Showing papers on "Bainite published in 1993"

Effects of Second Phase Morphology on Retained Austenite Morphology and Tensile Properties in a TRIP-aided Dual-phase Steel Sheet

Abstract: The relationship between second phase morphology and retained austenite morphology and the influences of these two kinds of morphology on tensile properties of a 0.17C-1.41Si-2.00Mn (mass%) TRIP-aided dual-phase steel have been investigated in a temperature range between 20 and 400°C.A large amount of fine retained austenite was obtained when the second phase morphology was "a network structure" or "an isolated fine and acicular one." The retained austenite particles were nearly isolated in the ferrite matrix away from bainite islands and were moderately stable. On the other hand, "an isolated coarse structure" of second phase resulted in a small amount of more stable retained austenite film along bainite lath boundary.The influence of second phase morphology on the flow curve significantly differed from that of a conventional ferrite-martensite dual-phase steel. Isolated retained austenite particles lowered the flow stress, and resultantly reduced the effects of second phase morphology (i.e., network effect or fine grain size effect) on flow stress. However, the isolated retained austenite particles enhanced effectively the ductility, particularly at 50-100°C, due to the moderate strain induced transformation. On the other hand, retained austenite films along bainite lath boundary scarcely influenced on tensile properties of the steel. These results were discussed on the basis of a continum theory.

Tensile properties and inhomogeneous deformation of ferrite-martensite dual-phase steels

Abstract: The tensile properties and inhomogeneous deformation of coarse ferrite-martensite dual-phase steels containing 17–50% martensite were analysed. The stress of dual-phase steels at equal strain increased with increasing volume fraction of martensite, f, but the rate of increase was reduced after f=0.3. The strain hardening rate was dependent on f at small strains (ɛ ⩽ 0.03), however, it became independent of f at larger strains. It was found that the deformation of the dual-phase steels divided into three different stages when f was less than about 0.3. The concurrent in situ stress-strain states of ferrite, martensite and their composite, and the stress ratios and strain ratios between ferrite and martensite were evaluated by means of a new stress and strain partition theory. The martensite phase deformed plastically after the uniform strain for f 0.25. The theoretical analyses for inhomogeneous deformation implied that the volume-fraction dependence of the stress and the characteristics of the strain-hardening rate were influenced by the plastic deformation of martensite. Further, the in situ stress-strain curves of ferrite and martensite and the internal stresses at respective phases were calculated from the partitioned stresses and strains.

Effect of cooling rate on intercritically reheated microstructure and toughness in high strength low alloy steel

Abstract: High strength low alloy steels have been shown to be adversely affected by the existence of regions of poor impact toughness within the heat affected zone (HAZ) produced during multipass welding. One of these regions is the intercritically reheated coarse grained HAZ or intercritical zone. Since this region is generally narrow and discontinuous, of the order of 0.5 mm in width, weld simulators are often employed to produce a larger volume of uniform microstructure suitable for toughness assessment. The steel usedfor this study was a commercial quenched and tempered steel of 450 MN m -2 yield strength. Specimen blanks were subjected to a simulated welding cycle to produce a coarse grained structure of upper bainite during the first thermal cycle, followed by a second thermal cycle where the peak temperature T p2 was controlled. Charpy tests carried out for T p2 values in the range 650-850°C showed low toughness for T p2 values between 760 and 790°C, in the intercritical regime. Microstructural investigation of the development of grain boundary martensite-retained austenite (MA) phase has been coupled with image analysis to measure the volume fraction of MAformed. Most of the MA constituent appears at the prior austenite grain boundaries during intercritical heating, resulting in a 'necklace' appearance. For values of T p2 greater than 790°C the necklace appearance is lost and the second phase areas are observed throughout the structure. Concurrent with this is the development of the fine grained, predominantly ferritic structure that is associated with the improvement in toughness. At this stage the microstructure is transforming from the intercritical regime structure to the supercritically reheated coarse grained HAZ structure. The toughness improvement occurs even though the MA phase is still present, suggesting that the embrittlement is associated with the presence of a connected grain boundary network of the MA phase. The nature of the second phase particles can be controlled by the cooling rate during the second cycle and variesfrom MA phase at high cooling rates to a pearlitic structure at low cooling rates. The lowest toughness of the intercritical zone is observed only when MA phase is present. The reason suggested for this is that only the MA particles debond readily, a number of debonded particles in close proximity providing sufficient stress concentration to initiate local cleavage. © 1993 The Institute of Materials.

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

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

Observation of deformation and transformation behavior of retained austenite in a 0.14C-1.2Si-1.5Mn steel with ferrite-bainite-austenite structure

Abstract: A 0.14wt.%C-1.21wt.%Si-1.57wt.%Mn steel was intercritically annealed at 770°C for 5 min and then isothermally held at 400°C for 4 min followed by oil quenching to room temperature. The as-annealed microstructure consisted of 75% ferrite, 13% bainite, and 12% retained austenite. The steel was used to establish a microscopic method to identify retained austenite, and to observe the deformation and transformation behavior of the retained austenite with tensile deformation. Submicron-sized articles of retained austenite could be distinguished from ferrite, bainite and martensite in light microscopy when etched with 5% nital followed by etching in a 10% sodium metabisulphite solution. The retained austenite particles were observed in three types of locations: type I at ferrite grain boundaries always in contact with bainite; type II at ferrite grain boundaries out of contact with bainite; and type III within ferrite grains. It was also observed that the larger retained-austenite particles transformed more easily to martensite during deformation at room temperature. Even after deformation to a tensile strain greater than 32%, about 4% of the retained austenite remained, and the retained-austenite particles were observed in the deformed structure.

Interphase precipitation in microalloyed engineering steels and model alloy

Abstract: Interphase precipitation of alloy carbide or carbonitride which occurs in association with the transformation interface between austenite and ferrite and between austenite and pearlite in steels can result in a fine particle dispersion that can contribute significantly to strength levels in a wide range of structural and engineering steels. Interphase precipitation has been found to occur in both proeutectoid and pearlitic ferrite, and various morphological aspects have been studied in a range of low carbon and higher carbon steels. Studies of this precipitation reaction are hindered by the fact that the transformation interface is lost upon cooling to room temperature, either by further transformation or by decomposition of the residual austenite phase to martensite. In the present work this has been avoided by developing a model alloy in which the precipitation reaction occurs, but in which the austenite is stabilised to room temperature, thus allowing a detailed examination of the interfacial r...

Escape of carbon from ferrite plates in austenite

Abstract: A newly developed computer program for the simulation of diffusional transformations has been applied to study the escape of carbon from a plate of ferrite assuming that the plate initially formed by a partitionless reaction from an FeC austenite. Thereafter the ferrite-austenite interface was assumed to be immobile and local equilibrium was assumed for carbon but not for iron. The process first follows a parabolic rate law and is there controlled by the rate of diffusion in ferrite. Later stages are not parabolic and are controlled by the diffusivity in austenite. Its concentration dependence was taken into account. It was found that the rate could be estimated analytically using the maximum value rather than the average value.

Physical metallurgy of direct-quenched steels

Abstract: This symposium was held during November 2-4, 1992 in Chicago as part of Materials Week '92''. This symposium focused on the metallurgy of steels containing martensitic or bainitic microstructures formed from thermomechanically processed austenite, and builds upon two recent topical meetings on the related subject of ferritic accelerated cooled steels. Papers in the first section deal with thermodynamics and kinetics of austenite transformation, the morphology of austenite transformation products, and alloy carbide precipitation. Results of investigations of relationships between processing variables, microstructure, and mechanical properties are contained in the following section. Section III is devoted specifically to boron hardenability effects. papers in the final section are concerned with product development; included here is a comprehensive overview of industrial accelerated cooling/direct quenching technology by researchers from the Nippon Steel Corporation.

The effect of alloying elements on the structure and mechanical properties of ultra low carbon bainitic steels

Abstract: Microalloying with Nb and B leads to a granular bainite microstructure which is composed of a bainitic ferrite matrix and a uniformly distributed martensite/austenite-constituent in the as-rolled condition. Due to this transformation strengthening mechanism, high strength and toughness could be achieved even though the C content was extremely low. It was found that both dissolved Nb in austenite and free B are prerequisites for granular bainite formation. Furthermore, there is a critical B content to achieve the complete bainitic transformation strengthening effect. The critical B content increases with C content. C thus diminishes the effect of B in promoting bainite transformation, due to the formation of boron carbides or the depletion of dissolved Nb in austenite. The effect of Mn, Mo and Ni on the decomposition of austenite is similar. A parameter“Mneq” which relates the effect of these alloying elements on the Bs temperature was derived. It was confirmed that the strength of bainitic steels is inversely proportional to theBs temperature.

Process for manufacturing cold-rolled steel sheets with high-strength, and high-ductility and its named article

Abstract: The primary object of the present invention is to provide a cold-rolled steel sheet with properties of high-strength, high-ductility, and a process for manufacturing it. The constituents of the cold-rolled steel sheet comprise: 0.08%-0.25% carbon by weight, 0.03%-2.0% silicon by weight, 0.6%-1.8% manganese by weight, 0.01%-0.10% niobium by weight, 0.01%-0.08% aluminium by weight, with the rest being substantially iron and unnoticed impurities. The process for manufacturing cold-rolled steel sheets of the present invention by using the molten steel material as described above includes the following steps: (a) preparing steel ingots by continuous casting the molten steel; (b) hot rolling the steel ingots into hot-rolled bands; (c) coiling the hot-rolled bands at a temperature below 600° C.; (d) after cold-rolling, forming steel sheets from the hot-rolled bands and soaking the steel sheets at a temperature in the two-phase range (equal to AC1+10° C.-AC3-10° C. shown in FIG. 1) for a time duration ranging from 1 minute to 10 minutes; (e) cooling the steel sheets to a temperature ranging from 350° C. to 500° C. at a cooling rate greater than 50° C./SEC; (f) soaking the steel sheets at a temperature ranging from 350° C. to 500° C. for a time duration from 1 minute to 10 minutes; (g) cooling the steel sheets by air so as to form the cold-rolled steel sheets having a microstructure of ferrite plus residual austenite plus bainite (or a small amount of martensite).

The influence of martensite shape, concentration, and phase transformation strain on the deformation behavior of stable dual-phase steels

Abstract: A continuum model is developed to examine the influence of martensite shape, volume fraction, phase transformation strain, and thermal mismatch on the initial plastic state of the ferrite matrix following phase transformation and on the subsequent stress-strain behavior of the dual-phase steels upon loading. The theory is developed based on a relaxed constraint in the ductile matrix and an energy criterion to define its effective stress. In addition, it also assumes the martensite islands to possess a spheroidal shape and to be randomly oriented and homogenously dispersed in the ferrite matrix. It is found that for a typical water-quenched process from an intercritical temperature of 760 °C, the critical martensite volume fraction needed to induce plastic deformation in the ferrite matrix is very low, typically below 1 pct, regardless of the martensite shape. Thus, when the two-phase system is subjected to an external load, plastic deformation commences immediately, resulting in the widely observed “continuous yielding” behavior in dual-phase steels. The subsequent deformation of the dual-phase system is shown to be rather sensitive to the martensite shape, with the disc-shaped morphology giving rise to a superior overall response (over the spherical type). The stress-strain relations are also dependent upon the magnitude of the prior phase transformation strain. The strength coefficienth and the work-hardening exponentn of the smooth, parabolic-type stress-strain curves of the dual-phase system also increase with increasing martensite content for each selected inclusion shape. Comparison with an exact solution and with one set of experimental data indicates that the theory is generally within a reasonable range of accuracy.

Effect of Compressive Deformation on the Transformation Behavior of an Ultra-Low-Carbon Bainitic Steel

Abstract: In this work, an experimental ultra-low-carbon-bainitic (ULCB) steel was prepared to study the effect of a prior compressive deformation on the transformation behavior during continuous cooling. It is found that prior deformation of austenite significantly enhances the bainitic transformation. At the same cooling rate the specimen with the prior deformation has a higher bainite start temperature (B s ) than the specimen without the prior deformation; in addition, the difference of B s temperature becomes much larger at the higher cooling rate. This result is not consistent with that reported by Tamehiro et al. (7) On the other hand, an isothermal experiment has been utilized to investigate the stability of the deformed austenite

Application of Hypereutectoid Steel for Development of High Strength Steel Wire

Abstract: Synopsis : The optimum patenting conditions for hypereutectoid steel to obtain a high drawability and a high work hardening rate were studied by metallographic examinations and laboratory drawing. Based on the present results, higher strength steel wire with small diameter has been manufactured on a production basis. 1) Provided that an appropriate cooling rate corresponding to carbon content is secured, the precipitation of thick proeutectoid cementite can be prevented. 2) In the practical patenting temperature range, the cementite plate thickness as well as the pearlite lamellar spacing decreases as the carbon content increases. 3) The work hardening rate during drawing and the delamination resistance are enhanced through elimination of the upper bainite in pearlite. 4) The maximum strength of 0.04mm wire manufactured from 0.96%C-0.2%Si-0.3%Mn-0.2%Cr steel without delamination occurrence has reached to as high as 5.70 GPa.

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

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

Banding and the nature of large, irregular pearlite nodules in a hot-rolled low-alloy plate steel: A second report

Abstract: The microstructure of a hot-rolled low-carbon plate steel has been examined using a combination of light microscopy and scanning electron microscopy. It has been found that in the hot-rolled condition, the microstructure consists of alternate bands of ferrite and pearlite, together with relatively large, irregular pearlite nodules. These large nodules were found to be comprised of pearlite, intragranularly nucleated ferrite (both Widmanstatten and idiomorphic), together with carbide-deficient and/or carbide-free regions. It is argued that the carbide-deficient and carbide-free regions form as a result of the premature initiation of the pearlite reaction, i.e. pearlite forms prior to the body of the austenite grains attaining the eutectoid composition. In order to model the formation of the banded structure, specimens were reaustenitized at 1050 °C for 10 min and furnace cooled. This heat-treatment cycle produced an austenite grain size which was less than the chemical banding wavelength. A model for the decomposition of austenite, under these conditions, is presented.

Effects of tensile-testing temperature on deformation and transformation behavior of retained austenite in a 0.14C-1.2Si-1.5Mn steel with ferrite-bainite-austenite structure

Abstract: A 0.14% C-1.21% Si-1.57% Mn steel was processed by intercritical annealing followed by isothermal transformation to produce a structure of 75% ferrite, 13% bainite and 12% retained austenite. The role of retained austenite was studied by directly observing the deformation and transformation behavior of the retained austenite. The stability of the retained austenite was changed by varying tensile-testing temperature from − 80 °C to 120 °C. With increasing temperature, the stability of the retained austenite with deformation increased. Furthermore, the austenite stability increased with a decrease in the austenite particle size. For samples tested at both 20 °C and 120 °C, retained austenite was observed to remain in the deformed structure at high strain. The deformed retained austenite improved ductility by suppressing void formation at the interface between retained austenite and either ferrite or bainite. In contrast, for samples deformed at − 80 °C, void formation preferentially occurred by interface decohesion of martensite-ferrite or martensite-bainite. The results of this study indicate that the ductility in low-carbon steel with high contents of retained austenite can be altered by control of the austenite stability.

High strength steel excellent in hydrogen embrittlement resistance and its production

Abstract: PURPOSE: To obtain a high strength steel having superior hydrogen embrittlement resistance even if heat treatment is omitted by treating a steel, containing specific amounts of C, Si, Mn, Al, and Fe, under prescribed conditions and forming the structure into martensite and/or bainite structure. CONSTITUTION: A steel, having a composition consisting of, by weight, 0.01-0.3% C, 0.01-2.5% Si, 0.01-3% Mn, 0.005-0.1% Al, and the balance Fe, is refined. After hot rolling or subsequent hot forging or heat treatment is applied to this steel, continuous cooling or isothermal transformation is performed, by which the structure can mainly be composed of martensite and/or bainite, thus the objective high strength steel excellent in hydrogen embrittlement resistance can be obtained. COPYRIGHT: (C)1994,JPO&Japio

Method of manufacturing high strength steel member with a low yield ratio

Abstract: A high tensile strength, low yield ratio steel member has a steel composition consisting essentially of, by weight: C: 0.15-0.40%, Si: 0.10-0.70%, Mn: 1.0-2.7%, Cr: 1.0-3.5%, sol.Al: 0.01-0.05%, P: not larger than 0.025%, S: not larger than 0.015%, Mo: 0-1.0%, Ni: 0-2.5%, V: 0-0.10%, Ti: 0-0.10%, Nb: 0-0.10%, B: 0-0.0050%. Fe and incidental impurities: balance the below-described bainite index (%) of the steel composition being 0-50%, the steel being comprised of a single phase of martensite or a martensite and bainite duplex structure containing 50% or less of bainite. Bainite Index (%)=-209C+43Si-48Mn-58Cr-0.416R+317 wherein R is a cooling rate (°C./min).

Incomplete reaction phenomenon

Abstract: Bainite forms by a displacive transformation mechanism and exhibits an incomplete reaction phenomenon. The kinetics and mechanism of bainite transformation have been studied in high- strength Fe-C-Si-Mn and Fe-C-Si-Ni steels using high-speed dilatometry. The new experiments reported here confirm the incomplete reaction phenomenon, with the bainite transformation stop- ping well before paraequilibrium is achieved. These results show that bainite probably grows without diffusion, but soon afterwards, excess carbon is partitioned into the residual austenite.

A transmission electron microscopy study of copper precipitation in the cementite phase of hypereutectoid alloy steels

Abstract: The precipitation of copper has been detected and studied in three of the main decomposition products of austenite: allotriomorphic grain-boundary cementite, pearlitic cementite, and Widmanstatten cementite plates. The investigation has been carried out on two high-alloy hypereutectoid steels containing copper contents of 1.0 and 2.5 wt pct. The main advantage of these high-alloy steels is that the parent austenite phase remains stable upon cooling to room temperature, thus preserving the parent phase and the parent/product interfaces in the microstructure for subsequent examination. Transmission electron microscopy (TEM) revealed that the copper precipitation occurs in proeutectoid allotriomorphic grain-boundary cementite in association with the transformation interface. The copper particles were dispersed in the form of rows (or sheets) within the allotriomorphs of cementite. Evidence for copper precipitate particles nucleated at structural features imaged at the growth interface was also obtained. Copper precipitation was found to occur in both the ferrite and cementite lamellae of pearlite, and again, examination of partially decomposed structures revealed copper particles nucleated at the austenite/pearlite transformation interface. In addition, copper particles were also observed at the ferrite/cementite interface of pearlite. Copper precipitation observed in Widmanstatten cementite plates revealed a precipitate-free midrib region in the plates and a higher concentration of copper particles toward the broad faces of the plate. Copper particles were also found located at coarse linear interface defects at the broad faces of the plate.

Elastic limit and microplastic response of hardened steels

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

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

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

Observations concerning transformation interfaces in steels

Abstract: The transformation interfaces of pearlite, allotriomorphic cementite, M[sub 23]C[sub 6], and Widmanstaetten cementite plates in high-Mn high-C alloy steels have been studied by TEM. Linear striations in the interface have been analyzed and related to intersections with stacking faults in the parent austenite phase. Emphasis is given to the pearlite interface where it is found that the striations at the interface increased as a result of thermomechanical treatment of the austenite prior to isothermal transformation, consistent with an increased density of planar defects. The effect of heat treatment, and Si alloying additions, are also considered. Both conventional and in situ TEM of the pearlite interface showed that the linear defects stretched across both ferrite and cementite phases at the pearlite interface, apparently without any deviation or change in image contrast. The results are compared with similar ones made of the static [gamma]/[alpha] interphase boundaries in duplex stainless steel. The effect of prior deformation structure in the parent austenite on the growth and interface structure of Widmanstaetten cementite plates has also been considered.

Deformation-induced microstructure and martensite effects on transgranular carbide precipitation in type 304 stainless steels

Abstract: Plastic deformation of 304 stainless steel (SS) induces transgranular (TG) carbide precipitation, which is critically dependent on deformation-induced microstructural changes occurring during thermal treatment of the SS. Uniaxial deformation of the 304 SS to 40% strain produces a high density of intersecting micro-shear bands composed of heterogeneous bundles of twin-faults and about 12–17% strain-induced α′-martensite at the intersections of the twin-faults. Thermal treatment of 670°C for 0.1–10 h, however, results in a rapid annihilation/transformation of the strain-induced martensite and the concurrent formation of zones containing mixed thermal martensite laths and fine-grained austenite, though the thermal martensite also decreases with increasing heat treatment time. Simultaneous with these thermomechanically-induced microstructural changes, TG chromium-rich carbides form at intersections of twin-faults and on fine-austenite or thermal martensite boundaries in the SS; however, no correlation between strain-induced α′-martensite and carbides was observed in this work. The mechanisms of deformation-induced microstructure and (strain-induced and thermal) martensite effects on TG carbide precipitation in 304 SS are discussed.

Cast steel piston ring material

Abstract: PURPOSE: To provide a piston ring material which is composed of fixed components, and has net-shaped nonsolved carbide in tempered martensite or bainite base to obtain fixed hardness, and thereby becomes excellent in rigidity, antiscarfing ability, and wear resistance, and is suitable for a marine Diesel engine etc.. CONSTITUTION: A cast steel piston ring material is composed of 0.6 to 1.0% of C, 2.0% or less of Si, 2.0% or less of Mn, 0.05% or less of P, 0.10% or less of S, 10 to 14% of Cr, 0.2 to 1.5% of Mo, 0.03 to 0.15% of V which are all in weight ratio, and remainder being practically Fe and impurities. A tempered martensite or bainite base has 5 to 20% net-shaped nonsolved carbide, whose hardness is set up to be HRC 32 to 45. Thus, in addition to antibreaking ability of steel, the net-shaped carbide is deposited by casting to produce the cast steel piston ring material being excellent in antiscarfing ability and wear resistance. COPYRIGHT: (C)1994,JPO&Japio

Wear resistant steel excellent in workability and weldability

Abstract: PURPOSE:To manufacture wear resistant steel excellent in workability and weldability by subjecting low carbon steel having a specified compsn. to heat treatment under specified conditions and incorporating its matrix structure of ferrite, bainite or the like with island shape martensite at a specified area ratio. CONSTITUTION:Ferritic-pearlitic steel or bainitic steel contg., by weight, 0.05 to 0.20% C, 0.50 to 2.00% Si and 0.5 to 2.50% Mn or furthermore contg. one or more kinds among 0.05 to 1.00% Cu, 0.05 to 2.00% Ni, 0.05 to 0.5% Cr, 0.05 to O.5% Mo, 0.005 to 0.10% Nb, 0.005 to 0.10% V, 0.005 to 0.10% Ti and 3 to 20ppm B, and the balance Fe is heated between the Ac1 to the Ac3 transformation point and is thereafter cooled at the cooling rate of that of air cooling or above. The steel cong. island shape martensite constituted of martensite and remaining austenite by >=5% area ratio and excellent in workability, weldability and wear resistance can be obtd.