Effect of Boron on the Strength and Toughness of Direct-Quenched Low-Carbon Niobium Bearing Ultra-High-Strength Martensitic Steel

Hannula, Jaakko; Kömi, Jukka; Porter, David; Somani, Mahesh C.; Kaijalainen, Antti; Suikkanen, Pasi; Yang, Jer−Ren; Tsai, Shao-Pu

doi:10.1007/s11661-017-4295-3

Cited by 31 publications

(32 citation statements)

References 26 publications

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“…It can be seen that pancaking was negligible i.e., grain aspect ratios were low (1.26-1.50) despite the fact that four passes of 0.2 strain each were applied in the temperature regime 900-835 °C. In comparison, Hannula et al [26] reported an aspect ratio of up to 3.5 for lowcarbon steel subjected to laboratory rolling. The low aspect ratios imply that recrystallization occurred even during the controlled rolling at or below 900 °C.…”

Section: Microstructural Characterizationmentioning

confidence: 94%

Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

Kantanen

Somani

Kaijalainen

et al. 2019

Metals

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A new experimental steel containing in weight percent 0.3C-2.0Mn-0.5Si-1.0Al-2.2Cr and 0.3C-1.9Mn-1.0Si-1.0Cr was hot rolled in a laboratory rolling mill and directly quenched within the martensite start and finish temperature range. It was then partitioned without reheating during slow furnace cooling to achieve tensile yield strengths over 1100 MPa with good combinations of strength, ductility and impact toughness. Gleeble thermomechanical simulations led to the selection of the partitioning at the temperatures 175 and 225 °C, which produced the desired microstructures of lath martensite with finely divided retained austenite in fractions of 6.5% and 10% respectively. The microstructures were analyzed using light and scanning electron microscopy in combination with electron backscatter diffraction and X-ray diffraction analysis. The mechanical properties were characterized extensively using hardness, tensile and Charpy V impact testing. In tensile testing a transformation induced plasticity mechanism was shown to operate with the less stable, carbon-poorer retained austenite, which transformed to martensite during straining. The auspicious results in respect to microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural steels through thermomechanical rolling followed by the direct quenching and partitioning route.

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Section: Microstructural Characterizationmentioning

confidence: 94%

Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

Kantanen

Somani

Kaijalainen

et al. 2019

Metals

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“…Previous studies have shown that the impact transition temperature is controlled by the largest grains in the grain size distribution, where grain size refers to the ECD of grains with grain boundary misorientations > 15°, for example d90%. 20,21 By alloying with Nb-Mo, a pancaked austenite structure was achieved after hot rolling, which then produced a finer and more uniform prior austenite structure after re-austenitization, presumably due to the presence of more nucleation sites for austenite grains. This led to a finer martensitic structure with higher strength and better impact toughness.…”

Section: Mechanical Properties After Hot Rolling Direct Quenching Anmentioning

confidence: 99%

Evaluation of Mechanical Properties and Microstructures of Molybdenum and Niobium Microalloyed Thermomechanically Rolled High-Strength Press Hardening Steel

Hannula

Porter

Kaijalainen

et al. 2019

JOM

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This article studied the effect of molybdenum and niobium on the microstructures and mechanical properties of laboratory control rolled steels based on grade 22MnB5. The constructed continuous cooling transformation diagrams revealed that an addition of Mo significantly increased the hardenability. Especially in the case of austenite compressed below its recrystallization temperature, an Mo addition delayed ferrite and bainite formation, and it increased martensite hardness. Laboratory hot-rolling experiments with a finish rolling temperature of 850°C produced a flattened pancaked austenite. After hot rolling and direct quenching, samples were rapidly reaustenitized at 900°C followed by water quenching to simulate an actual press hardening process. Especially in the case of Nb-Mo steel, a strongly pancaked austenitic structure was achieved after hot rolling, which led to a fine, uniform prior austenite grain structure after re-austenitization and quenching. The Nb-Mo steel had a tensile strength > 1500 MPa and $ 11% total elongation combined with good impact toughness, which can be considered excellent for this type of press hardening steel.

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“…The martensitic microstructure develops within the prior austenite grains present before quenching [36]. Therefore, austenite conditioning has a direct influence on the final martensite properties such as strength and toughness [37,38]. It was already demonstrated in Fig.…”

Section: Molybdenum Alloying Effects In Martensitic Steelsmentioning

confidence: 79%

Molybdenum alloying in high-performance flat-rolled steel grades

et al. 2020

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Considerable progress in developing flat-rolled steel grades has been made by the Chinese steel industry over the recent two decades. The increasing demand for high-performance products to be used in infrastructural projects as well as in production of consumer and capital goods has been driving this development until today. The installation of state-of-the-art steel making and rolling facilities has provided the possibility of processing the most advanced steel grades. The production of high-performance steel grades relies on specific alloying elements of which molybdenum is one of the most powerful. China is nearly self-sufficient in molybdenum supplies. This paper highlights the potential and advantages of molybdenum alloying over the entire range of flat-rolled steel products. Specific aspects of steel property improvement with respect to particular applications are indicated.

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Effect of Boron on the Strength and Toughness of Direct-Quenched Low-Carbon Niobium Bearing Ultra-High-Strength Martensitic Steel

Cited by 31 publications

References 26 publications

Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

Evaluation of Mechanical Properties and Microstructures of Molybdenum and Niobium Microalloyed Thermomechanically Rolled High-Strength Press Hardening Steel

Molybdenum alloying in high-performance flat-rolled steel grades

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