Influence of the cutting edge micro-geometry of PCBN tools on the flank wear in orthogonal quenched and tempered turning M2 steel

Quenched and tempered high-speed steels obtained by powder metallurgy are commonly used in automotive components, such as valve seats of combustion engines. In order to machine these components, tools with high wear resistance and appropriate cutting edge geometry are required. This work aims to investigate the influence of the edge preparation of polycrystalline cubic boron nitride (PCBN) tools on the wear behavior in the orthogonal longitudinal turning of quenched and tempered M2 high-speed steels obtained by powder metallurgy. For this research, PCBN tools with high and low-CBN content have been used. Two different cutting edge geometries with a honed radius were tested: with a ground land (S shape) and without it (E shape). Also, the cutting speed was varied from 100 to 220 m/min. A rigid CNC lathe was used. The results showed that the high-CBN, E-shaped tool presented the longest life for a cutting speed of 100 m/min. High-CBN tools with a ground land and honed edge radius (S shaped) showed edge damage and lower values of the tool’s life. Low-CBN, S-shaped tools showed similar results, but with an inferior performance when compared with tools with high CBN content in both forms of edge preparation.

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

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.

Otimização do fresamento de roscas internas com a técnica de interpolação helicoidal

In machining of internal threads, dedicated tools, known as taps, are needed for each profile type, diameter, and low cutting speed values are used when compared to main machining processes. This restriction in the cutting speed is associated with the difficulty of synchronizing the tool s rotation speed and feed velocity in the process. This fact restricts the flexibility and makes machining lead times longer when manufacturing of components with threads is required. An alternative to the constraints imposed by the tap is the thread milling with helical interpolation technique. The technique is the fusion of two movements: rotation and helical interpolation. The tools may have different configurations: a single edge or multiple edges (axial, radial or both). However, thread milling with helical interpolation technique is relatively new and there are limited studies on the subject, a fact which promotes challenges to its wide application in the manufacturing shop floor. The objective of this research is determine the performance of different types of tools in the thread milling with helical interpolation technique using hardened steel workpieces. In this sense, four tool configurations were used for threading milling in AISI 4340 quenched and tempered steel (40 HRC). The results showed that climb cut promoted a greater number of machined threads, regardless of tool configuration. The upcut milling causes chippings in cutting edge, while the climb cutting promotes abrasive wear. Another important point is that increase in hole diameter by tool diameter ratio increases tool lifetime

Improving minimum quantity lubrication in CBN grinding using compressed air wheel cleaning

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo da soldagem GMAW convencional e pulsada de aço estrutural temperado e revenido utilizando eletrodo de alma metálica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of Single and Double Austenitization heat treatments on the Microstructure and Hardness of AISI D2 Tool Steel

This investigation is concerned with the study of effect of Double Austenitization (DA) and Single Austenitization (SA) heat treatment processes on microstructure and mechanical property of AISI D2type cold worked tool steel. To maximize hardness, tool steels are used in a quenched and tempered condition. This involves heating the material to the austenitizing temperature (∼850−1100 °C), quenching at an appropriate rate to form martensite, and tempering to reduce the retained austenite content and induce toughness. The merits of DA treatment isto promote dissolution of carbides at the same time proscribe grain coarsening significantly was attempted in D2 tool steel. The study has found that DA treatment has induced high hardness with insignificant growth in grains. The increase in hardness is attributed to increase in carbon content in matrix due to dissolution of carbides; whereas finer grains due to role of inclusions.

Effect of Single and Double Austenitization heat treatments on the Microstructure and Hardness of AISI D2 Tool Steel

This investigation is concerned with the study of effect of Double Austenitization (DA) and Single Austenitization (SA) heat treatment processes on microstructure and mechanical property of AISI D2type cold worked tool steel. To maximize hardness, tool steels are used in a quenched and tempered condition. This involves heating the material to the austenitizing temperature (∼850−1100 °C), quenching at an appropriate rate to form martensite, and tempering to reduce the retained austenite content and induce toughness. The merits of DA treatment isto promote dissolution of carbides at the same time proscribe grain coarsening significantly was attempted in D2 tool steel. The study has found that DA treatment has induced high hardness with insignificant growth in grains. The increase in hardness is attributed to increase in carbon content in matrix due to dissolution of carbides; whereas finer grains due to role of inclusions.

Effects of temper level on the dependence of fatigue crack growth threshold and crack closure on the prior austenitic grain size

An attempt has been made to systematically investigate the effects of microstructural parameters, such as the prior austenite grain size (PAGS), in influencing the resistance to fatigue crack growth (FCG) in the near-threshold region under three different temper levels in a quenched and tempered high-strength steel. By austenitizing at various temperatures, the PAGS was varied from about 0.7 to 96 μm. The microstructures with these grain sizes were tempered at 200 °C, 400 °C, and 530 °C and tested for fatigue thresholds and crack closure. It has been found that, in general, three different trends in the dependence of both the total threshold stress intensity range, ΔK th , and the intrinsic threshold stress intensity range, ΔK eff, th , on the PAGS are observable. By considering in detail the factors such as cyclic stress-strain behavior, environmental effects on FCG, and embrittlement during tempering, the present observations could be rationalized. The strong dependence of ΔK th and ΔK eff, th on PAGS in microstructures tempered at 530 °C has been primarily attributed to cyclic softening and thereby the strong interaction of the crack tip deformation field with the grain boundary. On the other hand, a less strong dependence of ΔK th and ΔK eff, th on PAGS is suggested to be caused by the cyclic hardening behavior of lightly tempered microstructures occurring in 200 °C temper. In both microstructures, crack closure influenced near-threshold FCG (NTFCG) to a significant extent, and its magnitude was large at large grain sizes. Microstructures tempered at the intermediate temperatures failed to show a systematic variation of ΔKth and ΔKeff, th with PAGS. The mechanisms of intergranular fracture vary between grain sizes in this temper. A transition from “microstructure-sensitive” to “microstructure-insensitive” crack growth has been found to occur when the zone of cyclic deformation at the crack tip becomes more or less equal to PAGS. Detailed observations on fracture morphology and crack paths corroborate the grain size effects on fatigue thresholds and crack closure.

Formation, microstructure and development of the localized shear deformation in low-carbon steels

An investigation has been made into the effect of microstructural parameters on the propensity for forming shear localization produced during high speed torsional testing by split Hopkinson bar with different average rates of 610, 650 and 1500 s(-1) in low carbon steels. These steels received the quenched, quenched and tempered as well as normalized treatments that provide wide microstructural parameters and mechanical properties. The results indicate that the occurrence of the shear localization is susceptible to the strength of the steels. In other words, the tendency of the quenched steel to form a shear band is higher than that of the other two steels. It is also found that there is a critical strain at which the shear localization occurs in the steels. The critical strain value is strongly dependent on the strength of the steels. Before arriving at this point, the material undergoes a slow work-hardening. After this point, the material suffers work-softening, corresponding to a process during which the deformation is gradually localized and eventually becomes spatially correlated to form a macroscopic shear band. Examinations by SEM reveal that the shear localization within the band involves a series of sequential crystallographic and non-crystallographic events including the change in crystal orientation, misorientation, generation and even perhaps damage in microstructures such as the initiation, growth and coalescence of the microcracks. It is expected that the sharp drop in the load-carrying capacity is associated with the growth and coalescence of the microcracks rather than the occurrence of the shear localization, but the shear localization is seen to accelerate the growth and coalescence of the microcracks. The thin foil observations by TEM reveal that the density of dislocations in the band is extremely high and the tangled arrangement and cell structure of dislocations tends to align along the shear direction. The multiplication and interaction of dislocations seems to be responsible for work-hardening of the steels. The avalanche of the dislocation cells corresponds to the sharp drop in shear stress at which the deformed specimen is broken. Double shear bands and kink bands are also observed in the present study. The principal band develops first and its width is narrower than that of the secondary band.

Delamination Fracture Related to Tempering in a High-Strength Low-Alloy Steel

The delamination or splitting of mechanical test specimens of rolled steel plate is a phenomenon that has been studied for many years. In the present study, splitting during fracture of tensile and Charpy V-notch (CVN) test specimens is examined in a high-strength low-alloy plate steel. It is shown that delamination did not occur in test specimens from plate in the as-rolled condition, but was severe in material tempered in the temperature range 500 °C to 650 °C. Minor splitting was seen after heating to 200 °C, 400 °C, and 700 °C. Samples that had been triple quenched and tempered to produce a fine equiaxed grain size also did not exhibit splitting. Microstructural and preferred orientation studies are presented and are discussed as they relate to the splitting phenomenon. It is concluded that the elongated as-rolled grains and grain boundary embrittlement resulting from precipitates (carbides and nitrides) formed during reheating were responsible for the delamination.

Effect of hydrogen charging on the stability of SAE 10B22 steel surface in alkaline solutions

The influence of hydrogen charging into a quenched and tempered boron steel membrane electrode (SAE 10B22) was studied using borate buffer (pH 8.4) and NaOH solutions (pH 12.7), with or without the addition of 0.01 M EDTA. At the hydrogen input side, hydrogen charging influenced cyclic voltammograms increasing the anodic charge of iron(II) hydroxide formation, and decreasing the donor density of passive films. These results suggest that the hydrogen ingress caused instability of metallic surface, increasing the surface area activity. (C) 2005 Elsevier Ltd. All rights reserved.

CHARACTERIZATION OF A AISI/SAE 4340 STEEL IN DIFFERENT MICROSTRUCTURAL CONDITIONS

The 4340 are classified as ultra-high strength steels used by the aviation industry and aerospace applications such as aircraft landing gear and several structural applications, usually in quenched and tempered condition. In this situation occurs reduction of toughness, which encourages the study of multiphasic and bainitic structures, in order to maintain strength without loss of toughness. In this study, ferritic-pearlitic structure was compared to bainitic and martensitic structure, identified by the reagents Nital, LePera and Sodium Metabisulfite. Sliding wear tests of the type pin-on-disk were realized and the results related to the microstructure of these materials and also to their hardnesses. It is noted that these different microstructures had very similar behavior, concluding that all three tested pairs can be used according to the request level.

Grinding of AISI 4340 steel with interrupted cutting by aluminum oxide grinding wheel

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Toughness variations during the tempering of a plain carbon, martensitic steel

The aim of this paper is to present results of toughness measurements and fractographic observations made on a quenched and tempered 0. 6%, carbon steel and to use these as a basis for a discussion of the factors affecting "623K (350 °C) embrittlement" (one-step temper embrittlement).

Vertical dynamic interaction of trains and rail steel bridges

Rail steel bridges are vulnerable to high impact forces due to the passage of trains; unfortunately the determination of these transient impact forces is not straightforward as these are affected by a large number of parameters, including the wagon design, the wheel-rail contact and the design parameters of the bridge deck and track, as well as the operational parameters – wheel load and speed. To determine these impact forces, a detailed rail train-track/bridge dynamic interaction model has been developed, which includes a comprehensive train model using multi-body dynamics approach and a flexible track/bridge model using Euler– Bernoulli beam theory. Single and multi-span bridges have been modelled to examine their dynamic characteristics. From the single span bridge, the train critical speed is determined; the minimum distance of two peak loadings is found to affect the train critical speed. The impact factor and the dynamic characteristics are discussed.