Delamination toughening assisted by phosphorus in medium-carbon low-alloy steels with ultrafine elongated grain structures

Min, Xiaohua; Kimura, Yuuji; Kimura, Takashi; Tsuzaki, Kaneaki

doi:10.1016/j.msea.2015.09.102

Cited by 32 publications

(24 citation statements)

References 25 publications

(94 reference statements)

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“…From the opposite viewpoint, the Charpy impact property of TF steel with an UFEG structure can be also controlled through the addition of P. [68][69][70] Intergranular embrittlement attributed to P segregation along the boundaries of UFEGs was observed to assist the occurrence of crack-arrestertype delamination over a wide temperature range in 1.1 GPa-class high-strength Cr-Mo steel (JIS-SCM 440 steel base). For example, a TF sample of 0.09% P steel exhibited a better impact property than a QT sample of 0.001% P steel.…”

Section: Microstructural Factors Controlling the Charpymentioning

confidence: 99%

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

Kimura

Inoue

2020

ISIJ Int.

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Section: Microstructural Factors Controlling the Charpymentioning

confidence: 99%

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

Kimura

Inoue

2020

ISIJ Int.

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“…The fracture surface consists of almost flat terraces formed parallel to RD-TD plane [17,42]. The delamination cleavage frequently initiates on parallel cleavage {100} planes lying almost parallel to the rolling plane [17,20]. An average dimension of terraces is approx.…”

Section: Fractographymentioning

confidence: 99%

“…Delamination results from anisotropic microstructures, i.e., the grains/subgrains highly elongated along the rolling direction (RD) and the second phase particles precipitated at the longitudinal grain/subgrain boundaries. Delamination was observed in various structural steels and alloys [12,[17][18][19][20][21][22][23][24][25][26][27][28][29], leading to so-called delamination toughening. The delamination toughening can decrease DBTT in low-alloy steels by reducing the triaxial stress concentration at the crack tip [18][19][20][21][22]25,26].…”

Section: Introductionmentioning

confidence: 99%

“…Delamination was observed in various structural steels and alloys [12,[17][18][19][20][21][22][23][24][25][26][27][28][29], leading to so-called delamination toughening. The delamination toughening can decrease DBTT in low-alloy steels by reducing the triaxial stress concentration at the crack tip [18][19][20][21][22]25,26]. The dominating factors controlling the delamination toughening are considered to be the ultrafine grains, the grain shape and the 〈110〉 || RD fiber texture [9,13,22,23,[29][30][31], which vary depending on the starting microstructure [9,23] and the processing conditions, such as rolling temperature and rolling reduction [9,22].…”

Section: Introductionmentioning

confidence: 99%

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Impact toughness of an S700MC-type steel: Tempforming vs ausforming

Dolzhenko

Yanushkevich

Nikulin

et al. 2018

Materials Science and Engineering: A

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A B S T R A C TThe effect of different thermomechanical treatments, i.e., ausforming and tempforming, on the microstructure and mechanical properties including impact fracture behavior of high-strength low-carbon S700MC-type steel was investigated. The tempforming resulted in the development of ultrafine grained elongated grain microstructure with the transverse grain size of 530 nm, whereas the ausforming led to the formation of typical tempered martensite structure with a distance between high-angle boundaries of 1.5 µm. The tempered microstructures involved the formation of carbides with an average particle size about 50 nm and M(C, N)-type carbonitrides with average size of 10 nm. The tempformed steel exhibited the ultimate tensile strength of 1110 MPa and the impact toughness, KCV, above 450 J/cm 2 at a temperature of 293 K, and KCV of 109 J/cm 2 at liquid nitrogen temperature for impact direction perpendicular to rolling plane. In contrast, KCV of the ausformed steel was 180 and 10 J/cm 2 at 293 and 77 K, respectively. The enhancement of toughness was associated with delamination cracks which occurred in the ultrafine elongated grain structure with anisotropic properties.

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“…Similarly, the intergranular fracture stress in the SD is low, as a result of the elongated grain shape and the good grain boundary continuity along the RD. 19,35,36) Therefore, these provide the necessary conditions to cause the brittle delamination along the RD, on the basis of the Yoffee diagram, which indicates the relationship between the σ t and σ c , for the UFEG structure. [8][9][10] Since the refinement in transverse grain size may enhance the σ c//45° as well as the σ y , the occurrence of the transverse cracking may be suppressed, leading to the occurrence of delamination.…”

Section: )mentioning

confidence: 99%

Combined Effect of Ausforming and Warm Tempforming on the Strength and Toughness of An Ultra-High Strength Steel

Kimura

Inoue

2016

ISIJ International

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Recently, we have reported that ultrafine elongated grain (UFEG) structures with strong < 110 > //rolling direction (RD) fiber textures, which are similar to those in cold drawn steel wires, [4][5][6] are particularly effective in toughening of medium-carbon low-alloy steel bars.7-11) A 0.4C-2Si-1Cr-1Mo steel (mass%) with an UFEG structure had an average yield strength (σ y ) of 1.84 GPa and an average Charpy V-notch absorbed energy (vE) of 226 J at room temperature. 7,9,11) Furthermore, the UFEG structure steels were observed to exhibit an inverse temperature dependence of toughness at subzero temperatures, as a consequence of delamination, in which cracks branched and propagated in the longitudinal direction of impact bars.7-11) The vE of the UFEG structure steels increased as the temperature decreased, in contrast to a ductile-to-brittle transition of conventional ultra-high strength steels. It has also been clarified that the microstructural factors controlling the occurrence A 0.4C-2Cr-1Mo-2Ni steel (in mass%) was austenitized at 1 123 K, followed by ausforming (AF) using multi-pass caliber rolling with a rolling reduction of 74%. The AF samples were subsequently tempered at 773 K and deformed by multi-pass caliber rolling (i.e. warm tempforming, WTF) with a rolling reduction of 46%. Their microstructures and mechanical properties were investigated and compared to those of the quenched and tempered samples (non-AF samples) which were subjected to the sequent WTF with rolling reductions of 46% and 74%. The WTF with rolling reductions ranging 46 to 74% resulted in the strengthening and toughening of the AF and non-AF samples through the evolution of anisotropic and ultrafine grain structures with strong < 110 > //rolling direction (RD) fiber textures. The AF sample demonstrated the faster kinetics of the microstructural changes, i.e. refinement in the transverse grain size and development of highly elongated grains than the non-AF sample. As a result, the AF sample exhibited a better combination of ultra-high strength and toughness than the non-AF sample, when compared at the rolling reduction of 46%. The combined effect of AF and WTF was especially pronounced in the enhancement of toughness resulting from delamination.

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Delamination toughening assisted by phosphorus in medium-carbon low-alloy steels with ultrafine elongated grain structures

Cited by 32 publications

References 25 publications

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

Impact toughness of an S700MC-type steel: Tempforming vs ausforming

Combined Effect of Ausforming and Warm Tempforming on the Strength and Toughness of An Ultra-High Strength Steel

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