Continuous Cooling Transformation of Undeformed and Deformed High Strength Crack-Arrest Steel Plates for Large Container Ships

2019 ◽  
Vol 38 (2019) ◽  
pp. 183-191 ◽  
Author(s):  
Yongfeng Qi ◽  
Jing Li ◽  
Chengbin Shi ◽  
Qintian Zhu
Keyword(s):  
High Strength ◽  
Crack Arrest ◽  
Steel Plates ◽  
Granular Bainite ◽  
Deformation Condition ◽  
Stored Energy ◽  
Transformation Behavior ◽  
Continuous Cooling ◽  
Upper Bainite ◽  
Large Container

AbstractThe phase transformation behavior of crack-arrest steel during continuous cooling either with or without deformation at high temperatures was investigated. By carefully examining the microstructures of continuous cooled samples, we found that pearlite, quasi-polygonal ferrite (QPF), acicular ferrite (AF), granular bainite (GB), upper bainite, lath-like bainite and martensite/austenite will exist depending on cooling rates and transformation temperatures in both conditions of deformation and without deformation after austenization. The transformation curves of AF and GB moved toward the left in deformation condition in comparison with that of without deformation condition, which indicated that deformation promoted the formation of QPF and AF; meanwhile, deformation inhibited the formation of bainite. Finer bainite and the accompanying M/A could be obtained by reducing the bainite nucleation activation energy as follows: (i) increasing the undercooling by increasing the cooling rate; (ii) increasing the stored energy by deformation of the austenite.

scholarly journals Morphology and Crystallography Analyses of HSLA Steels with Hardenability Enhanced by Tailored C–Ni Collocation

Metals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 32
Author(s):  
Zhipeng Liu ◽  
Yishuang Yu ◽  
Jie Yang ◽  
Zhiquan Wang ◽  
Hui Guo ◽  
...  
Keyword(s):  
Driving Force ◽  
Nickel Content ◽  
High Strength ◽  
Transformation Strain ◽  
Steel Plates ◽  
Granular Bainite ◽  
Variant Selection ◽  
High Hardenability ◽  
Hsla Steels ◽  
Lath Bainite

High hardenability is of great importance to ultra-heavy steel plates and can be achieved by tailoring the composition of steel. In this study, the continuous cooling transformation (CCT) curves of two high-strength low-alloy (HSLA) steels (0.16C-0.92Ni steel and 0.12C-1.86Ni steel) were elucidated to reveal the significance of C–Ni collocation on hardenability from the perspective of morphology and crystallography. At a low cooling rate (0.5 °C/s), the 0.12C-1.86Ni steel showed higher microhardness than 0.16C-0.92Ni steel. The microstructure in 0.16C-0.92Ni steel was mainly granular bainite with block-shaped martensite/austenite islands (M/A islands), while that in 0.12C-1.86Ni steel was typically lath bainite with film-shaped M/A islands, denoting that the 0.12C-1.86Ni steel is of higher hardenability. Moreover, the 0.12C-1.86Ni steel exhibited a higher density of block boundaries, especially V1/V2 boundaries. The higher density of block boundaries resulted from the weakened variant selection due to the larger transformation driving force and more self-accommodation of transformation strain induced by the reduced carbon and increased nickel content.

Continuous Cooling Transformation Behavior of High Strength Low-Alloyed Cold Rolled Sheet Steel

2007 ◽  
Vol 26-28 ◽  
pp. 27-31 ◽  
Author(s):  
Hao Liu ◽  
Ding Zhong Zhong ◽  
Long Qi Zhao ◽  
Tao Peng ◽  
Li Xin Wu ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Sheet Steel ◽  
High Strength ◽  
Deformation Condition ◽  
Rolled Sheet ◽  
Transformation Temperatures ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Critical Phase ◽  
Cold Rolled

The dilatometry curves and the critical phase transformation temperatures of high strength low-alloyed (HSLA) cold rolled sheet steel were determined by thermal simulation test machine. The samples were austenitized at 900°C,deformed at 40% of deformation and cooled at different rates of 0.1°C/s~ 60°C/s. The continuous cooling transformation (CCT) diagram under deformation condition can be drawn. The results showed that the critical phase transformation temperatures are as follows: Ac3=900°C, Ac1=735°C, Ar3=825°C, Ar1=695°C. A few amount of martensite in high strength low-alloyed cold rolled steel can be obtained at the cooling rate of 60°C/s. The experimental data provide the technical references for rolling control, cooling control and heat treatment in real production.

Microstructure and Mechanical Properties of ULCB Steels Affected by Advanced TMCP Technology

2011 ◽  
Vol 689 ◽  
pp. 289-295
Author(s):  
Zi Yong Hou ◽  
Yun Bo Xu ◽  
Di Wu ◽  
Wei Hua Sun ◽  
She E Hu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Strength Steel ◽  
Critical Factor ◽  
High Strength ◽  
Steel Plates ◽  
Granular Bainite ◽  
Finish Rolling ◽  
Ultra High Strength Steel ◽  
Lath Width ◽  
Hot Rolled

Good combination of high strength and high toughness has been considered as a critical factor of ultra-high strength steel plates. In this paper, a novel high strength steel plate of HSLA type containing Cu with 910MPa yield strength and 1163MPa tensile strength has been developed using an advanced TMCP (thermo-mechanical control processing) technology. The steel plates provide excellent combination of high strength, toughness and deformability. Microstructural evolution and mechanical properties of this steel during hot-working have been investigated. It is demonstrated that, at the relatively higher finish rolling temperature and cooling rate, the microstructure consists of acicular and granular bainite structures and a small amount of low bainite /martensite whose lath width is approximately 200~300nm. For the as-rolled conditions, despite the high strength and so low yield ratio, impact energy about 154J and fully ductility fracture at -90°C can still be obtained as documented for as-hot rolled plates.

Phase Transformation Behavior of Niobium Containing Microalloyed Steel with Predeformation and Continuous Cooling

2014 ◽  
Vol 804 ◽  
pp. 281-284
Author(s):  
Yuan She ◽  
Zhao Hui Zhang ◽  
Jian Tao Ju ◽  
Bo Jin
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Microalloyed Steel ◽  
Stored Energy ◽  
Transformation Behavior ◽  
Phase Transformation Behavior ◽  
Continuous Cooling ◽  
Cooling Phase ◽  
Niobium Microalloyed Steel ◽  
Change Of Microstructure

The continuous cooling phase transformation behavior of niobium microalloyed steel was studied by Thermecmastor-Z thermomechanical simulator; the continuous cooling transformation curves (CCT) were established. The change of microstructure under different cooling rates was observed, and the influence of deformation in austenite non-recrystallization region on transformation was discussed. Based on these work, it was possible to know that the phase transformation is retarded and the ferritic grain is refined dramatically as the cooling rate increasing. The deformation in austenite non-recrystallization region caused deformation stored-energy, which improved the grain refinement of transformation to some extent, but not significant.

Brittle Crack Propagation/Arrest Behavior in T-Joint Structure of Heavy Gauge Steel Plates

2012 ◽  
Vol 706-709 ◽  
pp. 914-919 ◽  
Author(s):  
Tsunehisa Handa ◽  
Kimihiro Nishimura ◽  
Hiroshi Shiomi ◽  
Seishi Tsuyama
Keyword(s):  
Crack Propagation ◽  
Steel Plate ◽  
Crack Arrest ◽  
Steel Plates ◽  
Brittle Crack ◽  
K Value ◽  
Joint Structure ◽  
Large Heat ◽  
Large Container ◽  
Arrest Toughness

Brittle crack arrestability is extremely important in welded joints of heavy gauge steel plates used in large container ships. Recently, much attention has been focused on potential crack propagation along welds using large heat input. This paper examines the application of a T-joint to the strength deck structure of container ships to enhance crack arrestability. The crack arrest toughness, Kca, for crack arrest was varied. The ESSO test of T-joint components showed that brittle crack was arrested at the T-joint if the steel plate used for the flange had a high Kca value in the range from 4900 to 7300N/mm3/2. FE-analysis of the stress intensity factor K indicated that brittle crack propagation was arrested under the condition that the K-value at the running crack tip was less than the Kca of the material. In the T-joint, it was noted that the K-value around the area of the deepest point of the crack decreased and was finally less than the Kca of the flange plate when the brittle crack penetrated suddenly into the flange plate to a 10mm depth. This phenomenon shows the advantage of using a T-joint for brittle crack arrest in the flange plates of strength deck structures.

Development of Low Carbon Bainitic Cr-B Steel with High Strength and Good Toughness

2010 ◽  
Vol 146-147 ◽  
pp. 937-940
Author(s):  
Xiang Dong Huo ◽  
Zhang Guo Lin ◽  
Yu Tao Zhao ◽  
Yu Qian Li
Keyword(s):  
High Strength ◽  
Polygonal Ferrite ◽  
Steel Plates ◽  
Granular Bainite ◽  
High Yield ◽  
Low Carbon ◽  
Experimental Steel ◽  
Large Size ◽  
Final Microstructure ◽  
Lath Bainite

In order to develop low carbon bainitic Cr-B steel, experimental procedures including melting, thermal simulation study and laboratory hot rolling were adopted. The dynamic CCT diagram was established, microstructure and properties of experimental steel were also analyzed. The transformation temperature of experimental steel lies between 650～400°C and final microstructure changes fromquasi-polygonal ferrite, granular bainite to lath bainite as cooling rate increases from 0.2 to 50°C.s-1. The microstructure of steel plates, air cooled or water cooled to 530°C then air cooled, is mainly composed of granular bainite and quasi-polygonal ferrite, and the large size islands in granular bainite are responsible for the low strength and poor toughness. However, steel plate with lath bainite, water cooled to roomtemperature, boasts high yield strength (672MPa) and superior impact toughness (127J at -20°C). Therefore, it is feasible to produce low carbon bainitic Cr-B steel with high strength and good toughness through controlling cooling parameters.

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