the coating. The corroded Al₂O₃/316L suffered significant weight loss, and most of the coatings were peeled off. However, the surface morphology of TiO₂/316L was relatively dense and the thickness of the coating was not found to decrease obviously.     

An investigation into TiN-coated 316L stainless steel as a bipolar plate material for PEM fuel cells

In order to reduce the cost, weight and volume of the bipolar plates, considerable attention is being paid to developing metallic bipolar plates to replace the non-porous graphite bipolar plates that are in current use. However, metals are prone to corrosion in the proton exchange membrane (PEM) fuel cell environments, which decreases the ionic conductivity of the membrane and lowers the overall performance of the fuel cells. In this study, TiN was coated on SS316L using a physical vapor deposition (PVD) technology (plasma enhanced reactive evaporation) to increase the corrosion resistance of the base SS316L. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods were used to characterize the TiN-coated SS316L. XRD showed that the TiN coating had a face-centered-cubic (fcc) structure. Potentiodynamic tests and electrochemical impedance tests showed that the corrosion resistance of SS316L was significantly increased in 0.5 M H₂SO₄ at 70 °C by coating with TiN. In order to investigate the suitability of these coated materials as cathodes and anodes in a PEMFC, potentiostatic tests were conducted under both simulated cathode and anode conditions. The simulated anode environment was −0.1 V versus SCE purged with H₂ and the simulated cathode environment was 0.6 V versus SCE purged with O₂. In the simulated anode conditions, the corrosion current of TiN-coated SS316L is −4 × 10⁻⁵ A cm⁻², which is lower than that of the uncoated SS316L (about −1 × 10⁻⁶ A cm⁻²). In the simulated cathode conditions, the corrosion current of TiN-coated SS316L is increased to 2.5 × 10⁻⁵ A cm⁻², which is higher than that of the uncoated SS316L (about 5 × 10⁻⁶ A cm⁻²). This is because pitting corrosion had taken place on the TiN-coated specimen.     

An investigation into nickel implanted 316L stainless steel as a bipolar plate for PEM fuel cell

A nickel-rich layer about 100 μm in thickness with improved conductivity was formed on the surface of austenitic stainless steel 316L (SS316L) by ion implantation. The effect of ion implantation on the corrosion behavior of SS316L was investigated in 0.5 M H₂SO₄ with 2 ppm HF solution at 80 °C by potentiodynamic test. In order to investigate the chemical stability of the ion implanted SS316L, the potentiostatic test was conducted in an accelerated cathode environment and the solutions after the potentiostatic test were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES). The results of potentiodynamic test show that the corrosion potential of SS316L is shifted toward the positive direction from −0.3 V versus SCE to −0.05 V versus SCE in anode environment and the passivation current density at 0.6 V is reduced from 11.26 to 7.00 μA cm⁻² in the cathode environment with an ion implantation dose of 3 × 10¹⁷ ions cm⁻². The potentiostatic test results indicate that the nickel implanted SS316L has higher chemical stability in the accelerated cathode environment than the bare SS316L, due to the increased amount of metallic Ni in the passive layer. The ICP results are in agreement with the electrochemical test results that the bare SS316L has the highest dissolution rate in both cathode and anode environments and the Ni implantation markedly reduces the dissolution rate. A significant improvement of interfacial contact resistance (ICR) is achieved for the SS316L implanted with nickel as compared to the bare SS316L, which is attributed to the reduction in passive layer thickness caused by the nickel implantation. The ICR values for implanted specimens increase with increasing dose.     

Evaluation of hydrogen permeation through standalone thermally sprayed coatings of AISI 316L stainless steel

This research evaluates hydrogen permeation and its diffusion characteristics through standalone thermally sprayed coatings of AISI 316L stainless steel. The effects of various charging currents and other parameters on hydrogen diffusion coefficient were scrutinized using electrochemical hydrogen permeation tests. Hydrogen permeation through the thermally sprayed coatings displayed anomalous behavior such that a maximum pinnacle was observed in the permeation curves, attributed to heavily trapped hydrogen atoms in the delayed surface cracks. Therefore, new diffusion parameters were defined for modeling of the anomalous permeation curves. The fitted diffusion parameters were consistently identified, and hence, the model perfectly explained experimental data. The results showed that the increase in charging current caused fast activation and development of surface cracks. The measured diffusion coefficient of hydrogen in the stainless steel thermally sprayed coating was relatively high because the microstructure of the coating contained some ferritic phases and dense dendritic structure, which configure fast diffusion paths.     

Notched-tensile properties under high-pressure gaseous hydrogen: Comparison of pipeline steel X70 and austenitic stainless type 304L, 316L steels

The effect of high-pressure gaseous H₂ on the fracture behavior of pipeline steel X70 and austenitic stainless steel type 304L and 316L was investigated by means of notched-tensile tests at 10 MPa H₂ gas and various test speed. The notch tensile strength of pipeline X70 steel and austenitic stainless steels were degraded by gaseous H₂, and the deterioration was accompanied by noticeable changes in fracture morphology. The loss of notch tensile strength of type 316L and X70 steels was comparable, but type 304L was more susceptible to hydrogen embrittlement than the others. In the X70 steel, hydrogen embrittlement increased as test speed decreased until the test speed reached 1.2 × 10^?3 mm/s, but the effect of test speed was not significant in 304L and 316L steels.