Tempered Specimens Research Articles

Influence of Tempering Temperature and Microstructure on Wear Properties of Low Alloy PM Steel with 1-2 % Ni Addition

The effect of tempering temperature and microstructure on dry sliding wear behavior of quenched and tempered PM steels was investigated. For this purpose, atomized iron powder was mixed with 0.3 % graphite and 1-2 % Ni powders. The mixed powders were cold pressed and sintered at 1200°C. The sintered specimens were quenched from 890°C and then tempered at 200°C and 600°C for 1 hr. Wear tests were carried out on the quenched+tempered specimens under dry sliding wear conditions using a pin-on-disk type machine at constant load and speed. The experimental results showed that the wear coefficient effectively increased with increasing tempering temperature. With increasing Ni content, the wear coefficient slightly decreased at all tempering temperatures due to the high amount of Ni-rich austenitic areas.

Recrystallization of Lath Martensite with Bulge Nucleation and Growth Mechanism.

The recrystallization behavior of lath martensite during tempering was investigated in high-chromium martensitic steels by means of hardness testing, optical and transmission electron microscopy. The role of carbide particles on the recrystallization was also discussed in terms of the grain boundary pinning effect. The hardness of tempered specimens was plotted as a function of the tempering parameter, T(logt+20), for a low-carbon steel (Fe-9Cr-0.1C mass%) and an ultra-low carbon steel (Fe-9Cr-1Ni-0.006C mass%). The low-carbon steel exhibited gradual softening with recovery but did not undergo recrystallization. However, the ultra-low carbon steel suffered abrupt softening owing to the discontinuous recrystallization of lath martensite. Microstructural observations in the ultra-low carbon steel indicated that the recrystallization of lath martensite occurs with the 'bulge nucleation and growth (BNG) mechanism'. The possibility of recrystallization via this mechanism depends upon both the spacing of carbide particles on grain boundaries and the dislocation density of martensite. An energetic analysis on the formation of a recrystallized grain revealed the critical carbide spacing minimum required for the occurrence of recrystallization as a function of dislocation density. In the case of the low-carbon steel, carbide precipitates on grain boundaries with spacing smaller than the critical value, thus suppressing recrystallization.

Ｃｒ‐Ｍｏ鋼熱影響部の焼もどし脆化に関する研究 第４報 ＳＲ処理後の再加熱によって２ １／４Ｃｒ‐１Ｍｏ鋼ＨＡＺに生じる焼もどし脆化

Temper embrittlement, which occurs in HAZ of 2 1/4Cr-1Mo steel subjected to SR treatment and subsequent reheating, was investigated by using synthetic HAZ specimen, and it was compared with embrittlement observed in specimens tempered in same temperature range without SR treatment (direct tempering). With a suitable SR treatment (975 K for 5 hours) synthetic HAZ specimen became de-embrittled state. However, subsequent reheating at 775 to 925 K produced in specimens four different types of embrittlement. Those were second, third, fourth and fifth types, which had already been recognized in direct tempered specimens. The first type of embrittlement which arose in direct tempering in shortest time range did not appear after SR treatment. The second type (the short time type), which occurred in a wide time-temperature range in direct tempering, arose only in a narrow one after SR treatment. The third and fourth types (the long time types) arose intensively as case of direct tempering. The fifth type (the high temperature type) appeared also after SR treatment. It will be concluded that embrittlement in short time range is suppressed to some extent by SR treatment, but those arising in long time range and high temperature one arose after SR treatment as well. It was found that the step-cooling also could reveal temper embrittlement of this steel. However, an essential advantage of this process over isothermal tempering shown above was not recognized from view point of promoting embrittlement.

Fracture of hot formed ledeburitic chromium steels

Due to the hot forming procedure the overall mechanical properties of ledeburitic chromium steels become anisotropic. As shown by experiments the fracture toughness K Ic of these steels depends on the hardness of the metal matrix and the orientation of the load with respect to the axis of hot forming. The degree of crack deflection, expressed by the width of the crack path, was found to be the governing quantity for differences in the resistance against crack propagation. The K Ic- tests were modelled by the finite element method using an orthotropic elasto-plastic material law. While the behaviour of the hardened and low tempered specimens could be well predicted by this model, differences between simulation and experiment in the case of a ductile state indicate the occurrence of additional effects acting on a microscopical scale.

Eigenschaften von bei niedrigen Temperaturen angelassenen SAE-43xx-Stählen

Uniaxial tensile tests were performed on 4330, 4340 and 4350 steels in the as-quenched condition and after quenching and tempering at 150, 175 and 200°C for times of 10 minutes, 1 hour and 10 hours. Strength parameters decreased and ductility parameters increased continuously with increasing tempering. Mechanical properties are presented as a function of tempering conditions and steel carbon content, and hardness and ultimate strength changes are given as a function of Hollomon-Jaffe tempering parameters. All tempered specimens, except for some lightly tempered 4350 specimens, deformed plastically through necking instability and failed by ductile fracture. The stresses required for the ductile fracture, estimated from an analysis of the interfacial stresses at particles in the neck at fracture, showed no systematic variation with carbon content or tempering conditions despite significant variations in deformation and strain hardening. As-quenched specimens of the 4340 and 4350 steels, and some of the lightly tempered 4350 steels failed by brittle mechanisms. The deformation and fracture of the low-temperature-tempered 43xx steels are discussed in terms of the changes in fine structure caused as, during tempering, transition carbides increasingly replace dislocations with and without carbon atom segregation in the as-quenched martensite.

Deformation, fracture, and mechanical properties of low-temperature-tempered martensite in SAE 43xx steels

Uniaxial tensile tests were performed on 4330, 4340, and 4350 steels in the as-quenched (AQ) condition and after quenching and tempering at 150 °C, 175 °C, and 200 °C for times of 10 minutes, 1 hour, and 10 hours, respectively. Strength parameters decreased and ductility parameters increased continuously with increasing tempering. Mechanical properties are presented as a function of tempering conditions and steel carbon content, and hardness and ultimate strength changes are given as a function of Hollomon—Jaffe tempering parameters. All tempered specimens, except for some lightly tempered 4350 specimens, deformed plastically through necking instability and failed by ductile fracture. The stresses required for the ductile fracture, estimated from an analysis of the interfacial stresses at particles in the neck at fracture, showed no systematic variation with carbon content or tempering conditions despite significant variations in deformation and strain hardening. The AQ specimens of the 4340 and 4350 steels, and some of the lightly tempered 4350 steels, failed by brittle mechanisms. The deformation and fracture of the low-temperature-tempered 43xx steels are discussed in terms of the changes in fine structure, namely, the formation of transition carbides and a rearranged dislocation substructure that evolve from an AQ martensitic substructure consisting of dislocations with and without carbon atom segregation.

Influence of a lead melt on plastic deformation of high-alloyed heat-resistant steels

The effect of liquid-metal embrittlement in lead melt is typical of Kh12MVSFBR ferrite-martensitic steel and is observed in the temperature range of 300 – 500°C at a deformation rate of 8 · 10−4 sec−1. The maximum decrease in the plasticity of tempered specimens occurs at a temperature of 450°C. A decrease in the amount of δ-ferrite in the composition (martensite hardening without high-temperature annealing) results in a substantial decrease in plasticity and in broadening of the temperature range of embrittlement. 08Kh16N11S3MB austenitic steel is not affected by liquid metal embrittlement in the investigated temperature range for the deformation rates under consideration.

Analysis of Tempering Stresses in Bilayered Porcelain Discs

Previous studies of opaque-porcelain/body-porcelain discs have shown that compressive stresses which develop in the porcelain surface by being tempered in air can inhibit the sizes of cracks induced within the surface. The objective of this study was to develop a theoretical model for analysis of transient and residual stresses in opaque-porcelain/body-porcelain discs which were produced under variable cooling conditions. The model incorporates the effects of stress and structural relaxation. Transient and residual stresses were calculated for bilayered porcelain discs 16 mm in diameter and 2 mm in thickness for three opaque-porcelain/body-porcelain combinations. Transient temperature distributions in the discs for simulated convective cooling were calculated by finite-element analysis. Data from microhardness indentations reported by Anusavice et al. (1989) indicate that crack lengths measured for bilayered porcelain discs subjected to slow cooling conditions, for which the model predicted residual tensile stresses, were greater than those combinations for which residual compressive stresses were calculated. Calculated values of residual compressive stress for tempered specimens were considerably higher than those for specimens that were slowly cooled and those that were cooled by free convection. In general, residual stress levels calculated by use of the analytical model were in fairly good agreement with the trends observed for crack lengths and bi-axial flexural strengths reported by Anusavice and Hojjatie (1991). The results of the present study indicate that a visco-elastic model is a viable approach for determination of transient and residual stresses in opaque-porcelain/body-porcelain discs.

Effect of Thermal Tempering on Strength and Crack Propagation Behavior of Feldspathic Porcelains

The objective of this study was to test the hypothesis that tempering stress can retard the growth of surface cracks in layered porcelain discs with variable levels of contraction mismatch. Porcelain discs, 16 mm in diameter and 2 mm thick, were prepared with a 0.5-mm-thick layer of opaque porcelain (O) and a 1.5-mm-thick layer of body porcelain (B). The materials were selected to produce contraction coefficient differences, alpha O-alpha B, of +3.2, +0.7, -0.9, and -1.5 ppm/degrees C. Body porcelain discs with a thickness of 2 mm were used as the thermally compatible control specimens (delta alpha = 0). The discs were fired to the maturing temperature of body porcelain (982 degrees C) and were then subjected to three cooling procedures: slow cooling (SC) in a furnace, fast cooling (FC) in air, and tempering (T) by blasting the surface of the body porcelain with compressed and dried air for 90 s. The dimensions of cracks induced by a Vickers microhardness indenter under a load of 4.9 N were measured at baseline and six months after indentation at 80 points along diametral lines within the surface of body porcelain. In addition, biaxial flexure tests were performed to determine the influence of mismatch and tempering on flexure strength. The results of ANOVA indicate that crack dimensions were influenced significantly by the interaction of cooling rate and contraction mismatch (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Initial Flaw Size on Crack Growth in Air-tempered Porcelain

Tempering of dental porcelain by forced convective cooling in air has been shown previously to inhibit the sizes of cracks induced in porcelain surfaces. However, the depth of compressive stress that is produced by tempering of feldspathic porcelain has not been determined. It can be assumed that the potential of tempered specimens to inhibit crack formation is reduced as the flaw size exceeds some critical value, since the compressive stress decreases with distance from the surface. The objective of this study was to test the hypothesis that the effectiveness of tempering stress in porcelain decreases with the increasing size of initial surface flaws. Body porcelain discs, 16 mm in diameter and 2 mm in thickness, were tempered (T) by forced convective cooling in air from an initial temperature of 982 degrees C at a pressure of 0.34 MPa for 90 s. Nontempered control discs (NT) were slowly cooled by termination of power to the furnace. The half crack-lengths (c) of surface cracks induced by a Vickers microhardness indenter at loads ranging from 2.0 to 39.2 N were determined initially and over a period of 24 h. The initial half crack-lengths, co, for the tempered specimens were significantly smaller (p less than 0.05) than the corresponding values for the slow-cooled specimens. The mean value of the stress corrosion susceptibility coefficient (n), which is inversely related to the slope of log crack size vs. log time, was only slightly smaller for the NT specimen groups (15.3), compared with the mean value for the T groups (17.1).(ABSTRACT TRUNCATED AT 250 WORDS)

マルテンサイト系焼結ステンレス鋼のち密化および引張特性に及ぼす炭素量の影響

SUS410L (Fe-12 wt%Cr) and graphite mixed powder compacts are sintered at 1473 K to 1598 K, followed by heat treatment for controlling the matrix microstructure to martensite. The effects of carbon content on the sintering behavior and tensile properties are discussed, in order to develop the high strength P/M martensitic stainless steels. The results are summarized as follows:The amount of δ-ferrite at sintering temperature decreases and that of austenite increases with increase in carbon content and decrease in temperature. Specimens containing much amount of δ-ferrite undergo densification and pore-rounding during sintering, because of high self-diffusibility of δ-ferrite.0.1 wt% of carbon is necessary at least in order to control the matrix microstructure to martensite through optimum solution treatment.Tensile strength of low temperature tempered specimens increases with increasing carbon content as well as advance in densification. The latter method might be better for strengthening the specimens in view of corrosion resistance.

Influence of tempering and contraction mismatch on crack development in ceramic surfaces.

Tempering of glass produces a state of compressive stress in surface regions which can enhance the resistance to crack initiation and growth. The objective of this study was to determine the influence of tempering on the sizes of surface cracks induced within the tempered surfaces of opaque porcelain-body porcelain discs, with contraction coefficient differences (alpha O-alpha B) of +3.2, +0.7, 0.0, -0.9, and -1.5 ppm/degrees C. We fired the discs to the maturing temperature (982 degrees C) of body porcelain and then subjected them to three cooling procedures: slow cooling in a furnace (SC), fast cooling in air (FC), and tempering (T) by blasting the body porcelain surface with compressed air for 90 s. We used body porcelain discs as the thermally compatible (delta alpha = 0) control specimens. We measured the diameters of cracks induced by a microhardness indenter at an applied load of 4.9 N at 80 points along diametral lines within the surface of body porcelain. The mean values of the crack diameters varied from 75.9 microns (delta alpha = -1.5 ppm/degrees C) to 103.3 microns (delta alpha = +3.2 ppm/degrees C). The results of ANOVA indicate that significant differences in crack dimensions were controlled by cooling rate, contraction mismatch, and their combined effect (p less than 0.0001). Multiple contrast analysis (Tukey's HSD Test) revealed significantly lower (p less than 0.05) crack sizes for tempered specimens compared with those of fast-cooled and slow-cooled specimens.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of the mechanism of stress‐corrosion crack propagation in AISI 4340 steel in aqueous 3.5 wt.% NaCl solution

Stress‐corrosion (SC) crack propagation in AISI 4340 steel has been studied with 2 mm thick single edge‐notched (SEN) specimens under constant load conditions as a function of applied potential and tempering conditions in an aqueous 3.5 wt.% NaCI solution at 30°C. The SC crack lengths were estimated by using the electrical potential method. As the amount of cathodic polarization increased, the SC crack propagation rate increased. Anodic polarization yielded opposite results. These polarization effects on the SC crack propagation are discussed in terms of absorbed hydrogen resulting from a cathodic reaction on the specimen surface. SC cracks propagated by intergranular fracture through most of the inner region, but shear lips were formed at the near subsurface, irrespective of applied potential and tempering temperature. This is explained in terms of the stress state dependency of hydrogen behaviour. Above experimental evidence well supports the theory that SC crack propagation is controlled by the hydrogen embrittlement (HE) process. The SC crack propagation rate decreased in the sequence of 300, 200, and 400°C‐tempered specimens. This is discussed as being related to the microstructural and yield stress effects.

Influence of quenchant temperature on the surface residual stress and impact fracture of carburized steel

The influence of quenchant temperature in the range 50 °C to 270 °C on the surface residual stress and impact fracture behavior was studied for carburized SAE 4130 and SAE 1526 steels. The surface compressive residual stress of both steels increased as the quenchant temperature was raised with the most significant increase occurring at quenchant temperatures above 200 °C. Tempering at 165 °C reduced the surface compressive residual stress of both steels by the same amount independent of quenchant temperature. The impact fracture resistance of the carburized case of untempered and tempered SAE 4130 was relatively unaffected by quenchant temperature. However, for carburized SAE 1526, increasing the quenchant temperature in the range 50 °C to 235 °C resulted in an increase in the impact fracture resistance of untempered specimens and a decrease in the fracture resistance of tempered specimens. Quenching carburized SAE 1526 to 270 °C produced the highest fracture resistance for both the untempered and tempered conditions. The dependence of the impact fracture resistance of carburized SAE 1526 on quenchant temperature was related to the formation of upper or lower bainite in the surface region of the carburized case.

The effect of structure on the deformation of as-quenched and tempered martensite in an Fe-0.2 pct C alloy

As-quenched and tempered martensite in an Fe-0.2 pct C alloy were subjected to tensile testing and structural characterization by light and transmission electron microscopy. The light temper, 400°C-l min, did not change packet morphology, but did reduce dislocation density, coarsen lath size and cause the precipitation of carbides of a variety of sizes. The yield strength of the as-quenched martensite was strongly dependent upon packet size according to a Hall-Petch relationship, but tempering significantly diminished the packet size dependency, a result attributed to packet boundary carbide precipitation and the attendant elimination of carbon segregation present in the as-quenched martensite because of autotempering. Examination of thin foils from strained tensile specimens showed that a well-defined cell structure developed in the as-quenched martensite, but that the random distribution of jogged dislocations and carbide particles produced by tempering persisted on deformation of the tempered specimens.

The Effect of the Cyclic Stress during the Tempering Treatment on the Temper Brittleness of Ni-Cr Steel

In order to clarify the effect of cyclic loading during the tempering on the temper brittleness of Ni-Cr steel, the transition temperatures of specimens which had been tempered under various loading and cooling conditions were examined, and the precipitation and the grain boundary etching in each tempered specimen were observed by the electron microscope.The summarized results are as follows:(1) In all cases of the cooling methods, such as water cooling, furnace cooling A (cooling rate: 4°C/min), furnace cooling B (cooling rate: 1°C/min) and furnace cooling A with loading, the effect of cyclic loading during the tempering on the transition temperature clearly exists and the transition temperature rises with the increase of stress amplitude. And the effect of cyclic loading on the transition temperature is more remarkable at higher cooling rate. The transition temperatures in both conditions of the furnace cooling A and the furnace cooling A with loading are nearly the same value at all stress amplitudes.(2) The grain size and the hardness in the tempered specimens under the various conditions are almost constant, that is, the grain size is about 40μm in diameter and the hardness is about 20HRC. There are no effects of cyclic loading during the tempering on the grain size and the hardness in the tempered specimens.(3) There is a slight correlation between the volume of precipitation and the transition temperature. The transition temperature has a tendency to rise with the increase of the volume fraction of precipitation, but this tendency is not so clear. There is a clear correlation between the extent of boundary etching and the transition temperature. When the cyclic load during tempering increases, the extent of boundary etching increases and the transition temperature move to the higher side in temperature. In other words, when the cyclic load during tempering increases, the diffusion of some component or the micro precipitation on the grain boundary might be facilitated and the temper brittleness might be promoted.

Oriented thermomechanical hardening and recrystallization of high-carbon steels

Recrystallization of austenite in high-carbon steels after light (ɛ = 20–25%) deformation is not a uniform process because of the nonuniform and localized character of the deformation of austenite grains. The largest increase in the average grain size of austenite in steel ShKh15 takes place during the first 1.5 min of post-deformation annealing, and the grain growth rate is much faster in the transverse than in the longitudinal direction. As a result of recrystallization processes during HTMT of high-carbon steels, their strength and ductility are sometimes reduced below the level recorded for quench-hardened and tempered specimens. Recrystallization during HTMT leads to a reduction in the degree of anisotropy of mechanical properties determined in tests under direct and inverse loads. The results of mechanical tests show, however, that oriented inclusions and a striated structure confer a considerable degree of anisotropy on the properties of recrystallized specimens. The reduction of quasi-brittle strength of martensite after HTMT (followed by recrystallization) is to a large degree attributable to the oriented growth of recrystallized grains; this relation is described by Eq. (2). The reduction in ductility is associated with the reduced quasi-brittle strength of martensite formed from recrystallized austenite.

Effect of reactor radiation on the phase composition of low-alloyed uranium alloys

1. The effect of reactor radiation at 60–80°C on the electrical resistivity of binary uranium alloys containing iron, aluminum, and silicon was studied and the changes in resistivity for these materials after being irradiated were found. 2. Conclusions were made for the radiation changes in the phase composition of the alloys on the basis of the above-given linear curve representing the resistivity of these binary alloys as a function of alloying-additive content in the metastable solid solution. 3. The radiation increase in resistivity for uranium alloys containing iron and aluminum and tempered at 350°C is due to the dissolution resulting from radiation diffusion of the finely-dispersed intermetallic inclusions and to their formation around these zones enriched by the alloying additive. It was established that the rate of radiation dissolution for the inclusions increases when their size decreases. 4. From data obtained for the change in electrical resistivity of γ-quenched alloys upon irradiation we concluded that irradiation causes the metastable solid solutions to partially break up because the point defect concentration is decreased and inclusion generation centers are formed. 5. Isochronous annealing of tempered specimens irradiated by 4.2·1017 neutron/cm2 leads to a rapid restoration in resistivity; this is probably due to the restoration of initial intermetallide inclusions. Irradiation of γ-quenched alloys facilitates the breakdown process in the metastable solid solutions when they are then annealed isochronously.

Effect of aging regime on amount of residual austenite in fuel equipment parts

1. The existing methods of quenching fix the residual austenite in the structure of ShKh15 and KhVG steels. 2. The aging of tempered specimens at 130–140° for 24–48 hours does not cause any further reduction in the residual austenite and should not be recommended. 3. The aging of parts made of ShKh15 and KhVG steels at 160° reduces the amount of residual austenite by 1.5–2.5%, the most intensive decomposition occurring in the case of KhVG steel within the first 2 to 4 hours, and in the case of ShKh15 steel within the first 5–7 hours. Further soaking is technologically inadvisable. 4. Tempering at temperatures not above 160° as well as prolonged aging at 130–140° do not harden the residual austenite. Stable dimensions of parts made of ShKh15 and KhVG steels are only obtained after cold working (−30–70°) if the latter is applied immediately after quenching. 5. We can recommend the following heat treatment regime for parts made of ShKh15 or KhVG steels for fuel equipment: a) quenching from 830–840° in alkali or oil; b) cold working at −30–−70°; c) tempering at 160° for 4 or 5 hours, cooling in air; d) aging after machining for 2 or 3 hours at 160°.

焼入した鋼のクリープにおよぼす炭素量の影響

In the previous paper, the microplasticity of hardened ball-bearing steel under sustained twristing moment (shear stress of 1.8∼15.0 kg/mm2) between room temperature and 300°C, had been reported. It was suggested that the total strain increment between designated temperatures (named cumulative flow) of quenched specimens depends upon the carbon concentration of quenched martensite. In the present paper the cumulative flow for quenched carbon steels of various carbon contents was investigated and its dependency on the carbon concentration of martensite was established. For tempered specimens the cumulative flow below tempering temperature was also influenced by the primary carbon concentration. By means of twisting-creep tests, cold-drawn ball-bearing steel also exhibited a tendency fairly resembling that of quenched low-carbon steel.