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An Investigation into the Hot Tensile Properties of a Heat Resistant Steel

Mohammad Karimi, Sanaz | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47017 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic heat-resistant steel was investigated using hot tensile tests over the range of 650- 950‘C temperature and 0. 001 – 0.1 s-l strain rate. The microstructure and precipitation of carbides and the fracture surfaces of the tensile specimens were exmined using the optical and electron microscopy. The results indicate that at temperatures of 650 and 750 °C and strain rate 0.01 s-l dynamic strain aging occurs.Thermal resistance of the alloy was high in temperature rang of about 600-800 °C. All three strain rates At 950°C The stress - strain curve reaches a steady state, hence, it was concluded that at this temperature and the appropriate strain rates the softening mechanisms including dynamic recovery occurs in the alloy. Finally based on these experimental results, an artificial neural network model (Levenberg - Marquardt( is developed to predict the constitutive flow behaviors of the steel during hot deformation. Also constitutive equation was presented the relationship between temperature, strain rate and stress. Consequently, the constitutive equation of steel at high temperatures corresponded with a good approximation of the hyperbolic sinus equation and the activation energy was calculated about 440 kJ / mol
  9. Keywords:
  10. Neural Network ; Stainless Steel ; Hot Tension ; Tensile Test ; Heat Resistant Steel ; Constitutive Equations

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