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

Kimura, Yuuji; Inoue, Tatsuo

doi:10.2355/isijinternational.isijint-2019-726

Cited by 26 publications

(49 citation statements)

References 74 publications

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“…Decreasing the transverse grain size is effective to suppress the occurrence of transverse cracking. 1,3) As for the TFA sample annealed at 973 K, the transverse brittle cracking became more pronounced at lower temperatures rather than the delamination cracking along the RD, resulting in a decrease in vE. This is considered to be due to the larger and more equiaxial grain structure (IL HAB_T = 0.69 μm).…”

Section: Resultsmentioning

confidence: 98%

“…Some of the impact bars were broken into two pieces, as indicated by +. However, it should be noted that the occurrence of delamination toughening was significantly shifted toward the lower temperature side through the annealing at 843 K. The delamination finish temperature (T DF ), below which vE decreased to the level of vE US or less, 1,3) was estimated to be approximately 233 K for the TF sample, and 173 K for the TFA sample annealed at 843 K.…”

Section: Resultsmentioning

confidence: 99%

“…2) The microstructural factors controlling the delamination toughening have been clarified to be the transverse grain size, grain shape, <110>//RD fiber texture, and carbide particle distribution in the UFEG structure. 1) The delamination toughening was observed to be enhanced at lower temperatures as the volume fraction of cementite particles decreased in (0.2-0.6)%C-2%Si-1%Cr-1%Mo steels (mass%). 3) However, in the Mo-bearing steels, it is still not clear whether nanoscale Mo-rich precipitates 4) can influence the delamination toughening or not.…”

Section: Introductionmentioning

confidence: 92%

“…1) Excellent combinations of strength and toughness were demonstrated in the warm tempformed (TF) steels with UFEG structures. 1) Toughening in the UFEG structure steels is attributed to the occurrence of crack-arrester-type delaminations, where cracks are deflected toward the longitudinal direction (//RD) of notched bars. This phenomenon is referred to as delamination toughening.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

Kimura

Inoue

2022

ISIJ Int.

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Ultrafine elongated grain (UFEG) structure with a strong <110>// rolling direction fiber texture was created for a 0.4%C-2%Si-1%Cr-1%Mo steel (mass%) through deformation of tempered martensite using multi-pass caliber rolling at 773 K with a rolling reduction of 78% (i.e. warm tempforming). Annealing of the warm tempformed steel at 843 K enhanced delamination toughening at lower temperatures without a significant loss of tensile strength at 1.8 GPa. It was suggested that delamination toughening was controlled through the precipitation of nanoscale Mo-rich precipitates in the UFEG structure.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

Kimura

Inoue

2022

ISIJ Int.

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“…The first impressive results on the combination of high strength and impact toughness achieved by tempforming have been obtained in medium carbon (0.4%) high-strength steel [3,49]. Then, Kimura et al have carried out a series of studies, using steels with 0.2%C to 0.6%C [51,[59][60][61]79,81]. The obtained results can be summarized as follows.…”

Section: Carbon Effectmentioning

confidence: 99%

Tempforming as an Advanced Processing Method for Carbon Steels

Dolzhenko

Kaibyshev

Belyakov

2020

Metals

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The microstructural mechanisms providing delamination toughness in high-strength low-alloyed steels are briefly reviewed. Thermo-mechanical processing methods improving both the strength and impact toughness are described, with a close relation to the microstructures and textures developed. The effect of processing conditions on the microstructure evolution in steels with different carbon content is discussed. Particular attention is paid to tempforming treatment, which has been recently introduced as a promising processing method for high-strength low-alloyed steel semi-products with beneficial combination of strength and impact toughness. Tempforming consists of large strain warm rolling following tempering. In contrast to ausforming, the steels subjected to tempforming may exhibit an unusual increase in the impact toughness with a decrease in test temperature below room temperature. This phenomenon is attributed to the notch blunting owing to easy splitting (delamination) crosswise to the principle crack propagation. The relationships between the crack propagation mode, the delamination fracture, and the load-displacement curve are presented and discussed. Further perspectives of tempforming applications and promising research directions are outlined.

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Friction Stir Welding‐Induced Microstructural Changes in Low‐Alloy Steel Post‐Tempforming

Dolzhenko,

Malopheyev,

Lugovskaya

et al. 2024

steel research int.

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A feasibility of friction stir welding for a high‐strength low‐alloy steel subjected to tempforming, that is, tempering followed by large‐strain warm rolling at tempering temperature, is presented. The martensite microstructure tempered at 873 K for 1 h and then subjected to warm rolling to total strain of 1.5 is characterized by a lamellar‐type ultrafine‐grained microstructure consisting of pan‐caked grains with the transverse size of 560 nm and exhibits the tensile strength of 1020 MPa. The friction stir welding is accompanied by heating the stir zone of the welded sample well above Ac1 temperature. Hence, the welding seam experiences austenite reversion followed by martensitic transformation. The microstructure evolved in the stir zone is composed of near‐equiaxed grains with an average size of 1.3 μm. Nevertheless, the stir zone possesses increased hardness up to 350 HV as compared to that of 290 HV in the base material after tempforming. Upon tensile test of the welded joint, the strain localization followed by fracture occurs in the heat‐affected zone close to the stir zone. The tensile strength of 970 MPa is obtained for the welded joint that is quite close to the base material after temforming.

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

Cited by 26 publications

References 74 publications

Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

Tempforming as an Advanced Processing Method for Carbon Steels

Friction Stir Welding‐Induced Microstructural Changes in Low‐Alloy Steel Post‐Tempforming

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