Hydrogen Content In Steel Research Articles

The regulation of dislocation and precipitated phase improving hydrogen embrittlement resistance of pipeline steel in high pressure hydrogen environment

In this study, the hydrogen embrittlement behavior of quenched pipeline steel tempered at 550 °C to 650 °C in a high-pressure hydrogen environment was analyzed. Hydrogen permeation tests and microstructural analyses indicated that the dislocation density of the steel decreases with increasing tempering temperature, while precipitates gradually nucleate and grow. These hydrogen traps interact with hydrogen atoms, resulting in significantly higher diffusible hydrogen content in steel tempered at 550 °C compared to that tempered at 600 °C and 650 °C. Fatigue crack growth (FCG) test results show that steel tempered at 600 °C and 650 °C exhibits significantly better hydrogen embrittlement resistance than steel tempered at 550 °C. This is primarily due to the combined effect of the high hydrogen concentration, high dislocation density and low nano carbide content in the steel tempered at 550 °C, which inhibits dislocation slip and emission, leading to high crack tip stress and rapid crack propagation. In contrast, the low dislocation density and and dispersed nano carbides in steel tempered at 600 °C and 650 °C facilitate some dislocation slip and emission, result in crack tip stress relaxation and reduced crack propagation rate. Properly controlling the initial dislocation density and increasing the density of irreversible hydrogen traps can enhance the strength of materials while improving their resistance to hydrogen embrittlement.

Experimental studies of bearing capacity of pipe steel of sewage systems

The results of experimental studies on the kinetics of crack growth, its relationship with the parameters of crack resistance and long-term strength of pipe steels of different service life and their structural and phase composition are presented. It was found that the value of the critical stress SK for all test steels increases with the increase in the service life, and the impact viscosity decreases, which indicates the structural embrittlement of the pipe steels associated with their sudden flooding. It is shown that the new 06G2BA steel, which is economically modified with a carbide-forming element (vanadium) and has a fine-grained structure and a low content of harmful impurities (sulfur, phosphorus), has the highest visco-plastic properties and resistance to brittle fracture. The microstrain of the α-Fe crystal lattice, as well as the quantitative decay of cementite and the redistribution of carbon between ferrite and pearlite, were evaluated by X-ray structural methods. 06G2BA steel is recommended for use in the construction of pipelines and, for example, bridge structures, which are constantly under cyclic loads with simultaneous contact with a corrosive-aggressive environment. The influence of the service life of water pipes on the hydrogen content and microcracks in pipe steels was determined. A diagram of the relationship between long-term and static strength depending on the hydrogen content in steels is recommended, which can be used by designers to rationally choose the type of steels with high crack resistance in aggressive technological environments. In order to extend the service life of pipe structures, it is necessary to use economically modified steels.

Effect of Snow Depth on the Hydrogen Content of Steels in Snowy Environment

Effect of Snow Depth on the Hydrogen Content of Steels in Snowy Environment

A study on reducing hydrogen content in steel using ultrasonic cavitation process

In this study, a novel process utilizing ultrasonic cavitation(UC) was proposed to decrease hydrogen content in steel. Electrochemical hydrogen-charging and UC were performed on steels with different elemental species and ratios, and hydrogen embrittlement(HE) susceptibility was evaluated by slow strain rate tensile(SSRT). UC effectively reduced hydrogen-induced plasticity loss by removing hydrogen trapped by traps, particularly in SA508Gr.3. Dehydrogenation effects and recovery mechanisms were explored. Hydrogen trapped by low-energy traps played a critical role in hydrogen-induced hardening. The cleavage platforms of the specimen after UC was reduced, but a large number of microcracks appeared in the fracture due to residual hydrogen.

Metal degassing in vacuum-chamber of circulating vacuum degasser of JSC EVRAZ NTMK

For smelting of high-quality metal for transport purposes, it is necessary to limit the content of harmful impurities in it, including dissolved gases. For example, hydrogen content in the finished product should not exceed more than 2 ppm. In order to obtain low residual hydrogen content in steel in the converter shop of JSC EVRAZ NTMK, the transport metal is processed at circulating vacuuming plants. Circulating vacuum degasser is the last stage of steel processing before casting on continuous casting machine, so it is important to study and improve the technological processes in it. To investigate the physico-chemical processes occurring in this metallurgical unit, a hydrodynamic model of the system circulating vacuum degasser – steel ladle was created. Based on theoretical calculations and experiments conducted on a physical model, the main dependencies between the structural and technological parameters of the metallurgical unit were determined. The resulting equation makes it possible to determine the rate of metal circulation in vacuum chamber depending on gas flow rate supplied to inlet snorkel and its inner diameter at circulating vacuuming plants designed for metal processing in steel ladles with a capacity of 140 – 180 tons. Theoretical calculations were confirmed by practical smelting in a steelmaking unit. It is shown that during the wear of lining of the inlet snorkel vacuum chamber, in order to obtain stable residual hydrogen content, it is necessary to make changes in the technological process of vacuuming. Additionally, rational technological parameters of steel processing at the circulating vacuuming plant were determined on the basis of theoretical calculations.

Metal Degassing in Vacuum-Chamber of Circulating Vacuum Degasser of JSC EVRAZ NTMK

For smelting of high-quality metal for the applications in transport vehicles, it is necessary to limit the content of harmful impurities in it, including dissolved gases. For example, hydrogen content in the finished product should not exceed more than 2 ppm. In order to obtain low residual hydrogen content in steel in the converter shop of JSC EVRAZ NTMK, the transport metal is processed at circulating vacuuming plants. Circulating vacuum degasser is the last stage of steel processing before casting on continuous casting machine, so it is important to study and improve the technological processes in it. To investigate the physico-chemical processes occurring in this metallurgical unit, a hydrodynamic model was created for the system that includes the circulating vacuum degasser and the steel ladle. Based on theoretical calculations using physical model and experiments conducted, the main dependencies between the structural and technological parameters of the metallurgical unit were determined. The resulting equation makes it possible to determine the rate of metal circulation in vacuum chamber depending on the gas flow rate supplied to inlet snorkel and its inner diameter at circulating vacuuming plants designed for metal processing in steel ladles with a capacity of 140–180 tons. Theoretical calculations were confirmed by practical smelting in a steelmaking unit. It is shown that in order to obtain stable residual hydrogen content during the wear of lining of the inlet snorkel vacuum chamber, it is necessary to make changes in the technological process of vacuuming. Additionally, rational technological parameters of steel processing at the circulating vacuuming plant were determined on the basis of theoretical calculations.

Hydrogen permeation behavior of QP1180 high strength steel in simulated coastal atmosphere

The hydrogen permeation behavior of QP1180 high strength steel for automobile was studied in simulate coastal atmosphere environment by using Devanathan-Stachurski dual electrolytic cell, the cyclic corrosion test (CCT), thermal desorption spectrometry (TDS) and electrochemical measurement methods. The current density of hydrogen permeation generally increases with reducing the relative humidity from 95% to 50% and periodically changes in the CCT process. These mainly result from the evolution of corrosion and rust layer on the specimen surface with the atmospheric humidity and intermittent salt spraying. The contents of diffusible hydrogen and non-diffusible hydrogen in the steel enlarge slightly in the CCT process. The plastic deformation about 11.3% results in much higher diffusible hydrogen content in steel, but noticeably reduces the hydrogen permeation current and almost has no influence on the non-diffusible hydrogen content. The combination of double electrolytic cell and standard cyclic corrosion test can effectively characterize the hydrogen permeation of high strength steel in atmospheric service environments.

A predictive model for hydrogen content in steel in non-degassed heats

Hydrogen may cause several problems during steel processing. Issues caused or enhanced by hydrogen range from different types of bubbles such as pinholes to breakout during continuous casting. Further down the line, segregation and embrittlement may lead to cracking such as flaking or blistering. These problems impact plant productivity and have cost impacts on equipment maintenance and the need for additional steel treatment. Some of the problems lead to scraping. Although vacuum degassing effectively controls the hydrogen content of steel, it introduces additional costs that are not justifiable for many products. This work aims to identify the main sources of hydrogen in liquid steel in the Ternium Brazil steelmaking plant and to propose a model to decide the need for hydrogen measurement for the degassing process, focusing on steels for which vacuum degassing is not a specification requirement. It is essential for these steels to guarantee a controlled level of dissolved hydrogen to avoid problems, mostly at casting. Once the sources are identified, a model is developed to predict the hydrogen content at the beginning of the secondary metallurgy treatment. Based on the model, it is proposed that hydrogen should be measured or not at this step to decide if vacuum degassing is required to assure safety in casting.

Experimental Investigation on the Evolution of Hydrogen in Steel during the Electroslag Remelting Process

Hydrogen, which is a harmful element, has a great effect on the mechanical properties of steel, should be removed during the steel manufacture process. The evolution of hydrogen content in steel during electroslag remelting process is experimentally investigated. The results show that during the electroslag remelting process, the hydrogen content in steel firstly increases steeply to maximum, then decreases to minimum and reaches the equilibrium. For a prefixed slag composition, the final hydrogen content in steel depends on the initial hydrogen content and the atmospheric moisture. When the electroslag remelting is operated under the argon protected atmosphere, the hydrogen in steel increased slightly. With the increase of the atmospheric moisture, the hydrogen content in steel increased significantly, and the larger atmospheric moisture is, the more significant influence on the hydrogen content in steel is. Moreover the mathematical formula to predict the hydrogen content in steel from the initial hydrogen content and the atmospheric moisture is derived: w%He=0.359w%HS+0.016pH2O/pΘ+0.525 It could be used to forecast the final hydrogen content in ESR ingot.

Research on the reduction of the hydrogen content in steels treated in vacuum

This paper discusses the results of the research on the influence of the vacuuming technological factors on the hydrogen content in the steel produced in an electric furnace type EBT, treated outside the furnice in Ladle-Furnace (LF) and Vacuum Degassing (VD) facilities, and then continuously casted as semi round products designed for pipes manufacturing. Vacumming main parameters were followed such as: the total duration of vacuuming, the duration of advanced vacuuming, the pressure in the vacuum facility, the vacumming temperature drop during the treatment (considered independent parameters) and the amount of hydrogen removed from the metal bath during the vacuuming. The obtained data was processed in the MATLAB calculation program, using three types of equations, the results obtained being presented both in analytical and graphical form. The technological analysis of the correlation equations and the graphical representations allowed to establish the variation limits of the independent parameters in order to advancely reduce the steel hydrogen content.

Changes in Hydrogen Content During Steelmaking

Abstract Štore Steel produces steel grades for spring, forging and engineering industry applications. Steelmaking technology consists of scrap melting in Electric Arc Furnace (EAF), secondary metallurgy in Ladle Furnace (LF) and continuous casting of billets (CC). Hydrogen content during steelmaking of various steel grades and steelmaking technologies was measured. Samples of steel melt from EAF, LF and CC were collected and investigated. Sampling from Electric Arc Furnace and Ladle Furnace was carried out using vacuum pin tubes. Regular measurements of hydrogen content in steel melt were made using Hydris device. Hydrogen content results measured in tundish by Hydris device were compared with results from pin tube samples. Based on the measurement results it was established that hydrogen content during steelmaking increases. The highest values were determined in tundish during casting. Factors that influence the hydrogen content in liquid steel the most were steelmaking technology and alloying elements.

Effect of the production factors on the hydrogen saturation of steel

The available data on the influence of hydrogen on the steel quality and its main hydrogen-induced defects are analyzed. The factors that influence the hydrogen content in steel under conditions of the oxygen-converter plant of the Magnitogorsk metallurgical works have been revealed. The methods of decreasing the hydrogen content in steel are considered.

Metallurgical Investigation into the Incidence of Delayed Catastrophic Cracking in Low Nickel Austenitic Stainless Steel Coils

An incidence of delayed catastrophic cracking in commercially processed low nickel austenitic stainless steel coils during unwinding of the material at a customer’s end has been investigated. The fracture surfaces of failed steel coil samples revealed a brittle intercrystalline mode of fracture with typical manifestations of clear grain facets. Optical and scanning electron microscopy of polished, unetched steel specimens exposed a preponderance of branched as well as discrete stepwise microcracks, commonly observed in hydrogen-induced delayed failures. The specimens, electrolytically etched in 10% oxalic acid, were found to exhibit pronounced intergranular cracking, stepwise microcracking, grain dropping, and intergranular ditching in the annealed austenite microstructure of low nickel stainless steel. Investigations also revealed unusual levels of residual hydrogen to the extent of 11 ppm in steel specimens and a marked loss of tensile ductility was also noticeable in the defective steel with elongations barely approaching 8% in comparison to an overall elongation of 50% at the time of its dispatch to the customer. Based on the delayed nature of cracking, which transpired at customer’s premises after several days/months of dispatch, and the fact that the failure of the coils occurred at the time of uncoiling, when the operating stresses are well below the yield point of the material, it is surmised that the failure is attributable to hydrogen-induced damage. This article also takes a critical look at the possible sources of hydrogen pickup during steel making and elucidates remedial measures for control of hydrogen content in steels.

高強度鋼の水素脆化研究のための水素ガス放出測定

Since the hydrogen content causing delayed fracture (hydrogen embrittlement) of some high strength steels is in the order of 0.01 weight ppm, accurate measurement is required. The present situation of hydrogen gas desorption analysis for the studies of hydrogen embrittlement of high strength steels is reviewed, and evaluation techniques of hydrogen embrittlement property using constant load test and slow strain rate test of hydrogen precharged specimens in conjunction with hydrogen desorption analysis are illustrated. In addition, measurement of hydrogen entry from the atmospheric corrosion environment is presented. Both critical hydrogen content for delayed fracture, obtained by means of the above mentioned tensile tests, and hydrogen content from environment are important parameters to evaluate delayed fracture susceptibility of high strength steels. The results of round robin tests of measurement of hydrogen content in steels using thermal desorption analysis is also introduced.

Production of DMR 249A Steel at SAIL, Bokaro Steel Plant

Low alloy steels are an attractive option for high performance structural applications due to cost and availability factors. A low carbon low alloyed steel, DMR 249A, was developed for strategic applications by Indian Navy at Steel Melting Shop II, Bokaro Steel Plant (SMS II, BSL). This paper enumerates the detail process variables modified for this development. DMR 249A grade was having the specified gas contents of hydrogen <2 ppm in final product for the avoidance of detrimental phenomenon like “Hair Line Cracks”. So the Hydrogen content of liquid steel was to be less than 3 ppm and this demand vacuum treatment of the steel. In absence of any Degassing unit at SMS II, BSL, making of DMR 249A steel was a challenging task. The hydrogen content of steel was controlled through restriction of hydrogen in input raw materials, control in degree of deoxidation during tapping, slag basicity at ladle furnace, argon rinsing regime and cooling of slabs i.e. control over diffusion of H2. The steel was produced with the existing infrastructure at Bokaro Steel Plant with various alloying elements and processed suitably to obtain the desired yield strength, toughness and gaseous content. The control was exercised at various stages of steel making and hot strip rolling to enable achievement of a higher degree of consistency in mechanical properties and microstructure. Quality fulfillment was a great challenge without vacuum degasser unit but Bokaro successfully made the steel with 100% customer satisfaction.

Hydrogen Pick-Up During Electroslag Remelting Process

The pick-up of hydrogen during electroslag remelting process for several slags consisting of CaF 2-Al 2O 3-CaO-SiO 2-MgO had been investigated. The laboratory-scale remelting experiments had been carried out in open air and water-free argon atmosphere, and then the influencing factors were analyzed. It had been found that the hydrogen content in steel varied with different slag compositions. The compositions and state of slag had significant effect on the hydrogen level in steel. Partial return slag and premelted slag could avoid the hydrogen pick-up especially in the early stages of the process. However, premelted slag was the optimum state to control the hydrogen pick-up in steel. Experimental results indicated that water-free argon atmosphere was very favorable to the control of hydrogen in steel in the normal remelting period.

低炭素オーステナイト系ステンレス鋼の大気酸化挙動に及ぼす鋼中水素の影響

The influence of hydrogen content in steel on atmospheric oxidation behavior of low carbon austenitic stainless steel SUSF316L was investigated for clarifying the mechanism of SCC initiation in a boiling water reactor environment, which is closely associated with the localized oxidation and its acceleration. The stainless steel was charged with hydrogen by the means of cathodic electrolysis followed by subjecting the hydrogen-charged steels to the atmospheric oxidation test at 300°C for 10 h. The oxide films that formed on the non-charged and hydrogen-charged specimens were analyzed by optical microscopy, scanning electron microscopy, laser Raman spectroscopy and glow discharge optical emission spectroscopy. Experimental results revealed that relatively thick oxide films were formed on the hydrogen-charged specimen resulting in the hydrogen accelerated oxidation (HAO), when the hydrogen content was 35 mass ppm. However, there was almost no difference between the non-charged and the hydrogen-charged from the viewpoint of oxidation behavior when the hydrogen content was 24 mass ppm. The spinel-type oxides such as Fe3O4 and FeCr2O4 were identified by laser Raman spectroscopy only on the specimen surface where the HAO occurred. In addition, the Cr concentration in the inner oxide layer of the oxidation-accelerated specimen was around 20% and was lower than that of the non-charged (30-35%). The HAO seemed to be closely associated with this decrease in Cr concentration in the inner oxide layer.

Ways of improving steel quality in the tundish

The role of the tundish in the continuous casting process has evolved from that of a buffer between the ladle and mold to being a grade separator, an inclusion removal device and a metallurgical reactor. For both grade separation and inclusion removal, the flow patterns inside the tundish play an important role. The separation of non-metallic inclusions at the interface between the steel and the slag in the tundish is to a great extent controlled by interfacial phenomena in the steel-slag-inclusion system. One constant in the world of high-purity, low-residual and clean steels is the continual drive to reduce and control the frequency of the inclusions. For example, there are high-purity, low-residual clean steels such as IF- steel sheets for automobiles which require the absence of oxide inclusions with diameters larger than 100 micrometers. Great efforts have been made to optimize the flow and turbulence in the tundish through weirs, dams or other systems. Furthermore, a new system, the porous annular well block for injecting argon, has been developed to optimize the bubble size and distribution and hence to achieve a high efficiency in trapping inclusions and in decreasing the hydrogen content in steel. Consequently, the steel quality is further improved in the tundish. Tested with success in a seamless steel shop, the new system gives results in agreement with the water models.

The influence of hydrogen on very high cycle fatigue properties of high strength spring steel

The influence of hydrogen on very high cycle fatigue (VHCF) properties of high strength spring steel 50CrV4 was studied in this paper. Three groups of specimens with different hydrogen contents ( C H) were prepared through different heat treatment procedures: quenched and tempered (specimen QT), annealed at 380 °C in a vacuum after QT (specimen VA), and treated by high-pressure thermal hydrogen charging (HPTHC) after QT (specimen HPTHC). Increase of hydrogen content ( C H) was definitely detrimental to the fatigue properties, especially for HPTHC specimens the fatigue strength at 10 9 cycles decreased considerably. The fatigue limit expression deduced by Murakami was revised in this paper. Basquin exponent was also discussed and it was found that the absolute value of Basquin exponent increases with hydrogen content increasing. Therefore, we could arrive at a conclusion that hydrogen content in steels is a very important factor influencing the VHCF properties of high strength spring steels.

Changing the hydrogen content of alloy steel in relation to the technology used to cool cast slabs

Results are reported from the production of two trial heats of alloy steel in which the cast slabs were cooled in a thermostatted chamber and in a dense stack. It is shown that cooling slabs in such a chamber makes it possible to reduce the hydrogen content of the steel 30% compared to slabs that are cooled while stacked.