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Article

Effect of Nb and Mo Additions in the Microstructure/Tensile Property Relationship in High Strength Quenched and Quenched and Tempered Boron Steels

1
Materials and Manufacturing Division, CEIT-Basque Research and Technology Alliance (BRTA), 20018 Donostia/San Sebastián, Basque Country, Spain
2
Tecnun, Mechanical and Materials Engineering Department, Universidad de Navarra, 20018 Donostia/San Sebastián, Basque Country, Spain
3
AG der Dillinger Hüttenwerke, 66763 Dillingen/Saar, Germany
4
NiobelCon BV, 2970 Schilde, Belgium
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Department of Materials Engineering (MTM), KU Leuven, 3001 Leuven, Belgium
*
Author to whom correspondence should be addressed.
Metals 2021, 11(1), 29; https://doi.org/10.3390/met11010029
Received: 4 December 2020 / Revised: 22 December 2020 / Accepted: 23 December 2020 / Published: 25 December 2020
Recently, advanced thermomechanical hot rolling schedules followed by direct quenching are being developed in order to avoid reheating and quenching treatment after hot rolling to eliminate an energy and cost consuming step. The use of boron as an alloying element is a widely known practice in high strength medium carbon steels to increase the strength due its potential for delaying phase transformation and improving hardenability. In addition, a significant synergetic effect on hardenability could be reached combining B with microalloying elements (adding Nb, Mo or Nb-Mo). With the purpose of exploring the effect of microalloying elements and thermomechanical rolling schedule, laboratory thermomechanical simulations reproducing plate mill conditions were performed using ultra high strength steels micro-alloyed with Nb, Mo, and Nb-Mo. To that end, plane compression tests were performed, consisting of an initial preconditioning step, followed by several roughing and finishing deformation passes and a final quenching step. After fast cooling to room temperature, a tempering treatment was applied. In the present paper, the complex interaction between the martensitic microstructure, the tempering treatment, the addition of microalloying elements, and the resulting tensile properties was evaluated. For that purpose, an exhaustive EBSD quantification was carried out in both quenched as well as quenched and tempered states for all the steel grades and the contribution of different strengthening mechanisms on yield strength was analyzed. Highest tensile properties are achieved combining Nb and Mo, for both quenched (Q) and quenched and tempered states (Q&T), reaching yield strength values of 1107 MPa and 977 MPa, respectively. Higher tempering resistance was measured for the Mo-bearing steels, making the CMnNbMoB steel the one with the lowest softening after tempering. For CMnB grade, the yield strength reduction after tempering of about 413 MPa was measured, while for NbMo micro-alloyed steel, yield strength softening is considerably reduced to 130 MPa. View Full-Text
Keywords: martensite; Q + T steels; thermomechanical simulations; tensile properties; microalloying elements martensite; Q + T steels; thermomechanical simulations; tensile properties; microalloying elements
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MDPI and ACS Style

Zurutuza, I.; Isasti, N.; Detemple, E.; Schwinn, V.; Mohrbacher, H.; Uranga, P. Effect of Nb and Mo Additions in the Microstructure/Tensile Property Relationship in High Strength Quenched and Quenched and Tempered Boron Steels. Metals 2021, 11, 29. https://doi.org/10.3390/met11010029

AMA Style

Zurutuza I, Isasti N, Detemple E, Schwinn V, Mohrbacher H, Uranga P. Effect of Nb and Mo Additions in the Microstructure/Tensile Property Relationship in High Strength Quenched and Quenched and Tempered Boron Steels. Metals. 2021; 11(1):29. https://doi.org/10.3390/met11010029

Chicago/Turabian Style

Zurutuza, Irati, Nerea Isasti, Eric Detemple, Volker Schwinn, Hardy Mohrbacher, and Pello Uranga. 2021. "Effect of Nb and Mo Additions in the Microstructure/Tensile Property Relationship in High Strength Quenched and Quenched and Tempered Boron Steels" Metals 11, no. 1: 29. https://doi.org/10.3390/met11010029

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