Microhardness Gradient Research Articles

Study of screw mixing of tungsten-nickel-copper heavy alloy

Combined surface hardening with boron, carbon and nitrogen was used for low-carbon chromium and nickel-based steels. The microstructure, boron and nitrogen contents, carbon profiles and chosen properties of borided layers produced on the carbonitrided steels have been examined. These complex (B+C+N) layers are termed borocarbonitrided layers. Gas boriding applied to these steels that have been previously carbonitrided enables the production of wear-resistant diffusion layers. After combined surface hardening with boron, carbon and nitrogen in the microstructure two zones have been observed: iron borides (FeB+Fe2B) and carbonitrided zone. The iron borides show the tendencies towards lose of the needle-like nature. Although borocarbonitriding causes reducing of the depth of iron borides zone, it also reduces the microhardness gradient across the case. Probably, the brittleness of borocarbonitrided layer is lower. In the consequence, the frictional wear resistance of borocarbonitrided layers is essentially higher than that obtained in case of only borided layers. The similar values of wear intensity factors are characteristic for borocarburized layers. The carbonitriding used before boriding make possible the application of lower temperature and shorter time in comparison with carburizing process.

Properties of seams with electron-beam welding of tubing to tube sheets

As the result of two heat treatments the structural heterogeneity, microhardness gradient in the seam and the base metal, and the residual internal stresses in weldments decreased considerably. The best properties were obtained after heat treatment 1: heating at a rate of 20 deg/h at 1050–1080°, holding 30 min, and furnace cooling to room temperature at a rate of 65 deg/h.

Deformation Zone Geometry and Texture Gradients in Cold‐Rolled Niobium

Several niobium plates were cold‐rolled at room temperature to a total reduction of 60% maintaining the geometry of the zone of deformation constant for each plate. Pole figures were obtained by means of the Schulz x‐ray reflection technique from various depths in the thickness direction for plates rolled with different ∆, the ratio of the mean height of the deformation zone to its contact length. Severe texture gradients were noted and characterized for Δ > 1; a modified texture different from the normal texture was observed at intermediate through‐the‐thickness locations. Both lateral widening and microhardness gradients were also in evidence for this case. No previously proposed theoretical explanation could account for these results.

Successive saturation of steel KhVG with carbon and boron in powdered mixtures

1. The conditions were determined for successive saturation of steel KhVG with carbon and boron from powdered materials. Complex diffusion layers consisting of (Fe, M)B needles and a carburized transition layer are formed that reduce the microhardness gradient from the diffusion layer to the base metal as compared with borided steel KhVG after quenching and low-temperature tempering. 2. Operating tests of dies in tableting machines showed that the cyclic strength of carboborided dies is 200–250% that of borided dies. The treatment is recommended for parts of stamping and pressing machines.

879. Development of a series of metallo-ceramic components for power units: E A Kotyurgin et al, Tr Konf Elektron Tekhn, 1, 1966, 175 ( in Russian)

This paper presents the results of Electron Back-Scatter Diffraction (EBSD) analyses of the borided layers produced on substrate of varying carbon content. Two types of materials were investigated: borided Armco iron of very low carbon content and borocarburized chromium- and nickel-based steels of high carbon content beneath iron borides. The tetragonal phase Fe2B was identified in all materials studied. It was difficult to obtain an EBSD pattern from iron boride (FeB) because of its presence at low depths below the surface, and because of the rounded corners of the specimens. EBSD provided information on the orientation of Fe2B crystals. In case of the low-carbon Armco iron the crystallographic orientation was constant along the full length of the Fe2B needle. The EBSPs obtained from borocarburized steel indicate that the crystallographic orientation of the Fe2B phase changes along the length of the needle. This is the result of hindered boron diffusion due to boriding of the carburized substrate. The increased resistance to friction wear of borocarburized layers arises from two reasons. One is the decreased microhardness gradient between the iron borides and the substrate, which causes a decrease in the brittleness of the iron borides and an improved distribution of internal stresses in the diffusion layer. The second is the changeable crystallographic orientation of iron borides, which leads to the lower texture and porosity of borided layers. These advantageous properties of the borocarburized layer can be obtained if the carbon content beneath the iron borides is no more than about 1.0–1.2 wt.% C.