The demand for improved materials is continuously pushing producers to obtain a fine grain struct... more The demand for improved materials is continuously pushing producers to obtain a fine grain structure and tight restrictions on grain size uniformity in forged superalloy rod. Understanding flow and recrystallization behavior is critical for optimizing forge and annealing practices to meet these requirements. The flow behavior of INCOLOY (r) alloy 945, a newly developed hybrid of alloys 718 and 925 with a unique combination of strength and corrosion resistance, was performed using uniaxial compression testing at elevated ...
Résumé/Abstract Spot welding of advanced high-strength steels (AHSS) poses significant challenges... more Résumé/Abstract Spot welding of advanced high-strength steels (AHSS) poses significant challenges because the high-carbon equivalent of AHSS can result in welds that are perceived to be of lower quality based on conventional weld quality criteria. Specifically, welds in AHSS are more prone to interfacial fracture, whereas button pullout failure is the preferred fracture mode because it indicates the weld is stronger than the base material. However, some evidence suggests that welds in AHSS that exhibit interfacial fracture ...
Potential methods to enhance the fatigue performance of automotive components are considered. The... more Potential methods to enhance the fatigue performance of automotive components are considered. The importance of design is illustrated with results on spot weld fatigue behavior, which was shown to be largely independent of base metal properties and dependent only on geometry in the high cycle fatigue regime. Selected results from several recent studies are used to illustrate some unique steel alloying and processing concepts that can lead to steel parts with improved fatigue performance, primarily by increasing the ...
Quenched and partitioned (Q&P) steels are one family of steels that has received some recent inte... more Quenched and partitioned (Q&P) steels are one family of steels that has received some recent interest for high-strength automotive applications. Previous Q&P steel research has usually focused on cold rolled and annealed products. In the current study, the thermomechanical profile was modified such that Q&P simulations were developed to characterize material as if it might be produced directly from a hot strip mill.
Penetrating Radiation Systems and Applications VIII, 2007
The ability to manufacture large scale scintillating crystals is directly linked to the mechanica... more The ability to manufacture large scale scintillating crystals is directly linked to the mechanical properties of the crystal. In this paper, estimated mechanical properties, including hardness, modulus, and fracture toughness of novel and established scintillating single crystals including CsI(Tl), CdWO4, NaI(Tl), and LaBr3(Ce). Lanthanum and cerium halide crystals have shown particular promise as scintillating materials because of their high luminosity
A modified quantitative microstructure characterization technique has been developed based on con... more A modified quantitative microstructure characterization technique has been developed based on constituent chord-length distribution (CLD). The modified technique, called the categorical CLD (CCLD), is capable of quantifying both size and volume fraction of the constituent of interest in a multi-constituent microstructure as a function of adjacent microstructure. The capability of the CCLD is demonstrated by its application to the investigation of the effect of microstructure on the stability of retained austenite (RA) during mechanical deformation in transformation-induced plasticity steels. By quantifying microstructures deformed to different levels of strains, it is found that RA is stabilized by fine grain size and adjacent bainitic ferrite.
ABSTRACT Low carbon martensitic steels are often produced by reaustenitizing and quenching (RA/Q)... more ABSTRACT Low carbon martensitic steels are often produced by reaustenitizing and quenching (RA/Q). Direct quenching (DQ) has gained interest in the past few decades and requires quenching immediately after working above or below the austenite recrystallization temperature to form martensitic microstructures. In the current study, microalloyed ASTM A514 steel is used to produce martensite from either equiaxed or pancaked prior austenite grain (PAG) microstructures. The equiaxed PAG conditions simulate microstructures produced by RA/Q and the pancaked PAG conditions simulate microstructures produced by controlled rolling (CR) before DQ. Controlled rolling followed by DQ was simulated with double hit compression in a Gleeble® 3500. The prior austenite grain size (PAGS) was varied between 9 and 75 μm prior to controlled rolling. The strengthening and toughening mechanisms are being investigated in the as-quenched (AsQ), low temperature tempered (LTT: 200 °C), and high temperature tempered (HTT: 600 °C) conditions. The equiaxed PAG condition has a Hall-Petch (H-P) relationship between yield strength (or microhardness) and PAGS in the AsQ condition. There is not a H-P relationship between PAGS and microhardness in the CR-DQ conditions. The CR-DQ conditions generally exhibit higher microhardness than the RA/Q conditions with similar PAGS, with the most significant differences in the larger PAGS conditions. Toughness was only measured in the equiaxed PAG conditions. The smallest PAGS has the lowest ductile-to-brittle transition temperature (DBTT) with the highest strength in the AsQ and LTT conditions. The smallest PAGS has the lowest DBTT and the lowest strength in the HTT condition.
The influence of Si and Al on the lattice parameter and stacking fault energy (SFE) of austenitic... more The influence of Si and Al on the lattice parameter and stacking fault energy (SFE) of austenitic steel was studied. X-ray diffraction indicated that 2.5 wt.% Al alloying increased the austenite lattice parameter by 1.41 × 10−3 nm, whereas 2.5 wt.% Si alloying had little effect. Partial dislocation separation measurements from weak-beam dark-field images indicated that 2.5 wt.% Al alloying increased the SFE by 12–17 mJ m−2 and 2.5 wt.% Si alloying decreased the SFE by 6–7 mJ m−2.
ABSTRACT One mode that limits the usefulness of hot forging die steels is localized plastic defor... more ABSTRACT One mode that limits the usefulness of hot forging die steels is localized plastic deformation in regions of high pressure. To understand this behavior the yield strength of the steel needs to be measured at working temperatures in order to determine the likelihood of localized plasticity. One of the issues in using die steels for hot forging applications is that they are initially tempered to a hardness value when put into service. As the die is used to produce forged components, the contact with the hot forging causes the die to continue to temper and hence soften with continued used. To explore these issues three different die steels were obtained and tested experimentally. Experimental compressive yield strengths were determined for the three die steels (FX, 2714 and WF). The die steels were tempered to various hardness values prior to compression testing. The five room-temperature hardness values after tempering ranged from 20 to 38 HRC. The five temperatures for compression testing ranged from 593 to 704 °C (1100 to 1300 oF). From these tests a good characterization of the high temperature plastic behavior of each steel was obtained. It was found that the WF steel which had the highest alloy content was the strongest of the three steels under all test conditions. The FX and 2714, which had similar alloy contents (with FX having slightly less carbon, nickel and vanadium), had yield strengths that were close to each other at the intermediate temperatures, but at the high and low end of the testing range for temperature the FX was stronger than the 2714. Hence, to obtain the greatest resistance to localized plastic deformation during operations the choice of die steel should be WF, followed by FX and then 2714.
Penetrating Radiation Systems and Applications VIII, 2007
ABSTRACT Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl3... more ABSTRACT Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl3 type structure. These scintillating alloys exhibit high luminosity and proportional response, making them the first scintillators comparable to room temperature semiconductors for gamma spectroscopy; Ce(III) activated lanthanum bromide has recently enabled scintillating gamma ray spectrometers with < 3% FWHM energy resolutions at 662 keV. However brittle fracture of these materials impedes development of large volume crystals. Low fracture stress and perfect cleavage along prismatic planes cause material cracking during and after crystal growth. These and other properties pose challenges for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Recent progress on basic structure and properties of the lanthanide halides is reported here, including thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. Observations including reversible hydrate formation under atmospheric pressure, loss of stoichiometry at high temperature, anisotropic thermal expansion, reactivity towards common crucible materials, and crack initiation and propagation under applied loads are reported. The fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. Analysis of the symmetry and crystal structure of this system suggests possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. This proposed failure mechanism and its implications for scale up to large diameter crystal growth are also discussed.
To obtain a copy of this Journal Article, link to the DOI if present for specific Publisher infor... more To obtain a copy of this Journal Article, link to the DOI if present for specific Publisher information. Library patrons may click here to search WorldCat to identify libraries that hold this journal title; check beforehand to verify the library holds the volume needed. ... Select a citation type above to copy/paste or download the reference. ... Some links on this page may take you to non-federal websites. Their policies may differ from this site.
Surface hardened components are used in fatigue critical applications such as axles and gears. In... more Surface hardened components are used in fatigue critical applications such as axles and gears. Inclusions are critical microstructural features where fatigue cracks have been observed to nucleate in these parts. In this investigation, the effect of inclusion populations on fatigue performance of induction hardened 1045 steel was examined. The steel was heat treated to have a tempered martensite starting microstructure and was induction hardened to two different case depths. Utilizing extreme value statistical analysis, the largest inclusion as well as the largest inclusion in each of five categories, MnS, MnCaS, MnAlS, Al 2 O 3 , and Al 2 O 3 -MgO, was estimated for a critically stressed area in a fully reversed cantilever bending fatigue sample. The inclusion size estimates were used to predict the endurance limit of the sample with a fracture mechanics-based model. This methodology has been traditionally used for homogeneous materials but has been modified here for bending fatigue and inhomogeneous case hardened material. The predicted endurance limits are closely correlated to experimentally measured endurance limits.
In view of the need to understand low cycle fatigue (LCF)-microstructure relationships in carburi... more In view of the need to understand low cycle fatigue (LCF)-microstructure relationships in carburized steels, bending fatigue tests and fatigue modeling were conducted on carburized 4320 steel. The starting case microstructure of the specimens, directly quenched and tempered after carburizing, consisted of plate martensite and retained austenite. This paper compares linear elastic fracture mechanics (LEFM) based models that predict crack growth rates in the transgranular crack growth region with an effective stress intensity reduction due to stress/strain induced transformation of austenite to martensite in front of the crack tip. These models more accurately predict fatigue lives than a simple linear elastic fracture mechanics model without a reduction in the stress intensity. A sensitivity analysis on the model results as a function of input parameters was also performed.
A modeling approach that captures the plastic strain amplitude dependence of strain induced marte... more A modeling approach that captures the plastic strain amplitude dependence of strain induced martensite fraction evolution during low cycle fatigue (LCF) loading of metastable austenitic steels has been developed. The model is based on a modified version of the Olson-Cohen kinetic equation that retains connection to the underlying mechanisms of the transformation by relating cyclic austenite stability to monotonic stability. The kinetic model is then input into an evolving composite mechanical model that relies on a simple rule of ...
ABSTRACT The fatigue behavior of induction-hardened calcium-treated 4140 steel with three differe... more ABSTRACT The fatigue behavior of induction-hardened calcium-treated 4140 steel with three different case depths was evaluated using rotating bending fatigue tests. The as-received microstructure of the steel was banded and the orientation of microstructural banding with respect to the fatigue specimen was varied. Due to the inclusion shape control resulting from the calcium additions, inclusions in the steel were not elongated in the direction of the banding. It was found that microstructure banding does not have a significant influence on the fatigue properties of the steel tested. Furthermore, the fatigue limit increase with case depth is primarily related to the bending stress near the location of crack nucleation.
Abstract The influence of annealing temperature and time on solute carbon levels was investigated... more Abstract The influence of annealing temperature and time on solute carbon levels was investigated in four ultralow-carbon (ULC) bake-hardenable steels; two Ti-V ULC steels with different V/C levels and two Ti-Nb ULC steels with different Nb/C levels. Internal-friction and scanning transmission electron microscopy (STEM) techniques were used to understand the precipitation/dissolution behavior in the various steels. An effect of annealing time on the carbon Snoek-peak height was observed in both Ti-V steels and in the Ti-Nb steel having ...
The demand for improved materials is continuously pushing producers to obtain a fine grain struct... more The demand for improved materials is continuously pushing producers to obtain a fine grain structure and tight restrictions on grain size uniformity in forged superalloy rod. Understanding flow and recrystallization behavior is critical for optimizing forge and annealing practices to meet these requirements. The flow behavior of INCOLOY (r) alloy 945, a newly developed hybrid of alloys 718 and 925 with a unique combination of strength and corrosion resistance, was performed using uniaxial compression testing at elevated ...
Résumé/Abstract Spot welding of advanced high-strength steels (AHSS) poses significant challenges... more Résumé/Abstract Spot welding of advanced high-strength steels (AHSS) poses significant challenges because the high-carbon equivalent of AHSS can result in welds that are perceived to be of lower quality based on conventional weld quality criteria. Specifically, welds in AHSS are more prone to interfacial fracture, whereas button pullout failure is the preferred fracture mode because it indicates the weld is stronger than the base material. However, some evidence suggests that welds in AHSS that exhibit interfacial fracture ...
Potential methods to enhance the fatigue performance of automotive components are considered. The... more Potential methods to enhance the fatigue performance of automotive components are considered. The importance of design is illustrated with results on spot weld fatigue behavior, which was shown to be largely independent of base metal properties and dependent only on geometry in the high cycle fatigue regime. Selected results from several recent studies are used to illustrate some unique steel alloying and processing concepts that can lead to steel parts with improved fatigue performance, primarily by increasing the ...
Quenched and partitioned (Q&P) steels are one family of steels that has received some recent inte... more Quenched and partitioned (Q&P) steels are one family of steels that has received some recent interest for high-strength automotive applications. Previous Q&P steel research has usually focused on cold rolled and annealed products. In the current study, the thermomechanical profile was modified such that Q&P simulations were developed to characterize material as if it might be produced directly from a hot strip mill.
Penetrating Radiation Systems and Applications VIII, 2007
The ability to manufacture large scale scintillating crystals is directly linked to the mechanica... more The ability to manufacture large scale scintillating crystals is directly linked to the mechanical properties of the crystal. In this paper, estimated mechanical properties, including hardness, modulus, and fracture toughness of novel and established scintillating single crystals including CsI(Tl), CdWO4, NaI(Tl), and LaBr3(Ce). Lanthanum and cerium halide crystals have shown particular promise as scintillating materials because of their high luminosity
A modified quantitative microstructure characterization technique has been developed based on con... more A modified quantitative microstructure characterization technique has been developed based on constituent chord-length distribution (CLD). The modified technique, called the categorical CLD (CCLD), is capable of quantifying both size and volume fraction of the constituent of interest in a multi-constituent microstructure as a function of adjacent microstructure. The capability of the CCLD is demonstrated by its application to the investigation of the effect of microstructure on the stability of retained austenite (RA) during mechanical deformation in transformation-induced plasticity steels. By quantifying microstructures deformed to different levels of strains, it is found that RA is stabilized by fine grain size and adjacent bainitic ferrite.
ABSTRACT Low carbon martensitic steels are often produced by reaustenitizing and quenching (RA/Q)... more ABSTRACT Low carbon martensitic steels are often produced by reaustenitizing and quenching (RA/Q). Direct quenching (DQ) has gained interest in the past few decades and requires quenching immediately after working above or below the austenite recrystallization temperature to form martensitic microstructures. In the current study, microalloyed ASTM A514 steel is used to produce martensite from either equiaxed or pancaked prior austenite grain (PAG) microstructures. The equiaxed PAG conditions simulate microstructures produced by RA/Q and the pancaked PAG conditions simulate microstructures produced by controlled rolling (CR) before DQ. Controlled rolling followed by DQ was simulated with double hit compression in a Gleeble® 3500. The prior austenite grain size (PAGS) was varied between 9 and 75 μm prior to controlled rolling. The strengthening and toughening mechanisms are being investigated in the as-quenched (AsQ), low temperature tempered (LTT: 200 °C), and high temperature tempered (HTT: 600 °C) conditions. The equiaxed PAG condition has a Hall-Petch (H-P) relationship between yield strength (or microhardness) and PAGS in the AsQ condition. There is not a H-P relationship between PAGS and microhardness in the CR-DQ conditions. The CR-DQ conditions generally exhibit higher microhardness than the RA/Q conditions with similar PAGS, with the most significant differences in the larger PAGS conditions. Toughness was only measured in the equiaxed PAG conditions. The smallest PAGS has the lowest ductile-to-brittle transition temperature (DBTT) with the highest strength in the AsQ and LTT conditions. The smallest PAGS has the lowest DBTT and the lowest strength in the HTT condition.
The influence of Si and Al on the lattice parameter and stacking fault energy (SFE) of austenitic... more The influence of Si and Al on the lattice parameter and stacking fault energy (SFE) of austenitic steel was studied. X-ray diffraction indicated that 2.5 wt.% Al alloying increased the austenite lattice parameter by 1.41 × 10−3 nm, whereas 2.5 wt.% Si alloying had little effect. Partial dislocation separation measurements from weak-beam dark-field images indicated that 2.5 wt.% Al alloying increased the SFE by 12–17 mJ m−2 and 2.5 wt.% Si alloying decreased the SFE by 6–7 mJ m−2.
ABSTRACT One mode that limits the usefulness of hot forging die steels is localized plastic defor... more ABSTRACT One mode that limits the usefulness of hot forging die steels is localized plastic deformation in regions of high pressure. To understand this behavior the yield strength of the steel needs to be measured at working temperatures in order to determine the likelihood of localized plasticity. One of the issues in using die steels for hot forging applications is that they are initially tempered to a hardness value when put into service. As the die is used to produce forged components, the contact with the hot forging causes the die to continue to temper and hence soften with continued used. To explore these issues three different die steels were obtained and tested experimentally. Experimental compressive yield strengths were determined for the three die steels (FX, 2714 and WF). The die steels were tempered to various hardness values prior to compression testing. The five room-temperature hardness values after tempering ranged from 20 to 38 HRC. The five temperatures for compression testing ranged from 593 to 704 °C (1100 to 1300 oF). From these tests a good characterization of the high temperature plastic behavior of each steel was obtained. It was found that the WF steel which had the highest alloy content was the strongest of the three steels under all test conditions. The FX and 2714, which had similar alloy contents (with FX having slightly less carbon, nickel and vanadium), had yield strengths that were close to each other at the intermediate temperatures, but at the high and low end of the testing range for temperature the FX was stronger than the 2714. Hence, to obtain the greatest resistance to localized plastic deformation during operations the choice of die steel should be WF, followed by FX and then 2714.
Penetrating Radiation Systems and Applications VIII, 2007
ABSTRACT Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl3... more ABSTRACT Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl3 type structure. These scintillating alloys exhibit high luminosity and proportional response, making them the first scintillators comparable to room temperature semiconductors for gamma spectroscopy; Ce(III) activated lanthanum bromide has recently enabled scintillating gamma ray spectrometers with < 3% FWHM energy resolutions at 662 keV. However brittle fracture of these materials impedes development of large volume crystals. Low fracture stress and perfect cleavage along prismatic planes cause material cracking during and after crystal growth. These and other properties pose challenges for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Recent progress on basic structure and properties of the lanthanide halides is reported here, including thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. Observations including reversible hydrate formation under atmospheric pressure, loss of stoichiometry at high temperature, anisotropic thermal expansion, reactivity towards common crucible materials, and crack initiation and propagation under applied loads are reported. The fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. Analysis of the symmetry and crystal structure of this system suggests possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. This proposed failure mechanism and its implications for scale up to large diameter crystal growth are also discussed.
To obtain a copy of this Journal Article, link to the DOI if present for specific Publisher infor... more To obtain a copy of this Journal Article, link to the DOI if present for specific Publisher information. Library patrons may click here to search WorldCat to identify libraries that hold this journal title; check beforehand to verify the library holds the volume needed. ... Select a citation type above to copy/paste or download the reference. ... Some links on this page may take you to non-federal websites. Their policies may differ from this site.
Surface hardened components are used in fatigue critical applications such as axles and gears. In... more Surface hardened components are used in fatigue critical applications such as axles and gears. Inclusions are critical microstructural features where fatigue cracks have been observed to nucleate in these parts. In this investigation, the effect of inclusion populations on fatigue performance of induction hardened 1045 steel was examined. The steel was heat treated to have a tempered martensite starting microstructure and was induction hardened to two different case depths. Utilizing extreme value statistical analysis, the largest inclusion as well as the largest inclusion in each of five categories, MnS, MnCaS, MnAlS, Al 2 O 3 , and Al 2 O 3 -MgO, was estimated for a critically stressed area in a fully reversed cantilever bending fatigue sample. The inclusion size estimates were used to predict the endurance limit of the sample with a fracture mechanics-based model. This methodology has been traditionally used for homogeneous materials but has been modified here for bending fatigue and inhomogeneous case hardened material. The predicted endurance limits are closely correlated to experimentally measured endurance limits.
In view of the need to understand low cycle fatigue (LCF)-microstructure relationships in carburi... more In view of the need to understand low cycle fatigue (LCF)-microstructure relationships in carburized steels, bending fatigue tests and fatigue modeling were conducted on carburized 4320 steel. The starting case microstructure of the specimens, directly quenched and tempered after carburizing, consisted of plate martensite and retained austenite. This paper compares linear elastic fracture mechanics (LEFM) based models that predict crack growth rates in the transgranular crack growth region with an effective stress intensity reduction due to stress/strain induced transformation of austenite to martensite in front of the crack tip. These models more accurately predict fatigue lives than a simple linear elastic fracture mechanics model without a reduction in the stress intensity. A sensitivity analysis on the model results as a function of input parameters was also performed.
A modeling approach that captures the plastic strain amplitude dependence of strain induced marte... more A modeling approach that captures the plastic strain amplitude dependence of strain induced martensite fraction evolution during low cycle fatigue (LCF) loading of metastable austenitic steels has been developed. The model is based on a modified version of the Olson-Cohen kinetic equation that retains connection to the underlying mechanisms of the transformation by relating cyclic austenite stability to monotonic stability. The kinetic model is then input into an evolving composite mechanical model that relies on a simple rule of ...
ABSTRACT The fatigue behavior of induction-hardened calcium-treated 4140 steel with three differe... more ABSTRACT The fatigue behavior of induction-hardened calcium-treated 4140 steel with three different case depths was evaluated using rotating bending fatigue tests. The as-received microstructure of the steel was banded and the orientation of microstructural banding with respect to the fatigue specimen was varied. Due to the inclusion shape control resulting from the calcium additions, inclusions in the steel were not elongated in the direction of the banding. It was found that microstructure banding does not have a significant influence on the fatigue properties of the steel tested. Furthermore, the fatigue limit increase with case depth is primarily related to the bending stress near the location of crack nucleation.
Abstract The influence of annealing temperature and time on solute carbon levels was investigated... more Abstract The influence of annealing temperature and time on solute carbon levels was investigated in four ultralow-carbon (ULC) bake-hardenable steels; two Ti-V ULC steels with different V/C levels and two Ti-Nb ULC steels with different Nb/C levels. Internal-friction and scanning transmission electron microscopy (STEM) techniques were used to understand the precipitation/dissolution behavior in the various steels. An effect of annealing time on the carbon Snoek-peak height was observed in both Ti-V steels and in the Ti-Nb steel having ...
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