A systematic study of grain refinement during impact of 4340 steel

Boakye‐Yiadom, Solomon; Khan, Abdul Khaliq; Bassim, Nabil

doi:10.1016/j.msea.2014.03.066

Cited by 25 publications

(20 citation statements)

References 21 publications

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“…DRX has been defined as a structural rearrangement as a result of refinement of initial grain structures of materials to a point where new nanograins form and grow [1]. It is inferred that the high impact momentum/strain rate of deformation 02001-p. 4 DYMAT 2015 results in the onset of dynamic recrystallization. Prior to the onset of dynamic recovery and recrystallization, the microstructure within the shear band reaches the saturation dislocation density due to dislocation multiplication and dislocation cell formation processes.…”

Section: Discussionmentioning

confidence: 99%

“…The machined specimens were impacted at high strain rates and large strains using the Direct Impact Hopkinson Pressure Bar (DIHPB) at different projectile velocities resulting in several impact momentums. During the impact, an AISI 4340 steel projectile (18.67 N, 38 mm diameter by 127 mm length) with a hardness of 47HRC is fired by a gas gun, and strikes the specimen attached to a transmitter bar at a high impact velocity [4,5].…”

Section: Methodsmentioning

confidence: 99%

“…1. The predominant platelet carbides were aligned on the lath boundaries (interlath carbides) and within the laths the tempered steel specimens have been published in references [4,5]. Figure 2 shows the trajectory of an evolved ASB in a single steel specimen impacted at 51 kg · m/s.…”

Section: Microstructural Evolution Of Shear Bands In Steel During Impactmentioning

confidence: 99%

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Mechanism of grain refinement and its effect on Adiabatic Shear Bands in 4340 steel and pure copper during impact

Bassim

Boakye‐Yiadom

2015

EPJ Web of Conferences

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Abstract. Pre-deformation and post-deformation microstructure characterization was conducted on tempered 4340 steel and commercial pure copper specimens under impact to determine the microstructural changes and the mechanism of grain refinement that occur during the evolution of ASBs. It was observed that the movement and multiplication of dislocations, elongation of grains, breaking of elongated grains, rotation, carbide fragmentation and boundary refinement of broken grains occur simultaneously during the evolution of ASBs in the impacted 4340 steel specimens. The extent of these mechanisms depends on the imposed local strain and strain rate. Extensive grain refinement coupled with high density of dislocations results in the shear band structures being more susceptible to crack nucleation and propagation. In copper, it was observed that sequential occurrence of emergence of dislocations, dislocation cell formations with varying cell boundaries and cell interiors, dynamic recovery and extensive micro-twinning results in the formation of the shear bands. The structure within the evolved shear bands becomes less brittle after the onset of dynamic recovery and micro-twinning. The differences in the mechanism of grain refinement and evolution of the shear bands in both materials is attributed to the differences in the mobility of dislocations, the rate of strain hardening and strain hardening exponents in both materials studied.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Mechanism of grain refinement and its effect on Adiabatic Shear Bands in 4340 steel and pure copper during impact

Bassim

Boakye‐Yiadom

2015

EPJ Web of Conferences

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“…Com o aprofundamento das pesquisas no campo da falha a elevadas taxas de deformação, percebeu-se que os mecanismos de fratura são provenientes de bandas de cisalhamento. Por isso, atualmente, diversos grupos têm buscado melhor entender a sua formação para evitá-la ou reduzi-la, o que consequentemente melhoraria a capacidade de proteção desses aços de blindagem [2][3][4]. As bandas de cisalhamento podem ser formadas no material independente da estrutura do grão, do modo e da quantidade de deformação [5].…”

Section: Introductionunclassified

“…al. [3] são dois grupos de pesquisa, que têm demonstrado grande interesse nas bandas de cisalhamento adiabático, pois as mesmas exercem um papel de extrema importância para as falhas ocorridas em materiais dúcteis, que sofrem altas taxas de deformação [4]. Em 2005, Odeshi et al [2] demonstraram que a banda de cisalhamento era um dos mecanismos de falha gerados em um aço de alta resistência e baixa liga (AISI 4340).…”

Section: Introductionunclassified

Caracterização De Um Aço De Alta Dureza, Após O Ensaio Balístico Com Projétil 7.62 Pf

Oliveira¹,

Souza²,

Weber³

et al. 2018

ABM Proceedings

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ResumoA exigência atual de novos materiais com alta resistência mecânica levou a um aumento da pesquisa abordando os aços de alta dureza e baixa liga. Estes aços possuem características que os qualificam para uma elevada gama de aplicações, dentre as quais destaca-se o uso em blindagem balística. O estudo das falhas decorrentes à altas taxas de deformação apontam como principal causa o surgimento das bandas de cisalhamento adiabático. Este trabalho visa caracterizar a microestrutura de um aço de alta dureza e baixa liga, após a realização de um ensaio balístico com um projétil 7.62x51 mm perfurante (Pf). A análise superficial do material foi realizada por meio de microscopia eletrônica de varredura (MEV), onde pode-se observar a ocorrência de uma fratura após a formação da banda de cisalhamento adiabático (adiabatic shear band). Palavras-chave: Alta dureza e baixa liga; Banda de cisalhamento adiabático; Ensaio balístico; Caracterização microestrutural. CHARACTERIZATION OF A HIGH HARDNESS STEEL, AFTER A BALLISTIC TEST WITH A PROJECTILE 7.62 AP AbstractThe current demand for new materials with high mechanical strength has led to increased research addressing the high hardness and low alloy steels. These steels have characteristics that qualify them to a high range of applications, among which stands out the use in ballistic armor. The study of failure due to high strain rates indicate the main cause the appearance of adiabatic shear bands. This work aims to characterize the microstructure of a high hardness and low alloy steel, after conducting a ballistic test with a projectile 7.62x51 mm armor piercing (AP). The superficial analysis of the material was performed by scanning electron microscopy (SEM), where one can observe the occurrence of a fracture after the formation of adiabatic shear band.

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The Minimum Energy Density Criterion for the Competition between Shear and Flat Fracture

Zhang

et al. 2018

Adv Eng Mater

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It is generally recognized that the fracture toughness K IC of materials represents the crack resistance during fracture, i.e., the energy consumption. In this study, AISI 4340 steels with different strength are applied to systematically investigate the intrinsic mechanism of fracture toughness. It is found that the fracture surface morphologies of AISI 4340 steels change from quasi-cleavage fracture to dimple fracture with increasing the tempering temperature. While, the specimen size has almost no effect on the fracture mechanism of shear/flat fracture region, demonstrating that the fracture toughness depends on the proportion of shear and flat fracture region. Additionally, the shear lip width of the K IC specimen will increase to a constant value with enhancing the specimen thickness. Based on the energy balance principle, the maximum shear lip width can be obtained at the minimum fracture energy density of materials; consequently, there is an essential relationship between the shear fracture and fracture toughness, i.e., the minimum energy density criterion. The new finding, which provides a scaling law to well evaluate the plane strain fracture toughness of new materials with high toughness (e.g., nanostructured materials and metallic glasses), may broad the understandings on the fracture toughness.

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A systematic study of grain refinement during impact of 4340 steel

Cited by 25 publications

References 21 publications

Mechanism of grain refinement and its effect on Adiabatic Shear Bands in 4340 steel and pure copper during impact

Mechanism of grain refinement and its effect on Adiabatic Shear Bands in 4340 steel and pure copper during impact

Caracterização De Um Aço De Alta Dureza, Após O Ensaio Balístico Com Projétil 7.62 Pf

The Minimum Energy Density Criterion for the Competition between Shear and Flat Fracture

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