Microsegregation behavior during solidification and homogenization of AerMet100 steel
- PDF / 536,454 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 51 Downloads / 260 Views
I.
INTRODUCTION/BACKGROUND
AERMET100* is a commercial high-alloy steel produced in wrought forms by Carpenter Technology, Inc. for applications requiring a combination of high strength, high fracture toughness, and resistance to stress-corrosion cracking.[1] The nominal composition is (wt pct) 13.4 pct Co, 11.1 pct Ni, 3.1 pct Cr, 1.2 pct Mo, 0.23 pct C, and the balance Fe. Standard mechanical property specifications for the wrought alloy are 2065 MPa UTS, 1860 MPa YS, and 132 MPa=m KIC. The alloy is produced by vacuum-induction melting (VIM) and vacuum-arc remelting (VAR) to ensure the very low impurity levels necessary to achieve the property specifications. The possibility of industrial applications using cast AerMet100 was sparked by the remarkably high mechanical properties obtained from VIM quality-control test ingots prior to VAR processing. Strength and toughness properties of the homogenized and tempered VIM castings were found to be equal or superior to the wrought properties of the high-strength steels Marage 250, 300M, H11, and 4340.[2] This investigation explored the applicability of using thermodynamic/kinetic modeling software to predict microsegregation of the as-cast material and the optimal homogenization treatment to eliminate microsegregation. Most of the previous work[3–13] in the field of compositional analysis and, particularly, in the modeling of microsegregation has been limited to ternary and a few quaternary systems. Recent studies have included six or more elements by thermodynamic modeling of superalloys.[14] The software used for this investigation was able to model fully the effects of the six major constituents of this commercial alloy on microsegregation. Macrosegregation was not included in the computer simulation models. To predict the microsegregation in a multicomponent alH.E. LIPPARD, C.E. CAMPBELL, Graduate Students, V.P. DRAVID, and G.B. OLSON, Professors, are with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208. ¨ RKLIND, U. BORGGREN, and P. KELLGREN, Students, are with T. BJO the Division of Computational Thermodynamics, Royal Institute of Technology, Stockholm, Sweden S-100 44. Manuscript submitted January 22, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
loy requires both multicomponent thermodynamic phase descriptions and diffusion coefficients. The SGTE[15] database, as implemented in the Thermo-Calc**[16,17] program (version K), uses the CALPHAD method to extrapolate thermodynamic descriptions for use in an n-component system based on the assessment of binary and available ternary and quaternary experimental data. The thermodynamics of the liquid phase are described by a regular solution model and the solid phases by the sublattice model.[18] The phase equilibria are calculated by a free-energy minimization determined by a Newton–Raphson technique. The CALPHAD method has been extended by Jo¨nsson[19] to the assessment of concentration-dependent diffusion coefficients in multicomponent alloys and is implemented in th
Data Loading...
