- Email: [email protected]
Development of high strength spring steel
alloy. Luckey,
range, at least through • certain adaptation of the unnotched specimen Wohler curve of Eurocode No. 3 to the actual behaviour of the material. Graphs. 21 refs.
The use of porous metallic coatings for fixation of total joint prostheses by bone ingrowth has become • widespread alternative to fixation with PMMA bone cement. However, concerns about such coatings include long-term effects of metal ion release, potential coating loss, end decreased subatrate fatigue strength. The biological fixation capability of a non-porous, high-integrity plasma-sprayed F75 CoCr with low surface area, coated on cylindrical test plugs fabricated from CoCrMo alloy, was compared with a conventional aintered bead coating in goat cortical and cancellous bone sites after 8 and 16 weeks of implantation. Histological evaluation showed substantial variations in fixation quality between individual animals and between surgical sites with no consistent difference between implant types, Shear testing of bone-implant interfaces showed that although conventional porous coating exhibited higher overall average shear strengths in cortical bone sites at both time periods, the differences were not statistically significant. In cancellous sites, the average shear strengths achieved with conventional porous and plasmasprayed coatings were essentially equal. Analysis using average paired differences, however, related that when porous end plasma-coated implants are pieced in identical sites of contraiateral limbs, the plasma coatings consistently yielded higher shear strengths in cancellous bone sites at the later time period. Since current design theory for biological fixation favours metaphysical fixation, this surface may offer potential advantages over conventional porous coatings. Graphs, photomicrographs. 11 refs.
D e v e l o p m e n t o f high s t r e n g t h spring steel. Kutsu, T., Tange, A., Satoh,
Bone a p p o s i t i o n t o plasma-sprayed c o b e f t - c h r o m i u m
H.A., Lamprecht, E.G. and Walt, M.J. J. Biomed. Mater. Res. M a y 1992 26 (5) 5 5 7 - 5 7 5
The effect o f s h o t peening on t h e f a t i g u e s t r e n g t h o f cerburizing steels.
Hatano, A. and Namiki, K. Denki Seiko Jan. 1992 53 (1) 2 2 - 3 2 (in Japanese)
Shot peening is one of the cold-working processes performed by projecting hard particles on to the surface of works. Although it involves old technology, it has been reconsidered in automotive industries as the means to improve fatigue durability in terms of 'hard shot peening'. Hard shot peening is a high-intensity peening technology resulting in a larger amount of compressive residual stress and higher fatigue resistance than conventional intensity peening. In the hard shot peening process, however, the peak value of the stress is located at a depth of 0.05 mm below the surface and the surface value is not so high. To compensate for this stress depression at sub-surface, additional beads peening for SCr420 steel was studied. By applying the additional beads peening, further improvement of fatigue resistance has been confirmed. The beads peening process is effective to give residual compressive stress at the surface without surface degradation. Graphs, photomicrographs. 16 refs. Plasma cerburizing
characteristics
and f a t i g u e properties of super
cerburizing steel. Kimura, T. and Namiki, K.. Denki Seiko Jan. 1992 63 (1) 4 - 1 4 (in Japanese)
Super cerburizing is one of the carburizing processes whereby surface carbon content is increased by up to 2-4%, much higher than that of the conventional process. This is characterized by its carbide precipitation in the case and is expected to show superior fatigue durabilities. At first, the effect of plasma super-carburizing conditions on the carbide morphology was studied using Fe-0.18C-0.5Si2.25Cr-0.4Mo steel. Low-temperature carburizing at 1143 K was confirmed to be effective to obtain finely and uniformly dispersed carbides. Furthermore, the optimum condition was selected taking other case properties into account. The bending and contact fatigue tests were carried out as a next step, and it was revealed that plasma super-carburized steel exhibited fatigue durabilities superior to those of conventionally carburized JIS-SCM 420. The superiority was considered to be due to its higher surface hardness, finer grain, intergranular oxidation-free case and higher elevsted-temperature hardness. Graphs, photomicrographs. 27 refs. S t u d y of t h e interface in d i s s i m i l a r w e l d s b e t w e e n austenitic stainless and carbon steels, de Aguirre, I.F. Report EUR 13467 1992 72 pp (in Spanish/English) In some industrial applications it is necessary to carry out welds between ferritic carbon steels (Naval) and austenitic stainless steels (317LN). With the aid of the available technical literature about this matter and the recommendations of the manufacturers of consumables, a series of welded joints has been designed and the operations carried out by different procedures using two types of consumables. In each of these joints tests of the representative physical characteristics have been made (tensile, bend and fatigue) and the metallurgical structure of the interface studied. As a consequence of the experiments carried out, conclusions are given to help the users to manufacture this type of joint with the best possible results. Photomicrographs, graphs. 9 refs. A d m i s s i b l e stresses f o r t h e f a t i g u e design of w e a t h e r i n g structural steels after a six years" exposure. Seeger, T., Degenko/be, J. and Olivier, R. Stahl Eisen Nov. 1991 11 (11) 1 0 1 - 1 1 0 (in G e r m a n ) Components and structures subjected to cyclic load are designed according to various codes, eg DASt Directive 011 for high-strength steels or Eurocode No. 3 for steel structures. The application of weathering steels raises the question regarding the need to increase the safety factors because of surface alterations during longterm exposure. The aim is to point out the extent of the effect of weathering on the fatigue strength of welded joints and unnotched test specimens after six-year exposure. The admissible stresses derived on the basis of tests for unexposed and exposed welded joints of weathering structural steel W-I'St 52-3 are covered by relevant standard specifications and codes. Despite certain discrepancies, no action is required in this respect and the rules applicable to welded joints of standard structural steel St 52-3 can be accepted as such, even at butt welds ground flush to plate surface with low admissible stresses in codes covering a possible influence of weathering on fatigue. For unnotched specimens of weathering structural steel WTSt 52-3, a decrease in fatigue strength as a result of outdoor exposure requires a reduction of the admissible stresses according to pertinent German codes. It is, however, questionable whether a corresponding revision of existing German codes is still appropriate: the comparatively low specifications of Eurocode No. 3 for the unnotched specimen of standard structural steel cover, on the one hand, this reduction in fatigue strength. On the other hand, in view of future codes, it would be desirable to specify clearly higher admissible stresses for the fatigue strength
Int J Fatigue March 1993
Y., Arai, Y., Kurebayashi, Y. and Takagi, M. Denki Seiko Jan, 1992 63 (1) 7 0 - 7 5 (in Japanese) Automobile industries have searched for more reliable steel with higher strength. In the case of spring steel, much effort has been made to develop high-strength steel to endure an applied stress of 130 kgf mm -2, For this purpose, a fundamental study on the alloy design of ultra-high-strength steel was made. ND 250S (0.4C-2.5Si-0.8Mn-2Ni-O.85Cr-0.4Mo-0.2V) was confirmed as showing • good possibility of application to high-strength coil springs. Coil springs made of this steel were evaluated in terms of fatigue properties, sag resistance end delayed fracture property. The following results were obtained. The mechanical properties of ND 250S are superior to those of SUP 7, especially in toughness. The threshold stress intensity factor range of ND 250S is larger than that of SUP 7, which indicates greater notch toughness. ND 250S is proven to exhibit superior properties necessary for coil springs compared with conventional spring steels end to show potential as a 130 kg mm -2 grade high-strength coil spring. Graphs. 2 refs. of plastic deformation processes at f a t i g u e crack t i p i n 18Cr-10Ni austenitic stainless steel (304L) Brahmi, S., Chappuis, G.. and Lehr, P. Mere. Etud. Sci. Rev. Metall. Jan. 1992 89 (1) 4 9 - 6 1 (in French)
Analysis
Induced structural modifications in the monotonous end cyclical plastified zones at the fatigue crack point of Z2CN 18-10 steel (304L) were studied. The correlation between the extent of these zones and the local cracking speed on the one hand and theoretical models on the other hand is discussed. Behaviour was studied at ambient temperature and at -196 °C. Photomicrographs, graphs. 28 refs. Surface d e g r a d a t i o n of a nickel-base superalloy under S O 2 environment.
Aghion, E. Fatigue Fract. Eng. Mater. Struct. Apr. 1992 15 (4) 4 1 7 - 4 1 9
Surface degradation resulting from the combined effect of cyclic loading and the products of combustion of jet engines has a detrimental effect on the service life of these engines. One important component of the combustion gas environment produced at th¢ hot stage of a jet engine is SO2. At this hot stage, one of the common structural materials used for turbine blades is the MAR-M200 + Hf Nibase superaiioy. The effects of analogous combustion gas mixtures containing 3% SO2 on the surface degradation and the resulting failure mechanism under high temperature low-cycle fatigue (HTLCF) conditions are investigated. Photomicrographs, 3 refs. Interaction of high-strain and high-cycle f a t i g u e in t u r b i n e materials.
Suhr, R.W. Fatigue Fract. Eng. Mater. Struct. Apr. 1992 15 (4) 3 9 9 - 4 1 5
The interaction between high-strain and high-cycle fatigue under combined cycling conditions on 2% NiCrMoV and a 12% CrNiMo alloy was examined. The results reveal that the application of high-strain fatigue cycles prior to low-strain high-cycle fatigue is significantly less damaging than the equivalent number of single highstrain cycles applied between periods of high-cycle fatigue, indicating a much greater damaging interactive effect under the combined cycling condition. A damage summation, based on high-strain and high-cycle fatigue initiation curves and calculated at various endurances, was found to approach zero under combined cycling conditions, indicating that a prediction of damage using the Palmgren-Miner linear damage rule is inapplicable. Cumulative damage curves, based on an assessment of hypothetical Crack growth beheviour under high-strain end highcycle fatigue conditions, can be constructed to explain the large departure from the Palmgren-Miner prediction of unity. Such curves, however, fail to predict the more damaging interactive effect observed under combined cycling conditions. The apparent contradiction between experimental results and theoretical assessment is discussed and a mechanism is proposed to account for the observed interactive effect. Graphs. 27 refs.
Crack initiation and propagation behaviour o f a heat-treated carbon steel in corrosion fatigue. Goto, M. and Nisitani, H. Fatigue Fract. Eng. Mater. StrucL Apr. 1992 15 (4) 3 5 3 - 3 6 3 When estimating fatigue damage quantitatively, it is important to clarify its physical basis. Rotating bending fatigue tests of a heat-treated 0.45% carbon steel were carried out in 3% NaCI solution, to clarify the physical basis of corrosion fatigue damage from successive observations of plastic replicas. The results show that corrosion pits are generated during the early stages of cycling, then most of them grow with further cycling until a crack is initiated from each corrosion pit. The initiation of corrosion pits from slip bands is observed only in the case when the stress range is relatively large, and in the range of stress for which slip bands are produced in air. After initiation of a crack, the crack propagates by frequent interactions and coalescence with other cracks. The growth rate of an especially small crack in NaCI solution is larger than that in air. However, the growth rate of a comparatively large crack is smaller in NaCI solution than in air, Photomicrographs, graphs. 26 refs. Crack o p e n i n g stress m e a s u r e m e n t s o f surface cracks in 7075-1"6 aluminium alloy plate specimen t h r o u g h electron frectogrophy. Putra,
I.S. and Schijve, J. Fatigue Fract. Eng. Mater. Struct. Apr. 1992 15 (4) 3 2 3 - 3 3 8
Crack opening stress measurements were carried out on 9.6 mm thick specimens of 7075-T6 AI alloy with semi-elliptical surface cracks. Measurements were made through a fractographic technique based on a load sequence which can produce distinct striation characteristics on the fraCture surface. The crack opening stress Sop is deduced from the striation pattern. The variation of Sop along the crack periphery and during crack extension was measured. Close to the front surface, Sop is higher owing to the plane stress condition. At a large crack depth, a strong influence of plasticity in the ligament on Sop was found, ie Sop decreases as the crack extends to breakthrough. The agreement of da/dN = AKeff curves between surface-cracks end through-cracks data was only found for e limited range of crack depth of the elliptical cracks. Photomicrographs, graphs. 18 refs.
157
range, at least through • certain adaptation of the unnotched specimen Wohler curve of Eurocode No. 3 to the actual behaviour of the material. Graphs. 21 refs.
The use of porous metallic coatings for fixation of total joint prostheses by bone ingrowth has become • widespread alternative to fixation with PMMA bone cement. However, concerns about such coatings include long-term effects of metal ion release, potential coating loss, end decreased subatrate fatigue strength. The biological fixation capability of a non-porous, high-integrity plasma-sprayed F75 CoCr with low surface area, coated on cylindrical test plugs fabricated from CoCrMo alloy, was compared with a conventional aintered bead coating in goat cortical and cancellous bone sites after 8 and 16 weeks of implantation. Histological evaluation showed substantial variations in fixation quality between individual animals and between surgical sites with no consistent difference between implant types, Shear testing of bone-implant interfaces showed that although conventional porous coating exhibited higher overall average shear strengths in cortical bone sites at both time periods, the differences were not statistically significant. In cancellous sites, the average shear strengths achieved with conventional porous and plasmasprayed coatings were essentially equal. Analysis using average paired differences, however, related that when porous end plasma-coated implants are pieced in identical sites of contraiateral limbs, the plasma coatings consistently yielded higher shear strengths in cancellous bone sites at the later time period. Since current design theory for biological fixation favours metaphysical fixation, this surface may offer potential advantages over conventional porous coatings. Graphs, photomicrographs. 11 refs.
D e v e l o p m e n t o f high s t r e n g t h spring steel. Kutsu, T., Tange, A., Satoh,
Bone a p p o s i t i o n t o plasma-sprayed c o b e f t - c h r o m i u m
H.A., Lamprecht, E.G. and Walt, M.J. J. Biomed. Mater. Res. M a y 1992 26 (5) 5 5 7 - 5 7 5
The effect o f s h o t peening on t h e f a t i g u e s t r e n g t h o f cerburizing steels.
Hatano, A. and Namiki, K. Denki Seiko Jan. 1992 53 (1) 2 2 - 3 2 (in Japanese)
Shot peening is one of the cold-working processes performed by projecting hard particles on to the surface of works. Although it involves old technology, it has been reconsidered in automotive industries as the means to improve fatigue durability in terms of 'hard shot peening'. Hard shot peening is a high-intensity peening technology resulting in a larger amount of compressive residual stress and higher fatigue resistance than conventional intensity peening. In the hard shot peening process, however, the peak value of the stress is located at a depth of 0.05 mm below the surface and the surface value is not so high. To compensate for this stress depression at sub-surface, additional beads peening for SCr420 steel was studied. By applying the additional beads peening, further improvement of fatigue resistance has been confirmed. The beads peening process is effective to give residual compressive stress at the surface without surface degradation. Graphs, photomicrographs. 16 refs. Plasma cerburizing
characteristics
and f a t i g u e properties of super
cerburizing steel. Kimura, T. and Namiki, K.. Denki Seiko Jan. 1992 63 (1) 4 - 1 4 (in Japanese)
Super cerburizing is one of the carburizing processes whereby surface carbon content is increased by up to 2-4%, much higher than that of the conventional process. This is characterized by its carbide precipitation in the case and is expected to show superior fatigue durabilities. At first, the effect of plasma super-carburizing conditions on the carbide morphology was studied using Fe-0.18C-0.5Si2.25Cr-0.4Mo steel. Low-temperature carburizing at 1143 K was confirmed to be effective to obtain finely and uniformly dispersed carbides. Furthermore, the optimum condition was selected taking other case properties into account. The bending and contact fatigue tests were carried out as a next step, and it was revealed that plasma super-carburized steel exhibited fatigue durabilities superior to those of conventionally carburized JIS-SCM 420. The superiority was considered to be due to its higher surface hardness, finer grain, intergranular oxidation-free case and higher elevsted-temperature hardness. Graphs, photomicrographs. 27 refs. S t u d y of t h e interface in d i s s i m i l a r w e l d s b e t w e e n austenitic stainless and carbon steels, de Aguirre, I.F. Report EUR 13467 1992 72 pp (in Spanish/English) In some industrial applications it is necessary to carry out welds between ferritic carbon steels (Naval) and austenitic stainless steels (317LN). With the aid of the available technical literature about this matter and the recommendations of the manufacturers of consumables, a series of welded joints has been designed and the operations carried out by different procedures using two types of consumables. In each of these joints tests of the representative physical characteristics have been made (tensile, bend and fatigue) and the metallurgical structure of the interface studied. As a consequence of the experiments carried out, conclusions are given to help the users to manufacture this type of joint with the best possible results. Photomicrographs, graphs. 9 refs. A d m i s s i b l e stresses f o r t h e f a t i g u e design of w e a t h e r i n g structural steels after a six years" exposure. Seeger, T., Degenko/be, J. and Olivier, R. Stahl Eisen Nov. 1991 11 (11) 1 0 1 - 1 1 0 (in G e r m a n ) Components and structures subjected to cyclic load are designed according to various codes, eg DASt Directive 011 for high-strength steels or Eurocode No. 3 for steel structures. The application of weathering steels raises the question regarding the need to increase the safety factors because of surface alterations during longterm exposure. The aim is to point out the extent of the effect of weathering on the fatigue strength of welded joints and unnotched test specimens after six-year exposure. The admissible stresses derived on the basis of tests for unexposed and exposed welded joints of weathering structural steel W-I'St 52-3 are covered by relevant standard specifications and codes. Despite certain discrepancies, no action is required in this respect and the rules applicable to welded joints of standard structural steel St 52-3 can be accepted as such, even at butt welds ground flush to plate surface with low admissible stresses in codes covering a possible influence of weathering on fatigue. For unnotched specimens of weathering structural steel WTSt 52-3, a decrease in fatigue strength as a result of outdoor exposure requires a reduction of the admissible stresses according to pertinent German codes. It is, however, questionable whether a corresponding revision of existing German codes is still appropriate: the comparatively low specifications of Eurocode No. 3 for the unnotched specimen of standard structural steel cover, on the one hand, this reduction in fatigue strength. On the other hand, in view of future codes, it would be desirable to specify clearly higher admissible stresses for the fatigue strength
Int J Fatigue March 1993
Y., Arai, Y., Kurebayashi, Y. and Takagi, M. Denki Seiko Jan, 1992 63 (1) 7 0 - 7 5 (in Japanese) Automobile industries have searched for more reliable steel with higher strength. In the case of spring steel, much effort has been made to develop high-strength steel to endure an applied stress of 130 kgf mm -2, For this purpose, a fundamental study on the alloy design of ultra-high-strength steel was made. ND 250S (0.4C-2.5Si-0.8Mn-2Ni-O.85Cr-0.4Mo-0.2V) was confirmed as showing • good possibility of application to high-strength coil springs. Coil springs made of this steel were evaluated in terms of fatigue properties, sag resistance end delayed fracture property. The following results were obtained. The mechanical properties of ND 250S are superior to those of SUP 7, especially in toughness. The threshold stress intensity factor range of ND 250S is larger than that of SUP 7, which indicates greater notch toughness. ND 250S is proven to exhibit superior properties necessary for coil springs compared with conventional spring steels end to show potential as a 130 kg mm -2 grade high-strength coil spring. Graphs. 2 refs. of plastic deformation processes at f a t i g u e crack t i p i n 18Cr-10Ni austenitic stainless steel (304L) Brahmi, S., Chappuis, G.. and Lehr, P. Mere. Etud. Sci. Rev. Metall. Jan. 1992 89 (1) 4 9 - 6 1 (in French)
Analysis
Induced structural modifications in the monotonous end cyclical plastified zones at the fatigue crack point of Z2CN 18-10 steel (304L) were studied. The correlation between the extent of these zones and the local cracking speed on the one hand and theoretical models on the other hand is discussed. Behaviour was studied at ambient temperature and at -196 °C. Photomicrographs, graphs. 28 refs. Surface d e g r a d a t i o n of a nickel-base superalloy under S O 2 environment.
Aghion, E. Fatigue Fract. Eng. Mater. Struct. Apr. 1992 15 (4) 4 1 7 - 4 1 9
Surface degradation resulting from the combined effect of cyclic loading and the products of combustion of jet engines has a detrimental effect on the service life of these engines. One important component of the combustion gas environment produced at th¢ hot stage of a jet engine is SO2. At this hot stage, one of the common structural materials used for turbine blades is the MAR-M200 + Hf Nibase superaiioy. The effects of analogous combustion gas mixtures containing 3% SO2 on the surface degradation and the resulting failure mechanism under high temperature low-cycle fatigue (HTLCF) conditions are investigated. Photomicrographs, 3 refs. Interaction of high-strain and high-cycle f a t i g u e in t u r b i n e materials.
Suhr, R.W. Fatigue Fract. Eng. Mater. Struct. Apr. 1992 15 (4) 3 9 9 - 4 1 5
The interaction between high-strain and high-cycle fatigue under combined cycling conditions on 2% NiCrMoV and a 12% CrNiMo alloy was examined. The results reveal that the application of high-strain fatigue cycles prior to low-strain high-cycle fatigue is significantly less damaging than the equivalent number of single highstrain cycles applied between periods of high-cycle fatigue, indicating a much greater damaging interactive effect under the combined cycling condition. A damage summation, based on high-strain and high-cycle fatigue initiation curves and calculated at various endurances, was found to approach zero under combined cycling conditions, indicating that a prediction of damage using the Palmgren-Miner linear damage rule is inapplicable. Cumulative damage curves, based on an assessment of hypothetical Crack growth beheviour under high-strain end highcycle fatigue conditions, can be constructed to explain the large departure from the Palmgren-Miner prediction of unity. Such curves, however, fail to predict the more damaging interactive effect observed under combined cycling conditions. The apparent contradiction between experimental results and theoretical assessment is discussed and a mechanism is proposed to account for the observed interactive effect. Graphs. 27 refs.
Crack initiation and propagation behaviour o f a heat-treated carbon steel in corrosion fatigue. Goto, M. and Nisitani, H. Fatigue Fract. Eng. Mater. StrucL Apr. 1992 15 (4) 3 5 3 - 3 6 3 When estimating fatigue damage quantitatively, it is important to clarify its physical basis. Rotating bending fatigue tests of a heat-treated 0.45% carbon steel were carried out in 3% NaCI solution, to clarify the physical basis of corrosion fatigue damage from successive observations of plastic replicas. The results show that corrosion pits are generated during the early stages of cycling, then most of them grow with further cycling until a crack is initiated from each corrosion pit. The initiation of corrosion pits from slip bands is observed only in the case when the stress range is relatively large, and in the range of stress for which slip bands are produced in air. After initiation of a crack, the crack propagates by frequent interactions and coalescence with other cracks. The growth rate of an especially small crack in NaCI solution is larger than that in air. However, the growth rate of a comparatively large crack is smaller in NaCI solution than in air, Photomicrographs, graphs. 26 refs. Crack o p e n i n g stress m e a s u r e m e n t s o f surface cracks in 7075-1"6 aluminium alloy plate specimen t h r o u g h electron frectogrophy. Putra,
I.S. and Schijve, J. Fatigue Fract. Eng. Mater. Struct. Apr. 1992 15 (4) 3 2 3 - 3 3 8
Crack opening stress measurements were carried out on 9.6 mm thick specimens of 7075-T6 AI alloy with semi-elliptical surface cracks. Measurements were made through a fractographic technique based on a load sequence which can produce distinct striation characteristics on the fraCture surface. The crack opening stress Sop is deduced from the striation pattern. The variation of Sop along the crack periphery and during crack extension was measured. Close to the front surface, Sop is higher owing to the plane stress condition. At a large crack depth, a strong influence of plasticity in the ligament on Sop was found, ie Sop decreases as the crack extends to breakthrough. The agreement of da/dN = AKeff curves between surface-cracks end through-cracks data was only found for e limited range of crack depth of the elliptical cracks. Photomicrographs, graphs. 18 refs.
157