Effect of hydrogen environment on the notched tensile properties of T-250 maraging steel annealed by laser treatment

In the present work, slow displacement rate tensile tests were performed to find out the influence of ageing condition and hydrogen-charging on the notched tensile strength and fracture characteristics of T-250 maraging steel aged at various conditions. The influence of embrittling species in the environment on the notched tensile strength was accessed by comparing the measured properties in air, gaseous hydrogen and H₂S-saturated solution. The hydrogen diffusivity, permeation flux and apparent solubility of various specimens determined by electrochemical permeation method, were correlated well with the microstructures and mechanical property. The results indicated that the peak-aged (H900) specimen was highly sensitive to hydrogen embrittlement even in gaseous hydrogen. In contrast, the microstructures of over-aged (H1100) specimen comprising of reverted austenite and incoherent precipitates could trap large amount of hydrogen atoms, resulting in decreased hydrogen permeability and hydrogen embrittlement susceptibility. The solution-annealed specimen had the highest diffusion coefficient and the lowest quantity of trapped hydrogen among the specimens, showing high susceptibility to sulfide stress corrosion cracking. In the presence of notches, hydrogen atoms were prone to segregate and trap at grain boundaries, resulting in the formation of intergranular fracture.     

Embrittlement of T-200 maraging steel in a hydrogen sulfide solution

Slow displacement rate tensile tests were carried out to investigate the effect of hydrogen embrittlement (HE) on notched tensile strength (NTS) and fracture characteristics of aged T-200 maraging steel. Hydrogen diffusivity, permeation flux and apparent hydrogen solubility were determined by an electrochemical permeation method, and correlated with the HE susceptibility and microstructures of the specimens. The results indicated that all aged specimens were susceptible to HE in the saturated H₂S solution, to different degrees. The susceptibility in the decreasing order of severity was observed to be under-aged, peak-aged, and over-aged conditions. The main trend was that the specimen with the highest diffusivity and permeation flux of hydrogen had the greatest NTS loss. Reverted austenite, if present in the microstructure, acted as irreversible traps for hydrogen and hence, improved the HE resistance. At similar strength and hydrogen solubility level, the more reverted austenite the less susceptibility to HE of specimens was resulted. The detailed microstructures of distinct specimens and their performances in hydrogen-containing environments are discussed.     

Notch tensile properties of laser-surface-annealed 17-4 PH stainless steel in hydrogen-related environments

Slow displacement rate tensile tests were performed to determine the notched tensile strength (NTS) of 17-4 PH stainless steel with various microstructures in hydrogen-related environments. Solution-annealed (SA), peak-aged (H900), over-aged (H1025), and laser-annealed (LA) specimens were included in the study. Based on the results of NTS in air, the NTS loss in both gaseous hydrogen and H₂S-saturated solution was used to access the detrimental effects of hydrogen in 17-4 PH steel subjected to different treatments. Electrochemical permeation tests were also employed to determine the hydrogen permeation characteristics of the 17-4 PH steel plate with various microstructures. The result indicates that all the specimens have low NTS loss in gaseous hydrogen but significantly suffer from sulfide stress corrosion cracking (SCC), especially for the soft SA specimen. It was deduced that high hydrogen diffusivity and less trapped hydrogen atoms in the SA matrix provided rapid transport of massive hydrogen atoms into highly stressed region, and deteriorated the NTS tested in the saturated sulfide solution. On the other hand, H1025 specimen consists of the blocky austenite together with Cu-rich precipitates uniformly distributed in the grain interior; dense and coarse precipitates are also observed along prior austenite grain boundaries. Hydrogen atoms tend to be trapped along grain boundaries, and lead to the formation of intergranular fracture for H1025 specimen tested in the H₂S solution. Fine and homogeneously distributed precipitates in the H900 matrix result in uniformly trapping of hydrogen atoms, so it behaves superior properties than other specimens. The decohesion of precipitate/matrix interfaces induces quasi-cleavage fracture of the H900 specimen tested in H₂S solution. Finally, the application of laser-annealing treatment on the H900 specimen cannot improve its resistance to sulfide SCC, because the laser-annealed zone is susceptible to hydrogen embrittlement in the H₂S solution.     

The effect of grain size and aging on hydrogen embrittlement of a maraging steel

Notched tensile tests were conducted under a slow displacement rate to evaluate the influences of grain size and aging on hydrogen embrittlement (HE) of T-200 maraging steel. In addition, an electrochemical permeation method was employed to measure the effective diffusivity (D_eff) and apparent solubility (C_app) for hydrogen of various heat-treated specimens. The results indicated that the aged (482 °C/4 h) specimens comprised of numerous precipitates led to a raised C_app and a decreased hydrogen diffusivity as compared to those of the solution-treated ones. The solution-treated specimens were resistant to gaseous HE, whereas aged specimens were susceptible to it, implying the strength level was the controlling factor to affect the HE susceptibility of the specimens. Nevertheless, all specimens suffered from sulfide stress corrosion cracking (SSCC) severely but to different degrees. The aged specimens were more likely to form intergranular (IG) fractures in H₂S but quasi-cleavage (QC) in H₂. For the solution-treated specimens, a fine-grained structure was susceptible to HE in H₂S and revealed mainly QC that differed from the IG fracture of the coarse-grained one. The fracture mode of the specimens could also be related to the transport path and / or the supply of hydrogen to the plastic zone of notched specimens in hydrogen-containing environments.     

Notched tensile tests of cold-rolled 304L stainless steel in 40 wt.% 80 °C MgCl2 solution

The effects of cold-rolling (20% thickness reduction) and sensitization treatment (600 °C/10 h) on the microstructure, tensile properties and susceptibility to stress corrosion cracking of 304 stainless steel in 80 °C MgCl₂ (40 wt.%) solution were investigated. The increase in hydrogen traps, which retarded hydrogen diffusion to the strained region, accounted for the low loss in notched tensile strength (NTS) of such a cold-rolled specimen, as compared to the solution-treated specimen in the corrosive environment. By contrast, the high NTS loss of sensitized specimens in MgCl₂ solution was attributed mainly to the formation of stress-induced martensite near grain boundary regions.     

Effect of hydrogen on the properties and fracture characteristics of TRIP 800 steels

The paper describes effect of hydrogen on the properties and fracture characteristics of two variants of TRIP 800 C–Mn–Si steels. The effect of hydrogen was studied by means of tensile tests on specimens previously charged by hydrogen. Hydrogen provoked embrittlement in both variants but only for very high hydrogen content. Hydrogen embrittlement manifested itself mainly by a loss of plasticity. Both steel variants were able to absorb a large amount of hydrogen, up to 50 ppm. Concerning fractographic characteristics, steels containing higher hydrogen content displayed transgranular cleavage fracture. In exceptional cases, an irreversible embrittlement was revealed initiating on non-metallic inclusions.     

Effect of hydrogen on tensile behaviour of micrometre-sized specimen fabricated from a metastable austenitic stainless steel

This study was conducted by micro mechanical testing and scanning white-light interferometry (SWLI) to clarify the intrinsic effect of hydrogen on tensile properties of a metastable austenitic stainless steel. The stress–strain behaviour of the micrometre-sized specimens exhibited two distinct strain hardening stages controlled by dislocation gliding and martensitic transformation. In-situ SWLI of the micrometre-sized specimens during the tensile test revealed that plasticity localization caused by hydrogen is predominantly responsible for the hydrogen embrittlement (HE) of the austenite stainless steel.     

Environmental embrittlement of automobile spring steels caused by wet-dry cyclic corrosion in sodium chloride solution

The susceptibility to environmental embrittlement (EE) of automobile spring steels was investigated using six different steels. Slow strain rate tensile test and thermal desorption spectroscopic analysis were applied to specimens subjected to wet-dry cyclic corrosion tests in a NaCl solution. Experimental results revealed that the reduction in ductility after the corrosion tests was pronounced with increasing strength level. This degradation was closely associated with the resistance to pitting corrosion. Consequently, the hydrogen absorbed in steel and the corrosion pit as a geometric damage were responsible for the EE of spring steels. The hydrogen in rust layer had no significant influence on the EE.     

Environmentally assisted cracking of 18%Ni maraging steel

Slow strain rate testing of notched cylindrical specimens of 18Ni2400 maraging steel has been carried out in air with 30% relative humidity and synthetic seawater environments. Peak-aged condition has been chosen, considering the relevance to engineering applications. Studies have also been carried out with different notch geometries to understand the effect of stress concentration factor. It is concluded from the study that (i) degree of stress concentration at the notch influences the notched tensile strength (ii) mild hydrogen embrittlement seems to occur in air environment, (iii) synthetic seawater environment drastically brings down the notched tensile strength and time to fracture (iv) environmentally assisted cracking occurs in air tests in quasicleavage and microvoid coalescence modes and in seawater tests in intercrystalline mode.     

Strengthening and hydrogen embrittlement of ultrafine-grained Fe–0.01 mass% C alloy processed by high-pressure torsion

This study was conducted to elucidate the effects of annealing and hydrogenation on the tensile properties of an Fe–0.01 mass% C alloy processed by high-pressure torsion (HPT). By HPT processing, the tensile strength was increased to ∼1500 MPa through grain refinement. Low-temperature annealing further strengthened the HPT-processed specimen because of a simultaneous effect of carbide precipitation and grain refinement. Reduction in the dislocation density and the fraction of low-angle grain boundaries through warm-temperature annealing led to a decrease in hydrogen uptake when the specimens were exposed to high-pressure gaseous hydrogen, and they became less sensitive to hydrogen embrittlement (HE).     

回火温度对DP600钢氢扩散及氢脆敏感性的影响

利用慢应变速率拉伸和双电解池氢渗透试验,结合SEM、TEM、EBSD表征手段研究了不同回火温度下DP600钢中显微组织变化对其氢扩散及氢脆敏感性的影响。结果表明,DP600钢的氢脆敏感性和有效氢扩散系数均随回火温度的升高呈下降趋势,这主要与钢中位错、小角度晶界等可逆氢陷阱浓度降低以及碳化物/基体界面、大角度晶界等不可逆氢陷阱浓度增加有关。其中弥散分布的碳化物使碳化物/基体界面捕获的氢原子分布均匀,导致试验钢的氢脆敏感指数由44.6%(270 ℃)下降至1.8%(350 ℃)。综合考虑回火温度对试验钢强度和氢脆敏感性的影响,DP600钢的最佳回火温度为330 ℃。     

The effects of sacrificial coatings on hydrogen embrittlement and re-embrittlement of ultra high strength steels

This paper describes an investigation of electrodeposited Zn-14% Ni and aluminium-based SermeTel 1140/962 coatings as possible replacements for cadmium. Slow strain rate tests were performed to measure the extent of direct hydrogen embrittlement of a high strength steel substrate as a result of the coating process and of hydrogen re-embrittlement caused by coating corrosion. The level of re-embrittlement was shown to depend on both the electrochemical potential of the coating and its barrier properties. Zn-14% Ni coatings caused the most re-embrittlement as they had the most active potential and contained through-thickness defects which left the steel exposed to hydrogen uptake. The microstructure of the high strength steel was also shown to be an important factor affecting the extent of embrittlement. AerMet 100 steel was more resistant than 300M steel and this was attributed to the presence of reverted austenite surrounding the martensite laths in AerMet 100, which trapped absorbed hydrogen and prevented a critical hydrogen concentration being reached in the more susceptible martensite phase.     

Hydrogen transport and embrittlement in 300 M and AerMet100 ultra high strength steels

This paper describes how hydrogen transport affects the severity of hydrogen embrittlement in 300 M and AerMet100 ultra high strength steels. Slow strain rate tests were carried out on specimens coated with electrodeposited cadmium and aluminium-based SermeTel 1140/962. Hydrogen diffusivities were measured using two-cell permeation and galvanostatic charging methods and values of 8.0 × 10⁻⁸ and 1.0 × 10⁻⁹ cm² s⁻¹ were obtained for 300 M and AerMet100, respectively. A two-dimensional diffusion model was used to predict the hydrogen distributions in the SSR specimens at the time of failure. The superior embrittlement resistance of AerMet100 was attributed to reverted austenite forming around martensite laths during tempering.     

Study of the effect of δ phase on hydrogen embrittlement of Inconel 718 by notch tensile tests

This article describes the effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 conducted by notch tensile tests. Notch tensile specimens were subjected to proper heat treatment to produce various precipitation morphologies of δ phase. Hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to hydrogen charging has been used as a criterion to evaluate the hydrogen embrittlement sensitivity. The study suggests that δ phase has deleterious effect on NTS. Fracture origins of hydrogen-charged specimens locate near the notch surfaces. The loss of NTS caused by hydrogen charging can be greatly decreased by dissolving δ. δ-free Inconel 718 has been proposed for applications in hydrogen environments.     

Fatigue crack growth behavior of laser-annealed IN 718 alloy in hydrogen

The effect of hydrogen embrittlement on the fatigue crack growth of IN 718 plate and laser-annealed specimens in hydrogen containing environment were investigated. Although the differences in tensile strength and impact toughness between solution-annealed (S) and aged (A) IN 718 specimens were significant, the experimental results indicated that both specimens within the low ΔK regime exhibited a similar fatigue behavior. As the ΔK increased above 30 MPa , the solution-annealed specimen revealed a higher fatigue crack growth rate (FCGR) than the aged one. In general, the IN 718 alloy had a low sensitivity to hydrogen-enhanced fatigue crack growth, independent of hydrogen sources. Residual compressive stresses ahead of the crack tip were responsible for the improved resistance to fatigue crack growth in a laser-annealed specimen. For alloys with similar strength, IN 718 alloy trapped a huge amount of hydrogen in the matrix showing a less susceptibility to hydrogen-enhanced fatigue crack growth in comparison with the maraging steel. Additionally, fatigue-fractured appearance near crack initiation sites reveals quasi-cleavage fracture in embrittled specimens.     

贝氏体/马氏体复相高强钢中的氢陷阱

运用电化学渗透技术研究了传统高强钢(42CrMo)和贝氏体/马氏体复相高强钢(U20Si)中氢的扩散和氢陷阱。结果表明，氢在U20Si钢中的扩散系数远小于在淬火回火的42CrMo高强钢中的。另外，两种材料中氢陷阱的情况不同，U20Si钢中的氢陷阱主要为高度均匀弥散分布的贝氏体/马氏体板条界和薄膜状残留奥氏体，而42CrMo钢中的氢陷阱主要为铁素体/渗碳体界面。U20Si钢中的氢陷阱数量超过42CrMo钢的。力学性能测试表明，U20Si钢的氢脆敏感性低于传统的42CrMo钢的。断口分析显示前者的断口为准解理，后者的断口为沿晶断裂。U20Si钢氢脆敏感性低与其氢陷阱数量多且分布均匀密切相关。     

A comparison of hydrogen embrittlement susceptibility of two austenitic stainless steel welds

Slow displacement rate tensile tests were carried out to assess the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of AISI 316L and 254 SMO stainless steel (SS) plates and welds. 254 SMO generally exhibited a better resistance to hydrogen embrittlement than 316L. The strain-induced transformation of austenite to martensite in the 316L SS was responsible for the high hydrogen embrittlement susceptibility of the alloy and weld. Sensitized 254 SMO (i.e., heat-treated at 1000 °C/40 min) base plate and weld comprised of dense precipitates along grain boundaries. Interfacial separation along solidified boundaries was observed with the tensile fracture of 254 SMO weld, especially the sensitized one. Dense grain boundary precipitates not only reduced the ductility but also raised the susceptibility to sulfide stress corrosion cracking of the sensitized 254 SMO plate and weld.     

Hydrogen embrittlement of stainless steel overlay materials for hydrogenators

An investigation was carried out of the effect of hydrogen absorption on the tensile ductility of composite specimens representing stainless steel weld overlays on low alloy steel substrates as used in the fabrication of hydrogenators. Specimens of the two stainless steels (AISI 309 and 347) involved in hydrogen cracking were also fractured in tension at strain rates between 5.9 × 10⁻⁶ and 1.5 × 10⁻³ s⁻¹ after thermal charging with hydrogen. Results indicated that only the 347 samples suffered significant embrittlement by hydrogen and the original ductility could be restored by subsequent annealing for a time and temperature determined by the hydrogen diffusivity.     

Electrodeposition of Zn–Ni coatings as Cd replacement for corrosion protection of high strength steel

Electrodeposition of Zn–Ni coatings performed in acidic baths are not suitable for high strength steels due to their high susceptibility to hydrogen embrittlement.In this work, Zn–Ni coatings were deposited on a high strength steel (4340) upon stirring conditions from an alkaline bath. A complete characterisation of the coatings (corrosion, morphology and composition) has been accomplished, correlating the electrodeposition conditions with these features. The best protective properties of the grown coatings were achieved for the alloys with a single phase structure of γ-Ni₅Zn₂₁ and a denser morphology. Additionally, the hydrogen content incorporated is lower than even cadmium-coated 4340 steel which has undergone a postbaking dehydrogenation treatment.     

The effects of cold rolling and sensitisation on hydrogen embrittlement of AISI 304L welds

The notched tensile strength (NTS) of 304L stainless steel welds subjected to cold rolling (20% thickness reduction) and sensitisation treatment (600 °C/10 h) was measured in a MgCl₂ (40 wt.%) solution at 80 °C. The NTS loss, which is used for comparing the susceptibility to hydrogen embrittlement (HE), was consistent with the extent of embrittled area on the fracture surface of various welds. The HE susceptibility of the weld decreased after cold working but increased with the additional sensitisation treatment of the cold-rolled welds. Besides, cracks tended to propagate along the skeletal boundaries for all welds tested in the MgCl₂ solution.