Effect of microadditions on the structure and properties of powder carbon steel

Dyachkova, L. N.; Glukhova, N. P.; Zvonarev, E. V.; Samal, G. I.

doi:10.1007/bf00775040

Cited by 5 publications

(1 citation statement)

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“…Активирование диффузионных процессов при спекании порошковых углеродистых сталей возможно также за счет введения либо углерода в виде активной углеродсодержащей добавки [10], либо добавок, вызывающих окислительно-восстановительные реакции, в результате которых образуется атомарный углерод, активно диффундирующий в железную основу.…”

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Features of the formation of the structure and properties of powder steels with additives that activate diffusion processes during sintering

Dyachkova

2020

Vescì Akademìì navuk Belarusì. Seryâ fizika-tehničnyh navuk

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Effect of activating the sintering process of powder steel alloyed with nickel or chromium by grinding the initial powders and introducing alkali metal compounds was investigated. The kinetics of grinding the initial iron powders, Cr30, and a mixture of iron powders with 4 % nickel was studied. It is shown that, depending on the hardness of the powder, it is grinded in three or two stages. When grinding more hard powders, there is no stage of intensive deformation of particles and an increase in their size. Crystalline lattice defects resulting from grinding of powders accelerate diffusion processes. This reduces sintering temperature by 100–200 °С compared to the sintering temperature of steels from the initial powders, contributes to a homogeneous structure, reduces porosity by 4–17 %, and increase strength of powder steels by 1.5–1.6 times. The mechanism of the effect of sodium bicarbonate on the acceleration of diffusion of carbon, nickel and chromium into iron has been established. With the introduction of sodium bicarbonate under the action of water vapor, formed upon its decomposition to carbonate, thin oxide films are formed on iron particles, which are actively recovered in a protective-recovering atmosphere during sintering. This leads to formation of a metal contact between the particles, acceleration of the self-diffusion of iron atoms and the diffusion of alloying additives into iron by 5–7 times, depending on the sintering temperature and the amount of added additive. Sodium forms nanodispersed complex compounds of the ferritic type Na3Fe5O9 along the grain boundaries of the iron base, which provide grain refinement and the formation of a homogeneous structure. Changes in the structure of powder steel with the introduction of sodium bicarbonate cause an increase in its strength by 1.5–1.7 times. The results can be used to obtain structural products from alloyed powder steels.

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Features of the formation of the structure and properties of powder steels with additives that activate diffusion processes during sintering

Dyachkova

2020

Vescì Akademìì navuk Belarusì. Seryâ fizika-tehničnyh navuk

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Rolling contact fatigue of hot-deformed powder steels with calcium microadditives

Dorofeyev

Свиридова

Berezhnoy

et al. 2019

IOP Conf. Ser.: Mater. Sci. Eng.

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Fatigue damage of the surface layers of metal is a characteristic cause of failure of rolling bearings, gears and a number of other machine parts operating under cyclically repeated contact loads. Resistivity to the development of contact damage of steels obtained by hot forging porous blanks is determined by the presence of cohesive bonds between the particles of the base powder, as well as by the presence of non-metallic inclusions and grain size. The possibility of increasing the contact endurance of hot-deformed powder steels due to micro-doping with calcium has been studied. Iron powders with various content of impurities, as well as atomized powder of low-alloyed chromium-molybdenum steel were used as the basis for preparation of the blends. Calcium was doped as calcium carbonate. Mixing was performed in a planetary centrifugal mill. Samples for mechanical testing were obtained by hot forging porous blanks. After hot forging the samples were carburized to compensate for the loss of carbon in the surface layer. It has been established that doping calcium microadditives is favourable for increasing the energy content of damage under the conditions of exposure to contact-fatigue and bending loads. This is due to a decrease in the size of austenite grains at the expense of inhibition of their growth during the adsorption of calcium at the grain boundaries. Microalloying with calcium changes the localization of seats of contact fatigue damage. In samples-witnesses without microadditives of calcium cracks originate near non-metallic inclusions of sharp-angled shape in the near-surface zone. In microalloyed specimens the cracks are located in the subsurface layer in the area of Hertz maximum shear stresses.

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Formation of structure and properties of hot-deformed powder steels microalloyed with sodium and calcium during thermal and thermomechanical treatment

Дорофеев¹,

Свиридова²,

Samoilov³

2021

Izv. VUZ. Poroshk. Met.

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One of the main problems limiting further growth in the production of parts by the hot forging of porous performs (HFPP) is that the obtained materials are prone to brittle fracture due to the poor quality of interparticle jointing formed during hot deformation, as well as the presence of impurities in the composition of initial powders. The paper studies the possibility of increasing the mechanical properties and endurance performance of hot-deformed powder steels by doping them with sodium or calcium microadditives and using thermomechanical treatment. Sodium bicarbonate and calcium carbonate were used for microalloying. Carbon was added as pencil graphite powder. The temperature of heating porous preforms before hot forging and the carbon content in steels were varied; the content of microalloying additives was, wt.%: 0.2 for sodium, and 0.3 for calcium. Mechanical properties as well as contact and low-cycle fatigue life were tested on 5 × 10 × 55 mm and 10 × 10 × 55 mm prismatic specimens, as well as ∅ 26 × 6 mm cylindrical specimens. In comparison with carburizing and thermal treatment, thermomechanical treatment improves the impact strength and endurance performance of hot-deformed powder steels with Na or Ca microadditives under the contact and low-cycle fatigue loading, and the hot repressing temperature of porous preforms is reduced without compromising the mechanical properties of powder steels obtained. It may be associated with the formation of a more fine-grained structure and higher microstresses of the crystal lattice. The cooling down of preform surface layers during hot forging process operations creates conditions for ausforming in them.

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Effect of microadditions on the structure and properties of powder carbon steel

Cited by 5 publications

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Features of the formation of the structure and properties of powder steels with additives that activate diffusion processes during sintering

Features of the formation of the structure and properties of powder steels with additives that activate diffusion processes during sintering

Rolling contact fatigue of hot-deformed powder steels with calcium microadditives

Formation of structure and properties of hot-deformed powder steels microalloyed with sodium and calcium during thermal and thermomechanical treatment

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