- Email: [email protected]
Stainless steel for blades of axial-flow turbocompressors
Shot-Peening Under Alternating Fatigue. Effect o f Residual Stresses on Fatigue Seheviour. Perrin, R. and .Ng,uy,. ~. _ ..... Etablissement Technique Central oe YArmement Heporr reo r'uuu211426/XAB Jan 1990 69 pp (in French) The behaviours of residual stresses in 35NCD16 steel treated to a tensile strength (Rm) close to 1800 MPa for two types of alternating and undulating stresses were compared. The shot-psening used produces a 30% gain on the fatigue limit in one case, none in the second. During the first cycles, stresses will relax in proportion to the load (adaptation). Then, they remain nearly stable. The Haigh criterion makes it possible to predict the effect of shot-peening on the Woehler curve of the material (load ratio R = -1). Nevertheless, a multiaxial criterion would yield a more accurate determination of fatigue limit values.
A Study of Inclusions Causing Fatigue Cracks in Steels for Cerburized and Shot-Peened Gears. Toyoda, T., Kanazawa, T. and Matsumoto, K. JSAE Rev. Jan. 1990 11, (1), 5 0 - 5 4 The fatigue fractures of carburized and shot-peened gears tend to be caused by the non-metallic inclusions under the surface because the fatigue strength of the surface of the gears is improved by shot-peening operations. The quantitative relationship between the size and locations of the inclusions, and the fatigue strength is discussed. The fatigue strength values were obtained by rotating-bending fatigue tests of a newly developed clean steel SCM420H for carburized gears. Also discussed is the clean steel's remarkably improved fatigue strength. Graphs, photomicrographs. 3 refs.
General Microstructure and High Bending Fatigue Strength in Carburized Steel. Pacheco, J. L. and Krauss, G, Hart.-Tech. Mitt. M a n - A p r . 1990 45, (2), 7 7 - 8 4 (in German) Cantilever fatigue specimens with a reduced section and rounded tension-side corners were machined from SAE 8719 steel bars. The specimens were plasma and gas cerburized to a surface hardness of 65 HRC and case depths of 1.2 mm at 50 HRC. Some specimens were direct quenched from 850 °C after carburizing and some were reheated to 850°C and quenched. All specimens were tempered at 150 °C. Excellent high-cycle bending fatigue resistance correlated with fine austenitic grain size and tow retained austenite. Reheating reduced the auste~jte grain size of the carburized specimens and resulted in improved fatigue resist~ance for both the plasma- and gas-carburized specimens. Graphs, photomicrographs. 21 refs.
Characteristics o f Sialon Ceramic Roll and Its P e r f o r m a n c e in Cold Roiling. Nakagawa, M., Sobue, M. and Taguchi, M. Tetsu-to-Hagane (J. Iron Steel Inst. Jpn.) Mar. 1990 76, (3), 4 0 6 - 4 1 3 (in Japanese) Steel rolls have been predominantly adopted for cold rolling of thin strips. They, however, appear to approach the limit of rolling performance. To provide rolls with performance levels that steel can never attain, the use of ceramics has been studied, because ceramics generally possess a higher hardness, and a larger Young's modulus, than steels and the property of non-adhesion to rolled strips. For this work, sialon ceramic was selected and its characteristics and performance in cold rolling were examined. Results obtained were as follows: (1) the rolling fatigue strength was >2.8 GPa, (2) a 25% thinner gauge under a 9% lighter load was obtained in rolling mild steel, (3) a 30% glossier rolled surface was obtained in rolling stainless steel. 7 refs. Cyclic Deformation Bohaviour of Cu-16 st.% AI Single Crystals. II. Cyclic Hardening and Slip Band Behaviour. Hong, S. I. and Laird, C. Mater. Sci. Eng. A Aug. 1990 A128, (1), 5 5 - 7 5 In an attempt to understand cyclic hardening and slip band behaviour of planar slip alloys, studies have been carried out in strain control on Cu-16 at.% AI single crystals oriented for easy glide. The gauge section was observed to become completely filled with slip bands by the repetition of strain bursts irrespective of strain amplitude. Slip in the old bands which carried the whole strain just before a strain burst seems to become inactive after a few successive strain bursts. Since the localized strain shifts around the gauge length because of the short active life of the slip bands, the overall deformation becomes rather homogeneous. This Luders-band-like behaviour persists for a large fraction of the fatigue life, even after crack formation. A regular hill and valley surface morphology develops on the Cu-AI crystals with cycling. This morphology is related to strain burst behaviour, the wavelength of the morphology increasing with strain amplitude because the strain bursts are larger in the early stages of life. The development of sharp extrusions commonly observed in Cu is not observed in Cu-16 at.% AI single crystals. Sharp extensions are not expected to develop in this alloy because of its low stacking fault energy and its Luders-band-like slip behaviour. Graphs, photomicrographs. 51 refs.
Current Design and Manufacturing Practices for Gas Turbine Axial Compressor Blades. Valentini, E. Diesel Gas Turbine Worldwide J u n e 1990 22, (5), 56, 58, 60 Today's axial compressors must be designed to meet the increasing high efficiency and reliability demands of modern advanced-technology industrial gas turbines. How well the compressor designs succeed depends not only on the compressor fluid dynamics, but also to a large extent on the design and manufacture of the compressor blading. The compresor blades are often produced from Ti alloys, such as Ti-6At-4V, to withstand and minimize centrifugal and vibratory stresses. Precision forging is recommended to blade manufacturers because it can reduce material costs, eliminate machining costs, increase airfoil accuracy, and can increase fatigue resistance. A review of current design and manufacturing for the gas turbine axial compressor blades covers: designing axial compressor blades to enhance fatigue resistance; designing a precision forging manufacturing process; die fabrication; predicting die stresses and forging load; and trends in precision forging. Graphs.
Int J Fatigue March 1991
Carlburized S t e e l - - U p d a t e o n a M a t u r e Composite. Doane, D. V. J. Heat Treat. 1990 8, (1), 3 3 - 5 3 This review of properties and applications of carburized steel (e.g., 16MnCr5, 20MoCr4, 20NiMoCr6, 18CrNi8, 9310, 4118, 4626, 4620, 4817, 8615, 8620, 8625, 5NiMo, EX60, EX62, PS59, PS61, CBS600, CBS10OOM) provides a historical perspective from which to examine current efforts to improve this important ferrous composite. The carbon-rich case, useful for its wear resistance, also interacts with the Iow-C core during quenching to generate favourable residual stresses which enhance the load-carrying ability of the composite. The control of the core and case microstructure, the importance of the case hardenability, and the influence of surface oxidation are reviewed. Fatigue behaviour, with and without superimposed overloads, is summarized, and a relationship between overload fatigue and impact fracture is reviewed. Good evidence that the performance of carburized steel can be optimized by alloying, and that alloy selection can have a significant effect on the engineering properties is presented. Metallurgical data can aid the processing of carburizing steel; available data, and their effect on machinability and distortion control, are reviewed. Grdphs. 41 refs. A Look s t M a g n e t i c T r e a t m e n t of Tools and Wear Surfaces. Miller, P.C. Tool. Prod. Mar. 1990 55, (12), 100-103 Many chemical and physical treatments improve tool life, machinability, and even product performance, but most processes are hot, messy, expensive, time consuming, or difficult. The FluxaTron U102 cutting-tool-treatment system, however, is fast, easy to use, and relatively inexpensive. A six-month payback is common. The electromagnetic device is designed to relax stress produced along the cutting edge of cutting tools during grinding or coating. It does its job in 42 s, and does not require sending tools out of the plant. In fact, the magnetizing unit can go right into the production line. Innovex Inc., Hopkins, Minnesota, manufacturer of the FluxaTron system, suggests its use on a variety of HSS and carbide tools, and some small components. In certain applications, the process can increase tool life by up to 175% (typical improvement ranges from 20-50%). Magnetically processed tools have a longer fatigue life and provide machined parts with better finishes. Examples of HSS drilling A2 steel are given. Graphs.
Stainless Steel f o r Blades o f A x i a l - F l o w Turbocompressors. B., Radon, J. and Bouska, P. Czech. Heavy Ind. 1990 (2), 3 4 - 3 8
Kopecky,
A new steel is developed for rotor blades in axial-flow turbocompressors for use with gases that contain sulphur oxides, nitrous oxides and chlorides. The original material was 14Cr17Ni2, which developed cracks at the root of the blades after 3500 h of operations. The new steel composition resulted from testing 10.100 kg heats. The optimum composition was 0.11% carbon, 16% Cr, 2% Ni and 1% Mo (11Cr16Ni2Mo1). The steel was made in a 30 ton electric furnace and vacuum oxygen decerbonized. Graphs.
Mechanism Maps for Cyclic Plasticity and Fatigue o f Single-Phsse Materials. Pedersen, 0. B. Acta Metal/. Mater. J u l y 1990 38, (7), 1221-1239 Mechanism maps for strain-hardening and fatigue in single-phase materials are introduced for isothermal cyclic deformation at constant amplitudes of plastic strain in tsnsion-compression. The maps are drawn for single crystals and polycrystals in diagrams of plastic strain against cycle number. The successive stages of structural evolution and cracking appear as two-dimensional fields. The dominant micromechanicel characteristics of each field can be described by modifications of the theory of two-phase materials. A more complete theory of the maps remains to be developed; but a partial prediction of the effects of temperature, strain rate and crystal structure on the field pattern is already possible, if the lattice friction and cross-slip of screw dislocations are invoked. The maps give a unified view of the basic mechanisms of work hardening and fatigue, and they provide useful criteria for design against fatigue. Graphs, photomicrographs, maps. 105 refs.
A Point Defect Model for Fatigue Crack initiation in NisAI + B Single Crystals. Hsiung, L. M. and Stoloff, N. S. Acta Metall. Mater. J u n e 1990 38, (6), 1191-1200 Transmission electron microscopy of boron-doped Ni3AI single crystals, oriented for single slip and cyclically deformed at room temperature, revealed a high density of dislocation dipoles and point defect clusters. Observations of circular perfect dislocation loops, Frank loops, vacancy tetrahedra and spherical voids provide evidence of vacancy condensation during fatigue cycling at room temperature. It is suggested that lattice misfit develops between persistent slip bands (PSB) and the matrix as a result of the generation and coalescence of excess vacancies in PSBs. The misfit strain at PSB/mstrix interfaces is considered to increase with increasing cumulative plastic strain. Together with SEM observations of surface topography, it is suggested that fatigue damage in Ni3AI single crystats is initiated by the formation of microvoids (microcracks) at PSB/matrix interfaces. The microvoids (microcracks} break down the coherency of the PSR/metrix interfaces and thereby relieve the accumulated misfit strain at the interfaces. A model of fatigue crack initiation based upon a surface energy criterion is proposed. Graphs, photomicrographs, spectra. 24 refs.
The ' W h i t e Layer" Phenomenon on Gear Teeth. Winter, H., Knauer, G. and Gabel, J. J. Tecnol. Mecc. Jan. 1990 21, (1), 144-150 (in Italian) Investigations into the occurrence of white etching areas on the flanks of heavily stressed gear teeth are reviewed end details given of tests carried out on carburized Cr-Mn gears subjected to high levels of stress in service. Micrographic and microhardness tests showed that the white layer was associated with incipient fatigue cracks below the surface of the gear teeth. The white layer is thought to have been caused by rapid cooling from temperatures approaching the fusion point of the steel caused by friction following a breakdown of the lubricant film. Graphs, photomicrographs. 13 refs.
183
A Study of Inclusions Causing Fatigue Cracks in Steels for Cerburized and Shot-Peened Gears. Toyoda, T., Kanazawa, T. and Matsumoto, K. JSAE Rev. Jan. 1990 11, (1), 5 0 - 5 4 The fatigue fractures of carburized and shot-peened gears tend to be caused by the non-metallic inclusions under the surface because the fatigue strength of the surface of the gears is improved by shot-peening operations. The quantitative relationship between the size and locations of the inclusions, and the fatigue strength is discussed. The fatigue strength values were obtained by rotating-bending fatigue tests of a newly developed clean steel SCM420H for carburized gears. Also discussed is the clean steel's remarkably improved fatigue strength. Graphs, photomicrographs. 3 refs.
General Microstructure and High Bending Fatigue Strength in Carburized Steel. Pacheco, J. L. and Krauss, G, Hart.-Tech. Mitt. M a n - A p r . 1990 45, (2), 7 7 - 8 4 (in German) Cantilever fatigue specimens with a reduced section and rounded tension-side corners were machined from SAE 8719 steel bars. The specimens were plasma and gas cerburized to a surface hardness of 65 HRC and case depths of 1.2 mm at 50 HRC. Some specimens were direct quenched from 850 °C after carburizing and some were reheated to 850°C and quenched. All specimens were tempered at 150 °C. Excellent high-cycle bending fatigue resistance correlated with fine austenitic grain size and tow retained austenite. Reheating reduced the auste~jte grain size of the carburized specimens and resulted in improved fatigue resist~ance for both the plasma- and gas-carburized specimens. Graphs, photomicrographs. 21 refs.
Characteristics o f Sialon Ceramic Roll and Its P e r f o r m a n c e in Cold Roiling. Nakagawa, M., Sobue, M. and Taguchi, M. Tetsu-to-Hagane (J. Iron Steel Inst. Jpn.) Mar. 1990 76, (3), 4 0 6 - 4 1 3 (in Japanese) Steel rolls have been predominantly adopted for cold rolling of thin strips. They, however, appear to approach the limit of rolling performance. To provide rolls with performance levels that steel can never attain, the use of ceramics has been studied, because ceramics generally possess a higher hardness, and a larger Young's modulus, than steels and the property of non-adhesion to rolled strips. For this work, sialon ceramic was selected and its characteristics and performance in cold rolling were examined. Results obtained were as follows: (1) the rolling fatigue strength was >2.8 GPa, (2) a 25% thinner gauge under a 9% lighter load was obtained in rolling mild steel, (3) a 30% glossier rolled surface was obtained in rolling stainless steel. 7 refs. Cyclic Deformation Bohaviour of Cu-16 st.% AI Single Crystals. II. Cyclic Hardening and Slip Band Behaviour. Hong, S. I. and Laird, C. Mater. Sci. Eng. A Aug. 1990 A128, (1), 5 5 - 7 5 In an attempt to understand cyclic hardening and slip band behaviour of planar slip alloys, studies have been carried out in strain control on Cu-16 at.% AI single crystals oriented for easy glide. The gauge section was observed to become completely filled with slip bands by the repetition of strain bursts irrespective of strain amplitude. Slip in the old bands which carried the whole strain just before a strain burst seems to become inactive after a few successive strain bursts. Since the localized strain shifts around the gauge length because of the short active life of the slip bands, the overall deformation becomes rather homogeneous. This Luders-band-like behaviour persists for a large fraction of the fatigue life, even after crack formation. A regular hill and valley surface morphology develops on the Cu-AI crystals with cycling. This morphology is related to strain burst behaviour, the wavelength of the morphology increasing with strain amplitude because the strain bursts are larger in the early stages of life. The development of sharp extrusions commonly observed in Cu is not observed in Cu-16 at.% AI single crystals. Sharp extensions are not expected to develop in this alloy because of its low stacking fault energy and its Luders-band-like slip behaviour. Graphs, photomicrographs. 51 refs.
Current Design and Manufacturing Practices for Gas Turbine Axial Compressor Blades. Valentini, E. Diesel Gas Turbine Worldwide J u n e 1990 22, (5), 56, 58, 60 Today's axial compressors must be designed to meet the increasing high efficiency and reliability demands of modern advanced-technology industrial gas turbines. How well the compressor designs succeed depends not only on the compressor fluid dynamics, but also to a large extent on the design and manufacture of the compressor blading. The compresor blades are often produced from Ti alloys, such as Ti-6At-4V, to withstand and minimize centrifugal and vibratory stresses. Precision forging is recommended to blade manufacturers because it can reduce material costs, eliminate machining costs, increase airfoil accuracy, and can increase fatigue resistance. A review of current design and manufacturing for the gas turbine axial compressor blades covers: designing axial compressor blades to enhance fatigue resistance; designing a precision forging manufacturing process; die fabrication; predicting die stresses and forging load; and trends in precision forging. Graphs.
Int J Fatigue March 1991
Carlburized S t e e l - - U p d a t e o n a M a t u r e Composite. Doane, D. V. J. Heat Treat. 1990 8, (1), 3 3 - 5 3 This review of properties and applications of carburized steel (e.g., 16MnCr5, 20MoCr4, 20NiMoCr6, 18CrNi8, 9310, 4118, 4626, 4620, 4817, 8615, 8620, 8625, 5NiMo, EX60, EX62, PS59, PS61, CBS600, CBS10OOM) provides a historical perspective from which to examine current efforts to improve this important ferrous composite. The carbon-rich case, useful for its wear resistance, also interacts with the Iow-C core during quenching to generate favourable residual stresses which enhance the load-carrying ability of the composite. The control of the core and case microstructure, the importance of the case hardenability, and the influence of surface oxidation are reviewed. Fatigue behaviour, with and without superimposed overloads, is summarized, and a relationship between overload fatigue and impact fracture is reviewed. Good evidence that the performance of carburized steel can be optimized by alloying, and that alloy selection can have a significant effect on the engineering properties is presented. Metallurgical data can aid the processing of carburizing steel; available data, and their effect on machinability and distortion control, are reviewed. Grdphs. 41 refs. A Look s t M a g n e t i c T r e a t m e n t of Tools and Wear Surfaces. Miller, P.C. Tool. Prod. Mar. 1990 55, (12), 100-103 Many chemical and physical treatments improve tool life, machinability, and even product performance, but most processes are hot, messy, expensive, time consuming, or difficult. The FluxaTron U102 cutting-tool-treatment system, however, is fast, easy to use, and relatively inexpensive. A six-month payback is common. The electromagnetic device is designed to relax stress produced along the cutting edge of cutting tools during grinding or coating. It does its job in 42 s, and does not require sending tools out of the plant. In fact, the magnetizing unit can go right into the production line. Innovex Inc., Hopkins, Minnesota, manufacturer of the FluxaTron system, suggests its use on a variety of HSS and carbide tools, and some small components. In certain applications, the process can increase tool life by up to 175% (typical improvement ranges from 20-50%). Magnetically processed tools have a longer fatigue life and provide machined parts with better finishes. Examples of HSS drilling A2 steel are given. Graphs.
Stainless Steel f o r Blades o f A x i a l - F l o w Turbocompressors. B., Radon, J. and Bouska, P. Czech. Heavy Ind. 1990 (2), 3 4 - 3 8
Kopecky,
A new steel is developed for rotor blades in axial-flow turbocompressors for use with gases that contain sulphur oxides, nitrous oxides and chlorides. The original material was 14Cr17Ni2, which developed cracks at the root of the blades after 3500 h of operations. The new steel composition resulted from testing 10.100 kg heats. The optimum composition was 0.11% carbon, 16% Cr, 2% Ni and 1% Mo (11Cr16Ni2Mo1). The steel was made in a 30 ton electric furnace and vacuum oxygen decerbonized. Graphs.
Mechanism Maps for Cyclic Plasticity and Fatigue o f Single-Phsse Materials. Pedersen, 0. B. Acta Metal/. Mater. J u l y 1990 38, (7), 1221-1239 Mechanism maps for strain-hardening and fatigue in single-phase materials are introduced for isothermal cyclic deformation at constant amplitudes of plastic strain in tsnsion-compression. The maps are drawn for single crystals and polycrystals in diagrams of plastic strain against cycle number. The successive stages of structural evolution and cracking appear as two-dimensional fields. The dominant micromechanicel characteristics of each field can be described by modifications of the theory of two-phase materials. A more complete theory of the maps remains to be developed; but a partial prediction of the effects of temperature, strain rate and crystal structure on the field pattern is already possible, if the lattice friction and cross-slip of screw dislocations are invoked. The maps give a unified view of the basic mechanisms of work hardening and fatigue, and they provide useful criteria for design against fatigue. Graphs, photomicrographs, maps. 105 refs.
A Point Defect Model for Fatigue Crack initiation in NisAI + B Single Crystals. Hsiung, L. M. and Stoloff, N. S. Acta Metall. Mater. J u n e 1990 38, (6), 1191-1200 Transmission electron microscopy of boron-doped Ni3AI single crystals, oriented for single slip and cyclically deformed at room temperature, revealed a high density of dislocation dipoles and point defect clusters. Observations of circular perfect dislocation loops, Frank loops, vacancy tetrahedra and spherical voids provide evidence of vacancy condensation during fatigue cycling at room temperature. It is suggested that lattice misfit develops between persistent slip bands (PSB) and the matrix as a result of the generation and coalescence of excess vacancies in PSBs. The misfit strain at PSB/mstrix interfaces is considered to increase with increasing cumulative plastic strain. Together with SEM observations of surface topography, it is suggested that fatigue damage in Ni3AI single crystats is initiated by the formation of microvoids (microcracks) at PSB/matrix interfaces. The microvoids (microcracks} break down the coherency of the PSR/metrix interfaces and thereby relieve the accumulated misfit strain at the interfaces. A model of fatigue crack initiation based upon a surface energy criterion is proposed. Graphs, photomicrographs, spectra. 24 refs.
The ' W h i t e Layer" Phenomenon on Gear Teeth. Winter, H., Knauer, G. and Gabel, J. J. Tecnol. Mecc. Jan. 1990 21, (1), 144-150 (in Italian) Investigations into the occurrence of white etching areas on the flanks of heavily stressed gear teeth are reviewed end details given of tests carried out on carburized Cr-Mn gears subjected to high levels of stress in service. Micrographic and microhardness tests showed that the white layer was associated with incipient fatigue cracks below the surface of the gear teeth. The white layer is thought to have been caused by rapid cooling from temperatures approaching the fusion point of the steel caused by friction following a breakdown of the lubricant film. Graphs, photomicrographs. 13 refs.
183