Abstract
High boron steel is prone to brittle failure due to the boride distributed in it with net-like or fishbone morphology, which limit its applications. The Quenching and Partitioning (Q&P) heat treatment is a promising process to produce martensitic steel with excellent mechanical properties, especially high toughness by increasing the volume fraction of retained austensite (RA) in the martensitic matrix. In this work, the Q&P heat treatment is used to improve the inherent defect of insufficient toughness of high boron steel, and the effect mechanism of this process on microstructure transformation and the change of mechanical properties of the steel has also been investigated. The high boron steel as-casted is composed of martensite, retained austensite (RA) and eutectic borides. A proper quenching and partitioning heat treatment leads to a significant change of the microstructure and mechanical properties of the steel. The net-like and fishbone-like boride is partially broken and spheroidized. The volume fraction of RA increases from 10% in the as-cast condition to 19%, and its morphology also changes from blocky to film-like. Although the macro-hardness has slightly reduced, the toughness is significantly increased up to 7.5 J·cm−2, and the wear resistance is also improved.
Highlights
In recent years, high boron steel gains many scholars’ attention and has been widely used in the production of related workpieces in the fields of automotive industry, mining machinery, machine tools, etc., for its low cost [1,2], good hot workability [3,4,5], and high hardness
Boride, as a strengthening phase in high boron steel, is superior to carbide in hardness (1450–1800 HV) and modulus of elasticity, which ensures that the steel has higher hardness and better wear resistance than white cast iron and high chromium cast iron [6,7]
Alloying and high-temperature heat treatment are effective ways to improve the toughness of high boron steel
Summary
High boron steel gains many scholars’ attention and has been widely used in the production of related workpieces in the fields of automotive industry, mining machinery, machine tools, etc., for its low cost [1,2], good hot workability [3,4,5], and high hardness. Fe2 B exhibits serious brittleness because of the weak B–B bond along [2] crystal orientation [9,10,11,12,13], which will make it peeled off during the wear process and deteriorate the wear resistance of the steel [14]. These extremely limit the application of high boron steel on the impacting condition. Except for these, the net-like Fe2 B can be disconnected by high temperature austenization [23,24]
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