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Linder, D., Hou, Z., Xie, R., Hedström, P., Ström, V., Holmström, E. & Borgenstam, A. (2019). A comparative study of microstructure and magnetic properties of a Ni–Fe cemented carbide: Influence of carbon content. International Journal of Refractory Metals and Hard Materials, 80, 181-187
Open this publication in new window or tab >>A comparative study of microstructure and magnetic properties of a Ni–Fe cemented carbide: Influence of carbon content
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2019 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 80, p. 181-187Article in journal (Refereed) Published
Abstract [en]

Due to the renewed interest in alternative binders for cemented carbides it is important to understand how the binder composition influences not only mechanical properties but also the microstructure and related measurements for quality control. Microstructure and chemical composition of WC-Co is often evaluated by magnetic measurements. However, when the binder composition deviates significantly from conventional Co-based binders it should not be assumed that the standard measurements can be used to directly evaluate the same parameters. In this paper we investigate the influence of relative C-content on the microstructure and magnetic properties of an alternative binder cemented carbide. It is shown that the saturation magnetization is related to the relative C-content and the magnetic coercivity is related to the microstructure, more specifically to the binder phase distribution, but could not be directly linked to the carbide grain size in the same manner as for standard WC-Co. Furthermore, a direct correlation between Curie temperature and saturation magnetization is observed for this system which means that the Curie temperature potentially could be used for calibration of empirical relations or as a method to accurately determine the binder volume fraction.

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Alternative binder, Cemented carbide, Cermet, Cobalt substitution, Magnetic properties, Metal-matrix composite, Microstructure
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-246465 (URN)10.1016/j.ijrmhm.2019.01.014 (DOI)000460992100018 ()2-s2.0-85060087544 (Scopus ID)
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-08-27Bibliographically approved
Hou, Z., Babu, R. P., Hedström, P. & Odqvist, J. (2019). Early stages of cementite precipitation during tempering of 1C-1Cr martensitic steel. Journal of Materials Science, 54(12), 9222-9234
Open this publication in new window or tab >>Early stages of cementite precipitation during tempering of 1C-1Cr martensitic steel
2019 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, no 12, p. 9222-9234Article in journal (Refereed) Published
Abstract [en]

The precipitation of cementite (M3C) from as-quenched martensite during tempering at 500 and 700 degrees C was investigated in a Fe-1C-1Cr (wt%) alloy. Tempering for a short duration at 700 degrees C results in a Cr/Fe ratio in the core region of M3C precipitates which is equal to the bulk alloy composition, while a shell on the surface of the precipitates exhibits a higher Cr concentration. With a prolonged tempering up to 5h, the shell concentration gradually increases toward the equilibrium value, but the core region has not yet reached the equilibrium value. After tempering for 5s at 500 degrees C, there is no Cr enrichment found at the M3C-matrix interface, while a transition to partitioning of Cr is found during the first 5min of tempering at 500 degrees C. These experimental results indicate that M3C grows without significant partitioning of substitutional elements at both temperatures initially, i.e., growth is carbon diffusion controlled. This stage is, however, very short, and soon after 5s at 700 degrees C and 5min at 500 degrees C, Cr diffusion becomes important. Calculations using the diffusion simulation software DICTRA and precipitation simulation software TC-PRISMA were performed. The diffusion simulations using the local equilibrium interface condition show excellent agreement with experiments concerning Cr enrichment of the particles, but the size evolution is overestimated. On the other hand, the precipitation simulations underestimate the size evolution. It is suggested that a major improvement in the precipitation model could be achieved by implementing a modified nucleation model that considers nucleation far from the equilibrium composition.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-249841 (URN)10.1007/s10853-019-03530-8 (DOI)000462633100031 ()2-s2.0-85063202343 (Scopus ID)
Note

QC 20190430

Available from: 2019-04-30 Created: 2019-04-30 Last updated: 2019-06-11Bibliographically approved
Hou, Z., Linder, D., Hedström, P., Forsberg, A., Holmström, E. & Ström, V. (2019). Effect of carbon content on the Curie temperature of WC-NiFe cemented carbides. International Journal of Refractory Metals and Hard Materials, 78, 27-31
Open this publication in new window or tab >>Effect of carbon content on the Curie temperature of WC-NiFe cemented carbides
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2019 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 78, p. 27-31Article in journal (Refereed) Published
Abstract [en]

We have investigated the effect of the carbon content on the Curie temperature of a cemented carbide composite material with a Ni-Fe alloy as the binder phase and WC as the hard phase. In the carbon concentration range from 5.72 to 5.83 wt% carbon, which covers the interval where WC coexists with fcc Ni-Fe without other phases (the ‘carbon window’), the Curie temperature rises from 200 to 527 °C. This result indicates the possibility to use the Curie temperature to determine the carbon balance in the system. With thermodynamic calculations and kinetic simulations we can quantitatively establish the correlation between the carbon and tungsten content of the binder phase and the Curie temperature. This strong compositional effect on the Curie temperature is quantitatively very different from the conventional Co-based cemented carbides, with Curie temperatures of about 950–1050 °C.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Alternative binder, Carbon window, Cemented carbide, Curie temperature, Hard metals, Binary alloys, Binders, Carbide tools, Carbides, Cobalt compounds, Iron alloys, Nickel alloys, Carbon concentrations, Cemented carbide composites, Cemented carbides, Compositional effects, Effect of carbons, Kinetic simulation, Thermodynamic calculations, Temperature
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-236334 (URN)10.1016/j.ijrmhm.2018.08.010 (DOI)000451489300003 ()2-s2.0-85052282006 (Scopus ID)
Note

QC 20181109

Available from: 2018-11-09 Created: 2018-11-09 Last updated: 2018-12-11Bibliographically approved
Hou, Z., Linder, D., Hedström, P., Ström, V., Holmström, E. & Borgenstam, A. (2019). Evaluating magnetic properties of composites from model alloys – Application to alternative binder cemented carbides. Scripta Materialia, 168, 96-99
Open this publication in new window or tab >>Evaluating magnetic properties of composites from model alloys – Application to alternative binder cemented carbides
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2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 168, p. 96-99Article in journal (Refereed) Published
Abstract [en]

The magnetic properties of 85Ni-15Fe model alloys containing Co, W and C have been studied with the intent to isolate the influence of alloy chemistry on quality control measurements of alternative binder cemented carbides. The results show a strong influence of dissolved W on the Curie temperature and the saturation magnetization. The amount of dissolved C, and the presence of WC precipitates, on the other hand, is shown to have negligible effect. Furthermore, the magnetic coercivity is indicated to be entirely dominated by the microstructural features and quite insensitive to composition.

Place, publisher, year, edition, pages
Acta Materialia Inc, 2019
Keywords
Alternative binder, Cemented carbide, Magnetic properties, Metal-ceramic composite, Ni-Fe model alloy, Binary alloys, Binders, Carbide tools, Carbides, Cobalt alloys, Nickel alloys, Saturation magnetization, Alloy chemistry, Cemented carbides, FE model, Magnetic coercivities, Metal-ceramic composites, Microstructural features, Properties of composites, Quality control measurement, Iron alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-252472 (URN)10.1016/j.scriptamat.2019.04.033 (DOI)000470798400021 ()2-s2.0-85064921201 (Scopus ID)
Note

QC 20190715

Available from: 2019-07-15 Created: 2019-07-15 Last updated: 2019-07-15Bibliographically approved
Molnár, D. S., Engberg, G., Li, W., Lu, S., Hedström, P., Kwon, S. K. & Vitos, L. (2019). Experimental study of the γ-surface of austenitic stainless steels. Acta Materialia, 173, 34-43
Open this publication in new window or tab >>Experimental study of the γ-surface of austenitic stainless steels
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2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, p. 34-43Article in journal (Refereed) Published
Abstract [en]

We introduce a theory-guided experimental approach to study the γ-surface of austenitic stainless steels. The γ-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys.

Keywords
stacking fault energy, twinning, electron backscatter diffraction, plasticity, first-principles
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-252729 (URN)10.1016/j.actamat.2019.04.057 (DOI)2-s2.0-85065259834 (Scopus ID)
Funder
Vinnova, 2014-03374
Note

QC 20190617

Available from: 2019-06-04 Created: 2019-06-04 Last updated: 2019-07-29Bibliographically approved
Zhou, T., Faleskog, J., Babu, P., Odqvist, J., Yu, H. & Hedström, P. (2019). Exploring the relationship between the microstructure and strength of fresh and tempered martensite in a maraging stainless steel Fe-15Cr-5Ni. Materials Science & Engineering: A, 745, 420-428, Article ID DELL AJ, 1985, METALLURGICAL TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, V16, P2131.
Open this publication in new window or tab >>Exploring the relationship between the microstructure and strength of fresh and tempered martensite in a maraging stainless steel Fe-15Cr-5Ni
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2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 745, p. 420-428, article id DELL AJ, 1985, METALLURGICAL TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, V16, P2131Article in journal (Refereed) Published
Abstract [en]

Hierarchical microstructure engineering is an efficient design path for ultra-high strength steels. An excellent example of this is maraging stainless steel, which achieves its high-performance by combining the hierarchic martensitic microstructure and nano-sized precipitates. Relating this complex microstructure with mechanical properties, e.g. strength, is not trivial. In the present work, we therefore explore the relationship between the hierarchic microstructure, evolving with the tempering of a Cu-containing maraging stainless steel 15-5 PH, and its strength. Comprehensive microstructure characterization, including the quantification of dislocation density, effective grain size, precipitates and retained austenite fraction is performed after quenching and tempering at 500 degrees C. The microstructure data is subsequently used as input for assessing the evolution of individual strength contributions and thus the increase in strength of tempered martensite contributed by Cu precipitation strengthening is evaluated. It is found that the Cu precipitation and dislocation annihilation are two major factors controlling the evolution of the yield strength of the tempered martensite. The Cu precipitation strengthening is also modelled using our previous Langer-Schwartz-Kampmann-Wagner model based predictions of the Cu precipitation, and modelled precipitation strengthening is compared with the evaluated Cu precipitation strengthening from the experiments. The work exemplifies the promising approach of combining physically based precipitation modelling and precipitation-strengthening modelling for alloy design and optimization. However, more work is needed to develop a generic predictive framework.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Mechanical properties, Modelling, Maraging stainless steel, Cu precipitation strengthening, Martensite
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-244522 (URN)10.1016/j.msea.2018.12.126 (DOI)000457819400045 ()2-s2.0-85059590155 (Scopus ID)
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-04Bibliographically approved
Rahaman, M., Mu, W., Odqvist, J. & Hedström, P. (2019). Machine Learning to Predict the Martensite Start Temperature in Steels. Metallurgical and Materials Transactions. A, 50A(5), 2081-2091
Open this publication in new window or tab >>Machine Learning to Predict the Martensite Start Temperature in Steels
2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 5, p. 2081-2091Article in journal (Refereed) Published
Abstract [en]

The martensite start temperature (M-s) is a critical parameter when designing high-performance steels and their heat treatments. It has, therefore, attracted significant interest over the years. Numerous methodologies, such as thermodynamics-based, linear regression and artificial neural network (ANN) modeling, have been applied. The application of data-driven approaches, such as ANN modeling, or the wider concept of machine learning (ML), have shown limited technical applicability, but considering that these methods have made significant progress lately and that materials data are becoming more accessible, a new attempt at data-driven predictions of the M-s is timely. We here investigate the usage of ML to predict the M-s of steels based on their chemical composition. A database of the M(s)vs alloy composition containing 2277 unique entries is collected. It is ensured that all alloys are fully austenitic at the given austenitization temperature by thermodynamic calculations. The ML modeling is performed using four different ensemble methods and ANN. Train-test split series are used to evaluate the five models, and it is found that all four ensemble methods outperform the ANN on the current dataset. The reason is that the ensemble methods perform better for the rather small dataset used in the present work. Thereafter, a validation dataset of 115 M-s entries is collected from a new reference and the final ML model is benchmarked vs a recent thermodynamics-based model from the literature. The ML model provides excellent predictions on the validation dataset with a root-mean-square error of 18, which is slightly better than the thermodynamics-based model. The results on the validation dataset indicate the technical usefulness of the ML model to predict the M-s in steels for design and optimization of alloys and heat treatments. Furthermore, the agility of the ML model indicates its advantage over thermodynamics-based models for M-s predictions in complex multicomponent steels. (C) The Author(s) 2019

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-251196 (URN)10.1007/s11661-019-05170-8 (DOI)000463991300003 ()2-s2.0-85063028004 (Scopus ID)
Note

QC 20190523

Available from: 2019-05-23 Created: 2019-05-23 Last updated: 2019-05-23Bibliographically approved
Hoseini-Athar, M. M., Mahmudi, R., Babu, P. & Hedström, P. (2019). Microstructural evolution and superplastic behavior of a fine-grained Mg-Gd alloy processed by constrained groove pressing. Materials Science & Engineering: A, 754, 390-399
Open this publication in new window or tab >>Microstructural evolution and superplastic behavior of a fine-grained Mg-Gd alloy processed by constrained groove pressing
2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 754, p. 390-399Article in journal (Refereed) Published
Abstract [en]

In the current study, microstructural evolution and superplasticity of an extruded Mg-2wt% Gd sheet were studied after the constrained groove pressing (CGP) process. Microstructural observations by scanning electron microscopy and electron backscattered diffraction revealed that after 4 cycles of CGP, a rather homogeneous fine-grained microstructure with an average grain size of 4.3 mu m, and a large fraction of high angle grain boundaries was obtained. By performing shear punch tests (SPT) at different temperatures and various shear strain rates, a peak strain rate sensitivity index (m-value) of 0.49 was obtained after 4 cycles of CGP process at 673 K, while peak m-values of 0.31 and 0.36 were obtained for the as-extruded and 2 cycle CGP process conditions, respectively. An m-value of 0.49 and an activation energy of 113 kJ/mol, obtained for the fine-grained material after 4 cycles of CGP, suggest that the dominant deformation mechanism in the superplastic regime is grain boundary sliding (GBS) controlled by grain boundary diffusion.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Constrained groove pressing, Mg-Gd alloy, Shear punch test, Superplasticity
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-252396 (URN)10.1016/j.msea.2019.03.082 (DOI)000466249400040 ()2-s2.0-85063280438 (Scopus ID)
Note

QC 20190716

Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2019-07-16Bibliographically approved
Xu, X., Wessman, S., Odqvist, J., King, S. M. & Hedström, P. (2019). Nanostructure, microstructure and mechanical properties of duplex stainless steels 25Cr-7 Ni and 22Cr-5Ni (wt.%) aged at 325 degrees C. Materials Science & Engineering: A, 754(ALGUE A, 1990, JOURNAL OF MATERIALS SCIENCE, V25, P4977), 512-520
Open this publication in new window or tab >>Nanostructure, microstructure and mechanical properties of duplex stainless steels 25Cr-7 Ni and 22Cr-5Ni (wt.%) aged at 325 degrees C
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2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 754, no ALGUE A, 1990, JOURNAL OF MATERIALS SCIENCE, V25, P4977, p. 512-520Article in journal (Refereed) Published
Abstract [en]

The nanoscale concentration fluctuation evolution due to phase separation (PS) and the corresponding mechanical property changes in two duplex stainless steels, 22Cr-5Ni (2205) and 25Cr-7N1 (2507), have been studied after aging at 325 degrees C for up to 6000 h. The nanostructure characterization is performed using small-angle neutron scattering (SANS) and the microstructure and fractography analyses, including observations on fracture surfaces and fracture cross-sections, are performed by scanning electron microscopy and electron backscatter diffraction. The results show that the kinetics of PS in grade 2507 is faster than that in grade 2205, leading to greater hardening and deterioration in toughness for grade 2507 as compared to grade 2205. The evolution of the nanostructure in the ferrite phase changes the deformation mode from the original ductile fracture to a quasi-cleavage type fracture where deformation twins form in the hardened ferrite. Delamination, grain fragmentation in ferrite and plastic slip deformation of the austenite are suggested to dissipate most of the energy absorbed by the crack during brittle fracture.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Duplex stainless steel, Phase separation, Spinodal decomposition, Small-angle neutron scattering (SANS), Mechanical property, Nanostructure
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-252397 (URN)10.1016/j.msea.2019.03.046 (DOI)000466249400052 ()2-s2.0-85063511012 (Scopus ID)
Note

QC 20190716

Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2019-07-16Bibliographically approved
Tian, Y., Forsberg, A. & Hedström, P. (2018). Comparing the deformation-induced martensitic transformation with the athermal martensitic transformation in Fe-Cr-Ni alloys. Journal of Alloys and Compounds, 766, 131-139
Open this publication in new window or tab >>Comparing the deformation-induced martensitic transformation with the athermal martensitic transformation in Fe-Cr-Ni alloys
2018 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 766, p. 131-139Article in journal (Refereed) Published
Abstract [en]

The microstructure of martensite formed athermally or via deformation in Fe-Cr-Ni alloys with different austenite (gamma) stability has been investigated using microscopy. Two different types of microstructures, viz. blocky and banded structure, are observed after athermal and deformation-induced martensitic transformation (AMT and DIMT, respectively). The blocky structure form during AMT or DIMT if the stability of gamma is low. In both cases, there is a significant chemical driving force for the transformation from gamma to alpha'-martensite (alpha'), and if it is not hindered by e.g. planar defects it can grow uninhibited into a blocky morphology without the necessity to nucleate new crystallographic variants to accommodate the transformation strains. On the other hand, the banded structure is due to the formation of epsilon-martensite (epsilon) during AMT, or the wider concept shear bands in the case of DIMT. The shear bands, and in particular epsilon, lower the nucleation barrier for alpha' that forms within individual shear bands if the stability of gamma is low. Neighbouring alpha' units predominantly have a twin-related orientation relationship to accommodate the transformation strains. With increasing y stability during DIMT, variant selection becomes pronounced with preferred formation of variants favorable oriented with respect to the applied stress/strain field. The formation of alpha' at individual shear bands is also rare, since nos is present and instead alpha' forms at the intersection of shear bands for more stable gamma. In conclusion, AMT and DIMT for low gamma stability lead to similar microstructures, whereas the DIMT microstructure for high y stability is distinct. 

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
Metastable austenite, Deformation-induced martensitic transformation, Deformation microstructure, Variant pairing tendency, Variant selection
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-235554 (URN)10.1016/j.jallcom.2018.06.326 (DOI)000444617200014 ()2-s2.0-85049301116 (Scopus ID)
Note

QC 20181002

Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2018-10-02Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1102-4342

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