Full Description

The effects of niobium (Nb) and vanadium (V) additions on the properties of plain carbon (C) steel have been well known for some years now. Recently, through refinements in processing technology, very effective use has been made of relatively small amounts of Nb or V (up to 0.2 wt-%) to significantly increase yield strength and improve notch toughness. These improvements have resulted through optimization of Nb and V carbonitride precipitation hardening, ferrite grain size refinement, and a reduction in C content. The latter item also significantly improves weldability.

Nearly all of the industrialized countries of the world have taken advantage of the economy of producing higher strength steels with a minimum of extra alloying cost. This is especially true for structural applications where weight savings is so important. The United States is certainly one of the leaders in this area and one only has to look at a recent American Society for Metals (ASM) survey of high-strength low-alloy (HSLA) structural steels to see the wide variety of Nb- and V-containing steels available.

Many countries have also made effective use of these steels for pressure vessel applications. Although the United States is very active in high-pressure line-pipe development, very little activity has been directed toward using Nb and V steels for pressure vessels and other containers. The principal reason is that allowable-stress calculation as specified by the American Society for Mechanical Engineers (ASME) Boiler and Pressure Vessel Code is usually governed by the tensile strength. While yield strength is increased significantly by Nb and V additions, there is a relatively small effect on tensile strength. Consequently, no direct advantage can be gained in pressure vessel design by an increase in yield strength.

It is the purpose of this report to summarize the state of the art of Nb- and V-containing C-Mn steels for pressure vessel applications and to identify areas needing further research. Specifically, this report will cover low-alloy steels with an upper yield-strength range of about 75 ksi (53 kg/mm2). A brief summary of the pressure vessel codes around the world is presented in order to provide a basis for important material properties in the design of pressure vessels.

Product Details

Published: 1975 Number of Pages: 43 File Size: 1 file , 3.2 MB