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Iron and steel society of Iran - Volume:3 Issue: 1, Winter and Spring 2006

International Journal of iron and steel society of Iran
Volume:3 Issue: 1, Winter and Spring 2006

  • تاریخ انتشار: 1385/10/28
  • تعداد عناوین: 6
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  • A. Najafizadeh, J. J. Jonas Page 1
    Experiments were carried out in which the depend ence of the fractional softening on temperature, time and strain rate was determined in a 304H stainless steel. Three prestrain ranges were identified pertaining to three different post-deformation softening behaviors: 1) prestraining to below the DRX critical strain: strongly strain dependent softening by SRX alo ne with so ftening kinetics controlled by gro wth rate of the nuclei;2) prestraining to above the DRX critical strain: SRX + MDRX softening with weaker strain dependence of the kinetics but still controlled by grain gro wth; 3) at a prestrain of * and beyond: nucleation-controlled MDRX softening with the full inhibition of SRX. The transition prestrain * can exceed the peak strain if the DRX grain refinementratio g= D0/DD RX > 4. The transition to MDRX-dominated softening can be attributed to a constant value of the normalized strain hardening rate independent of the preloading temperature and strain rate. The softening data fro m the compression tests show that at *, the time for half softening t5 0 exhibits a minimum. These data differ somewhat from observations obtained in the torsion testing of solid bars, in which no strain dependence of t5 0 was detected at * and beyond. Whether or not the strain dependence of t5 0 vanishes in the MDRX range is sensitive to the test method emplo yed to study the post-deformation softening.
  • A. Shokuhfar, S. M. Abbasi, N. Ehsani Page 8
    Dynamic recrystallization, DRX, behaviour of a precipitation hardened, PH, stainless steel was studied in connection with microstructural develo pments in a compression test. The experimental results showed that the dominant mechanism of softening is DRX, but at high strain rates and low temperatures, ie, high Zener-Holman parameter, Z, work hardening and dynamic recovery, DRV, produced a pancked structure. When Z values decreased, the flow curves displayed DRX in two ways: sing le peak behav ior observed at low Z values and multiple peak behavior at the lowest ones. In addition, the peak strain, p, necessary for DRX is also determined as a function of peak stress, p, and Z. According to the o bserved and calculated data, at lo w p values, p is directly proportional to p, while in higher amounts, p rarely depends on it. Besides, p expotenentially depends on Z.
  • Page 13
    Modern vehicle bodies make intensive use of high strength steel grades to meet the contradicting demand of lighter weight and simultaneously better mechanical performance. For many steel grad es microalloying by niobium is the key to achieve their characteristic property profile. In HSLA steels niobium enhances the strength primarily by grain refinement. In interstitial free high strength steels niob ium serves as a stabilizing element. So me modern multiphase steels rely on niobium to achieve additional strength via grain refinement and precipitatio n hardening. Microstructural con trol constitutes a powerful means to further optimize properties relevant to automotive processing such as cutting and forming. The role of niobium microalloying in that respect will be outlined.
  • B. Fange., H. Han, M. Elboujdaini, W. Zheng, J. Li, R. W. Revie Page 20
    Stress-co rrosion cracking (SCC) tests were conducted in the near-neutral pH standard solution, NS4, and in an actual soil solutio n, using four-point bending at a high stress ratio and low frequency conditions very similar to those o f op erational pipelines. Pitting incubation appeared first and then pitting initiated and grew in both solutions although there were many more pits on the specimen tested in soil purged with 5% CO2 +95 %N2 than in the specimen tested in NS4 solution purged with the same gas. These observations sho w that samples in soil solution are more susceptible to pitting than those in NS4 solution. When the pit reached a critical size, the increased stress concentration around the pits, resulted in transition to a crack.
  • A. Saboonchi, N. Mansouri Page 26
    Transfer tab le is an essential stage between roug hing and finishing rolling stands in a hot strip ro lling mill. High temperature and long time that strip is exposed to air at this stage cause a considerable heat loss that accounts for uneven temperature distribution, non-uniform surfaces, reduced product quality and increased production costs. Using thermal shields on the transfer table is considered an efficient means of reducin g energy consumption and of improving product quality. In this p aper, temperature distribution and heat loss from the strip is investigated while passing through transfer table in the hot-rolling at Mo barakeh Steel Complex (MSC), Isfahan, Iran. Three cases are considered; namely, in the absence of thermal shield, in the presence of thermal shield, and with both thermal shield and heat source. The results obtained from the numerical solution indicate that the case with both thermal shield and heat source on the transfer table has the mo st favorable effect on reducing heat losses and even temperature distribution in the strip.
  • M. Adjabshiri, S. Sharafi Page 33
    Master moulds are used to cast copper anod e moulds. These iron moulds are made of grey or nodular cast irons. According to desirab le properties of ductile irons, it was expected that ductile cast iron moulds could have performed their nominal life. But in service, these moulds have not performed their nominal life and they have experienced premature failures due to warping and cracking. Also grey cast iron moulds fail because of generalized surface cracks. In this p aper, the failure of master moulds is investigated according to the metallographic and hardness measurement tests. Then pearlitic and austempered ductile iron alloys are proposed and tested through sho rt time high temperature tensile and thermal shock tests with respect to working conditions of the moulds. Also master mo uld is modeled by Finite Element Method to evaluate the thermal conditions. Finally it is concluded that compared with pearlitic ductile iron, austemp ered ductile iron has higher resistance to thermal shock