Pentti Karjalainen | University of Oulu (original) (raw)
Papers by Pentti Karjalainen
Materialia, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metals, 2019
Hot forming combined with austempering and quenching and partitioning (QP) processes have been us... more Hot forming combined with austempering and quenching and partitioning (QP) processes have been used to shape two cold rolled high silicon steel sheets into hat profiles. Thermal simulation on a Gleeble instrument was employed to optimize processing variables to achieve an optimum combination of strength and ductility in the final parts. Microstructures were characterized using optical and scanning electron microscopy and X-ray diffraction. Tensile strengths (Rm) of 1190 and 1350 MPa and elongations to fracture (A50mm) of 8.5 and 7.4%, were achieved for the two high-silicon steels having 0.15 and 0.26 wt % C, respectively. Preliminary results show that press hardening together with a QP heat treatment is an effective method of producing components with high strength and reasonable tensile ductility from low carbon containing steels that have the potential for carbide free bainite formation. The QP treatment resulted in faster austenite decomposition during partitioning in the steels ...
Metals, 2018
Heavy cold rolling is generally required for efficient grain size refinement in the martensitic r... more Heavy cold rolling is generally required for efficient grain size refinement in the martensitic reversion process, which is, however, not desirable in practical processing. In the present work, the influence of cold rolling reductions of 32%, 45% and 63% on the microstructure evolution and mechanical properties of a metastable austenitic AISI 301LN type steel were investigated in detail adopting scanning electron microscopy with the electron backscatter diffraction method and mechanical testing. A completely austenitic microstructure and a partially reversed counterpart were created. It was found that the fraction of grains with a size of 3 µm or larger, called medium-sized grains, increased with decreasing the prior cold rolling reduction. These grains are formed mainly from the shear-reversed austenite, transformed from slightly-deformed martensite, by gradual evolution of subgrains to grains. However, in spite of significant amounts of medium-sized grains, the tensile properties after the 32% or 45% cold rolling reductions were practically equal to those after the 63% reduction. The austenite stability against the formation of deformation-induced martensite in subsequent straining was reduced by lowering the cold rolling reduction, due to the larger grain size of medium-sized grains and the shift of their orientation towards {211} .
Social Science Research Network, 2022
Zavarivanje i zavarene konstrukcije, 2011
Članstvo u strukovnoj asocijaciji DUZS je referenca za Vaš profesionalni status Članarina za 2011... more Članstvo u strukovnoj asocijaciji DUZS je referenca za Vaš profesionalni status Članarina za 2011. godinu je 3500,00 dinara Uplatom članarine stičete pravo na GRATIS godišnje izdanje časopisa "ZAVARIVANJE I ZAVARENE KONSTRUKCIJE"
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Jul 1, 2022
B 4 C-TiB 2-SiC composites were fabricated via hot pressing using ball milled B 4 C, TiB 2 , and ... more B 4 C-TiB 2-SiC composites were fabricated via hot pressing using ball milled B 4 C, TiB 2 , and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84 GPa, 858 MPa and 8.21 MPa m 1/2 , respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B 4 C-TiB 2-SiC composite. 2. Experimental 2.1. Materials Commercially available B 4 C powder (D 50 = 2.5 μm, Jingangzuan Boron Carbide Co., Ltd., Mudanjiang, China), TiB 2 powder (D 50 = 8.0 μm, Dandong Chemical Research Institute Co., Ltd., Dandong, China) and SiC powder (D 50 = 0.5-0.7 μm Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China) were used as the raw materials. The characteristics of the raw material powders, including mean particle size, specific surface area, oxygen content and certain metal impurities content are shown in Table 1.
Revista De Metalurgia, Oct 30, 2004
La Metallurgia Italiana
The influence of C in the range of 0.011-0.043 wt-% on the phase transformation characteristics, ... more The influence of C in the range of 0.011-0.043 wt-% on the phase transformation characteristics, mechanical properties and microstructure of Fe-2.0Mn-0.25Mo-0.8Ni-0.05Nb-0.03Ti steel was investigated. In the dilatometric experiments, it was found that a reduction in the C content increased the phase transformation temperatures, decreased the hardness and promoted quasi-polygonal ferrite (QF) formation over granular bainitic ferrite (GBF) and bainitic ferrite (BF), but at the same time the sensitivity of the phase transformation temperatures and hardness to cooling rates was reduced. Mechanical testing of laboratory hot rolled plates revealed that the targeted yield strength of 500 MPa was reached even in the steel with the lowest C content (0.011wt-%). An increase in C content did not considerably increase the yield strength, although the tensile strength was more significantly increased. Impact toughness properties, in turn, were markedly deteriorated due to this C content increment. Microstructural analysis of the hot rolled plates showed that an increase in C content decreased the fraction of QF and consequently increased the fraction of GBF and BF, as well as the size and fraction of C-enriched secondary microconstituents. In addition, the size of the coarsest crystallographic packets seemed to be finer in the low C steel with QF dominated microstructure than in its higher C counterparts with higher fractions of GBF-BF, even thought the average crystallographic packet size was slightly finer in these higher C steels. Mechanical testing of the simulated CGHAZ's showed that their toughness properties are not strongly dependent on C content, although there exists a general trend for toughness to slightly weaken with increasing C content. It could be concluded that HAZ toughness properties of these types of steels are acceptable. On the basis of dilatometric experiments, mechanical testing and microstructural analysis it can be stated that a good combination of strength, toughness and weldability as well as microstructural stability can be reached in very low C steels with QF dominated microstructures. Finally, an example of this type of microstuctural concept, which has been successfully
Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microst... more Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microstructures were investigated at ambient temperature and the effect of grain refinement was evaluated. Two different microstructural states of material were introduced by different annealing conditions during special thermomechanical treatment. Fatigue life curves were obtained and compared for both coarse-grained and ultrafine-grained states of austenitic stainless steel. Magnetic measurements before, during and after cyclic loading were performed to reveal structural changes, i.e. formation of deformation-induced martensite. Relationship between microstructure refinement, phase composition and fatigue properties was discussed.
Proceedings of the 2nd International Conference Super High Strength Steels, Peschiera del Garda (... more Proceedings of the 2nd International Conference Super High Strength Steels, Peschiera del Garda (Verona), Italy, 17 - 20.10.2010
Materials
A novel processing route is proposed to create a heterogeneous, multiphase structure in a medium ... more A novel processing route is proposed to create a heterogeneous, multiphase structure in a medium Mn steel by incorporating partial quenching above the ambient, warm deformation, and partial recrystallization at high partitioning temperatures. The processing schedule was implemented in a Gleeble thermomechanical simulator and microstructures were examined by electron microscopy and X-ray diffraction. The hardness of the structures was measured as the preliminary mechanical property. Quenching of the reaustenitized sample to 120 °C provided a microstructure consisting of 73% martensite and balance (27%) untransformed austenite. Subsequent warm deformation at 500 °C enabled partially recrystallized ferrite and retained austenite during subsequent partitioning at 650 °C. The final microstructure consisted of a heterogeneous mixture of several phases and morphologies including lath-tempered martensite, partially recrystallized ferrite, lath and equiaxed austenite, and carbides. The volum...
Metallurgical and Materials Transactions A, 2022
Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) t... more Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) treatment to develop bulk grain-refined microstructures. The tensile properties and formability of the DRA structures were determined by high-speed tensile and Erichsen cupping tests at a strain rate of 1.5 s−1 (50 mm s−1) and compared with those of coarse-grained steel. Detailed microstructural features of the DRA structures were characterized using the electron backscatter diffraction technique and X-ray diffraction analysis. The DRA structures achieved by annealing for 1 second at 800 °C and 900 °C exhibited a superior combination of yield (~ 950 and 770 MPa, respectively) and tensile (~ 1050 and 950 MPa, respectively) strengths and ductility (~ 35 and 40 pct, respectively, as well as reasonable Erichsen index values under high-speed biaxial strain. Due to adiabatic heating, the DRA structures had higher austenite stability during high-speed stretch forming, i.e., were less prone to st...
SSRN Electronic Journal, 2022
Isij International, 2021
Ferritic stainless steels (FSS) are used in a wide variety of applications due to their combinati... more Ferritic stainless steels (FSS) are used in a wide variety of applications due to their combination of formability, weldability and excellent corrosion resistance. FSS with high chromium contents have become alternatives to the more highly alloyed austenitic steels, which are more expensive primarily due to their nickel content. One drawback sometimes encountered with FSS is a surface defect known as ridging. Ridging occurs along the rolling direction, and its severity is highest when tensile axis is parallel to the rolling direction and lowest along the transverse direction. The height differences between the ridges and adjacent valleys are in the range of 20–50 μm. The phenomenon becomes noticeable for example after deep drawing operations and can result in the need for additional polishing of the drawn product. Early research proposed that the segregation of alloying elements such as chromium, molybdenum or carbon may be one of the possible reasons for ridging.1–3) Later studies ...
Steel Research, 1997
Flow stress data on fine-grained material are needed for FEM modelling of the final passes in hot... more Flow stress data on fine-grained material are needed for FEM modelling of the final passes in hot rolling. However, a fine grain size may be difficult to retain in reheated specimens for hot compression tests, and the flow stress usually has to be determined using specimens with rather coarse grain sizes. The results for several steels tested in austenitic condition show that the increase in grain size from about 15 μm to 50 μm causes a decrease of 5 - 25% in the mean flow stress (calculated over the strain range of 0 - 0.15) and further coarsening has hardly any influence. The effect of grain size variation can be described by respective alterations in the strain-hardening exponent and it can be accounted for by mathematical correction.
Materials Science Forum, 2008
Severely deformed surface layers have been created by ultrasonic attrition technique on four stee... more Severely deformed surface layers have been created by ultrasonic attrition technique on four steel sheets to investigate their influence on fatigue behaviour. A low-carbon (0.05%) ferritic steel and a medium-carbon (0.47%) normalized ferritic-pearlitic steel were selected to study the effect of carbon content on fatigue properties of carbon steels. Two stainless steels, Type 316L and Type 301LN, were also tested to study the influence of stability of the austenitic structure. Microstructural features were characterized by hardness measurements, X-ray diffraction and optical and electron microscopy. Fatigue properties were determined in flexural bending in the range 104 to 107 cycles. Crack nucleation and propagation stages were followed. In the attrition treatment thin severely deformed surface layers were found to form. Highly increased hardness was measured in these layers, especially for stainless steels, where also strain-induced martensite was formed. Drastic improvement in fat...
Materialia, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metals, 2019
Hot forming combined with austempering and quenching and partitioning (QP) processes have been us... more Hot forming combined with austempering and quenching and partitioning (QP) processes have been used to shape two cold rolled high silicon steel sheets into hat profiles. Thermal simulation on a Gleeble instrument was employed to optimize processing variables to achieve an optimum combination of strength and ductility in the final parts. Microstructures were characterized using optical and scanning electron microscopy and X-ray diffraction. Tensile strengths (Rm) of 1190 and 1350 MPa and elongations to fracture (A50mm) of 8.5 and 7.4%, were achieved for the two high-silicon steels having 0.15 and 0.26 wt % C, respectively. Preliminary results show that press hardening together with a QP heat treatment is an effective method of producing components with high strength and reasonable tensile ductility from low carbon containing steels that have the potential for carbide free bainite formation. The QP treatment resulted in faster austenite decomposition during partitioning in the steels ...
Metals, 2018
Heavy cold rolling is generally required for efficient grain size refinement in the martensitic r... more Heavy cold rolling is generally required for efficient grain size refinement in the martensitic reversion process, which is, however, not desirable in practical processing. In the present work, the influence of cold rolling reductions of 32%, 45% and 63% on the microstructure evolution and mechanical properties of a metastable austenitic AISI 301LN type steel were investigated in detail adopting scanning electron microscopy with the electron backscatter diffraction method and mechanical testing. A completely austenitic microstructure and a partially reversed counterpart were created. It was found that the fraction of grains with a size of 3 µm or larger, called medium-sized grains, increased with decreasing the prior cold rolling reduction. These grains are formed mainly from the shear-reversed austenite, transformed from slightly-deformed martensite, by gradual evolution of subgrains to grains. However, in spite of significant amounts of medium-sized grains, the tensile properties after the 32% or 45% cold rolling reductions were practically equal to those after the 63% reduction. The austenite stability against the formation of deformation-induced martensite in subsequent straining was reduced by lowering the cold rolling reduction, due to the larger grain size of medium-sized grains and the shift of their orientation towards {211} .
Social Science Research Network, 2022
Zavarivanje i zavarene konstrukcije, 2011
Članstvo u strukovnoj asocijaciji DUZS je referenca za Vaš profesionalni status Članarina za 2011... more Članstvo u strukovnoj asocijaciji DUZS je referenca za Vaš profesionalni status Članarina za 2011. godinu je 3500,00 dinara Uplatom članarine stičete pravo na GRATIS godišnje izdanje časopisa "ZAVARIVANJE I ZAVARENE KONSTRUKCIJE"
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Jul 1, 2022
B 4 C-TiB 2-SiC composites were fabricated via hot pressing using ball milled B 4 C, TiB 2 , and ... more B 4 C-TiB 2-SiC composites were fabricated via hot pressing using ball milled B 4 C, TiB 2 , and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84 GPa, 858 MPa and 8.21 MPa m 1/2 , respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B 4 C-TiB 2-SiC composite. 2. Experimental 2.1. Materials Commercially available B 4 C powder (D 50 = 2.5 μm, Jingangzuan Boron Carbide Co., Ltd., Mudanjiang, China), TiB 2 powder (D 50 = 8.0 μm, Dandong Chemical Research Institute Co., Ltd., Dandong, China) and SiC powder (D 50 = 0.5-0.7 μm Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China) were used as the raw materials. The characteristics of the raw material powders, including mean particle size, specific surface area, oxygen content and certain metal impurities content are shown in Table 1.
Revista De Metalurgia, Oct 30, 2004
La Metallurgia Italiana
The influence of C in the range of 0.011-0.043 wt-% on the phase transformation characteristics, ... more The influence of C in the range of 0.011-0.043 wt-% on the phase transformation characteristics, mechanical properties and microstructure of Fe-2.0Mn-0.25Mo-0.8Ni-0.05Nb-0.03Ti steel was investigated. In the dilatometric experiments, it was found that a reduction in the C content increased the phase transformation temperatures, decreased the hardness and promoted quasi-polygonal ferrite (QF) formation over granular bainitic ferrite (GBF) and bainitic ferrite (BF), but at the same time the sensitivity of the phase transformation temperatures and hardness to cooling rates was reduced. Mechanical testing of laboratory hot rolled plates revealed that the targeted yield strength of 500 MPa was reached even in the steel with the lowest C content (0.011wt-%). An increase in C content did not considerably increase the yield strength, although the tensile strength was more significantly increased. Impact toughness properties, in turn, were markedly deteriorated due to this C content increment. Microstructural analysis of the hot rolled plates showed that an increase in C content decreased the fraction of QF and consequently increased the fraction of GBF and BF, as well as the size and fraction of C-enriched secondary microconstituents. In addition, the size of the coarsest crystallographic packets seemed to be finer in the low C steel with QF dominated microstructure than in its higher C counterparts with higher fractions of GBF-BF, even thought the average crystallographic packet size was slightly finer in these higher C steels. Mechanical testing of the simulated CGHAZ's showed that their toughness properties are not strongly dependent on C content, although there exists a general trend for toughness to slightly weaken with increasing C content. It could be concluded that HAZ toughness properties of these types of steels are acceptable. On the basis of dilatometric experiments, mechanical testing and microstructural analysis it can be stated that a good combination of strength, toughness and weldability as well as microstructural stability can be reached in very low C steels with QF dominated microstructures. Finally, an example of this type of microstuctural concept, which has been successfully
Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microst... more Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microstructures were investigated at ambient temperature and the effect of grain refinement was evaluated. Two different microstructural states of material were introduced by different annealing conditions during special thermomechanical treatment. Fatigue life curves were obtained and compared for both coarse-grained and ultrafine-grained states of austenitic stainless steel. Magnetic measurements before, during and after cyclic loading were performed to reveal structural changes, i.e. formation of deformation-induced martensite. Relationship between microstructure refinement, phase composition and fatigue properties was discussed.
Proceedings of the 2nd International Conference Super High Strength Steels, Peschiera del Garda (... more Proceedings of the 2nd International Conference Super High Strength Steels, Peschiera del Garda (Verona), Italy, 17 - 20.10.2010
Materials
A novel processing route is proposed to create a heterogeneous, multiphase structure in a medium ... more A novel processing route is proposed to create a heterogeneous, multiphase structure in a medium Mn steel by incorporating partial quenching above the ambient, warm deformation, and partial recrystallization at high partitioning temperatures. The processing schedule was implemented in a Gleeble thermomechanical simulator and microstructures were examined by electron microscopy and X-ray diffraction. The hardness of the structures was measured as the preliminary mechanical property. Quenching of the reaustenitized sample to 120 °C provided a microstructure consisting of 73% martensite and balance (27%) untransformed austenite. Subsequent warm deformation at 500 °C enabled partially recrystallized ferrite and retained austenite during subsequent partitioning at 650 °C. The final microstructure consisted of a heterogeneous mixture of several phases and morphologies including lath-tempered martensite, partially recrystallized ferrite, lath and equiaxed austenite, and carbides. The volum...
Metallurgical and Materials Transactions A, 2022
Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) t... more Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) treatment to develop bulk grain-refined microstructures. The tensile properties and formability of the DRA structures were determined by high-speed tensile and Erichsen cupping tests at a strain rate of 1.5 s−1 (50 mm s−1) and compared with those of coarse-grained steel. Detailed microstructural features of the DRA structures were characterized using the electron backscatter diffraction technique and X-ray diffraction analysis. The DRA structures achieved by annealing for 1 second at 800 °C and 900 °C exhibited a superior combination of yield (~ 950 and 770 MPa, respectively) and tensile (~ 1050 and 950 MPa, respectively) strengths and ductility (~ 35 and 40 pct, respectively, as well as reasonable Erichsen index values under high-speed biaxial strain. Due to adiabatic heating, the DRA structures had higher austenite stability during high-speed stretch forming, i.e., were less prone to st...
SSRN Electronic Journal, 2022
Isij International, 2021
Ferritic stainless steels (FSS) are used in a wide variety of applications due to their combinati... more Ferritic stainless steels (FSS) are used in a wide variety of applications due to their combination of formability, weldability and excellent corrosion resistance. FSS with high chromium contents have become alternatives to the more highly alloyed austenitic steels, which are more expensive primarily due to their nickel content. One drawback sometimes encountered with FSS is a surface defect known as ridging. Ridging occurs along the rolling direction, and its severity is highest when tensile axis is parallel to the rolling direction and lowest along the transverse direction. The height differences between the ridges and adjacent valleys are in the range of 20–50 μm. The phenomenon becomes noticeable for example after deep drawing operations and can result in the need for additional polishing of the drawn product. Early research proposed that the segregation of alloying elements such as chromium, molybdenum or carbon may be one of the possible reasons for ridging.1–3) Later studies ...
Steel Research, 1997
Flow stress data on fine-grained material are needed for FEM modelling of the final passes in hot... more Flow stress data on fine-grained material are needed for FEM modelling of the final passes in hot rolling. However, a fine grain size may be difficult to retain in reheated specimens for hot compression tests, and the flow stress usually has to be determined using specimens with rather coarse grain sizes. The results for several steels tested in austenitic condition show that the increase in grain size from about 15 μm to 50 μm causes a decrease of 5 - 25% in the mean flow stress (calculated over the strain range of 0 - 0.15) and further coarsening has hardly any influence. The effect of grain size variation can be described by respective alterations in the strain-hardening exponent and it can be accounted for by mathematical correction.
Materials Science Forum, 2008
Severely deformed surface layers have been created by ultrasonic attrition technique on four stee... more Severely deformed surface layers have been created by ultrasonic attrition technique on four steel sheets to investigate their influence on fatigue behaviour. A low-carbon (0.05%) ferritic steel and a medium-carbon (0.47%) normalized ferritic-pearlitic steel were selected to study the effect of carbon content on fatigue properties of carbon steels. Two stainless steels, Type 316L and Type 301LN, were also tested to study the influence of stability of the austenitic structure. Microstructural features were characterized by hardness measurements, X-ray diffraction and optical and electron microscopy. Fatigue properties were determined in flexural bending in the range 104 to 107 cycles. Crack nucleation and propagation stages were followed. In the attrition treatment thin severely deformed surface layers were found to form. Highly increased hardness was measured in these layers, especially for stainless steels, where also strain-induced martensite was formed. Drastic improvement in fat...