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Development of Mechanical Properties of 420 AISI Martensitic Stainless Steel Using the Age Hardening Nano Precipitates and ANN Analysis

Azarnoush, Mohammad | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43360 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. The Austenitization, influence of ageing condition and the prediction kinetics of AISI 420 martensitic stainless steel were studied in this paper. The Austenitizing temperature of 9200C, 9500C and 10200C were achieved. The specimens were heated for 15, 30 and 60 minutes then quenched in 250C Oil. The cooled samples were tempered at 2000C for 1 hour. The maximum tensile strength obtained at 10200C and 60 minutes were about 1800 MPa. The effect and ageing temperature and time on the strengthening behavior of this steel was modeled and analyzed by shear punch test and means of artificial neural networks (ANNs). Johnson-Mehl-Avrami-Kolmogorov (JMAK) analyses were applied to characterize the precipitation kinetics of this martensitic age hardenable alloy. Moreover, the hardening, overaging, and softening behaviors in accordance to ageing reactions (precipitation and coarsening of Cr, recovery, and reversion of martensite to austenite) were determined from this ANN model. Time exponents (0.43) were within the range reported for maraging steels. Also, precipitation rate showed an exponential dependence on aging temperature. The activation energy for precipitation reaction was determined as 219.89 KJmol-1 which is consistent with the activation energy for diffusion of chromium in ferrite. Furthermore, the microstructure of the steel at optimum ageing process corroborates the precipitation of chromium carbide with nanometer size.

  9. Keywords:
  10. Age Hardening ; Shear Punch Test ; Artificial Neural Network ; Artificial Intelligence ; Ageing Kinetics ; Nanoprecipitation

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