Energy Saving Melting and Revert Reduction Technology (Energy SMARRT): Development of CCT Diagrams
One of the most energy intensive industries in the U.S. today is in the melting and casting of steel alloys for use in our advanced technological society. While the majority of steel castings involve low or mild carbon steel for common construction materials, highly-alloyed steels constitute a critical component of many industries due to their excellent properties. However, as the amount of alloying additions increases, the problems associated with casting these materials also increases, resulting in a large waste of energy due to inefficiency and a lack of basic information concerning these often complicated alloy systems. Superaustenitic stainless steels constitute a group of Fe-based alloys that are compositionally balanced to have a purely austenitic matrix and exhibit favorable pitting and crevice corrosion resistant properties and mechanical strength. However, intermetallic precipitates such as sigma (³) and Laves can form during casting or exposure to high-temperature processing, which degrade the corrosion and mechanical properties of the material. Knowledge of the times and temperatures at which these detrimental phases form is imperative if a company is to efficiently produce castings of high quality in the minimum amount of time, using the lowest amount of energy possible, while producing the least amount of material waste. Anecdotal evidence from company representatives revealed that large castings frequently had to be scrapped due to either lower than expected corrosion resistance or extremely low fracture toughness. It was suspected that these poor corrosion and / or mechanical properties were directly related to the type, amount, and location of various intermetallic phases that formed during either the cooling cycle of the castings or subsequent heat treatments. However, no reliable data existed concerning either the time-temperature-transformation (TTT) diagrams or the continuous-cooling-transformation (CCT) diagrams of the super-austenitics. The goal of this study was to accurately characterize the solid-solid phase transformations seen in cast superaustenitic stainless steels. Heat treatments were performed to understand the time and temperature ranges for intermetallic phase formations in alloys CN3MN and CK3McuN. Microstructures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy and wavelength dispersive spectroscopy (EDS, WDS). In this way TTT and CCT diagrams could be developed for the matrix of samples chosen. As this study consisted of basic research into the development of TTT and CCT diagrams as an aid to the US steel casting industry, there is no formal commercialization plan associated with this task other than presentations and publications via the Steel Founders Society of America to their members. The author is confident that the data contained in this report can be used by steel foundries to refine their casting procedures in such a way as to reduce the amount of waste produced and energy wasted by significantly reducing or eliminating the need for remelting or recasting of material due to unwanted, premature intermetallic formation. This development of high alloy steel CCT diagrams was predicted to result in an average energy savings of 0.05 trillion BTU's/year over a 10 year period (with full funding). With 65% of the proposed funding, current (2011) annual energy saving estimates, based on initial dissemination to the casting industry in 2011and market penetration of 97% by 2020, is 0.14 trillion BTU's/year. The reduction of scrap and improvement in casting yield will also result in a reduction of environmental emissions associated with the melting and pouring of the steel. The average annual estimate of CO2 reduction per year through 2020 is 0.003 Million Metric Tons of Carbon Equivalent (MM TCE)
- Research Organization:
- Advanced Technology Institute
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Office of Technology Development (EE-20)
- DOE Contract Number:
- FC36-04GO14230
- OSTI ID:
- 1022742
- Report Number(s):
- NA; TRN: US201118%%831
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALLOY SYSTEMS
ALLOYS
CARBON STEELS
CASTING
CASTINGS
CORROSION
CORROSION RESISTANCE
CREVICE CORROSION
FRACTURE PROPERTIES
HEAT TREATMENTS
HIGH ALLOY STEELS
MECHANICAL PROPERTIES
MELTING
PHASE TRANSFORMATIONS
SCANNING ELECTRON MICROSCOPY
STAINLESS STEELS
STEELS
TRANSMISSION ELECTRON MICROSCOPY
Casting
metalcasting
steel casting
manufacturing
CCT diagrams