Showing papers on "Tempering published in 1993"

Transmission electron microscopy examination of hardening and toughening phenomena in Aermet 100

Abstract: The effect of tempering on the microstructure and mechanical properties of ultrahigh strength Aermet 100 steel was examined. In the as-quenched condition, the steel contained a dispersion of relatively fine, undissolved, (CrTiFeMo)C and (CrFeMo)23C6 carbides in a martensitic matrix. Upon tempering at 427 °C, the martensite decomposed to form a high density of cementite particles concomitant with a significant drop in toughness. Tempering at 454 °C resulted in peak strength (yield strength ∼ 1756 MPa) due to the precipitation of coherent zones of fine carbides. The peak in toughness (170 MPa√m), attained at a tempering temperature of 482 °C, was attributed to both the absence of cementite and the formation of reverted, stable austenite. Tempering at higher temperatures resulted in loss of both strength and toughness, which was suggested to be the result of precipitate coarsening and formation of unstable austenite, respectively. The details of the electron microscopy studies and mechanism of strengthening and toughening are discussed in light of the current understanding of this subject.

Effect of microstructure on mechanical properties of isothermally bainite-transformed 300M steel

Abstract: A study has been made of the effect of the microstructure on the mechanical properties of commercial-aircraft quality 300M steel which has been isothermally transformed in various bainitic temperature regions (593–673 K) after austenitization at 1173 K. The results were compared with those obtained by conventional quenching and tempering. Isothermal transformation of the steel at and below 623 K produced a dispersion of retained austenite (12–18 vol.%) in a carbon-free upper bainite matrix. The treatment improved the K I c value, owing to an increase in the Charpy impact energy; however, no improvement in strength was observed. As aresult of the isothermal transformation at and above 648 K, the retention of a large amount of retained austenite (22–25 vol.%) was encouraged, in conjunction with carbon-free upper-bainite; however, this was found to have a very detrimental effect on the strength and toughness. The results are described and discussed in terms of the microstructure and fractography.

Recent Trends in the Production and Use of High Strength Stainless Steels

Abstract: The strengthening mechanisms of steels have been well studied widely, and are the same of the mechanisms in high strength stainless steel, e.g., grain refinement by the thermomechanical treatment, solid solution strengthening by lattice distortion through the addition of alloying element, transformation strengthening by martensite transformation, work hardening by the formation of strain induced martensite through rolling, strain aging hardening by the tempering or aging of martensite, and precipitation strengthening of intermetallic compounds which are coherent with the matrix. These strengthening mechanisms relate to the thermomechanical treatment of the steel as well as the chemical composition. Various high strength stainless steels are produced by a combination of these mechanisms, and have peculiar mechanical properties depending on the final microstructure.Recently, the need for various other properties than high strength, e.g., ductility, toughness and weldability has been recognized. Work-hardened stainless steel, for example, has greater strength than SUS301 and is used for ID blades (inner diameter blade for cutting Si single crystal), etc. The additional strength of the steel results from solid solution hardening and strain aged hardening. Martensite stainless steel and ultra microduplex stainless steel were also developed and are now in use fitting a variety of needs. The former steel has high toughness with more than 1700 N/mm2 tensile strength, and the latter has good strength and ductility but is not softened on welding.

The relationship between ductility and material parameters for dual-phase steel

Abstract: A modified Crussard-Jaoul analysis has been employed to describe the strain hardening behaviour (the ln(dσ/de) versus In σ curves) of a 1020 dual-phase steel with quenching and quenching+tempering treatments and with different predeformations, which demonstrated that this dual-phase steel exhibits two stages of strain-hardening in the range of plastic deformation. An analysis of instability for dual-phase steel is also presented and the relationship between the maximum uniform strain and the material parameters is proposed, which shows good agreement with the experimental results for the present 1020 dual-phase steel and other dual-phase steels.

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

Abstract: PURPOSE:To produce a high strength steel pipe excellent in sulfide stress corrosion cracking resistance by forming a steel pipe in such a manner that the componental compsn. and seamless rolling temp. are specified, completing its bainitic transformation and executing hardening and tempering at specified temps. CONSTITUTION:A billet contg., by weight; 0.15 to 0.4%, C, 0.1 to 1% Si, 0.3 to 1% Mn, 0.1 to 1.5% Cr, 0.1 to 1% Mo, =two kinds among 0.01 to 0.05% Nb, 0.01 to 0.5% V and 0.01 to 0.03% Ti, and the balance Fe with inevitable impurities is subjected to seamless rolling so as to regulate the final finish temp. into the recrystallization temp. + or -50 deg.C and is worked into a steel pipe. This steel pipe is subjected to accelerated cooling to complete its bainitic transformation, is heated in the temp. range of the Ac3 transformation point (790 to 830 deg.C) to the Ac3 transformation point+<100 deg.C, is hardened from the same temp. and is thereafter tempered at the Ac1 transformation point or below.

Tempering of AISI 403 stainless steel

Abstract: The tempering behaviour of AISI 403 martensitic stainless steel over the temperature range from 480 to 720 °C has been investigated, with particular attention being paid to the secondary hardening and sensitization effects produced by the formation of alloy carbides during tempering. The secondary hardening effect was determined by means of a standard hardness test. The extent of sensitization and its effect on the mechanical properties of the tempered steel were assessed by means of a modified Strauss test and a low speed tensile test in brine respectively. The results show that the following four distinctive processes occurred during tempering of AISI 403 martensitic stainless steel: annealing, secondary hardening, sensitization and healing. The tempering conditions over which each of these four processes dominates are presented in the form of a tempering map for easy reference.

Microstructure–property relationships in tempered low alloy Cr–Mo–3·5Ni–V steel

Abstract: The effect of varying normalising and hardening temperatures, before tempering at ~620°C, on the strength and toughness of a low alloy Cr–Mo–3·5Ni–V (wt-%) steel has been examined Microstructural features including martensite packet and lath size, dislocation density, and precipitate size were measured and used in a Hall–Petch analysis of the strengthening components It was found that a rms summation of the strengthening contributions to the 0·2% proof stress gave values in good agreement with experimental results The 50% fracture appearance transition temperature could be described by a relationship involving the fracture facet size and the strengthening contributions from dislocations and precipitatesMST/1802

The effect of the precipitation of coherent and incoherent precipitates on the ductility and toughness of high-strength steel

Abstract: The effect of the coexistence of coherent and incoherent precipitates, such as M2C and NiAl, on the ductility and plane strain fracture toughness of 5 wt pct Ni-2 wt pct Al-based high-strength steels was studied. In order to disperse coherent and incoherent precipitates, the heat treatments were carried out as follows: (a) austenitizing at 1373 K, (b) tempering at 1023 or 923 K for dispersing the incoherent precipitates of M2C and NiAl, and then (c) aging at 843 K for 2.4 ks to disperse the coherent precipitate of NiAl into the matrix, which contains incoherent precipitates, such as M2C and NiAl. The results were obtained as follows: (a) when the strengthening precipitates consist of coherent ones, such as M2C and/or NiAl, the ductility and toughness are extremely low, and (b) when the strengthening precipitates consist of coherent and incoherent precipitates, such as M2C and NiAl, the ductility and fracture toughness significantly increase with no loss in strength. It is shown that the coexistence of coherent and incoherent precipitates increases homogeneous deformation, thus preventing local strain concentration and early cleavage cracking. Accordingly, the actions of coherent precipitates in strengthening the matrix and of incoherent precipitates in promoting homogeneous deformation can be expected to increase both the strength and toughness of the material.

TEM investigation of precipitation phenomena occurring in PH 15-5 alloy

Abstract: The ageing of PH 15-5 alloy, previously quenched from 1050°C, is characterized by a hardness peak at 450°C, then by a softening and finally by a second increase in hardness from 650°C. TEM observations reveal the successive formation (between 450 and 650°C) of coherent precipitates (A and B types) which become respectively as rods (D) the growth directions of which have been determined and as partially coherent (C) globular precipitates. All these types of precipitates are enriched in copper. After tempering in temperatures higher than 650°C, new (E) precipitates are observed which are coherent at first, then become partially coherent after tempering at 750–850°C.

Method for soldering hard substances onto steels

Abstract: When hard-substance parts are soldered onto steel bases, thermal stresses are produced between the hard substance and the steel. These stresses can be reduced by means of using a multilayer solder in which the middle layer consists of a precipitation-hardenable copper alloy or nickel alloy provided on both sides with a layer of a hard-solder alloy whose working temperature is at least 50° C. below the melting point of the precipitation-hardenable copper alloy or nickel alloy. A tempering treatment at 250° to 550° C. is carried out after the soldering in order to achieve a precipitation hardening of the middle layer.

Toughness of tempered upper and lower bainitic microstructures in a 4150 steel

Abstract: The effects of tempering on the Charpy impact toughness and tensile properties of upper and lower bainite in a 4150 steel have been studied. The results correlate with quantitative measurements taken from both the fracture surfaces and the microstructures of Charpy test specimens. The fracture surfaces from impact specimens having a lower bainitic microstructure were characterized by quasicleavage fracture, whereas those having an upper bainitic microstructure exhibited only cleavage fracture. The quasicleavage facet size and cleavage facet size correlate with bainite packet size and bainite block size. After tempering at high temperatures, the impact toughness is greatly improved for both the upper and lower bainitic microstructures. Changes in toughness correlate with the microstructural change in carbide shape and distribution resulting from the different tempering operations.

Microstructure of tempered AISI 403 stainless steel

Abstract: The microstructure of AISI 403 martensitic stainless steel (AISI 403 MSS) tempered at various temperatures for various times was investigated by transmission electron microscopy (TEM). The microstructure consisted of tempered martensite laths together with carbides and a small amount of σ-ferrite. At lower tempering temperatures of 480 and 540 °C, two types of carbides, Cr 23 C 6 and Cr 6 C 3 , were present. The majority of the Cr 23 C 6 carbides were in the martensitic matrix and a chain of Cr 23 C 6 carbide was seen at and in the vicinity of grain boundaries. Upon tempering at 600 or 660 °C, Cr 23 C 6 became the predominant carbide and was mainly distributed at the boundaries of the martensitic laths. The results showed that secondary hardening in AISI 403 MSS, produced by tempering at lower temperatures, especially 480 °C, resulted from Cr 23 C 6 carbides heterogeneously precipitated in the martensicic matrix. For specimens tempered at 600 °C and above, severe sensitization and loss of corrosion resistance of the steel occurred owing to large Cr 23 C 6 precipitates which were concentrated at the grain boundaries, forming a zone of reduced chromium content adjacent to the carbides in the grain boundaries.

Production of coil spring

Abstract: PURPOSE:To produce a high strength coil spring in which breaking is difficult to occur and excellent in fatigue resistance by subjecting a cold drawn wire rod having a specified compsn. constituted of a metallic group of C, Si, Mn or the like, a metallic group of V or the like and Fe to oil tempering treatment and thereafter executing high temp. tempering. CONSTITUTION:A stock having a compsn. contg., by weight, 0.55 to 0.75% C, 1.00 to 2.50% Si, >= two or more kinds among 0.30 to 1.50% Mn, 1.00 to 4.00% Ni, 0.50 to 2.50% Cr and 0.10 to 1.00% Mo, one or more kinds of 0.05 to 0.60% V and 0.05 to 0.60% Nb, and the balance substantial Fe and subjected to cold wire drawing is subjected to oil tempering treatment. Thereafter, this wire rod is subjected to high temp. tempering to regulate its tensile strength to sigmab=1370 to 1670N/mm . This wire rod is subjected to annealing and is successively subjected to cold coiling, hardening and tempering, grinding, gas nitriding, high strength two stages shot peening and low temp. annealing. In this shot peening, compressive residual stress is imparted to the inner depth part by a first stage, and residual stress is sufficiently imparted to the vicinity of the surface by a secondary stage.

Thermochemical-thermal treatment of case hardening steels - with deep cooling between hardening and tempering

Abstract: Thermochemical-thermal treatment of case hardening steels comprise the following steps. Case hardening or carbo-nitriding (1) takes place at 900 to 1950 deg.C. This is followed by quenching (2) down to a temp. below the Ar1 point at a rate chosen to avoid cementite precipitation at grain boundaries. The subsequent hardening process (3) involves heating at a rate from 20 to 80 deg.C/min and holding at 770 to 830 deg.C for 5 to 15 min. The treatment is concluded by tempering (5). Deep cooling (5) down to -70 to 120 deg.C is foreseen between the hardening (4) and tempering (6) processes. The structure in the boundary zone has finely dispersed inter-crystalline carbide precipitations, with an area greater than 8 per cent of the total and a grain size finer than 10 according to ASTM E112. USE/ADVANTAGE - For mfr. of components of internal combustion engines. Improves the wear resistance of severeley loaded components also under unfavourable lubricating conditions.

Method for thermally treating rolling bearing

Abstract: PURPOSE:To extend the fatigue life to foreign matter included lubrication by forming a race from an alloy steel containing C, Si, Cr, Mn in specified weight ratios, hardening and tempering it at specified temperatures after carbonitriding treatment to make the residual austenite on the surface layer part to a specified %. CONSTITUTION:At least a race is formed of an alloy steel containing 0.8-1.2%, by weight, of C, 0.4-1.0% of SiO, 0.2-1.2% of Cr, and 0.8-1.5% of Mn, hardened at 830-870 deg.C after carbonitriding treatment, and tempered to 160-190 deg.C to make the residual austenite on the surface layer part to 25-50%. When a bearing material is molded from this alloy steel and carbonitrided, the austenite undeformed by hardening is present in the surface layer part more than in the core part since the nitrogen content in the surface layer part is increased to reduce the Ms point lower than in the core part. Since the nitrogen is therefore rich in the surface layer part to enhance the hardening starting temperature, the residual austenite in the surface layer part can be enhanced to 25% or more. Thus, the rolling fatigue life under foreign matter included lubricating oil environment can be improved.

Martensitic hot work tool steel die block article and method of manufacture

Abstract: A martensitic hot work tool steel die block for use in the manufacture of die casting die components and other hot work tooling components and a method for manufacturing the same. The article has a hardness within the range of 35 to 50 HRC and a minimum transverse Charpy V-notch impact toughness of 5 foot pounds when heat treated to a hardness of 44 to 46 HRC and when tested at both 72° F. and 600° F. The article is a hot worked, heat treated and fully dense consolidated mass of prealloyed particles of the composition, in weight percent, 0.32 to 0.45 carbon, 0.20 to 2.00 manganese, 0.05 to 0.30 sulfur, up to 0.03 phosphorous, 0.80 to 1.20 silicon, 4.75 to 5.70 chromium, 1.10 to 1.75 molybdenum, 0.80 to 1.20 vanadium, and balance iron. The alloy may be any conventional wrought AISI hot work tool steel or wrought maraging or precipitation-hardening steel having 0.05 to 0.30 percent sulfur, and having sulfide particles which exhibit a maximum size of 50 microns in their longest dimension. The article is manufactured by compacting of prealloyed particles of the aforementioned composition followed by hot working, annealing, hardening and tempering.

Volume fraction dependent particle coarsening in plain carbon steel

Abstract: Literature indicates that the kinetics of cementite particle coarsening should be enhanced by the increase of volume fraction of carbides, but none of the investigators has confirmed it by quantitative experimental data analysis. In the present work three hypoeutectoid plain carbon steels have been hardened by water quenching and tempered isothermally between 861–973 K for 1.5–209 h. Mean particle diameter d , volume fraction Vv, specific interfacial energy, σ activation energy Qeff, diffusivity Deff and effect of volume fraction Km have been estimated and an attempt has been made to throw some light on the mechanism of cementite particle coarsening including the effect of volume fraction on the kinetics of coarsening.

Elastic limit and microplastic response of hardened steels

Abstract: Tempered martensite-retained austenite microstructures were produced by direct quenching a series of 41XX medium carbon steels, direct quenching and reheating a series of five 0.8C-Cr- Ni-Mo steels and intercritically austenitizing at various temperatures, and quenching a SAE 52100 steel. All specimens were tempered either at 150 °C or at 200 °C. Specimens were subjected to compression and tension testing in the microstrain regime to determine the elastic limits and microplastic response of the microstructures. The retained austenite and matrix carbon content of the intercritically austenized specimens were measured by X-ray diffraction and Mossbauer spectroscopy. The elastic limit of the microstructures decreases with increasing amounts of retained austenite. Refining of the austenite distribution increases the elastic limit. Low elastic limits are mainly due to low flow stresses in the austenite and not internal stresses. The elastic limit correlates with the largest austenite free-mean path by a Hall-Petch type equation. The elastic limit increases with decreasing intercritical austenitizing temperature in the SAE 52100 due to (1) a lower carbon content in the matrix reducing the retained austenite levels and (2) retained carbides that refine grain size and, therefore, the austenite distribution in quenched specimens. The microplastic response of stable austenite-martensite composites may be modeled by a rule of mixtures. In the microplastic region, the strain is accommodated by successively smaller austenite regions until the flow strength matches that of the martensite. Reheating and quenching refines the microstructure and renders the austenite unstable in the microplastic regime, causing transformation of the austenite to martensite by a strain-induced mechanism. The transformation of austenite to martensite occurs by a stress-assisted mechanism in medium carbon steels. The low elastic limits in medium carbon steels were due to the inability of the strain from the stress-assisted transformation of austenite to martensite to balance the plastic strain accumulated in the austenite.

Influence of carbon content on microstructure and tempering behaviour of 2 1/4 Cr 1 Mo steel

Abstract: Transmission electron microscopic studies aimed at elucidating the effect of carbon level on the tempering behaviour of 2 1/4 Cr 1 Mo steels have been carried out. Specimens with two different carbon levels (0.06% and 0.11 %) were cooled in flowing argon gas (AC) from an austenitization temperature of 1323 K and tempered at 823, 923 and 1023 K for times ranging from 2 to 50 h. The tempering behaviour at these temperatures for the two carbon levels is found to differ in the nature of secondary hardening at lower temperatures, variation in the time to peak hardness and the saturation level of hardness at long tempering times. Based on a detailed study, using analytical electron microscopy, on the morphology, crystallography and microchemistry of secondary phases, the factors governing the observed variations in tempering behaviour are related to the difference in the dissolution rate of bainite, nucleation of acicular M2C carbides and transformation rate of primary carbides into secondary alloy carbides. The carbides which promote softening were identified as M7C3, M23C6 and M6C, whereas hardening is mainly imparted by M2C.

Effects of Initial Temperature and Tempering Medium on Thermal Tempering of Dental Porcelains

Abstract: The objective of this study was to test the hypothesis that quenching of porcelain in silicone oil rather than in compressed air will significantly increase the flexure strength by reducing the potential for crack formation during transient cooling. A secondary hypothesis to be tested is that the initial tempering temperature can be reduced significantly below the porcelain maturing temperature of 982°C but well above Tg without a decrease in strength. Opaque-body porcelain disks, 16 mm in diameter and 2 mm in thickness, with a thermal contraction mismatch (Δα) of -1.5,0, and +3.2 ppm/°C were tempered from initial temperatures of 650, 750, 850, and 982°C in silicone oil with kinematic viscosities of 50,1000, and 5000 centistokes. Porcelain disks were also subjected to three cooling procedures in air: slow cooling in a furnace (SC), free convective cooling in a laboratory bench (FC), and tempering (T) by blasting the surface of body porcelain with air.The crack size induced by a Vickers microhardness inden...

Effects of tempering on the sliding-wear behavior of a sintered high speed steel. A quantitative image analysis approach

Abstract: Tribological properties are considered as system properties and not as intrinsic properties of materials. The great number of parameters which can influence the wear resistance does not permit one to simply characterize a material as good'' or bad'' for low-wear applications. However, the wear behavior of materials is strongly dependent on microstructural parameters: type and mechanical properties of the matrix, second phase distribution, presence of hard particles, solid lubricants or pores. High speed steels are conventional cutting tool materials with a high wear resistance. The purpose of the present work is the investigation of the microstructure of a powder metallurgical M3 class 2 high speed steel before and after tempering at 600[degree]C, by means of the development of Quantitative Image Analysis (QIA) techniques for analyzing complex microstructures such as those exhibited by high speed steels. In particular, the effect of tempering on the mean size and distribution of the primary M[sub 6]C and MC carbides, as well as on the porosity, is studied. These microstructural features influence to a significant degree the general wear behavior of high speed steels. Therefore, the results of Quantitative Image Analysis are discussed in association with the role of primary carbides and porosity on themore » tribological properties of the studied material.« less

Nozzle assembly for a flat-glass tempering machine

Abstract: A nozzle assembly for a flat-glass tempering machine having a nozzle cover (2) which includes two distinct types of orifices side by side. A first series of orifices (7,8) are linked to a first source of compressed air, a compressor (11), and a second series of orifices (6) are linked to a second source of compressed air, a blower (12). Thus, the different orifices supply air of different pressures, suitable for tempering thin glass sheets, and an increase in cooling power can be achieved together with reduction in size of the compressor and blower.

Wearable ductile iron

Abstract: The invention discloses a kind of nodular cast iron and its technological process. Its composition is (wt.%): C 2.8-3.8%, Si 3.0-4.0%, Mn 1.8-3.5%, Cu 0.3-1.0%, Re 0.02-0.08%, Mg 0.015-0.06%, B 0.009-0.025, Fe and impurities the rest. After quenching and low temp. tempering, its tensile strength reaches 800-1200 N/sq.mm, impact toughness 20-40 J/sq.cm, and hardness HRC 35-55. It is an ideal wear resistant material for making lining jplate of ball grinding mill.

Production of steel with high strength and high toughness from non-heat-treated steel

Abstract: PURPOSE:To reduce the weight of a structure by simplified and inexpensive means by subjecting a steel, having a specific composition containing Cr, Mo, B, Ti, etc., to hot working, to cold working at specific amount of strain, and then to specific tempering treatment. CONSTITUTION:The steel has a composition consisting of, by weight, 0.05-0.25% C, 0.10-1.00% Si, 0.50-3.00% Mn, =10min. By this method, the use of the non-heat-treated steel as heavy weight structural material is made possible.

High strength and high toughness martensitic stainless steel and method of manufacturing the same

Abstract: A high strength, high toughness stainless steel consisting, by weight, of C more than 0.16% but less than 0.25%, Si not more than 2.0%, Mn not more than 1.0%, Ni not more than 2.0%, Cr from 11 to 15%, Mo not less than 0.5% but less than 3.0%, Co from 12 to 21%, at least one kind selected from the group consisting of V from 0.1 to 0.5% and Nb less than 0.1% which at least one kind is added as occasion demands, and the balance Fe and incidental impurities. This steel is produced by a method comprising the steps of: preparing a stainless steel having the composition of any one of the claims 1 to 4; subjecting the stainless steel to a solution heat treatment at a temperature of 950 to 1150° C.; quenching the steel; subjecting the steel to a sub zero treatment at a temperature of -50° to -100° C.; and subjecting the steel to a tempering at a temperature of 120° to 450° C.