Fracture and Crack Propagation Behavior of 560 MPa Microalloyed Pipeline Steel under Different Cooling Schedules

2017 ◽  
Vol 898 ◽  
pp. 1094-1102 ◽  
Author(s):  
Jin Hua Zhao ◽  
Dong Fang Li ◽  
Guo Yuan ◽  
Xue Qiang Wang ◽  
Rui Hao Li ◽  
...  
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crack Propagation ◽  
Pipeline Steel ◽  
Crack Arrest ◽  
Dominant Factor ◽  
Cooling Schedules ◽  
Effective Grain Size ◽  
Mixed Microstructure ◽  
Low Temperature Toughness

Three kinds of pipeline steel with different microstructures were fabricated by varying cooling schedules during thermo-mechanical controlled processing (TMCP). Charpy impact property of the pipeline steels were obtained, and the fracture and crack-arrest mechanisms were further studied. The results indicated that the steels were classified into two kinds according to their microstructures, the mixture of acicular ferrite (AF), quasi-polygonal ferrite (QF), granular bainite (GB) and small fraction of degenerate pearlite (DP), and the mixed microstructure of AF and GB, respectively. The processed steel with microstructure of AF and GB exhibited more excellent low-temperature toughness and crack-arrest properties with upper shelf energy of ~281 J and energy transition temperature of ~-76°C. The mixed microstructure (AF + GB) possessing smaller effective grain size hindered the propagating of crack and consumed large amount of energy during fracture. The effective grain size of microstructure was the dominant factor controlling low-temperature toughness and crack-arrest properties of pipeline steel, which increased the high-angle boundary length per unit area and further increased the crack propagation energy during fracture.

Study on Mechanical Properties Anisotropy of X80 Pipeline Steel

2013 ◽  
Vol 803 ◽  
pp. 413-418
Author(s):  
Qiang Duan ◽  
Jun Yan ◽  
Guo Hui Zhu ◽  
Qing Wu Cai
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Impact Toughness ◽  
Crack Propagation ◽  
Grain Boundaries ◽  
Pipeline Steel ◽  
Rolling Direction ◽  
High Angle ◽  
X80 Pipeline Steel ◽  
Effective Grain Size

The microstructure of X80 pipeline steel in different directions were observed by SEM technique and its effective grain size and misorientation were statistically analyzed by EBSD system. Based on these results, the mechanical properties at 0°, 45° and 90° to the rolling direction of X80 pipeline steel were studied. The results show that, owing to finer grain size and less low-angle grain boundaries, strengths and impact toughness of X80 pipeline steel at 90° direction are optimal. While the pipeline steel possesses finer grain size, more high-angle grain boundaries and less low-angle grain boundaries, the crack propagation is effectively suppressed, then its impact toughness is improved.

scholarly journals Effect of Bainitic Microstructure on Low-Temperature Toughness of High-Strength API Pipeline Steels

2020 ◽  
Vol 58 (5) ◽  
pp. 293-303
Author(s):  
Seung-Wan Lee ◽  
Sang-In Lee ◽  
Byoungchul Hwang
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crack Initiation ◽  
High Strength ◽  
Processing Conditions ◽  
Absorbed Energy ◽  
Pipeline Steels ◽  
Bainitic Microstructure ◽  
Effective Grain Size ◽  
Low Temperature Toughness

In this study the correlation between bainitic microstructure and the low-temperature toughness of high-strength API pipeline steels was discussed in terms of crack initiation and propagation in the microstructure. Three types of API pipeline steels with different bainitic microstructures were fabricated using varying alloying elements and thermo-mechanical processing conditions, and then their microstructure was characterized by optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). In particular, the effective grain size and microstructure fraction of the steels were quantitatively measured by EBSD analysis. Although all the steels were composed of polygonal ferrite (PF), and complex bainitic microstructures such as acicular ferrite (AF), granular bainite (GB), and bainitic ferrite (BF), they had different effective grain sizes and microstructure fraction, depending on the alloying elements and thermomechanical processing conditions. Charpy impact test results showed that when the martensite-austenite constituent fraction was lowest, it resulted in higher upper-shelf energy, and absorbed energy at room temperature due to the decrease in crack initiation. In contrast, excellent low-temperature toughness, such as lower ductile-brittle transition temperature and higher absorbed energy at low temperatures, could be achieved with a bainitic microstructure with fine effective grain size and high fraction of high-angle grain boundaries, which act as obstacles to prevent cleavage crack propagation.

Effects of Low-Angle Grain Boundaries on the Yield-Strength Ratio of High Grade Pipeline Steels

2010 ◽  
Vol 168-170 ◽  
pp. 1581-1585 ◽  
Author(s):  
Dong Ying Xu ◽  
Hao Yu
Keyword(s):  
Grain Size ◽  
Tensile Strength ◽  
Yield Strength ◽  
Grain Boundaries ◽  
Pipeline Steel ◽  
High Grade ◽  
Strength Ratio ◽  
Pipeline Steels ◽  
Effective Grain Size ◽  
Electron Back Scattered Diffraction

Orientations distribution between grains of two high grade pipeline steels were investigated by electron back-scattered diffraction (EBSD). Then the percentage of low-angle grain boundaries was studied qualitatively to analyze the effect of low-angle grain boundaries on the yield-strength ratio of high grade pipeline steels. From the mode of coordinate deformation and the ability to resist deformation by the grain boundaries, the results show that when the effective grain size are almost the same, the pipeline steel which has the smaller percentage of low-angle grain boundaries, the larger difference between the yield strength and tensile strength, which makes the yield-strength ratio of pipeline steel lower.

Research and Development of Deep-Sea Pipeline Steel

2010 ◽  
Vol 152-153 ◽  
pp. 1492-1498
Author(s):  
Jin Qiao Xu ◽  
Bin Guo ◽  
Lin Zheng ◽  
Yin Hua Li ◽  
Le Yu
Keyword(s):  
Low Temperature ◽  
Deep Sea ◽  
Pipeline Steel ◽  
High Strength ◽  
Steel Company ◽  
Line Pipe ◽  
Iron And Steel ◽  
Company Group ◽  
Pipeline Project ◽  
Low Temperature Toughness

This paper provides a detailed description of deep-sea pipeline steel developed at Wuhan Iron and Steel Company(Group), WISCO for short. The thickness of the trial produced plates is 28mm. The chemical composition of low C-high Mn-Nb-Ti with proper content of other alloys and thermo-mechanical controlled process were applied. The results show that the deep-sea pipeline steel developed at Wuhan Iron and Steel Company has a good match of high strength, low temperature toughness and excellent deformability with fine uniform microstructure. The LSAW line pipe manufactured by JCOE method has high strength, good low temperature toughness and low yield ratio which comprehensively meet the requirements of the South China Sea Liwan pipeline project.

Effects of Cooling Processes on Microstructure Evolution of X80 Pipeline Steel

2014 ◽  
Vol 788 ◽  
pp. 378-383 ◽  
Author(s):  
Feng Qin Ji ◽  
Guo Dong Wang
Keyword(s):  
Low Temperature ◽  
Pipeline Steel ◽  
Bainitic Ferrite ◽  
Development Trend ◽  
Optical Microscope ◽  
Granular Bainite ◽  
X80 Pipeline Steel ◽  
Pipeline Steels ◽  
Low Temperature Toughness ◽  
Strength And Plasticity

With the development of pipeline industry, the pipeline steels with higher strength and plasticity, better low-temperature toughness and weldability are the main development trend. For bainitic pipeline steels, M/A constituent is the main hard phase. Although the M/A constituent can enhance the strength, the larger block-form M/A constituent can deteriorate low-temperature toughness. Therefore, it is essential to further investigate how to refine the M/A constituent. In the present paper, X80 pipeline steel was cooled to room temperature with various cooling paths after hot compression deformation at the temperature of 800oC. The evolution of microstructure of X80 pipeline steel has been analyzed by optical microscope (OM) and scanning electron microscope (SEM). The experimental results show that increasing the cooling rate can significantly refine M/A constituent and promote the formation of granular bainite, and the bainitic ferrite can be also greatly refined. In addition, the effects of five final temperatures of fast cooling were also investigated.

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