Pct Cr Research Articles

A new equation for the Cr equivalent in 9 to 12 pct Cr steels

In advanced 9 to 12 pct Cr steels, the Cr equivalent is used as a measure to check the formation of δ-ferrite. In the present analysis, 29 alloys of varying composition were vacuum induction melted, and the amounts of δ-ferrite were measured in as-tempered conditions. Based on this and previous results on 9 to 12 pct Cr steels, a new equation for the Cr equivalent is proposed and correlated with the amount of δ-ferrite formation. Results indicate that the new Cr equivalent equation shows better correlation than previous equations and predicts the amount of δ-ferrite formed reasonably well.

High-temperature deformation behavior of the intermetallic Ti-47 At. Pct Al-3 At. Pct Cr alloy

A study of the high-temperature deformation behavior of a binary α 2+γTi-47 at. pct Al-3 at. pct Cr alloy was undertaken. The alloy was produced by induction melting and exhibited a structure of coarse columnar grains oriented in the radial direction. After a solution treatment at 1653 K for 3600 seconds and aging at 1223 K for 28,800 seconds, a nearly lamellar structure was formed. Deformation behavior was investigated by compression-strain-rate-change tests at strain rates ranging from 10−6 to 10−3 s−1 and temperatures ranging from 1073 to 1373 K. This alloy shows at low temperature/high stress a stress exponent of about 5. The deformation behavior is explained in this regimen by a dislocation climb mechanism, which includes a threshold stress. Finally, at the lowest stress levels and highest temperatures of testing, a stress exponent of about 3 is observed, which suggests that deformation is controlled by the viscous glide of dislocations.

Simultaneous Aluminizing and Chromizing of Steels to Form (Fe, Cr)3Al Coatings

A cementation pack involving halide activatorsand elemental Al and Cr powders has been used to achievethe codeposition and diffusion of aluminum and chromiuminto low-alloy steels. A two-step treatment at 925°C and 1150°C yields dense anduniform ferrite coatings of about 400-μm thickness,with surface compositions of approximatelyFe3Al plus several percent Cr. The two stepheating schedule prevents the formation of a blocking chromium carbide atthe substrate surface. An attempt was made to add atrace of Ce to the Al + Cr content of the coating byintroducing Ce oxide into the pack, but there is no evidence that this doping was achieved. Uponcyclic oxidation in air at 700°C, the coated steelexhibits a negligible 0.085 mg/cm2 weightgain for 1900 one-hour cycles. Virtually no attack wasobserved on coated steels tested in a simulated boileratmosphere at 500°C for 500 hr. But coatings with asurface composition of only 8 wt.% Al and 6 wt.% Crsuffered limited sulfidation attack in the simulated boiler atmosphere at temperatures higher than500°C for 1000 hr.

Anodic Oxidation of Al‐Cr Alloys and the Valence State of Chromium

The anodic oxidation of Al‐4 atom percent (a/o) Cr [7.4 weight percent (w/o) Cr] and Al‐10 a/o Cr (17.6 w/o Cr) sputter‐deposited alloy films was investigated by transmission electron microscopy and by x‐ray absorption studies. The oxidation behavior of both alloys is explained by initial formation of a chromium‐free anodic alumina film with accumulation of chromium in a thin underlying alloy layer. On sufficient enrichment of the alloy, chromium and aluminum are oxidized at the alloy/film interface in their approximate alloy proportions. The resultant ions migrate outward through the film more slowly than ions. Oxidation of chromium is followed by production of what is probably oxygen gas within the film, which is likely to generate a high pressure, leading to film rupture and gas release. Consequently, a complex, irregular film morphology, associated with voids, channels and cracks, develops. X‐ray absorption studies reveal that Cr(VI) species are detected in significant quantities only after the mechanical breakdown of the film. Such species probably form as a result of the high electrochemical potential of the alloy that is freshly exposed to the environment following film rupture.

Modeling of rolling texture development in a ferritic chromium steel

The development of crystallographic texture during rolling of a ferritic chromium steel containing 11 pct Cr was examined experimentally as well as by polycrystal modeling at large strains (up to 90 pct thickness reduction). The initial shape of the grains was very much elongated in the direction of rolling. A strong rolling direction (RD) fiber ( parallel to the rolling direction) has been observed at large strains in the experiment. The Taylor viscoplastic model, the relaxed-constraints pancake model, and the self-consistent viscoplastic approach were employed to simulate the texture development. Strain hardening was accounted for by microscopic hardening laws, for which the parameters were obtained from uniaxial tensile tests. It has been found that among the three models considered, the self-consistent viscoplastic model (the version tuned to finite-element results) yielded the best agreement with the experimentally observed texture evolution. Strong effects of grain shape and hardening have been found. The pancake model was also able to reproduce the main characteristics of the texture because of the flattened initial grain shape.

Phase transitions and microstructure of a laser-induced steel surface alloying

Alloying the surface of AISI 1045 steel with CrB by laser irradiation causes partial dissolution of the chromium boride in the melt and the formation of different borides of Fe and Cr in the treated layer. At a low laser scan velocity (0.01 m/s), the dissolution of CrB is almost complete, and the microstructure and properties of the top layer are uniform. At a higher scan velocity (0.05 m/s), a large number of CrB particles remain undissolved in the layer, and its properties are heterogeneous. The matrix consists of columns of iron boride, with up to 20 pct Cr dissolved in it, and between them a eutectic containing α-Fe and chromium-boride with dissolved Fe. Iron boride grows on a transitional layer of Cr2B coating the surface of residual CrB particles, which cannot serve as nucleation sites because of the incompatibility of their crystal structure with that of (Fe,Cr)2B.

Effect of cooling after welding on microstructure and mechanical properties of 12 Pct Cr steel weld metals

The microstructure of three 12 pct cr steel weld metals with different nickel and nitrogen contents was studied in as-welded condition and after postweld heat treatment with and without intercooling. Tensile strength and impact toughness of the weld metals were investigated in different postweld heat treatment conditions. In weld metals heat treated without intercooling, austenite decomposed by a eutectoid reaction that resulted in M23C6 aggregates around retained δ-ferrite. Two morphologies of M2N and MN precipitates were found in a low-dislocation α-ferrite. It was concluded that these phases were also transformed from austenite. In weld metals heat treated with intercooling, M23C6 precipitates were smaller and more homogeneously distributed. Different MN precipitates were found in the tempered martensite. The fracture mode of the weld metals at room temperature was mainly transgranular cleavage with some fibrous fracture. Intercooling treatment improved Charpy impact toughness of the 12 pct Cr steel weld metals substantially. It was found that the important microstructural factors affecting the impact toughness of the weld metals which were heat treated without intercooling were the sizes of the α-ferrite grains, nonmetallic inclusions, and M23C6 aggregates. For the weld metals heat treated with intercooling, the factors which affect the toughness of the weld metals were the sizes of martensite packets and nonmetallic inclusions.

The effects of composition and γ′/γ lattice parameter mismatch on the critical resolved shear stresses for octahedral and cube slip in NiAlCrX alloys

Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements, Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the γ′ phase, and about 3 at. pct of X in the γ′. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured at 760 °C, which is about the peak strength temperature. The CRSSOct and CRSScube are discussed in relation to those of Ni3 (Al, X) γ′ alloys taken from the literature and the γ′/γ lattice mismatch. The CRSSOct of the γ+γ′ alloys reflected a similar compositional dependence to that of both the CRSSOct of the γ′ phase and the γ′/γ lattice parameter mismatch. The CRSScube of the γ+γ′ alloys also reflected the compositional dependence of the γ′/γ mismatch, but bore no similarity to that of CRSScube for γ′ alloys since it is controlled by the γ matrix. The ratio of CRSScube/CRSSOct was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSScube/CRSSOct was related to the degree in which elements partition to the γ′ rather than the γ phase.

Hydrogen embrittlement of Ni-Cr-Fe alloys

The purpose of this work was to investigate the role of chromium on hydrogen embrittlement of Ni-Cr-Fe alloys and thus to develop a better understanding of the low-temperature stress corrosion cracking (SCC) phenomenon. The effect of chromium on hydrogen embrittlement was examined using tensile tests followed by material evaluation via scanning electron microscopy (SEM) and light optical microscopy. Four alloys were prepared with chromium contents ranging from 6 to 35 wt pct. In the uncharged condition, ductility, as measured by the percent elongation or reduction in area, increased as the alloy chromium content increased. Hydrogen appeared to have only minor effects on the mechanical properties of the low-chromium alloys. The addition of hydrogen had a marked effect on the ductility of the higher-chromium alloys. In the 26 pct chromium alloy, the elongation to failure was reduced from 53 to 14 pct, with a change in fracture mode from mixed ductile dimple and ductile intergranular failure to a brittle appearing intergranular failure. A maximum in embrittlement was observed in the 26 pct Cr alloy. The maximum in embrittlement coincided with the minimum in stacking-fault energy. It is proposed that the increased hydrogen embrittlement in the high-chromium alloys is due to increased slip planarity caused by the lower stacking-fault energy. Slip planarity did not appear to affect the fracture of the uncharged specimens.

High cycle fatigue of low alloy carbon steels

The presence of chromium and nickel elements no more than maximum 0.8 wt pct Cr, Ni in plain carbon steels has put them between two large groups of carbon steels and low-alloy steels. The purpose of this study is to determine the effect of chemical composition and microstructure on fatigue strength and fatigue crack growth rates in these steels. The effect of chemical composition on fatigue limit and on growth rate of fatigue cracks in plain carbon steels and and low-alloy steels is known [1–8]. We wish to study the main effects and the interactions of Cr and Ni factors on fatigue strength and fatigue crack propagation. Furthermore, we wish to examine the validity of Paris equation for describing fatigue crack growth rates in these steels and to determine how is related the value of the “m” exponent and fatigue strength to microstructure. There are different opinions for this problem. There are a lot of authors accepting the least effects of microstructure and mean stress at the midrange growth rate [9–18]. In their studies the values of the “m” exponent were found to lie between 2–4. Some other authors accept an influence of microstructure and mean stress (R ratio) on the midrange crack growth rate [8, 19, 20]. In order to obtain a more precise insight into effect of chemical composition and microstructure into fatigue strength and fatigue crack propagation, a study on this group of steels is presented in this paper.

Bainitic chromium-tungsten steels with 3 Pct chromium

Previous work on 3Cr-1.5MoV (nominally Fe-3Cr-2.5Mo-0.25V-0.1C), 2.25Cr-2W (Fe-2.25Cr-2W-0.1C), and 2.25Cr-2WV (Fe-2.25Cr-2W-0.25V-0.1C) steels indicated that the impact toughness of these steels depended on the microstructure of the bainite formed during continuous cooling from the austenitization temperature. Microstructures formed during continuous cooling can differ from classical upper and lower bainite formed during isothermal transformation. Two types of nonclassical microstructures were observed depending on the cooling rate: carbide-free acicular bainite at rapid cooling rates and granular bainite at slower cooling rates. The Charpy impact toughness of the acicular ferrite was considerably better than for the granular bainite. It was postulated that alloying to improve the hardenability of the steel would promote the formation of acicular bainite, just as increasing the cooling rate does. To test this, chromium and tungsten were added to the 2.25Cr-2W and 2.25Cr-2WV steel compositions to increase their hardenability. Charpy testing indicated that the new 3Cr-W and 3Cr-WV steels had improved impact toughness, as demonstrated by lower ductile-brittle transition temperatures and higher upper-shelf energies. This improvement occurred with less tempering than was necessary to achieve similar toughness for the 2.25Cr steels and for high-chromium (9 to 12 pct Cr) Cr-W and Cr-Mo steels.

Internal sulfide precipitation in low Cr-Fe alloys

The present article examines the internal sulfide precipitation in low Cr-Fe alloys that resulted from solid-state diffusion experiments at 600 °C. The internal sulfide precipitate microstructure is shown in alloys ranging from 11.3 wt pct Cr to 51.1 wt pct Cr. The diffusion composition profile and sulfide phase compositions have been measured using electron probe microanalysis (EPMA). Based on the microprobe data and some calculations using established internal sulfidation theory, a description of the internal sulfide precipitation sequence and depth is explained and the sulfide precipitate morphology is quantified. The solid-state diffusion experiments indicate that the optimum Cr composition range for sulfidation resistance at 600 °C is between 20 and 40 wt pct Cr. The results have also been compared with existing low-temperature gas-solid sulfidation literature and the differences in results are explained.

Microstructural basis for the effect of chromium on the strength and toughness of AF1410-based high performance steels

The variation in strength and Charpy impact toughness as a function of tempering temperature in the range of 200 ‡C to 650 ‡C was investigated in AF 1410 and AF 1410 + 1 pct Cr steels produced in a laboratory-scale, and a commercially produced AerMet 100 steel. The tensile test results showed that AF 1410 + 1 pct Cr had lower strength compared to AF 1410, while AerMet 100 had the highest strength of the three steels examined. Transmission electron microscopy (TEM) studies demonstrated that the strength variations among the steels can be attributed to differences in the matrix/carbide coherency strain and the volume fraction of the strengthening M2C carbides. The toughness values of the three steels were comparable when tempered up to 424 ‡C. Tempering at and above 454 ‡C resulted in a relative enhancement of toughness in AF 1410 + 1 pct Cr steel compared to AF 1410. This toughening was attributed to the destabilization of cementite at lath and prior austenite boundaries and the formation of reverted austenite.

Influence of chromium and impurities on the grain- refining behavior of aluminum

The grain-refining behavior of high purity aluminum (HPA1) and commercial purity aluminum (CPA1) containing Fe and Si as impurities (<0.2 wt pct each) has been studied with and without the presence of Cr in small and large quantities (0.2 and 2 wt pct). The Al-5Ti-lB master alloy ingot (0.2 wt pct) was used as a grain refiner. The emphasis was on the influence of individual elements and their interactions with the other elements on the grain-refining behavior of Al. Good grain refinement with insignificant fading in CPA1 was observed in comparison to HPA1. Similar results were obtained with a small concentration of Cr in HPA1 in HPA1-0.2 wt pct Cr alloy. The CPA1 and HPA1-0.2 wt pct Cr alloy have given the best grain-refining results among all the cases studied. A combination of small quantities of Fe, Si, and Cr (CPA1-0.2 wt pct Cr) has shown early and significant fading. A large concentration of Cr (2 wt pct) has shown a poisoning effect irrespective of the presence or absence of impurities such as Fe and Si in Al. Thus, Cr was found to be beneficial for grain refinement at smaller concentrations in the absence of impurities. But at higher concentrations of Cr, it had an adverse effect,i.e., led to coarser grain sizes both in the presence and absence of impurities.

Origin of Proterozoic metal-rich black shales from the Bohemian Massif, Czech Republic

Proterozoic metal-rich black shales (metasiltstones) in the Bohemian Massif are always closely associated with submarine mafic volcanic rocks and occur in (semi)isolated basins that formed most likely in connection with the evolution of an Upper Proterozoic intracontinental rift. The black shales are characterized by an average of 3.5 wt percent C organic , and 5.2 wt percent S and carry up to 0.42 wt percent Zn, 0.21 wt percent V, 0.12 wt percent Ni, 0.12 wt percent Cr, 0.12 wt percent Cu, 0.06 wt percent As, 0.03 wt percent Mo, 132 ppb Au, 102 ppb Pd, 25 ppb Pt, 1.7 ppb Rh, and 1.3 ppb Ru. Their thickness varies from about 1 to 45 m. Sulfide minerals often include abundant framboidal pyrite, which occurs widely in C organic -rich layers. Grainy pyrite, Zn, Ni, Cu, and Mo sulfides appear to be restricted to late quartz and carbonate veinlets. Mo selenide, Mo telluride, galena, berthierite, and gold are very rare. Sulfur isotope results suggest the dominant source of sulfur to have been seawater sulfate, reduced by bacteria under different conditions. The delta 13 C values of the organic matter (-24.2 to -37.5ppm) reflect the combination of the carbon isotope composition of dissolved HCO 3 , its high concentration, and the type of organisms. The results of Rock-Eval pyrolysis as well as laser Raman spectroscopy show a high maturity, close to that of well-crystallized graphite. Fluid inclusion and stable isotope data from quartz and carbonate veinlets of very low grade regionally metamorphosed metalrich black shales at Kamenec and highly metamorphosed facies at Hromnice indicate that they resulted from the interaction between 18 O-rich fluids, volcanics, and metasediments. The interaction could have occurred during subsea-floor or later regional metamorphism.

Experimental investigation of the transformation texture in hotrolled ferritic stainless steel using single orientation determination

Two ferritic stainless steels (≈16.5 mass pct Cr) were hot-rolled using seven subsequent passes. The first sample was rolled within the range 1280 °C to 750 °C,i.e., the deformation started in the ferritic region. The second sample was rolled within the range 1080 °C to 770 °C,i.e., the deformation started in the ferritic-austenitic region. In both cases, up to 40 vol pct of the ferrite transformed into austenite during hot rolling. During the last passes, the austenite transformed into cubic martensite. After hot rolling, these former austenitic regions were identified using a selective etching technique and examined using single orientation determination in the scanning electron microscope. The regions which remained ferritic throughout the hot-rolling process were investigated as well. Whereas the texture of the martensite considerably depended on the hot-rolling conditions, especially on the temperature and on the intervals between the rollings, the texture of the ferrite was less affected. The textures of the martensite were interpreted in terms of the crystallographic transformation rules between austenite and martensite. The textures of the ferrite were discussed in terms of recovery and recrystallization.

Atomic structure of interphase boundary enclosing bcc precipitate formed in fcc matrix in a Ni-Cr alloy

The atomic structure of the interphase boundaries enclosing body-centered cubic (bcc) lath-shape precipitates formed in the face-centered cubic (fcc) matrix of a Ni-45 mass pct Cr alloy was examined by means of conventional and high-resolution transmission electron microscopy (HRTEM). Growth ledges were observed on the broad faces of the laths. The growth ledge terrace (with the macroscopic habit plane\( \sim (112)_{fcc} //(23\bar 1)_{bcc} \)) contains a regular array of structural ledges whose terrace is formed by the (111)fcc//(110)bcc planes. A structural ledge has an effective Burgers vector corresponding to an\(a/12[1\bar 21]_{fcc} \) transformation dislocation in the fcc → bcc transformation. The side facet (and presumably the growth ledge riser) of the bcc lath contains two distinct types of lattice dislocation accommodating transformation strains. One type is glissile dislocations, which exist on every six layers of parallel close-packed planes. These perfectly accommodate the shear strain caused by the stacking sequence change from fcc to bcc. The second set is sessile misfit dislocations (∼10 nm apart) whose Burgers vector isa/3[111]fcc =a/2[110]bcc. These perfectly accommodate the dilatational strain along the direction normal to the parallel close-packed planes. These results demonstrate that the interphase boundaries enclosing the laths are all semicoherent. Nucleation and migration of growth ledges, which are controlled by diffusion of substitutional solute atoms, result in the virtual displacement of transformation dislocations accompanying the climb of sessile misfit dislocations and the glide of glissile dislocations simultaneously. Such a growth mode assures the retention of atomic site correspondence across the growing interface.

Gravity segregation of complex intermetallic compounds in liquid aluminum-silicon alloys

Primary crystals of intermetallics that are rich in iron, manganese, and chromium form at temperatures above the liquidus, and because their density is higher than that of liquid alumi-num, they cause gravity segregation in the melt. Segregation may occur either in the mold at slow cooling rates or in the bulk liquid in furnaces or ladles. The kinetics of settling of these intermetallic compounds in a melt of Al-12.5 pct Si having 1.2 pct Fe, 0.3 pct Mn, and 0.1 pct Cr has been studied. Sedimentation was investigated at 630 ‡C for settling times of 30, 90, and 180 minutes in an electric resistance furnace. The effect of settling time and height of melt on the volume percent, number, and size of intermetallic compounds was studied by image anal-ysis. The volume percent of intermetallics increases with distance from the melt surface. Both the number of particles and the average size increase during sedimentation. The rate of settling varies with position in the melt due to depletion of intermetallics near the surface and an increase near the bottom. The settling velocities obtained experimentally were compared with terminal velocities calculated by Stokes’ law. Good agreement was generally found. The settling speed of intermetallics reaches the terminal velocity at very short times and very close to the liquid surface. Stokes’ law is therefore applicable to virtually all locations within the melt.

Microstructure and crystallographic texture of strip-cast and hot-rolled austenitic stainless steel

The microstructure and texture of a strip-cast as well as a hot-rolled austenitic stainless steel (18 pct Cr, 8.5 pct Ni) are investigated by the use of optical metallography and quantitative X-ray texture analysis. In the hot band, a homogeneous microstructure is revealed together with a through-thickness texture gradient consisting of a weak cold rolling type of texture in the center layer and a shear texture close to the surface layers. The result is discussed in terms of the through-thickness shear profile that is generated during hot rolling. In the strip-cast material, a random orientation distribution as well as the development of martensite close to the center layer is attributed to the impingement and deformation of the films that are solidified on the surfaces of the casting rolls. The texture close to the surface is attributed to the growth selection of {001}〈uvw〉 oriented grains.

The Electrodeposition of Ni‐Fe‐Cr Alloys for Magnetic Thin Film Applications

A new bath for the electrodeposition of Ni‐Fe‐Cr magnetic thin films has been developed. The bath is similar to a typical Permalloy electrodeposition bath, being modified only by the addition of 0.020M chromic chloride and 0.10M acetic acid. Deposits with up to 8 weight percent Cr were produced; the chromium content of the deposit increased with increasing current density. Current efficiencies of up to 50% were attained when at least one‐half of the chromium in the bath was present as Cr2+. The acetic acid serves to limit the precipitation of nonmetallic material on the electrode by forming a soluble complex with Cr3+ and/or by buffering the pH at the electrode surface. The incorporation of chromium into the deposit is limited by the reduction rate of Cr2+ to Cr0.