Beitrag zum Einfluß von Druckwasserstoff auf die mechanischen Eigenschaften von Stählen

Contribution to the Influence of Pressurized Hydrogen on the Mechanical Properties of Steels The investigation method of using hollow specimens in tensile tests to examinate steels for hydrogen service is described. Reduction of area after fracture, Z, resulting from these tensile tests with constant strain rates shows not only a significant but also a constant difference between hydrogen and nitrogen when being plotted versus strain rate. Therefore a newly introduced term named “Index of embrittlement” and characterized by the relation of Z with nitrogen and with hydrogen was found to be independent of strain rate. With strain rate ε = 10^?6 s^?1 chosen for a “critical” one because of lacking in a maximum index of embrittlement several European steels for hydrogen service were tested to find out their individual index of embrittlement. Assisted by light optical microscopy it was found that there is a special correlation between microstructure, index of embrittlement and tensile strength of a given steel grade.     

Effects of deformation on hydrogen degradation in a duplex stainless steel

Hydrogen embrittlement of annealed, 20 and 40% cold worked 2205 duplex stainless steels has been evaluated using electrochemical permeation measurement, hydrogen microprint technique and tensile test in this study. Due to hydrogen transport in 2205 duplex stainless steel is mainly lattice diffusion in ferritic phase, more hydrogen distribution, higher permeation rate and effective diffusion in ferritic phase were detected. Hydrogen trapping and mechanical property effects were studied for cold worked specimens. Fractographic investigation revealed that hydrogen absorption promoted transgranular fracture in cold worked specimens. These results exhibits that the cold worked duplex stainless steels are more susceptible to hydrogen embrittlement.     

Neue Beobachtungen über das Phänomen der Wechseldehnungs-Versprödung an einer Rißfront anhand von Sprödbruchversuchen

New Observations about the Phenomenon of Cyclic Strain Embrittlement at the Fatigue Crack Tip by Means of Brittle Fracture Tests . Fracture tests were performed on flat samples notched on both sides (net section 120 × 30 mm²) of material 19 Mn 5 to determine the influence of a local embrittlement on the nominal fracture stresses. The local embrittlement in a very small area could be produced by pulsating tensile tests due to cyclic strain could be produced by pulsating tensile tests due to cyclic strain embrittlement at 350°C gradually different in the base of the notch respectively at the tip of the growing fatigue crack. Fractures due to “low” nominal stress tend to occur in those cases where the rate of crack growth in the pulsating tensile test is approaching zero or is equal to zero.     

Effect of Hydrogen Charging on the Tensile and Constant Load Properties of an Austenitic Stainless Steel Weldment

The effect of cathodic hydrogen charging on the tensile and constant load properties was determined for an austenitic stainless steel weldment comprising a 304L steel in the solution treated condition as a base metal and a 308L filler steel as a weld metal. Part of the 304L solution treatedsteel was separately given additional sensitization treatment to simulate the microstructure that would develop in the heat affected zone. Tests were performed at room temperature on notched round bar specimens. Hydrogen charging resulted in a pronounced embrittlement of the tested     

Bruchverhalten eines vergüteten und eines kaltgezogenen Stahles im Gleichgewichtszustand mit Druckwasserstoff

Fracture of Tempered and Cold Drawn Steel in Equilibrium with Compressed Hydrogen Tensile specimens are surface activated and stored in compressed hydrogen until equilibrium is attained. Charged and uncharged reference specimens are tested in air and in compressed hydrogen. The embrittlement of colddrawn steel (plenty of traps) is independent of strain rate and is caused mainly by the prior charging. Tempered steel (fewer traps) is not embrittled by charged hydrogen but by the effect of external hydrogen during the test. The degree of embrittlement decreases with increasing strain rate. In all cases of embrittlement there is in addition a strong notch sensitivity.     

Hydrogen-induced microtwinning in ferritic stainless steels

Electrochemical hydrogen charging of thin foil specimens of ferritic stainless steels resulted in extensive microtwinning. Microtwins were plate- or needle-like on {110}-planes with a common 〈111〉 growth direction. Hydrogen-induced microtwinning was similar in both steels. Hydrogen embrittlement is expected to be related to hydrogen-induced microtwinning of the ferritic stainless steels.     

Rißfortschritt an Baustählen in Meerwasser

Crack Growth Behaviour of Structural Steels in Seawater The influence of a synthetic seawater environment upon the crack growth behaviour of two structural steels was investigated. The results were presented in terms of the stress intensity fracture toughness parameter. Data were generated in air and in seawater with or without a cathodic protection. Results show that seawater environment and a cathodic protection influence the crack propagation at the applied frequencies of 0,04 and 0,25 Hz. The use of cathodic protection raises questions concerning the resistance to hydrogen embrittlement of the two steels. Some fractographic examinations of selected specimens show the microstructure of the two steels at various test conditions.     

Hydrogen in stress corrosion cracking of X-70 pipeline steels in near-neutral pH solutions

The effect of hydrogen on the stress corrosion cracking (SCC) for X-70A and X-70B pipeline steels in near-neutral pH environments was studied by monotonic tensile tests on slow strain rate tests (SSRT) machine and cyclic tests on SSRT machine and fatigue machine. The results showed that SCC intensity increased at high cathodic protection potential. Hydrogen charged at high pressure enhanced SCC sensitivity. Cyclic tests under elastic strain condition could not take the specimens to fracture and the hydrogen content was very low. However, when the load was raised to produce plastic deformation, the specimens failed within limited time and there was brittle fracture appeared on the fracture surface. Moreover, the hydrogen content was higher than that under elastic strain condition. The SCC mechanism of X-70A and X-70B pipeline steels in near-neutral pH environments was related to hydrogen accumulation induced by plastic strain.     

Druckversuch an Scheiben zur Prüfung der Wasserstoffversprödung von Metallen

Disc-Pressure-Testing of Hydrogen Embrittlement An apparatus for disc-pressure-tests is presented. The bursting pressure with helium and with hydrogen is measured versus the rate of pressure increase. Under hydrogen most metals show a distinct minimum of bursting pressure. Some explanations for this minimum are proposed. The maximum ratio of bursting pressures x = (P_He/H_H2)_max is taken as an indicator for hydrogen embrittlement. Steel similar to SAE 4137 (34 CrMo 4) is tested in several states (tempered, normalized, cold-rolled), as well as austenitic steel, various other metals (V, Nb, Ta, Mo) and some amorphous metals. The disc-pressure-test is shown to be easy and useful for determining hydrogen embrittlement. Even austenitic steel exhibits some embrittlement (x = 1.5). The strongest embrittlement occurred in amorphous metal Vitrovac 0040 with x = 9.8.     

AN ACCELERATED TEST METHOD FOR DETERMINING NEAR-THRESHOLD STRESS INTENSITY VALUES IN HSLA STEELS

Abstract— A new method for accelerating the collection of near-threshold corrosion fatigue crack propagation data, using local hydrogen embrittlement in the crack tip region, has been investigated for ASTM A710 HSLA steel. Fatigue tests were conducted at 10 and 0.2 Hz (stress ratio, R = 0.1) on "constant K " contoured double cantilever beam (CDCB) specimens, to establish near-threshold crack growth rates in a locally hydrogen charged region at the crack tip. Hydrogen charging was then discontinued and crack growth rates were monitored in the uncharged material. Near-threshold fatigue crack growth rates were found to be 100 times faster in the locally hydrogen charged specimens than in the uncharged material. Fatigue thresholds, Δ K _th, were defined in less than one fifth the time required for load shedding tests in air at 0.2 Hz. Although demonstrated for HSLA steels, the technique is applicable to any material which can be embrittled by hydrogen.     

Effect of hydrogenation on mechanical properties and tensile fracture mechanism of a high-nitrogen austenitic steel

Austenitic stainless steels are frequently used for hydrogen applications due to their high ductility at low temperatures and lower hydrogen environment embrittlement compared to ferritic steels. We study the effect of electrochemical hydrogen saturation up to 40 h on tensile behavior and fracture mechanisms in high-nitrogen austenitic 17Cr–24Mn–1.3V–0.2C–1.3N steel. Hydrogen saturation weakly influences the characteristic of stress–strain curves, but decreases steel ductility, yield stress, and ultimate tensile stress. Hydrogenation provides a change in steel fracture peculiarities—a hydrogen-assisted thin brittle surface layer of ≈5 μm and ductile subsurface layer of 50–150 μm in width in hydrogen-saturated specimens. The subsurface layer shows ductile transgranular fracture with elongated dimples and flat facets. The central parts of fracture surfaces for hydrogenated specimens show ductile fracture mode similar to hydrogen-free state, but they include numerous secondary cracks both for central part and for transition zone between ductile central part and subsurface layer associated with highest hydrogen saturation. The possible reasons of decrease in hydrogen-associated ductility and change in fracture character are discussed.     

Effect of hydrogen on structure and slow strain rate embrittlement of mill annealed Ti6AI4V

Abstract

The slow tensile straining of smooth specimens of mill annealed Ti6Al4V with different hydrogen contents revealed hydrogen induced slow strain rate embrittlement when the hydrogen content exceeded about 2000 ppm. The effect of hydrogen on the mechanical behaviour of the Ti6Al4V at lower hydrogen levels was not so pronounced and may be interpreted in terms of the partitioning of hydrogen between the α and β phases and the effect of hydrogen in solution on the lattice parameters of these phases. Hydrogen levels in excess of about 1200 ppm promote an increase in the amount of β phase at the charging temperature employed and the effect of this on mechanical properties is discussed. The effect of hydrogen solubility and hydride precipitation at the α/β interface on hydrogen induced slow strain rate embrittlement is also considered.

MST/3431     

Effect of pre-charged hydrogen on fatigue crack growth of low alloy steel at 288 °C

Hydrogen effects on mechanical strength and crack growth were studied at high temperatures. The study was motivated by the fact that the environmentally assisted cracking (EAC) of pressure vessel steel SA508 Cl.3 in 288 °C water was suspected to be related to hydrogen embrittlement. Fatigue crack growth rate and tensile tests were performed with hydrogen pre-charged specimens at high temperatures. At 288 °C the fatigue crack growth rate of the hydrogen pre-charged specimen was faster than that of as-received; the fatigue fracture surface of hydrogen pre-charged specimen correspondingly showed EAC like feature. Meanwhile, ductile striation was evident for the case of as-received in both air and argon gas environments. In the dynamic strain aging (DSA) loading condition at 288 °C during tensile tests, the pre-charged hydrogen induced a marked softening (decrease in ultimate tensile strength; UTS) as well as a little ductility loss; this was accompanied by the macrocracks grown from microvoids/microcracks promoted by DSA and hydrogen. These experiments showed that hydrogen embrittlement is an effective mechanism of EAC not only at low temperature but also at the high temperature.     

Effects of nitrogen on hydrogen embrittlement in AlSl type 316, 321 and 347 austenitic stainless steels

Hydrogen embrittlement of AlSl type 316, 321 and 347 stainless steels with nitrogen alloying has been studied by a tensile test through cathodic charging. The results show that addition of nitrogen improved resistance to hydrogen cracking regardless of the failure mode. Fracture surfaces of cathodically charged steels showed intergranular brittle zones on each side of the fracture surfaces. AlSl type 316 with nitrogen alloying stainless steel is more resistant to hydrogen embrittlement than AlSl type 321 with nitrogen alloying steel, whereas AlSl type 347 with nitrogen alloying steel is susceptible to hydrogen embrittlement. Nitrogen alloying of stainless steel increased the mechanical properties in hydrogen environments by increasing the stability of austenite.     

Einige Gesichtspunkte für die Auswahl von Stählen in der chemischen Höchstdrucktechnik

Some Aspects of Selecting Materials in the Chemical High Pressure Technology . Steels for chemical industry in the pressure range between 2000 and 3000 bar must have high yield strengths in order to be able to bear the static internal pressure. Even with high yield strengths the wall thickness is so high that steels must be selected which can be thoroughly and evenly quenched and tempered. They should be insensitive to tempering embrittlement. For components stressed by static internal pressure the safety against bursting and the bursting behaviour play a major rǒle. In addition to that, under pulsating pressures, the fatigue characteristics of a component are of importance. Steels with the high fatigue strengths necessary in high pressure application are notch sensitive. It is shown which measures are to be taken from the metallurgical side and in fabrication to increase their fatigue strength. Results of fatigue tests on high pressure tubes with different surface treatment are given. The fatigue strength can be improved by improving tube manufacturing, mechanically or electrochemically smoothening the inner tube surface, nitriding or autofrettage. For special purposes it is sometimes necessary to use steels whose strength is too low for high pressure applications. One must then apply a strength calculation conceding partial plastic deformation. This is illustrated for an age hardening austentitic steel.     

Beitrag zum Einfluß der dendritischen Erstarrung von 19 Cr-9 Ni-Nb-Bandplattierungsschweißgut auf das Korrosionsverhalten

Contribution to the Influence of the Dendritic Solidification of 19 Cr 9 NiNb Submerged-Arc-Welding-Strip-Cladding on Corrosion Behavior SAW-strip-claddings out of 19%Cr9%Ni + Cb tempered at 650 °C were tested in 8%-sulphuric acid at room temperature. A mechanical pulsating load was superimposed to corrosion. Only a slight corrosion attack could be found on the surface after 50 000 cycles, i.e. 18 days test duration. The metallographic investigation showed selective attack of the ferritic grains, modified by the post weld heat treatment. The specific dendritic solidification form of the SAW-cladding had no detrimental influence under the chosen conditions.     

氢对低合金钢上不锈钢堆焊层性能的影响(英文)

本工作研究了高温高压氢 (35 0℃ ,2 5 MPa H2 ) ,对国产氢反应器壁 30 9L 和 34 7L 不锈钢堆焊层性能的影响 .结果表明 :未经热渗氢的原始试样 ,无论是光滑试样还是缺口试样 (除缺口开在 30 9L 区域试样外 ) ,均断裂在 34 7L 区域内 .而经热渗氢后 ,无论起裂于 2 (1/4 ) Cr- 1Mo和 30 9L 熔合线 ,还是 30 9L 和34 7L的熔合线处 ,最后都断在 30 9L区域内 .这是因为热渗氢使 30 9L和 34 7L的断裂应力 ,分别从 885 MPa降至 478MPa和从 799.9MPa降至 5 6 4MPa,它们的氢脆系数分别为 86 .8%和 80 .9% .SEM断口分析结果与上述结论一致     

Effect of grain size on the hydrogen-assisted cracking in duplex stainless steels

The embrittlement behavior of 2205 duplex stainless steels with two different grain sizes in 26 wt% NaCl (pH 2) under cathodic potential were investigated by slow strain rate testing. The electrochemical permeation technique was used to characterize the permeation rate and effective diffusivity of hydrogen. The results indicated that both the effective diffusivity and the susceptibility of hydrogen embrittlement were lower for the finer grain size specimen. Ultimate tensile strength (UTS) and uniform elongation (UEL) decrease linearly with decreasing logarithm of strain rate. The dependence of UTS and UEL on the logarithm of strain rate was higher for the finer grain specimen. The microstructural examination revealed that internal cracks resulted from hydrogen embrittlement of the ferrite phase under cathodic charging conditions were arrested by austenite in duplex stainless steels.     

Reversible hydrogen embrittlement of steels as a physical phenomenon

Reversible hydrogen embrittlement of structural steels results in serious technological problems, but the physical nature of this complex phenomenon has been insufficiently studied. We present new ideas on its mechanism and use fundamental concepts of the modern physics of metals, literature data, and results of our experiments with specimens made of St3 steel, 09G2S low-carbon steel, and a low-alloyed high-strength steel of type AB to substantiate these ideas. We show that plastic strain causing the appearance of incipient cracks in a metal is a necessary condition for development of reversible hydrogen embrittlement. Hydrogen, having a high diffusive mobility, is transported by moving dislocations to the places of crack initiation in the course of plastic deformation. The physical reason for the embrittling influence of hydrogen consists in the decrease in the critical stress necessary for the loss of stability of incipient microcracks and the transition to their autocatalytic propagation. The new ideas enable us to explain the established regularities of reversible hydrogen embrittlement and can also serve as a basis for further investigations of this phenomenon and the development of methods for its prevention. Paton Institute of Electric Welding, Ukrainian Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 4, pp. 5–15, July–August, 1999.     

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental,modelling and design progress from atomistic to continuum

Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.