Showing papers on "Tempering published in 1985"

Mechanical properties of 0. 40 Pct C-Ni-Cr-Mo high strength steel having a mixed structure of martensite and bainite

Abstract: A study has been systematically made of the effect of bainite on the mechanical properties of a commercial Japanese 0.40 pct C-Ni-Cr-Mo high strength steel (AISI 4340 type) having a mixed structure of martensite and bainite. Isothermal transformation of lower bainite at 593 K, which appeared in acicular form and partitioned prior austenite grains, in association with tempered marprovided provided a better combination of strength and fracture ductility, improving true notch tensile strength (TNTS) and fracture appearance transition temperature (FATT) in Charpy impact tests. This occurred regardless of the volume fraction of lower bainite present and/or the tempering conditions employed to create a difference in strength between the two phases. Upper bainite which was isothermally transformed at 673 K appeared as masses that filled prior austenite grains and had a very detrimental effect on the strength and fracture ductility of the steel. Significant damage occurred to TNTS and FATT, irrespective of the volume fraction of upper bainite present and/or the tempering conditions employed when the upper bainite was associated with tempered martensite. However, when the above two types of bainite appeared in the same size, shape, and distribution within tempered martensite approximately equalized to the strength of the bainite, a similar trend or a marked similarity was observed between the tensile properties of the mixed structures and the volume fraction of bainite. From the above results, it is assumed that the mechanical properties of high strength steels having a mixed structure of martensite and bainite are affected more strongly by the size, shape, and distribution of bainite within martensite than by the difference in strength between martensite and bainite or by the type of mixed bainite present. The remarkable effects of the size, shape, and distribution of bainite within martensite on the mechanical properties of the steel are briefly discussed in terms of the modified law of mixtures, metallographic examinations, and the analyses of stress-strain diagrams.

The nitriding behaviour of iron-chromium-carbon alloys

Abstract: The nitriding behaviour of an FeCrC (3.16 wt% Cr, 0.20 wt% C) alloy, as a model system for En40B (a classical gas-nitriding steel), was investigated. By comparing the response of a hardened structure, a quenched and tempered structure and an annealed structure, the effect on nitriding of different initial chromium and carbon disbributions over the phases present could be studied. The structure after nitriding was described employing metallographic methods (optical and scanning electron microscopy; hardness measurements), electron microprobe analysis (concentrationdepth profiles) and X-ray diffractometry (residual macrostress determination; phase identification). Further the weight and thickness increases of the specimens during nitriding were determined. During initial stages of nitriding, excess-nitrogen uptake and the development of grain-boundary carbides and a compressive residual surface macrostress took place. At later stages discontinuous precipitation, void formation, decarburization and relaxation of the compressive residual macrostress occurred. The observations lead to a model description for the nitriding of an FeCrC alloy.

The stability of precipitated austenite and the toughness of 9Ni steel

Abstract: A correlation was confirmed between the good low temperature Charpy toughness of 9Ni steel and the stability of its precipitated austenite against the martensitic transformation. Changes in the microstructure during isothermal tempering were studied in detail. The austenite/martensite interface is originally quite coherent over ∼100 A distances. With further tempering, however, the dislocation structure at the austenite/martensite interface changes, and this change may be related to the increased instability of the austenite particles. The reduction in austenite carbon concentration does not seem large enough to account for the large reduction in austenite stability with tempering time. The strains inherent to the transformation of austenite particles create dislocation structures in the tempered martensite. The large deterioration of the Charpy toughness of overtempered material is attributed, in part, to these dislocation structures.

Sulfide stress cracking of high strength modified Cr-Mo steels

Abstract: The influence of composition, heat-treatments, and microstructure of quenched and tempered Cr-Mo steels on their behavior under sulfide stress corrosion cracking is studied. Starting from a lCr-0.2Mo steel, with a UTS of 1015 MPa, laboratory heats of lCr-0.8Mo, lCr-0.2Mo-V, lCr-0.2Mo-V-Ti, and lCr-0.8Mo-V-Ti steels are prepared and tempered to UTS of 900 to 1000 MPa. SSC tests are conducted in NACE solutions and show the beneficial influence of isolated or combined Mo, V, and Ti additions. The microstructural characterizations and a fundamental study of hydrogen permeation and hydrogen trapping in the microstructure (through high resolution autoradiography and vacuum desorption measurements) give the explanation of the SSC behavior of the steels. The good performances of the lCr-0.8Mo-V-Ti steel are attributed to the precipitation of very finely dispersed particles with an MC carbide type structure, which act both by retarding the tempering process and playing a role of good traps for hydrogen.

Crystallography and tempering behavior of iron-nitrogen martensite

Abstract: Iron-nitrogen martensite was prepared by the gaseous nitrogenization of iron in the austenite-phase field, followed by quenching. Low- and high-nitrogen contents (lathvs plate morphology) were investigated. Optical microscopy, transmission electron microscopy and diffraction, and differential thermal analysis were employed to study the crystallography and the tempering behavior of the martensites. The orientation relation between austenite and martensite, the habit plane and types of (post-) transformation twins were determined. Tempering-induced changes in hardness and release of heat were related to structural changes as revealed by electron diffraction. Differences with analogous iron-carbon martensites were discussed. Aging at room temperature leads to nitrogen diffusion-controlled precipitation of coherentα″-Fe16N2 platelets, which process is completed after about one day. Aging at higher temperatures (up to about 475 K) results in incoherentα″particles, which, at temperatures above 460 K, exhibit small deviations (≃18 deg) from the usual {001}α′/α habit plane.

The mechanical stability of precipitated austenite in 9Ni steel

Abstract: The strains inherent to the martensitic transformation of austenite particles in 9Ni steel create dislocation structures in the tempered martensite. These dislocation structures were studied by the complementary techniques of X-ray line profile analysis and transmission electron microscopy. The energy required to form these dislocation structures affects the thermodynamics of the transformation. We propose that changes in these dislocation structures reduce the “mechanical stability” of the austenite particles as they grow larger during isothermal tempering.

Carbide precipitation, grain boundary segregation, and temper embrittlement in NiCrMoV rotor steels

Abstract: This paper presents a study of carbide precipitation, grain boundary segregation, and temper embrittlement in NiCrMoV rotor steels. One of the steels was high purity, one was doped with phosphorus, one was doped with tin, and one was commercial purity. In addition, two NiCrV steels, one high purity and one doped with phosphorus, were examined. Carbide precipitation was studied with analytical electron microscopy. It was found that after one hour of tempering at 600 ‡C only M3C carbides were precipitated in the NiCrMoV steels. These were very rich in iron. As the tempering time increased, the chromium content of the M3C carbides increased significantly, but their size did not change. Chromium rich M7C3 precipitates began to form after 20 hours of tempering, and after 50 hours of tempering Mo-rich M2C carbides were precipitated. Also, after 100 hours of tempering, the matrix formed bands rich in M3C or M7C3 and M2C particles. Tempering occurred more rapidly in the NiCrV steels. Grain boundary segregation was studied with Auger electron spectroscopy. It was found that the amount of phosphorus and tin segregation that occurred during a step-cooling heat treatment after tempering was less if a short time tempering treatment had been used. It will be proposed that this result occurs because the low temperature tempering treatments leave more carbon in the matrix. Carbon then compctes with phosphorus and tin for sites at grain boundaries. This compctition appears to affect phosphorus segregation more than tin segregation. In addition to these two impurity elements, molybdenum and nickel segregated during low temperature aging. The presence of molybdenum in the steel did not appear to affect phosphorus segregation. Finally, it will be shown that all of the steels that contain phosphorus and/or tin exhibit some degree of temper embrittlement when they are aged at 520 ‡C or are given a step-cooling heat treatment. Of the NiCrMoV steels, the phosphorus-doped steel showed the least embrittlement and the commercial purity steel the most. The phosphorus-doped NiCrV steel was also more susceptible to temper embrittlement than the phosphorus-doped NiCrMoV steel. This latter difference was attributed to molybdenum improving grain boundary cohesion. It was also found that as the segregation of phosphorus or tin to the grain boundaries increased, the measured embrittlement and the amount of intergranular fracture increased. However, there was a large amount of scatter in all of these data and the trends were only qualitative. All parts of this study are compared in detail to others in the literature, and general trends that can be discerned from all of these results are presented.

The effect of microstructural changes on the caustic stress corrosion cracking resistance of a NiCrMoV rotor steel

Abstract: This paper presents a study of the effects of microstructural changes on the caustic stress corrosion cracking resistance of a NiCrMoV rotor steel. All tests were run in 9 M NaOH at 98 °C and at an electrochemical potential of −400 mVHg/Hgo. Different microstructures were obtained by tempering martensitic samples for different times at 600 °C or by using a slow controlled cool from the austenite to produce a bainitic structure. The results show that heat treatments which produced large, chromiumrich carbides are beneficial. These carbides are preferentially corroded and cause pits to form at the crack tip. We propose that these pits cause crack tip blunting and slow crack propagation. It is further shown that, although changes in microstructure can produce improvements in the susceptibility to stress corrosion cracking, these changes cannot compensate for the detrimental effects of phosphorus segregation to grain boundaries.

Induction tempering of steel: Part I. Development of an effective tempering parameter

Abstract: Time-temperature relationships for short-time tempering cycles were determined. The accuracy of conventional tempering parameters, such as the one proposed by Grange and Baughman, for short-time treatments at a fixed temperature (“isothermal” treatments) was established in salt-pot experiments for a variety of carbon and alloy steels fully hardened to martensite. In addition, the concept of an effective tempering parameter for tempering processes consisting of continuous heating and cooling (typical of induction-heating techniques) was developed. Determination of this effective tempering parameter is based on finding an effective time and temperature which allows the continuous cycle to be described in terms of an equivalent isothermal cycle. The applicability of this new technique was verified through laboratory induction tempering trials.

Production of hot rolled steel products having high strength and high toughness

Abstract: PURPOSE: To obtain the titled steel products without requiring a tempering treatment entailing hardening and tempering after reheating by subjecting a specifically composed steel to quick cooling under prescribed conditions then to direct hardening after hot rolling and subjecting the steel to self tempering under prescribed conditions by the heat internally retained therein. CONSTITUTION: The ingot contg., by weight, 0.20W0.60% C, 0.10W0.35% Si, 0.30W1.80% Mn, and if necessary ≥1 kinds among ≤1.50% Cr, ≤0.30% Mo and ≤0.005% S and consisting of the balance iron is hot rolled. The steel is quickly cooled from A 3 WA 3 +150°C down to the temp. above 50°C and below the M s point after the end of said rolling to provide the internally retained heat in such a manner that the surface temp. attains 100W600°C to effect the self tempering. The rolled steel products, more particularly, rolled steel bars, which consist essentially of the tempered martensite structure in the surface layer part and tempered martensite and bainite or supercooled ferrite pearlite structure in the central part and are much improved in the strength and toughness are thus obtd. COPYRIGHT: (C)1987,JPO&Japio

High strength steel excelling in resistance to delayed fracture

Abstract: PURPOSE: To develop a high strength steel having superior yield strength and resistance to delayed fracture by subjecting an Ni-Cr-Mo low alloy steel containing trace constituents of various kinds to heat treatment under specific conditions. CONSTITUTION: The low alloy steel contains, by weight, 0.15W0.45% C, <1.50% Si, 0.01W1.50% Mn, 0.10W4.00% (not including 0.10%) Ni, 0.50W2.00% Cr, either or both of Mo and W in the amount satisfying Mo+1/2W=0.30W1.50%, 0.01W0.20% V, 0.005W0.20% Nb, 0.01W0.15% Zr and 0.01W0.10% Al, to which specific small amounts of Cu, Ca, Ti and B are further added independently or in combination. This steel is subjected to hardening from the temp. of AC 3 point or above and then to tempering from the temp. between 580° and AC 1 point under the condition that PLM represented by expression (1) is 16.8×10 3 or more. In this way, the steel stock having austenite grains of ASTM No.8.5 or above, excelling in resistance to delayed fracture and suitable for ultra-high strength oil well pipes can be obtained. COPYRIGHT: (C)1986,JPO&Japio

Heat treatment deformation of steel products

Abstract: The heat treatment deformation of steel products is reviewed and the thermal stress, which is one of the initiators of the deformation, is theoretically analysed taking into account transformation. Other initiators are also discussed, i.e. stress relaxation on heating, creep at high temperature, and change of microstructure on tempering. It was found that the thermal stress during quenching changes the profile of steel products, decreased long axis, increased short axis, and convex cross–section for non–hardenable and for marquenched or oil–quenched small steel parts, and increased long axis, decreased short axis, and concave cross–section for water/oil–quenched hardenable steels. These differences are the results of the different strain hardening rates of the various phases and the temperature distribution through the cross–section over the temperature range of martensite transformation. Some solutions to the problems of deformation are also discussed.MST/21

Prediction of the Remaining Life of High-Temperature/Pressure Reactors Made of Cr-Mo Steels

Abstract: The Cr-Mo steels widely used for pressure vessels have a potential for temper embrittlement. Therefore, embrittlement during long-term service is expected, and it leads to the decrease of the critical flaw size of brittle fracture and/or to the reduction of the remaining life of a pressure vessel. In this paper, the concept of a remaining life prediction model is presented. And also, experimental data on the temper embrittlement and fracture toughness after long-term exposure and subcritical crack growth rate, such as creep crack growth rate, were collected, and the data were analyzed for use in the remaining life prediction model. Examples of the remaining life prediction of a 2 1/4 Cr-1Mo steel hydrogenation reactor and a 1 1/4 Cr-1/2 Mo steel catalytic reforming reactor were calculated from the statistical data base.

Sintering and Heat Treatment of Steels Made from A Partially Prealloyed Iron Powder

Abstract: Compacts of partially prealloyed steels, containing 1·75%Ni, 1·5%Cu, 0·5%Mo, and 0, 0·3, or 0·5%C, with initial porosities of about 6 or 15%, were sintered at 1150°C for times ranging from 0·25 to 128 h and cooled through the critical range at about 30 K min −1. The chemical heterogeneity of the compacts, which was very marked after short sintering times, gradually decreased with increasing sintering time, but complete homogeneity was not achieved in 128 h. The changes in microchemistry with elapse of sintering time brought about complex microstructural changes in the relatively slowly cooled compacts. These caused the mechanical properties of the compacts to vary in a complex manner with sintering time. Optimum properties of sintered and relatively slowly cooled compacts were obtained after sintering times of ∼ 1 h, when the compacts were still very heterogeneous. Other compacts that had been sintered for 1 h were subjected to conventional austenitizing, quenching, and tempering treatments. The ...

Method and steel alloy for producing high-strength hot forgings

Abstract: This invention concerns a method and a steel alloy for producing high-strength hot forgings, the forging billet being cold-sheared from cast or hot-rolled steel and the finished forging being immediately quenched from the forging temperature, machined and used without tempering. The forgings can also be assembled by fusion welding a number of parts together. For manufacturing the forging, a steel is used with the following composition: the remainder being iron and the usual impurities. The tensile strength of the forgings when quenched and without tempering is at least 900 N/mm 2 , 0.2-proof stress at least 700 N/mm 2 and the impact toughness at room temperature is at least 25 J measured on a V-notched impact testpiece. The hardness of steel, when air cooled, is at most 225 HB.

Fatigue crack growth of SNCM 439 steel in high pressure hydrogen at room temperature.

Abstract: The fracture toughness and the fatigue crack growth properties of heat treated SNCM439 steel were investigated under high pressure of hydrogen up to 9.9MPa at room temperature.The results obtained are as follows;(1) The fracture toughness, KQ value, of the steel in hydrogen was smaller than that in argon independent of heat treatments. KQ values of the quenched and the tempered steel were smaller than that of the annealed steel in hydrogen. On the fracture surface of these steels, the streched zone was not observed in hydrogen but in argon.(2) The fatigue crack growth rate of the steel in hydrogen was larger than that in argon, and KFc of the steel in hydrogen was smaller than that in argon independent of heat treatments. The order to hydrogen susceptibility of fatigue crack growth properties increased from the annealed to the quenched and then to the tempered steel.(3) The quasi-cleavage fracture did not occur in argon but in hydrogen on the fatigue fracture surface of the annealed steel. Both the amount of the intergranular fracture and the surface roughness of the transgranular fracture in hydrogen were larger than those in argon on the fatigue fracture surface of the quenched and the tempered steels.

Tough and hard bolt steel

Abstract: PURPOSE: To improve the delayed fracture and impact characteristics of a steel contg. specified amounts of C, Si, Mn, Cr, B, Al, Ti and Zr by tempering the steel at a prescribed temp. CONSTITUTION: A tough and hard bolt steel contg., by weight, 0.25W0.4% C, ≤0.5% Si, 0.4W1% Mn, 0.4W1.5% Cr, 0.0005W0.005% B, 0.01W0.08% Al and 0.01W0.1% Ti and/or 0.01W0.1% Zr is tempered at ≥380°C or ≤300°C to obtain 110W145kgf/mm 2 tensile strength, 30W44 hardness HR c and ≥-0.356B+57.5kgfm/ cm 2 impact value. The minimum impact value is 8kgfm/cm 2 . COPYRIGHT: (C)1987,JPO&Japio

Production of heat resisting steel having excellent creep rupture resistance characteristic

Abstract: PURPOSE:To produce a heat resisting steel having an excellent creep rupture resistance characteristic by subjecting a steel contg. a specific ratio each of C, Si, Mn, P, S, Ni, Cr, Mo, etc. to heating, hot working, accelerated cooling and tempering under specific conditions. CONSTITUTION:The steel contg., by weight 5, 0.02-0.25% C, =1050 deg.C. The steel is then subjected to hot working at 850-1000 deg.C and at least at 20% cumulative draft and is then subjected to accelerated cooling at the fastest possible point of the time. The steel is further tempered at 550-750 deg.C, by which the heat resisting steel is produced. The heat resisting steel having good creep rupture strength and excellent toughness is thus obtd.

Effect of tempering temperature on monotonic and cyclic properties of a high–strength low–alloy chain steel

Abstract: The influence of tempering temperature in the range 200–600°C on the monotonic and cyclic response of a high-strength, low–alloy steel used for haulage chains has been investigated. Static properties are little affected by tempering up to 400°C, with a small loss of strength arising from carbide coarsening. At higher tempering temperatures, dislocation annihilation is substantial and the strength falls markedly. On undergoing high–strain fatigue, the alloy exhibits cyclic softening at all tempering temperatures, but with a maximum of about 25% after a 400°C temper. The microstructural changes producing this are difficult to detect directly, but it is thought that dislocation unpinning has an important role. For tempering temperatures in excess of 400°C, the reduced softening can clearly be equated with a dislocation redistribution and the formation of cell substructure within the ferrite grains. Estimations of the magnitude of the various components of strength are made.MST/199

Split heat mechanical property comparison of ESR and VAR 4340 steel

Abstract: This report addresses a mechanical property characterization of a split argon-oxygen decarburized (AOD) heat of 4340 steel which was further processed by vacuum arc remelting (VAR) and electroslag remelting (ESR) into 12.7 cm (5 inch) square forgings. Properties examined were hardness, tensile, Charpy V-notch impact, and fracture toughness as a function of tempering temperature over the range of 163 °C (325 °F) to 649 °C (1200 °F)for both the longitudinal and transverse orientations. Microstructural aspects are also addressed. Results indicate nearly identical tensile properties for the ESR and VAR processed material. Ductility measurements were anisotropic for both remelting techniques. Charpy impact values were consistently higher for VAR material, especially at tempering temperatures exceeding 260 °C (500 °F). A significant amount of scatter in impact data was observed at tempers from 163 °C (325 °F)to 204 °C (400 ° F ). Fracture toughness, Kq, was higher for VAR material in both the LT and TL orientations for tempering temperatures up to 427 °C (800 °F). It is believed that the lower fracture toughness of the ESR material is associated with the presence of calcium aluminate inclusions, and possibly the material’s higher gas content.

High strength bolt

Abstract: A high strength bolt made of a steel having a specifically defined chemical composition, ie, by weight C: 030-050%; Si: not more than 015%; Mn: not more than 040%; Cr: 030-150%; Mo: 010-070%; and V: 015-040%, the balance being Fe and inevitable impurities such as P, S, etc in trace amount The manufacturing method therefor is featured in a strictly controlled heat treatment in respect to the temperature range such as: hardening by quenching from 940°±10° C and tempering 575°±25° C

Manufacture of wear resistant steel sheet having satisfactory weldability

Abstract: PURPOSE: To obtain a low-cost wear resistant steel sheet having satisfactory weldability by subjecting a steel having a prescribed composition contg restricted amounts of C, Cr and Mo which deteriorate weldability to quenching and tempering under specified conditions CONSTITUTION: A steel consisting of 010W019% C, 005W055% Si, 090W160% Mn and the balance Fe and having 035W044% Ceq represented by the formula is prepd The steel is hot rolled, quenched directly from 950W850°C or quenched after reheating to 900W950°C and tempered at 300W500°C Thus, a wear resistant steel sheet having superior bendability and causing no weld crack is obtd The steel sheet is suitable for construction and transfer machinery such as a power shovel COPYRIGHT: (C)1987,JPO&Japio

Production of steel having high strength and high ductility

Abstract: PURPOSE:To obtain a heat-treated steel provided with high strength, excellent ductility and toughness in a combined austempering method of a specifically composed middle and high carbon steel by stabilizing positively residual austenite. CONSTITUTION:A middle and high carbon steel contg., by weight, 0.40-1.10% C and 0.8-2.7% Si among the elements in the steel is held at a temp. region of the Ac3 point -Ac3 point of said steel +150 deg.C to austenitize the steel. The steel is then hardened from said temp. region to a temp. region of the Ms point -M80% point of the steel. The steel is thereafter heated from the state in which >=20vol% untransformed austenite is maintained to a temp. region of 300- 450 deg.C so that the tempering of martensite and the bainite transformation of the untransformed austenite is effected. The steel is at the same time cooled to an ordinary temp. by regulating the holding time in said heating temp. region in such a way that the residual amt. of the austenite stable at an ordinary temp. attains >=5vol%. The bainite transformation is interrupted by such regulation. The steel in which the three phases, martensite, bainite and residual austenite, coexist, is thus obtd.

Device for tempering in a magnetic field

Abstract: A continuous-flow furnace for tempering ferromagnetic layers is specified, which has a magnet for producing a magnetic field, and a heating coil for producing a temperature gradient. The continuous-flow furnace is used for magnetising ferromagnetic layers and for reducing the anistropic field strength.

Method for producing high-strength steel having improved weldability

Abstract: METHOD FOR PRODUCING HIGH-STRENGTHSTEEL HAVING IMPROVED WELDABILITY ABSTRACT OF THE DISCLOSURE High-strength steel having a tensile strength of 80 kgf/mm2 or more is produced by on-line quenching or on-line quenching and tempering. The steel has also excellent low-temperature toughness and excellent weldability, which makes high temperature preheating unnecessary prior to welding. The composition is:C = 0.04% to 0.11%; Si ? 1.0%; Mn = 0.5% to 2.00%;Mo = 0.10% to 1.0%; Nb = 0.005% to 0.05%; B ? 0.01%;Al ? 0.1%; and N ? 0.0060%.

Susceptibility to hydrogen attack of a thick-section 3Cr–1 Mo–1 Ni pressure-vessel steel-role of cooling rate

Abstract: A study has been made of the susceptibility to hydrogen attack of a newly developed 3Cr–1 Mo–1Ni pressure-vessel steel, intended for use in coal-conversion vessels, following long-term exposure to high-pressure (14-17 MPa) gaseous hydrogen at 550 and 600°C; the results are compared to the behaviour of 2·25Cr–1Mo steel. To simulate the condition of both surface and mid-section locations of thick-section (400 mm) plate during commercial normalizing, oil quenched and slowly cooled (8 K min−1) structures were examined after tempering at 650 and 700°C, with respect to their strength, ductility, and impact toughness properties. Compared to unexposed samples, structures exposed to hydrogen were observed to show some softening (up to 20% reduction in yield stress) and ‘embrittlement’ (up to 22% reduction in upper-shelf Charpy energies and increases in the transition temperatures by 65–100 K), although there were no visible signs of major microstructural damage. Moreover, the behaviour of the oil-quenched ...