Formation of carbonitride precipitates in hardfacing alloy with niobium addition

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Rare Met. (2013) 32(1):52–56 DOI 10.1007/s12598-013-0016-2

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Formation of carbonitride precipitates in hardfacing alloy with niobium addition Ke Yang*, Qin Yang, Ye-Feng Bao

Received: 22 February 2012 / Revised: 11 June 2012 / Accepted: 22 June 2012 / Published online: 27 February 2013 Ó The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2013

Abstract Niobium, as the most effective second-phase forming element, was added in the Fe–Cr13–C–N hardfacing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were studied by optical microscopy, scanning electron microscopy, and electron probe microanalyzer. The thermodynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that niobium carbonitrides are complex Nb(C, N) precipitate distributed on grain boundary and matrix of the hardfacing alloy. Under as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. Under heat treatment condition, a large number of secondary carbonitrides can precipitate out with very fine size and make a great secondary hardening effect on the matrix. As a result, addition of niobium in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and intergranular chromium depletion.

excellent resistance to wear and oxidation is deposited onto equipment. The second phase material particles that precipitate out have an important effect on the wearing life of metal [1–5]. Niobium is a kind of element that has a strong combination with C or N. If Nb is added to the steel, hardening phase, which is dispersedly distributed, has regular shape, high melting temperature, and high degree of hardness that will be precipitated from the matrix; this will strengthen the matrix, raise the mechanical property, and improve the thermal fatigue property and the abradability [6, 7]. The researches related to the combination of Nb with C or N in structure steel are frequently reported, but the researches about the precipitated shape and behavior of the combination of Nb with C and N in the hardfacing alloy are rarely seen. Therefore, this paper aimed at elucidating the form of carbonitride and assessing the effect of niobium on the formation of carbonitride in Fe–Cr13–C–N hardfacing alloy.

2 Experimental Keywords Precipitate

Niobium; Carbonitride; Hardfacing alloy;

1 Introduction Weld hardfacing technique is chiefly employed to extend or improve the service life of mechanical equipment and to reduce their cost, of which hardfacing alloy that has K. Yang*, Q. Yang, Y.-F. Bao College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022, China e-mail: [email protected]

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The test materials consisted of steel strip and alloy powders, such as low-carbon ferrochrome, manganese–iron, silicon–iron, niobium–iron, chromium nitrid