A series of piston hypereutectic silumin based on Al – (15÷20) % Si, alloyed with copper, magnesium, nickel, chromium is investigated. The mechanical characteristics of ingots from experimental alloys were determined: temporary tensile strength, hardness, relative elongation depending on the composition of the alloys, and temperature coefficient of linear expansion (TCLE). It is shown that the tensile strength of forged blanks is 1.5-2.4 times higher than ingots of hypereutectic silumins. The resulting structure of forgings ensures their high plasticity (relative elongation δ = 5.7÷7.5%; relative narrowing Ψ = 10.3÷14.2%). The optimal mode of heat treatment of deformed silumin is determined: quenching from step heating and aging, which allows increasing the strength of forgings up to 370-470 MPa. Moreover, the plasticity indicators remain at a high level, and the average thermal expansion coefficient of the alloys is (18.0 ÷ 19.2) · 10-6 K-1 in the range of 50 ÷ 200 ° C.
Author: Prudnikov А.
Effect of thermal-cyclic deformation and heat treatment on the structure and electrical properties of Ст3
The results of the effect of preliminary thermal-cyclic deformation on the microstructure of hot-rolled low-carbon steel Ст3пс are presented. It is shown that the regime of thermal-cyclic rolling leads to a decrease in the average grain size of ferrite from 8 to 6 microns in comparison with the structure of steel after industrial production. There is a decrease in the size of pearlite colonies and their volume fraction in the structure of steel after using thermal-cyclic deformation. The results of the effect of heat treatment: normalization and tempering on the electrical resistivity of the hot-rolled carbon steel sheet Ст3пс produced using thermal-cyclic mode of deformation processing (DTCT). DTCT preliminary thermal-cyclic was rolled (5 cycles at a reduction of 10-15 % in each cycle and cooled to a temperature below the Ar1). And normalizing annealing was carried out in the range from 100 to 900 °C increments to 100 °C for 1 hour. The possibility to reduce the magnitude of the specific electrical resistance of the hot-rolled steel manufactured using DTCT mode through the use of subsequent normalizing at 700 °C on average 10 %, and by annealing – no more than 5 %. A further increase in the time of normalization at 700 °C to 3, 5 and 10 hours has no significant effect on the value of the electrical resistance of the steel subjected DTCT. However, the downward trend in resistivity is maintained. Overall reduction of electrical resistivity of the hot-rolled steel Ст3пс by using
mode DTCT and subsequent normalizing at 700 °C for 1 hour is more than 12 %.
This paper presents new methods of thermal processing of the aluminum alloys. It analyses the effects of boiling treatment of alloys Al–Cu and Al–Si in an oxidizing atmosphere on their microstructure, hydrogen content and the coefficient of linear thermal expansion (CLE). An increase of boiling time from 15 to 75 hours results in an initial increase in the hydrogen content in alloys later followed by a decline in the hydrogen content. These changes in the hydrogen content correlate with the dynamics of alloys’ microstructure and their CLE. This study shows that atmosphere with a high oxygen content induces an acceleration of diffusion processes in aluminum alloys. If boiling time does not exceed 30 hours, the hydrogen content in a solid solution and etchability of grain boundaries of α-solid solution decrease and intermediate phases get partially dissolved. We demonstrate that boiling treatment of aluminum alloys in an oxidizing atmosphere leads to a decline of the CLE measured under the temperature 50-450°С which is especially strong when measured under the temperature 250-350°С.
INFLUENCE OF THERMAL-CYCLIC DEFORMATION AND HEAT TREATMENT ON THE STRUCTURE AND PHYSICAL PROPERTIES OF STEEL 10
The results of the influence of preliminary thermal-cyclic deformation and subsequent annealing in the range of 100÷900 ºС with a step of 100 ºС on the microstructure, coercive force and linear expansion of hot-rolled sheet steel 10 are presented. It was found that the use of preliminary thermal-cyclic deformation results in increase in coercive force no more than by 8% in comparison with the steel sheet produced by an industrial technology. Decreasing feasibility in coercive force of the sheet steel produced with the use of thermal-cyclic forging almost by 3 times in comparison with the initial raw condition due to the subsequent annealing at 900ºС during 10 h. is shown. In addition, annealing in accordance with this mode reduces a temperature coefficient of linear expansion of a sheet steel on average by 6 % within the range of the test temperatures 50-450 ºС.
The results of the influence of preliminary thermal-cyclic deformation and subsequent hardening heat treatment on the microstructure and mechanical properties of hot-rolled sheet steel 10 are presented. It is shown that the use of preliminary thermal-cyclic deformation of the steel 10 stock material results in a fine-grained structure of a hot-rolled sheet (3 mm thick) produced by an industrial technology. Deformation occurred at a temperature above AC3 (1250 °C), with cooling to 200-300 °C during 10 cycles and the deformation ratio per cycle being 6-8 %. The magnitude of the overall reduction ratio was 1.90 and the total amount of deformation was 65÷68 %. Such a treatment before sheet hot-rolling allows increasing the strength characteristics (tensile strength, yield strength) by almost 30 %. It has been established that the use of subsequent heat treatment (quenching, 900 °C, water and tempering 1 h, 600 °C) leads to a further increase in strength characteristics by 15-20 % while maintaining a sufficient level of ductility of sheet steel.