Keywords and Phrases
Atom probe tomography; Orientation image microscopy
"Alloy modifications by addition of niobium (Nb ), vanadium (V), nitrogen (N) and cobalt (Co) to cast 17-4 PH steel were investigated to determine the effect on mechanical properties. Additions of Nb, V, and N increased the yield strength from 1120 MPa to 1310 MPa while decreased the room temperature charpy V notch (CVN) toughness from 20 J to four Joules. The addition of Co to cast 17-4 PH steel enhanced the yield strength and CVN toughness from 1140 MPa to 1290 MPa and from 3.7 J to 5.5 J, respectively. In the base 17-4 PH steel, an increase in block width from 2.27 ± 0.10 µm in the solution treated condition to 3.06 ± 0.17 µm upon aging at 755 K was measured using orientation image microscopy. Cobalt inhibited recrystallization and block boundary migration during aging resulting in a finer martensitic block structure. The influence of Co on copper (Cu) precipitation in steels was studied using atom probe tomography. A narrower precipitate size distribution was observed in the steels with Co addition. The concentration profile across the matrix / precipitate interface indicated rejection of Co atoms from the copper precipitates. This behavior was observed to be energetically favorable using first principle calculations. The activation energies for Cu precipitation increased from 205 kJ/ mol in the non-cobalt containing alloy, to 243 kJ/ mol, and 272 kJ/ mol in alloys with 3 wt. %Co, and 7 wt. %Co, respectively. The role of Co on Cu precipitation in cast 17-4 PH steel is proposed as follows: (i) Co is rejected out of the Cu precipitate and sets up a barrier to the growth of the Cu precipitate; (ii) results in Cu precipitates of smaller size and narrower distribution; (iii) the coarsening of Cu precipitates is inhibited; and (iv) the activation energy for Cu precipitation increases"--Abstract, Page iv.
Van Aken, David C.
Lekakh, S. N. (Semen Naumovich)
Medvedeva, Julia E.
Materials Science and Engineering
Ph. D. in Materials Science and Engineering
Casting for Defense Readiness (CIDR)
Steel Founders' Society of America
Missouri University of Science and Technology
xiv, 135 pages
© 2012 Arpana Sudershan Murthy, All rights reserved.
Dissertation - Open Access
Strength of materials
Print OCLC #
Electronic OCLC #
Link to Catalog Record
Murthy, Arpana S., "Role of alloy additions on strengthening in 17-4 PH stainless steel" (2012). Doctoral Dissertations. 2253.