Pearlite Banding Research Articles

Effect of Pearlite Banding and Weld Texture on Wheel Rim Failure in Resistance Upset Butt Welding

Effect of Pearlite Banding and Weld Texture on Wheel Rim Failure in Resistance Upset Butt Welding

Determination of fracture toughness in the short transverse direction of low carbon steel pipes by compact-tension specimens completed by welded attachments

An experimental procedure for direct measurement of the fracture toughness values (KIC) in the short transverse directions, of low carbon steel pipes, is proposed. The method consists of enlarging the material strip to be tested, by welding extensions so as to complete the dimensions of a valid compact tension specimen. Validation of the KIC results was done by the comparison between the values obtained from one-piece compact tension specimens and welded-completed specimens, both in the longitudinal direction (CL). Additionally, the effect of the steel microstructure orientation on the KIC in the short transversal direction was studied. The results show that the KIC values in the short transversal direction of low carbon steel pipes is as much as 20% lower than the CL direction. This is directly related to the relative orientation parameter (Ω12) and the banding degree (Ai) of the pearlite bands in the microstructure, and the location of the crack plane with respect to the pearlite banding plane.

Impact of the Spheroidization Annealing on the Intensification or Mitigation of the Initial Pearlite Banding Degree Presented in Wire Rolled State

Abstract In this study, two initial conditions of the steel 16MnCrS5 are considered: the industrially hot-rolled pearlite structures in their ferritic matrix and a specifically adjusted microstructure in the lab condition. Based on the experimental investigations and quantitative microstructural analyses, an empirical model for the prediction of pearlite banding within a broad range of annealing durations could be derived. Both, experiment and model, agree that pronounced pearlite bands in the initial state almost disappear after 25 h of spheroidization annealing. On the other hand, a marginal degree of pearlite banding in the initial state increases slightly during annealing. This fact could be explained by inhomogeneous cementite formation inside and outside the primary segregation regions of manganese.

Effect of Spheroidization Annealing on Pearlite Banding

The present paper deals with the influence of the duration of isothermal spheroidization annealing on the evolution of pearlite bands in various initial states. In this study, two initial conditions of the steel 16MnCrS5 are considered: a) industrially hot-rolled pearlite structures in their ferritic matrix and b) a specifically adjusted microstructure in the lab condition. Based on the experimental investigations and quantitative microstructural analyses, an empirical model for the prediction of pearlite banding within a broad range of annealing durations could be derived. Both, experiment and model, agree that pronounced pearlite bands in the initial state almost disappear after 25 h of spheroidization annealing. On the other hand, a marginal degree of pearlite banding in the initial state increases slightly during annealing. This fact could be explained by inhomogeneous cementite formation inside and outside the primary segregation regions of manganese.

Grain refinement of C-Mn steel through thermo-mechanical processing

Purpose – The application of new technologies requires, however, modern rolling mills. Indeed, in manufacturing plants of older types, strict compliance with the developed rolling regimes is not always feasible. Improving the mechanical properties in such cases is possible only by means of cooling. Compressive deformation behavior of carbon–manganese (C-Mn) grade has been investigated at temperatures ranging from 800-900°C and strain rate from 0.01-50 s−1 on Gleeble-3800, a thermo-mechanical simulator. Simulation studies have been conducted mainly to observe the microstructural changes for various strain rate and deformation temperatures at a constant strain of 0.5 and a cooling rate of 20°C s−1. Design/methodology/approach – The project begins with simulation of a hot rolling condition using the thermo-mechanical simulator; this was followed by microstructural examination and identification of phases present by using an optical microscope for hot-rolled coil and simulated samples; grain size measurement and size distribution studies; and optimization of finishing temperature, coiling temperature and cooling rate by mimicking plant processing parameters to improve the mechanical properties. Findings – As the strain rate and temperature increase, pearlite banding decreases gradually and finally gets completely eliminated, thereby improving the mechanical properties. True stress–strain curves were plotted to extrapolate the effect of strain-hardening and strain rate sensitivity on austenite (γ) and austenite–ferrite (γ-a) regions. To validate the effect of strain rate and temperature over the grain size, the hardness of simulated samples was measured using the universal hardness tester and the corresponding tensile strength was found from the standard hardness chart. Practical implications – The results of the study carried out have projected a new technology of thermo-mechanical simulation for the studied C-Mn grade. These results were used to optimize the plant processing parameter like finishing and coiling temperature and finishing stands strain rate. Originality/value – By controlling the hot rolling conditions like finishing, coiling temperature and cooling rate, structures differing in mechanical properties can be obtained for the same material. Accurate understanding of a structure being formed when different temperatures are applied enables the control of the process that assures intended structures and mechanical properties are achieved.

The effects of heat treatment on the machinability of mild steels

In this study, the effects of microstructure and mechanical properties on the machinability of hot rolled SAE 1050 steel that was annealed and normalised before machining, have been investigated. The machinability has been characterised by measuring the tool life, chip root morphology, cutting forces, surface finish, and tool/chip interface temperature. Here, the optimum machinability, especially from the stand point of tool life, has been determined for hot rolled steel which had minimum impact energy and minimum ductility. By annealing this material, a coarse pearlitic microstructure and a microstructure having 10% spherical cementite was obtained with an increasing ferrite+pearlite banding. This led to an increase in ductility and impact energy, but the decrease in hardness shortened the tool life and worsened the machinability. With normalising heat treatment, on the other hand, the banding disappeared, hardness, ductility and impact energy increased; but the tool life shortened more and more. The maximum built-up edge (BUE) thickness occurred at lower cutting speeds in machining annealed specimens. The minimum surface roughness was observed on the hot rolled specimen at final cutting speeds. The heat treatment operations applied did not bring about a considerable difference in cutting forces. A significant correlation between the machinability and the hardness of specimens could not be determined.

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

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.

Assessment of pearlite banding using automatic image analysis: application to hydrogen-induced cracking

Methods to quantify ferrite-pearlite banding using automatic image analysis have been proposed and tested, for example, in relation to classical banding charts. The method that is found to have the most general applicability is based on the measurement of the Feret's diameter distributions in two directions parallel and perpendicular to the rolling direction. The quantity related to banding is the ratio between the slopes of the cumulative frequency distribution curves. Structural steels with banded ferritic-pearlitic structures were investigated with regard to hydrogen-induced cracking (HIC) in previous work. The results show that the development of HIC depends on microstructural heterogeneities such as pearlife banding and inclusions. In the present work, the quantitative relationship between HIC parameters and banding is investigated. Banding quantification was used to interpret results of HIC tests. It was found that there is a significant correlation between banding and HIC in the National Association of Corrosion Engineers solution. No corresponding correlation was observed for the less acidic British Petroleum solution.

Copper containing sulphide phases present in controlled rolled niobium–titanium bearing high strength low alloy steels

AbstractComplex copper bearing sulphide phases have been observed for the first time in controlled rolled niobium bearing high strength low alloy steels. Analytical electron microscopy studies were carried out on these copper bearing sulphides. The observations show that, in many cases, these particles have duplex sizes and are multiphase. The smaller particles have diameters from 0·2 to 0·7 μm with round or ellipsoidal disclike morphology, mainly present close to and/or within the pearlite banding where the segregation of the alloying elements is severe; they tend to be associated with other precipitates such as manganese sulphide, and titanium carbonitrides in the steels having titanium additions. The larger particles (>1 μm) occur occasionally, and are often associated with spinel MgO.Al2O3 and/or A12O3, Ti(C,N), MnS, and silica. These particles have complex chemical compositions with a ratio of (Cu + Mn)/S ranging from 0·77 to 1·42; their electron diffraction patterns lead to lattice parameters which ...

Copper containing sulphide phases present in controlled rolled niobium–titanium bearing high strength low alloy steels

Complex copper bearing sulphide phases have been observed for the first time in controlled rolled niobium bearing high strength low alloy steels. Analytical electron microscopy studies were carried out on these copper bearing sulphides. The observations show that, in many cases, these particles have duplex sizes and are multiphase. The smaller particles have diameters from 0·2 to 0·7 μm with round or ellipsoidal disclike morphology, mainly present close to and/or within the pearlite banding where the segregation of the alloying elements is severe; they tend to be associated with other precipitates such as manganese sulphide, and titanium carbonitrides in the steels having titanium additions. The larger particles (>1 μm) occur occasionally, and are often associated with spinel MgO.Al2O3 and/or A12O3, Ti(C,N), MnS, and silica. These particles have complex chemical compositions with a ratio of (Cu + Mn)/S ranging from 0·77 to 1·42; their electron diffraction patterns lead to lattice parameters which are very close to either that of covellite (CuS) or digenite (Cu1·765S to Cu1·79S), The particles are probably the complexes of different phases, such as covellite phases and manganese sulphide, or digenite, covellite phases, and manganese sulphide. Some of the observed manganese sulphide particles also contain a small percentage of copper. With segregation of copper and sulphur in the as cast state, and in the presence of more strongly sulphide forming elements, such as manganese, the formation of copper bearing sulphide complexes can occur as the temperature decreases.MST/1603

Formation of pearlitic banded structures in ferritic‐pearlitic steels

The conditions for ferrite and pearlite banding in strip and plate made of structural steels were investigated. Factors found to influence the formation of banded structures were the cooling rate during the γ/α‐transformation, the former austenite grain size, and the work‐hardened condition of the former austenite. Analyses with the aid of an electron beam microprobe made it possible to demonstrate that the carbon‐rich bands correspond locally with banded manganese enrichments, yet that they do not form before the course of the γ/α‐transformation as a result of secondary segregation. It was possible to explain the mechanism of action of the influencing factors on the basis of this model.

Effect of Pearlite Banding on Mechanical Properties of Hot-rolled Steel Plates

Effect of Pearlite Banding on Mechanical Properties of Hot-rolled Steel Plates

Influence of warm working and tempering on fissure formation

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) into the rolling schedule encouraged fissure formation. This is probably due to a small number of elongated grains not recrystallising during the two phase rolling sequence and being further elongated at the lower rolling temperatures, combined with a greater alignment of the ferrite boundaries in the rolling direction. By rolling the steels and Fe alloys with the same reduction at temperatures insufficient to allow recrystallisation (600–400°C), it has been possible to keep the aspect ratio constant and vary the dislocation density. At constant aspect ratio, increasing the dislocation density by warm working increased the number of deep fissures formed. On the basis of these results, it is suggested that the weakness at the grain boundaries which gives rise to these fissures may be caused by dislocation interaction with the boundary together with boundary alignment giving a well defined crack path. Subsequent tempering at 600°C which allowed some recovery to take place without grain boundary movement did not reduce the number of fissures. Fissuring was only removed when the tempering temperature was high enough to allow grain boundary movement.MST/769

Effect of sulfide inclusion morphology and pearlite banding on anisotropy of mechanical properties in normalized C-Mn steels

The influence of sulfur content, sulfide shape, and pearlite banding on the anisotropy of mechanical properties was evaluated in a series of 0.2 pct carbon, 1.0 pct manganese steels containing either 0.004 or about 0.013 pct sulfur with and without rare-earth additions. Both globular and stringered sulfide inclusions had a detrimental effect on reduction of area and Charpy shelf energy; this effect was particularly evident in the deterioration of through-thickness properties and was much more severe for stringered inclusions than for globular inclusions. The effect of the sulfide inclusions in the different steels on the through-thickness reduction of area and Charpy shelf energy correlated with differences in their mean free distances or nearest-neighbor distances, both of which depended upon the inclusion characteristics of volume fraction, size, and aspect ratio. The projected length of sulfide inclusions per unit area on a plane perpendicular to the transverse direction seemed to reflect the overall effect of the inclusion characteristics on through-thickness reduction of area and Charpy shelf energy and appeared to be a useful parameter for assessment of steel’s susceptibility to fracture. Pearlite banding had no obvious effect on reduction of area or Charpy shelf energy in any of the steels studied. The improvement observed for the steel with stringered sulfide inclusions as a result of the removal of pearlite banding was a consequence of the inclusions coarsening during the short-time high-temperature treatment used to remove banding.

Texture and Cleavage in Molybdenum

It is of considerable technological importance to establish how far textures introduced into controlled‐rolled steels by finish rolling at low temperatures may affect the fracture strength. The purely textural effect is difficult to isolate in such steels because of anisotropy associated with grain shape, inclusions and pearlite banding. Consequently, an investigation was carried out using molybdenum, a b.c.c. single phase material showing good structural homogeneity, as a model. Texture development was studied using crystallite orientation distribution function analysis to identify a suitable processing route leading to a sharp texture with a suitable distribution of {100} cleavage planes. The behaviour of a sharply textured specimen was analysed by taking fracture specimens from various orientations in the plate. The energy absorbed in impact showed a positive correlation with the density of 100 planes in the crack direction, but the extent of the variation was less than would have been expected had crack propagation been the controlling step in the fracture process.

Effects of Interrupted Accelerated Cooling after Controlled Rolling on the Mechanical Properties of Low Alloy Steels

The effects of the accelerated cooling after the controlled rolling (CR) on mechanical properties were investigated of the various microalloyed steels. The controlled rolling conditions were a reheating temperature of 1 100°C or 1 200°C, cumulative rolling reduction of 70% below 900°C, and a finishing rolling temperature of 800°C with a plate thickness of 20mm. The interrupted accelerated cooling (IAC) was carried out in the temperature range from 780 to 600°C, followed by air cooling, and the maximum cooling rate was 12°C/s. The increase in cooling rate by IAG caused microstructural changes such as the refinement of ferrite grain size, the disappearance of pearlite banding and the formation of refined bainite in place of pearlite. The increment of strength due to IAC with cooling rate of around 10°C/s that gave rise to the very refined duplex structure of ferrite and bainite was 5 to 10kg f/mm2, depending on the content of the microalloying elements such as Nb, V, or Ti. The Charpy V-notch transition temperature was improved by IAC when the reheating temperature was 1 100°C, and the superior low temperature toughness (such as a transition temperature below -100°C) was attained with occurrence of very few splittings on the fracture surface of the Charpy V-notch impact specimens. The optimum cooling conditions and the transformation behavior resulting from IAC are discussed. The increment of strength due to IAC was analyzed based on quantitative investigation of the transformed microstructure.

Formability of high-strength, low-alloy sheet steels

High-strength, low-alloy steel sheet (HSLA) is now replacing some low-carbon steels in the manufacture of pressed components in both commercial and private vehicles; the need for higher payloads in the former, andfor higher strength to meet increasingly stringent safety regulations in the latter, require their utilization. In this paper, the authors describe the investigation of five high-strength steels and compare their tensile properties and microstructural features with laboratorydetermined forming limit diagrams (FLDs). The tension-compression region is relatively insensitive to microstructure and is n value (or uniform elongation) controlled, with the limit line at ∼45° to the ε2=0 axis in accordance with theory. The tension-tension region varies widely with microstructure, particularly with inclusion content and pearlite banding, but only significantly at strain states where ε2/ε1>0·5. It is concluded that high-strength, low-alloy steels, with their higher yield and tensile strengths and so lower elongations and n values, have limited formability; this is reflected in the lower levels of the FLDs of these steels. The mechanical property which has the most influence upon the levels of the FLDs is the strain-hardening behaviour, as represented by the n value; microstructure is only significant in the tension-tension region. The mechanical anisotropy of these steels means that in some cases it is essential to determine the limit strains at both 0° and 90° to the rolling direction, but as most industrial pressings fall into the band ε2=±0·15, for the niobium-containing steels investigated, a single FLD, an ‘average’ of those determined here, would be in order for press-shop use.

鋼破面の電子顕微鏡的研究

Fracture surface of plain carbon steel were observed with an electron microscope.The crack initiation and the process of its propagation in a steel which was slowly given tension were examined to some extent in relation to the structure of steel.The results were as follows:1) The point of crack initiation had a relation with a pearlite banding.2) The grain boundaries had a function to absorb the cracks. i. e. ductility of steel was increased in accordance with the grain refining.3) The ball-type nonmetallic inclusions (under about 0·5μ) had no effect on crack propagation.4) The elongated type nonmetallic inclusions did not arrest the crack propagation.5) The nonmetallic inclusions above 5p directly had little effect on initiation and propagation of cracks.6)“Tongue” peeled surface was seemed to be an initial stage of twin formation and such deformation absobed the energy at the fracture surface.