S. G. Napara-Volgina

Layered Powder Metallurgy Wear- and Corrosion-Resistant Materials for Tool and Tribological Applications. Structure and Properties

Three-layered non-tungsten hard alloys for tool applications of the type KKhNFT5 ― KKhNFT25 ― KKhNFT5 and layered powder metallurgy materials for tribological applications with a working layer of composites based on stainless steels were investigated. Basic requirements for the creation of wear- and corrosion-resistant powder metallurgy materials for tool and tribological applications were formulated. These mainly concern their composition and structure.

Corrosion and tribotechnical properties of materials based on Kh18N15 stainless steels with MoS2 and Cr3C2 additives

The corrosive and tribological properties of sintered chromium nickel stainless steel Kh18N15 (18% Cr, 15% Ni) materials, with additions of 2, 4, 6 and 8% MoS2 and 10% Cr3C2 are studied. Adding those amounts of MoS2 are found to have no significant effect on the corrosive and tribological properties of the steel. Simultaneous addition of MoS2 and Cr3C2 to Kh18N15 can alter the tribological properties without any appreciable change in the corrosion resistance.

Structure formation processes in sintering of stainless-steel-base heterophase materials 1. Sintering of austenitic stainless-steel-base materials with additions of Cr3C2

Earlier [1-3], a series of basic and applied investigations of the processes of pressing, sintering, and hot compacting of chromium and chromium-nickel stainless steel powders were presented. These works are devoted primarily to powdermetallurgy steels with a single-phase homogeneous structure basically not differing from the structure of the stainless steels produced by traditional methods. Of interest is development of stainless-steel-base materials with a heterophase structure. Together with good corrosion resistance such materials may possess such specific properties as increased wear resistance. This is obtained by addition to the metallic matrix of various additions such as carbides, intermetallides, nitrides, borides, sulfides, etc. However, certain additions reduce the corrosion and certain mechanical properties of stainless steels, particularly plasticity. In order to provide the optimum combination of properties of such materials it is necessary to optimize their composition and structure. In this work the structure and properties of austenitic chromium-nickel stainless-steel-base materials with additions of chromium carbide Cr3C 2 in a quantity of up to 10% were studied. The powders of types Khl8N12, Khl8N15, Khl8N12, Khl8N12M2, and K.h23N18 stainless steels were prepared by atomization, calcium hydride reduction, and diffusion impregnation [4]. The specimens for tensile, bend, and impact mechanical tests were prepared by a single pressing and sintering in hydrogen and vacuum at 1200~ After sintering the microstructure was investigated and the density and hardness of the specimens and the microhardness of the structural constituents were determined. In addition, selective micro-x-ray spectral and x-ray structural analyses were made for the purpose of studying the composition of the matrix and the carbide inclusions and also of establishing the crystalline lattice parameters of the base. In order to study the influence of the degree of dispersion of the chromium carbide additions on the character of their interaction with the matrix a preliminary investigation including use of types Khl8N15, Kh18N12, and Khl8N12M5 stainless steel powders obtained by the above methods was made. Monodispersed chromium carbide powder with average particle sizes of 30, 80 130, and 200 #m (sifted through -0056, -0100 + 0063, -0160 + 0100, and -0250 + 0160 screens) was used. In all cases the quantity of Cr3C 2 was 10 wt. %. The specimens were sintered in vacuum at 1200~ It was established that the hardness and microhardness of the base of the specimens containing carbides are higher and their density somewhat lower than of the standard specimens. At the same time the microhardness of the carbides themselves also drops significantly as the result of sintering (Fig. 1). With a decrease in carbide inclusion size, all of these rules are strengthened, which is an indication of the more active interaction of the more dispersed carbides with the base. The nature of the powders of the base has significantly less influence on the character of its interaction with the carbides than their degree of dispersion. The more active interaction with the metallic matrix of specimens of atomized type Khl8N12M2 powder is confirmed by the higher absolute and relative increase in microhardness of the base of the these specimens in compared with those prepared from Khl8N12 and Kh18N15 powders prepared by methods of diffusion impregnation and calcium hydride reduction (Figs. 1, 2). The increase by several percent in the chromium content in the metallic matrix and the increase in its crystallin lattice parameters in comparison with the standard specimens simultaneously established by methods of micro-x-ray spectral and xray structural analyses (Table I) are apparently caused by diffusion of chromium and carbon from the carbides into the base. The greatest change in the crystalline lattice parameters of the base is observed with use of dispersed additions with an average

Effect of the Silicon Introduction Method on the Structurization of Sintered Fe–Si–C and Fe–Si–B–C Steels

The methods to introduce silicon into Fe–Si–C and Fe–Si–B–C powder composites and its distribution in the alloy matrix are studied. Two types of silicon-containing additions, such as silicon carbide and low-carbon ferrosilicon, may be used. Silicon carbide promotes more uniform distribution of silicon in the iron matrix of the composites, while ferrosilicon leads to better compaction. Selective doping of individual phase components of the Fe–Si–B–C alloys is established: in particular, silicon diffuses only in the iron matrix and does not interact with the boron eutectic.

Investigating the dependence of the properties of sintered boron-containing steels on conditions of synthesis and the content of employed foundry alloys

Results from investigating the effect of technological conditions for the synthesis of powdered boron-containing foundry alloys on their chemical and phase compositions and the content of foundry alloys in the charge on the structure and properties of sintered steels fabricated using them are presented. It is shown that using denser briquettes obtained at a pressure of ≥700 MPa allows us to reduce substantially boron evaporation through the gas phase during the synthesis of foundry alloys, relative to briquettes compacted at lower pressures. Using an elevated foundry alloy synthesis temperature (1200°C) leads to higher density of the post-sintered material, and thus to enhanced strength characteristics. Increasing the boron content in the initial charge increases the hardness and lowers the strength of sintered steels, while the curve of the strength’s dependence on the boron content after thermal treatment peaks at ∼0.8% B.

Production Conditions and Properties of Layered Materials Type of Composite Based on a Stainless Steel ― Steel

Fabrication conditions and some properties of wear-resistant and corrosion-resistant layered materials type of composite based on a stainless steel ― steel were investigated. The materials were produced by joint pressing and sintering of the layers. The working layer was based on stainless steel Kh18N15 with additions of Cr3C2 and MoS2, and the substrates were unalloyed iron, low-alloy chromium steel, and stainless steel. The quality of layer bonding was evaluated by metallographic investigation and electron-probe microanalysis of the interface between layers, and also determination of the strength properties. It was established that the most favorable conditions for structure and property formation in the layered composites are obtained by using a stainless steel substrate and a working layer with an intermediate sublayer.

Thermodynamic modeling of chemical reactions in the heating of stainless steel H18N15 with Cr2C3, MoS2, and carbon additions in a hydrogen atmosphere

A thermodynamic modeling of the chemical reactions occurring during the heating of H18N35 stainless steel with Cr3C2, MoS2 and C additions in a hydrogen atmosphere at the 1000–1800 K temperature interval has been conducted. The formation of CrS, MoS2, Cr7C2, and the (Cr0.66Fe0.34)2.52C double carbide with the emission of H2S, CH4, C2H2, and the components of the steel into the gaseous phase at 1600 K (or above) has been detected. The results of the thermodynamic modeling are confirmed by the experimental data.

Mechanical properties of heterogeneous-structure wear-resistant high-chromium powder materials

Studies have been made on the effects of the production technology and composition of the initial material on the microstructure and some properties of powder materials having high chromium contents, which have heterogeneous structures. The materials were prepared from mixtures of iron powder and finely divided chromium and chromium carbide Cr3C2. The materials have a high wear resistance and also good mechanical characteristics and high resistance to corrosion in fresh water and sea water.

Wear-Resistant Heterophase Fe–Si–B–C Powder Materials

The microstructure, mechanical characteristics, and tribological properties of Fe–Si–B–C powder composites are analyzed to determine scientific and engineering principles for their production by single pressing and sintering followed by heat treatment. The composites have heterophase structure and can be recommended for wear-resistant parts for dry friction applications.

Mechanical, tribological, and corrosion properties of stainless steel of the austenitic class grade Kh23N18 with additions of chromium carbide

The mechanical, tribological, and corrosion-resistance properties of stainless steel Kh23N18 with additions of 2.5 and 10% Cr3C2 are studied. It is established that chromium carbide reduces the ductility properties and in most cases steel strength, but there is an increase in hardness and tribological properties with a Cr3C2 content of 10%. There is a slight reduction in corrosion resistance but in some cases it may be improved.