Microstructure and mechanical properties of two tool steels with ultrahigh boron content

[ES] En el presente trabajo se han modificado dos aceros para herramientas convencionales por la presencia de un contenido de boro entre 0,5 y 1 % en masa. Ambos aceros se procesaron por la ruta pulvimetalúrgica, incluyendo atomización por argón y compactación isostática en caliente. El material compactado presentó una microestructura caracterizada por una distribución de partículas de borocarburos M23(C,B)6 fma y homogénea en una matriz de ferrita-martensita. Esta microestructura permanece prácticamente inalterada tras los ensayos de cambios en la velocidad de deformación durante el ensayo de compresión a temperaturas entre 750 y 1.000 °C. En el caso del acero Fe-lB-lC se obtuvo un valor para el exponente de la tensión de 4,5, que sugiere que la deformación plástica está controlada por un mecanismo de fluencia por movimiento de dislocaciones. Por otro lado, para el acero Fe-0,5B-l,5C, se obtuvieron valores para el exponente de la tensión comprendidos entre 2 y 3, que sugieren que la deformación plástica está controlada por un mecanismo de deslizamiento de fronteras de granos. En ambos casos, se encontró un valor de la energía de activación para la deformación plástica que se asoció con la energía de autodifusión del hierro a través de la red.[EN] In the present work, two selected tool steels have been modified by a boron addition of 0.5 and 1 mass %. Both steels were processed by powder metallurgy methods, including argón atomization and hot isostatic pressing. The Consolidated materials presented a microstructure consisting of a fine and homogeneous distribution borocarbides M23(C,B)6 in a ferrite-martensite matrix. No changes are observed in the microstructure after deformation by compression-strain-rate-change tests at temperatures ranging from 700 to 1,100 °C. For the Fe-lB-lC steel, a stress exponent of 4.5 was obtained, that suggests that slip creep is the controlling deformation mechanism. On the other hand, a stress exponent between 2 and 3 was obtained for the Fe-0.5B~1.5C steel that suggests that grain boundary sliding is the controlling deformation mechanism. In both cases, the activation energy for creep was related to the activation energy for iron self-diffusion.Peer reviewe

Dual phase patterning during a congruent grain boundary phase transition in elemental copper

The phase behavior of grain boundaries can have a strong influence on interfacial properties. Little is known about the emergence of grain boundary phases in elemental metal systems and how they transform. Here, we observe the nanoscale patterning of a grain boundary by two alternating grain boundary phases with distinct atomic structures in elemental copper by atomic resolution imaging. The same grain boundary phases are found by computational grain boundary structure search indicating a first-order transformation. Finite temperature atomistic simulations reveal a congruent, diffusionless transition between these phases under ambient pressure. The patterning of the grain boundary at room temperature is dominated by the grain boundary phase junctions separating the phase segments. Our analysis suggests that the reduced mobility of the phase junctions at low temperatures kinetically limits the transformation, but repulsive elastic interactions between them and disconnections could additionally stabilize the pattern formation

Nano-Carbides and the Strength of Steels as Assessed by Electrical Resistivity Studies

The work of Frommeyer on electrical conductivity measurements in pearlitic steels is reviewed to provide insight into microstructures developed during wi wire drawing. Electrical re conductivity measurements were made as a function of drawing strain (up to {var_epsilon} = 6.0) for wires with strength exceeding 3500MPa. The results show that electrical conductivity increases during wire wire-drawing to a maximum value, then decreases with further deformation finally reaching a steady state value that is equal to the original conductivity. The initial increase is the result of pearlite plate orientation in the direction of wire wire-drawing, which makes the path of conduction through the ferrite plates more accessible. At a critical strain the cementite plates begin to fragment and the electrical conductivity decreases to a steady state value that is the same as that observed prior to wire drawing. With increasing strain, the cementite particles are refined and the strength increases due to the reduction in inter inter-particle spacing. It is concluded that the electrical conductivity of the wires is solely dependent on the amount of iron carbides provided they are randomly distributed as plates or as particles. An estimate was made that indicates the carbide particle size is approximately 3-5 nm in the steady state range of electrical conductivity

Relations between Japan and Korea : a diachronic survey in search of a pattern

Ever since Korea and Japan established kingdoms in the 6th century, both countries greatly influenced each other politically, militarily, socially, culturally, and economically through international exchange. Korea and Japan kept their close relationship throughout history because of geographic proximity. It is also notable that 54 per cent of Japanese males and 66 per cent of Japanese females carry Sino-Korean genes in present-days and there are records that Japan carried a close relationship with Paekche, a kingdom of the Korean peninsula which introduced script, Confucianism, and Buddhism to Japan at an early stage. In the Medieval Period, Korea and Japan maintained a friendly trade policy but there were incidents such as Mongol invasions, wakō (Japanese pirates) raids and two invasions by Toyotomi Hideyoshi, which worsened the relations between the two countries. And yet, during Japan’s period of isolation (from 1639 to1854), Korea was the only nation with which full and free trade was permitted. The 20th century is based on invasion and colonisation of Japan over Korea. For 35 years from 1910 to 1945, under the control of Japan, the Japan-Korea relationship was nothing but misfortune: forced labour, suppression of Korean culture and language, press-gangs, sex slaves, and so forth. The aim in this thesis is to go into greater detail about each significant event and its effect on the relationship between Japan and Korea to uncover some rationale or pattern such as gekokujō (the master being outdone by the pupil, and being treated thereafter with contempt)

Intraoperative Defibrillation Testing of Subcutaneous Implantable Cardioverter‐Defibrillator Systems—A Simple Issue?

Background: The results of the recently published randomized SIMPLE trial question the role of routine intraoperative defibrillation testing. However, testing is still recommended during implantation of the entirely subcutaneous implantable cardioverter‐defibrillator (S‐ICD) system. To address the question of whether defibrillation testing in S‐ICD systems is still necessary, we analyzed the data of a large, standard‐of‐care prospective single‐center S‐ICD registry. // Methods and Results: In the present study, 102 consecutive patients received an S‐ICD for primary (n=50) or secondary prevention (n=52). Defibrillation testing was performed in all except 4 patients. In 74 (75%; 95% CI 0.66–0.83) of 98 patients, ventricular fibrillation was effectively terminated by the first programmed internal shock. In 24 (25%; 95% CI 0.22–0.44) of 98 patients, the first internal shock was ineffective and further internal or external shock deliveries were required. In these patients, programming to reversed shock polarity (n=14) or repositioning of the sensing lead (n=1) or the pulse generator (n=5) led to successful defibrillation. In 4 patients, a safety margin of <10 J was not attained. Nevertheless, in these 4 patients, ventricular arrhythmias were effectively terminated with an internal 80‐J shock. // Conclusions: Although it has been shown that defibrillation testing is not necessary in transvenous ICD systems, it seems particular important for S‐ICD systems, because in nearly 25% of the cases the primary intraoperative test was not successful. In most cases, a successful defibrillation could be achieved by changing shock polarity or by optimizing the shock vector caused by the pulse generator or lead repositioning.<br

Відцентровий дезінтегратор з гідростатичною підвіскою розгінного ротора

Постановка проблеми. Стаття стосується випробовування відцентрового дезінтегратора ЦД-10 з гідростатичною підвіскою розгінного ротора. Мета. Введення у науковий обіг дослідницької інформації щодо результатів випробування дезінтегратора ЦД-10 для дроблення магнетитових руд, будівельних матеріалів і промислових відходів (пластин феритових магнітів). Методи і апаратура. Відцентровий дезінтегратор ЦД-10. Результати. Розроблена вітчизняна конструкція дезінтегратора відцентрового типу з гідростатичною підвіскою розгінного ротора. Проведені випробування дезінтегратора підтвердили його достатню працездатність і надійність та можливість отримання необ-хідних технологічних показників. Наукова цінність розробки. Випробувано інноваційну конструкцію відцентрованого дезінтегратора, особливістю якого є гідростатичний вузол підвіски ротора, який дозволяє зменшити дисбаланс ротора і вібраційні навантаження. Практичне значення. Встановлено високу ефективність застосування розробленої конструкції дезінтегратора ЦД-10 для дроблення магнетитових руд, будівельних матеріалів і промислових відходів. Науково-технічні розробки по гідростатичній підвісці розгінного ротора реалізовані при для дезінтегратора продуктивністю 5-10 т/год.Formulation of the problem. The article concerns the test of a centrifugal disintegrator СD-10 with hydrostatic suspension of an accelerating rotor. Goal. Introduction into scientific circulation of research information on the results of testing the СD-10 disintegrator for crushing ores, building materials and industrial waste (ferrite magnet plates). Methods and equipment. Centrifugal disintegrator CD-10. Results. A domestic design of a centrifugal disintegrator with a hydrostatic suspension of an accelerating rotor has been developed. The tests of the disintegrator confirmed its sufficient performance and reliability and the ability to obtain the necessary technological indicators. Scientific value of development. The innovative design of the centrifugal disintegrator is tested, the feature of which is the hydrostatic rotor suspension assembly. Such a unit that allows you to reduce the imbalance of the rotor and vibration loads. Practical value. The high efficiency of using the developed design of the CD-10 disintegrator for crushing ores, building materials and industrial waste has been established. Scientific and tech-nical developments on the hydrostatic suspension of an accelerating rotor are implemented for a disintegrator with a productivity of 5-10 t/h

Plastic localization phenomena in a Mn-alloyed austenitic steel

A 0.5 wt pct C, 22 wt pct Mn austenitic steel, recently proposed for fabricating automotive body structures by cold sheet forming, exhibits plastic localizations (PLs) during uniaxial tensile tests, yet showing a favorable overall strength and ductility. No localization happens during biaxial Erichsen cupping tests. Full-thickness tensile and Erichsen specimens, cut from as-produced steel sheets, were polished and tested at different strain rates. During the tensile tests, the PL phenomena consist first of macroscopic deformation bands traveling along the tensile axis, and then of a series of successive stationary deformation bands, each adjacent to the preceding ones; both types of bands involve the full specimen width and yield a macroscopically observable surface relief. No comparable surface relief was observed during the standard Erichsen tests. Because the stress state is known to influence PL phenomena, reduced-width Erichsen tests were performed on polished sheet specimens, in order to explore the transition from biaxial to uniaxial loading; surface relief lines were observed on a 20-mm-wide specimen, but not on wider ones