Showing papers on "Pearlite published in 1988"

Magnetic properties and microstructure of AISI 1000 series carbon steels

Abstract: The magnetic properties of a number of specimens of AISI 1000 series plain carbon steels have been measured as functions of chemical composition, microstructure and heat treatment. The results showed that for a given morphology of the carbides the magnetic properties such as coercivity and permeability varied smoothly as a function of carbon content. Coercivity increased with carbon content by 2.0 Oe for every 0.1 wt.% carbon added at low carbon contents while initial permeability decreased by 57% on the addition of 0.2 wt.% carbon in the form of lamellar carbides (pearlite), but by only 21% when those carbides were in the form of spheroidised particles. In all cases the spheroidised specimens were found to be magnetically softer than the lamellar specimens and the difference increased with the amount of carbon present. Grain size did not seem to affect the magnetic properties significantly above a carbon content of 0.2 wt.%, although it was known that grain size is a significant factor in determining magnetic properties in iron alloys with lower carbon content.

Eutectoid decomposition mechanisms in hypoeutectoid Ti-X alloys

Abstract: A TEM study has been made of the bainite reaction in five hypoeutectoid Ti-X alloys, where X was successively cobalt, chromium, copper, iron and nickel. Rational orientation relationships were demonstrated amongst eutectoid α, eutectoid intermetallic compound and the β matrix in Ti-Ni, Ti-Co and Ti-Cr. Formation of Ti2Co at α:β boundaries was observed. Eutectoid α in bainite was found to be slightly misoriented with respect to proeutectoid α, indicating that it is separately nucleated, perhaps sympathetically, rather than the result of the continued growth of proeutectoid α. Eutectoid Ti2Co and Ti2Cu crystals in bainite were approximately equiaxed whereas Ti-Cr2 crystals were elongated, a result ascribed to a ledge height-to-spacing ratio ν/λ at intermetallic compound crystal: β boundaries approaching that of eutectoid (α:β boundaries in Ti-Cr but not in the other two systems. In the Ti-Fe alloy, eutectoid α and eutectoid TiFe were directly observed to have ledged interphase boundaries with their β matrix, but with different inter-ledge spacings and growth directions. Observation of pearlite lamellae growing normal to the broad faces of proeutectoid α plates in the Ti-Ni alloy indicates that this mode of eutectoid decomposition, like that of bainite, can develop from partially coherent interphase boundaries. The suggestion was offered that pearlite forms when λ approachesh at the nucleating proeutectoid α:β interface and that bainite develops when λ h at this interface.

Laser transformation hardening of iron-carbon and iron- carbon- chromium steels

Abstract: The laser transformation hardening response of Fe-0.5C-0.8Mn and Fe-0.5C-0.8Mn-0.8Cr steels was examined. A 2 kW CO2 laser was used to scan the steel surfaces at various rates. Complete transformation of pearlite to austenite, and hence to martensite, occurred in the laser heated surface layer of the Fe-C-Mn steel. During equivalent heat treatment of the Fe-C-Mn-Cr steel, incomplete austenitization of the pearlite colonies left the cementite plates largely undissolved. However, the maximum surface hardness was approximately the same for both alloys. Comparison of calculated and measured hardened depths yielded values of the effective coupling coefficient of the laser beam to the steel which varied as a function of beam interaction time. Modeling the process allowed a dis-tinction to be made between the effects of alloying elements and of pearlite spacing upon the depth of complete austenitization. In this case, the effect of the difference in pearlite spacing between the two steels was negligible. In the alloy steel, Cr and Mn were strongly partitioned to the cementite before heat treatment, and remained so after laser processing. Incomplete austenitization of that steel is attributed to partitioning of alloying elements to the cementite and their retarding influence on the diffusion controlled dissolution kinetics of the alloyed carbide.

The growth of microstructurally small fatigue cracks in a ferritic‐pearlitic steel

Abstract: — The growth behaviour of microstructurally small fatigue cracks was investigated with smooth specimens of a ferritic-pearlitic steel, S45C. under rotating bending. The effects of microstructure, particularly the role of pearlite structure, on crack growth were evaluated based on detailed microscopic observations. In the region smaller than a certain crack length. small cracks tended to grow preferentially in the ferrite structure, and the crack growth rates decreased markedly at ferrite-pearlite boundaries when small cracks grew into the pearlite from the ferrite. The above region of crack length, i.e. the length of microstructurally small cracks, depended on stress level, increasing with decreasing stress level. The growth mechanism is also discussed in terms of the results obtained from fractogrdphy.

Effect of pearlite morphology on impact toughness of eutectoid steel containing vanadium

Abstract: The effect of a change in the morphology of the pearlite colonies on the Charpy impact energy of a fully pearlitic steel containing 0·76%C, 1·20%Mn, and 0·085% V was examined over the range of testing temperatures from −50 to 200°C. The change from a multicolony nodular pearlite structure produced from austenite of grain size 185 μm to a structure composed of individually formed colonies produced from austenite of grain size 25 μm caused a decrease in the transition temperature of 75 K and an almost 100% increase in the Charpy impact energy measured at room temperature. It is proposed that the impact toughness of pearlitic steel can be affected by pearlite morphology, at constant interlamellar spacing, only at temperatures above the ductile–brittle transition temperature of the ferrite, when local plastic deformation in the pearlitic ferrite at high angle boundaries can arrest propagating brittle cracks.MST/730

Predicting properties and minimizing residual stress in quenched steel parts

Abstract: Quenching refers to the process of rapidly cooling metal parts from the austenitizing or solution treating temperature, typically in the range of 845 to 870°C (1550 to 1600°F) for carbon and low alloy steels, for the purpose of forming martensite. Several factors determine whether a particular part can be successfully hardened, including the type, molecular weight, and thermal characteristics of the quenchant, the quenchant use conditions (such as velocity, temperature, and polymer concentration, etc.), section thickness of the part, and the transformation characteristics of the specific alloy being quenched. Successful hardening usually means achieving the required hardness, strength, or toughness while minimizing residual stress, distortion, and the possibility of cracking. Heat removal from parts during quenching can be described in terms of the effective interface heat transfer coefficient. A quenchant must impart a sufficiently high interface heat transfer coefficient to produce a cooling rate that will minimize transformation of austenite to ferrite or pearlite and yield the desired amount of martensite. A quench factorQ has been devised that interrelates quenching variables and transformation kinetics of steel to provide a single number indicating the extent to which a part can be hardened at various locations within the part. The quenchant and the quenchant operating conditions should be selected to provide the proper quench factor while minimizing thermal gradients that can cause distortion or cracking. Cooling curves, interface heat transfer coefficients, quench factors, and thermal gradients produced by a variety of quenchants are presented.

The effect of alloying elements and microstructure on the strength and fracture resistance of pearlitic steel

Abstract: The processes of ductile and brittle fracture in fully pearlitic steel and their relation to both the scale of the microstructure and the presence of substitutional alloy elements have been investigated at room temperature using smooth tensile and over a range of temperatures using V-notched Charpy impact specimens. The results show that the early stages of cracking, revealed in both types of specimen, are largely the result of shear cracking of the pearlite lamellae. These cracks grow and can reach a size when they impinge upon the prior austenite boundary; afterward the character of fracture can be either microvoid coalescence or cleavage, depending on test conditions and metallurgical variables. Further, the carbide plates of the pearlite lamellae can act as barriers to the movement of dislocations as is the case normally with grain boundaries. For pearlite an optimum spacing of approximately 0.2 μm resulting from a balance between carbide plate thickness and interlamellar spacing was found to enhance toughness, although such changes are much smaller than corresponding changes due to varying alloy elements. Specific alloy elements used herein strengthened the lamellar ferrite in pearlite, inhibiting the movement of dislocations while also usually decreasing the lamellar cementite plate thickness for the same spacing. This dual behavior results in enhanced resistance to the initiation and propagation of microcracks leading to an improvement in strength, ductility, and toughness. The most effective alloy elements for the composition ranges studied in fully pearlitic steels are Si and Ni for strength improvement, and Ni and Mn for toughness.

Magnetic and metallurgical properties of high-tensile steels

Abstract: An investigation into the relation between magnetic and metallurgical properties of 26 types of high-strength constructional steel is reported. Correlation between chemical composition and coercive field was found. An independent correlation between coercivity, grain size and relative pearlite and ferrite fractions was also found. The coercivity and initial permeability varied with ultimate tensile strength but Vickers hardness measurements were not found to be a reliable method of predicting coercivity over the hardness range found in the sample set. For a larger hardness range, produced by heat treating one steel type, an excellent linear relationship was found between hardness and coercivity.

Influence of warm working and tempering on fissure formation

Abstract: The influence of warm working and tempering on the formation of fissures on the fractured faces of Charpy V-notch samples has been examined for a variety of ferrite–pearlite steels and iron alloys which had been rolled in the temperature range 600–400°C and tempered in the range 600–725°C. In accordance with fissures being initiated by the ease of intergranular failure along the ferrite grain boundaries, the number of deep fissures produced on warm working increased with the degree of grain boundary alignment in the rolling direction and the grain aspect ratio (maximum grain diameter/minimum grain diameter). Pearlite banding and the presence of grain boundary carbides were found not to influence the number of fissures formed, fissuring behaviour being the same for the Fe–Mn alloys and plain C–Mn steels. The presence of low levels of S and P also did not influence fissure formation. At a given average grain aspect ratio it was found that the introduction of a two phase rolling sequence (760–720°C) ...

Structure and microhardness of laser-hardened 1045 steel

Abstract: Observations are reported on the effect of continuous CO2 laser irradiation on the structure and microhardness of AlSI 1045 steel. In the case of isolated beam passes, martensite formed in the melt zone and in former pearlite regions of the austenitization zone exhibits very high Vickers hardness values (HV 750 and 900, respectively). However, in the case of contiguous or partly overlapping passes a zone of tempered martensite with hardness down to HV 400 forms behind each pass, thus resulting in a seesaw hardness distribution across the processed surface. It has been found that a drastic decrease in the size of the laser-affected region occurs when the beam power density exceeds a certain threshold level.

The interlamellar atomic habit plane in Cu-6% Be pearlite

Abstract: This investigation has sought to gain a better understanding of interphase boundaries in lamellar solid-solid phase transformations. Transmission electron microscopy has been used to characterize the f.c.c./ordered b.c.c. interface in the eutectoid Cu-6% Be binary. The atomic habit plane is established to be (111)f.c.c.//(110)b.c.c. with [110]f.c.c.//[111]b.c.c. Direction steps similar to those described by Hackney and Shiflet in ferrous pearlites were the only interfacial defect observed. Using point group intersection theory and our experimental results, it is shown that although the atomic habit plane is not a symmetry-dictated energy extremum, it is a minimum in energy space.

Manufacture of high strength cold rolled steel sheet having superior press formability

Abstract: PURPOSE: To manufacture a high strength cold rolled steel sheet having superior press formability by successively subjecting a steel sheet contg. specified amts. of C, Si, Mn and Al and obtd. by finish hot rolling at a specified temp. to cold rolling at a specified draft, heating to a specified temp. and cooling at stepwise varied cooling rates. CONSTITUTION: A steel contg., by weight, 0.12W0.40% C, 0.50W2.00% Si, 0.20W2.50% Mn and 0.005W0.10% sol. Al is hot rolled at 700W850°C finishing temp., cold rolled and heat-treated to regulate the ratio of pearlite : retained austenite to (1.5W2.5):1. The resulting steel sheet is pickled and cold rolled at 35W65% draft. This cold rolled steel sheet is heated to 730W900°C, cooled to 600W700°C at 1W10°C/sec cooling rate, further cooled to 200W400°C at 20W200°C/sec cooling rate, held for 2W50sec, further held at 350W450°C for 15secW10min and then cooled to ≤150°C within 30sec. A high strength cold rolled steel sheet having superior press formability can be manufactured. COPYRIGHT: (C)1989,JPO&Japio

Heat cycling of carbon steel wire

Abstract: 1. For refining the structure of carbon steel wire it is recommended to use HC. 2. The structure of steel after HC is granular pearlite of 1–2 points. Such a structure has a large margin of plasticity permitting cold drawing with a total deformation ɛt = 95–98%. 3. Heat cycling is an effective method of removing the cemenitite network in the structure of hypereutectoid steels. It helps improve the plastic properties of steel, and no graphitization is encountered.

Effect of laser beam irradiation on AISI 1045 steel

Abstract: The effect of the parameters of laser irradiation (beam power and travel velocity) as well as of various surface coatings and protecting atmospheres on the size, structure, and hardness of the laser-affected region was studied in the case of commercial 1045 steel and a continuous CO 2 laser. The action of the laser beam depends more strongly on its traverse velocity than on its power. When the power density exceeds a certain threshold level, a drastic decrease in the size of the laser-affected region takes place. The action can be enhanced by surface treatment in orthophosphoric acid as well as by some painted surface coatings. Unlike the latter, electroplated Cr and Ni layers were found to cause substantial alloying of the laser-treated layer. The laser-affected region formed by a single pass consists of two distinct zones: a melt zone, surrounded by an austenitization zone with a duplex structure representing former pearlite and ferrite regions. The hardness of the melt zone (about HV 750) exceeds that of conventionally hardened 1045 steel; even higher values (up to HV 900) are observed in the former pearlite regions of the austeniti zation zone, that of the former ferrite regions being about HV 250. In the case of an extended surface processed by a series of equidistant passes, a relatively wide region of tempered martensite is formed (with minimum hardness values down to HV 400) due to the heating generated by each pass in the previously hardened layer. As a result, a periodic hardness distribution is observed, whose fcatures depend on the degree of overlapping. High tensile residual stresses were found by x-ray diffraction in surface layers both in the cases of overlapping and separated passes.

Microstructural Aspects of Crack Initiation and Propagation in Extremely Low Cycle Fatigue

Abstract: A study has been made of the crack initiation and propagation in a low cycle fatigue of annealed carbon steel including extremely short fatigue life (N f < 100), with an emphasis on the establishment of the relation between the microfracture behavior and the damage accumulation process depending on the plastic strain range, Δ∈ p , as well as the mean strain, ∈ m . It was found that at the small Δ∈ P the surface damage due to the initiation and propagation of surface microcracks is predominant, while at the very large Δ∈ P giving fatigue life less than N f = 10, the internal cracking originated from the fracture of a pearlite becomes a primary source of the damage which results in the reduction of the residual ductility, ∈ F R . The transition from the surface damage to the internal one takes place when Δ∈ P becomes so large that the pearlite cracking may start inside the material at each level of ∈ m Good correlation was obtained between the reduction of residual ductility and the cracked pearlite ratio newly defined as a parameter for the evaluation of the internal microfracture behavior.

Interfacial coherency and hydrogen damage in plain carbon steel

Abstract: A low-alloy medium carbon steel with a variety of microstructures was cathodically hydrogen charged and the preferred microstructural sites for hydrogen-induced damage examined. Microcracks or microvoids initiated by the charging treatments were found to nucleate at both the grain and the interphase boundaries. Severe surface blistering was always associated with molecular hydrogen recombination and gas precipitation at manganese sulfide inclusions. The combination of spheroidized cementite particles on the grain boundaries provided more favorable microvoid and/or microcrack nucleation sites than for either individual grain boundaries or carbide particles within the grain interiors. Subgrain boundaries in quenched-and-annealed samples were found to be much less favorable sites than the large-angle grain boundaries for microvoid and/or microcrack nucleation under the same charging conditions. A mixed spheroidized and lamellar cementite (pearlite) microstructure was produced to examine the role of carbide-ferrite interfacial coherency in susceptibility to hydrogen damage. The nucleation of microcracks and/or microvoids along the broad faces of the cementite plates was observed to occur much less frequently than at the cementite plate edges or the spheroidized cementite-ferrite interphase boundaries. The results of this research indicate that the tendency for hydrogen to interact with and cause irreversible damage at a grain or interphase boundary increases with decreasing interfacial coherency.

Effect of inclusions on the fatigue limit of a heat-treated carbon steel

Abstract: The fatigue ratio, which is defined as the ratio of the fatigue limit to the ultimate tensile strength, of a carbon rail steel was determined experimentally after different heat treatments. Limited amounts of strengthening achieved by reducing the mean intercementite spacing in pearlite caused a small reduction in the fatigue ratio. Martensitic microstructures had a relatively low fatigue ratio. Such a behaviour is explained by the enhanced damaging effects of inclusions and impurities in the harder microstructures.

Modelling of Structure Formation and Relation to Mechanical Properties of Nodular Cast Iron

Abstract: The computer simulation of shaped castings is now in progress and introduced to foundry industry. The simulation of. solidification and cooling processes in a casting is a useful tool in the process of designing a casting optimally with respect to several phenomena like microstructure development and mechanical properties. Today the heat transfer calculations can be done in a FEM or FDM environment including solidification and solid state relations in shaped castings. The macroscopic heat transfer have been coupled to kinetic growth laws to describe the transformation rate. The macro and micro models of solidification and solid state transformation have been used to calculate the fraction and coarseness in nodular cast iron. The coarseness of the solidified structure is an input to the austenite transformation to ferrite and pearlite. The amount of structure has been related to mechanical properties. the mechanical properties of nodular cast iron depend on the cooling rate and other metallurgical factors. It is of great interest to calculate the variation of mechanical properties in a casting. Iso hardness graphs have been plotted for experimental castings. Good agreement has been achieved between experiments and calculations.

Manufacture of rail combining high strength with high toughness

Abstract: PURPOSE:To manufacture a rail excellent in strength and toughness, by working a medium-carbon steel bloom with a specific composition into a rail by means of hot rolling and then by applying heat treatment to the above rail under specific conditions CONSTITUTION:A steel bloom which has a composition containing, by weight, 050-085wt% C, 01-10% Si, 05-15% Mn, =2 kinds among 005-15% Cr, 001-02% Mo, 003-01% V, 01-10% Ni, and 0005-005% Nb is hot-rolled at =5% reduction in area so as to be formed into a rail, which is subjected to the refining of austenitic grains in the rail structure, further to reheating at 750-900 degC for 5min before the transition point from austenite to pearlite is reached, and then to accelerated cooling at 1-15 degC/sec cooling rate In this way, the rail combining high strength with high toughness can be manufactured

Manufacture of high strength steel wire having excellent resistance to cracking induced by hydrogen

Abstract: PURPOSE: To manufacture a high strength wire having excellent resistance to cracking induced by hydrogen even in the environment of humid hydrogen sulfide by subjecting a medium carbon steel material having specific compsn. to patenting treatment, thereafter to cold working at the specific sectional reduction rate into a wire rod and successively subjecting the wire rod to spheroidal annealing. CONSTITUTION: A steel material having the compsn. of, by weight, 0.40-0.70% C, 0.1-1.0% Si, 0.20-1.0% Mn, <0.025% P and <0.010% S and furthermore contg. at need 0.008-0.050% Al is subjected to patenting treatment to reduce the structure into uniformly fine pearlite. The material is subjected to wire drawing at 25-75% sectional reduction rate into a wire rod and is thereafter subjected to spheroidal annealing at 500-700°C to remove the working strain and to convert the pearlite structure into the structure where fine spheroidal cementite is dispersed in a ferrite matrix, by which the title steel wire material having ≥50kgf/mm 2 tensile strength can be manufactured. COPYRIGHT: (C)1989,JPO&Japio