Showing papers on "Tempering published in 1989"

Fracture and fatigue crack propagation properties of hardened 52100 steel

Abstract: Good toughness in hardened 52100 ball bearing steel is important in order to prevent premature fracture during mounting or service of bearing elements. Steel cleanliness, residual copper content, and carbon content effects have been investigated in relation to fracture mechanics properties, and it was observed that only the carbon content has any relevance for the range of compositions investigated. The effect of hardening and tempering temperatures for conventional furnace-hardening techniques on toughness was investigated, theKlcbeing generally much less sensitive to these parameters than blunt notch toughness testing. Cold deformation of the material prior to martensitic hardening significantly increased the blunt notch toughness. Thermal grain refining treatments did not give the same improved blunt notch toughness as observed for prior cold deformation. Short austenitization cycles (ten seconds) for martensitic hardening resulted in microstructures with high retained austenite contents. This microstructure resulted in higher fracture toughness and retardation of the crack growth rates, the mechanism being associated with transformation toughening in the plastic zone. Inductive tempering of martensitic-hardened 52100 was observed to result in similar blunt notch toughnesses as compared to furnace tempered material of the same hardness. A poor correlation between fracture toughness and blunt notch toughness was observed, particularly for the unstable structures,i.e., microstructures with high levels of retained austenite. Fracture toughness does not represent the intrinsic toughness of high carbon martensite with related high contents of retained austenite.

Fatigue strength characteristics of high strength steel.

Abstract: In order to clarify the fatigue strength charactaristics of low alloy steels which were strengthed by tempering at low temperature (150∼200°C) after conventional quenching treatment and/or carburizing in generated gas, rotating bending fatigue tests were conducted in laboratory air and dry air using smoothened specimens with 8 mm diameter. The influence of moisture in air was only recognized for the carburized steel. The S-N diagrams of both steels revealed two knees on those curves regardless of the test enviroments and no fatigue limits were observed in the long life range up to 109 cycles (10 months). The reasons were discovered from the results of fractography and the equation proposed by Murakami et al. for the prediction of fatigue limit of steel with micro defects.

Influence of Tempering and Contraction Mismatch on Crack Development in Ceramic Surfaces

Abstract: Tempering of glass produces a state of compressive stress in surface regions which can enhance the resistance to crack initiation and growth. The objective of this study was to determine the influence of tempering on the sizes of surface cracks induced within the tempered surfaces of opaque porcelain-body porcelain discs, with contraction coefficient differences (αO- αB) of +3.2, +0.7, 0.0, -0.9, and -1.5 ppm/°C. We fired the discs to the maturing temperature (982°C) of body porcelain and then subjected them to three cooling procedures: slow cooling in a furnace (SC), fast cooling in air (FC), and tempering (T) by blasting the body porcelain surface with compressed air for 90 s. We used body porcelain discs as the thermally compatible (Δα = 0) control specimens. We measured the diameters of cracks induced by a microhardness indenter at an applied load of 4.9 N at 80 points along diametral lines within the surface of body porcelain.The mean values of the crack diameters varied from 75.9 μm (Δα = -1.5 ppm/°...

Heat treatment behavior and tensile properties of Cr-W steels

Abstract: Ferritic steels containing Cr, W, and V are being developed for fusion reactor applications. These steels would be alternatives to the Cr−Mo steels that are being considered for structural components. Eight experimental steels were produced. Chromium concentrations of 2.25, 5, 9, and 12 pct were used. Steels with these chromium compositions and with 2 pct W and 0.25 pct V were produced. To determine the effect of tungsten and vanadium, 2.25Cr steels were also produced with 2 pct W and no vanadium, and with 0.25 pct V and zero and 1 pct W. A 9Cr steel containing 2 pct W, 0.25 pct V, and 0.07 pct Ta was also studied. For all alloys, carbon was maintained at 0.1 pct. Tempering behavior of the steels was similar to that of the Cr−Mo steels being considered. Tensile studies indicated that the 2.25Cr−2W−0.25V and 9Cr−2W−0.25V−0.07Ta steels had the highest strengths with properties similar to those of the 9Cr−1MoVNb and 12Cr−1MoVW steels, which are the strongest of the Cr−Mo steels of interest.

Theoretical analysis of changes in cementite composition during tempering of bainite

Abstract: An attempt has been made to model the kinetics of changes of composition in cementite during the aging of creep resistant low alloy steels of the type used in power plant. In the model a finite difference method is used for calculating the rate at which alloying elements redistribute between ferrite and cementite, subject to the thermodynamic constraints which determine the equilibrium compositions of these phases. It has also been possible to derive approximate analytical solutions which give good physical insight into the factors controlling the approach to equilibrium. Particle size has been found to have a strong influence on the rate at which the cementite composition is changed. A theoretical basis for the time dependence of cementite composition is also provided. The method is easily adapted to multiple or anisothermal heat treatments. Further work is suggested to account for simultaneous coarsening and changes in composition and also to allow for the formation of alloy carbides at long ag...

Effects of Mn, Si, and purity on the design of 3.5NiCrMoV, 1CrMoV, and 2.25Cr-1Mo bainitic alloy steels

Abstract: Three high-temperature bainitic alloy steels were evaluated in the laboratory to determine the effects of Mn, Si, and impurities (i.e., S, P, Sn, As, and Sb) on microstructure and mechanical properties. The alloy steels were 3.5NiCrMoV and CrMoV, which are used for turbine rotors, and 2.25Cr-1Mo, which is used in pressure vessel applications. The important effects of Mn, Si, and impurities, which should control the design of these high-temperature bainitic steels, are presented. Key results are used to illustrate the influence of these variables on cleanliness, overheating, austenitizing, hardenability, tempering, ductility, toughness, temper embrittlement, creep rupture, and low-cycle fatigue. Low levels of Mn, Si, and impurities not only result in improved temper embrittlement resistance in these steels but also lead to an improvement in creep rupture properties (i.e., improved strength and ductility). These results have produced some general guidelines for the design of high-temperature bainitic steels. Examples illustrating the implementation of the results and the effectiveness of the design guidelines are provided. Largely based on the benefits shown by this work, a high-purity 3.5NiCrMoV steel, which is essentially free of Mn, Si, and impurities, has been developed and is already being used commercially.

Tempering Stresses in Feldspathic Porcelain

Abstract: The objective of this study was to develop an analytical model to calculate transient and residual (tempering) stresses in dental porcelain plates subjected to cooling rates used by commercial laboratories. The model incorporates linear viscoelasticity and structural relaxation effects.The viscosities of three experimental body porcelains and three experimental opaque porcelains as a function of temperature were calculated from creep rates measured in a bending beam viscometer. Measurements were made under thermal equilibrium conditions for temperatures ranging from 550°C to 625°C. Thermal expansion data measured in a differential dilatometer at slow heating rates were supplied by the manufacturer. Temperature distribution in the plates as a function of convective heat transfer coefficient, initial plate temperature, and plate thickness was calculated by use of standard numerical techniques.Calculations of transient and residual stress were performed for one body porcelain, for two plate thicknesses, and ...

Correlation of microstructure and tempered martensite embrittlement in two 4340 steels

Abstract: This study is concerned with a correlation between the microstructure and fracture behavior of two AISI 4340 steels which were vacuum induction melted and then deoxidized with aluminum and titanium additions. This allowed a comparison between microstructures that underwent large increases in grain size and those that did not. When the steels were tempered at 350°C,K Ic and Charpy impact energy plots showed troughs which indicated tempered martensite embrittlement (TME). The TME results of plane strain fracture toughness are interpreted using a simple ductile fracture initiation model based on large strain deformation fields ahead of cracks, suggesting thatK Icscales roughly with the square root of the spacing of cementite particles precipitated during the tempering treatment. The trough in Charpy impact energy is found to coincide well with the amount of intergranular fracture and the effect of segregation of phosphorus on the austenite grain boundaries. In addition, cementite particles are of primary importance in initiating the intergranular cracks and, consequently, reducing the Charpy energy. These findings suggest that TME in the two 4340 steels studied can be explained quantitatively using different fracture models.

Method of forming hard steels by case hardening, shot-peening and aging without tempering

Abstract: A method of manufacturing a steel member comprising the steps of: carburizing and quenching or carbo-nitriding and quenching a steel material; shot-peening the steel material quenched in the first step without tempering; and aging the steel material shot-peened in the second step. Preferably the steel material comprises 0.1 to 0.4 wt. % C, 0.06 to 0.15 wt. % Si, 0.3 to 1.0 wt. % Mn, 0.9 to 1.2 wt. % Cr, 0.3 to 0.5 wt. % Mo, and the remainder Fe. The steel member is preferably used in transmission gears for automobiles, which require superior strength.

Role of carbides in tempered martensite embrittlement

Abstract: Tempered martensite embrittlement has been studied in a commercial purity AISI 4340 steel and the results are given in the present paper. In particular the role of carbides in the embrittlement process is examined. It is shown by the results that the standard tempered martensite embrittlement is observed in this steel. The fracture energy after 1 h tempering treatments decreases with increasing tempering temperature between 200 and 350°C. However, a significant amount of intergranular fracture was found only on the surface of the specimen that was tempered at 350°C. Initially, M3C carbides are precipitated after tempering at 250°C. As the tempering temperature increases, both the number density and thickness of the carbides increase. Also, the length of the grain boundary carbides increases significantly with increasing tempering temperature. The carbides are all ribbon-shaped and are essentially pure Fe3C. It is shown using Auger electron spectroscopy that the grain boundaries were enriched in ph...

Development of Sintered Low Alloy Steels

Abstract: Three routes for increasing the strengths of sintered steels are identified First, strength can be increased by increasing the density of the material, either during the compaction process or during sintering: several possible approaches are suggested Second, strength can be increased through alloying the metallic matrix: the reasons for the selection of alloying elements, and the methods of alloying are considered Third, the alloyed metallic matrix can be strengthened either by quench hardening and tempering, or by precipitation hardening heat treatments, but the response to heat treatment depends on the homogeneity of the matrix The extremely heterogeneous compositions and structures of steels made from elemental or master alloy mixes, partially prealloyed powders, or coated powders present a unique opportunity to engineer structures that have desired combinations of properties PM/0492

The microstructure of submerged arc-weld deposits for high-strength steels

Abstract: Recent theoretical work on the design of unusually high-strength steel weld deposits is compared with microstructural studies of an experimental, multipass submerged arc weld deposit. The as-deposited microstructure is found to consist of a mixture of acicular ferrite, bainite and low-carbon martensite. Owing to its low carbon concentration, the structure is highly resistant to tempering, and because the alloy becomes austenitic at a relatively low temperature, the effect of reheating due to the deposition of several layers is found to be minimal. The overall microstructure of the multirun weld thus turns out to be fairly homogeneous, differing little from the as-deposited microstructure.

Coherent precipitation of M2C carbides in AF1410 steel

Abstract: The effect of elastic coherency on the composition and stoichiometry of M 2 C carbide precipitates ( M ≡ Cr , Mo , Fe ) in AF1410 steel is analyzed utilizing thermodynamic conditions for mechanical, chemical and interfacial equilibrium between the ferrite (tempered martensite) and the M 2 C phase. An equilibrium calculation at the standard tempering temperature of 783 K predicts a substantial deviation from stoichiometry and a measurable solubility of iron in the M 2 C phase, both of which have been verified experimentally. It is shown that the carbide composition trajectory during precipitation is such to approach the incoherent composition, following a direction of increasing carbon, decreasing iron and increasing chromium.

Development of mechanical properties of structural high-carbon low-alloy steels through modified heat treatment

Abstract: The modified heat treatment, which produces a mixed structure of martensite and lower bainite through short-term isothermal transformation at just above the martensitic transformation temperature,Mstemperature, followed by oil quenching (after conventional austenitization), has been applied to three high-carbon low-alloy steels with different levels of nickel and chromium contents at similar molybdenum levels, in which carbon was allowed to replace relatively expensive additions of nickel and chromium, for their ultra-high strength application. The significant conclusions are as follows: an ultra-high strength steel of 1900 M Pa yieldstress grade with a high toughness level can be obtained when about 60 vol % lower bainite is associated with 473 K tempered martensite of 0.60% C-1.80% Ni-0.80% Cr-0.25% Mo steel. If approximately 25 vol % lower bainite appears in 673 K tempered martensite of the steel, a 1700 M Pa yield-stress grade steel with high toughness and moderate ductility levels can be attained. However, alloying nickel is essential to some extent for development of the mechanical properties with the modified heat treatment suggested in the present work.

Martensitic stainless steel having excellent corrosion resistance and its manufacture

Abstract: PURPOSE: To obtain the martensitic stainless steel having excellent corrosion resistance in a wet carbon dioxide environment and having high resistance to cracking caused by wet hydrogen sulfide by forming it from the compsn. contg. each prescribed amt. of C, Si, Mn, Cr, Ni, Al and N. CONSTITUTION: The above martensitic stainless steel is formed from the compsn., in which C is reduced, by weight, to 15 to 18% Cr, 1 to 5% Ni, 0.005 to 0.2% Al, 0.03 to 0.15% N and the balance Fe with impurities. For obtaining the stainless steel, the steel having the above componental compsn. is austenitized at 900 to 1100°C, is thereafter cooled to satisfactorily form martensite and is then subjected to tempering treatment at 560°C to the Ac 1 temp. or below. Next, the steel after subjected to the tempering treatment is cooled at a cooling rate more than that in air cooling, by which the objective martensitic stainless steel having excellent corrosion resistance can be obtd. COPYRIGHT: (C)1991,JPO&Japio

Influence of Microstructure on SSC Susceptibility of Low-Alloy, High-Strength Oil Country Tubular Goods

Abstract: The influences of microstructural factors, such as a distribution of precipitates and internal strain after tempering, on sulfide stress cracking (SSC) susceptibilities are investigated. It is revealed that (1) a homogeneous dispersion of spheroidized fine carbides and (2) a reduction of locally concentrated internal strains during recovery and recrystallization are preferable for improving the SSC resistance of low-alloy steel. Microstructure refinement is effective in increasing Luders elongations and permits larger amounts of plastic deformation to initiate SSC. Regarding the maximum hardness or strength limitation for sour service, existence of the critical strain for SSC is discussed. Using the microstructure control technique, C-100 grade oil country tubular goods (OCTG) is developed. SSC susceptibilities of trial products are examined using various kinds of SSC evaluation methods. Characteristics and comparisons of test methods are also discussed.

Manufacture of high-strength oil well tube excellent in corrosion resistance

Abstract: PURPOSE:To manufacture a high-strength oil well tube excellent in corrosion resistance by successively applying respective treatments of hardening, tempering, plastic working, hardening, and tempering to a tube of low alloy steel with a specific composition under respectively specified conditions. CONSTITUTION:Hardening is applied at 880-980 deg.C to a tube of a low alloy steel having a composition consisting of, by weight, 0.15-0.45% C, 0.1-1% Si, 0.3-1.8% Mn, <=0.01% SolAl, <=0.002% N, <=0.005% AlN, and the balance essentially Fe. Subsequently tempering is applied to the above tube at 600-730 deg.C, and also, plastic working is applied in the above temp. region once or plural times so that the total amount of strain reaches 1-20%. Further, the above tube is subjected to hardening at 800-950 deg.C and tempering at 600-730 deg.C. By this method, the high-strength oil well tube excellent in corrosion resistance, particularly in sulfide stress corrosion cracking resistance, can be manufactured.

Production of high-strength oil well pipe having excellent corrosion resistance

Abstract: PURPOSE:To produce the high-strength oil well pipe having excellent sulfide stress corrosion cracking resistance by subjecting a low-alloy steel pipe having a specific compsn. to hardening end tempering under specific temp. conditions, then to plastic working and subjecting the pipe again to hardening and tempering treatments in succession thereto. CONSTITUTION:The high-strength oil well pipe having the compsn. contg., by weight %, 0.15-0.45% C, 0.1-1.0% Si, 0.3-1.8% Mn, =2 kinds of 0.05-2% Cr, 0.02-0.8% Mo, 0.005-0.2% Nb, 0.005%-0.2% V, and 0.0001-0.003% B is hardened from 880-980 deg.C and is then tempered at 600-730 deg.C. This pipe is subjected to 1 -several passes of plastic working at said temp. in such a manner that the total strain quantity attains 1-20%. The pipe is in succession hardened again from 800-950 deg.C and is then subjected to the tempering treatment at 600-730 deg.C. The high-strength oil well pipe having the excellent wear resistance and particularly sulfide stress corrosion cracking resistance is thus produced.

Study of the effect of heat treatment on hydrogen embrittlement of AISI 4340 steel

Abstract: Delayed failure tests were performed on fully-quenched AISI 4340 steel tempered at 500 and 700° C, subjected to sustained tensile loads and cathodically charged with hydrogen (current density 10 mA cm−2) in an aqueous solution of 0.1 N sulphuric acid. The aim was to study the effect of the microstructure on the behaviour of steel towards the embrittling action of hydrogen. The tests were carried out with two different research techniques in order to highlight this behaviour better. This was done with a view to making the use of the steel safer. With the methods used the results obtained, although substantially different from each other, showed that thermodynamically more stable structures are less sensitive to the phenomenon of hydrogen embrittlement.

Test chamber providing rapid changes of climate temperature

Abstract: The heat exchanger located in an air-conditioning room adjourning the test room of a climatic test chamber for testing equipment and devices for their resistance to extremes of climate is equipped for producing rapid changes of test chamber air temperature towards extremes of cold and heat by means of a so called "tempering" heat transfer medium which boils or condenses in the heat exchanger in the air-conditioning room. The heat transfer loop of the tempering medium is designed to withstand pressures from a low value such a 0.1 bar to a high value such as 20 bar in order that the boiling point of the tempering medium may automatically rise and fall with the air temperature of the testing room while heat is transferred in one direction or the other in great quantity through a low temperature gradient at the boiling point temperature. For cooling, a condensate separator is included in the tempering medium loop and is cooled by the cooling loop of another cooling medium. For heating, a vaporizer is included in the circulation loop of the tempering medium and is heated by a built-in heater. Both for cooling and heating the tempering medium moves around its loop by gravity feed of the condensate, making pumps unnecessary and likewise all but a minimum of valves.

Martensitic stainless steel having high strength and excellent corrosion resistance and its manufacture

Abstract: PURPOSE: To obtain the martensitic stainless steel having excellent corrosion resistance in a wet carbon dioxide environment and having high resistance to cracking caused by wet hydrogen sulfide by forming it from the compsn. contg. each prescribed amt. of C, Si, Mn, Cr, Ni, Al and N. CONSTITUTION: The above martensitic stainless steel is formed from the compsn. contg., by weight, 0.03 to 0.12% C, ≤1% Si, ≤2% Mn, >15 to 18% Cr, 1 to 5% Ni, 0.005 to 0.2% Al, 0.005 to 0.15% N and the balance Fe with inevitable impurities. For obtaining the stainless steel, the steel having the above componental compsn. is austenitized at 900 to 1100°C and is thereafter cooled at a cooling rate more than that in air cooling to satisfactorily form martensite. Next, the steel after cooled is subjected to tempering treatment at 580°C to the Ac 1 temp. or below and is thereafter cooled at a cooling rate more than that in air cooling, by which the objective martensitic stainless steel having high strength and excellent corrosion resistance can be obtd. COPYRIGHT: (C)1991,JPO&Japio

Investigation into the structural evolutions of a low alloy steel during tempering

Abstract: The structural transformations occurring during tempering in a high strength, low alloy steel containing 1.72 wt.%Si were studied using various and complementary methods of analysis such as differential dilatometry, hardness measurements, X-ray diffraction experiments and transmission electron microscopy (TEM), In situ TEM observations were performed in order to determine the transformation mechanisms involved. Two different structural states of the steel were considered (water and air quenched from the γ field). Furthermore, changes in mechanical properties were also characterized in various tempered states. A single tempering carried out at 300 °C for 2 h seems to be sufficient to produce the complete decomposition of the retained austenite (air-quenched state) and to lead to the best compromise of mechanical properties.

The effects of surface hardening on fracture toughness of carburized steel

Abstract: This research program was carried out to evaluate the effects of surface hardening on the fracture toughness of carburized steel. The materials AISI 8620 steel was machined into compact-tension (CT) specimens. The specimens were pack carburized at 930°C (1706°F) for different periods of time, cooled to ambient temperature and subsequently tempered at various temperatures for one hour. The fractured specimens were examined by hardness tests, metallography, X-ray diffraction analysis for retained austenite in the case, and scanning electron microscope fractographic analysis of the fracture surfaces. The experimental results revealed that theKIC values of the carburized, AISI 8620 steels were improved by the increase in case depth. Martensitic/tempered-martensitic structure in the case was the major constituent contributing to the improved toughness. The amount of retained austenite at the case increased as the thickness of the hardened layer increased. But retained austenite as well as large grain size were found to have adverse effects on fracture toughness of the carburized steel. The tempering temperature of 500°C (932°F) provided maximumKIC values. Higher tempering temperatures resulted in sharp decrease of fracture, toughness values.

High-strength coil spring and method of producing same

Abstract: TITLE OF THE INVENTION HIGH-STRENGTH COIL SPRING AND METHOD OF PRODUCING SAME ABSTRACT OF THE DISCLOSURE The present invention relates to a high-strength coil spring useful for an engine and other high-strength springs requiring a high fatigue-resistance and a method of producing the same. In general, a higher tensile strength is desired for spring materials but it has been known that if a tensile strength exceeds a certain limit, a toughness and a fatigue resistance are contrarily reduced. In addition, a coil spring has been used after forming and then being subjected to a quenching treatment followed by being subjected to a shot peening treatment to add a compressive residual stress to a surface thereof but an effective shot peening treatment gives a surface roughness Rmax of 6 to 20 µm, so that not only it has been impossible to remove surface defects having a surface rough-ness of 6 to 20 µm or less but also impressions due to the shot peening have covered the surface defects to be turned into injured portions and fatigue nuclei in many cases. In view of the above description, the present invention has found a high-strength coil spring with high fatigue resistance using a clean steel wire, such as chromium-vanadium steel wire and chromium-silicon steel wire, by forming it in the shape of a spring, quenching and tempering at lower temperatures to heighten the tensile strength, and being subjected to a shot peening treatment followed by being subjected to an electrolytic polishing treatment, which does not exert a bad influence on fatigue resistance, to remove surface defects and a method of producing the same.

Production of seamless stainless steel pipe

Abstract: PURPOSE:To produce the above seamless pipe having excellent toughness and stress corrosion cracking resistance by heating a martensitic stainless steel ingot to a specific temp. and subjecting the steel ingot to piercing and rolling, then successively to cooling, reheating, finish rolling, cooling, heating in a two-phase region, cooling, and tempering. CONSTITUTION:The martensitic stainless steel ingot is heated to 1,050-1,250 deg.C and is subjected to piercing and rolling. The worked steel is then cooled down to the temp. below the martensite transformation start temp. at >=30 deg.C/min cooling rate at least down to 500 deg.C to form the structure in which the martensite occupies at >=80vol.%. This steel is then reheated to the temp. region of the Ac1 transformation point - (Ac1 transformation point - 200 deg.C) where there is substantially no formation of austenite. The steel is thereafter subjected to the finish rolling at >=5% reduction of section and held for 30min in the temp. region of the Ac1 transformation point - Ac3 transformation point immediately thereafter or after the steel is once cooled. The steel pipe is further cooled down to the martensite transformation start temp. or below at >=30 deg.C/min cooling rate at least down to 500 deg.C to form the structure in which the martensite occupies at >=80vol.%, following which the steel pipe is tempered at the temp. below the Ac1 transformation point.

Manufacture of two-phase stainless steel having high yield strength and high corrosion resistance

Abstract: PURPOSE:To manufacture a member made of two-phase stainless steel excellent in corrosion resistance, toughness, corrosion fatigue resistance, and strength by subjecting a member made of stainless steel with a specific composition to solution heat treatment and then to tempering treatment under specific temp. conditions. CONSTITUTION:A cast member of stainless steel having a composition consisting of, by weight, <0.08% C, 0.2-2% Si, 0.2-2% Mn, 23-26% Cr, 6-8% Ni, 1-5% Mo, 0.2-1% Cu, 0.2-4% Co, 0.05-0.25% N, and the balance Fe is heated up to 1,050-1,150 deg.C and water-cooled to undergo solution heat treatment. Subsequently, this member is heated to 500-600 deg.C an held at this temp. for a proper length of time and then air-cooled to undergo tempering treatment, by which the member made of stainless steel having a two-phase structure of ferrite and austenite and excellent in strength and corrosion fatigue resistance as well as in corrosion resistance can be obtained.

Production of rapidly solidified thick deposited layers of FeCCr alloys by flame spraying

Abstract: Four types of FeCCr alloy powder having 3.39–3.84 wt.%, 9.6–38.8 wt% Cr and about 1 wt.% Si were flame sprayed onto a water-cooled steel substrate using a gun with a special attachment to cool the deposited layers, and rapidly solidified thick deposits were produced. The constitutents of the as-sprayed deposited layers of the lowest chromium content were metastable austenite and cementite. As the chromium content increased, ferrite appeared and its amount increased. Self-annealing of the deposited layers hardly occurred during spraying. There were two types of flattened particle in the deposited layers with a high chromium content in the as-sprayed condition and after tempering below 473 or 673 K, one type being etched and the other unetched with an etching reagent consisting of 2 parts of HNO 3 and 3 parts of HCl. The hardness of the latter was higher than that of the former. The deposited layers showed secondary hardening at tempering temperatures of 473–673 K.