The Experts below are selected from a list of 78 Experts worldwide ranked by ideXlab platform
Christoph Kirchlechner - One of the best experts on this subject based on the ideXlab platform.
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The fracture toughness of Martensite Islands in dual-phase DP800 steel
Journal of Materials Research, 2021Co-Authors: Chunhua Tian, Christoph KirchlechnerAbstract:In situ microcantilever bending tests were performed on Martensite Islands in a dual-phase (DP) steel to extract the fracture toughness of Martensite at the microscale and to understand damage initiation during forming of DP steels. All microcantilevers were produced through FIB milling. The Martensite Islands do not exhibit linear elastic brittle fracture; instead, significant ductile tearing is observed. The conditional fracture initiation toughness extracted by definition and by Pippan’s transfer criterion is K _ i = 6.5 ± 0.4 MPa m^1/2 and K _ i,2% = 10.1 ± 0.3 MPa m^1/2, respectively. The obtained value is well-represented by the strength-toughness trend of other ferritic steel grades. Considering the yield stress of the same Martensite Island, we found that crack initiation can occur only in very large Martensite Islands or in a banded or agglomerated Martensite structure. Graphic abstract
Chunhua Tian - One of the best experts on this subject based on the ideXlab platform.
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The fracture toughness of Martensite Islands in dual-phase DP800 steel
Journal of Materials Research, 2021Co-Authors: Chunhua Tian, Christoph KirchlechnerAbstract:In situ microcantilever bending tests were performed on Martensite Islands in a dual-phase (DP) steel to extract the fracture toughness of Martensite at the microscale and to understand damage initiation during forming of DP steels. All microcantilevers were produced through FIB milling. The Martensite Islands do not exhibit linear elastic brittle fracture; instead, significant ductile tearing is observed. The conditional fracture initiation toughness extracted by definition and by Pippan’s transfer criterion is K _ i = 6.5 ± 0.4 MPa m^1/2 and K _ i,2% = 10.1 ± 0.3 MPa m^1/2, respectively. The obtained value is well-represented by the strength-toughness trend of other ferritic steel grades. Considering the yield stress of the same Martensite Island, we found that crack initiation can occur only in very large Martensite Islands or in a banded or agglomerated Martensite structure. Graphic abstract
P. Krauklis - One of the best experts on this subject based on the ideXlab platform.
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Relationship Between Martensite Islands and Haz Fracture Toughness in Welded Ni-Cu Structural Steels
Journal de Physique IV Colloque, 1995Co-Authors: R. Ranade, F. Barbaro, J. Williams, P. Munroe, P. KrauklisAbstract:The relationship between high carbon Martensite Island constituent (M*) and the HAZ CTOD fracture toughness has been evaluated in four HSLA plate steels containing varying amounts of C, Ni and Cu. Test pieces with plane fusion boundaries were made by first pass welding and the M* constituent was produced by thermal simulation of second pass welding, intercritically reheating the HAZ to 1043 K. M* was evaluated by quantitative light microscopy and the CTOD fracture toughness was measured in the coarse-grained region of the HAZ. The volume fraction of M* increases with the carbon content of ths steel, and also with the combined content of nickel and copper, but the latter occurs at a much lower rate. The amount of M* does not correlate well with the IIW carbon equivalent, being lower than expected at high Ni and Cu contents. The CTOD fracture toughness decreases with increasing volume fraction of M*. The weldability of steels containing nickel and copper is significantly better than indicated by hardenability based formulae, such as IIW Ceq.
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Relationship Between Martensite Islands and Haz Fracture Toughness in Welded Ni-Cu Structural Steels
Journal De Physique Iv, 1995Co-Authors: R.s. Ranade, P. Munroe, F. J. Barbaro, J.g. Williams, P. KrauklisAbstract:The relationship between high carbon Martensite Island constituent (M*) and the HAZ CTOD fracture toughness has been evaluated in four HSLA plate steels containing varying amounts of C, Ni and Cu. Test pieces with plane fusion boundaries were made by first pass welding and then M* constituent was produced by thermal simulation of second pass welding, intercritically reheating the HAZ to 1043 K M* was evaluated by quantitative light microscopy and the CTOD fracture toughness was measured in the coarse-grained region of the HAZ. The volume fraction of M* increases with the carbon content of the steel, and also with the combined content of nickel and copper, but the latter occurs at a much lower rate. The amount of M* does not correlate well with the IIW carbon equivalent, being lower than expected at high Ni and Cu contents. The CTOD fracture toughness decreases with increasing volume fraction of M*. The weldability of steels containing nickel and copper is significantly better than indicated by hardenability based formulae, such as IIW C eq .
Hamid Azizi - One of the best experts on this subject based on the ideXlab platform.
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New insights into Martensite strength and the damage behaviour of dual phase steels
Acta Materialia, 2018Co-Authors: Colin Scott, B. Shalchi Amirkhiz, Irina Pushkareva, Fateh Fazeli, S.y.p. Allain, Hamid AziziAbstract:Abstract A detailed investigation of Martensite Islands in ultra-high strength dual phase (DP) steels using TEM EELS carbon measurements, nano-indentation studies and micro-mechanical modelling has been carried out. EELS analysis showed that the dispersion in the Martensite Island-to-Island carbon content increases at lower intercritical annealing temperatures due to the influence of undissolved cementite. In a coarse-grained DP alloy, the median Martensite Island nano-hardness values and those calculated from EELS carbon data were in excellent agreement. However, in a fine-grained (microalloyed) DP alloy significant and unexplained softening occurred that is not consistent with the measured Martensite carbon content. In both steels, the dispersion in Martensite nano-hardness was greater than that expected from the measured carbon variations. Micro-mechanical modelling using the continuous composite approach (CCA) method was employed to calculate the Martensite flow stress distribution required to fit the bulk tensile response of the two materials. The median Martensite nano-hardness values derived from the fitted CCA stress spectra were in good agreement with those measured by nano-indentation, corroborating the observed Martensite softening. These results provide experimental support for the CCA approach and suggest that the physical origins of the Martensite stress spectrum can be strongly influenced by mechanisms other than carbon segregation. Finally, these data explain why the beneficial effect of reducing the α'/α phase strength ratio (PSR) on DP damage properties is highly asymmetrical, depending on whether the ferrite is strengthened or the Martensite is softened (by tempering).
Jin Guang-can - One of the best experts on this subject based on the ideXlab platform.
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Microstructure and fracture mechanism of 1000 MPa hot dip galvanized dual phase steel
Journal of University of Science and Technology Beijing, 2009Co-Authors: Jin Guang-canAbstract:1 000 MPa grade hot dip galvanized dual phase steel was produced by simulating the process of hot dip galvanizing.The fracture behavior of the dual phase steel was observed by in-situ tension experiment,and its fracture mechanism was further analyzed by SEM and TEM.The results show that dual phase steel(F+M)with a tensile strength of 1 022 MPa and an elongation of 9.5% can be obtained when the annealing temperature is 820 ℃.During the process of dynamic tension,new micro-cracks initiate in the plastic zone of crack tips and wave-like slip bands generate in ferrite grains in the plastic zone.When the crack meets Martensite,it changes its propagation direction and get around the Martensite Island;but when the crack meets ferrite,the ferrite grain is plastically broken up through the way of joining micro-pores.The final fracture pattern is plastic fracture and the fracture morphology of the sample is a dimple pattern.