Showing papers on "Tempering published in 1980"

Carbide reactions (M3C→M7C3→M23C6→M6C) during tempering of rapidly solidified high carbon Cr-W and Cr-Mo steels

Abstract: Carbide transformations of M3C → M7C3 → M23C6 → M6C and crystallographic relationships among these carbides were examined by transmission electron microscopy. Two kinds of high carbon-chromium steels containing tungsten or molybdenum were quenched rapidly from the melts and tempered at temperatures up to 700°C. By tempering at 600°C, M7C3 carbides nucleated mostly on cementite/ferrite interfaces and grew inward the cementite byin- situ transformation.In-situ transformations from M7C3 to M23C6 and from M23C6 to M6C were also found in these alloy steels during tempering at higher temperatures. Mutual relationships of crystal orientations among M3C, M7C3, M23C6 and M6C were decided as follows: {fx739-01}.

Structure-property relations and the design of Fe-4Cr-C base structural steels for high strength and toughness

Abstract: Some design guidelines for improving strength-toughness combinations in medium car-bon structural steels are critically reviewed. From this, quaternary alloy development based on Fe/Cr/C steels with Mn or Ni additions for improved properties is described. Transmission electron microscopy and X-ray analysis reveal increasing amounts of retained austenite in these alloys with Mn content up to 2 wt pct and Ni additions at 5 wt pct after quenching from 1100°C. A corresponding improvement in toughness properties is also found. Grain refining results in a further increase in the amount of retained austenite. In addition, the excellent combinations of strength and toughness in these quaternary alloys are attributed to the production of dislocated lath martensite from a homogeneous austenite phase free from undissolved alloy carbides. The question of thermal instability of retained austenite following tempering is considered in detail and it is shown that the decomposition of retained austenite is closely related to the ease of nucleation and growth of cementite. Thus, graphitizing alloying elements such as Ni are beneficial in postponing the decomposition of retained austenite.

High tensile steel and process for producing the same

Abstract: A high tensile steel which has a satisfactory yield strength of 60 kg/mm2 or more and excellent resistances to sulfide corrosive cracking and corrosion, and which comprises, as indispensable components, 0.05 to 0.50 wt % of C, 0.1 to 1.0 wt % of Si, 0.1 to 2.0 wt % of Mn, 0.05 to 1.50 wt % of Co and the balance consisting of Fe, is produced by hot- or cold-rolling it, rapidly heating the rolled steel to austenitize it, quenching the austenitized steel and, finally, tempering the quenched steel at a temperature not higher than the Ac1 point of the steel.

Thermal processing of ferritic 5Mn steel for toughness at cryogenic temperatures

Abstract: It is shown that a thermal treatment which combines grain refinement with an intercritical temper (the 2BT treatment) may be used to achieve a promising combination of strength and toughness in a nickel-free ferritic steel of nominal composition Fe-5Mn-0.2Mo-0.04C at temperatures as low as -196 °C. The properties achieved are attributed to a symbiotic influence between the grain refinement treatment and the introduction of thermally stable retained austenite during intercritical tempering, a conclusion supported by a comparison of the results to those obtained with simpler heat treatments. The influence of carbon, manganese, and nickel additions to the base compositions are studied. An increase in carbon content above 0.04 wt pct causes a deterioration in toughness, as does an increase in manganese to 8 wt pct. An addition of 1 to 3 wt pct nickel is beneficial giving an increase in alloy strength at -196 °C without loss of toughness.

Martensite lattice changes during tempering

Abstract: An X-ray diffractometer study of martensite formed in an 18 wt pct nickel, 0.98 wt pct carbon austenite single crystal yields the shapes, positions, and integrated intensities of 200, 020, and 002 peaks. Martensite, which forms below − 60 °C, was tempered at successively higher temperatures from −45 to 450 °C. The results show that after subambient aging, during which C atoms in c-oriented octahedral sites have clustered, carbide precipitation starts and small regions (∼30A in the [001]) with negative tetragonality appear. Upon subsequent tempering these are augmented by larger regions which have small positive tetragonality. In this process the “c” lattice parameter changes markedly but the “a” and “b” lattice parameter increase very little. These results indicate the formation of carbon depleted martensite which is coherently strained by the carbide particles. At and just above 100 °C the 200, 020, and 002 peaks all become doublets as the martensite matrix discontinuously breaks free of coherency and becomes highly imperfect ferrite. This change also occurs during the so-called “first stage of tempering.” Further tempering decreases the defect content of this ferrite. The lattice of the martensite is extensively reoriented during tempering just above room temperature. These reorientations probably accommodate the lattice parameter changes described above and may be carried out by movement of twin boundaries.

Theoretical and Practical Aspects of Rough Rice Tempering

Abstract: A theoretical model was developed to simulate the dry-ing and tempering of rough rice. The model was bas-ed on liquid diffusion theory and assumes the grain to consist of a spherical core (starchy endosperm) surround-ed by two concentric shells (bran and hull respectively). During tempering, measured changes in relative humidi-ty in the void volume of a mass of rough rice were com-pared to predicted changes in surface liquid concentra-tion of a rough rice kernel. The results of modeling are presented in terms of equations which predict tempering time. The effects of drying variables on the tempering model were investigated. Multipass drying was simulated to determine how various degrees of tempering effected the drying curve.

The effect of heat treatment on microstructure and cryogenic fracture properties in 5Ni and 9Ni steel

Abstract: Heat treatments were utilized in 5Ni and 9Ni steel which resulted in the development of tempered microstructures which contained either no measurable retained austenite (<0.5 pct) or approximately 4 to 5 pct retained austenite as determined by X-ray diffraction. Microstructural observations coupled with the results of tensile testing indicated that the formation of retained austenite correlated with a decrease in carbon content of the matrix. Relative values ofKIC at 77 K were estimated from slow bend precracked Charpy data using both the COD and equivalent energy measurements. In addition, Charpy impact properties at 77 K were determined. In the 9Ni alloy, optimum fracture toughness was achieved in specimens which contained retained austenite. This was attributed to changes in yield and work hardening behavior which accompanied the microstructural changes. In the 5Ni alloy, fracture toughness equivalent to that observed in the 9Ni alloy was developed in grain refined and tempered microstructures containing <0.5 pct retained austenite. A decrease in fracture toughness was observed in grain refined 5Ni specimens containing 3.8 pct retained austenite due to the premature onset of unstable cracking. This was attributed to the transformation of retained austenite to brittle martensite during deformation. It was concluded that the formation of thermally stable retained austenite is beneficial to the fracture toughness of Ni steels at 77 K as a result of austenite gettering carbon from the matrix during tempering. However, it was also concluded that the mechanical stability of the retained austenite is critical in achieving a favorable enhancement of cryogenic fracture toughness properties.

The structure of tempered martensite and its susceptibility to hydrogen stress cracking

Abstract: A series of 4130 steels modified with 0.50 pct Mo and 0.75 pct Mo were tempered at temperatures between 300 and 700 °C for one hour. The changes in the carbide dispersion and matrix substructure produced by tempering were measured by transmission electron microscopy. These measurements were correlated with resistance to hydrogen stress cracking produced by cathodic charging of specimens in three-point bending. Scanning electron microscopy showed that specimens tempered between 300 and 500 °C failed by intergranular cracking while those tempered at higher temperatures failed by a transgranular fracture mode. Auger electron spectroscopy showed that the intergranular fracture was associated with hydrogen interaction with P segregation and carbide formation at prior austenite grain boundaries. Transgranular cracking was initiated at inclusion particles from which cracks propagated to produce flat fracture zones extending over several prior austenite grains. The 4130 steels modified with higher Mo content resisted tempering and showed better hydrogen stress cracking resistance than did the unmodified 4130 steel. The transition in fracture mode is attributed to a decohesion mechanism in the low temperature tempered samples and a pressure mechanism in the highly tempered samples.

Transformations in high-speed steels during cold treatment

Abstract: 1. Shock cooling of quenched steel induces transformation not only of austenite but also martensite. For this reason, the cold treatment should be used for parts and tools with no retained austenite in order to intensify the processes of tempering and precipitation hardening. Tool life increases 20–30% in this case. 2. Cold treatment of tools with 15–20% retained austenite restores the cutting ability to almost the same level as for tools without retained austenite. 3. To prevent cracking and embrittlement of tools and to increase tool life by 50–100%, it is recommended that the cold treatment be conducted after tempering at 560° for 1 h with final tempering at 400° for 30–60 min.

The use of a boron addition to prevent intergranular embrittlement in Fe-12Mn

Abstract: Fe-12 Mn alloys undergo failure by catastrophic intergranular fracture when tested at low temperature in the as-austenitized condition, a consideration which prevents their use for structural applications at cryogenic temperatures. The present research was undertaken to identify modifications in alloy composition or heat treatment which would suppress this embrittlement. Chemical and microstructural analyses were made on the prior austenite grain boundaries within the alloy in its embrittled state. These studies failed to reveal a chemical or microstructural source for the brittleness, suggesting that intergranular brittleness is inherent to the alloy in the as-austenitized condition. The addition of 0.002 to 0.01 wt pct boron successfully prevented intergranular fracture, leading to a spectacular improvement in the low temperature impact toughness of the alloy. Autoradiographic studies suggest that boron segregates to the austenite grain boundaries during annealing at temperatures near 1000 °C. The cryogenic toughness of a Fe-12Mn-0.002B alloy could be further improved by suitable tempering treatments. However, the alloy embrittled if inappropriate tempering temperatures were used. This temper embrittlement was concom-itant with the dissolution of boron from the prior austenite grain boundaries, which reestablishes the intergranular fracture mode.

The influence of thermal history on internal stress distributions in sheets of PMMA and polycarbonate

Abstract: The through-thickness birefringent patterns (nx – nz) of PMMA and polycarbonate (PC) are measured as a function of thickness, cooling rate, and annealing time. A method is demonstrated for separating the elastic stress from the residual birefringence. The residual birefringence is explained as the residual orientation induced when cooling through the galss transition. The shape of the elastic (tempering) stress distribution is apparently independent of the cooling rate and annealing time, the choice of polymer, and the sheet thickness. The magnitude of the tempering stres is dependent on cooling rate but nearly independent of choice of polymer and sheet thickness. The decays of both the tempering stress and the residual orientation are measured as a function of annealing time at 120°C for polycarbonate. The measured birefringence decays only slightly; however, the elastic tempering stress reverts, on annealing, to permanent (anelastic) orientational strain. The tempering stress at the sheet surface is not an adequate criterion for defining toughness in polycarbonate.

Role of carbon in embrittlement phenomena of tempered martensitic 12Cr-0.15%C steel

Abstract: In order to explain the influence of carbon on the embrittlement of 12%Cr steels, a systematic study of the effects of tempering on AISI 410 steel was carried out. Reversible temper embrittlement was detected and related to the mechanical properties and microstructural variations and to the segregation of carbon and alloy elements. Carbon was directly localized on samples using high-resolution autoradiography and was detected whatever its chemical state (in solution or as precipitates). It was observed that embrittlement was associated with the concentration of carbon in solid solution at martensitic lath interfaces but also with a decrease in the elemental carbon content of the prior austenitic interfaces.

Effect of austenitizing temperature on constitution, transformation, and tempering of 9Cr-1Mo steel

Abstract: The effect of solution-treatment (austenitizing) temperature has been investigated on the constitution, transformation, and tempering characteristics of a 9Cr-1 Mo steel. It has been shown that the austenite grain size and phase constitution are markedly influenced by the austenitizing temperature, as also are the transformation characteristics. It has been possible to explain the 15-fold variation in the rate of transformation in terms of the nucleating effect of undissolved carbides or ferrite, and the partitioning of alloying elements to or from the austenite as a function of constitution. Apart from influencing the overall level of hardness obtained on tempering, there was little effect of varying the austenitizing temperature between 900° and 1200°C.

On the scavenging effect of precipitated austenite in a low carbon fe-5, 5ni alloy

Abstract: The scavenging effect of precipitated austenite in a low carbon, commercial Fe-5.5Ni cryogenic alloy was investigated through observation of the dissolution of cementite precipitates during intercritical tempering and study of the associated change in Charpy impact toughness. Cementite precipitates initially located along prior austenite grain boundaries were gradually dissolved into reverted austenite as the intercritical tempering proceeded. The austenite tends to form at or around the carbide particles and may be catalyzed by their presence. The Charpy impact energy is changed through both a decrease in the ductile-brittle transition temperature and an increase in the upper shelf energy. The latter effect is specifically associated with the dissolution of the carbides which act as preferential void nucleation sites in the untempered alloy.

Spring steel with superior wear resistance

Abstract: PURPOSE: To enhance the wear resistance of a high-Si spring steel by adding an adequate amount of one or more among V, Nb and Mo to the steel. CONSTITUTION: To a spring steel contg. 0.50W0.80% C, 1.50W2.50% Si and 0.50W1.50% Mn are added one or more among 0.05W0.50% V, 0.05W0.50% Nb and 0.05W0.50% Mo. V, Nb and Mo carbides are dissolved in austenite by heating during hardening, and a martensite structure contg. a supersatd. solid soln. of these elements is obtd. by quench hardening. Said fine carbides are reprecipitated by tempering, and they hinder the shift of dislocation in the steel, accelerate secondary hardening, and enhance the wear resistance. The fatigue resistance and toughness are also increased. COPYRIGHT: (C)1982,JPO&Japio

Tempering treatment method for inorganic glass

Abstract: PURPOSE:To obtain tempered glass for a watch having high mechanical strength by contacting inorg. glass such as borosilicate glass to a K salt at a high temp. and applying ultrasonic waves to the glass to increase the ion exchange rate of chemical tempering treatment. CONSTITUTION:Inorg. glass such as borosilicate glass is formed into a watch cover glass shape and finished to a mirror surface. This cover glass is preheated, e.g. to 410 deg.C and held in a molten bath of a K salt such as KNO3 of the same temp. After applying ultrasonic waves the glass is allowed to cool, washed with water to remove the K salt, and dried. By this method the rate of chemical tempering treatment is increased, and a tempering effect higher than that of a conventional method is obtd. in a short time.

Replacement of vanadium by niobium in 86–5–2 high-speed tool steels

Abstract: The microstructure and mechanical properties of a series of experimental high-speed steels based on the S6–5–2 (M2) composition have been investigated. In these alloys the 2% vanadium component of the S6–5–2 composition has been partially or completely replaced by niobium additions of up to 3%. It has been shown that niobium-replacement steels have superior cutting properties, which are attributed to the formation of a high volume fraction of niobium-rich carbides. X-ray energy analysis indicates that NbC replaces VC as the MC phase, and niobium changes the chemical composition of the M6C and/or M23C6 carbides. The niobium-replacement grades undergo secondary hardening on tempering, and niobium raises the liquation temperature allowing higher hardening temperatures to be used. Since niobium-rich carbides replace carbides containing the more expensive tungsten, molybdenum, and vanadium alloying elements, it is suggested that niobium could be used to reduce the amounts of these elements needed, and ...

A New Tempering Parameter and Its Application to the Integration of Tempering Effect of Continuous Heat Cycle

Abstract: Synopsis: A new tempering parameter (ƒÉ-value) has been defined basing on Arrhenius' equation so as to express the degree of tempering and to maintain the equivalence of time and temperature over a wide range of tempering conditions. Activation energy of the tempering process governing the changes in such mechanical properities as tensile and yield strength and hardness was determined by using a plain carbon steel and low alloy steels containing manganese, chromium and molybdenum. The activation energies obtained were to be 70 kcal/ mol (295 kJ/mol) in carbon steel and about 100 kcal/mol (420 kJ/mol) in Cr-Mo steel, increasing with alloy contents. Using these activation energies, mechanical properties of tempered steel can be approximately expressed as a function of ƒÉ-value in a linear fashion for any combination of temperature and time, ranging from 400 ° c to 700 •Ž and from 0.01 h to 1 000 h, respectively. In addition, making use of the parameter, an analytical method of tempering effect is applied to a practical heat program by summarization of the tempering effects of two individual processes or integration of the tempering effect over a whole process of heat cylce in which temperature steadily changes. Predicted mechanical properties by this method were in good accordance with observed values.

Process for the improved heat treatment of steels using direct electrical resistance heating

Abstract: A process for the energy efficient heat treatment of steels wherein a steel workpiece is rapidly heated to a temperature above the A 3 temperature of the steel to convert the steel to austenite, the workpiece is then rapidly quenched in a liquid quench medium to convert the austenite to a predominantly martensitic microstructure, and the steel is then tempered by rapid heating while the workpiece is under tension, the tempering serving to convert the steel to a tempered martensitic form. The present invention virtually eliminates the problem of quench cracking and minimizes quench distortion as well as providing a finished product with improved uniformity, improved surface quality, and improved mechanical properties.

Low cycle fatigue behavior of a quenched and tempered niobium bearing HSLA steel

Abstract: The low cycle fatigue behavior of a quenched and tempered niobium (columbium) bearing high strength low alloy steel heat treated to give tempered martensitic microstructures presumably with and without fine niobium carbides was studied by transmission electron microscopy, stress relaxation, X-ray diffraction line broadening and strain-controlled fatigue testing. The steel without the niobium carbides cyclically softened rapidly at all strain amplitudes studied. This softening was attributed to the rearrangement of the dislocation substructure into a cell structure and to the accompanying decrease in internal stress. The steel presumably containing the fine niobium carbides cyclically softened to a lesser extent. This correlated with the observation that dislocations in this steel did not rearrange themselves into a cell structure and, hence, there was less change in the internal stress during cycling. The steel without the niobium carbides exhibited somewhat better strain-life behavior at large strain amplitudes. This was attributed to the cell structure being able to accommodate a greater amount of plastic strain in that steel.

Continuous hardening of high speed steel

Abstract: A wire of high speed steel is hardened and straightened by a continuous method wherein an annealed high speed steel wire is subjected to steps of austenitizing; quenching; tempering and cooling; and then tempering and cooling under tension. The hardened and straightened high speed steel wire can be cut, centerless ground and fluted to make hardened, straight, high speed steel twist drills.

Influence of grain boundaries on fissure formation during impact testing of ferritic stainless steels

Abstract: In the hot-rolled conditions (Fig.l), the microstructure of the steels consisted of elongated coarse ferritic grains (~220fLm long x 40fLm thick), with elongated thin martensitic grains and grain-boundary carbides at the ferrite grain boundaries. Tempering at 750°C produced no change in the ferrite and resulted in the martensite tempering to a fine dispersion of carbides (Fig.2). Normalizing at 950°C caused the martensitic areas to transform to Y which on cooling retransformed to give martensite islands which have a more equiaxed appearance (Fig.3). The volume fraction of the second phase was greater than for the hot-rolled condition but the difference was small (~3 %), suggesting that the major effect of this heat treatment was to change the shape of the martensitic areas. The ferrite/ martensite grain boundaries can now be seen to be broken up (see Figs. 1-3), the boundary having changed from planar to undulating. Tensile results (Table 2) showed th~t whereas the 0·2% proof stress (the steels are·'non-straln The ferritic stainless steel examined had the composition given in Table 1. The steel had been hot rolled to 25mm plate and was examined in three conditions: (i) hot rolled (ii) hot rolled and tempered at 750°C. for 1h and air cooled (iii) hot rolled and normalized for 1h at 950°C. Longitudinal Charpy V-notch impact transition curves were obtained for the three conditions (testpieces notched in the through-thickness direction). Longitudinal tensile testpieces 4·4mm dia. with a 16mm gauge length were also obtained and tested on an Instron machine at a crosshead speed of 0·5mmmin -1. Microhardness measurements were taken within the ferrite grains using a 50g load, and the grain elongation of the ferritic grains in the rolling direction was measured by the method of mean linear intercept. The fracture appearance was examined and photographs taken of the fissures. Impact testpieces of controlled-rolled steels notched in the through-thickness direction often reveal fissures on the fracture surfaces after breaking, the fissures forming parallel to the plate surfaces. There appear, therefore, to be 'planes of weakness' in these steels parallel to the rolling plane which fracture ahead of the notch to form fissures, which by relieving the triaxial stress system associated with a notch reduce the possibility of brittle fracture. 1 A considerable amount of work2-6 has been carried out in recent years into the origin of these splits or' fissures and it is noticeable that the controlled-rolled ferrite-pearlite steels which give rise to fissures generally have elongated ferrite grains and a preferred orientation as a result of deformation in the ferrite temperature range. Both these factors, indeed, have been quoted as playing a part in controlling fissure formation since normalizing generally prevents their formation.2,6 However, work by Mintz et a1.7 has shown that grain shape rather than texture is the important factor in controlling fissure formation and this has been substantiated further by the recent metallographic observations of Morrison et al.2 In the latter work, the fissures were observed to nucleate at seCond-phase particles, generally non-metallic inclusions, in both controlled-rolled and normalized steels. However, whereas in normalized steels the holes associated with second-phase particles became blunted, those in the controlled-rolled steel were able to initiate cracks which propagated in a brittle manner giving the characteristic appearance of fissures. The growth of a crack large enough to propagate in a brittle manner appeared to take place by intergranular decohesion. Although inclusions are favoured initiation sites, fissure formation has been shown not to be critically dependent on the cleanliness of the steel, sufficient inclusions always being present to initiate a crack even in the cleanest of steels.5,8 The critical event appears to be the ability to decohese a grain boundary for a sufficiently long enough length to promote brittle fracture. It would therefore be expected that the longer and more closely aligned are the ferrite grain boundaries, the easier it would be to decohese along them. It is not surprising, therefore, that the tendency to fissure formation increases with increase in grain elongation. 2,3, 7 For example, normalized steels which have equiaxed grains do not give rise to fissures and it is only after the grains have been elongated to a critical amount that fissures are first observed. 6, 7 Increasing the dislocation density by warm w,orking has also been shown to favour their formation 7 and, because of this, it has be((n suggested that raising the strength of the grain matrix concentrates the strain on to the grain boundaries thereby encouraging decohesion. However, the reason for the apparent weakness of the grain-boundary regions after warm working is by no means clear and further studies are required. During a recent study into the impact behaviour of Fe-13Cr ferritic steels, some interesting observations were made with regard to the manner in which grain boundaries

Hot work steel

Abstract: A hot work steel with very high resistance to tempering and a very high strength at elevated temperatures, a good ductility and a comparatively low content of expensive alloying elements; the steel contains in weight percent: 0.30-0.45 C, 0.2-1.0 Si, 0.3-2.0 Mn, 2.0-3.5 Cr, 1.5-2.5 (W/2+Mo), 0.8-1.5 V, 0-0.01 B, balance essentially only iron and impurities in normal quantities; for a further embodiment the steel contains a maximum of 1.0, preferably a maximum of 0.5 and suitably a maximum of 0.3% cobalt; in the hardened and tempered condition the steel has a fine grain lath-martensitic or partly bainitic microstructure which is free from retained austenite, and which contains a very finely dispersed intergranular precipitation of carbides, among which vanadium carbides are the dominating carbide phase.

Process for the chemical and thermal treatment of steel parts to improve the strength properties thereof

Abstract: The present invention relates to a process for the chemical and thermal treating of steel parts such as gear wheels, shafts and sleeves, for increasing their fatigue strength, hardness and wear resistance, the process being characterized by following the successive applied steps of phosphatizing, carburizing, hardening and tempering.

Control of temper embrittlement in Ni-Cr-Mo-V steel by combining intercritical and low temperature austenitizing heat treatments

Abstract: It is demonstrated in three heats of a Ni-Cr-Mo-V steel that dramatic reductions in both initial transition temperatures and susceptibility to temper embrittlement may be achieved by intercritical heat treatments. However, it appears that the temperature control necessary to ensure sufficient strength in large forgings of this class of steel will preclude the use of the treatment as a substitute for a complete austenitize. An approach to exploit the intercritical treatment as a conditioning procedure is described following the discovery that much of the reduced embrittlement susceptibility is remembered after a low temperature austenitize. Thus, by combining an intercritical and low temperature austenitize, the available temperature range for the intercritical treatment is widened because the minimum strength requirement is eliminated. Also, the full austenitize allows conventional tempering treatments to be used. The results are supported by fractography, metallography and Auger analysis.

Improvement for sulfide stress corrosion cracking of low alloy steel

Abstract: PURPOSE: To impart superior sulfide stress corrosion cracking characteristics to a low alloy steel by hardening the low alloy steel from an austenite temp. region to turn the greater part thereof to martensite structure then tempering the same for a shor time at a prescribed temp. region below an Ac 1 transformation point. CONSTITUTION: A low alloy steel contg. 0.05W0.35% C, 0.01W0.30% Si, 0.15W 1.5% Mn, and 0.005W0.10% Al is prepd. Next, this low alloy steel is hardened from an austenite temp. to turn ≥90% to martensite structure. Thence, said low alloy steel turned mostly to martensite structure is tempered in a short time in respective temp. regions of ≥700°C and below the Ac 1 point in the case of ≤30sec holding time and ≥680°C and below the Ac 1 point in the case of ≥30sec. As a result, the steel which has 60W80kgf/mm 2 yield point and is superior in sulfide stress corrosion cracking resistance characteristics is obtained. COPYRIGHT: (C)1982,JPO&Japio