Jonathan Lentz, Arne Röttger, W. Theisen

Alloy design in the system Fe-C-B

Introduction

Alloy design in the system fe-c-b. Investigate Fe-C-B-Cr alloy design for tool steels. Boron forms hard phases, Cr stabilizes M2B borides & M23(C,B)6 carboborides. Study microstructure, hardness via nanoindentation & wear mechanisms.

Abstract

In this study, the Fe-C-B system is used as a basis for alloy development of tool steels. Thereby,boron is used as hard phase forming element. The effect of chromium on the phase stability,microstructure and hard phase properties of Fe-C-B-Cr alloys is investigated. In this manner,thermodynamic equilibrium calculations are performed and experimentally validated. Laboratoryalloys were casted and investigated using scanning electron microscopy (SEM), energy dispersivespectroscopy (EDS) and electron backscatter diffraction (EBSD). Nanoindentation was performedto investigate the effect of Cr on the micromechanical properties of the particular hard phases(elastic modulus and indentation hardness). It is shown, that Cr stabilizes the orthorhombic, Cr-richM2B type boride with a hardness of 22.8 GPa. In addition Cr stabilizes the Cr-rich M23(C,B)6carboboride, which possess a lower hardness (14 GPa). In a next step, the findings areimplemented in an alloy development and alloying additions of chromium, silicon and manganeseare used to specifically stabilize the M2B type boride with high Cr content to adjust a high hardnessof the M2B phase. Subsequently, a scratch test is performed to investigate the governing wearmechanisms in the developed alloy.

Review

This study presents a highly relevant and comprehensive investigation into alloy design for tool steels, specifically focusing on the novel application of the Fe-C-B system with boron as a primary hard phase forming element. The research adopts a rigorous approach by combining thermodynamic equilibrium calculations with extensive experimental validation, providing a strong scientific basis for understanding complex phase relationships. The chosen methodology addresses a critical need in materials science for developing advanced high-performance alloys, making a valuable contribution to the field of ferrous metallurgy and engineering. A major strength of this work lies in its detailed exploration of chromium's effect on phase stability, microstructure, and hard phase properties within Fe-C-B-Cr alloys. The authors successfully identify that chromium stabilizes two distinct boride/carboboride phases: the orthorhombic, Cr-rich M2B type boride with an impressive hardness of 22.8 GPa, and the Cr-rich M23(C,B)6 carboboride, albeit with a lower hardness of 14 GPa. The use of advanced characterization techniques such as SEM, EDS, EBSD, and particularly nanoindentation, allows for a precise quantification of micromechanical properties of these specific hard phases. Crucially, these fundamental insights are then strategically applied to an alloy development stage, where additions of Cr, Si, and Mn are used to optimize the M2B phase for superior hardness, demonstrating a clear path from fundamental understanding to practical application. The findings from this study have significant implications for the rational design of high-performance tool steels. By clearly elucidating the role of chromium and demonstrating the ability to selectively stabilize high-hardness M2B borides, the research provides a powerful framework for developing wear-resistant materials. The subsequent scratch test to investigate wear mechanisms further underscores the practical relevance of the developed alloys. This work represents a significant step forward in understanding and manipulating boride-based hard phases in iron alloys and lays robust groundwork for future investigations into optimizing the overall mechanical properties, including fracture toughness and fatigue resistance, for real-world industrial applications. It is a well-executed study that will be of great interest to materials scientists and engineers.

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