In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delaminat...In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delamination tension was adopted. In this paper, the thin tensile samples with 3 mm thickness from the surface, 1/4 positions and center along the thickness orientation of test plate were measured, also the relationship between microstructure and mechanical properties was probed. The results show that the center region of hot rolled ferrite/pearlite steel plate exists granular bainite and ferrite mixed grains, which leads to lower plasticity and toughness of this region. During the tensile process, microcracks are generated and extended at the center of steel plate due to the inconsistency of deformation and fracture on the adjacent structures, finally leading to laminated fracture of steel plate.展开更多
The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculat...The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculated based on unit cell model. The effects of volume fraction, distribution and the aspect ratio of pearlite on tensile properties have been investigated.展开更多
Considering the specialities of the steel plate production, the TMCP study has been carried out with Gleeble 2000 tester to explore the possibility of fine grained ferrite in the low carbon steel plates with the chemi...Considering the specialities of the steel plate production, the TMCP study has been carried out with Gleeble 2000 tester to explore the possibility of fine grained ferrite in the low carbon steel plates with the chemical composition of C 0.13--0.18, Si 0.12-0.18, Mn 0.50-0. 65, P 0. 010-0. 025, and S 0. 005-0. 028. The plates with thickness of 8. 7 mm in which the ferrite grain size is smaller than 8μm have been produced by special de- formation process in the laboratory. Furthermore, the trial production of special plain carbon steel plates of 16-25 mm in thickness and 2 000- 2 800 mm in width with fine grained ferrite has been successfully carried out in the Shougang Steel Plate Rolling Plant. The ferrite grain size is 5.5-7μm in the surface layers and 9.5-15μm in the central layer respectively. The yield strength is 320- 360 MPa, tensile strength is 440-520 MPa and the elongation is 25%- 34 %. It is very important for the rolling plants to improve the low carbon steel plates＇ mechanical properties. The results show that the ferrite grains in the surface layer can be refined effectively by the appropriate rolling process, and the strength can be also increased.展开更多
The characteristic of near-surface microstructure and its effects on the torsion performance of cold-drawn pearlitic steel wires for bridge cables were investigated by focused ion beam-scanning electron microscope,tra...The characteristic of near-surface microstructure and its effects on the torsion performance of cold-drawn pearlitic steel wires for bridge cables were investigated by focused ion beam-scanning electron microscope,transmission electron microscopy and differential scanning calorimetry.The samples with similar tensile strength before and after hot-dip galvanizing process are,respectively,characterized as delaminated and non-delaminated in torsion test which indicates that the tensile strength is independent of the toughness value(i e,reduction area and torsion ability).It is interesting to find that there exists submicron granular ferrite on near-surface of the wires,which can be attributed to dislocation rearrangement and sub-grains rotation during cold drawing and hot-dip galvanizing process.And their distribution can suggest homogeneousness of deformation degree to a certain extent:the closer to the surface of their distribution,the more homogeneous deformation of the wires.There is a close relationship between the thermal stability of the cementite layer and distribution of granular ferrite:differential scanning calorimetry(DSC)analysis shows that the sample is accompanied by submicron granular ferrite which is located closer to the surface has higher thermal stability under galvanizing temperature(450°C).A new mechanism of the torsion delamination of pearlitic steel wires is discussed in terms of the thermal stability of the cementite layer and distribution of granular ferrite.展开更多
Up to now, the exact reason of hydrogen-induced fracture for ferrite-pearlite(FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim t...Up to now, the exact reason of hydrogen-induced fracture for ferrite-pearlite(FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim to reveal the hydrogen-induced cracking initiation and propagation processes. Slow strain rate tensile(SSRT) testing shows that the FP steel is sensitive to hydrogen embrittlement(HE). Focused ion beam(FIB)was used to prepare samples for TEM observations after HE fracture. The corresponding fractographic morphologies of hydrogen charged specimen exhibit intergranular(IG) and quasi-cleavage(QC) fracture feature. Pearlite colony, ferrite/pearlite(F/P) boundary and the adjacent ferrite matrix are found to be responsible for the initial HE fracture and the subsequent propagation. With increasing of the stress intensity factor, fracture mode is found to change from mixed IG and QC to entire QC feature which only occurs at the ferrite matrix. No crack is observed at the ferrite/cementite(F/C) interface. This may be mainly due to the limited pearlite lamella size and relatively low interface energy.展开更多
A new approach describing the flow stress of ferrite-pearlite steel has been proposed,which divided the deformation process into three stages based on whether ferrite or pearlite yielded. Iso-work increment assumption...A new approach describing the flow stress of ferrite-pearlite steel has been proposed,which divided the deformation process into three stages based on whether ferrite or pearlite yielded. Iso-work increment assumption was applied to describe the transfer of load between the components. The physically based model to describe ferrite was approximated with Swift＇s equation in order to obtain the analytic solution.The tensile strength of ferrite-pearlite had a linear relation with pearlite volume fraction,square root reciprocal of ferrite grain size and reciprocal of pearlite interlamellar spacing. Moreover,a model to calculate the tensile strength of ferrite-pearlite steel was proposed. The predicted values of tensile strength were in good agreement with experimental results when the pearlite volume fraction was less than 20%.Considering the plastic relaxation mechanisms,the internal stress was modified with pearlite volume fraction,total strain,yield stress of ferrite and pearlite when the pearlite volume fraction was more than 20%.展开更多
The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investi...The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO-Al2O3-Ti2O3-MnS inclusions with size around 2 μm are effective nucleation sites for IAF, whereas Al2O3-MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain （PAG） size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 μm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 μm. Therefore, the nucleation of IAF can hardly be observed.展开更多
文摘In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delamination tension was adopted. In this paper, the thin tensile samples with 3 mm thickness from the surface, 1/4 positions and center along the thickness orientation of test plate were measured, also the relationship between microstructure and mechanical properties was probed. The results show that the center region of hot rolled ferrite/pearlite steel plate exists granular bainite and ferrite mixed grains, which leads to lower plasticity and toughness of this region. During the tensile process, microcracks are generated and extended at the center of steel plate due to the inconsistency of deformation and fracture on the adjacent structures, finally leading to laminated fracture of steel plate.
文摘The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculated based on unit cell model. The effects of volume fraction, distribution and the aspect ratio of pearlite on tensile properties have been investigated.
文摘Considering the specialities of the steel plate production, the TMCP study has been carried out with Gleeble 2000 tester to explore the possibility of fine grained ferrite in the low carbon steel plates with the chemical composition of C 0.13--0.18, Si 0.12-0.18, Mn 0.50-0. 65, P 0. 010-0. 025, and S 0. 005-0. 028. The plates with thickness of 8. 7 mm in which the ferrite grain size is smaller than 8μm have been produced by special de- formation process in the laboratory. Furthermore, the trial production of special plain carbon steel plates of 16-25 mm in thickness and 2 000- 2 800 mm in width with fine grained ferrite has been successfully carried out in the Shougang Steel Plate Rolling Plant. The ferrite grain size is 5.5-7μm in the surface layers and 9.5-15μm in the central layer respectively. The yield strength is 320- 360 MPa, tensile strength is 440-520 MPa and the elongation is 25%- 34 %. It is very important for the rolling plants to improve the low carbon steel plates＇ mechanical properties. The results show that the ferrite grains in the surface layer can be refined effectively by the appropriate rolling process, and the strength can be also increased.
基金Funded by the National Key R&D Program of China(No.2017YFB0304801)。
文摘The characteristic of near-surface microstructure and its effects on the torsion performance of cold-drawn pearlitic steel wires for bridge cables were investigated by focused ion beam-scanning electron microscope,transmission electron microscopy and differential scanning calorimetry.The samples with similar tensile strength before and after hot-dip galvanizing process are,respectively,characterized as delaminated and non-delaminated in torsion test which indicates that the tensile strength is independent of the toughness value(i e,reduction area and torsion ability).It is interesting to find that there exists submicron granular ferrite on near-surface of the wires,which can be attributed to dislocation rearrangement and sub-grains rotation during cold drawing and hot-dip galvanizing process.And their distribution can suggest homogeneousness of deformation degree to a certain extent:the closer to the surface of their distribution,the more homogeneous deformation of the wires.There is a close relationship between the thermal stability of the cementite layer and distribution of granular ferrite:differential scanning calorimetry(DSC)analysis shows that the sample is accompanied by submicron granular ferrite which is located closer to the surface has higher thermal stability under galvanizing temperature(450°C).A new mechanism of the torsion delamination of pearlitic steel wires is discussed in terms of the thermal stability of the cementite layer and distribution of granular ferrite.
基金financially supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U1608257)
文摘Up to now, the exact reason of hydrogen-induced fracture for ferrite-pearlite(FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim to reveal the hydrogen-induced cracking initiation and propagation processes. Slow strain rate tensile(SSRT) testing shows that the FP steel is sensitive to hydrogen embrittlement(HE). Focused ion beam(FIB)was used to prepare samples for TEM observations after HE fracture. The corresponding fractographic morphologies of hydrogen charged specimen exhibit intergranular(IG) and quasi-cleavage(QC) fracture feature. Pearlite colony, ferrite/pearlite(F/P) boundary and the adjacent ferrite matrix are found to be responsible for the initial HE fracture and the subsequent propagation. With increasing of the stress intensity factor, fracture mode is found to change from mixed IG and QC to entire QC feature which only occurs at the ferrite matrix. No crack is observed at the ferrite/cementite(F/C) interface. This may be mainly due to the limited pearlite lamella size and relatively low interface energy.
基金supported by Fundamental Research Funds for the Central Universities of China(Grant No.FRF-IC-14-005)
文摘A new approach describing the flow stress of ferrite-pearlite steel has been proposed,which divided the deformation process into three stages based on whether ferrite or pearlite yielded. Iso-work increment assumption was applied to describe the transfer of load between the components. The physically based model to describe ferrite was approximated with Swift＇s equation in order to obtain the analytic solution.The tensile strength of ferrite-pearlite had a linear relation with pearlite volume fraction,square root reciprocal of ferrite grain size and reciprocal of pearlite interlamellar spacing. Moreover,a model to calculate the tensile strength of ferrite-pearlite steel was proposed. The predicted values of tensile strength were in good agreement with experimental results when the pearlite volume fraction was less than 20%.Considering the plastic relaxation mechanisms,the internal stress was modified with pearlite volume fraction,total strain,yield stress of ferrite and pearlite when the pearlite volume fraction was more than 20%.
文摘The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO-Al2O3-Ti2O3-MnS inclusions with size around 2 μm are effective nucleation sites for IAF, whereas Al2O3-MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain （PAG） size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 μm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 μm. Therefore, the nucleation of IAF can hardly be observed.
