Pct Cr Research Articles

The Benfontein kimberlite sills; magmatic reactions and high intrusion temperatures

The kimberlite sills at Benfontein, South Africa, were intruded as xenolith-poor, phenocryst-rich carbonated peridotite magmas. The dominant pre-intrusion phenocryst phases are olivine (Fo (sub 86-92) ), Mg-ilmenite ss (13.0-18.0 wt percent MgO, 0.5-3.0 wt percent Cr 2 O 3 ), Mg-Al-chromite, and REE-perovskite. Post-intrusion magmatic reaction mantling has encapsulated all pre-existing groundmass oxides in Mg-Al-titanomagnetite. The Benfontein sills appear to have been emplaced at much higher temperatures than are probably typical for most other kimberlites. In a high heat flow environment, comparable to that recorded by the Lesotho geotherm, under open system vapor composition conditions, an adiabatic diapiric upwelling of peridotitic magma may be capable of producing the high temperatures that apparently prevailed during the intrusion. The temperature of reaction for coupled Fe-based and C-based fO 2 buffers in the upper mantle (for example, EMOG-MH (hematite mol percent isopleths)) increases with decreasing pressure and at near-surface pressures approximates the temperature of intrusion for the phase compositions observed at Benfontein.--Modified journal abstract.

Magnetic hardening of PrCo<inf>5</inf>by oxide additives

Powder oxides, as sintering additives, have been found to increase the coercivity of PrCo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> containing Sm-Co sintering aid. These additives inhibit grain growth of the 2-7 phase and produce lanthanide oxides during the sintering. Pr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</inf> Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> magnets containing 0.4-1 weight percent Cr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> display magnetic properties similar to SmCo <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> Possible hardening mechanisms consistent with the observed effects are discussed.

Microstructure-strength relations in a hardenable stainless steel with 16 pct Cr, 1.5 pct Mo, and 5 pct Ni

Metallographic studies have been conducted on a 0.024 pct C-16 pct Cr-1.5 pct Mo-5 pct Ni stainless steel to study the phase reactions associated with heat treatments and investigate the strengthening mechanisms of the steel. In the normalized condition, air cooled from 1010 °C, the microstructure consists of 20 pct ferrite and 80 pct martensite. Tempering in a temperature range between 500 and 600 °C results in a gradual transformation of martensite to a fine mixture of ferrite and austenite. At higher tempering temperatures, between 600 and 800 °C, progressively larger quantities of austenite form and are converted during cooling to proportionally increasing amounts of fresh martensite. The amount of retained austenite in the microstructure is reduced to zero at 800 °C, and the microstructure contains 65 pct re-formed martensite and 35 pct total ferrite. Chromium rich M23C6 carbides precipitate in the single tempered microstructures. The principal strengthening is produced by the presence of martensite in the microstructure. Additional strengthening is provided by a second tempering treatment at 400 °C due to the precipitation of ultrafine (Cr, Mo) (C,N) particles in the ferrite.

Mechanical properties and precipitation-hardening response in ASTM A710 Grade A and A736 alloy steel plates

Addition of 1.0/1.3 pct copper has been used for precipitation hardening in a lowalloy steel containing less than 0.07 pct C, 0.40/0.70 pct Mn, 0.6010.90 pct Cr, 0.70/1.0 pct Ni, 0.15/0.25 pct Mo, and at least 0.02 pct Nb. This steel is included in ASTM Specifications as A710 Grade A for structural plates and as A736 for pressure vessel plates. A variety of strength and toughness combinations are provided by the selection of Class 1, Class 2, and Class 3 heat treatments.

Microalloying and precipitation in Cr-V rail steels

A study of alloying effects in Cr-V rail steels has been carried out to determine the microstructural strengthening mechanisms. The laboratory steels investigated were based on the commercial 1 pct Cr rail steel chemistry (0.75C−0.8Mn−1 .25Cr−0.30Si) and represented two levels of nitrogen (nominally 0.007 and 0.015 wt pct) and two types of deoxidation practice. It is found that vanadium microalloying produces a yield stress increment of approximately 90 MPa for low-nitrogen steels and 140 M Pa for highnitrogen steels. This strengthening effect appears to saturate at or below 0.15 wt pct vanadium, with no further strength increase for higher vanadium concentration. The hardness and UTS exhibit the same variation with vanadium content as the yield stress. There is no consistent effect of aluminum content (deoxidation practice). Several distinct precipitate morphologies, a wide range of precipitate sizes, and a nonhomogeneous distribution of precipitates are observed. There is also significant partitioning of V, Cr, and Mn to cementite. It is suggested that an increase in the amount of coarse, austenitenucleated V(C,N) and possibly other coarse precipitate modes is responsible for the saturation of the vanadium strengthening effect.

Heat treatment, aging effects, and microstructure of 12 Pct Cr steels

The 12 pct Cr steels are attractive materials for advanted steam generators. In support of the DEBENE project for the development of a sodiumcooled fast reactor, a materials program is in progress to show the applicability of these steels. The program comprises mechanical, corrosion, and weldability tests. Additionally, extensive microstructural investigations are carried out, including optical microscopic examinations, scanning electronmicroscopy, and transmission electronmicroscopy on thin foils and extraction replicas are used. In this paper, some of the results, mainly obtained from a number of heats of 12CrlMoV steel (DIN X20CrMoV121) have been described. Information has been given concerning general features of the microstructure, in relation to the chemical composition and the heat treatment; microstructural changes due to thermal aging; and influence of melting method, product form, and size of the steel on structure and properties.

Experimental Investigation on Denting in PWR Steam Generators: Causes and Corrective Actions

Denting studies have been undertaken in order to assess the influence of the most important parameters which could initiate corrosion of the carbon steel occurring in the tube-tube support plate crevices of some PWR steam generators. Tests have been carried out in model boilers where feedwater was polluted with sea or river water. Specific effects of chloride or sulfate and influence of oxygen content, magnetite addition and pH value were investigated. In magnetite prepacked crevices, denting is obtained within 1000 hrs for seawater pollution of 0.3 ppm chloride at the blowdown. In neutral chloride or in river water, denting is observed only with oxygen addition. Denting prevention is effective in the case of an on-line addition of phosphate, boric acid, or calcium hydroxide. For denting stopping, boric acid or calcium hydroxide is efficient even with a high seawater pollution. Soaks cannot stop denting if they are not followed by an on-line treatment (boric acid, calcium hydroxide). With quadrifoil holes, denting doesn’t occur. In very severe test conditions, 13 percent Cr steel can be corroded, but the corrosion rate is low and oxide morphology is different from that growing on carbon steel.

Effects of metallurgical factors on service performance of duplex stainless steel for deep sour gas wells

This paper deals with the effects of alloying elements on hot workability, mechanical properties, pitting corrosion, and stress corrosion cracking of duplex stainless steel. Test materials are laboratory-melted 20 to 30 pct Cr duplex stainless steels, containing different amounts of Ni, Mo, N, and other elements. Corrosion resistance, tensile properties, and hot workability depend on the ferrite content in the microstructure. Cr, Mo, and N are beneficial in improving the resistance to pitting and general corrosion. Susceptibility to stress corrosion cracking in sour gas environments depends on the microstructure. Based on these test results, duplex stainless steel tube containing 22 pct Cr-5.5 pct Ni-3 pct Mo-0.15 pct N for deep corrosive well service has been developed on a mill production basis. This tube has a ferrite content of about 50 pct and can be produced in three grades of yield strength, 9.4, 16, and 20 MPa (65, 110, and 140 ksi).

Phase equilibria and kinetics in the solid state reaction between silicon and NiCrAI

The result of the solid state reaction of silicon with a model superalloy consisting of 70 at. pct Ni, 20 at. pct Cr, and 10 at. pct Al at 900 °C is examined using light microscopy, electron microprobe analysis, and analytical electron microscopy. Extensive reaction is observed, with the formation of seven distinct reaction zones. The crystallography and chemistry of the phases present in each zone are determined using the analytical electron microscope. The reaction paths are described with reference to binary and ternary phase equilibrium diagrams. The kinetics of the reaction are presented. The nature and extent of the reaction are compared with previous experiments in which silicon carbide and reaction-bonded Si-SiC were reacted with the model superalloy.

Corrosion behavior of 25 Pct Cr duplex stainless steel in CO2-H2S-Cl− environments

The corrosion behavior of duplex stainless steels in sour gas well environments was studied by examining the effects of environmental factors and alloying elements on their susceptibility to stress corrosion cracking and weighted-loss corrosion in CO/sub 2/-H/sub 2/S-Cl/sup -/ atmospheres. The results indicated that DP3 duplex stainless steel has an excellent work-hardening property compared with austenitic Type 317L stainless steel. Moreover, DP3 is resistant to SCC in CO/sub 2/-Cl/sup -/ environments up to temperatures of 480/sup 0/F. The presence of H/sub 2/S and cold working, however, make it more sensitive to cracking. Incorporating Cr, Ni, and Mo into duplex stainless steels increases the corrosion resistance in these environments. Duplex stainless steels that are composed of 3% Mo and 6% Ni maintain the corrosion resistance in high-temperature CO/sub 2/-Cl/sup -/ conditions, even after low-temperature aging treatment.

The effect of point defects on the dissolution of zinc oxide in sodium hydroxide solutions

The dissolution behavior of sintered zinc oxide in aqueous solutions of NaOH has been studied as a function of varying concentrations of lithia, alumina, and chromia as solid state dopants. Both the pure and doped zinc oxide samples were found to obey the shrinking particle model of dissolution, and there was a lack of dependence of the dissolution rate on agitation speed. An activation energy of 48.1 kJ/mol (11.5 kcal/mol) was obtained for the undoped ZnO material. It is proposed that the desorption of surface hydroxyl complexes constitutes the rate controlling step. Additions of up to 1.0 mol percent Cr 2,O 3 and Al 2O 3 decreased the dissolution rate. An opposite effect was observed for the addition of Li 2O. Dopant-induced changes in zinc oxide surface chemistry have been used to interpret the observed difference in the effects of the higher-valent and lower-valent dopants. Zinc oxide is an n-type semiconductor with an equivalent amount of zinc interstitials and quasi-free electrons. Doping with alumina and chromia results in an increase in negatively charged point defects (quasi-free electrons), reducing adsorption of OH − species on the zinc oxide surface and thereby decreasing dissolution. Doping with lithia increases the concentration of positively charged point defects (zinc interstitials), thus facilitating surface hydroxylation and dissolution.

High temperature embrittlement of NI and Ni-Cr alloys by trace elements

The effects of Sb, Sn, and Zr additions on the creep properties of Ni and Ni + 20 pct Cr are reported. Antimony and tin additions (~1 wt pct) induce extensive grain boundary cavitation in nickel, while smaller antimony additions had little effect on Ni + 20 pct Cr. Addition of 0.11 pct Zr to Ni + 20 pct Cr greatly inhibited grain boundary cavitation and reduced its Coble creep rate. Auger electron spectroscopy of cavitated specimens provided direct evidence of impurity segregation to cavity surfaces. Residual sulfur segregated most strongly, and was observed on cavity surfaces in all cavitated specimens. Tin segregated somewhat less intensely than sulfur, and antimony segregated only slightly. Segregation of antimony and sulfur to uncavitated portions of Ni + 1 pct Sb grain boundaries was also observed. These results are discussed in terms of segregation effects on energetic and transport properties of the grain boundaries and cavity surfaces.

Effect of solidification conditions on the solidification mode in austenitic stainless steels

The effect of the solidification conditions on the solidification mode in the composition range in which the primary austenitic and ferritic modes compete is studied by varying the welding parameters in gas tungsten arc (GTA) welding and by comparing the results with those obtained from other laboratory experiments. A good agreement holds if the effect of the composition is described by the ratio Creq/Nieq (Creq = pct Cr + 1.37 × pct Mo + 1.5 × pct Si + 2 × pct Nb + 3 × pct Ti and Nieq = pct Ni + 0.31 × pct Mn + 22 × pct C + 14.2 × pct N + pct Cu) and the effect of the solidification conditions by the growth rate. The critical value of the ratio Creq/Nieq corresponding to the transition from primary austenitic to ferritic solidification increases from 1.43 to 1.55 with increasing growth rate. The upper limit is valid in GTA welding at high welding speeds, while the lower limit corresponds to the practical conditions which exist in ingot and shaped casting. The validity and applicability of this solidification model are discussed.

Solid state SiC/Ni alloy reaction

The solid state reaction between silicon carbide and a model superalloy consisting of 70 at. pct Ni, 20 at. pct Cr, and 10 at. pct Al was studied between 700 °C and 1150 °C for times ranging from “0” hours to 330 hours. Reaction couples consisting of SiC/Ni, SiC/Cr, and SiC/NiCr were also studied. The reactions were carried out in air with the materials, in the shape of discs, maintained in contact under a pressure of 7 MPa. A reaction was detected with SiC and the model alloy at all temperatures studied, and the reaction was diffusion controlled with an activation energy of 184 kJ/mole. In the ceramic the reaction was dominated by the diffusion of Ni into the ceramic forming a banded structure consisting of alternating layers of δ-Ni2Si and a two phase mixture of graphite and δ. On the metal side, the reaction was very dependent on the presence of alloying elements, with pure Ni reacting to the greatest extent, followed by the binary NiCr alloy, and finally by NiCrAl. The growth and presence of the phases detected in these reactions is consistent with phase equilibria concepts.

The Effect of Metal Composition on the Adsorption of Zinc Di-Isopropyldithiophosphate

Rates of adsorption of zinc di-isopropyldithiophosphate from n-hexadecane on to iron and steel (13 percent Cr) disks have been measured using 65Zn and 14C radiolabelling. Concentration, stirring, and temperature dependence have been examined. A selective rinsing technique has been used to investigate chemisorption which occurs extensively on iron but not at all on the steel. On iron, adsorption occurs with some release of zinc at all temperatures investigated. On the steel, no zinc is lost from the adsorbed layer. Absence of stirring effects indicates that rates are surface rather than diffusion controlled. Results have been compared with those of previous workers.

Microstructural investigation of the oxidation of an Fe-3 pct Cr alloy

The microstructure and microchemistry of the oxide scale on an Fe-3 wt pct Cr alloy have been investigated after oxidation in the temperature range 700 to 800 °C. Transmission and scanning electron microscopy along with energy dispersive X-ray analysis and Auger electron spectroscopy techniques were used for the investigation. Multilayered scales are observed which vary in composition and structure; the innermost oxide is an Fe-Cr spinel of the type Fe(Fe2•xCrx)O4. The intermediate layer and the outer oxide layer are both α-Fe2O3 hematite. The outer hematite layer is nonadherent and wrinkling is observed. Spallation occurs readily at the inner hematiteJspinel interface and at the spinel oxideJalloy interface. The poor oxidation resistance of the alloy is discussed in terms of these observations.

An examination of chromium substitution in stainless steels

A series of lower Cr stainless steels containing various levels of Mo, Si, Cu, V, N, and Ni were examined. In less severe environments it was possible to achieve corrosion resistance comparable to 18-8 type stainless steels in alloys containing about 9 pct Cr, along with additions of Ni, Mo, Cu, and V. The hot working behavior, weldability, and mechanical properties appear comparable to conventional grades of stainless. Alloys of this type could be used in decorative, aqueous, and some industrial applications, but should not be adequate for more severe environments.

Superplasticity in Rapidly Solidified White Cast Irons

Superplastic properties of three different composition white cast irons were investigated in the temperature range of 630 to 725 °C. Fine structures consisting of 1 to 2 μm ferrite grains were developed in these materials by consolidation of rapidly solidified powders at intermediate temperatures below the A1 critical temperature. Tensile elongations of 1410 pct were found for a 3.0 pct C + 1.5 pct Cr white cast iron, 940 pct for a 3.0 pct C white cast iron, and 480 pct for a 2.4 pct C white cast iron when tested at 700 °C and at a strain rate of 1 pct per minute. The superplastic white cast irons exhibited a high strain rate sensitivity exponent,m, of 0.5 and activation energies for plastic flow were found to be nearly equal to the activation energy for grain boundary self-diffusion in iron. These observations are in agreement with the creep behavior of superplastic materials controlled by grain boundary diffusion.

Fracture toughness of aisi M2 high-speed steel and corresponding matrix tool steel

The influence of microstructural variations on the fracture toughness of two tool steels with compositions 6 pct W-5 pct Mo-4 pct Cr-2 pct V-0.8 pct C (AISI M2 high-speed steel) and 2 pct W-2.75 pct Mo-4.5 pct Cr-1 pct V-0.5 pct C (VASCO-MA) was investigated. In the as-hardened condition, the M2 steel has a higher fracture toughness than the MA steel, although the latter steel is softer. In the tempered condition, MA is softer and has a higher fracture toughness than M2. When the hardening temperature is below 1095 °C (2000 °F), tempering of both steels causes embrittlement,i.e., a reduction of fracture toughness as well as hardness. The fracture toughness of both steels was enhanced by increasing the grain size. The steel samples with intercept grain size of 5 (average grain diameter of 30 microns) or coarser exhibit 2 to 3 MPa√m (2 to 3 ksi√in.) higher fracture toughness than samples with intercept grain size of 10 (average grain diameter of 15 microns) or finer. Tempering temperature has no effect on the fracture toughness of M2 and MA steels as long as the final tempered hardness of the steels is constant. Retained austenite has no influence on the fracture toughness of as-hardened MA steel, but a high content of retained austenite appears to raise the fracture toughness of as-hardened M2 steel. There is a temperature of austenitization for each tool steel at which the retained austenite content in the as-quenched samples is a maximum. The above described results were explained through changes in the microstructure and the fracture modes.

The stress corrosion susceptibility of a quenched and tempered 12 pct crmov martensitic stainless steel

The stress corrosion susceptibility of a martensitic 12 pct Cr 1 pct MoV stainless steel in alkaline chloride solution has been measured as a function of tempering heat treatment. The microstructures produced during tempering have been characterized by transmission electron microscopy and related to measured hardness values. In addition, scanning transmission electron microscopy combined with energy dispersive X-ray microanalysis has allowed the distribution of alloying elements within the microstructure to be examined. Electron energy loss spectroscopy was used to establish fully precipitate compositions, and the microanalysis results have been explained in terms of a diffusion controlled growth of grain boundary precipitates. The overall stress corrosion cracking susceptibility has been correlated with the development of chromium solute depletion profiles about prior austenite grain boundaries.