Static fracture toughness of ultra-fine grained steels processed by thermo-mechanical warm rolling

Qiu, Hai; Enami, Keitaro; Hiraoka, Kazuo; Nagai, Kotobu; Hagihara, Yukito

doi:10.1007/s10853-007-2430-z

Cited by 7 publications

(4 citation statements)

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“…By multi‐pass warm caliber rolling of low carbon steels ultrafine‐grained (UFG) steel bars can be fabricated, which show higher toughness values. After quenching and tempering, ferrite with fine disperse cementite particles is multiple rolled at very low temperatures to a high accumulated strain of about 4.…”

Section: Successful Tmcp Applications For Flat Productsmentioning

confidence: 99%

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

Buchmayr

2017

steel research int.

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The basic concept of thermomechanical treatment (TMT) or thermomechanical controlled processing (TMCP) is responsible for the development of many advanced steel grades with improved mechanical properties during the last 50 years. A retroperspective view, an explanation of the most important influencing factors and a presentation of the enormous benefits for the costumer are given in this review. A sound knowledge on the synergism of recrystallization, precipitation, and transformation phenomena forms the basis to produce fine, homogeneous microstructures with improved properties. Starting from structural steels, improvements can be achieved with respect to higher strength and toughness values combined with better weldability and formability, mainly based on reduction of carbon content and finer grain sizes. The benefits in the application areas are described in detail. TMCP is not only used for flat products, but also for long products and forgings of different steel grades. Physical simulation and modeling contribute significantly to these developments, which also form the basis for computer-aided control or real-time online-models. In the next years, a complete shift to cyber physical systems (CPS) is predicted, which needs an aligned education effort. REVIEW A Brief Historical ReviewSince the mid-sixties, steel mills began to produce fine grained structural steels by lowering the final rolling temperature. Based on fundamental research in Germany, USA, UK, Germany, and Japan, the fundamental understanding was further developed in metallurgical laboratories. Pioneers at that time were Haneke, [10] Schmidtmann, [11,12] Meyer, [13,14] Kaspar, [15][16][17][18][19][20][21][22][23][24] Streißelberger, [9,15,[25][26][27] DeArdo, [28,29] Jonas, [30][31][32][33] Sellars, [34][35][36][37] Hodgson, [38][39][40][41][42] Tamura und Tanaka, [43] Saito, [44] Ouchi, [45] Militzer, [46,47] and many others. The basic idea was to improve the strength and toughness behavior of structural steels by grain refining. Compared to conventional hot rolling at high rolling temperatures, the new steels were rolled at lower final rolling temperature. It was found that repeated recrystallization of the austenite structures leads to a decrease of grain size, but there is a limit, which is difficult to overcome. Deformation at temperatures, where no recrystallization takes place was successful in the conditioning of austenite having a dense population of glide planes, high dislocation density, and a high intrinsic energy, which provided a high density of nucleation sites for the transformation products of austenite.At the beginning, mainly ferrite plus pearlite microstructures were considered and later the role of rapid cooling became an additional opportunity to increase the strength level.Higher cooling rates or higher undercooling increase the driving force and with a lower diffusivity a finer microstructure like bainite and martensite can be reached.A comparison of the contributions of the strengthening mechanism in a commercial hot rolle...

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Section: Successful Tmcp Applications For Flat Productsmentioning

confidence: 99%

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

Buchmayr

2017

steel research int.

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“…[4][5][6][7] The ultra-fine grained ferrite (about 1 μm)/cementite steels exhibited low sensitivity to temperature and excellent fracture toughness (crack tip opening displacement). 7) As compared to the brittle and ductile/brittle fracture modes, less attention was paid to the ductile fracture mode because it is usually regarded as being much safer than the two former fracture modes. With the progress of metallurgical technology, the occurrence of accidents caused by a completely brittle fracture in structural steels has been significantly reduced.…”

Section: Introductionmentioning

confidence: 99%

Influence of Grain Size on the Ductile Fracture Toughness of Ferritic Steel

2014

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The ductile fracture toughness of ferritic steel was assessed in terms of crack tip opening displacement (CTOD). The CTOD is composed of two parts: elastic and plastic. In the ductile fracture region, as compared to the elastic part, the fraction of the plastic part is dominant. The CTOD linearly increases with an increase in ferrite grain size, but grain coarsening simultaneously increases the possibility of cleavage fracture. As yield strength increases, the CTOD decreases due to the decreased plastic deformation ability.

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“…The toughness of ferritic steel has been confirmed to increase with a decrease in ferrite grain size. [1][2][3][4][5] In all the parameters applied to evaluate toughness, such as fracture toughness (stress intensity factor, crack tip opening displacement, J integral, etc.) and impact toughness (absorbed energy, ductile-brittle transition temperature (DBTT), and so on), only DBTT directly reflects the variation in fracture mode.…”

Section: Introductionmentioning

confidence: 99%

Physical Interpretation of Grain Refinement-induced Variation in Fracture Mode in Ferritic Steel

et al. 2013

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Static fracture toughness of ultra-fine grained steels processed by thermo-mechanical warm rolling

Cited by 7 publications

References 4 publications

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

Influence of Grain Size on the Ductile Fracture Toughness of Ferritic Steel

Physical Interpretation of Grain Refinement-induced Variation in Fracture Mode in Ferritic Steel

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