Effects of Vanadium and Processing Parameters on the Structures and Properties of a Direct Quenched Low Carbon Mo-B Steel


Abstract:

The structures and mechanical properties of a series of thermomechanically processed, direct-quenched martensitic 0.IC-1.4Mn-0.5Mo-B steels containing from 0 to 0.24 wt pct vanadium have been investigated and compared to those obtained after a conventional austenitizing and quenching treatment. For all processing conditions, vanadium additions to the base composition are found to increase hardenability (ideal critical parameter, D1); the largest effects (up to a 90 pct increase in D1) are noted when samples are hot-rolled prior to direct quenching. Vanadium additions are also observed to provide significant strengthening in the quenched-and-tempered condition as the result of the precipitation of fine V -Mo carbides. The strengthening increment due to these precipitates is approximately 100 MPa/0.1 wt pet V over the range of vanadium additions examined. At the same time, however, these precipitates reduce notch toughness; on the average, the 20 J transition temperature increases by about 4°C for each 10 MPa increment in yield strength. For the conditions examined, the best balance of strength and toughness is obtained in direct-quenched samples which are control-rolled (i.e., rolling is completed below the austenite recrystallization temperature) prior to quenching.

Keywords:

low-carbon Mo-B martensitic steel, vanadium addition, direct-quenched, quenched and tempered, precipitation of f vanadium- rich carbides, molybdenum, boron, hardenability.


Author:

K. A. Taylor and S. S. Hansen

Affiiation

The Research Department, Bethlehem Steel Corporation, Bethlehem, PA 18016.


Source:

Metallurgical Transactions A, Vol. 22A, Oct., 1991, pp. 2359-2374