Optimization of Electric-Pulse Consolidation Regimes to Obtain High-Density Dispersion-Hardened Reactor Steel

Abstract

Research on the development of EP-450 high-density, Y 2 O 3 -oxide dispersion-hardened, reactor ferritemartensite steel is described. All available parameters infl uencing the fi nal density of the compacts were varied in the course of the preparation of the powders and electric-pulse consolidation. The research established that samples with density equal to 99% of the theoretical value can be obtained for the following optimized mechanical activation and electric-pulse consolidation parameters: mechanical alloying time 30 h, optimal Y 2 O 3 amount 0.2-0.5 wt.%, sintering temperature 825-890°C, climb rate to the prescribed temperature >300°C/min, load 70-80 MPa, holding time at the load -without isothermal holding or holding for ≥3 min.Intense research and development work has been conducted in the last few decades on chromium steel because the swelling of such steel is signifi cantly smaller than that of austenitic steel. The main drawback of chromium steel is low high-temperature strength under operating conditions in the core of a fast reactor. The aim of this research is to develop oxide dispersion-hardened chromium steel [1-6], since its mechanical properties and high-temperature strength are better than those of the conventionally used steel [1,4,5]. The main method of producing such steel is powder metallurgy and the commonly used methods of powder consolidation (in decreasing order) -hot extrusion, hot isostatic pressing, and the electric-pulse method [7][8][9][10][11].Two basic problems must be solved in order to produce oxide-dispersion-hardened steel: obtaining a uniform volumetric distribution of hardening nanoparticles and obtaining high-density compacts. This can be accomplished in two basic ways: optimization of the mechanical alloying regime (time, mill rotation speed, and avoidance of overheating of the powder) and optimization of the electric pulse consolidation regimes. The dispersity of the oxide particles has been studied previously and it has been shown that even during mechanical alloying the Y 2 O 3 particles are quite uniformly distributed in the powder within 15 h [10] and they are uniformly distributed in the volume of the sample during grinding in optimized regimes [11].The aim of the present work is to determine the regularities of the structure formation in dispersion-hardened reactor ferrite-martensite steel depending on the electric pulse consolidation regimes.Materials and Procedure. Reactor ferrite-martensite steel EP-450 (12Kh13M2BFR) in the form of brittle fl akes was fi rst ground for 2 h in a MTI SFM-1 (USA) planetary mill and then mixed with yttrium oxide powder followed by alloying conducted in an optimized regime in a Pulverizette-5 (Germany) planetary ball mill (argon atmosphere) [11]. The basic parameters of the process were varied in order to obtain blanks with the maximum density: grinding time 30, 40, and 50 h;

Automatic Distributed Control Method for Indoor Low-Voltage Electricity Based on Modal Symmetry Algorithm

“…With the interconnection of cross-regional power grids and constraints from economy and technology, in order to make the full use of existing system resources, power grids are often forced to operate near the critical point, and the voltage stability margin is very low, which increases the probability of power accidents such as voltage collapse [10][11][12]. In order to ensure voltage quality and reactive power balance, and realize the optimal coordination between voltage stability and reactive power optimization, the automatic distributed control of indoor low-voltage electricity system has become an important measure [13,14]. At present, the relevant researchers have studied the lowvoltage electricity control method and achieved some research results.…”