scholarly journals A Comparative Study of Acicular Ferrite Transformation Behavior between Surface and Interior in a Low C–Mn Steel by HT-LSCM

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 699
Author(s):  
Xiaojin Liu ◽  
Guo Yuan ◽  
Raja. Devesh Kumar Misra ◽  
Guodong Wang
Keyword(s):  
Grain Boundaries ◽  
Cooling Rate ◽  
Acicular Ferrite ◽  
Laser Scanning ◽  
Sample Surface ◽  
Surface Microstructure ◽  
In Situ Observation ◽  
Low Carbon ◽  
Transformation Behavior ◽  
Ferrite Transformation

In this study, the acicular ferrite transformation behavior of a Ti–Ca deoxidized low carbon steel was studied using a high-temperature laser scanning confocal microscopy (HT-LSCM). The in situ observation of the transformation behavior on the sample surface with different cooling rates was achieved by HT-LSCM. The microstructure between the surface and interior of the HT-LSCM sample was compared. The results showed that Ti–Ca oxide particles were effective sites for acicular ferrite (AF) nucleation. The start transformation temperature at grain boundaries and intragranular particles decreased with an increase in cooling rate, but the AF nucleation rate increased and the surface microstructure was more interlocked. The sample surface microstructure obtained at 3 °C/s was dominated by ferrite side plates, while the ferrite nucleating sites transferred from grain boundaries to intragranular particles when the cooling rate was 15 °C/s. Moreover, it was interesting that the microstructure and microhardness of the sample surface and interior were different. The AF dominating microstructure, obtained in the sample interior, was much finer than the sample surface, and the microhardness of the sample surface was much lower than the sample interior. The combined factors led to a coarse size of AF on the sample surface. AF formed at a higher temperature resulted in the coarse size. The available particles for AF nucleation on the sample surface were quite limited, such that hard impingement between AF plates was much weaker than that in the sample interior. In addition, the transformation stress in austenite on the sample surface could be largely released, which contributed to a coarser AF plate size. The coarse grain size, low dislocation concentration and low carbon content led to lower hardness on the sample surface.

scholarly journals Effect of Thermomechanical Treatment on Acicular Ferrite Formation in Ti–Ca Deoxidized Low Carbon Steel

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 296 ◽  
Author(s):  
Chao Wang ◽  
Xin Wang ◽  
Jian Kang ◽  
Guo Yuan ◽  
Guodong Wang
Keyword(s):  
Mechanical Properties ◽  
Carbon Steel ◽  
Grain Boundaries ◽  
Cooling Rate ◽  
Thermomechanical Treatment ◽  
Acicular Ferrite ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Transformation Mechanism ◽  
Ferrite Formation

Transformation behaviors and mechanical properties under thermomechanical treatment conditions of Ti–Ca deoxidized low carbon steel were studied in comparison to Al–Ca treated steel. A thermomechanical simulation and a hot rolling experiment were carried out. Inclusions and microstructures were characterized, and the transformation mechanism was analyzed. The results indicated that typical inclusions in Ti–Ca deoxidized steel were TiOx-MnS-Al2O3-CaO, TiOx-MnO-Al2O3-CaO, and TiOx-MnS, which were effective for acicular ferrite (AF) nucleation. Acicular ferrite formation temperature decreased with an increase in cooling rate. A fine AF dominant microstructure was formed under a high driving force for the transformation from austenite to ferrite at lower temperatures. A high deformation of 43–65% discouraged the formation of acicular ferrite because of the increase in austenite grain boundaries serving as nucleation sites. The fraction of high-angled grain boundaries that acted as obstacles to cleavage cracks was the highest in the sample cooled at 5 °C/s because of full AF structure formation. The hardness increased significantly as the cooling rate increased from 2 to 15 °C/s, whereas it decreased under the condition of deformation because of the formation of (quasi-)polygonal ferrite. By applying accelerated water cooling, the mechanical properties, particularly impact toughness, were significantly improved as a result of fine AF microstructure formation.

Continues Cooling Transformation Behavior of Low Carbon Mn-Nb-B Steel

2011 ◽  
Vol 335-336 ◽  
pp. 595-598 ◽  
Author(s):  
Zheng Tao Duan ◽  
Yan Mei Li ◽  
Fu Xian Zhu ◽  
Hui Yun Zhang
Keyword(s):  
Cooling Rate ◽  
Acicular Ferrite ◽  
Granular Bainite ◽  
Low Carbon ◽  
Transformation Behavior ◽  
Cct Curve ◽  
Lath Bainite ◽  
Left Corner ◽  
Cct Diagrams

The continues cooling transformation (CCT) of a low carbon Mn-Nb-B steel in the undeformed and deformed conditions were investigated, respectively. The CCT diagrams of the steel were constructed. The microstructures and microhardness were analysized. The results showed that the microsructures contains ferrite, pearlite, granular bainite, acicular ferrite and lath bainite depending on cooling rate; Deformation moved the CCT curve to the top left corner, increased the transformation start temperatures slightly, and promoted the formation of ferrite and pearlite. Furthmore deformation also fined the transformed microstructures.

In situ observation of growth behaviour of acicular ferrite in low-carbon steel containing 13 ppm magnesium

2017 ◽  
Vol 46 (2) ◽  
pp. 176-183 ◽  
Author(s):  
Chi-Kang Lin ◽  
Yan-Chi Pan ◽  
Weng-Sing Hwang ◽  
Ying-Chien Fang ◽  
Yen-Hao Su ◽  
...  
Keyword(s):  
Carbon Steel ◽  
Acicular Ferrite ◽  
Low Carbon Steel ◽  
In Situ Observation ◽  
Low Carbon ◽  
Growth Behaviour

Influence of Chromium Content and Prior Deformation on the Continuous Cooling Transformation Diagram of Low-Carbon Bainitic Steels

2020 ◽  
Vol 835 ◽  
pp. 58-67
Author(s):  
Mohammed Ali ◽  
Antti J. Kaijalainen ◽  
Jaakko Hannula ◽  
David Porter ◽  
Jukka I. Kömi
Keyword(s):  
Cooling Rate ◽  
Hot Deformation ◽  
Laser Scanning ◽  
Chromium Content ◽  
Bainitic Ferrite ◽  
Granular Bainite ◽  
Low Carbon ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling

The effect of chromium content and prior hot deformation of the austenite on the continuous cooling transformation (CCT) diagram of a newly developed low-carbon bainitic steel has been studied using dilatometer measurements conducted on a Gleeble 3800 simulator with cooling rates ranging from 2-80 °C/s. After austenitization at 1100 °C, specimens were either cooled without strain or given 0.6 strain at 880 °C prior to dilatometer measurements. The resultant microstructures have been studied using laser scanning confocal microscopy, scanning electron microscopy and macrohardness measurements. CCT and deformation continuous cooling transformation (DCCT) diagrams were constructed based on the dilatation curves, final microstructures and hardness values. Depending on the cooling rate, the microstructures of the investigated steels after cooling from the austenite region consist of one or more of the following microstructural components: lath-like upper bainite, i.e. bainitic ferrite (BF), granular bainite (GB), polygonal ferrite (PF) and pearlite (P). The proportion of BF to GB as well as the hardness of the transformation products decreased with decreasing cooling rate. The cooling rate at which PF starts to appear depends on the steel composition. With both undeformed and deformed austenite, increasing the chromium content led to higher hardenability and refinement of the microstructure, promoting the formation of BF and shifting the ferrite start curve to lower cooling rates. Prior hot deformation shifted the transformation curves to shorter times and higher temperatures and led to a reduction in hardness at the low cooling rates through the promotion of ferrite formation.

Continuous Cooling Phase Transformation Rule of 20CrMnTi Low-Carbon Alloy Steel

2019 ◽  
Vol 944 ◽  
pp. 303-312
Author(s):  
Li Zhang Li ◽  
He Wei ◽  
Lin Lin Liao ◽  
Yin Li Chen ◽  
Hai Feng Yan ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Vickers Hardness ◽  
Rolling Process ◽  
Transformation Rule ◽  
Low Carbon ◽  
Continuous Cooling ◽  
Starting Time ◽  
Ferrite Transformation ◽  
The Ideal

Gear steel is a ferritic steel. In the rolling process, the ideal structure is ferrite + pearlite, and bainite or martensite is not expected. However, due to the high alloy content, the hardenability is good, and the bainite or martensite structure is very likely to be generated upon cooling after rolling. In this paper, phase transformation rules during continuous cooling of 20CrMnTi with and without deformation were studied to guide the avoidance of the appearance of bainite or martensite in steel. A combined method of dilatometry and metallography was adopted in the experiments, and the dilatometer DIL805A and thermo-simulation Gleeble3500 were used. Both dynamic and static continuous cooling transformation (CCT) diagrams were drawn by using the software Origin. The causes of those changes in starting temperature, finishing temperature, starting time and transformation duration in ferrite-pearlite phase transformation were analyzed, and the change in Vickers hardness of samples with different cooling rate was discussed. The results indicate that with different cooling rate, there are three phase transformation zones: ferrite-pearlite, bainite and martensite. Deformation of austenite accelerates the occurrence of transformation obviously and moves CCT curve to left and up direction. When the cooling rate is lower than 1 °C/s, the phases in samples are mainly ferrite and pearlite, which is the ideal microstructure of experimental steel. As the cooling rate increases, starting temperature of ferrite transformation in steel decreases, starting time reduces, transformation duration gradually decreases, and the Vickers hardness of samples increases. Under the cooling rate of 0.5 °C/s, ferrite transformation in deformed sample starts at 751.67 °C, ferrite-pearlite phase transformation lasts 167.9 s, and Vickers hardness of sample is 183.4 HV.

Modeling austenite–ferrite transformation in low carbon steel using the cellular automaton method

2004 ◽  
Vol 19 (10) ◽  
pp. 2877-2886 ◽  
Author(s):  
Y.J. Lan ◽  
D.Z. Li ◽  
Y.Y. Li
Keyword(s):  
Carbon Steel ◽  
Cellular Automaton ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Low Carbon Steel ◽  
Carbon Diffusion ◽  
Cellular Automaton Model ◽  
Low Carbon ◽  
Austenite Grain ◽  
Ferrite Transformation

Austenite–ferrite transformation at different isothermal temperatures in low carbon steel was investigated by a two-dimensional cellular automaton approach, which provides a simple solution for the difficult moving boundary problem that governs the ferrite grain growth. In this paper, a classical model for ferrite nucleation at austenite grain boundaries is adopted, and the kinetics of ferrite grain growth is numerically resolved by coupling carbon diffusion process in austenite and austenite–ferrite (γ–α) interface dynamics. The simulated morphology of ferrite grains shows that the γ–α interface is stable. In this cellular automaton model, the γ–α interface mobility and carbon diffusion rate at austenite grain boundaries are assumed to be higher than those in austenite grain interiors. This has influence on the morphology of ferrite grains. Finally, the modeled ferrite transformation kinetics at different isothermal temperatures is compared with the experiments in the literature and the grid size effects of simulated results are investigated by changing the cell length of cellular automaton model in a set of calculations.

Continuous Cooling Transformation Behavior of Vercooling Austenite of Low Carbon-Manganese Steel

2011 ◽  
Vol 418-420 ◽  
pp. 523-527
Author(s):  
Li Wei Duan ◽  
Yun Li Feng ◽  
Xue Jing Qi
Keyword(s):  
Cooling Rate ◽  
Manganese Steel ◽  
Accelerated Cooling ◽  
Low Carbon ◽  
Transformation Behavior ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Transformation Rules ◽  
Experimental Deformation ◽  
Gleeble 3500

Continuous cooling transformation rules of Low Carbon-Manganese Steel were investigated on Gleeble-3500 thermomechanical simulator. The study indicates that as cooling rate increases, Ar3 loweres and Ar1 behaves similarly but much slowly. The microstructure composes of dominant ferrite and some pearlite. As cooling rate enhances, the ferritic grain become finer, when cooling rate is up to 30°C/s, a little bainite appears. With the increasing of cooling rate the dimension of ferrite decreases. Under the experimental deformation conditions, ferritic grain refinement gets weak when the cooling rate is greater than or equal to 20°C/s. Therefore, with a certain strain, ferritic grain can refined to some degree by accelerated cooling.

Transformation Behavior of Austenite Continuous Cooling of Nb-Ti Micro-Alloyed Low Carbon Steel

2013 ◽  
Vol 652-654 ◽  
pp. 967-970 ◽  
Author(s):  
Jun Cheng Bao ◽  
Jun Xing Ma ◽  
Jie Zhao ◽  
Bao Qun Ning
Keyword(s):  
Carbon Steel ◽  
Cooling Rate ◽  
Low Carbon Steel ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Metallographic Analysis ◽  
Low Carbon ◽  
Transformation Behavior ◽  
Continuous Cooling ◽  
Cct Diagrams

The transformation behavior of Nb-Ti micro-alloyed low carbon steel during continuous cooling was studied trough thermomechanical simulator and metallographic analysis. The results show that the dynamic CCT diagrams shift to the left and upper compared with the static ones, the begin temperature of γ→α transformation is gradually lower with the increase of cooling rate. The high temperature deformation improves Ferrite and Pearlite transformation, also improves Bainite transformation and decreases ferrite transformation zone. The rapid cooling can obtain better obdurability mixed microstructure of Martensite and Bainite within a certain cooling rate after deformation.

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