Showing papers on "Tempering published in 1983"

Precipitation reactions during the heat treatment of ferritic steels

Abstract: The precipitation reactions in two ferritic steels, 9Cr-1Mo-V-Nb and 12Cr-1Mo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-1Mo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-1Mo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-1Mo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-1Mo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-1Mo-V-Nb alloy, a combination of chromium-rich M23C6 and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-1Mo-V-W alloy were identified as chromium-rich M23C6 and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations.

Microstructural sources of toughness in QLT-Treated 5.5Ni cryogenic steel

Abstract: In commercial practice 5.5Ni steel is toughened for cryogenic service by a three-step heat treatment designated the “QLT” treatment. To determine why this treatment is necessary and successful, a series of two-step heat treatments was applied to 5.5Ni steel and the resulting microstructural states were characterized and compared with that obtained through the QLT treatment. It was concluded from this analysis that the QLT treatment lowers the ductile-brittle transition temperature by precipitating a dense distribution of thermally stable austenite along the boundaries of martensite laths, which interrupts the crystallographic alignment of laths within martensite packets and prevents cooperative trans-packet cleavage. Essentially, it reduces the mean free fracture path for cleavage. The multistep heat treatment is necessary because of the low nickel content; a single step heat treatment leads to an austenite precipitate which is either too lean in solute to be retained or too coarse in its distribution to be effective. The problem is avoided in the QLT treatment since the intercritical anneal (L) serves to create regions of high solute content along the prior martensite lath boundaries. The intercritical temper (T) then precipitates a dense distribution of high solute, stable austenite within these enriched regions.

Retained austenite and tempered martensite embrittlement in medium carbon steels

Abstract: Electron microscopy, diffraction and microanalysis, X-ray diffraction, and auger spectroscopy have been used to study quenched and quenched and tempered 0.3 pct carbon low alloy steels. Somein situ fracture studies were also carried out in a high voltage electron microscope. Tempered martensite embrittlement (TME) is shown to arise primarily as a microstructural constraint associated with decomposition of interlath retained austenite into M3C filMs upon tempering in the range of 250 °C to 400 °C. In addition, intralath Widmanstatten Fe3C forms from epsilon carbide. The fracture is transgranular with respect to prior austenite. The sit11Ation is analogous to that in upper bainite. This TME failure is different from temper embrittlement (TE) which o°Curs at higher tempering temperatures (approximately 500 °C), and is not a microstructural effect but rather due to impurity segregation (principally sulfur in the present work) to prior austenite grain boundaries leading to intergranular fracture along those boundaries. Both failures can o°Cur in the same steels, depending on the tempering conditions.

The Aging and Tempering of Iron-Nickel-Carbon Martensites

Abstract: The aging and tempering of freshly quenched (Ms > RT) and virgin (M < RT) martensites with lath and plate morphologies in Fe-Ni-C alloys have been studied to obtain kinetic and structural information. At subambient temperatures, the first change is attributed to isothermal conversion of a small amount of retained austenite or to slight relaxations in the martensite, but this is not a significant part of the martensite aging process. Aging above -40 °C to about 70 °C is accompanied by the diffusion-controlled clustering of carbon atoms, resulting in an increase in electrical resistivity proportional to the carbon content but independent of the martensitic morphology. This regime is followed above 100 °C by the precipitation of e-carbide (i.e., the conventional first stage of tempering), which may emerge directly from the carbon-rich clusters. At still higher temperatures, cementite forms separately (i.e., the conventional third stage of tempering) in competition with the e-carbide. These two precipitation processes overlap, and their kinetics appear to be controlled by iron-atom diffusion away from the growing carbide particles along dislocation paths. No evidence was found in this investigation for a regime reflecting carbon migration to dislocations or other defects, but this possibility is not ruled out by the experimental methods employed.

Niobium Bearing Ferrite-Bainite High Strength Hot-rolled Sheet Steel with Improved Formability

Abstract: Dual phase steels have not shown superior characteristics with regard to the properties such as hole expansion, Charpy impact, fatigue and especially flash butt welding which is closely related to wheel rim fabrication. Through the investigation of the nature and volume fraction of second phase and alloying elements, it has been clarified that Nb bearing steels, whose microstructure contains ferrite and 10 to 20% bainite, eliminate these problems in dual phase steels and exhibit excellent characteristics. We will discuss the effects of the different second phases and the volume fraction of bainite on the mechanical properties.It is found that as far as flash butt welding is concerned, Nb bearing ferrite+bainite steel does not show any remarkable softening or localized necking in the heat affected zone which often occurs in dual phase steel because of the tempering of martensite. The superiority of the stretch flangeability of Nb bearing ferrite+bainite steel is ascribed to the superior ductility of bainite compared to that of martensite or pearlite.

Cold tool steel

Abstract: PURPOSE: To provide a cold tool steel which is provided with high hardness and high toughness and has a long life by subjecting a steel material consisting of specifically composed C, Si, Mn, Cr, Mo, V and Fe, etc. to annealing and hardening then to high temp. tempering. CONSTITUTION: A cold tool steel is obtd. by subjecting a steel material contg. 0.75W1.75% C, 0.5W3.0% Si, 0.1W2.0% Mn, 5.0W11.0% Cr, 1.3W5.0% Mo, and 0.1W5.0% V, contg. further ≥1 kind among 0.001W0.5% REM, 0.1W2.0% Cu, 0.2W2.0% Ni, 0.1W3.0% W, 0.1W5.0% Co, 0.01W3% Nb, ≤2.0% Ti and ≤2.0% Zr and/or ≥1 king among ≤0.20% S, ≤0.40% Pb, ≤0.3% Se, ≤0.50% Bi, ≤0.30% Te, and 0.002W0.010% Ca, and consisting of the balance Fe and impurities to tempering at ≥450°C and has high hardness and high toughness at which the steel withstands thoroughly severe conditions of use. COPYRIGHT: (C)1984,JPO&Japio

An atom probe study of the aging of iron- nickel- carbon martensite

Abstract: The atom probe field ion microscope has been used to study the redistribution of carbon in iron-nickel-carbon martensites aged in the temperature range 22 to 250 °C. The Ms temperature of the alloy used was -50 °C. During all stages of aging a considerable amount of redistribution of carbon was detected in the form of carbon segregation to twin boundaries and other lattice defects and in the formation of small clusters and carbides. Small carbon-rich areas were detected at 40 °C, and disc-shaped carbide particles were found after 24 hours at 100 °C. Thin cementite lamellae were observed after one hour at 250 °C. It is evident that a close similarity exists between the sequence of reactions o°Curring during the tempering process and the sequence of precipitation reactions observed in age-hardening alloys. The main additional complications that arise in the case of martensites are due to the high densities of lattice defects that are present and to the strong interaction between carbon atoMs and such defects.

The evaluation of tempered martensite embrittlement in 4130 steel by instrumented charpy V-notch testing

Abstract: Tempered martensite embrittlement (TME) was studied in vacuum-melted 4130 steel with either 0.002 or 0.02 wt pct P. TME was observed as a severe decrease in Charpy V-notch impact energy, from 46 ft-lb. at 200 °C to 35 ft-lb. at 300 °C in the low P alloy. The impact energy of the high P alloy was consistently lower than that of the low P alloy in all tempered conditions. Fracture was transgranular for all specimens; therefore, segregation of P to the prior austenitic grain boundaries was not a factor in the occurrence of TME. Analysis of load-time curves obtained by instrumented Charpy testing revealed that the embrittlement is associated with a drop in the pre-maximum-load and post-unstable-fracture energies. In specimens tempered at 400 °C the deleterious effect of phosphorus on impact energy became pronounced, a result more consistent with classical temper embrittlement rather than TME. A constant decrease in pre-maximum-load energy due to phosphorus content was observed. The pre-maximum-load energy decreases with increasing tempering temperature in the range of 200 °C to 400 °C, a result explained by the change in work hardening rate. Carbon extraction replicas of polished and etched as-quenched specimens revealed the presence of Fe2MoC and/or Fe3C carbides retained after austenitizing. Ductile crack extension close to the notch root was related to the formation of fine microvoids at the retained carbides.

Tempering of Mn and Mn-Si-V Dual-Phase Steels

Abstract: Changes in the yield behavior, strength, and ductility of a Mn and a Mn-Si-V d11Al-phase (ferrite-martensite) steel were investigated after tempering one hour at 200 to 600 °C. The change in yield behavior was complex in both steels with the yield strength first increasing and then decreasing as the tempering temperature was increased. This complex behavior is attributed to a combination of factors including carbon segregation to dislocations, a return of discontinuous yielding, and the relief of resid11Al stresses. In contrast, the tensile strength decreased continuously as the tempering temperature was increased in a manner that could be predicted from the change in hardness of the martensite phase using a simple composite strengthening model. The initial tensile ductility (total elongation) of the Mn-Si-V steel was much greater than that of the Mn steel. However, upon tempering up to 400 °C, the ductility of the Mn-Si-V decreased whereas that of the Mn steel increased. As a result, both steels had similar ductilities after tempering at 400 °C or higher temperatures. These results are attributed to the larger amounts of retained austenite in the Mn-Si-V steel (9 pct) compared to the Mn steel (3 pct) and its contribution to tensile ductility by transforming to martensite during plastic straining. Upon tempering at 400 °C, the retained austenite decomposes to bainite and its contribution to tensile ductility is eliminated.

Chi-Carbide in Tempered High Carbon Martensite

Abstract: Martensite in an Fe-1.22C alloy was tempered at 523, 573, and 623 K and examined by transmission electron microscopy (TEM) and Mossbauer effect spectroscopy (MES) to identify the morphology and type of carbide formed at the beginning of the third stage of tempering. Carbides formed in three morphologies: on twins within the martensite plates, in the matrix of twin-free areas of the martensite plates, and along the interfaces of the martensite plates. Chi-carbide (χ), as identified by selected area diffraction (SAD), was associated with each carbide morphology in specimens tempered at 573 K. Cementite (θ) together with chi-carbide was observed in specimens tempered at 623 K. Small amounts (about 2 pct) of retained austenite were observed by MES of specimens tempered at 523 K. The transformation of the 25 pct retained austenite in as-quenched specimens was related to the χ-carbide formed at the martensite plate interfaces during tempering. The MES results also show the presence of χ-carbide in the specimen tempered at 523 K and yields parameters indicative of a mixture of χ and θ carbides for the specimens tempered at 573 K and 623 K. MES measurements of the magnetic transition temperatures of the carbides show diffuse transitions but suggest thatχ is the dominant carbide in the tempering temperature range examined.

Tempering of cast nickel–aluminium bronze

Abstract: Microstructural changes associated with the tempering at 675°C of cast nickel–aluminium bronze, of nominal composition (wt-%) Cu–10Al–5Ni–5Fe, have been investigated using optical, electron optical, and microprobe analysis techniques. The tempering treatment resulted in the elimination of the non-equilibrium martensitic (‘retained β’) phase, precipitation with the α grains, and a coarsening of the as-cast structure. On heating to 675°C the martensite phase, which contained a high density of NiAl precipitates, reconstituted to form the high temperature bcc β phase and, after extended times at 675°C, this phase progressively decomposed into NiAl and α. The precipitates which formed in α grains were based on NiAl and had the B2 structure. These precipitates nucleated as laths either in the α matrix or on the pre-existing particles of Fe3Al; the two morphologies exhibited the Kurdjumov–Sachs and the Nishiyama–Wasserman orientation relationships, respectively, with α.

Edge cracking in high strength steels

Abstract: A study has been made of the sheared edge ductility of a series of coldroll gage high strength steels. It is found that inclusion shape control is beneficial, especially for steels with tensile strengths ranging from 345 to 550 MPa (50 to 80 ksi). Edge ductility is increased for all the materials when the quality of the edge is improved; this involves removing the heavily coldworked sheared region either by machining, trimming (repunching), or a heat treatment which results in the recrystallization of the edge. Following a heat treatment, the steels with no inclusion shape control have hole expansion values similar to those observed in materials with inclusion shape control before heat treatment. It is suggested that for the steels with the stringer type inclusions, low edge ductility will be exhibited when fracture initiates in the deformed shear edge region and propagates along the inclusionferrite interface. The elimination of this coldworked region makes crack initiation more difficult and, thus, there is greater ductility. A tempering study of dualphase steels suggests that the hard martensite islands play a similar role to the stringer type inclusions in reducing sheared edge elongation. It was also observed that the load to punch out a disc is proportional to both the thickness and the tensile strength of the material.

The effects of tempering reactions on temper embrittlement of alloy steels

Abstract: The effects of tempering reactions which produce molybdenum-rich carbides on the temper embrittlement of NiCrMo, NiCrMoV, CrMo, and CrMoV steels, particularly embrittlement due to phosphorus segregation, are reviewed. Molybdenum can act as an effective scavenger for phosphorus and other embrittling impurities, but the scavenging is lost when the molybdenum is precipitated in carbides as a result of continued tempering during service at elevated temperatures. This leads to very slow embrittlement, controlled by the rates of alloy carbide formation, rather than by the diffusion of phosphorus, for example. The presence of vanadium apparently retards the embrittlement process even more by interfering with the formation of the molybdenum-rich carbides. Observations of the temper embrittlement behavior, and of the effects of service exposure, in three CrMoV steam turbine rotors are also reported and are shown to be consistent with the previous results.

Process for improving both fatigue strength and toughness of high-strength Al alloys

Abstract: The invention concerns a process for improving the characteristics in respect of fatigue strength and toughness of worked Al alloys in the treated state, by means of a thermo-mechanical treatment which is carried out on the cast and possibly homogenized product. It comprises the following steps: (a) casting an initial product along an axis XX' by a known method (b) optional homogenization (c) upsetting in the hot state, preferably by means of a press, along the axis XX', with an upsetting ratio (initial length/final length along axis XX')>1.4 (d) drawing in the hot state in the direction of the axis XX', with a rate of working (initial cross section/final cross section, considered perpendicularly to the axis XX')>1.5 (e) compression in the hot state along an axis perpendicular to the axis XX', with a rate of reduction (initial cross section-final cross section/initial cross section)>15% (f) rolling, hot extrusion or forging, under the usual conditions, and the usual operations for quenching and tempering with possible relief of stresses by cold working (states T6, T651 or T652 for example). For equivalent mechanical characteristics, it makes it possible to increase by up to 50% approximately the characteristics in respect of fatigue strength or toughness in the treated state.

Relationship between structure and fracture behaviour in 6W–5Mo–2V type high-speed steel

Abstract: The relationship between the microstructure and properties of high-speed steels has been examined, with particular reference to fracture toughness (as measured by KIC) and fatigue-crack growth rates. Different microstructures have been obtained by varying the heat-treatment parameters - austenitizing temperatures and tempering conditions; there are also inherent microstructural differences resulting from the steels’ composition and the method of manufacture. The range of microstructures studied varied, in terms of carbide distributions, from the fine homogeneous structures of powder-metallurgy steels to the heavily segregated microstructures typical of large bar sizes of cast and hot-worked high-speed steels. It has been shown that the presence of carbide segregation in the form of bands and ‘hooks’ significantly enhances the steel's fracture toughness, particularly at low hardnesses and regardless of the orientation of carbide ‘banding’ to the crack plane. This effect was found to be a direct res...

Restoration of elevated temperature tensile strength in 2.25Cr-1Mo steel

Abstract: Metallographic studies have been conducted on 2.25Cr-lMo steel specimens taken from pressure vessels after long term service exposures at 500 to 650 °C. The loss of strength in the 2.25Cr-lMo steel after the service exposure consists of two parts: (1) the strength loss accompanying the change in the carbide morphology as usually occurs during tempering, and (2) a strength loss which occurs without any noticeable microstructural change. This second part of the strength loss can also be produced by relatively short term thermal treatment such as step-cooling from the tempering temperature, and is reversible by retempering followed by air-cooling. This type of strength loss is associated with a reduction of molybdenum content in solid solution in the ferrite. It is hypothesized that the strength loss and recovery of 2.25Cr-lMo steel are produced by changes in the solid solution strengthening mainly due to molybdenum, carbon, and possibly nitrogen.

Manufacture of steel having high resistance against crack by sulfide

Abstract: PURPOSE:To manufacture the titled steel at low cost by repeating under special conditions procedures such as hot processing, cooling, hot-processing, direct quenching, heating and quenching and then tempering in that order on steel of special composition in the form of austenite. CONSTITUTION:Steel meeting the composition formula by its ingredients such as C 0.15-0.45, Si less than 0.80, Mn more than 0.01- not less than 0.30, Cr 0.20- 1.50, 1 or 2 kinds of Mo and W, Mo+1/2W 0.05-0.80, Nb 0.01-0.10, 1 or 2 kinds of Ti and Zr, Ti+1/2Zr 0.005-0.050 and Al 0.01-0.10 in terms of weight percent and the balance of Fe and inevitable impurities (P less than 0.010, S less than 0.010) is hot-processed in the form of austenite. After this procedure, it is cooled to complete its transformation. It is further hot-processed to a transformation point Ac3- (transformation point Ac3+200 deg.C). Next, it is directly quenched as it is in the form of austenite, and then is heated at a transformation point Ac3- (transformation point Ac3+200 deg.C) and quenching. These processes are further repeated more than once. Finally the steel is tempered at less than a transformation point Ac3.

Strength of initially virgin martensites at - 196 °C after aging and tempering

Abstract: The compressive strength at —196°C of martensites in Fe-0.26 pct C-24 pct Ni, Fe-0.4 pct C-21 pct Ni, and Fe-0.4 pct C-18 pct Ni-3 pct Mo alloys, all with subzero Ms temperatures, has been determined in the virgin condition and after one hour at temperatures from —80 to +400 °C. The effects of ausforming (20 pct reduction in area of the austenite by swaging at room temperature prior to the martensitic transformation) were also investigated. For the unausformed martensites, aging at temperatures up to 0 °C results in relatively small increases in strength. Above 0 °C, the age hardening increment increases rapidly, reaching a maximum at 100 °C. Above 100 °C, the strength decreases continuously with increasing tempering temperature except for the molybdenum-containing alloy, which exhibits secondary hardening on tempering at 400 °C. For the ausformed martensites, the response to aging at subzero temperatures is greater than for unausformed material. Strength again passes through a maximum on aging at 100 °C. However, on tempering just above 100 °C, the ausformed materials show a slower rate of softening than the unausformed martensites. The strengthening produced by the ausforming treatment is largest for the Fe-0.4 pct C-18 pct Ni-3 pct Mo alloy, but there is no evidence of carbide precipitation in the deformed austenite to account for this effect of molybdenum.

Fracture toughness and fatigue behavior of matrix II and M-2 high speed steels

Abstract: The effects of heat treatment and of the presence of primary carbides on the fracture toughness,KIc and the fatigue crack growth rates,da/dN, have been studied in M-2 and Matrix II high speed steels. The Matrix II steel, which is the matrix of M-42 high speed steel, contained many fewer primary carbides than M-2, but both steels were heat treated to produce similar hardness values at the secondary hardening peaks. The variation of yield stress with tempering temperature in both steels was similar, but the fracture toughness was slightly higher for M-2 than for Matrix II at the secondary hardening peaks. The presence of primary carbides did not have an important influence on the values ofKIc of these hard steels. Fatigue crack growth rates as a function of alternating stress intensity, ΔK, showed typical sigmoidal behavior and followed the power law in the middle-growth rate region. The crack growth rates in the near threshold region were sensitive to the yield strength and the grain sizes of the steels, but insensitive to the sizes and distribution of undissolved carbides. The crack growth rates in the power law regime were shifted to lower values for the steels with higher fracture toughness. SEM observations of the fracture and fatigue crack surfaces suggest that fracture initiates by cleavage in the vicinity of a carbide, but propagates by more ductile modes through the matrix and around the carbides. The sizes and distribution of primary carbides may thus be important in the initiation of fracture, but the fracture toughness and the fatigue crack propagation rates appear to depend on the strength and ductility of the martensite-austenite matrix.

Breakage Susceptibility Reduction by Short-Term Tempering of Corn

Abstract: THE effects of short-term (0-60 min) tempering of corn before cooling on the breakage susceptibility and moisture removal during cooling was studied using both thin-layer and deep bed drying processes. Thin-layer tests at three temperatures and four final moisture contents showed breakage susceptibility was dramatically increased for drying below 19% but can be reduced by tempering with most of the reduction occurring in the first thirty minutes. Moisture content removal by cooling was increased by increasing tempering time and drying air temperature. Study of crossflow, crossflow with turning and rack-type dryer configurations confirmed the effects of tempering on breakage susceptibility and moisture removal during cooling found by the thin layer tests. Moisture removal was also affected by the dryer configuration, with the largest removal for the crossflow configuration. Heat energy input per mass of water removed was significantly reduced by including cooling in the drying process, with larger reductions at 17% than at 15% moisture content.

Induction hardening of steel

Abstract: A method for induction hardening through hardened chromium-molybdenum hot work die steel comprising the steps of induction heating to a uniform temperature above the upper critical temperature, cooling, and double tempering at temperatures below the lower critical temperature to produce a workpiece having a tough core and a hard wear resistant surface. An apparatus is provided for induction hardening long workpieces with minimum distortion by providing an inductor coil which always remains centered around the workpiece during induction coil traverse. Mandrel bars for tube piercing mills can be induction hardened using this process and apparatus.

Softening in Weld Heat Affected Zone of Dual Phase Steel Sheet for Automotive Wheel Rim

Abstract: Dual phase steel offers potential for wheel weight reduction, but has not been completely succeeded, in part, because of a localized necking or a fracture during rim fabrication. This failure should be related to a softening in the weld heat affected zone (HAZ). This paper investigates mechanical properties through microstructural change produced in the HAZ of as-rolled dual phase steel and finally suggests a practical solution. The softening, caused by heating the steel up to Ac1 in the HAZ, is found to be affected not only by tempering of martensite, but also by the variation of hardness in ferrite matrix. Moreover strain aging as well as work hardening due to up-setting stage during the flash welding also concerns this problem. Coiling temperature in manufacturing as-rolled dual phase steel has a large effect on the conditions of ferrite and martensite. Control of the temperature is of great importance to avoid such a localized necking or a fracture in the HAZ.

Production of high tensile steel plate having excellent strength and toughness

Abstract: PURPOSE:To produce efficiently a high tensile steel plate having high strength and excellent toughness by heating and hot rolling a steel having a prescribed component compsn. respectively at regulated temp. regions and finishing the same to a steel plate having a prescribed size then hardening directly the steel plate from the temp. of the Ar3 transformation print or above and tempering the same at the temp. of the Ac1 transformation point or below in succession to said hardening. CONSTITUTION:A steel contg. 0.03-0.20% C, 0.03-0.50% Si, 0.60-1.80% Mn, 0.03- 0.010% Ti, 0.01-0.10% Nb, 0.002-0.100% Sol.Al, and 0.0020-0.0040% N, and consisting of the balance Fe and unavoidable impurities is prepd. Said steel is then heated to a temp. region of 1,050-1,200 deg.C in order to turn thoroughly hardly meltable carbide, etc. such as NbC to solid solution and to suppress the formation of the coarse grains of TiN. The steel subjected to the heating treatment is hot-rolled at a temp. region of >=900 deg.C and is finished to a steel plate having a prescribed size and thereafter the steel plate is hardened from the temp. of the Ar3 transformation point or above and is then tempered at the temp. of the Ac1 transformation point or below. The intended high tensile steel plate is thus obtd.

Manufacture of turbine rotor

Abstract: PURPOSE:To obtain a turbine rotor of 12Cr steel with superior creep rupture strength, toughness and ductility at high temp. by forging a steel ingot having a specified composition obtd. by electro-slag remelting to form a rough body for a turbine rotor and by subjecting the rough body to heating, quenching and tempering under specified conditions. CONSTITUTION:A steel ingot obtd. by electro-slag remelting is forged to form a rough body for a turbine rotor. The steel ingot has an alloy composition consisting of, by weight, 0.1-0.25% C, <=0.5% Si, 0.1-1.0% Mn, 0.1-1.0% Ni and/ or Co, 9.0-13.0% Cr, 0.5-2.0% Mo, 0.1-0.3% V, 0.03-0.3% Nb and/or Ta, 0.5-2.0% W, 0.03-0.1% N and the balance Fe with accompanying impurities. The rough body is heated to 1,020-1,150 deg.C, quenched, and tempered at 530- 730 deg.C.

Manufacture of steel for line pipe with superior characteristic of stopping propagation of brittle crack

Abstract: PURPOSE:To manufacture steel products with high strength and superior characteristics of stopping the propagation of brittle cracks by subjecting a steel contg specified amounts of C, Si, Mn, Nb, Al, N, V, Cu, Cr, etc to rolling, hardening and tempering under specified conditions CONSTITUTION:A steel contg 004-018% C, 001-090% Si, 030-200% Mn, 0008-0060% Nb, 003-010% Al, 00080-00200% N, 1 or >=2 kinds of metals selected from 001-010% V, 005-050% Cu, 005-10% Cr, 005-050% Mo, 0005-0050% Ti, 0007-0070% Ce and 00010-0070% Ca, and inevitable impurities is heated to >=1,200 degC and hot worked The hot worked steel is cooled to a temp below the Ar1 transformation point, austenitized again, cooled to a temp close to ordinary temp at a higher rate than air cooling rate, and tempered by heating to 400 degC- the Ac1 transformation point to convert most of the structure into a fine ferrite structure

The effects of heat treatment on fracture toughness and fatigue crack growth Rates in 440C and BG42 steels

Abstract: The fatigue crack growth rates,da/dN, and the fracture toughness, KIc have been measured in two high-carbon martensitic stainless steels, 440C and BG42. Variations in the retained austenite contents were achieved by using combinations of austenitizing temperatures, refrigeration cycles, and tempering temperatures. In nonrefrigerated 440C tempered at 150 °C, about 10 vol pct retained austenite was transformed to martensite at the fracture surfaces duringKIc testing, and this strain-induced transformation contributed significantly to the fracture toughness. The strain-induced transformation was progressively less as the tempering temperature was raised to 450 °C, and at the secondary hardening peak, 500 °C, strain-induced transformation was not observed. In nonrefrigerated 440C austenitized at 1065 °C,KIc had a peak value of 30 MPa m1/2 on tempering at 150 °C and a minimum of 18 MPa m1/2 on tempering at 500 °C. Refrigerated 440C retained about 5 pct austenite, and did not exhibit strain-induced transformation at the fracture surfaces for any tempering temperature. TheKIc values for corresponding tempering temperatures up to the secondary peak in refrigerated steels were consistently lower than in nonrefrigerated steels. All of the BG42 specimens were refrigerated and double or quadruple tempered in the secondary hardening region; theKIc values were 16 to 18 MPa m1/2 at the secondary peak. Tempered martensite embrittlement (TME) was observed in both refrigerated and nonrefrigerated 440C, and it was shown that austenite transformation does not play a role in the TME mechanism in this steel. Fatigue crack propagation rates in 440C in the power law regime were the same for refrigerated and nonrefrigerated steels and were relatively insensitive to tempering temperatures up to 500 °C. Above the secondary peak, however, the fatigue crack growth rates exhibited consistently lower values, and this was a consequence of the tempering of the martensite and the lower hardness. Nonrefrigerated steels showed slightly higher threshold values, ΔKth, and this was ascribed to the development of compressive residual stresses and increased surface roughening in steels which exhibit a strain-induced martensitic transformation.