Effect of the hardness on the service life of die-casting molds for aluminum alloys

Conclusions The service life of die-casting molds for aluminum alloys is greatest for steel 4Kh5MFS after quenching from 1010–1040°C and tempering at 560–570°C to hardness HRC 49–50.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 66–67, October, 1978.     

Oxidation of Low-Carbon,Low-Silicon Mild Steel at 450–900°C Under Conditions Relevant to Hot-Strip Processing

The oxidation behavior of a low-carbon, low-silicon mild steel was investigated in ambient air at 450–900°C to simulate steel strip oxidation during finishing hot rolling and coiling. Oxide scales developed at 880–900°C for a very short time (12 sec) had a structure similar to that formed on pure iron, but with a greater thickness ratio between the magnetite and wüstite layers. However, the scale structure after oxidation for a longer period (200 sec) at 900°C deviated significantly from that reported for pure iron. This difference was attributed to the loss of scale–steel adhesion at some locations. Oxide scales formed in the range of 580–700°C after oxidation for more than 2 hr also differed from those reported for pure iron. The scale structures were irregular, comprising mainly hematite and magnetite with no or very little wüstite, while the thickness ratio of these two layers differed considerably at different locations. The scale formed at 450–560°C was relatively uniform with a two-layered (hematite and magnetite) structure; however, the thickness ratio of these two scale layers varied for different oxidation temperatures and different oxidation durations. It was also found that limited oxygen supply (zero air flow) improved the scale–steel adhesion, and substantially reduced the relative thickness of the hematite layer. Continuous-cooling experiments proved that significant growth of the hematite layer, as well as the entire scale layer, may occur if the steel is cooled slowly through the temperature range 600–660°C, and even more significantly through the range 660–720°C.     

Low-temperature cyaniding of cylinder block sleeves

Conclusions We recommend the following heat treatment for the cylinder sleeves of certain tractor and automobile engines; it ensures a high wear resistance and does not induce warping: a) annealing for stress relief, with heating at 75–100 deg/h to 580–600°C, soaking, cooling at the rate of 40–50 deg/h to 200°C; final machining, including honing; b) gas cyaniding 6 h at 560–580°C in a medium of 70% carburizing gas and 30% ammonia.Bauman MVTU, Moscow Automobile Plant. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 60–62, July, 1967.     

Role of Growth Stresses on the Structure of Oxide Scales on Nickel at 800 and 900°C

The development and relief of intrinsic growth stresses in oxide scales on nickel of different purity have been investigated by combining the deflection test in monofacial oxidation (DTMO) with acoustic-emission analysis (AE). Parallel metallographic analysis gave information about the development of the physical- defect structure and all other structural features. The investigations were performed for 100 hr at 800 as well as 900°C in air. The assumption of elastic behavior led to the best correlation between models, literature data, and results of the present investigations. Microcracks are responsible for the relief of growth stress and inward oxygen penetration leads to the typical NiO duplex scale. The growth of the microcracks is initiated at large pore populations at the oxide–metal interface that most probably form due to outward cation-diffusion and vacancy condensation. The pore formation is increased by the presence of impurities. An equilibrium of microcracking and crack healing is finally reached, leading to a continuous growth of the inner and outer NiO layers of the duplex scale. The scale growth stresses are mainly compressive and can reach maximum values of –560 MPa at 900°C. An estimation of the fracture toughness of the oxide–metal interface assuming a wavy interface led to a K_Ic value of about 2 MNm^-3/2 at 900°C     

High temperature oxidation of iron-manganese-aluminum based alloys

The isothermal oxidation resistance of high purity iron-manganese-aluminum alloys containing from 0 to 40% manganese and from 0 to 15% aluminum was investigated at 600, 800, and 1000°C in pure oxygen at a pressure of 200 torr for periods up to 100 hr. They were subsequently examined using SEM and metallographic techniques, and an oxide map showing the alloy structure and general oxidation behavior at 800°C was produced. Scales formed on alloys which contain insufficient aluminum to form protective alumina have structures which depend largely upon the concentration of manganese in the alloy. Alloys which contain more than 7.5% manganese form manganese rich scales, whereas alloys which contain lower levels of manganese form scales that are composed almost entirely of the oxides of iron. Small manganese oxide nodules grow through the alumina scales which form on alloys containing in excess of 9% aluminum. The most oxidation resistant alloys, having compositions within the range Fe-(5–10)%Mn-(6–10)% Al, develop continuous protective alumina scales and are totally ferritic. Austenite is detrimental to the oxidation resistance of duplex alloys as it promotes the breakdown of preexisting alumina scales and the growth of bulky manganese rich oxides. Small additions of chromium are beneficial and reduce the concentration of aluminum required to form protective alumina scales.     

Heat Treatment of Cast Carburizing High-Speed Steel Alloyed with Ti, Nb, and V

Special features of the structure and phase composition of cast carburizing high-speed steel of the ferrite-carbide class and the laws of their variation in the process of the carburizing hold and subsequent heat treatment are described. The temperature of heating for quenching was varied within 1180 – 1220°C, and the tempering temperature was varied within 560 – 640°C using the hardness and heat resistance as criteria. The results of mechanical tests of heat treated steels are analyzed.     

Tungstenless high-speed steels 12M5F3SYu and 11M3F3SBTs

Conclusion Both investigated steels are characterized by reduced red hardness in the temperature range not causing fusion; this does not ensure the required resistance of the tools.Increasing the holding time at the hardening temperature by a factor of 1.2–1.5 does not help increase hardness and red hardness.Combined tempering at three different temperatures (350+570+550°C) has no advantages over ordinary threefold tempering at 560°C.Both investigated steels are characterized by good mechanical properties which practically do not depend on the hardening temperature in the range 1170–1190°C. Good mechanical properties are ensured with grain sizes up to No. 6.On the basis of metallographic investigations and cutting tests it was established that the experimental steels are not equivalent to steel R6M5.Production Association "Kirovskii Zavod." Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 6–8, August, 1988.     

Die steels for high-speed automatic hot die forging machines

Conclusions Steel 3Kh3M3F produced by ESR has the best combination of strength, hardness, and toughness, and also resistance to crazing. The life of punches made of this steel was double that of standard steel 3Kh2V8F and considerably higher than that of steels with a higher carbon content (0.4–0.5%).The life of 3Kh3M3F punches (ESR) was three to four thousand bearing races higher than that of the same steel melted in an open furnace.These data lead us to recommend that punches for high-speed water-cooled presses be manufactured from steel 3Kh3M3F (ESR) with the following chemical composition: 0.26–0.34% C, 2.8–3.3% Cr, 2.5–2.9% Mo, 0.40–0.60% V (ChMTU-1-963-70).The following heat treatment is recommended: preliminary heating in an electric furnace at 500–510°, salt bath at 850–860°, and salt bath at 1040±10°. The parts should be quenched in oil with a temperature of 120–150°. The first tempering after quenching should be conducted in a salt bath at 600° for 2 h, with cooling in air. The second tempering should be conducted in a salt bath at 560° for 2 h, with cooling in air. The hardness of the parts after heat treatment is HRC 49–51.All-Union Scientific-Research Institute of the Bearing Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 20–25, November, 1973.     

Cyclic-Oxidation Resistance of Protective Silicide Layers on Titanium

Titanium was powder siliconized and gas nitrided, in order to improve its cyclic-oxidation resistance. Siliconizing was performed in a pure-silicon powder at temperatures in the range of 800–1100° C for 3–48 h. Gas nitriding was carried out in pure N₂ at 1100° C/12 h. Cyclic-oxidation experiments with the siliconized and nitrided samples were conducted in air at 850 and 950° C for up to 560 h. It was found that the siliconized layers grew according to the parabolic law with the activation energy for siliconizing E_S being 47.2 kJ mol^–1. Powder siliconizing at 900–1100° C/3 h produced multi-phase layers, in which Ti₅Si₃ silicide predominated The siliconizing temperature of 800° C/3 h appeared to be insufficient, because it led to a non-uniform surface layer with a slight protective effect. The nitrided layers were composed of titanium nitride TiN and -Ti(N) intestitial solid solution. Measurement of the oxidation kinetics revealed that the titanium siliconized at 900–1100° C/3 h oxidized much more slowly than pure Ti, Ti–6Al–4V alloy and nitrided titanium. Microstructural investigation revealed the complex sub-structure of the scales on the siliconized samples which was composed of rutile+silica, rutile and nitrogen-rich sub-layers. The mechanism of high-temperature cyclic oxidation of the siliconized and nitrided titanium is discussed.     

Effect of heat treatment on the properties of deformed alloy 36N

Iron-nickel alloy 36N (Invar) is widely used in industry as a material having an anomalously low and almost constant thermal coefficient of linear expansion (TCLE) in the temperature range of 20 – 100°C. This value of the coefficient is attained after heat treatment of the deformed semifinished product by the regime of quenching from 830°C in water, tempering at 315°C for I h, and aging at 95°C for 48 h. The minimum value of the TCLE is provided by the quenching operation, whereas the tempering and aging prevent growth of the TCLE during long-term operation of Invar. The use of such heat treatment for rods and wire of alloy 36N guarantees a TCLE of at most 1.5 × 10^–6 °C^–1. It is known that the value of the TCLE and the level of the mechanical properties of Invar can be changed by changing the temperature and deformation regime of its treatment. The aim of the present work is to determine an optimum regime of heat treatment of the alloy after drawing that would ensure, without a finishing treatment, a TCLE not exceeding 1.0 × 10^–6 °C^–1 in the temperature range 20 – 100°C.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 31 – 32, April, 1996.     

Redistribution of alloy elements in aging of austenitic chrome-manganese steel containing nitrogen

Conclusions In interrupted decomposition of the austenite of chrome-manganese steel containing nitrogen in the 600–900°C range the alloy element content in the nitride phase formed changes. The quantity of chromium increases while that of iron decreases significantly. The manganese content in the nitride is low and remains approximately constant.The residual austenite in the grains which have undergone interrupted decomposition is gradually depleted of chromium and nitrogen.The growth of pearlitelike colonies consisting of transformed austenite and type M₂N nitride is controlled simultaneously by the mechanisms of grain-boundary and three-dimensional diffusion.Institute of Metallurgy and Metals Technology, Sofiya, Peoples Republic of Bulgaria. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 60–61, November, 1988.     

Heat test for semifinished products of an alloy of the system Al-Mg-Li

Conclusions Development of pores (bubbles) during heating for an alloy of the Al-Mg-Li system at 560°C is due to reaction of the alloy with a moist furnace atmosphere with hydrogen formation. The main role in this is played by magnesium and not lithium or aluminum.All-Union Institute of Aviation Materials Scientific Production Association. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 38–40, February, 1991.     

Oxidation of copper-manganese alloys under pure oxygen

Oxidation, in oxygen gas at atmospheric pressure, of copper-manganese alloys (Mn content less than 40 at.%) has been investigated between 600 and 850° C. The reaction kinetics, determined by thermogravimetry, follow a parabolic law for alloys having a low manganese content (less than 10 at.% Mn) but are more complex for higher concentrations, particularly in the first stages of the oxidation process. Whereas in the early stages of oxidation the kinetics are controlled by surface reactions which accompany the formation of the different oxide layers, they are later controlled by the diffusion of a mobile species when the parabolic law is followed. In this condition an apparent activation energy may be determined from the rate constants. These energies are of the order of 120–140 kJ mol^–1, comparable with that for oxidation of pure copper (134 kj mol^–1), indicating a similar oxidation mechanism.The oxide layers formed were identified by cross-checking results of X-ray diffraction, electron microprobe analysis, and from glow discharge spectrometry. External layers of CuO and Cu₂O formed on alloys of lower manganese concentration, evolving towards one or several mixed copper-manganese oxide layers with increasing manganese content. Under the external layers, which were weakly adherent to the sample, an internal-oxidation layer formed, which was adherent and consisted of precipitates of Mn₃O₄/MnO dispersed in the copper lattice. For alloys richer in manganese (36 at. % Mn) and at temperatures above 850°C (20 at.% Mn), the internal-oxidation layer evolved into two zones: MnO particles beneath a zone of Mn₃U₄ particles.     

Effect of Carbon on the Long-Term Oxidation Behavior of Fe3Al Iron Aluminides

Electroslag, remelted-iron aluminides having the compositions: (1) Fe–16Al–0.05C, (2) Fe–16Al–0.14C, (3) Fe–16Al–0.5C, and (4) Fe–16Al–1.0C were investigated to understand the effect of carbon on their oxidation behavior in the temperature range 700–1000°C. The oxidation behavior of these aluminides was compared with that of 310 SS, a reference alloy used in the study. Regardless of carbon content, the iron aluminides exhibit marginally higher oxidation tendency than that of 310 SS at 700°C. However, between 800 and 1000°C, they exhibit better oxidation resistance than 310 SS. Although the oxidation resistance of aluminides at 1000°C is better than that of 310 SS, they suffer severe spallation during long-term exposure and C exacerbates this effect. Examination of the early stages of oxidation of the alloys at 800 and 900°C shows that they do not gain a corresponding weight as they do for a temperature rise from 700 to 800°C. A further rise to 1000°C leads to a marginal inversion in the oxidation tendency of the alloys. Based on the literature, this inversion is attributed to the possible dissolution and/or change in compo- sition of Fe₃AlC_0.69 carbide phase with temperature.     

High-temperature oxidation of rhodium

The oxidation kinetics of Rh were measured in air at 1 atm. in the temperature range 600–1000°C. The oxidation weight gain proceeds logarithmically at the lower temperatures (600°C, 650°C) followed by a transition to power law behavior at the higher temperatures (800°C). The logarithmic growth kinetics result from thickening of a hexagonal Rh₂O₃ scale. The transition from logarithmic to power law growth kinetics occurs in the range 700–800°C, and reflects thickening of hexagonal and orthorhombic Rh₂O₃ scales. Above 800°C, the growth kinetics result from thickening of a predominately orthorhombic Rh₂O₃ scale. At 1000°C the oxide becomes volatile, leaving the metal surface exposed.     

High-temperature oxidation of copper-manganese alloys

The oxidation behavior of copper-manganese alloys (2–35 wt. % Mn) in pure oxygen at 760 Torr was investigated at 100° intervals between 550 and 850°C. Gravimetric measurements of the oxidation kinetics have been combined with microstructural studies of the reacted samples in order to evaluate the reaction mechanisms. The scales formed on Cu-2Mn, Cu-5Mn, Cu-10Mn are always composed of three different layers; in any case manganese is present only in the inner layer. The scales formed on Cu-20Mn and Cu-35Mn are composed of two layers, both containing manganese, with a more Cu-rich outer layer. In all the samples internal oxidation in combination with external scale formation is observed.     

TEM Study on the Internal Oxidation and Nitriding of Dual Phase Fe–Mn–Al–C Alloy AfterNaCl-Induced Corrosion

A dual-phase Fe–Mn–Al–C alloy was oxidized at 750°C in air with 2 initial mg/cm² NaCl deposits. After 9 hr of exposure a fine-void zone was observed in the middle subscale and a coarse-void layer in the inner subscale. The fine-void zone formed due mainly to the interaction between selective oxidation of manganese and the oxidation of metal chlorides, while the formation of the coarse-void layer was caused by chlorination. The product remaining in the fine-void zone was mostly Al₂O₃, and the structure of the substrate in this zone is oxidation-induced ferrite, where nitriding of aluminum occurs forming AlN. Fine Fe₃O₄ particles fill in the coarse voids and the structure of the substrate in this layer is secondary austenite. The mechanism of the formation and growth of the internal oxidation and nitriding in the void zones of the subscale are discussed.     

Heat treatment of cast aluminum alloys obtained by application of regulated pressure during crystallization

conclusion For castings of AK8 alloy obtained by application of regulated pressure during crystallization, we recommend the following heat treatment conditions: homogenization at 460–470°C for 8 h, quenching from 505–510°C, aging at 150–170°C for 3.5–4h. After treatment according to this procedure, a hardness of 72–74 HRB is achieved for the alloy.Vladimir Polytechnical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 36–39, October 1992.     

The oxidation of cobalt in air from room temperature to 467°C

The oxidation of cobalt in air is investigated for times ranging over three orders of magnitude up to 1000 hr and for temperatures ranging from room temperature up to 467°C. Three different growth processes are observed. When a clean surface is exposed to air at room temperature, an 8–10 Åfilm of Co(OH) ₂ forms in seconds or less. For temperatures of 50–100°C, very little additional film forms for times up to 1000 hr. For temperatures of 100–225°C, a film of CoO grows in a manner which can be described empirically with a fourth root rate law with an activated rate constant. Between 225 and 325°C there is a transition to a quadratic rate law. At 425°C the film appears to be a mixture of CoO and Co ₃O₄.