Showing papers on "Pearlite published in 1995"

Void initiation and microstructural changes during wire drawing of pearlitic steels

Abstract: Microstructural changes and void initiation in fully pearlitic steels during cold wire drawing were investigated by performing tensile tests and microstructural examination with scanning electron microscopy. In this investigation, the primary focus was on cementite lamellae aligned transversely to the drawing axis in pearlite colonies. Unlike the cementite lamellae aligned along the drawing axis that are deformed uniformly and thinned to a fibrous shape, those aligned transversely to the drawing axis are severely bent, curled and even fractured with increasing drawing strain. At high strain, a formation of globular cementite particles that are attributed to the densification of cementite was observed in colonies of lamellae aligned transversely to the drawing axis. In addition, it was found that voids were initiated in the vicinity of relatively large globular cementite particles due to the concentration of enhanced stress. The mechanisms of a formation of globular cementite particles and a void formation are discussed in conjunction with the deformation behavior of cementite lamellae during the drawing.

A mathematical model for the phase transitions in eutectoid carbon steel

Abstract: A mathematical model for the austenite-pearlite-martensite phase change in eutectoid carbon steel is presented. The model is based on Scheil's additivity rule and the Koistinen-Marburger formula. Existence and uniqueness results are established. To confirm the validity of the model, the Jominy end quench test has been simulated numerically for the carbon steels C 1080 and C 100 W1. The results are in good agreement with measurements

Pearlite phase transformation in Si and V steel

Abstract: Systematic research has been undertaken on the effects of single and combined additions of vanadium and silicon on the phase transformation and microstructure of pearlitic steels. Both alloy additions were found to result in the formation of nonlamellar products in the vicinity of austenite grain boundaries in hypereutectoid compositions (0.77 to 0.95 wt pct C). The products comprise discrete initial cementite particles and grain boundary ferrite, which is embedded with interphase precipitates of vanadium carbide. As the carbon content is increased further (up to 1.05 wt pct), the amount of grain boundary ferrite gradually decreases without any dramatic change in the morphology of the initial cementite particles. No continuous embrittling grain boundary cementite network was formed. The aspect ratios of the grain boundary cementite particles were decreased from 60:1 to 25:1 by the addition of the alloy elements. A compre-hensive model has been suggested to explain these effects. Other effects of these alloy elements on the microstructure of pearlitic steels have also been examined. For given austenitization conditions, an increase in carbon and vanadium content produced a decrease in austenite grain size. Silicon was found to increase the rate of interphase precipitation of vanadium carbides.

Effect of Inclusions and Microstructural Characteristics on the Mechanical Properties and Fracture Behavior of a High- Strength Low- Alloy Steel

Abstract: The strength and toughness properties of hot-rolled plates from three commercial heats of a high-strength low-alloy steel were investigated with respect to their intrinsic microstructural and inclusion characteristics. One heat was argon purged and contained relatively higher carbon and sulfur, whereas the other two heats, with lower carbon and sulfur levels, were sulfide shape controlled. The study revealed that although yield and tensile strengths specific to a heat were unaffected by testing direction, the anisotropy in tensile ductility was greater in steels with stringered sulfides. Despite similar grain sizes in all the steels, Charpy shelf energy and impact transition temperature were significantly affected by pearlite content and sulfide morphology and to a lesser extent by pearlite banding. The modification of stringer sulfides to tiny lenticular/globular oxysulfides resulted in considerably higher shelf energies, lowering of impact transition temperatures, and minimal anisotropy of impact properties. The macroscopic appearance of splitting on the fracture surfaces of transverse Charpy specimens associated with low impact energies confirmed failure by a low-energy mode. The presence of pancake-shaped ferrite grains and fractographic evidence of inclusion stringers inside furrows identified their role in accentuating the splitting phenomenon.

The effect of alloy elements on the microstructure and properties of austempered ductile irons

Abstract: Ductile cast iron has already demonstrated excellent mechanical properties. If given proper austempering, it can exhibit even more outstanding characteristics. The process of austempering for ductile cast iron is similar to steel, and requires an adequate completely, and then rapidly quenching the austenitizing temperature allowing the matrix of ductile iron to be austenitized completely, and then rapidly quenching the austenitized ductile iron down to 300 C--400 C. Caution is required to prevent austenite from transforming into proeutectoid ferrite or pearlite. Finally, the ductile iron must be kept in an isothermal condition for a proper length of time. Many kinds of experimental techniques such as quantitative metallography, magnetic change, dilatometry, X-ray diffraction, electrical resistivity change etc., may be used to measure the phase transformation during the austempering of ductile irons. However, the method of measuring the change of electrical resistivity, not only provides continuous and complete data, but also the time to start and to finish for both stages of the reaction can be significantly determined. In this paper, the effect of alloy elements on the microstructure and property of ADI was investigated. First, the specimens containing Mn, Cu, Ni and Mo were made separately, then a PC-controlled vacuum heat treatingmore » system was used for the heat treatments.« less

Fracture toughness of sub-zero-chilled cast iron

Abstract: A series of fracture toughness experiments were carried out involving sub-zero-chilled (using liquid nitrogen) cast iron containing 1.5% Cu, and chromium contents ranging from 0.0%–0.2%. By using copper chills of different thicknesses, the effect on fracture toughness of varying the chill rate was also examined. The fracture toughness tests were carried out using three-point bend specimens, each with a chevron notch, as per ASTM E 399-1974 standards. It was found that fracture toughness is highly dependent on the location on the casting from where the test specimens are taken and also on the chromium content of the material. Chill thickness, however, does not significantly affect the fracture toughness of the material. There was found to be an approximately linear relationship between fracture toughness and pearlite content, in which fracture toughness increases as pearlite content decreases and vice versa.

On the decomposition of β phase in some rapidly quenched titanium-eutectoid alloys

Abstract: The decomposition of the β phase in rapidly quenched Ti-2.8 at. pct Co, Ti-5.4 at. pct Ni, Ti-4.5 at. pct, and 5.5 at. pct Cu alloys has been investigated by electron microscopy. During rapid quenching, two compctitive phase transformations, namely martensitic and eutectoid transformation, have occurred, and the region of eutectoid transformation is extended due to the high cooling rates involved. The β phase decomposed into nonlamellar eutectoid product (bainite) having a globular morphology in Ti-2.8 pct Co and Ti-4.5 pct Cu (hypoeutectoid) alloys. In the near-eutectoid Ti-5.5 pct Cu alloy, the decomposition occurred by a lamellar (pearlite) type, whereas in Ti-5.4 pct Ni (hypereutectoid), both morphologies were observed. The interfaces between the proeutectoid α and the intermetallic compound in the nonlamellar type as well as between the proeutectoid α and the pearlite were often found to be partially coherent. These findings are in agreement with the Lee and Aaronson model proposed recently for the evolution of bainite and pearlite structures during the solid-state transformations of some titanium-eutectoid alloys. The evolution of the Ti2Cu phase during rapid quenching involved the formation of a metastable phase closely related to an “ω-type” phase before the equilibrium phase formed. Further, the lamellar intermetallic compound Ti2Cu was found to evolve by a sympathetic nucleation process. Evidence is established for the sympathetic nucleation of the proeutectoid a crystals formed during rapid quenching.

Effect of silicon on CGHAZ toughness and microstructure of microalloyed steels

Abstract: The aim of this article is to present the beneficial effect of a reduction of silicon content on coarse-grained heat-affected zone (CGHAZ) toughness. This study was achieved with experi-mental and industrial E355 structural steels. These 0.09 wt pct C steels were Ti-microalloyed with silicon contents ranging from 0.05 to 0.5 wt pct. First, we demonstrate that the CGHAZ toughness is predominantly affected by the volume fraction of retained austenite (γr). Second, we show that the existence of retained austenite pertains only to its carbon enrichment. This enrichment is promoted essentially by an increase of the silicon level due to the retarding action of silicon on the formation of carbides in ferrite as well as in austenite. In the same way, the increase of silicon content slows down the decomposition of retained austenite into pearlite. The reduction of the silicon content of the steel greatly increases the ductility of the CGHAZ through the decrease of the volume fraction of retained austenite.

Microscopic characterisation of ε-Cu interphase precipitation in hypereutectoid Fe-C-Cu alloys

Abstract: During isothermal pearlitic transformation in medium or high carbon copper steels the decomposition of austenite leads, apart from the formation of proeutectoid phases and pearlite, to the precipitation of the e-Cu phase. At temperatures close to that of the eutectoid of the system interphase precipitation of e-Cu occurs within proeutectoid ferrite (medium carbon steels), within grain boundary proeutectoid cementite (high carbon steels) and within both pearlitic ferrite and cementite. As the temperature of the isothermal pearlitic transformation is lowered the formation of copper supersaturated pearlitic ferrite occurs while within proeutectoid cementite (grain boundary or Widmanstatten) and pearlitic cementite interphase precipitation of e-Cu continues. This study of the isothermal pearlitic transformation in the Fe-Cu-C system revealed that interphase precipitation of e-Cu always occurs on moving cementite/austenite interphase boundaries but e-Cu interphase precipitation only occurs on moving ferrite/austenite boundaries at temperatures close to the eutectoid temperature range of the system.

A microscopic investigation of the precipitation phenomena observed during the pearlite reaction in vanadium alloyed carbon steels

Abstract: During the isothermal pearlitic transformation in vanadium alloyed low and medium carbon steels the formation of proeutectoid ferrite precedes that of pearlitic formation. Within this proeutectoid ferrite interphase precipitation of vanadium carbide (VC) occurs in a form of linear uniformly sized and shaped arrays of particles. When pearlite subsequently forms, two distinctive pearlitic morphologies exist. Lamellar and non-lamellar spheroidised types of pearlite. Within the pearlitic constituent of both of these pearlitic microstructures VC interphase precipitation occurs. However, in the lamellar type of pearlite curved arrays of uniformly sized and shaped VC particles whose direction is perpendicular to the cementite long axis are observed while in the non-lamellar type of pearlite apparently random distributions of VC particles exist. It was consistently found that VC interphase precipitation always occurred on the moving austenite/ferrite interphase boundaries at all temperature of isothermal pearlitic transformation.

A study of the behavior of boron diffusion in plain carbon steels

Abstract: Boronizing treatment of ferrous materials has been widely employed by industry as a surface-strengthening technology for inhibition of corrosion, wear and erosion. Pack boronization using a pack composition that produces a graded boride microstructure has been studied using AISI 1018 and 1045 steels. Carbon in these alloys creates a resistance to boron diffusion because a carbon-enriched zone forms in front of the boride layen The carbon concentration at the boride/pearlite interface was found to be as high as 3.0% in AISI 1045 steel. No significant layer phenomena could be distinguished inside the boron layer using the pack composition developed during this research. This result is significant because a graded microstructure with a continuous variation of the boron composition has been produced. Evidence developed during this study suggests that the boride layer consists of a mixture of FeB, Fe2B, and FeBx, which is probably FeB19. Analysis determined a measure of the resistance of carbon to boron diffusion at the boride/pearlite interface.

Strain hardening of steels at large strain deformation. Part II: Strain hardening of pearlitic and austenitic steels and the estimation of mechanical properties

Abstract: Continuing from Part I of this work, the strain hardening behaviour of eutectoid pearlitic and austenitic steels was investigated. Pearlitic steels with different lamellar distance and colony size were produced with sufficient deformability to obtain stage IV. The influence of microstructure on strain hardening of these steels can be described more accurately by an extended Kocks model (hybrid model) than the Kocks model. However, as for the Kocks model, the hybrid model is also violated in stage IV. The strain hardening rate of the pearlitic steels is much higher than of ferritic steels. With the help of austenitic stainless steels with different Ni content, the differences between the strain hardening behaviour of b.c.c. and f.c.c. steels were investigated. A significant influence of Ni content on strain hardening was found. Finally, based on the relationship between microstructure and strain hardening, the dependence of the ultimate tensile stress and uniform elongation on microstructures was estimated and compared with experimental results.

High strength steel wire excellent in twisting crack resistance

Abstract: PURPOSE: To improve the ductility of a high strength extra fine steel wire and to inhibit cracking in a longitudinal direction particularly during twisting tests by controlling the hardness distribution in a steel wire composed of carbon steel and the residual stress in the surface layer, respectively. CONSTITUTION: A carbon steel, having a composition containing 0.40-1.10wt.% C and also having a dual-phase structure of ferrite and pearlite or a pearlitic single-phase structure or a dual-phase structure of pearlite and cementite, is wiredrawn. The wire diameter is regulated to 0.60-0.10mm. The hardness distribution in the steel wire of 3000-4000MPa strength is regulated so that it satisfies the condition of 0.020 TS-105≤(HVR=0.8-HVR 0 )≤-0.060TS+260. At this time, R shows R=r/r 0 when r 0 and (r) represent the radius of the steel wire and the distance between the arbitrary position and the center of the steel wire, respectively, and HVR=0.8-HVR 0 shows the value obtained by subtracting the hardness in the central part from the hardness at a position of R=0.8, and further, TS represents the SI unit tensile strength. This hardness distribution can be attained, e.g. by properly regulating patenting treatment conditions and a reduction of area in the vicinity of the final stage of wiredrawing. COPYRIGHT: (C)1996,JPO

Steel material for induction hardened shaft parts, combining cold workability with torsional fatigue strength characteristic

Abstract: PURPOSE: To provide a steel material suitable for induction hardened shaft parts, excellent in cold workability before induction hardening and excellent in torsional fatigue strength after induction hardening. CONSTITUTION: This steel material has a composition containing, by weight ratio, 0.35-0.60% C, 0.01-0.15% Si, 1.0-1.8% Mn, 0.05-0.8% Mo, 0.01-0.15% S, 0.015-0.05% Al, 0.005-0.05% Ti, 0.0005-0.005% B, and 0.002-0.01% N and having P, Cu, and O contents limited to specific values, respectively, or further containing either or both of specific amounts of Nb and V, or further containing either or both of Cr and Ni. Moreover, this steel material has a microstructure consisting of ferrite and lamellar pearlite, and further, the fraction of structure of ferrite is <=35% and ferritic crystalline grain size is <=20μm.

Appraisal of recent work on role of crystallography in ferrous and non-ferrous pearlite

Abstract: Work on pearlite up to 1962 is briefly outlined and work on the crystallography of pearlite before 1984 is discussed. Studies of the heterophase boundaries in ferrous and non1errous pearlite by transmission electron microscopy over the past decade are introduced. The ‘ledge growth mechanism’ based on such studies is evaluated against the ‘classic’ view of pearlite growth. It is concluded that the hypothesis of the ledge growth mechanism offers a comprehensive explanation of pearlite phenomena and that the classic view fails to account for some features of pearlite. The implications of the new research on pearlite are addressed. The details of ledge motion and the velocity–spacing problem are discussed. The lack of work on the importance of crystallography on morphological evolution of pear lites is identified. Further work necessary to evaluate and advance the new understanding of pearlite is outlined.MST/3253

Modelling of microstructural evolution during accelerated cooling of hot strip on the runout table

Abstract: Microstructural evolution in the hot strip after finishing and subsequent accelerated cooling on the runout table has been modelled in order to assess their suitability for further processing. Transient heat transfer and kinetics of phase change comprising austenite to ferrite plus pearlite have been coupled to ascertain temperature profile, taking into accout the heat generated during phase change. Johnson-Mehl-Avrami relation together with Scheil's rule of additivity have been invoked. Several process parameters such as, coefficient of heat transfer, temperature at the exit of finishing stand, thickness and the speed of strip have been varied to determine their influence on the extent of phases engendered on the runout table. It has been demonstrated that greater spreadout in cooling arrangement with relatively lower heat transfer coefficient ensures homogeneity in microstructure. Cooling from comparatively higher finishing temperatures may result in greater microstructural uniformity. Two grades of steel - namely 0.05C-0.23Mn-0.015Si and 0.08C-0.37Mn-0.06Si - were chosen to carry out plant trials to validate the model. Special features of the microstructure have been brought out and the mechanical properties have been correlated.

Method of manufacturing of a cast iron alloy for brake disks and brake drums for vehicles

Abstract: A cast iron alloy is made by carburising a low phosphorous cast iron alloy to produce a carbon content of 3.6-3.9% and a nitrogen content of 0.005-0.025%. This also produces a thermal conductivity of at least 46 W/Km (at 0-100 deg.C) and a relatively high hardness (less than 200 HB). In a second stage, the cast iron is alloyed with 0.2-0.4% C; 0.2-0.4 Cu; 0.1-0.3 Ni; 0.1-0.2 Mo to stabilise the pearlite and raise the tensile strength. Finally, in a third stage, up to 0.1, pref. 0.06% Zr; up to 0.1, pref. 0.05 Nb/Ta; up to 0.12, pref. 0.07 Ti; and up to 0.2, pref. 0.1 V are added as nitrogen fixing agents. In the microstructure of the iron, finely divided extremely hard and high melting carbonitride crystals are precipitated.

High strength and high workability steel sheet for can producing excellent in baking hardenability, aging resistance and non-earing

Abstract: PURPOSE:To produce a high strength and high workability steel sheet for can producing having non-earing property by making the combined structure of ferrite and pearlite by means of subjecting a hot rolled low carbon sheet to first rolling and second rolling. CONSTITUTION:After the steel ingot consisting of, by weight, 0.08-0.15% C, =50 deg.C/sec and is coiled at 400-540 deg.C, this hot rolled sheet is subjected to the first cold rolling at a draft of 70-90% after acid pickling treatment, further by holding at the temp. of 10-50 deg.C higher than Ac1 point and =20sec, the ferrite structure with controlling the austenite quantity in the structure to 10-50% is obtained. Subsequently, it is cooled down to =70 deg.C/sec, after holding at >=300 deg.C for 20-60sec, it is subjected to the second cold rolling at a draft of 10-35%, the steel sheet for can producing of >50kbf/mm tensile strength and >5% elongation is produced.

Influence of Previous Structure on Laser Surface Hardening of AISI 1045 Steel

Abstract: The effect of laser surface hardening was studied in an AISI 1045 steel with different microstructures: ferrite and pearlite, or with carbides dispersed in the ferritic matrix produced by martensite tempering at 180, 450, 600 and 660°CThe laser treatments were carried out working with a 10×10 mm square beam of uniform power density and 15, 25 and 5 kW output power The scan rates permitted temperatures to range from those at the austenitization start to the melting point of the materialThe depths of the zones of affected material were revealed by metallographic observation and Vickers hardness measurement The results suggest that the initial structure of the steel has a considerable influence on laser surface hardening effect The differences are manifested in the depths of the distinct heat affected zones and in the obtained microstructures

Method of manufacture high carbon content steel

Abstract: Alloyed steel with high carbon content having a composition, expressed in percentage weight: carbon from 1.1 to 2.0%, manganese from 0.5 to 3.5%, chromium from 1.0 to 4.0%, silicon from 0.6 to 1.2%, the remainder being iron with the usual impurity content, such that it provides a metallographic structure mainly of non-equilibrium fine pearlite and that its hardness is between 47 Rc and 54 Rc.

Pearlite filtering aid

Abstract: This pearlite filtering aid is made of expanded pearlite and features no poison and abnormal odour, good chemical stability, high filter speed and wide adaptability. It is suitable for various filter equipment with positive or negative pressure operation, and has a packing density lower than that of the diatomite one.

Simulation of the hot rolling and accelerated cooling of a C-Mn ferrite-bainite strip steel

Abstract: By means of torsion testing, the microstructures and mechanical properties produced in a 0.14 Pct C-1.18 Pct Mn steel were investigated over a wide range of hot-rolling conditions, cooling rates, and simulated coiling temperatures. The austenite grain size present before accelerated cooling was varied from 10 to 150 μm by applying strains of 0 to 0.8 at temperatures of 850 °C to 1050 °C. Two cooling rates, 55 °C/s and 90 °C/s, were used. Cooling was interrupted at temperatures ranging from 550 °C to 300 °C. Optical microscopy and transmission electron microscopy (TEM) were employed to investigate the microstructures. The mechanical properties were studied by means of tensile testing. When a fine austenite grain size was present before cooling and a high cooling rate (90 °C/s) was used, the microstructure was composed of ferrite plus bainite and a mixture of ferrite and cementite, which may have formed by an interphase mechanism. The use of a lower cooling rate (55 °C/s) led to the presence of ferrite and fine pearlite. In both cases, the cooling interruption temperature and the amount of prior strain had little influence on the mechanical properties. Reheating at 1050 °C, which led to the presence of very coarse austenite, resulted in a stronger influence of the interruption temperature. A method developed at Institut de Recherche Siderurgique (IRSID, St. Germain-en-Laye, France) for deducing the Continuous-Cooling-Transformation (CCT) diagrams from the cooling data was adapted to the present apparatus and used successfully to interpret the observed influence of the process parameters.

Spheroidal graphite cast iron for crank shafts and a crank shaft manufactured from such cast iron

Abstract: Spheroidal graphite cast iron for crank shafts having a tensile strength of 75 kgf/mm 2 or more, and having excellent conformability and machinability, which cast iron consisting, by area ratio, of graphite of 5 to 15%, ferrite of not more than 10%, and the balance pearlite matrix, said cast iron having a Brinell hardness (HB) of 241 to 277.

Manufacture of lightweight fibre-cement slab

Abstract: The light fibre-cement slab is made of cement, vinylon fibre, pearlite, sepiolite, mica, paper pulp and glass fibre and features use of sepiolite to avoid cement loss, and small-granularity expansion pearlite for decreasing weight and vaoiding floating in slurry.

Process for producing hot wide strip

Abstract: of EP0686702A broad hot-rolled strip is produced in an installation consisting of a continuous thin-slab casting unit, a temperature equalisation furnace and a rolling mill, with the temperature of the slab at the exit of the casting unit having a value above 950 degrees C. Between the casting unit and the temperature equalisation furnace the surface temperature of the slab is reduced sufficiently to allow structural change of austenite into ferrite/pearlite to take place. The installation is also claimed and incorporates a cooling section (1) in the form of a water-cooling system with switchable cooling units (4).

Method for producing a rotatable gray iron brake component

Abstract: A method for producing a brake component involves providing a cast gray iron rotatable brake component where the gray iron has a carbon content between 3.4% and 4.0%. The brake component is subjected to an austempering heat treatment process. Then it is subjected to a re-tempering process to provide a microstructure which consists of spheroidized pearlite carbon in a matrix of bainitic and austenitic ferrite.