Materials Week '97: Tuesday PM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Tuesday afternoon, September 16.

PROCESS MODELING IN THE HIGH TEMPERATURE MATERIALS INDUSTRY: Session II

Session Chair: Carlos Ruiz, Allied Signal Aerospace, 1130 W. Warner Road, Tempe, AZ 85284

APPLICATION OF PROCESS MODELING TO AIRCRAFT ENGINE FORGINGS: Shesh K. Srivatsa, GE Aircraft Engines, Mail Drop M87, 1 Neumann Way, Cincinnati, OH 45215

This paper will describe the application of process modeling to the forging of critical aircraft engine rotating components. With parts getting larger in size and processing windows for new materials getting tighter, process modeling is a key tool in making new parts in a cost and time effective manner with improved quality and satisfactory properties. Today process modeling for forged components is a production tool and an up-front requirement and a key factor in "making right the first time" parts of size/shape/materials for which there is no prior experience. Generation of modeling inputs (i.e., material property data and boundary conditions) and validation of outputs will also be discussed. Without realistic inputs and validated outputs, the full potential of modeling cannot be realized.

2:30 pm

HOT WORKABILITY OF ALLOY C-276: G.T. Velarde¹, C.J. Van Tyne², Y-W Cheng³, F.S. Suarez⁴, ¹Kaiser Aluminum, Spokane, WA, ²Advanced Steel Processing and Products Research Center, Colorado School of Mines, Golden, CO 80401, ³NIST, Boulder, CO, ⁴INCO Alloys International, Huntington, WV

Alloy C-276, a nickel-based superalloy used primarily in flue-gas desulfurization scrubbers, has at times exhibited diminished ductility and surface cracking during hot rolling. Hot workability of Alloy C-276 was investigated by hot-compression testing on a Gleeble 1500. The as-received material exhibited extremely high workability at temperatures above 870°C. Below this temperature, recovery and recrystallization were sluggish, causing lower workability. In order to simulate more accurately the conditions of the commercial hot rolling operation, heat treatments in an oxidizing atmosphere were also used to control both surface condition and grain size prior to compression testing. The resulting ductility was lower than in the as-received material for all strain rates and temperatures tested. Surface oxides were observed to promote cracking by providing a brittle initiation site. Large grain size as well as segregation of residual elements to grain boundaries probably also enhanced cracking. A ductility trough was detected in the test temperature range from 925°C to 1040°C. A possible linkage between this trough and the precipitation of P-phase carbides is postulated. This work was conducted at the Advanced Steel Processing and Products Research Center, an NSF sponsored industry-university cooperative research center, at Colorado School of Mines.

3:00 pm

APPLICATIONS OF MODELING TO HOT DEFORMATION PROCESSES AT ALLVAC: Ramesh S. Minisandram, Laurence A. Jackman, Robin M. Forbes Jones, Chris OíBrien, Allvac-An Allegheny Teledyne Company, P.O. Box 5030, Monroe, NC 28110-0530

Process modeling at Allvac encompasses melting and solidification processes (VAR, ESR, PCHM) and hot deformation processes such as open die press forging, radial forging and rolling. Following a brief overview of these activities, specific applications of radial forging and rolling simulations will be provided. Improvements in computer technology have greatly extended modeling capabilities; however, limitations still prevail because of insufficient material property information and the inability to predict metallurgical features such as segregation during solidification and microstructures developed during hot deformation. Cooperative efforts with various research organizations are under way to address these issues.

3:30 pm

PROCESS MODLES: TOOLS FOR KNOWLEDGEABLE PROCESSES ENGINEERS AND METALLURGISTS: R.A. Jaramillo, D. Lambert, S.J. Patel, Inco Alloys International, 3200 Riverside Drive, Huntington, WV 25705-1771

A philosophy for developing and implementing relevant process models is presented along with current endeavors in process modelling. The recent advances in computational ability brought about by developing computer technologies is making process modelling a viable method for enhancing process control in industry. However, the investment in time and resources required to procure and develop accurate process models is significant. Issues regarding material properties, boundary conditions, numerical methods, hardware, etc. expand the expertise required to develop process models. Identifying the needs of process engineers and metallurgists as a foremost priority, a methodology for efficiently employing process models evolves. Also, current efforts in development and use of process models at Inco Alloys International is presented.

4:00 pm

DEFORMATION PROCESSING OF OXIDE-DISPERSION-STRENGTHENED SUPERALLOYS PRIOR TO RECRYSTALLIZATION: Marvin McKimpson, Institute of Materials Processing, Michigan Technological University, Houghton, MI 49931

Wrought oxide dispersion strengthened superalloys provide an attractive combination of creep and thermal fatigue resistance for very high temperature service. To develop these properties, however, the material must undergo secondary recrystallization to produce a characteristic coarse, elongated grain structure. Successful recrystallization is critically dependent on prior deformation processing of the material. Despite numerous empirical studies, the requirements for this prior deformation processing are not well understood and cannot be modeled effectively. In this presentation, prior empirical processing studies will be reviewed and a possible microstructure-based modeling approach will be proposed for selecting the deformation processing parameters required to develop a microstructure suitable for secondary recrystallization.

4:30 pm

FEEDBACK CONTROL OF MICROSTRUCTURE DEVELOPMENT DURING HOT FORGING: W. Garth Frazier, W.M. Mullins, R. Dennis Irwin, Enrique A. Medina, James C. Malas, Materials Process Design, Materials Directorate, WL/MLIM, Building 653, Wright-Patterson Air Force Base, OH 45433-7746

The advantages of using real-time feedback for the control of applied stress, strain and strain rate during a hot forging operation are investigated. At present, state of the art design for most commercial hot metal forming processes is limited to the use of open loop control. Limitations in model fidelity, however, always affect the performance these open loop control systems. By assuming that reliable sensors are available, this work evaluates the advantages of using real time feedback in a forging process. A high fidelity simulation of a system that includes dynamics of the forging press, workpiece loading, and microstructure evolution is developed. By using real-time measurements of applied stress, strain and strain rate, a closed loop control system for forging processes can modify parameters such as ram velocity and temperature in order to achieve desired deformation paths. Results of closed loop simulations are compared to those of existing open loop design approaches and recommendations are made.

5:00 pm

FINITE ELEMENT ANALYSIS OF RESIDUAL STRESSES IN ELECTROSLAG BUTT WELDS: Leilei Zhang and David Atteridge, Oregon Graduate Institute of Science and Technology, Department of Materials Science and Engineering, P.O. Box 91000, Portland, OR 97291-1000

Electroslag welding is a potentially attractive process for joining thick plates such as those used in constructing ships, storage tanks, pressure vessels, bridges, buildings and other heavy structures. However, concerns about low fracture toughness of the resulting weld have limited the use of the process for some thick-plate applications. Fracture mechanics analyses have generally assumed that the weld-induced tensile stress field is of yield strength magnitude. This assumption greatly reduces the allowable flaw size, and frequently results in allowable flaw sizes smaller than those which can be reliably detected by standard non-destructive testing techniques. In this paper, a computational model is developed to more accurately calculate the magnitude and distribution of residual stresses for electroslag welding of plates. The model consists of two parts, a temperature analysis model and thermal stress model. Elastic-plastic temperature dependent mechanical properties are included in this model. Based on these calculations, critical flaw sizes are reevaluated.