Molybdenum - Vanadium

Molybdenum. Molybdenum is a potent hardenability element and is found in many lowalloy steels. Molybdenum, like chromium, forms several types of carbides that are important for wear-resistant applications, e.g., tool steels. Molybdenum is added to minimize temper embrittlement in low-alloy steels. Temper embrittlement occurs when low-alloy steels are tempered in the temperature range of 260–370 C. The embrittlement is caused by tramp elements such as phosphorus that accumulate at the prior austenite grain boundaries and thus weaken the boundaries. Adding molybdenum prevents the accumulation of these undesirable elements at the boundaries. Molybdenum also enhances the creep strength of low-alloy steels
at elevated temperatures and is used in rotors and other parts of generators in electric power plants. Creep is an undesirable process that allows steel to slowly elongate or creep under load. Eventually the component will fail.

Vanadium. Although vanadium is a potent hardenability element, its most useful role is in the formation of a vanadium nitride and vanadium carbide (it can also be in a combined form of vanadium carbonitride). A very important role of vanadium is in microalloyed steels, also called high-strength, low-alloy (HSLA) steels. These steels are strengthened by precipitation of vanadium nitrides and vanadium carbides (vanadium carbonitrides). The formation of vanadium carbide is important for wear resistance. Vanadium carbide is much harder than
iron carbide, chromium carbide, and molybdenum carbide. Vanadium is thus important in high-speed tool steels, which are used as drill bits that retain their hardness as the tool heats by friction.

Bruce L. Bramfitt
International Steel Group, Inc.
Research Laboratories
Bethlehem, Pennsylvania

Reprinted from Handbook of Materials Selection, Wiley, New York, 2002, by permission of the publisher.
Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright  2006 by John Wiley & Sons, Inc.

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