Showing papers on "Tempering published in 1992"

The role of alloy composition in the precipitation behaviour of high speed steels

Abstract: The role of alloy composition in determining the microstructure and microchemistry of a series of related high speed steels has been investigated by a combination of analytical electron microscopy and atom-probe field ion microscopy. The four steels which were investigated (M2, ASP 23, ASP 30 and ASP 60) cover a large range of C, V and Co contents. Excepting the Co content, the composition of primary MC and M6C carbides and as-hardened martensite was similar in all four alloys and the major effect of increasing the content of C and V was to increase the volume fraction of MC primary carbides. Precipitation of proeutectoid carbides (mainly MC and M2C) occurred during hardening of all four steels and the extent of this was greatest in the highly alloyed ASP 60. Tempering at 560°C resulted in the precipitation of extremely fine dispersions of MC and M2C secondary carbides with very mixed compositions in all four steels. It was found that, as well as hindering the formation of autotempered M3C in the as-hardened martensite, additions of Co refined the secondary carbide dispersion and delayed overaging reactions. Overaging at 600°C resulted in the precipitation of M3C, M6C and M23C6 at the expense of the fine MC and M2C secondary carbide dispersion.

Laser transformation hardening of tempered 4340 steel

Abstract: A CO2 laser with a fixed laser power of 1.8 KW was employed to harden the surface of some AISI 4340 steel specimens, with a scan rate from 5 to 10 mm/s. The influence of scan rates and tempering treatments of the alloy on the hardness profile and microstructure of the laserhardened zone was analyzed. Microstructures in the hardened zone consisted of mainly lath and twinned martensites. However, depending on the scan rate, autotempered martensite has also been found. In the transition zone of laser-treated specimens, partially dissolved carbides with austenite envelopes and/or austenite islands in a matrix of martensite were observed. The time required for complete carbide dissolution into austenite during laser treatment depended on the tempering conditions. A lower tempering temperature of the alloy produced a deeper hardened zone and a narrower transition zone in the hardness profile. A simple mathematical estimation of the hardness profile, based on the carbon diffusion distance in austenite, was performed. The calculated results are in reasonably good agreement with the measured hardness profiles and the microstructural observations in the laser transformation hardening process.

Strengthening of Feldspathic Porcelain by Ion Exchange and Tempering

Abstract: This study investigated the effectiveness of tempering and ion-exchange treatments on crack growth and bi-axial flexural strength of seven feldspathic porcelains. The results showed that tempering treatment was more effective in strengthening porcelain than was the ion-exchange process as measured by the bi-axial flexural strength. However, the results of initial crack size induced by a microhardness tester showed that ion-exchange yielded a surface that was more resistant to crack initiation than was that yielded by the tempering treatment. EDX and microprobe analyses showed that there was evidence of exchange between Na+ within the porcelain surface and K+ from the ion-exchange agent applied on the surface.

Grain-boundary segregation and precipitation of boron in 0.2 percent carbon steels

Abstract: The segregation and precipitation of boron have been studied in two 0.2C−0.6Mn0.−5Mo steels containing (nominally) 10 and 50 ppm B. After heating to 1260 δC, samples were air-cooled to 870 °C and then held for times between 0 and 5000 seconds. Additional samples were heated to 1260 °C, air-cooled to 900 °C, reduced in thickness by 50 pct, and then held for various times at 870 °C, as above. The distributions of boron under these various conditions were investigated qualitatively by an autoradiographic technique. In both steels, segregation and/or precipitation of boron at austenite grain boundaries was detected under all conditions examined. Precipitation of iron borocarbide particles occurred along austenite grain boundaries in the 50 ppm B steel during cooling to the holding temperature of 870 °C, while in the 10 ppm B steel, such precipitation occurred only after long times at 870 °C. Mechanical properties of single-pass-rolled samples were measured after tempering to assess the effects of borocarbide precipitation on notch toughness. Such precipitation lowered the Charpy upper shelf energy and increased the transition temperature.

Tempering of Iron-Carbon-Nitrogen martensites

Abstract: The tempering behavior of ternary FeCN martensitic specimens, with a total amount of interstitials of about 5.5 at. pct and carbon and nitrogen contents between about 1.5 and 3.9 at. pct, was investigated in the temperature range 110 to 830 K. Analysis of the corresponding changes in crystalline structure (X-ray diffraction), volume (dilatometry), and hardness and enthalpy (calorimetry) revealed that the following processes occurred: (a) martensitic transformation of retained austenite between 110 and 200 K; (b) redistribution of interstitials in martensite up to 370 K; (c) formation of nitrogen containing α′ precipitates and carbon containing e/η) precipitates between 370 and 450 K; (d) conversion of α′ nitride into γ′ nitride and coarsening of e/η carbide between 450 and 560 K; (e) decomposition of retained austenite above 540 K; and (f) conversion of e/η carbide into cementite above 570 K. Significant precipitation of carbon and nitrogen together, as nitrocarbides or carbonitrides, was not observed. From a comparison with the tempering behavior of binary FeC and FeN alloys of similar interstitial content, it was concluded for the ternary FeCN alloy that the transformation of the transition nitride (α′) into the “equilibrium” nitride (γ′) was advanced and that the precipitation of the transition carbide(e/η) and its conversion into the equilibrium carbide (cementite) and the decomposition of retained austenite were retarded.

Microstructural changes during overtempering of high-speed steels

Abstract: To elucidate the mechanisms determining the creep resistance of high-speed steels during tool service, overtempering at 600°C has been investigated for two alloys modeling the matrix compositions of AISI M2 and T1. Composition changes and coarsening of the secondary hardening precipitates were studied by transmission electron microscopy and field-ion microscopy with atom probe analysis. Strengthening in the peak-hardened state is due to coherent precipitates of types M2C and MC. During overtempering, M2C coarsens too rapidly to be of importance for the sustained strength of the material. The MC precipitates, on the other hand, are fairly stable. Some coarsening does occur, but the MC population is replenished by a second wave of precipitation which makes use of the roughly 50 pct of carbide-forming elements, carbon, and nitrogen, which remained in solid solution after tempering to the peak-hardened state. This precipitation reaction continues for times of the order of the tool life.

Secondary Hardening in High Speed Steels

Abstract: Analyse par sonde atomique et microscopie ionique a emission de champ des precipites de carbures secondaires dans six aciers rapides de differentes compositions. Determination de la taille et de la composition chimique des precipites en fonction de la composition des aciers

Influence of Tempering Method on Residual Stress in Dental Porcelain

Abstract: The porcelain component of a porcelain-fused-to-metal restoration is strengthened by residual (tempering) stresses which are induced by cooling procedures followed in dental laboratories. The thermophysical properties of materials and cooling rate are the main factors which determine the residual stress. In this paper, the temperatures in the midplane of body-porcelain disks were measured from a heat-soak temperature (1000°C) to room temperature during two different cooling procedures: slow cooling in air and forced-air cooling. Experimental results approximated exponential cooling wherein the cooling rates could be represented by a linear equation of temperature. Residual stresses, as affected by the tempering method and thickness of a porcelain disk, were calculated by computer simulation for regions away from the edges. The following temperature-dependent factors were incorporated into the simulation: elastic modulus, viscosity, and coefficient of thermal expansion. The cooling rate dependencies of the...

Load sharing of the phases in 1080 steel during low-cycle fatigue

Abstract: By means of X-ray diffraction, the stress response of the individual phases in a 1080 steel were measured. Specimens with pearlitic, spheroidal, and tempered martensitic microstructures were subjected to low-cycle fatigue and the stress-strain hysteresis loops were separated into components for the carbide and matrix phases. Calculations of the microstresses formed by differential plastic deformation of the matrix and inclusions accurately model the spheroidite. Measured microstresses in the pearlite are smaller than the predicted values, probably due to yielding of the cementite and limitations on modeling the morphology. Work-hardening rates associated with the microstresses also qualitatively agree with the measurements. The tempered martensite cyclically softens with fatigue loading. The increased plastic strain range in the tempered martensite with cyclic softening is accompanied by an increase in the microstresses. These microstresses are significantly larger than predicted.

Strain hardening behaviour and its relationship to tensile mechanical properties of dual phase steel

Abstract: Using the modified Crussard–Jaoul analysis, the strain hardening behaviour of a predeformed 1020 dual phase steel with quenching and quenching plus tempering treatments was examined, showing that this dual phase steel deforms in two stages. The relationships between the maximum uniform strain eu, the stress ratio (true initial stress σ0 true maximum stress σu) and the strain hardening exponents in the first stage and the second stage (m1 and m2) were derived based on the Swift equation and the Considere instability criterion, which showed good agreement with the experimental results for the present 1020 dual phase steel. The dependence of strength σu and ductility ɛu of dual phase steel on the exponents m1 and m2 was discussed using the two derived relationships.MST/1631

Method and apparatus for bending and tempering a glass sheet

Abstract: The invention relates to a method and apparatus for bending and tempering a glass sheet. A glass sheet is supported by one and the same ring mould (3) throughout all its working operations. Following the preheating of a glass sheet from a temperature of about 500° C., its heating to a final bending and tempering temperature is effected at a high output and rate of speed. For example, on 4 mm thick glass, this final heating is performed within a period of time of 15-25 s. Therefore, the temperature of bending station is 800°-1000° C. Since rapidly heating glass bends quickly, the bending flexure or temperature of glass is monitored and the glass is advanced to tempering as soon as a predetermined bending flexure or temperature is reached.

Steel for spring excellent in fatigue property and steel wire for spring as well as spring

Abstract: PURPOSE: To obtain a steel for a spring having high strength and excellent in fatigue properties by specifying its compsn. constituted of C, Si, Mn, Cr, V, Nb and Fe and the properties of contained inclusions and percipitates. CONSTITUTION: In a steel contg., by weight, 0.5 to 0.8% C, 0.8 to 2.5% Si, 0.4 to 1.3% Mn and 0.4 to 2% Cr, furturemore contg., at need, 0.05 to 0.5% V and/or 0.05 to 0.5% Nb and moreover contg. 0.1 to 2% Ni and/or 0.1 to 0.5% Mo, and the balance Fe with inevitable impurities, the m.p. of oxide inclusions contained therein is regulated to ≤1500°C, and the size of carbide precipitates and nitride precipitates are regulated to ≤15μm. In this way, the objective steel for a high strength spring excellent in fatigue properties can be obtd. This steel is subjected to hardening and tempering treatment, by which the objective high strength steel wire for a spring having crystalline grain size, of No.11, or more 3 to 20% retained austenitic amt., ≥205kgf/mm 2 tensile strength and ≤0.95 proof stress ratio after low temp. annealing at ≥400°C and the objective spring having residual stress shown by the formula and inequalities can be obtd. COPYRIGHT: (C)1993,JPO&Japio

Effect of tempering on development of carbide particles in 2.7Cr-0.6Mo-0.3V steel

Abstract: To study the influence of tempering conditions (823–1058 K, 9–3600 ks) on the phase transformations and changes of morphology, size and chemical composition of carbide particles in 2.7Cr-0.6Mo-0.3V steel, the methods of, electron diffraction and EDXS/STEM have been used. Three carbide types: M3C, M7C3 and MC have been identified altogether, the last two of which are equilibrium ones under given conditions. Diagrams describing changes in chemical composition of carbide particles and the average size during tempering have been constructed. In the development of carbide chemical composition three stages have been recorded. The carbide particles grow continuously with the increasing of time and/or temperature of tempering.

Changes in the macrostresses and microstresses in steel with fatigue

Abstract: The residual stresses in both the ferrite and cementite phases of fatigued 1080 steel specimens with pearlite, spheroidite and tempered martensite microstructures were measured using X-ray diffraction giving both the macrostresses and microstresses. Specimens with no initial stresses showed little changes with fatigue. Specimens with initial macrostresses and microstresses showed fading of the stresses, the fading being slowest for the strongest microstructure. Hydrostatic microstresses are present after heat treatment owing to the differential thermal properties of the cementite and ferrite.

Bearing components and process for producing same

Abstract: A bearing component is prepared from a carburazing steel and having a surface hardness of 63 to 67 in terms of Rockwell hardness C and a surface retained austenite content of at least 20% to less than 25%. The bearing component is produced by a process including the step of carburizing and quenching a bearing component workpiece prepared from a carburizing steel and machined to a predetermined shape, the step of subjecting the resulting workpiece to a preliminary tempering treatment, the step of subjecting the tempered workpiece to a sub-zero treatment and the step of subjecting the treated workpiece to a main tempering treatment. Further, the bearing component is produced by another process including the step of carburizing and quenching a bearing component workpiece prepared from a carburizing steel and machined to a predetermined shape, the step of subjecting the resulting workpiece to a secondary hardening treatment and the step of subjecting the hardened workpiece to a main tempering treatment.

Production of high strength steel tube excellent in sulfide stress corrosion cracking resistance

Abstract: PURPOSE: To obtain the steel tube by directly working a continuously cast billet into a seamless steel tube, combinedly applying direct hardening to the steel tube, and specifying the composition of the steel tube. CONSTITUTION: A billet having a composition which consists of, by weight, 0.15-0.4% C, 0.1-1% Si, 0.3-1% Mn, 0.1-1.5% Cr, 0.1-1% Mo, ≤0.015% P, ≤0.005% S, 0.0005-0.003% B, 0.01-0.1% Al, 0.01-0.03% Ti, 0.003-0.01% N, and the balance Fe and where, when a PGS value represented by equation PGS=(0.3Ti+0.05Al)/N is determined, the contents of Al, Ti, and N are regulated so that PGS becomes 1.0 to 1.5 is prepared. This billet is worked at a temp. not lower than the Ac 3 transformation point into a seamless steel tube, which is subjected, without delay, to water quenching and to tempering at a temp. not higher than the Ac 1 transformation point. Moreover, Nb and/or V can further be incorporated by 0.01-0.05% into the above composition. By this method, the seamless steel tube for oil well and gas well use, excellent in SSCC resistance and having strength as high as ≥75kg/mm 2 yield point strength can be obtained. COPYRIGHT: (C)1994,JPO&Japio

Surface reforming method of aluminum alloy members

Abstract: An aluminum alloy member is heated to 470°-550° C., and is quenched to room temperature for hardening. Then the aluminum alloy member is heated to 160°-220° C., and is cooled, which is carried out in a cooling process of a tempering treatment. As the aluminum alloy member is in a softening state in the cooling process, plastic working such as shot peening treatment is performed on the surface of the aluminum alloy member. Thereafter, the temperature of the aluminum alloy member falls to room temperature. In this way, it is possible to generate a great amount of compression residual stress in the aluminum alloy member, without performing a severe plastic working treatment on the surface thereof. Since the present invention requires no severe plastic working treatments on the surface of the aluminum alloy member, this causes no severe surface roughness thereon.

Method for bending and tempering glass sheets

Abstract: The invention relates to a method for bending and tempering glass sheets, particularly automotive backlights and side windows. A glass sheet supported by a ring mould (6) is heated and bent gravitationally close to a correct shape. In a bending station (17) the glass sheet is pressed to its final shape by means of an overhead, non-contacting full-face mould, provided with a double channeling for blasting and vacuuming. The vacuum of a mould (15) is used to lift a bent glass sheet up from ring mould (6) and the glass sheet is heated for equalizing temperature differences and for increasing the temperature to a tempering temperature. Below the glass sheet is brought a tempering frame (8), upon which the glass is lowered from the full-face mould and which is used for carrying the glass to tempering.

Production of bearing parts

Abstract: PURPOSE: To obtain bearing parts excellent in toughness and having superior indentation resistance and wear resistance at the surface and high resistance to the propagation of cracks and, as a result, capable of improving the service life of a bearing in lubricating oil containing foreign matter. CONSTITUTION: The process for producing the bearing parts includes a hardening stage where hardening is applied to a bearing parts stock consisting of high carbon chromium bearing steel, a tempering stage where the above stock is tempered, a shot peening stage where residual compressive stress is applied by applying shot peening to the desired part of the above stock to transform residual austenite into martensite and increase hardness, and a finishing stage where the above stock is polished. Residual austenite in the surface layer part of the above desired part is regulated to ≤10% practically including zero, and also maximum residual compressive stress is regulated to 1500 to -1500MPa and hardness is regulated to 850-950 in terms of Vickers hardness. COPYRIGHT: (C)1993,JPO&Japio

Method for manufacturing a high-strength spring

Abstract: A spring steel containing 0.35 to 0.50% of carbon is refined to the hardness of φ 2.50 to 2.70 mm in Brinell indentation diameter (HBD) by rapid cooling for quenching and tempering. This spring steel is subjected to warm shot peening at a temperature of 150° to 300° C. (423 to 573 K.) by using long-lived practical shots with the normal hardness of φ 2.65 to 2.80 mm in HBD, whereupon a high-strength spring is obtained having a compressive residual stress in its surface and enjoying the maximum shearing stress of 110 to 135 kgf/mm 2 (1080 to 1325 MPa).

Production of high strength low alloy steel for oil well use, excellent in sulfide stress corrosion cracking resistance

Abstract: PURPOSE:To produce an oil well steel pipe having high strength and excellent in sulfide stress corrosion cracking resistance by subjecting a pipe made of low alloy steel with specific composition to hardening and tempering under respectively specified temp. conditions. CONSTITUTION:An ingot of a low alloy steel having a composition containing, by weight, 0.20-0.30% C, 0.10-1.50% Si, 0.40-1.50% Mn, =2 kinds among 0.01-0.10% Ti, 0.01-0.10% Nb, and 0.01-0.10% V is cogged, which is formed into a seamless steel pipe by means of hot rolling by a Mannesman process. This steel pipe is hardened from a temp. not lower than the Ac3 transformation point of this steel and tempered at 600-750 deg.C. By this method, the steel pipe having (63 to 87)kgf/mm yield strength, increased in threshold of stress intensity factor in a sulfide environment, and excellent in sulfide stress corrosion cracking resistance required of the steel tube for oil well or gas oil use in a sour environment can be obtained.

Fatigue Strength of Laser Beam Surface Treated Structural Steels

Abstract: An industrial advantage of laser processing is that it permits local treatment of mechanical components on those specific areas subject to high stress levels. The way in which this type of laser treatment enhances structural steel properties has been studied. The 42CD4 and X C42 steel specimens were notched to create a stress concentrationfactor identical to that observedfor gears. The work involved optimising three parameters: the laser beam itself, i.e. the beam energy-time of interaction couple; specimen preparation, i.e. selection of the best laser beam-specimen coupling medium (phosphating gave the best emissivity coefficient while avoiding specimen contamination); the metallurgical heat treatment, designed to obtain both high toughness and good ductility. Specimens tempered at various temperatures before the laser treatment were fatigue tested. The results enabled the selection of an intermediate tempering temperature resulting in the highest fatigue limit. They also showed that, in regard t...

Dispersion strengthening high-Cr steels by forming “V-Wings”

Abstract: In the effort to improve the creep resistance of high-chromium ferritic steels that are candidate materials for power plant applications, additions of Nb, V, and N were found to produce wing-like vanadium carbonitrides that adhere to spherical Nb(C,N) particles during tempering. The complex carbonitrides of niobium and vanadium strongly inhibit dislocation glide during high-temperature deformation. The same type of the carbonitrides can be observed in other niobium- and vanadium-modified, high-chromium ferritic steels, and similar high-temperature, dispersion-hardening effects can be observed.

Carbide- matrix interface mechanism of stress corrosion cracking behavior of high-strength CrMo steels

Abstract: The effects of tempering temperature and carbon content on the stress corrosion cracking (SCC) behavior of high-strength CrMo steels in 3.5 pct NaCl aqueous solution have been studied by means of Auger electron spectroscopy (AES) and scanning and transmission electron micros- copy (SEM and TEM). Experimental results show that the specimens with higher carbon content and tempered at lower temperatures have a higher tendency for intergranular fracture and lower threshold stress intensity KISCC The SCC behavior is significantly affected by the distribution of carbide particles, especially carbide coverage on prior austenitic grain boundaries, through a carbide-matrix interface mechanism as the interface is the preferential site for the nucleation and propagation of microcracks because of its strong ability to trap hydrogen atoms. In low- temperature tempered states, there is the serious segregation of carbon in the form of carbide particles at prior austenitic grain boundaries, causing low-stress intergranular fracture. After tempering at high temperatures (≥400 °C), both the coalescence of the carbide particles at the grain boundaries and the increase of carbide precipitation within grains cause the decrease of the tendency for intergranular fracture and the rise of KISCC. The higher the carbon content in steels, the more the carbide particles at the grain boundaries and, subsequently, the higher the tendency for low-stress intergranular fracture. The carbide effect on KISCC makes an important contribution to the phenomenon that KISCC decreases with the rise of yield strength of the steels.

Oxidation behaviour of 21/4Cr-1Mo steel with prior tempering treatments at 998 K for different durations

Abstract: Normalized 21/4Cr-1Mo steel has been tempered at 998 K for durations up to 50 h, and then oxidized in air at 773, 873 and 973 K for a maximum duration of 1000 H. The extent of the prior tempering treatment was found to influence the oxidation behaviour of the steel significantly. In general, the oxidation resistance of the steel decreased with increasing duration of prior tempering. However, a pronounced influence has been observed during oxidation at 973 K, when at the end of a 6 h exposure the specimens with prior tempering for 50 h were found to have a weight gain 2.5 times more than the specimen without prior tempering. From the results of the pre- and post-oxidation analyses of the oxide-alloy matrix interfaces by SEM/EDAX, the observed oxidation behaviour could be attributed to the degree of depletion of free (effective) chromium from the alloy by the precipitation of secondary phases of chromium compounds during tempering for different durations. The secondary precipitates in the specimen tempered for 50 h at 998 K can become enriched in chromium by one order of magnitude more than that in the specimen with no prior tempering. Such a drastic depletion of chromium from the matrix causes the formation of a less protective inner oxide layer during oxidation. Acoustic emission tests carried out to assess the mechanical stability of the scale showed that the 50 h tempered specimen suffered cracking after about 4 h oxidation at 973 K, which results in subsequent enhanced oxidation.

Method of estimating material of steel product

Abstract: A method of estimating the material of steel product on the basis of a final structure of steel, in which metallographic structure of steel is sequentially found by computing metallurgical phenomena on the basis of information about constituents of steel and manufacturing conditions ranging from casting to heat treatment, comprising steps of computing: a temperature of a steel billet on the basis of casting conditions, and the post-casting metallographic structure of steel on the basis of the temperature of the steel billet and information about constituents of steel; a post-rolling metallographic structure of steel on the basis of the pre-rolling metallographic structure and steel temperature calculated from rolling conditions; a post-cooling metallographic structure of steel on the basis of a pre-cooling metallographic structure and steel temperature calculated from cooling conditions; and the material of steel on the basis of a final metallographic structure thereof. Correspondingly to additionally performed manufacturing processes such as re-heating, heat-treatment for uniform diffusion, preparatory rolling, quenching, tempering, and annealing, steps are provided further each computing a metallographic structure of steel after a manufacturing process on the basis of a metallographic structure before that manufacturing process and conditions of that manufacturing process.