Effects of Applied Compressive Stress on Microstructure and Mechanical Properties of Cr-Mo Steel During Continuous Cooling Bainitic Transformation

2011 ◽  
Vol 194-196 ◽  
pp. 341-346
Author(s):  
Shou Bin Zhang ◽  
Wei Juan Li
Keyword(s):  
Thermal Expansion ◽  
Compressive Stress ◽  
Granular Bainite ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Hardness Tester ◽  
Compressive Stresses ◽  
Transformation Structure ◽  
Lath Bainite ◽  
Lath Width

The thermal expansion curves are measured by Gleeble-1500 thermomechanical simulator for Cr-Mo steel during continuous cooling transformation at the cooling rate ranging from 1°/s to 90° /s, and CCT curve is also determined; The thermal expansion curves of continuous cooling transformation are measured under the axial compressive stresses (40MPa, 80MPa and 120MPa) at the cooling rates of 50° /s, 70° /s and 90° /s respectively, then the CCT curves with applied compressive stress are determined. The transformation microstructures of steel after continuous cooling with and without stress are observed by SEM and TEM, and the hardness is measured by Vickers hardness tester. The results show that the Bs is increased and Bf is decreased owing to the effect of applied compressive stress; At the meantime the microstructure is also changed, with increasing applied compressive stress, the quantity of granular bainite, bulk ferrite and carbide increase gradually except lath bainite，the lath width of lath bainite becomes narrower gradually, and original grain boundaries become bent from straight; The hardness of transformation structure becomes lower with increasing applied compressive stress exceeding 40Mpa after continuous cooling.

Effects of Final Cooling Temperature on Microstructure Transformation and Properties of Q550 Low Carbon Bainite Steel

2020 ◽  
Vol 993 ◽  
pp. 550-558
Author(s):  
Zeng Qiang Man ◽  
Wei Yu ◽  
Huan Yang ◽  
Wen Gao Chang ◽  
Yun Fei Cao
Keyword(s):  
Great Influence ◽  
Granular Bainite ◽  
Low Carbon ◽  
Continuous Cooling Transformation ◽  
Cooling Temperature ◽  
Continuous Cooling ◽  
Bainite Steel ◽  
Lath Bainite ◽  
Transformation Curve ◽  
Low Carbon Bainite

The mechanical properties of low carbon bainite steel are closely related to the microstructure and proportion after phase transformation. The microstructure of the deformed austenite of low carbon bainite steel after isothermal transformation and continuous cooling transformation was studied by thermal simulation test. The metallographic structure was observed by optical microscopy (OM) and scanning electron microscopy (SEM). The metallographic and microhardness were used to judge the microstructure type, and the CCT (continuous cooling transformation) curve and TTT (time-temperature-transformation) curve of the test steel were drawn. It was found that at 700-430 °C isothermal, undergo a variety of medium-temperature microstructure transformations appeared for the test steels, such as ferrite, pearlite, granular bainite and lath bainite. The cooling rate and final cooling temperature have great influence on the type and performance of the final microstructure. The final cooling temperature was controlled at about 515°C. The mixed microstructures of granular bainite (GB) and fine martensite-austenite (M-A) island, a small amount of acicular ferrite and lath bainite were obtained. The yield and tensile strengths of this type of microstructure reached 639 MPa and 750 MPa respectively, the shrinkage rate reached 17%, and the better low-temperature impact performance was realized.

Simulated HAZ Continuous Cooling Transformation of X90 Pipeline Steel

2016 ◽  
Vol 850 ◽  
pp. 905-909
Author(s):  
Yu Liu ◽  
Ai Qing Ma ◽  
Bin Feng
Keyword(s):  
Pipeline Steel ◽  
Control Measures ◽  
Granular Bainite ◽  
Steel Weld ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Preheating Temperature ◽  
Optimization Control ◽  
Lath Bainite ◽  
Gleeble 3500

In this paper, the simulation heat affected zone (HAZ) continuous cooling transformation (SHCCT) curve of X90 pipeline steel was drew by using Gleeble 3500 simulator. The results show that the trend of hardening of the weld HAZ of X90 pipeline steel was moderate, and softening tendency was not significant. When cooling rate was between 1°C/s and 10°C/s, the microstructure of X90 pipeline steel weld HAZ were composed of granular bainite and lath bainite. The recommended welding heat input of X90 pipeline steel was between 21kJ/cm and 66.4kJ/cm, and the weld preheating temperature was controlled about 100°C. In conclusion, optimization control measures on the microstructure and properties of X90 pipeline steel weld HAZ are presented by above comprehensive analysis.

Continuous Cooling Transformation of Overcooling Austenite and Structure Evolution of Si Steel

2013 ◽  
Vol 652-654 ◽  
pp. 947-951
Author(s):  
Hui Li ◽  
Yun Li Feng ◽  
Da Qiang Cang ◽  
Meng Song
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Optical Microscope ◽  
Structure Evolution ◽  
Upward Trend ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Hardness Tester ◽  
Gleeble 3500 ◽  
Evolution Of Microstructure

The static continuous cooling transformation (CCT)curves of 3.15 Si-0.036 C-0.21 Mn-0.008 S-0.008 N-0.022 Al are measured on Gleeble-3500 thermal mechanical simulator, the evolution of microstructure and the tendency of hardness are investigated by optical microscope (OM) and hardness tester. The results show that there is no evident change in microstructure which mainly are ferrite and little pearlite under different cooling rates, but the transition temperature of ferrite is gradually reduced with the increase of cooling rate. When the cooling rate is increased from 0.5°C/s to 20°C/s, the ending temperatures of phase transformation are decreased by 118°C, when cooling rate reaches to 10, Widmanstatten ferrite appears. The hardness of the steel turns out gradual upward trend with the increase of cooling rate.

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.

Development of a Continuous Cooling Transformation Diagram for an Al-Zn-Mg Alloy Using Dilatometry

2015 ◽  
Vol 828-829 ◽  
pp. 188-193 ◽  
Author(s):  
Manoj Kumar ◽  
Nigel Ross ◽  
Iris Baumgartner
Keyword(s):  
Thermal Expansion ◽  
Coefficient Of Thermal Expansion ◽  
Rate Of Change ◽  
Precipitation Reaction ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Transformation Diagram ◽  
Multiple Devices ◽  
Continuous Cooling Transformation Diagram ◽  
Good Agreement

To develop CCT diagram using DSC requires the use of multiple devices in order to measure across the range of cooling rates required to develop the diagram. In the current work one dilatometer is used to characterize the precipitation reactions of the AA7020 alloy. Precipitation and dissolution reactions resulted in changes in the rate of change in the coefficient of thermal expansion. This was used to determine the start and finish temperatures of the MgZn2 precipitation reaction and produce the CCT diagram. Good agreement was found between the results of this technique and DSC results from the literature.

Dynamic continuous cooling transformation, microstructure and mechanical properties of medium-carbon carbide-free bainitic steel

2020 ◽  
Vol 39 (1) ◽  
pp. 304-316
Author(s):  
Xi Chen ◽  
Fuming Wang ◽  
Changrong Li ◽  
Jing Zhang
Keyword(s):  
Cooling Rate ◽  
Retained Austenite ◽  
Charpy Impact ◽  
Granular Bainite ◽  
Morphology Evolution ◽  
Bainitic Steel ◽  
Cooling Process ◽  
Medium Carbon ◽  
Continuous Cooling ◽  
Lath Bainite

AbstractThe effects of the cooling rate after hot deformation on phase transformation, the microstructure of the designed nonquenched and tempered medium-carbon carbide-free bainitic steel have been investigated during the dynamic continuous cooling process. The results show that with the increase of the cooling rate, the morphology of the carbide-free bainite of the experimental steel evolves from granular bainite to lath bainite. Meanwhile, the hardness increases, and the amount of the retained austenite decreases with the increase of the cooling rate. Besides, the morphology evolution of the retained austenite from block to film is revealed by EBSD. Moreover, 0.5°C/s is considered to be the favorable cooling rate to obtain the best strength–toughness matching. Furthermore, the semi-industrial experimental results proved that the tensile strength, yield strength and Charpy impact energy were 1,298 MPa, 847 MPa and 38 J, respectively.

Phase Transformation Behaviors of Nb-V-Ti Microalloyed Pipeline Steel X70

2013 ◽  
Vol 750-752 ◽  
pp. 380-384
Author(s):  
Yu Hui Wang ◽  
Ya Nan Zheng ◽  
Tian Sheng Wang ◽  
Bo Liao ◽  
Li Gang Liu
Keyword(s):  
Phase Transformation ◽  
Pipeline Steel ◽  
Polygonal Ferrite ◽  
Granular Bainite ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Continuous Cooling Transformation Diagrams ◽  
Transformation Diagrams

The CCT (continuous cooling transformation) diagrams of the Nb-V-Ti without Mo containing microalloyed pipeline steel X70 were investigated. The microstructures observed in continuous cooled specimens are composed of P (pearlite), PF (polygonal ferrite), QF (quasi-polygonal ferrite), and GF (granular bainite ferrite). At low cooling rates between 0.1°C/s and 1°C/s, the microstructure of the steel consisted of banded ferrite and pearlite but higher cooling rates suppressed its formation.

scholarly journals Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 939 ◽  
Author(s):  
Yun Zong ◽  
Chun-Ming Liu
Keyword(s):  
Impact Toughness ◽  
Cooling Rate ◽  
Vickers Hardness ◽  
Heat Affected Zone ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Low Carbon ◽  
Transformation Diagram ◽  
Lath Bainite ◽  
Continuous Cooling Transformation Diagram

In order to provide important guidance for controlling and obtaining the optimal microstructures and mechanical properties of a welded joint, the continuous cooling transformation diagram of a new low-carbon Nb-microalloyed bainite E550 steel in a simulated coarse-grain heat-affected zone (CGHAZ) has been constructed by thermal dilatation method in this paper. The welding thermal simulation experiments were conducted on a Gleeble-3800 thermo-mechanical simulator. The corresponding microstructure was observed by a LEICA DM2700M. The Vickers hardness (HV) and the impact toughness at −40 °C were measured according to the ASTM E384 standard and the ASTM E2298 standard, respectively. The experimental results may indicate that the intermediate temperature phase transformation of the whole bainite can occur in a wide range of cooling rates of 2–20 °C/s. In the scope of cooling rates 2–20 °C/s, the microstructure of the heat-affected zone (HAZ) mainly consists of lath bainite and granular bainite. Moreover, the proportion of lath bainite increased and granular bainite decreased as the cooling rate increasing. There is a spot of lath martensite in the microstructure of HAZ when the cooling rate is above 20 °C/s. The Vickers hardness increases gradually with the increasing of the cooling rate, and the maximum hardness is 323 HV10. When the cooling time from 800 °C to 500 °C (t8/5) is 5–15 s, it presents excellent −40 °C impact toughness (273–286 J) of the CGHAZ beyond the base material (163 J).

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