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Washington, MI, United States

Tung D.J.,Ohio State University | Lolla T.,Ohio State University | Babu S.S.,University of Tennessee at Knoxville | Cola Jr. G.M.,SFP Works
Advanced Materials and Processes | Year: 2013

The article discusses the specifics of flash processing, microstructural evolution during processing, the industrial impact of flash processed materials, and ongoing research to further extend the capabilities of FP steels. Flash processing is an extremely rapid heat treatment with a total process time of less than 10 seconds. A low-temperature, short-duration tempering treatment is often used to increase ductility. The process produces a well controlled, mixed microstructure consisting of martensite, bainite, and carbides. Flash-processed microstructures depend on the initial microstructure and nonequilibrium conditions resulting from high heating rates, short hold times, and high cooling rates. Due to the carbon concentration gradients, regions of high carbon undergo a martensitic transformation, while regions of low carbon undergo a bainitic transformation. Martensite is the primary strengthening constituent and bainite provides ductility, resulting in a balance of strength and ductility unique to flash processing.


Hanhold B.,Ohio State University | Hanhold B.,Ford Motor Company | Babu S.S.,Ohio State University | Cola G.,SFP Works
Science and Technology of Welding and Joining | Year: 2013

Flash processed (FP) steels have shown potential for armour applications based on the response to ballistic loading. In this research, weldability of these steels was studied and compared to commercial high hard (HH) armour steel. Simulated heat affected zone (HAZ) microstructures in these steels were investigated by comprehensive microscopy and hardness mapping. HAZ softening in HH steel was observed on heating to a peak temperature below Ac1 due to overtempering of original microstructure. In FP steel, the softening was associated with allotriomorphic ferrite formation when heated to a peak temperature between Ac1 and Ac3. The transformation kinetics, softening, and hardening characteristics are rationalised based on changes in prior austenite grain size, cooling rate and underlying chemical heterogeneity. © 2013 Institute of Materials, Minerals and Mining.


Hanhold B.,Ford Motor Company | Babu S.S.,Ohio State University | Cola G.,SFP Works
Science and Technology of Welding and Joining | Year: 2013

Heat affected zone (HAZ) softening in two armour steels (high hard and flash processed) was investigated by monitoring phase transformations during simulated welding thermal cycles. The high hard steel was produced by conventional thermomechanical processing followed by quench and tempering. Flash processed steel was produced by rapid heating and cooling of a spheroidised steel to produce a mixed microstructure. Heat affected zone softening in high hard steel was observed on heating to a peak temperature below Ac1 due to overtempering of the original microstructure. In flash processed steel, the softening was associated with allotriomorphic ferrite formation when heated to a peak temperature between Ac1 and Ac3. The above results demonstrate the importance of initial microstructure on HAZ on phase transformation transients and associated softening in armour steels. © 2013 Institute of Materials, Minerals and Mining.


Cola Jr. G.M.,SFP Works | Hanhold B.,Ford Motor Company | Lolla T.,Ohio State University | Radhakrishnan B.,Oak Ridge National Laboratory | Babu S.,Ohio State University
Iron and Steel Technology | Year: 2013

Conversion equations were employed to compare tensile elongations of various advanced high-strength steels (AHSS), which were tested with different sample geometries. Researchers were cautioned in using conversion equations for comparing total elongation of AHSS, which were processed by different routes with strengths greater than 1,000 MPa. Many researchers also realized that the sample gauge length and cross-sectional area of tensile test samples potentially had an effect on the total elongation of the sample. The need for a standard specimen for comparing the different steels was recognized, as researchers used different specimen geometries for testing of their advanced high-strength steels. Some researchers also proposed a methodology to convert the measured total elongation from tensile tests with differing sample sizes using the Oliver equation.


Lolla T.,Ohio State University | Cola G.,SFP Works | Narayanan B.,Ohio State University | Alexandrov B.,Ohio State University | Babu S.S.,Ohio State University
Materials Science and Technology | Year: 2011

Flash processing of an AISI8620 steel sheet, which involves rapid heating and cooling with an overall process duration of<10 s, produced a steel microstructure with a high tensile strength and good ductility similar to that of advanced high strength steels. Flash processed steel [ultimate tensile strength (UTS): 1694 MPa, elongation: 7·1%], showed at least 7% higher UTS and 30% greater elongation than published results on martensitic advanced high strength steel (UTS: 1585 MPa, elongation: 5·1%). The underlying microstructure was characterised with optical, scanning electron, transmission electron microscopy as well as hardness mapping. A complex distribution of bainitic and martensite microstructures with carbides was observed. A mechanism for the above microstructure evolution is proposed. © 2011 Institute of Materials, Minerals and Mining.

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