Showing papers on "Pearlite published in 2008"
TL;DR: In this paper, a modified ISO17081(2004) standard method is used to evaluate the hydrogen trapping by measuring the permeability (JssL) and apparent diffusivity (Dapp).
313 citations
15 Apr 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a new ultra-high strength niobium-microalloyed pipeline steel of yield strength ∼700 MPa has been processed, which is derived from the cumulative combination of fine grain size, solid solution strengthening with additional interstitial hardening, precipitation hardening from carbides, dislocation hardening and mixed microstructure.
Abstract: A new ultrahigh strength niobium-microalloyed pipeline steel of yield strength ∼700 MPa has been processed. The Charpy impact toughness at 0 °C was 27 J and tensile elongation was 16%. The ultrahigh strength is derived from the cumulative combination of fine grain size, solid solution strengthening with additional interstitial hardening, precipitation hardening from carbides, dislocation hardening, and mixed microstructure. The microstructure was characterized by polygonal ferrite, upper bainite, degenerated pearlite, and martensite–austenite (MA) constituents. The microstructure of weld and heat-affected zone (HAZ) was similar to the base metal such that the hardness is retained in the weld region implying insignificant softening in the weld zone. Niobium and titanium precipitates of different morphology and size range evolved during thermomechanical processing and include rectangular (∼500 nm), irregular (∼240–500 nm), cuboidal/spherical (∼125–300 nm), and very fine (
146 citations
TL;DR: In this article, a steel with spheroidal cementite particles dispersed in a ferrite matrix was subjected to surface mechanical attrition treatment and was examined using transmission electron microscopy.
145 citations
TL;DR: In this paper, the authors describe microstructural changes induced by compressive-shear, cyclic contact in rail, with data from worn and fatigued rails removed from track and from SUROS twin-disc, lubricated tests, where standard grade rail steel discs were tested both to failure initiation (detected by eddycurrent probe) and to proportions of fatigue life.
128 citations
15 Jan 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the morphology and the profile of the interface between the aluminum coating and the substrate steel were investigated using optical and scanning electron microscopy, and X-ray diffraction.
Abstract: In hot-dip-aluminized (HAD) steels, the morphology and the profile of the interface between the aluminum coating and the substrate steel, are affected both by the composition of the molten aluminum as well as by the composition, and even the microstructure, of the substrate steel. This effect has been investigated using optical and scanning electron microscopy, and X-ray diffraction. The reaction between the steel and the molten aluminum leads to the formation of Fe–Al inter-metallic compounds on the steel surface. The thickness of the inter-metallic compound layer as well as the morphology of the interface between the steel and the interlayer varies with the silicon content of the molten aluminum. In hot-dip-aluminizing with pure aluminum, the interlayer is ‘thick’ and exhibits a finger-like growth into the steel. With a gradually increasing addition of silicon into the aluminum melt, the thickness of the interlayer decreases while the interface between the interlayer and the substrate gradually becomes ‘smoother’. With an increase in the carbon content of the substrate steel the growth of the interlayer into the steel is impeded by the pearlite phase, whereas the ferrite phase appears to dissolve more readily. X-ray diffraction and electron microscopic studies showed that the interlayer formed in samples aluminized in pure aluminum, essentially consisted of orthorhombic Fe2Al5. It was further observed that the finger-like grains of Fe2Al5 phase exhibited a preferred lattice orientation. With a gradual addition of silicon into the aluminum melt, a cubic phase based on Fe3Al also started to form in the interlayer and replaced most of the Fe2Al5.
119 citations
TL;DR: In this paper, the grain size ratio of fine-grained austenite and ferrite, d α /d γ, increases by refining grain size, which results in an increase of hardness.
Abstract: Microstructure formed by diffusional or martensitic transformation from fine-grained austenite of which grain size is smaller than 5 μm was studied. Grain refinement of austenite was established through two kinds of reversion processes; (1) cyclic transformation between martensite and austenite and (2) reverse transformation from tempered and cold-rolled lath martensite (or pearlite). In the process of (1), the fine austenite structures whose grain sizes of 5-10 μm are obtained. Refinement of austenite grain size results in the increase of hardness. In the process of (2), austenite grain size can be refined down to about 2 μm in low-carbon Mn steels by microalloying through pinning of austenite grain growth by alloy carbides. The ferrite grain size after continuous cooling transformation becomes finer as austenite grain size is refined. However, the grain size ratio of austenite and ferrite, d α /d γ , increases by refining austenite grain size. For the austenite of grain size smaller than 5 μm, the ferrite grain size becomes coarser than that of austenite for slow cooling. A similar trend in the change of ferrite grain size by refinement of austenite was recognized for isothermal pearlite transformation in eutectoid alloys. Thus, it is suggested that extensive accelerated cooling is important to obtain fine-grained ferrite by diffusional transformations from the fine-grained austenite. Packet and block sizes of lath martensite in low carbon steels are also refined by decreasing the austenite grain size. Several packets and blocks are formed even from the austenite matrix of 2 μm in grain size.
115 citations
TL;DR: In this article, the face-centered-cubic (fcc) to hexagonal close-packed (hcp) martensitic transformation exhibited by an as-cast Co-Cr-Mo-C alloy was investigated.
Abstract: The face-centered-cubic (fcc) to hexagonal close-packed (hcp) martensitic transformation exhibited by an as-cast Co-Cr-Mo-C alloy was investigated in this work. The alloy was annealed at 1150 °C, water quenched, and then isothermally aged at 700 °C to 900 °C. Quantitative measurements of transformed hcp martensite (also known as e-martensite) as a function of time and temperature were used in plotting C curves describing the transformation kinetics. Moreover, microstructural characterization indicated that the transformation exhibited two distinctive e-martensite morphologies. In the neighborhood of coarse carbides, multiple nucleation events were linked to the formation of e-martensite, while in the bulk of the dendrite matrix, the dominant morphology was as straight plates. Kinetic determinations of activation energies, Q, in either region indicated that in platelike e-martensite, Q = 57.24 kcal/mol, but in “pearlite”-like morphologies, Q = 37.88 kcal/mol. Apparently, as the activation energy was reduced, multiple nucleation events were favored leading to the “pearlitic” appearance.
106 citations
TL;DR: In this article, the sliding wear resistance of a nanostructured spheroidal steel varies with grain size: it increases when the grain size of the ferrite phase (Dα) increases from 8 to 32, and decreases with a further increase in Dα.
99 citations
15 Jul 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the microstructure and mechanical properties of high boron white cast iron were studied, and it was shown that the hardness of this type of cast iron is almost similar to that of high chromium white cast, but the toughness is increased a lot.
Abstract: In this paper, high boron white cast iron, a new kind of wear-resistant white cast iron was developed, and its microstructure and mechanical properties were studied. The results indicate that the high boron white cast iron comprises a dendritic matrix and an interdendritic eutectic boride in as-cast condition. The distribution of eutectic boride with a chemical formula of M 2 B (M represents Cr, Fe or Mn) and with a microhardness of HV2010 is much like that of carbide in high chromium white cast iron. The matrix includes martensite and a small amount of pearlite. After quenching in air, the matrix changes to martensite, but the morphology of boride remains almost unchanged. In the course of austenitizing, a secondary precipitation with the size of about 1 μm appears, but when tempered at different temperature, another secondary precipitation with the size of several tens of nanometers is found. Both secondary precipitations, which all forms by means of equilibrium segregation of boron, have a chemical formula of M 23 (C,B) 6 . Compared with high chromium white cast iron, the hardness of high boron white cast iron is almost similar, but the toughness is increased a lot, which attributes to the change of matrix from high carbon martensite in the high chromium white cast iron to low carbon martensite in the high boron white cast iron. Moreover, the high boron white cast iron has a good hardenability.
92 citations
15 Apr 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, microstructure influences on damaging mechanisms in ferritic-pearlitic ductile cast irons (DCIs) were investigated, and in situ scanning electron microscope observations were performed during step by step tensile tests in a microtensile holder.
Abstract: Microstructure influences on damaging mechanisms in ferritic–pearlitic ductile cast irons (DCIs) were investigated. Four different ferrite/pearlite volume fractions were considered, and in situ scanning electron microscope observations were performed during step by step tensile tests in a microtensile holder. SEM observations allowed to identify an evident microstructure influence on ferritic–pearlitic DCIs damaging mechanisms and the key role played by graphite constituents. Phase volume fractions and distribution affect both crack initiation and crack propagation. The importance of the damage mechanism based on graphite nodules–matrix interface cracking, usually indicated as the most relevant, is only partially confirmed, depending on the DCI microstructure.
87 citations
25 Nov 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a microstructure based model for the mechanical behavior of non-microalloyed ferrite-pearlite steels is proposed, where the internal stresses evolving with strain are estimated.
Abstract: This study proposes a new microstructure based model for the mechanical behavior of non-microalloyed ferrite–pearlite steels. Its main originality consists in estimating the internal stresses evolving with strain. It takes into account two contributions corresponding to two different scales of the microstructure: the huge internal stresses generated in pearlite all along the deformation and the mesoscopic strain incompatibility between ferrite and pearlite. This estimation allows the distinction to be made between the isotropic and kinematical components of work-hardening. The parameters of the model have been adjusted on numerous results from the literature concerning fully ferritic or pearlitic steels. The performance of the model is then demonstrated on datasets from the literature concerning steels with different fractions of pearlite. The predictions of the model are excellent concerning both tensile behavior and Bauschinger effects. The size effects of lamellar pearlite have been reviewed in this paper, i.e., the impact of interlamellar spacing on mechanical properties. In pearlite, the yield strength scales with s −1 , the internal stress with s −1/2 and the macroscopic strain-hardening (i.e., slope of the tensile curve) do not depend on interlamellar spacing. This review gives new perspectives for the understanding of the mechanical behavior of lamellar structures, such as pearlite or bainite.
TL;DR: In this article, three different ferritic-pearlitic ductile cast irons, characterized by different ferrite/pearlite volume fractions, and an austempered cast iron were considered.
25 Oct 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the concept of using low manganese content in pipeline steels for hydrogen-induced cracking (HIC) applications was described and the microstructure of thermomechanically processed pipeline steel primarily consisted of polygonal ferrite and low fraction of pearlite.
Abstract: The paper describes the concept of using low manganese content in pipeline steels for hydrogen-induced cracking (HIC) applications The microstructure of thermomechanically processed pipeline steel primarily consisted of polygonal ferrite and low fraction of pearlite The cleanliness of the steel was evident as was the absence of centerline segregation The microstructure contained high dislocation density, sub-boundaries and dislocation substructures Fine-scale precipitation of niobium carbides occurred on parallel array of dislocations and on random dislocations that followed [0 0 1] NbC //[0 0 1] α-Fe relationship with the ferrite matrix
TL;DR: In this article, a multifrequency electromagnetic sensor was used to measure decarburization in steel rods for various times in air at 1000°C. The inductance value of the sensor at different frequencies varied as a function of decarbing depth due to the difference in magnetic permeability between ferrite and pearlite.
15 Jul 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors evaluated the variations in the as-cast mechanical properties of low-carbon steels with and without vanadium and niobium and showed that good combinations of strength and ductility can be achieved by microalloying additions.
Abstract: Tensile and room temperature Charpy V-notch impact tests along with microstructural studies were used to evaluate the variations in the as-cast mechanical properties of low-carbon steels with and without vanadium and niobium. Tensile test results indicate that good combinations of strength and ductility can be achieved by microalloying additions. While the yield strength and UTS increase up to respectively 370–380 and 540–580 MPa in the microalloyed heats, their total elongation range from 20 to 25%. TEM studies revealed that random and interphase fine-scale microalloy precipitates play a major role in the strengthening of the microalloyed heats. On the other hand, microalloying additions significantly decreased the impact energy and led to the dominance of cleavage facets on the fracture surfaces. It seems that heterogeneous nucleation of microalloy carbonitrides on dislocations along with coarse ferrite grains and pearlite colonies trigger the brittle fracture in the microalloyed heats.
TL;DR: In this paper, the eddy current measurement can be used for obtaining reliable and quick detection of pearlitic percentage in plain carbon steels, and the results showed that the measured eddy currents can yield different pearlitic microstructures in the samples.
TL;DR: In this paper, the evolution of austenite formation during a continuous heating in a low carbon niobium microalloyed steel with a pearlite and ferrite initial microstructure has been studied.
Abstract: Austenite formation during a continuous heating in a low carbon niobium microalloyed steel with a pearlite and ferrite initial microstructure has been studied. Characteristic transformation temperatures, Ac 1, Ac θ and Ac 3 and the evolution of austenite formation have been determined by combining dilatometry and metallography in a range of heating rates from 0˙05 to 10 K s–1. It has been observed that nucleation and growth of austenite depends highly on the applied heating rate. At low heating rates (0˙05 K s–1) nucleation of austenite takes place both at pearlite nodules and at ferrite grain boundaries, while for higher heating rates (≥0˙5 K s–1), nucleation at grain boundaries is barely present compared to the nucleation at pearlite nodules. The heating rate also affects the austenite growth path and morphology and, thus, the distribution of martensite in the dual phase microstructure obtained at room temperature.
TL;DR: In this article, the authors investigated the tensile behavior of severely drawn pearlite steel wires with tensile strength larger than 4 GPa and found that the wire deforms plastically by dislocation motion resulting in dimple fracture.
Abstract: With decreasing of grain size in ferritic steels, Luders elongation becomes larger while work-hardening is lowered, finally resulting in loss of uniform elongation. This drawback can be overcome by introducing the second phase like martensite or metastable austenite. The improvement of strength and uniform elongation balance by the second phase can well be estimated by applying the secant method of micromechanics approach. The stress partitioning between two constituents brings high work-hardening, which is verified by in situ neutron diffraction. The influences of strain rate and temperature are described by using the Kocks-Mecking model. It is found that the grain refinement and the above stress partitioning contribute mainly to the athermal stress component of flow stress. Hence the tensile properties obtained at a high speed deformation like 10 3 /s is excellent in fine-grained multi-phase steels. As an example of ultrafine-microstructure with 20-30 nm in size, the tensile behavior of severely drawn pearlite steel wires with tensile strength larger than 4 GPa is investigated. In spite of such ultra-high strength, the wire deforms plastically by dislocation motion resulting in dimple fracture. The strengthening consists of isotropic hardening due to microstructure refinement and anisotropic hardening caused by residual intergranular stresses which are determined by neutron diffraction.
TL;DR: In this article, a tensile behavior was investigated by using in situ TOF neutron diffraction comparatively for ferritic steels; ferrite (F), as-quenched martensite (QM), tempered martensitic (TM) and pearlite (P) steels.
Abstract: Tensile behavior was investigated by using in situ TOF neutron diffraction comparatively for ferritic steels; ferrite (F), as-quenched martensite (QM), tempered martensite (TM) and pearlite (P) steels. Changes in lattice spacing, diffraction intensity and FWHM with increasing of the applied stress were measured. Preferential plastic flow takes place depending on crystal orientation, so that intergranular stresses are yielded due to the misfit plastic strains in differently oriented [hkl] family grains for steel F, in blocks for the other steels. Because of the existence of cementite in steels TM and P, phase stresses are superposed upon the intergranular stresses. When the averaged phase strain is subtracted from the measured lattice strain, the trend in generation of intergranular strain in steel TM is similar to that observed in steels F and QM, while that in steel P differs from the other steels. The changes in [hkl] diffraction intensity and FWHM with tensile deformation are similar in steels F, TM and P, while those in steel QM are different from the others. FWHM decreases with tensile deformation suggesting the decrease in dislocation density in steel QM. That is, dislocations induced during martensitic transformation move preferentially and are annihilated by coalescence of dislocations with different signs in the beginning of deformation and hence transformation induced dislocation structure changes to deformation induced one that shows lower dislocation density but higher resistance to tensile flow. The preferential movement of transformation induced dislocations in steel QM leads to a different texture evolution which is recognized from the change in diffraction intensity with tensile deformation.
20 Aug 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the coarsening kinetics of cementite particles in severely cold-rolled and annealed pearlite in Fe-0.8C alloys with various contents of Cr, Mn and Si were investigated, and the effect of alloying elements was discussed.
Abstract: The coarsening kinetics of cementite (θ) particles in severely cold-rolled and annealed pearlite in Fe–0.8 mass% C alloys with various contents of Cr, Mn and Si were investigated, and the effect of alloying elements was discussed. The results showed that severely cold-rolled pearlitic cementite spheroidized rapidly during annealing at 923 K in the Fe–0.8C alloys, and the coarsening of θ particles is strongly suppressed by the addition of Cr, Mn and Si. The coarsening kinetics of θ particles obeys the relationship, d = kt n , and the staged change appears on the coarsening kinetics curves. In Fe–0.8C alloy, the solute atoms diffused mainly along dislocations at the first stage, but they diffused mostly along the grain boundaries during the subsequent annealing. The addition of Cr or Mn restrained coarsening of θ particles due to decrease of diffusivity of carbon atoms, but this suppression effect weakened after a long-time annealing (more than 3 h). The addition of Si accelerated exclusion of carbon atoms from the rolled α-Fe, thus it changed the diffusion pattern of solute atoms and increased the n value at the initial annealing stage (∼0.6 ks). During the subsequent annealing (0.6–10.8 ks), the addition of Si suppressed the coarsening of θ particles pronouncedly.
TL;DR: In this article, an ultrafine-grained ferrite/cementite (UGF/C) steel with a local high density of cementite particles was fabricated through caliber-warm-rolling followed by annealing and resulted in a bimodal-sized microstructure.
Abstract: An ultrafine-grained ferrite/cementite (UGF/C) steel with a local high density of cementite particles was fabricated through caliber-warm-rolling followed by annealing and resulted in a bimodal-sized microstructure. The characteristic bimodal-sized microstructure was attributed to the original ferrite-pearlite structure and cementite spacing, and reflected the original ferrite-pearlite structure. The smaller-sized clusters corresponded to the former pearlite regions and the larger-sized clusters to the proeutectoid ferrite regions. The cementite particles naturally localized within the former pearlite region. Most of the ferrite coarsening did not occur until the cementite particle spacing reached a critical value. The UGF/C microstructure with a bimodal grain size showed a yield strength elongation combination that was better than conventional ferrite pearlite steels, and is a significant improvement as a result of the processing and resultant microstructure. The Hall–Petch relationship was best demonstrated when the yield strength was correlated to the average size (determined from the two inverse grain sizes that were normalized by the area fractions) rather than the larger or smaller size of the bimodal distribution, which reflected the strengthening effect of the subgrained structure. The grain refinement contributed to the athermal component of the yield strength but hardly affected its thermal component.
TL;DR: In this article, the three-dimensional morphology and crystallography of cementite lamellae in a 0.8 mass% C-Fe alloy were examined by a combination of scanning electron microscopy using a double-beam field emission gun, electron back-scattered diffraction, and transmission electron microscope.
15 May 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The resistance of X52 and X60 API steels to sulphide stress cracking (SSC) was tested by tensile tests at a constant load and also by slow strain rate tensile (SSRT) tests.
Abstract: The resistance of X52 and X60 API steels to sulphide stress cracking (SSC) was tested by tensile tests at a constant load and also by slow strain rate tensile (SSRT) tests Both steels were tested after hot-rolling, when they had a microstructure which consisted predominantly of ferrite and pearlite They were then tested after laboratory quenching and tempering, when their microstructure was predominantly of tempered bainite or martensite The results showed that the resistance of the steel to SSC depended strongly on the microstructure when it was tested under a constant load In this case, the quenching and tempering considerably increased the resistance of the steel to SSC The results of SSRT tests were similar regardless of the heat treatment used Non-metallic inclusions seemed to play an important role as crack initiation sites during the SSRT tests; this may be due to the hydrogen–deformation interaction The resistance to SSC varied as a function of the specimen's orientation during the SSRT tests This may be related to the geometric characteristics of the non-metallic inclusions
TL;DR: In this paper, the sliding wear behavior of two types medium carbon microalloyed steels containing various microstructures was investigated on a 320 mesh SiC paper at a sliding speed of 0.33m/s with a load of 6n and sliding duration of 4min under dry sliding conditions.
TL;DR: In this article, the effect of microstructure on HIC was discussed for steels having two different levels of nonmetallic inclusions, and it was shown that the minimum permissible inclusion level for HIC not to develop varied according to the steel micro-structure.
Abstract: Hydrogen-induced cracking (HIC) has been studied phenomenologically. The effect of microstructure on HIC is discussed for steels having two different levels of nonmetallic inclusions. Steels with different microstructures were produced by a thermomechanically controlled process (TMCP) from two different heats, which had different levels of nonmetallic inclusions. Ferrite/pearlite (F/P), ferrite/acicular ferrite (F/AF), and ferrite/bainite (F/B) were three representative microstructures of the tested steels. For the steels with higher inclusion levels, the minimum permissible inclusion level for HIC not to develop varied according to the steel microstructure. On the other hand, HIC occurred in the martensite/austenite (M/A) constituents regardless of steel microstructure above a certain concentration. It was shown that M/A constituents were easily embrittled by hydrogen atoms. Steels having a F/AF were resistant to HIC in the tested service condition; they exhibited a wide range of diffusible hydr...
TL;DR: In this article, a railway wheel made of Si-Mn-Mo-V low-carbon steel is described, which is composed of carbide-free bainite that consists of bainitic ferrite laths and retained austenite films along the lath boundaries.
TL;DR: In this paper, the main thrust of the paper was to determine the solid solution hardening effect of Al in ferritic structures with varying Al levels from 0˙02 to ∼2% at two C levels, 0´02 and 0´1% were tensile tested after hot rolling.
Abstract: Aluminium in solution in the ferrite in ferrite/pearlite steels has been found to have little influence on strength of the ferrite probably because up-till recently it has been added in very small amounts (0˙02–0˙08 wt-%Al) as a grain refining addition. There is indeed some doubt in the literature as to whether Al can solid solution harden. This lack of knowledge has not been important while Al additions are small but recently Al has been added in much greater amounts 0˙5–2% in some new grades of transformation induced plasticity (TRIP) steels. These steels have often an essentially ferritic structure with retained austenite and bainitic ferrite. The main thrust of the paper has therefore been to determine the solid solution hardening effect of Al in ferritic structures. Steels with varying Al levels from 0˙02 to ∼2% at two C levels, 0˙02 and 0˙1% were tensile tested after hot rolling so as to determine the solid solution hardening effect of Al. It was found in the 0˙1%C steel that some of the pea...
TL;DR: In this article, the microstructure evolution of a pearlitic steel (0.81 mass pct C) during hot compression of undercooled austenite and subsequent annealing was studied by means of field-emission scanning electron microscopy, electron backscattered diffraction (EBSD), and TEM.
Abstract: Microstructure evolution of a pearlitic steel (0.81 mass pct C) during hot compression of undercooled austenite and subsequent annealing was studied by means of field-emission scanning electron microscopy, electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). The experiments were performed at 923 K, between A
1 and Ar
1, at strain rates of 0.01 to 1 s−1. Compared with the isothermal transformation and the spheroidizing annealing, the transformation of undercooled austenite and the spheroidization of pearlite were accelerated by hot deformation, leading to the formation of the microduplex structures that consisted of ultrafine ferrite grains with average size smaller than 1 μm and spheroidized cementite particles with average size smaller than 0.3 μm during hot deformation and subsequent annealing.
TL;DR: In this article, a series of melts with carbon content 1.38-4.16% and that of vanadium 5.25-15.50% was made and X-ray diffraction of the examined alloys revealed the presence of three phases, i.e. ferrite, alloyed cementite, and VC x carbide.
Abstract: A series of melts with carbon content 1.38-4.16% and that of vanadium 5.25-15.50% was made. The X-ray diffraction of the examined alloys revealed the presence of three phases, i.e. ferrite, alloyed cementite, and VC x carbide. The relationships between the content of carbon and vanadium corresponding to eutectic structure (the eutectic line) as well as the degree of eutectic saturation S c were determined. Besides eutectics, the high-vanadium cast iron holds the following constituents in its matrix: alloyed ferrite, granular pearlite, and lamellar pearlite as well as a mixture of alloyed ferrite+granular pearlite, granular pearlite+ lamellar pearlite. The results show that passing from ferritic matrix through granular pearlitic and to lamellar pearlitic matrix, hardness HB, tensile strength R m , and yield strength H 0.2 , increases while plastic properties of alloys represented by elongation As decreases. The wear behaviour of alloys was tested in two different modes "specimen-abrasive paper" test (P1) and "specimen-counterspecimen" test (P2). The results obtained in test P1 are following: a) alloys with ferritic matrix and of the lowest hardness (182-189 HB) are characterised by the lowest abrasion wear resistance (s=3.14-3.93 mg/m), b) in alloys with a pearlitic matrix and hardness in the range of 387-416 HB the abrasion wear resistance is comparable to that of Hadfield cast steel (about s=2 mg/m) and c) cast iron with lamellar pearlite+granular pearlite matrix and hardness 322 to 401 HB gives the highest abrasion wear resistance of s=0.24-0.62 mg/m. In general, it can be stated that the abrasion wear in test P2 is higher than in test P1.
01 Jan 2008
TL;DR: In this paper, a low-C-Mn-Si-Mo-Nb alloy design is proposed for transmission pipeline applications, with an Nb content between 0.080 and 0.11%.
Abstract: Increasing world demand for energy has resulted in plans to expand the oil and gas transmission pipeline infrastructure in many countries utilizing higher strength steels of API grade X70 and X80. Traditional transmission pipeline steels, up to grade X70, relied on a ferrite/pearlite microstructural design generated through traditional TMCP rolling of a niobium microalloyed C-Mn steel design. Increasing strengths up to X70 and X80 for transmission pipelines has resulted in a shift toward a ferrite/acicular ferrite microstructure designs. Traditionally, to generate the ferrite/acicular ferrite microstructure design for X70 or X80, TMCP rolling is applied to a C-Mn-Si-Mo-Nb alloy system. The Nb content is typically less than 0.070% in this alloy system. With the rising cost of alloys over the past three years, steel and pipe producers have been working with different alloy designs to reduce total costs to produce the ferrite/acicular ferrite microstructure. In recent developments it has been determined that an optimized low-C-Mn-Si-Cr-Nb alloy design (usually referred as NbCr steel), utilizing an Nb content between 0.080 – 0.11% can produce the same ferrite/acicular ferrite microstructure with either no, or minimal, use of molybdenum. This approach has been successfully used in several transmission pipeline projects such as the Cantarell, Cheyenne Plains and Rockies Express. Recognizing the success of previous projects around the world, the large ∼ 4500 Km 2nd West-East Pipeline Project specification in China has been modified to allow for the use of this NbCr design for both plate and coil for conversion to long seam or spiral pipe. The NbCr design allows the steel producer to utilize niobium’s unique ability to retard recrystallization at higher than normal TMCP rolling temperatures, hence the term for the alloy design High Temperature Processing (HTP), producing the desired ferrite/acicular ferrite microstructure with excellent strength, toughness and weldability. This paper will discuss the technical background, rolling strategy, mechanical properties, welding, specific projects, and specification modifications with practical examples.Copyright © 2008 by ASME