Effect of heat treatments on the hydrogen embrittlement susceptibility of API X-65 grade line-pipe steel

Delayed failure tests were carried out on hydrogen charged API X-65 grade line-pipe steel in as received (controlled rolled), normalized, and quenched and tempered conditions. The resistance to hydrogen embrittlement was found in the order of controlled rolled > quenched and tempered > normalized. The fracture mode in the hydrogen embrittled steel was ductile.     

ZnNi – Beschichtung hochfester Bauteile aus Stahl

ZnNi – Plating of high strength steel components Pre‐treatment and electroplating as well as post‐plating treatment of especially low alloyed high tensile strength steel components can be followed by a delayed hydrogen‐induced fracture known as hydrogen embrittlement. The entire coating process has to be controlled to avoid any failure. Most important is, that atomic hydrogen being evolved during the coating process and penetrating into the base metal after all shows an subcritical concentration within the system with respect to the mechanism of hydrogen embrittlement. Generally this will be obtained by a suitable post‐plating heat treatment of the coated components. There is evidence however that under special conditions for ZnNi – plating from alkaline solution this is not necessary. Results are reported concerning the nucleation and crystal growth and the hydrogen diffusion through ZnNi‐deposits. Further on hydrogen depth profiles of coated components and their mechanical properties will be presented and discussed.     

Hydrogen-induced embrittlement of nickel-chromium-molybdenum containing HSLA steels

ABSTRACT

Several advanced nickel-chromium-molybdenum high strength lowalloy steels newly developed by our research team exhibit excellent mechanical strength, toughness and hardenability. However, the phenomenon of hydrogen-induced embrittlement will easily occur for these high strength steels. In this research, the hydrogeninduced embrittlement of 8625-Modified steel (8625M steel) was studied. Experimental results show that the dominant hydrogen trapping site of the 8625M steel is dislocation, of which trapping energy is about 20 kJ/mol, indicating that the hydrogens trapped in the dislocations are diffusible. The as-quenched 8625M steel has the highest dislocation density and accordingly the highesthydrogen content after hydrogen charging. This makes the asquenched 8625M steel exhibit severe hydrogen embrittlement. After tempering at 200°C and 300°C, the dislocation density drops, and hence these tempered specimens have lower ultimate tensile strength loss. After 400°C tempering, the hydrogen embrittlement phenomenon becomes serious again, being ascribed to the formation of needlelike and film-like cementite which will weaken the strength of martensite. After 500°C tempering, the 8625M steel has the lowest dislocation density, and the inter-lath cementite become discontinuous and spheroidal, making the 500°C tempered specimen have the lowest ultimate tensile strength loss and the highest elongation after hydrogen charging in this study.     

亚温淬火对硼镍添加含铌低合金高强度H型钢组织性能的影响

将硼镍添加的含铌低合金高强度H型钢进行亚温淬火及完全淬火,对淬火以及淬火并高温回火后的试样进行了力学性能和微观组织的研究。结果表明:亚温淬火并回火后,这一新钢种的屈服强度达到512MPa,抗拉强度达到595MPa,伸长率达到27%,韧脆转变温度达到-88℃,具有优异的综合力学性能。近似等轴的铁素体及其上弥散分布的细小碳化物,使得回火时塑性大幅提高而强度下降不多;回火碳化物钉扎晶界,抑制了晶粒的长大,起到了细化晶粒的效果;不连续的细小碳化物分布在晶界上,没有对材料的韧性造成破坏。     

The effect of microstructure on the mechanical behaviour of a low carbon, low alloy steel

The effect of microstructure on the mechanical behaviour of a low carbon, low alloy steel was studied. The hot-rolled ferrite-pearlite showed low monotonic and cyclic strengths with high ductility in terms of true fracture strain and a high shreshold stress intensity. The quenched and tempered low carbon martensite showed high monotonic and cyclic strengths and high ductility. However, the threshold stress intensity was significantly lower than that of the ferrite-pearlite. Both the strength and threshold stress intensity of an austempered bainite and a duplex ferrite-martensite are greater than those of the hot-rolled ferrite-pearlite. At a same strength level, the ductility and the threshold stress intensity of the low carbon martensite are higher than those of a medium carbon martensite.     

The effect of temperature on hydrogen induced fracture in UNI 40NiCrM07 steel

The influence of the temperature on hydrogen embrittlement in UNI 40NiCrMo7 steel was evaluated by means of delayed failure tests. The tests were carried out in the temperature interval 2°–60°C using samples which had undergone two different heat treatments. Hydrogen was introduced into the samples in intensiostatic conditions (d.d.c. 10mA/cm²) by means of cathodic charge in a 0.1N sulphuric acid solution thermostatically maintained at the test temperatures. The results obtained showed a noticeable influence of the temperature on threshold load values and crack incubation times in the tests carried out on quenched material, whereas this influence was found to be negligible in the tests performed on tempered material. This different behaviour was attributed to the effect of the temperature on movement kinetics in the dislocations, responsible for the accumulation and transport of hydrogen into the zones of maximum stress, and on hydrogen diffusion in the metallic lattice.     

Versuchsführungsbedingte Unterschiede im zyklischen Verformungsverhalten von Vergütetem 42 CrMo 4 bei Spannungs- und Totaldehnungskontrolle

Differences in the cyclic deformation behaviour of quenched and tempered steel 42 CrMo 4 (AISI 4140) due to stress- and strain-control Cyclic stress-strain-curves and Manson-Coffin-plots of quenched and tempered steel 42 CrMo 4 (AISI 4140) strongly depend on whether they are determined under stress- or total-strain-control. At total-strain-controlled experiments, this is caused on the one hand by comparatively high initial stress-amplitudes which lead to distinctive cyclic worksoftening. On the other hand, the occurring differences in the evolution of inhomogeneous deformation patterns at both types of loading, which can be recorded by means of photoelasticity and microscopy, lead to differently distributed plastic deformations and to different integral values of plastic strain.     

Hydrogen embrittlement property of a 1700-MPa-class ultrahigh-strength tempered martensitic steel

The hydrogen embrittlement property of a prototype 1700-MPa-class ultrahigh-strength steel (NIMS17) containing hydrogen traps was evaluated using a slow strain rate test (SSRT) after cathodic hydrogen precharging, cyclic corrosion test (CCT) and atmospheric exposure. The hydrogen content in a fractured specimen was measured after SSRT by thermal desorption spectroscopy (TDS). The relationship between fracture stress and hydrogen content for the hydrogen-precharged specimens showed that the fracture stress of NIMS17 steel was higher, at a given hydrogen content, than that of conventional AISI 4135 steels with tensile strengths of 1300 and 1500 MPa. This suggests better resistance of NIMS17 steel to hydrogen embrittlement. However, hydrogen uptake to NIMS17 steel under CCT and atmospheric exposure decreased the fracture stress. This is because of the stronger hydrogen uptake to the steel containing hydrogen traps than to the AISI 4135 steels. Although NIMS17 steel has a higher strength level than AISI 4135 steel with a tensile strength of 1500 MPa, the decrease in fracture stress is similar between these steels.     

On the mechanism of fatigue failure in the superlong life regime (N>107 cycles). Part 1: influence of hydrogen trapped by inclusions

The fracture surfaces of specimens of a heat-treated hard steel, namely Cr–Mo steel SCM435, which failed in the regime of N = 10⁵ to 5 × 10⁸ cycles, were investigated by optical microscopy and scanning electron microscopy (SEM). Specimens having a longer fatigue life had a particular morphology beside the inclusion at the fracture origin. The particular morphology looked optically dark when observed by an optical microscope and it was named the optically dark area (ODA). The ODA looks a rough area when observed by SEM and atomic force microscope (AFM). The relative size of the ODA to the size of the inclusion at the fracture origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of superlong fatigue failure. It has been assumed that the ODA is made by the cyclic fatigue stress and the synergetic effect of the hydrogen which is trapped by the inclusion at the fracture origin. To verify this hypothesis, in addition to conventionally heat-treated specimens (specimen QT, i.e. quenched and tempered), specimens annealed at 300 °C in a vacuum (specimen VA) and the specimens quenched in a vacuum (specimen VQ) were prepared to remove the hydrogen trapped by inclusions. The specimens VA and VQ, had a much smaller ODA than the specimen QT. Some other evidence of the influence of hydrogen on superlong fatigue failure are also presented. Thus, it is concluded that the hydrogen trapped by inclusions is a crucial factor which causes the superlong fatigue failure of high strength steels.     

Effect of thermomechanical treatment on the susceptibility of structural steel to hydrogen embrittlement

It was established that high-temperature thermomechanical treatment (HTMT) produces a substantial reduction in the susceptibility of a medium-carbon steel 37KhN3A (tempered at a low temperature) to hydrogen embrittlement. An anisotropy of the ductility and the resistance to fracture of hydrogen-charged steel was observed after HTMT which points to a selective character of hydrogen charging and hydrogen embrittlement at the boundaries of the initial austenite grains. Torsion test results showed that hydrogen charging has practically no effect on the shear strength and affects only such structure-sensitive properties as tensile strength and ductility.     

Zum thermischen Abbau von Kugelstrahl-Eigenspannungen bei vergütetem 42 CrMo 4

Thermal relaxation of shot-peening-induced residual stress in quenched and tempered steel 42 CrMo 4 Thermal relaxation of shot-peening-induced macro and micro residual stress in a quenched and tempered state of the 42 CrMo 4 steel is investigated with X-rays and is described by the Avrami-approach. The parameters of this relationship can now be determined more exactly using a new, iterative method. By means of the parameters determined, the relaxation of macro and micro residual stress is evaluated and compared. The influence of annealing time and temperature on the dependence of macro residual stress on distance to surface is modelled using the Avrami-approach. The transient relaxation of macro residual stress during heating up to the temperature required can be determined by applying the stress-transient-method which will be presented here. It turns out that not the elapsed heating time but rather the relaxation of residual stress during heating up determines the further relaxation of residual stress.     

Hydrogen embrittlement property of a 1700-MPa-class ultrahigh-strength tempered martensitic steel

Abstract

The hydrogen embrittlement property of a prototype 1700-MPa-class ultrahigh-strength steel (NIMS17) containing hydrogen traps was evaluated using a slow strain rate test (SSRT) after cathodic hydrogen precharging, cyclic corrosion test (CCT) and atmospheric exposure. The hydrogen content in a fractured specimen was measured after SSRT by thermal desorption spectroscopy (TDS). The relationship between fracture stress and hydrogen content for the hydrogen-precharged specimens showed that the fracture stress of NIMS17 steel was higher, at a given hydrogen content, than that of conventional AISI 4135 steels with tensile strengths of 1300 and 1500 MPa. This suggests better resistance of NIMS17 steel to hydrogen embrittlement. However, hydrogen uptake to NIMS17 steel under CCT and atmospheric exposure decreased the fracture stress. This is because of the stronger hydrogen uptake to the steel containing hydrogen traps than to the AISI 4135 steels. Although NIMS17 steel has a higher strength level than AISI 4135 steel with a tensile strength of 1500 MPa, the decrease in fracture stress is similar between these steels.     

Hydrogen embrittlement,thermal aging,and role of carbides in fatigue of high strength steel

Abstract

The influences of thermal aging and environment on Paris-Erdogan regime fatigue crack growth rates and mechanisms in a high strength Cr–Ni steel (300M) have been investigated. Crack growth rates were measured in inert (vacuum) and aggressive (hydrogen) environments, for quenched and tempered material before and after thermal aging at 500°C. Aging induced an acceleration of crack growth in vacuum at low values of ?K, but a retardation at high values of ?K. The crack path was transgranular throughout, and followed carbide/matrix interfaces. These effects were associated with the embrittlement of carbide/matrix interfaces by phosphorus segregation, which facilitated transgranular crack growth at low ?K, but produced crack tip shielding by voids surrounding the crack at high ?K. Hydrogen acted synergistically with phosphorus to embrittle carbide/matrix interfaces, but it also localised slip deformation at crack tips, reducing void formation in surrounding material and associated crack tip shielding. This produced an enhancement of crack growth rates at all values of ?K significantly above the threshold regime. The role of carbide/matrix interface embrittlement constitutes a third mechanism of hydrogen embrittlement and temper embrittlement interaction in fatigue crack growth, additional to those of carbide precipitation and grain boundary embrittlement previously reported.

MST/1142     

Cold Cracking of Flux Cored Arc Welded Armour Grade High Strength Steel Weldments

In this investigation,an attempt has been made to study the influence of welding consumables on the factors that influence cold cracking of armour grade quenched and tempered(Q&T) steel welds.Flux cored arc welding(FCAW) process were used making welds using austenitic stainless steel(ASS) and low hydrogen ferritic steel(LHF) consumables.The diffusible hydrogen levels in the weld metal of the ASS and LHF consumables were determined by mercury method.Residual stresses were evaluated using X-ray stress analyze...     

Characterization of fracture behavior of a Ti alloyed supermartensitic 12%Cr stainless steel using Charpy instrumented impact tests

In this work, the toughness of a Ti-alloyed supermartensitic stainless steel with 12%Cr was evaluated by instrumented Charpy impact tests at − 46 °C. The material was heat treated by quenching and tempering at 500 °C or 650 °C. The temper embrittlement phenomena was detected in the specimen tempered at 500 °C, while the specimens as quenched and quenched and tempered at 650 °C presented a ductile fracture with high impact energy values. The predominance of cleavage fracture instead of intergranular cracks suggests that the temper embrittlement was caused by fine and disperse precipitation observed in the specimen tempered at 500 °C. The dynamic initiation fracture toughness (J_Id) was calculated from the force versus deflection curves using three different methods suggested in the literature to obtain the initiation energy.     

On the embrittlement of fracture toughness specimens of two high strength steels

Hydrogen embrittlement of two commercial materials, a 1$\text{1}\text{2}$ Ni-Cr-Mo steel and a 5 Cr-V-Mo steel both quenched and tempered to a nominal ilrength of 1.60 × 10³MN/m² has been studied. Frecture toughness testing was carried out on each steel in three conditions, (a) heat-treated and tested in air, (b) thermally charged with hydrogen and tested in air, and (c) uncharged and tested a an atmosphere of dry hydrogen. The effects of hydrogen pressure and loading rate on embrittlement were examined. The experimental results show that thermal charging had a greater embrittling effect on the 1$\text{1}\text{2}$ Ni-Cr-Mo steel than on the 5 Cr-V-Mo steel although the latter had a higher hydrogen concentration. In a hydrogen environment the 1$\text{1}\text{2}$ Ni-Cr-Mo steel was much more sensitive to embrittlement than the 5 Cr-V-Mo steel.     

Microstructure and residual stress distribution of similar and dissimilar electron beam welds – Maraging steel to medium alloy medium carbon steel

The influence of parent metal heat treatment condition on the residual stress distribution in dissimilar metal welds of maraging steel to quenched and tempered medium alloy medium carbon steel has been investigated. It has been observed that the residual stress distribution would be more compressive if the maraging steel is in soft condition. This is attributed to stress absorbing nature of highly yielding soft maraging steel.     

锌-镍合金电镀中氢的共沉积

用电化学渗透测试方法研究了电镀锌－镍合金时渗氢量的变化规律，能够监控和评价镀层的氢脆性能，初步筛选出两种呆用于高强度钢抗氢脆电镀用槽液组成。在氯化物－硫酸盐槽液体系和含有添加剂B的氯化物糟液中，常温下可获得耐氢脆性能良好的Zn－Ni镀层。此外，缺口拉伸试验结果与电化学渗透测试结果相吻合。     

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.     

Hydrogen and temper embrittlement interactions in fatigue of 2·25Cr–1Mo steel

Abstract

The influence of strength, precipitate microstructure, temper embrittlement, and environment on fatigue crack growth in 2·25Cr–1 Mo steel has been investigated. Particular attention was paid to the interaction between hydrogen embrittlement and temper embrittlement in fatigue. A range of tempered and aged conditions was examined in air, vacuum, and gaseous hydrogen environments at growth rates between 10^?10 and 10^?5 m/cycle. In this paper, discussion focuses on effects observed in hydrogen. Gaseous hydrogen was found to encourage crack growth by promoting intergranular fracture, which peaked at intermediate growth rates, and by reducing the general plasticity associated with transgranular fracture at high growth rates. Mechanisms underlying these effects, which involve stress-driven hydrogen segregation and the facilitation of crack-tip dislocation emission, are considered in detail. Reversible temper embrittlement encouraged crack growth at near-threshold and intermediate rates in hydrogen by increasing susceptibility to intergranular fracture. The magnitude of this effect was directly related to the degree of intergranular phosphorus enrichment, thus clearly demonstrating synergy between hydrogen embrittlement and temper embrittlement in fatigue. In contrast, one-step temper embrittlement encouraged transgranular crack growth in hydrogen only at high growth rates. This is considered to result from a concentration of slip on glide planes intersecting the crack tip under the combined influences of hydrogen and an increasingly dense precipitate microstructure.

MST/583