Ferrite Bands Research Articles

Synthesis, characterization and correlation studies on the Ni–Zn–Mn ferrite as a photocatalyst

Samples of Ni0.3Zn0.7−xMnxFe2O4 (x = 0, 0.15, 0.25, 0.35, 0.45, 0.55) nanoparticles (NPs) were synthesized by auto-combustion flash method. These ferrites were used as catalysts for photodegradation of methylene blue (MB) dye utilizing visible light energy. Structural analysis was carried out using the X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, while nanoparticle dimensions were elucidated through transmission electron microscopy (TEM). The magnetic and optical behaviours were unveiled via vibrating sample magnetometer and UV–VIS spectroscopy, respectively. The XRD outcomes established the presence of a cubic spinel-type structure for the studied ferrite samples. The FTIR spectra unveiled two absorption characteristic bands of the spinel ferrite. TEM images revealed nanoscale dimensions of ferrite NPs with the range from 21.1 to 51.8 nm. The optical features exhibited an indirect band gap energy spanning from 4.25 to 4.36 eV. Magnetization behaviour displayed a sinusoidal trend corresponding to varying Mn concentrations. The ferrite NPs catalyst (10 mg) yield photodegradation efficiency ranged from 22.8 to 33.9% for 100 ml MB dye solution after 120 min of light irradiation. The effects of dye concentration and catalyst dose on the degradation efficiency were examined using the Ni0.3Zn0.35Mn0.35Fe2O4 catalyst with highest degradation (= 33.9%). On the other hand, the dependence of the degradation efficiency on the structure, morphological, magnetic and optical properties of the photocatalyst was investigated. The findings of this study underscore the potential of the prepared ferrite nanoparticles for advanced applications in environmental restoration.Graphical abstract

Failure Analysis of Dissimilar Metal Welds between Ferritic Heat Resistant Steels and Austenitic Stainless Steels in Power Plant

This study analysed the failure of dissimilar metal welds (DMWs) between ferritic heat resistant steels and austenitic stainless steels and investigated its influencing factors by means of numerical simulation, microstructure characterization and mechanical property test. Under the long-term high-temperature service condition in practical power plant, the DMW failure mode was along the interface between nickel-based weld metal (WM) and ferritic heat resistant steel, and the failure mechanism was stress/strain concentration, microstructure degradation and oxidation coupling acting on the interface. The numerical simulation results show that interface stress/strain concentration was due to the differences in coefficient of thermal expansion and creep strength, and the degree of stress/strain concentration was related to service time. The ferrite band formed at the WM/ferritic steel interface was prone to cracking, attracting the fracture along the interface. The interface crack allowed oxidation to develop along the WM/ferritic steel interface. During long-term service, the interface stress/strain concentration, microstructure and oxidation all evolved, which synergistically promoted interface failure of DMW. However, only under the long-term service of low stress conditions could trigger the interface failure of DMW. Meanwhile, long-term service would reduce the mechanical strength and plasticity of DMW.

Tailoring Strength and Ductility of an Fe–Mn–Al–C Low‐Density Duplex Steel by Controlling the Cooling Path after Hot Rolling

The low‐density duplex steels provide a potential for the industrial application owing to their good strength‐ductility match and reduced density. In the present work, the microstructure of an Fe–8.03Mn–6.10Al–0.4C (wt%) low‐density duplex steel was adjusted by controlling the cooling path after hot rolling, which is a conventional process during the production of steel sheets and strips. A microstructure of ferrite and austenite has been achieved by annealing the air‐cooled samples, and the microstructure of furnace‐cooled annealed samples consists of banded ferrite, austenite, and martensite. This is mainly due to the fact that the austenite is more stable by refining the grain size via embedding the needle‐like α‐ferrite. The existing of martensite and the banded microstructure in furnace‐cooled annealed samples induces the occurrence of cracks during deformation, resulting in an abrupt fracture at a relatively lower strain level. However, for air‐cooled annealed samples, a good ductility of duplex microstructure ensures that the deformation can be sustained up to a much higher strain level, and the transformation induced plasticity effect plays a positive role at the later deformation stage; this contributes to the occurrence of an extra work hardening rate recovery during deformation and thus to a good strength‐ductility match.

Preventing molten copper penetration to steel grain boundaries during cladding through optimizing GTAW parameters and ferrite band formation

Preventing molten copper penetration to steel grain boundaries during cladding through optimizing GTAW parameters and ferrite band formation

Development of Desirable Fine Ferrite Grain Size and Random Second Phase Dual-Phase Steel Microstructures Using Composition and/or Processing Modifications

Microstructural morphology is known to have a significant impact on the mechanical properties of dual-phase steels. A fine ferrite grain size and random distribution of small second phase islands are desirable to provide superior isotropic properties compared to the banded second phase distribution that is typical for this type of steel. A rapid alloy prototyping (RAP) facility has been used to investigate three different DP 800 variants by systematically varying the compositions and/or process parameters compared to the ‘standard’ DP800 composition and processing that gives a banded microstructure. For Variant 1, the heating rate during the annealing cycle after cold rolling varied between 0.65 and 30 °C/s for the 45%, 60% and 75% cold reduction samples. It was found that a cold reduction of 75% and heating rate of 15 °C/s resulted in the microstructure that can give the best combination of strength and ductility because of the fine grain size and high martensite volume fraction. For Variant 2, the effect of changing the hot rolled (HR) microstructure (ferrite–pearlite, ferrite–bainite or martensite) on the final microstructure was investigated. Both the ferrite–50% bainite and fully martensite/bainite HR materials for all cold reductions resulted in annealed microstructures with necklace martensite morphology and finer ferrite grains compared to the ferrite–pearlite HR material, which gave a typical banded ferrite–martensite microstructure with a coarser ferrite grain size. For Variant 3, the Mn content was reduced, and increased Nb was used to achieve higher pancaking during the hot rolling stage, which refined ferrite grains in the HR condition with the same hardness. After annealing with the standard parameters only the 45% cold-reduced material produced a finer ferrite grain size than the standard material, whereas the 60% and 75% cold-reduced samples required a higher heating rate to achieve finer ferrite grain sizes due to rapid recrystallisation and growth kinetics.

Ferrite effects on the hydrogen embrittlement of 17-4PH stainless steel

PurposeThe purpose of this study is to investigate the effect of ferrite on hydrogen embrittlement (HE) of the 17-4PH stainless steels.Design/methodology/approachThe effects of ferrite on HE of the 17-4PH stainless steels were investigated by observing microstructure and conducting slow-strain-rate tensile tests and hydrogen permeability tests.FindingsThe microstructure of the ferrite-bearing sample is lath martensite and banded ferrite, and the ferrite-free sample is lath martensite. After hydrogen charging, the plasticity of the two steels is significantly reduced, along with the tensile strength of the ferrite-free sample. The HE susceptibility of the ferrite-bearing sample is significantly lower than the ferrite-free steel, and the primary fracture modes gradually evolved from typical dimple to quasi-cleavage and intergranular cracking. After aging at 480°C for 4 h and hydrogen charging for 12 h, the 40.9% HE susceptibility of ferrite-bearing samples was the lowest. In addition, the hydrogen permeation tests show that ferrite is a fast diffusion channel for hydrogen, and the ferrite-bearing samples have higher effective hydrogen diffusivity and lower hydrogen concentration.Originality/valueThere are a few studies of the ferrite effect on the HE properties of martensitic precipitation hardening stainless steel.

Structural and optical characterization of MnFe2O4 nanoparticles

Manganese ferrite nanoparticles with chemical formula MnFe2O4 have been synthesized by low temperature chemical co-precipitation method. The structural and optical properties of the nanoparticles were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), fourier transform infra-red spectroscopy (FTIR) and UV-visible absorption spectroscopy. XRD confirm pure spinel phase formation of the prepared sample. All the observed peaks correspond to the standard diffraction pattern of manganese ferrite having JCPDS card number 74-2403. From the XRD data, the average crystallite size was calculated and found to be 27.40 nm. The FTIR spectrum shows the characteristic bands of the spinel ferrite. Morphology of the nanoferrites was given by SEM image revealing that the particles are approximately spherical in shape. The elemental composition along with their relative ratios was given by EDAX and was found to be in agreement with their initial calculated values. UV- visible absorption spectrum of the prepared sample shows characteristic absorption in visible range and from the UV-visible absorption data the band gap of the prepared sample was determined. MnFe2O4 nanoparticles were found to possess a narrow band gap of 1.4 eV which may find applications in photocatalytic degradation of pollutants. The simple co-precipitation method proves to be an effective method for synthesis of pure phase manganese ferrite nanoparticles. Copyright © 2017 VBRI Press.

Friction resistance and bonding strength of high vanadium alloy steel/low carbon steel bimetal after heat treatments

The bimetals with high strength and toughness are expected to replace traditional single materials in the wear resistance field. In the present study, a high vanadium alloy steel (HVAS) was cladding on the low carbon steel (LCS), and the microstructure and mechanical properties of the HVAS/LCS bimetal before and after heat treatments were investigated. The Microstructure of the HVAS is Mo-rich and V-rich eutectic carbides distributed in the pearlite matrix. After quenched, the pearlites transformed to martensites that with amount of tiny secondary carbides. The hardened martensites transformed to tempered martensites after the tempering treatments. The hardness of the HVAS has been improved after heat treatments by martensitic transformation, the QT500 sample have the maximum hardness of 61 HRC, and shows good friction resistance. The HVAS and the LCS achieved metallurgical bonding, and shows a good bonding interface situation with no defects or unbonded regions. An uphill diffusion phenomenon was observed, C atoms diffused from the LCS to the HVAS forming a ferrite band and a pearlite diffusion zone. The HVAS/LCS bimetal has good bonding strength, the tensile strength of the interface exceeds 397 MPa. The bonding strength decreased after heat treatments, and decreased with the increasing tempering temperature.

Characterization and formation mechanism of ultra-fine ferrite grains in dissimilar metal weld between austenitic stainless steel and low alloy ferritic steel

The interfacial microstructures of ex-service dissimilar metal weld (DMW) between austenitic stainless steel TP347H and low alloy ferritic steel G102 were investigated. A band of ultra-fine grains were found at the nickel-based weld metal/G102 steel interface. The ultra-fine grain band was characterized in detail by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), electron backscatter diffraction (ESBD), focused ion beam (FIB), transmission electron backscatter diffraction (T-EBSD) and transmission electron microscopy (TEM). The formation mechanism of ultra-fine grain band was proposed and the effects of it on service performance were discussed. The ultra-fine grains were ferrite without carbides, which were transformed from pre-existing martensite layer by carbon migration and localized recrystallization. This type of ultra-fine ferrite band triggered interfacial oxide notch by preferential oxidation of grain boundaries and increased the risk of interfacial cracking by microstructure degradation, which was a potential factor contributing to interfacial failure of DMW. The present work provided a new insight into the premature failure of such kind of DMWs.

Heterogeneous Microstructure of Low-Carbon Microalloyed Steel and Mechanical Properties

The microstructure plays a major role in the performance of metallic materials, which can be tailored through the composition and/or processing technique. In this study, a heterogeneous microstructure was developed for low-carbon microalloyed API X65 steel, the most commonly used pipeline steel for oil and gas transportation, using a heat treatment process. The heat treatment process involved intercritical heating of the steel followed by high-temperature isotheral cooling, allowing for phase transformation, as well as alloying element partitioning. The heat treatment transformed the banded ferrite–pearlite microstructure of rolled steel to a quasi-polygonal ferrite microstructure, with the sporadic presence of austenite at the grain boundaries. The quasi-polygonal ferrite was distributed in a heterogeneous form with a fine-grain shell surrounding the coarse-grained core. The heterogeneity in the microstructure, despite being single phase, led to a significant improvement in the tensile yield strength, ultimate tensile strength, ductility and toughness of the steel, with a marginal reduction in microhardness values.

Clarifying effect of welding conditions on microstructure and mechanical properties of friction stir spot-welded DH590 automotive high-strength steel plates

Friction stir spot welding was successfully applied to the 1.2-mm-thick DH590 dual-phase steel plates by using a polycrystalline cubic boron nitride rotating tool. During welding, the rotation speed ranged from 600 to 1000 r/min and the penetration depth ranged from 0.1 to 0.3 mm. In the spot joints, the size of the stir zone increased with the increase in rotation speed as well as the penetration depth of the tool. Comparing with the banded ferrite and martensite structure of the base metal, a mixed microstructure of ferrite and tempered martensite, refined bainite structure and coarse martensite structure were found in the heat-affected zone, thermomechanically affected zone and stir zone of the joints, respectively. Two kinds of interfacial shapes were formed between the upper and lower steel plates, and the formation of the bonded interface was dominated mainly by the penetration depth of the rotating tool rather than the rotation speed. It was revealed that the joints with straight interfaces showed higher shear tensile loads comparing with those with hook-like interfaces. Shear tensile tests showed that the maximum shear tensile load reached about 15.56 kN when the rotation speed and penetration depth were set as 800 r/min and 0.3 mm, respectively. The specimen was fractured through plug failure mode with a total elongation of about 5.6 mm.

Synthesis, structural, magnetic and dielectric studies of aluminum substituted cobalt-copper ferrite

Nano-particles of Co0.5 Cu0.5 Alx Fe2-x O4 ferrite compounds with compositions (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were prepared using co-precipitation method. The IR spectra of the samples showed the main characteristic bands of the spinel ferrite. X-ray diffraction patterns confirmed the formation of a single spinel phase for all the samples except the compound with composition x = 0.4. The particle size of the samples confirmed the nano-size, which found in the range of 30–54 nm. The saturation magnetization and coercivity showed a decreasing trend with the increase of Al-content. The electrical and dielectric properties of the samples were investigated through the DC and AC measurements of the ferrite samples. Moreover, dielectric properties of the samples, such as dielectric constant, dielectric loss, and loss tangent, exhibited decreasing behavior with the increase of frequency, which explained in terms of the possible polarization process in ferrite.

Microstructural analysis, radiography, tool wear characterization, induced residual stress and corrosion behavior of conventional and cryogenic trepanning of DSS 2507

In the present study, an endeavour has been made in trepanning of Duplex steel (DSS 2507) under wet and cryogenic environments. DSS 2507 steel is predominantly used in the area of defence for warhead and rocket motor casing, marine applications of submarine rocket launchers, naval components and other high end applications due to their high strength provided by two phased structure. Reduction of 35.21 % and 14.80 % is observed in cryogenic trepanning correlated to conventional trepanning analogous to cutting force and cutting temperature, respectively. This has an explicit bearing on the machinability and surface characteristics of the hole formed. Attrition of immured austenite phase fraction and curtailed carbide structure aids to the increase in the residual (compressive in nature) stress by 3.25 % in cryogenic trepanning, further causing an accretion of wear resistance and hardness. An increase in work hardness and inherent machinability property is observed with a surge in microhardness by 11-26.07 %, due to the upsurge of ferrite band along the surface. Additionally, ferrite formation ensures abatement the formation of embedded chips along the surface in cryogenic trepanning. Increase in MRR is ascertained at 0.8 % in cryogenic trepanning compared to conventional trepanning. A decrease of 30.99 % and 72.30 % in flank and crater wear, respectively is ascertained in cryogenic trepanning in correlation to conventional trepanning of DSS 2507 steel is ascertained. The corrosion resistance in cryogenic trepanning increased by 59.78 % analogous to conventional trepanning of DSS 2507 steel. In cryogenic trepanning, a passivation barrier is ascertained with interatomic spacing curtailment along with a surge of ferrite phase, causing an upsurge in the compressive residual factor.

Structural and electromagnetic studies of Mg1-xZnxFe2O4 nanoparticles synthesized via a sucrose autocombustion route

Mg1−xZnxFe2O4 nanocrystalline ferrites (1.0 ≥ x ≥ 0.0) were prepared using a sucrose autocombustion-assisted route. X-ray diffraction (XRD) showed secondary phase formation at Zn contents higher than x = 0.2. The obvious increase in the lattice parameters from 8.3937 to 8.4454 A upon increasing the Zn content might be attributed to the ionic radius of Zn2+ ions being larger than that of Mg2+ ions. The crystallite sizes calculated using Scherrer’s formula confirmed the nanocrystalline nature of the prepared samples. The Fourier-transform infrared (FTIR) spectra exhibited characteristic ferrite bands attributed to tetrahedral and octahedral sites, and there was an obvious splitting in the tetrahedral absorption band attributed to the Jahn–Teller distortion effect. Transmission electron microscopy (TEM) images showed agglomerated spherical particles with sizes that are in full agreement with results obtained by XRD. A reliable cation distribution was suggested based on the obtained structural parameters to address the preferential occupation of the entirety of the cations with increasing Zn content. The magnetic parameters estimated by vibrating sample magnetometer (VSM) measurements were utilized to confirm the suggested cation distribution and address the effect of Zn substitution on the entire system. All the investigated samples, except for ZnFe2O4, exhibited soft ferromagnetic characteristics. The obtained coercivities were higher than those reported in the literature and suggested the presence of an elevated demagnetization field and reflected the impact of the present synthesis method. The AC conductivity indicated semiconducting properties, and there was a ferromagnetic-to-paramagnetic magnetic transition in all samples with increasing temperature. The dielectric measurements also confirmed this transition by exhibiting relaxations in the same temperature range.

Microstructural Evolution of Dissimilar Metal Welds Involving Grade 91

Dissimilar metal weld failures between low alloy Cr-Mo ferritic steels and austenitic stainless steels made with Ni-base filler metals are typically observed along the fusion line. Such DMW failures often exhibit the onset of damage well before their expected service life. Failure is typically associated with a carbon-depleted region in the ferritic steel and formation of creep voids along a row of so-called Type I carbides. More recently, the formation of Type I carbides adjacent to a carbide-free ferrite band has also been observed in DMWs where the ferritic steel was a 9 pct Cr creep strength-enhanced ferritic steel. However, it has not been completely clarified whether these microstructural features formed during welding, post-weld heat treatment or service. In this study, single pass bead-on-plate welds were prepared on a Grade 91 steel substrate using commonly specified Ni-base weld metals; ENiCrCoMo-1, ENiCrMo-3, ENiCrFe-3, ENiCrFe-2 and EPRI P87 (ENiFeCr-4) and were characterized in the as-welded, post-weld heat treatment (PWHT) and aged conditions. The evolution of the ferrite band was found to form by a diffusion-controlled process and was observed after PWHT and aging associated with regions exhibiting steep concentration gradients in the partially mixed zone (PMZ). In this study, steep concentration gradients were observed along the toe of the weld whereas relatively shallow gradients were observed at the weld bottom-center, resulting in a discontinuous ferrite band along the fusion line during PWHT and aging. The variation in chemical gradients in the PMZ corresponded to different chemical potential gradients, which lead to differences in carbon diffusion during high-temperature PWHT and aging. The results of this study provide insight into potential solutions for minimizing the risk of failure in future applications.

Enhancement of Saturation Magnetization and Remanence of BaFe12O19 Materials Prepared by NaCl–KCl and Hexamine as Flux

Hexagonal platelet barium ferrite was produced through a two-step molten salt synthesis calcined at 850 °C for 5 h with NaCl–KCl as flux, followed by calcination at 400 °C for 5 h with hexamine. Influence of NaCl–KCl and hexamine on the structural, phase composition, surface morphology, and magnetic properties of BaFe12O19 was studied by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric/differential analysis, scanning electron microscopy, and a superconducting quantum interference device. The particles exhibited M -type barium hexaferrite nanoparticles with a product yield of 97.8% with a mean crystallite size of 81 nm for NaCl–KCl and 50 nm for hexamine. The infrared spectrum showed tetrahedral and octahedral positions in the absorption bands of hexagonal ferrite. As the atomic ratio of Ba:Fe:O is found to be 1:12.3:17.6, which is close to the stoichiometric ratio of BaFe12O19, it confirms the hexagonal structure of the sample. The plates are found to agglomerate, and variation in particle size was observed using scanning electron microscopy. The samples revealed better magnetic properties with a high saturation magnetization of 165.3 emu/g, higher remanence of 58 emu/g, coercivity of 929 Oe, and a squareness ratio of 0.35. This investigation was performed to examine the microstructure and the effect of crystallinity of the submicrometer BaFe12O19 powders on magnetic properties. This study also provides a promising method and total processing parameters to synthesize hard ferrite powders with improved hard magnetic properties and fine crystallite size.

Brittle fracture manifestation in gas pipeline steels after long-term operation

Gas pipelines are exposed to operational loads combined with corrosive environment action during their long-term service. Complicated service conditions lead to a worsening of steel properties, a reduction of serviceability of the whole object, therefore, a risk of its premature failure rises. Aware of the importance of the existing problem, the aim of this study is the analysis of various mechanical properties of steels after their long-term operation on gas pipelines, and detecting and evaluating fractographic signs of this degradation.Mechanical properties of operated pipe steels characterizing their brittle fracture resistance were significantly decreased. Delamination areas as one of a feature of brittle fracture were identified on the fracture surfaces of specimens after SSRT of the operated steels in corrosive environment. Fracture was initiated from the outer surface of the specimens along the boundaries of ferrite and pearlite grains with significant secondary cracking.The obvious texture in the steels affects noticeably the results of the impact tests. Higher KCV values for the specimens cut in the longitudinal direction relative to the pipe axis comparing with the specimens of transversal orientation were obtained. This was explained by different length of narrow pearlite strips alternated by wide ferrite bands and interrupted by individual ferrite grains depending on the orientation of the specimen fracture surface relative to the pipe axis. Thus, a proper direction of specimen cutting to achieve the maximum sensitivity of KCV parameter to operational degradation of steels is discussed. The effect of specimen orientation on the results of the Charpy testing becomes much more pronounced with steel operation. Defects accumulated in steels during their service are preferentially oriented in the pipe axial direction along the boundaries between ferrite and pearlite strips. Analyzing the fracture surfaces of the Charpy specimens after their impact testing, certain signs of embrittlement were found for long term operated steels in the form of delaminations varying in size and shape, and some cleavage fragments. Furthermore, their percentage of total fracture surface (generally formed by dimples) correlates well with a drop in the impact toughness. The established relationship could be the basis for the introduction of fractographic criteria of the steel serviceability.

Double-sided friction stir welding of 40 mm thick low carbon steel plates using a pcBN rotating tool

Double-sided friction stir welding was conducted on 40 mm thick low carbon steel plates using a pcBN rotating tool with a probe length of 20 mm. During the welding, the tool rotation speed and travelling speed were maintained at 150 rpm and 25 mm/min, respectively, and the maximum applied load reached about 15 tons. The final welded area showed a vertically symmetric bowl-like shape with the overlapped area having a width of about 21.3 mm. The welded areas formed in the first pass and second pass welding process were very similar, which contained a large stir zone and wide thermal-mechanically affected zone. The microstructure of the stir zone consisted of a coarse acicular ferrite and bainite structure, compared with the banded ferrite and pearlite structure of the base metal. While the thermal-mechanically affected zone showed two types of microstructures, one contained fine ferrite and bainite structure and another one contained mixed ferrite and pearlite structure. The hardness distribution and tensile tests showed that the welded area had improved mechanical properties than that of the base metal. In addition, high density of BN particles caused by the tool wear was confirmed along the border of the stir zone on the advancing side. Inside the stir zone, BN particles were also observed, however, with a much lower density.

Precipitation behavior and strengthening mechanism of Ti micro-alloyed steel via CSP process

Two types of micro-alloyed steel with different carbon content and coiling temperature were produced by compact strip production (CSP) process. The microstructure characteristics and precipitation behavior of the Ti particles during casting, soaking, rolling, coiling and cooling stages were discussed to reveal the strengthening mechanism. The samples were composed of ferrite bands and discontinuous pearlite/bainite at the grain boundaries. The average grain sizes of the sample with low carbon content and high coiling temperature was confirmed as 5.6 μm by quantitative metallography method, while that with high carbon content and low coiling temperature was confirmed as 5.2 μm. Moreover, the TiN precipitated before soaking stage was large in size because of the high undercooling temperature, which had nearly no strengthening effect. The strength was mainly attributed by cooling and coiling stages with the TiC precipitated at the inter-phase or within the ferrite. Taking Q345B steel with yield strength of 505 MPa produced by CSP as contrastive sample, the strength increments of fine-grain/solution/dislocation/precipitation strengthening for the low carbon sample were 65, 0, 22 and 113 MPa, while those for the high carbon sample were 74, 33, 28 and 57 MPa. Fine-grain and precipitation strengthening were the main strengthening mechanisms for the high strength CSP plates.

Development of Structural Damage and Cracking in a Landing Head during Long-Term Operation under North Conditions

Abstract—The development of structural damage and cracking in a landing head used in Western Siberia is studied. The landing head is made of 20KhNL steel, which is an analog of T32MoCN8R steel produced in Romania. Crack growth is detected on the outer side of the landing head at the site of intersection of its end face with the ring surface. The experimental results obtained in this work demonstrate that the following two types of structural changes, which involve diffusion-mobile hydrogen, take place in the landing head during operation: the formation of a long chain of pores along the boundaries of the former austenite grains and the formation of ferrite bands, in which cementite particles dissolved.