Title

Nb-V Microalloyed Medium Carbon Steel and Its Free-Cutting Grade

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Authorship

AIGUO, CAI; HONGTAO, ZHANG; GANYUN, PANG; RUIZHEN, WANG

AIGUO, CAI

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HONGTAO, ZHANG

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GANYUN, PANG

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RUIZHEN, WANG

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DOI

10.5151/2594-5327-49v8-351-362

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Abstract

A study of Nb-V microalloying of medium carbon steel has been carried out. The study revealed the advantages of Nb-V microalloying in comparison with solely V-microalloyed medium carbon steel. Niobium in Nb-V microalloyed medium carbon steel brings about further grain refinement, stronger precipitation hardening, a larger volume fraction of ferrite, a change in precipitation pattern, and a change in pearlite–cementite morphology. Based on this study, a Nb-V microalloyed medium carbon steel, 35MnVNb, and its free-cutting grade 35MnVNbS, have been developed and commercialized for long products and forging applications. These steels achieve an ultimate tensile strength (UTS) of 745–785 MPa and show improved impact toughness. Physico-mechanical features of the steels are introduced. Special deoxidation and resulphurization practices are applied to modify the sulphide inclusions. The 35MnVNb steel possesses better fatigue properties than quenched and tempered 40Cr steel, with comparable induction surface hardenability. The machinability of 35MnVNbS steel is superior to that of 40Cr steel and has been successfully applied to machining on automatic machine tools.

Keywords

Nb-V microalloying, aço médio carbono, refino de grão, usinabilidade, resistência à fadiga