Mn-Series Low Carbon Air Cooling Bainitic Steels Containg Niobium

2010 ◽  
Vol 89-91 ◽  
pp. 112-117
Author(s):  
Chun Feng ◽  
Bing Zhe Bai ◽  
Y.K. Zheng ◽  
Hong Sheng Fang
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Small Addition ◽  
Granular Bainite ◽  
Precipitation Strengthen ◽  
Air Cooling ◽  
Low Carbon ◽  
Niobium Content ◽  
Bainitic Steels ◽  
The Impact

The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical properties of the thick plate(30mm) is: σb>1050MPa, σ0.2>700MPa,δ5>17%,Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4)It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5)Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6)This steel is with low production cost since the alloying element Mn is cheap.

Mn-Series Low Carbon Air Cooling Bainitic Steels Containing Niobium

2010 ◽  
Vol 638-642 ◽  
pp. 3038-3043
Author(s):  
Chun Feng ◽  
Bing Zhe Bai ◽  
Y.K. Zheng ◽  
Hong Sheng Fang
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Small Addition ◽  
Granular Bainite ◽  
Precipitation Strengthen ◽  
Air Cooling ◽  
Low Carbon ◽  
Niobium Content ◽  
Bainitic Steels ◽  
The Impact

The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical property of the thick plate (30mm) is: σb>1050MPa, σ0.2>700MPa, δ5>17%, Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4) It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5) Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6) This steel is with low production cost since the alloying element Mn is cheap.

Effect of 0.06%Nb on the Microstructure and Mechanical Properties of Mn-Series Low Carbon Air-Cooling Bainitic Steels

2011 ◽  
Vol 284-286 ◽  
pp. 1191-1195
Author(s):  
Chun Feng ◽  
Bing Zhe Bai ◽  
Yan Kang Zheng
Keyword(s):  
Mechanical Properties ◽  
Yield Strength ◽  
Granular Bainite ◽  
Air Cooling ◽  
Low Carbon ◽  
Microstructure And Mechanical Properties ◽  
Bainitic Steels ◽  
Superior Mechanical Properties ◽  
Allotriomorphic Ferrite ◽  
Strength Improvement

The effect of 0.06%Nb on the microstructure and mechanical properties of grain boundary allotriomorphic ferrite (FGBA) / granular bainite (Bg) air-cooling bainitic steels has been investigated in this paper. The results indicate that the steel acquires superior mechanical properties by adding 0.06%Nb. Compared with Non-Nb steel, the addition of 0.06%Nb increases the tensile strength and yield strength about 37.1% (From 780MPa to 1070MPa)and 26.6%(From 557MPa to 705MPa) respectively, remaining 18.3% elongation and 97J toughness. The addition of 0.06%Nb not only promotes the nucleation of intragranular ferrite but also refines the allotriomorphic ferrite grain , both of which in turn contribute to the refinement of granular bainite cluster including its ferrite platelets and M-A islands. Under the synthetic roles of the microstructure refinement and precipitation strengthening, 148MPa yield strength improvement has been acquired in the low carbon air-cooling bainitic steel by the adding of 0.06%Nb.

Effect of Small Addition of Niobium on the Mechanical Properties of FGBA/ BG Duplex Phase Air Cooling Bainitic Steel

2009 ◽  
Vol 79-82 ◽  
pp. 2003-2006
Author(s):  
Chun Feng ◽  
Y.K. Zheng
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Solute Drag ◽  
Small Addition ◽  
Granular Bainite ◽  
Air Cooling ◽  
Strengthening Effect ◽  
Bainitic Steel ◽  
Intragranular Ferrite ◽  
Allotriomorphic Ferrite

The effect of small addition of niobium on the mechanical properties of grain boundary allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steel has been investigated by tensile test, Optical Microscopy (OM), and scanning electron microscopy (SEM) observation. The results show that (1) The small addition of niobium improves the mechanical properties of the FGBA/BG steel obviously. Compared with Non-Nb FGBA/ BG steel, 0.02% Nb increases the tensile strength and yield strength about 20% (From 780Mpa to 937Mpa)and 17%(From 557Mpa to 650Mpa) respectively, remaining 18% elongation. (2) With the addition of 0.02%Nb, both the size and the volume fraction of FGBA decrease. Meanwhile, the volume fraction of refined intragranular ferrite and M-A islands increases. Compared with Non-Nb steel, the volume fraction of M-A island in 0.02Nb steel increases from 21% to 31%, and the average size of M-A island decreases from 1.2μm to 0.95um.(3)It is indicated that the small addition of Nb(0.02%) not only refines the allotriomorphic ferrite grain but also promotes the nucleation of intragranular ferrite, both of which in turn contribute to the refinement of granular bainite cluster including its ferrite platelets and M-A islands. (4)It is suggested that the strengthening effect of 0.02%Nb can be mainly attributed to the segregation of Nb to γ/α phase boundaries(solute drag-like effect) rather than the precipitation strengthening of Nb(C,N). Nb enrichment in the α/γ interphase causes the decrease of C-activities and activity gradient in the austenite matrix around the α/γ interphase and thus causes the decrease of C-diffusion rate in austenite, and further the restraint to ferrite growth. The effects also depress bainite transformation temperature and driving force, as a result, the bainite cluster is refined.

Effect of Final Cooling Temperature on Mechanical Properties of a Water Cooled Mn-Series Low Carbon Bainitic Steel as 8Mn2SiNb

2011 ◽  
Vol 396-398 ◽  
pp. 468-471
Author(s):  
Chun Feng ◽  
Zhi Yong Pan ◽  
Guang Shan Li ◽  
Bing Zhe Bai
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Lath Martensite ◽  
Granular Bainite ◽  
Air Cooling ◽  
Water Cooling ◽  
Bainitic Steel ◽  
Low Carbon ◽  
Cooling Temperature ◽  
Allotriomorphic Ferrite

The effect of final cooling temperature on the mechanical properties of a water cooled Mn-series low carbon bainitic steel as 8Mn2SiNb has been investigated in this paper. The results indicate that the optimum final cooling temperature is 450 °C, followed by air cooling to room temperature. Compared with air cooling, the condition of water cooling to 450 °C increases the tensile strength and yield strength about 13.3% (From 805MPa to 929MPa) and 59.0%(From 464MPa to 741MPa) respectively, remaining 21.5% elongation and 151J toughness. SEM observation reveals that the microstructure of the steel after water cooling to 450 °C is mainly granular bainite +lath martensite +refined grain boundary allotriomorphic ferrite (FGBA). Compared with air cooling, the condition of water cooling to 450 °C increases the volume fraction of strengthening phase (M-A island) from 28.2% to 38.1%.

scholarly journals Microstructure, Mechanical Properties, and Corrosion Behavior of Ultra-Low Carbon Bainite Steel with Different Niobium Content

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 311
Author(s):  
Yun Zong ◽  
Chun-Ming Liu
Keyword(s):  
Impact Toughness ◽  
Electrochemical Impedance ◽  
Charge Transfer Resistance ◽  
Granular Bainite ◽  
Low Carbon ◽  
Transfer Resistance ◽  
Niobium Content ◽  
Maximum Charge ◽  
Low Carbon Bainite ◽  
The Impact

Four types of ultra-low carbon bainite (ULCB) steels were obtained using unified production methods to investigate solely the effect of niobium content on the performance of ULCB steels. Tensile testing, low-temperature impact toughness testing, corrosion weight-loss method, polarization curves, electrochemical impedance spectroscopy (EIS), and the corresponding organizational observations were realized. The results indicate that the microstructure of the four steels comprise granular bainite and quite a few martensite/austenite (M/A) elements. The niobium content affects bainite morphology and the size, quantity, and distribution of M/A elements. The elongation, yield strength, and tensile strength of the four types of ULCB steels are above 20%, 500 MPa, and 650 MPa, respectively. The impact toughness of the four types of ULCB steels at −40 °C is lower than 10 J. Steel with Nb content of 0.0692% has better comprehensive property, and maximum charge transfer resistance in 3.5 wt.% NaCl solution at the initial corrosion stage. The corrosion products on the surface of steel with higher niobium content are much smoother and denser than those steel with lower niobium content after 240 h of corrosion. The degree of corrosion decreases gradually with the increase of niobium content at the later stage of corrosion.

Charpy Impact Properties of Grain Boundary Allotriomorphic Ferrite and Granular Bainite Duplex Microstructure

2014 ◽  
Vol 1004-1005 ◽  
pp. 1236-1244 ◽  
Author(s):  
Ping Luo ◽  
Gu Hui Gao ◽  
Xiao Lu Gui ◽  
Bai Feng An ◽  
Zhun Li Tan ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Grain Boundary ◽  
Crack Path ◽  
High Strength ◽  
Propagation Path ◽  
Granular Bainite ◽  
Air Cooling ◽  
Low Carbon ◽  
Allotriomorphic Ferrite ◽  
The Impact

A new type of high strength and low cost bainitic steel with ultra-low carbon content and high Si content has been developed on the basis of Mn-series air-cooling bainitic steels. The tensile properties of YS>690MPa and the impact toughness of AKV>60J at-40°C were obtained by controlling the processing parameters. This was attributed to the formation of the grain boundary allotriomorphic ferrite (FGBA) and the granular bainite (GB) with different shape of M/A islands. The high strength due to the inter-lath lamellar M/A islands or retained austenite companying with high dislocated bainitic ferrite laths of average 300nm width. The effect of microstructure on the impact crack initiation and propagation was studied. The results showed that crack initiation occurred in two different types of sites: at interphase boundaries of bainite ferrite (BF) and M/A islands, at grain boundaries. The FGBA and bainite ferrite (BF) both had blunting effect on microcrack tip to reduce the crack propagation path. Because of the presence of FGBA, the unit crack path was short, at less than 5μm. The blunting effect of BF could be enhanced by the M/A islands, which force the cracks change the propagation path and reduce the unit crack path to less than the size of bainite packets. The mechanism of low temperature microcrack origin of the ultra-low carbon bainitic (ULCB) steel with the microstructure of the FGBA and GB was also discussed.

Microstructure and Mechanical Properties of High Strength Hot-Rolled TRIP Steel Containing Vanadium

2010 ◽  
Vol 160-162 ◽  
pp. 324-329
Author(s):  
Xiao Ying Hou ◽  
Yun Bo Xu ◽  
Di Wu
Keyword(s):  
Mechanical Properties ◽  
Trip Steel ◽  
High Strength ◽  
Ferrite Matrix ◽  
Granular Bainite ◽  
Air Cooling ◽  
Low Carbon ◽  
Multiphase Microstructure ◽  
High Elongation ◽  
Vanadium Carbides

Laboratory hot rolling experiments on a low-carbon TRIP steel containing vanadium have been carried out to study the microstructure characteristics and mechanical properties. The results showed that the multiphase microstructure with ferrite, granular bainite and retained austenite could be obtained if the finish rolling initial temperature was properly decreased and the finishing temperature was controlled in the range of Ae3~ Ar3, and the tensile strength achieved 930 MPa or above. The average ferrite grain size was about 4.5 μm in this experiment, the vanadium nitrides and vanadium carbides precipitated dispersedly within ferritic grains or at grain boundaries, and the higher dislocation density existed in ferrite matrix. EBSD analyses revealed that the high angle boundaries accounted for a large proportion and the misorientation angles were within the interval between 29° and 60° mostly. When the finishing temperature was 800°C and the final air cooling temperature was 630°C, the steel had excellent mechanical properties, which was characterized by combination of high strength(about 930MPa), high elongation(21.7%), low yield/strength ratio(0.49) and as well as high work-hardening exponent(0.23).

Microstructure Development and Mechanical Properties of a Hot Stamped Low-Carbon Advanced High Strength Steel Treated by a Novel Dynamic Carbon Partitioning Process

2014 ◽  
Vol 1063 ◽  
pp. 42-46 ◽  
Author(s):  
Fei Bao Zhang ◽  
Hong Wu Song ◽  
Ming Cheng ◽  
Xin Li ◽  
Shi Hong Zhang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Hot Stamping ◽  
High Strength ◽  
Carbon Partitioning ◽  
Martensite Phase ◽  
Low Carbon ◽  
Step Method ◽  
The Impact

To make steel exhibit attractive properties as high strength and good ductility, this paper presents a novel one step method for forming-Q&P integration—Hot Stamping-Dynamic Partitioning (HS-DP) process. The proposed HS-DP process is simulated with salt bath heat treatment. The effect of microstructure and mechanical properties in a low-carbon AHSS with different cooling rate of the new process is investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and tensile test methods. Microstructure of the steel subjected to HS-DP treatment is mainly composed of initial quenched martensite phase , final quenched martensite phase and retained austenite phase formed. The impact of retained austenite is also discussed, especially the influence of elongation caused by various retained austenite volume fraction and carbon-content. This experiment illustrates the promising application potential of the hot stamping-dynamic carbon partitioning process.

scholarly journals Low-carbon cast microalloyed steel intercritically heat-treated at different temperatures: microstructure and mechanical properties

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
Hadi Torkamani ◽  
Shahram Raygan ◽  
Carlos Garcia Mateo ◽  
Yahya Palizdar ◽  
Jafar Rassizadehghani ◽  
...  
Keyword(s):  
Carbon Content ◽  
Volume Fraction ◽  
Block Size ◽  
Tensile Tests ◽  
Total Elongation ◽  
Martensite Phase ◽  
Low Carbon ◽  
Steel Increase ◽  
Different Temperatures ◽  
The Impact

AbstractIn this study, dual-phase (DP, ferrite + martensite) microstructures were obtained by performing intercritical heat treatments (IHT) at 750 and 800 °C followed by quenching. Decreasing the IHT temperature from 800 to 750 °C leads to: (i) a decrease in the volume fraction of austenite (martensite after quenching) from 0.68 to 0.36; (ii) ~ 100 °C decrease in martensite start temperature (Ms), mainly due to the higher carbon content of austenite and its smaller grains at 750 °C; (iii) a reduction in the block size of martensite from 1.9 to 1.2 μm as measured by EBSD. Having a higher carbon content and a finer block size, the localized microhardness of martensite islands increases from 380 HV (800 °C) to 504 HV (750 °C). Moreover, despite the different volume fractions of martensite obtained in DP microstructures, the hardness of the steels remained unchanged by changing the IHT temperature (~ 234 to 238 HV). Applying lower IHT temperature (lower fraction of martensite), the impact energy even decreased from 12 to 9 J due to the brittleness of the martensite phase. The results of the tensile tests indicate that by increasing the IHT temperature, the yield and ultimate tensile strengths of the DP steel increase from 493 to 770 MPa, and from 908 to 1080 MPa, respectively, while the total elongation decreases from 9.8 to 4.5%. In contrast to the normalized sample, formation of martensite in the DP steels could eliminate the yield point phenomenon in the tensile curves, as it generates free dislocations in adjacent ferrite.

The Influence of Oxide Inclusion on the Refinement of Bainite and Toughness in HAZ for Low Carbon Steels

2013 ◽  
Vol 651 ◽  
pp. 163-167
Author(s):  
Shu Rui Li ◽  
Xue Min Wang ◽  
Xin Lai He
Keyword(s):  
Mechanical Properties ◽  
Acicular Ferrite ◽  
Oxide Inclusion ◽  
Optical Microscope ◽  
Carbon Steels ◽  
Low Carbon ◽  
Low Carbon Steels ◽  
The Core ◽  
Ti Oxides ◽  
Bainitic Steels

The influence of Ti oxide on the toughness of heat affected zone for low carbon bainitic steels has been investigated. The optical microscope, SEM and TEM were used to analyze the composition, size and distribution of the inclusions, and the microstructure and mechanical properties after welding thermal simulation were also investigated. The effect of Ti oxide inclusion on the transformation of acicular ferrite has also been studied. The results show that after the melting with Ti dioxide technique the inclusion is complex, in the core is Ti oxides about 1-3 micron and around it is MnS. It has been found the acicular ferrite can nucleate at the inclusions and the Ti oxide inclusion will promote the nucleation of acicular ferrite, and the acicular ferrite will block the growth of bainite. Therefore by introducing the Ti oxide in the steels the microstructure of HAZ could be refined markedly therefore the toughness of HAZ can be improved evidently.

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