Estimation of the Effective Grain Size Controlling Brittle Crack Arrest Toughness of High-strength Steel

This review paper concerns the development of the chemical compositions and controlled processes of rolling and cooling steels to increase their mechanical properties and reduce weight and production costs. The paper analyzes the basic differences among high-strength steel (HSS), advanced high-strength steel (AHSS) and ultra-high-strength steel (UHSS) depending on differences in their final microstructural components, chemical composition, alloying elements and strengthening contributions to determine strength and mechanical properties. HSS is characterized by a final single-phase structure with reduced perlite content, while AHSS has a final structure of two-phase to multiphase. UHSS is characterized by a single-phase or multiphase structure. The yield strength of the steels have the following value intervals: HSS, 180–550 MPa; AHSS, 260–900 MPa; UHSS, 600–960 MPa. In addition to strength properties, the ductility of these steel grades is also an important parameter. AHSS steel has the best ductility, followed by HSS and UHSS. Within the HSS steel group, high-strength low-alloy (HSLA) steel represents a special subgroup characterized by the use of microalloying elements for special strength and plastic properties. An important parameter determining the strength properties of these steels is the grain-size diameter of the final structure, which depends on the processing conditions of the previous austenitic structure. The influence of reheating temperatures (TReh) and the holding time at the reheating temperature (tReh) of C–Mn–Nb–V HSLA steel was investigated in detail. Mathematical equations describing changes in the diameter of austenite grain size (dγ), depending on reheating temperature and holding time, were derived by the authors. The coordinates of the point where normal grain growth turned abnormal was determined. These coordinates for testing steel are the reheating conditions TReh = 1060 °C, tReh = 1800 s at the diameter of austenite grain size dγ = 100 μm.

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A simplified method for evaluation of brittle crack arrest toughness of steels in scaled-down bending tests

Engineering Fracture Mechanics ◽

10.1016/j.engfracmech.2019.03.047 ◽

2019 ◽

Vol 215 ◽

pp. 99-111 ◽

Cited By ~ 4

Author(s):

Yuki Nishizono ◽

Tomoya Kawabata ◽

Shuji Aihara ◽

Teppei Okawa

Keyword(s):

Crack Arrest ◽

Brittle Crack ◽

Bending Tests ◽

Simplified Method ◽

Arrest Toughness

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Simplified Evaluation of Brittle Crack Arrest Toughness in Heavy-thick Plate by Combined Small-scale Tests

International Journal of Offshore and Polar Engineering ◽

10.17736/ijope.2017.hj26 ◽

2017 ◽

Vol 27 (2) ◽

pp. 210-215 ◽

Cited By ~ 2

Author(s):

Teppei Okawa ◽

Hiroyuki Shirahata ◽

Kiyotaka Nakashima ◽

Kazuhisa Yanagita ◽

Takehiro Inoue

Keyword(s):

Thick Plate ◽

Crack Arrest ◽

Small Scale ◽

Brittle Crack ◽

Arrest Toughness

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

Materials Science Forum ◽

10.4028/www.scientific.net/msf.898.1094 ◽

2017 ◽

Vol 898 ◽

pp. 1094-1102 ◽

Cited By ~ 1

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.

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Effect of Heat Treatment on Mechanical Properties and Microstructure Morphology of Low-Alloy High-Strength Steel

Archives of Metallurgy and Materials ◽

10.1515/amm-2016-0066 ◽

2016 ◽

Vol 61 (2) ◽

pp. 475-480

Author(s):

K. Bolanowski

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Grain Size ◽

Tensile Strength ◽

Ultimate Tensile Strength ◽

Yield Strength ◽

High Strength Steel ◽

High Strength ◽

Strengthening Phase ◽

Average Grain Size

Abstract The paper analyzes the influence of different heat treatment processes on the mechanical properties of low-alloy high-strength steel denoted by Polish Standard (PN) as 10MnVNb6. One of the findings is that, after aging, the mechanical properties of rolled steel are high: the yield strength may reach > 600 MPa, and the ultimate tensile strength is > 700 MPa. These properties are largely dependent on the grain size and dispersion of the strengthening phase in the ferrite matrix. Aging applied after hot rolling contributes to a considerable rise in the yield strength and ultimate tensile strength. The process of normalization causes a decrease in the average grain size and coalescence (reduction of dispersion) of the strengthening phase. When 10MnVNb6 steel was aged after normalization, there was not a complete recovery in its strength properties.

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Relationship between the Effective Grain Size of Brittle Crack Propagation and Microstructural Size in Low-carbon Low-alloy Bainitic Steels

Tetsu-to-Hagane ◽

10.2355/tetsutohagane.tetsu-2015-084 ◽

2016 ◽

Vol 102 (6) ◽

pp. 286-294 ◽

Cited By ~ 1

Author(s):

Shigekazu Morito ◽

Taisuke Hayashi ◽

Anh Hoang PHAM ◽

Tomoya Kawabata

Keyword(s):

Grain Size ◽

Crack Propagation ◽

Low Carbon ◽

Brittle Crack ◽

Bainitic Steels ◽

Effective Grain Size

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Study on Unstable Brittle Crack Arrest Toughness of Extremely-Low Carbon Bainitic Steel Plates

Materials ◽

10.1115/imece2004-59739 ◽

2004 ◽

Author(s):

Tsunehisa Handa ◽

Takahiro Kubo ◽

Keniti Amano ◽

Mitsuhiro Okatsu ◽

Kazunori Miyamoto ◽

...

Keyword(s):

Transition Temperature ◽

Cross Section ◽

Test Piece ◽

Main Crack ◽

Crack Arrest ◽

Steel Plates ◽

Bainitic Steel ◽

Low Carbon ◽

Brittle Crack ◽

Arrest Toughness

The extremely-low carbon bainitic steel (ELCB steel) is a high strength steel with about 0.02 mass% or less carbon. In this research, unstable brittle crack arrest toughness of ELCB steel plates was investigated by temperature-gradient ESSO tests, compared with that of conventional TMCP steel plates. Both of ELCB and TMCP steel plates without pre-straining had sufficient crack-arrest toughness at 0°C. After 10% prestraining, the TMCP steel plate had not sufficient crack-arrest toughness at 0 °C . The ELCB steel plates, however, maintained high crack arrest toughness at 0°C. even after 10% pre-straining. ELCB steel were also different from TMCP steels in the correlation between transition temperature of crack arrest toughness and fracture appearance transition temperature (vTrs) obtained by Charpy impact test. When the vTrs of an ELCB steel and that of a TMCP steel were the same value, crack arrest toughness of an ELCB steel was higher than that of a TMCP steel. In the cross section of the ESSO test piece of the ELCB steels, many sub-cracks and micro-crack branching were observed. However, in the cross section of the ESSO test piece of the conventional TMCP steels, there were few subcracks and branching. Initiation of sub-cracks and branching around the main crack tip reduces the stress intensity factor of the main crack. It was considered that the above features of the ELCB steel were caused by initiation of sub-cracks and branching at the tip of the main brittle crack.

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