Spherical Carbide Research Articles

Influence of heat treatment on the spheroidization of the carbides in 40Kh steel

1. The formation of spherical carbides in cooling of 40Kh steel from the intercritical temperature range depends upon the degree of completeness of austenitization at these temperatures: it is necessary that undissolved spherical carbides remain in the structure. The use of accelerated heating makes it possible to broaden the temperature range of annealability of hypoeutectoid steels. 2. The optimum austenitizing conditions for 40Kh steel are hold at 760–780°C for 10 sec. In this case the degree of austenitization is 55%, which leads to the formation in subsequent decomposition of the austenite of spherical carbides and a decrease in hardness to 88 HRB in comparison with the original. 3. As the result of incomplete austenitization of the steel with the use of accelerated heating the hold time at subcritical annealing temperatures decreases. 4. Thermal cycling in the area of critical temperatures with accelerated heating has a positive influence on spheroidization of the carbides obtained in the first treatment cycle conducted according to the optimum conditions (austenitize at 760–780°C for 10 sec; isothermal hold at 700°C for 10 min). Spheroidization and carbide growth during thermal cycling occur significantly more rapidly than in isothermal annealing.

Single particle impact damage of fused silica

Single-impact damage of fused silica by spherical and conical tungsten carbide (WC) projectiles of velocities up to 200 m sec−1 has been investigated with a high-speed framing camera photographing at a rate of up to 1.7×106 frames per second. For spherical particles the Hertzian cone cracks, which for higher impact velocities are accompanied by median and radial cracks, form during the loading part of the impact; some growth of all these cracks also occurs during unloading. With the conical particles the Hertzian cone cracks do not form; only radial and median cracks form during the loading; in this case both radial and median cracks grow during the unloading. In both cases “lateral” cracks form during unloading. From these experiments values of the static equivalent of the dynamic stress-intensity factor for high-velocity cracks are also obtained; these are found to be considerably lower than those obtained from quasi-static indentation experiments. Finally, the extent of the damage produced by a single impact has been discussed.

The microstructure and fracture of a carburized steel

The case microstructure and fracture of a coarse-grained 8620 steel carburized to 1 pet surface carbon are quite sensitive to austenitizing conditions. Reheating martensitic speci-mens below theAcm produces in the case a refined austenitic grain size, a very fine mar-tensite, spherical carbide particles and a minimum of retained austenite and microcrack-ing. Overload fracture through the latter microstructure is transgranular and scanning electron microscopy shows both microvoid coalescence around thecarbide particles and an apparent fine cleavage in other areas. As-carburized specimens and specimens re-austenitized above theAcm developed a case microstructure characterized by a coarse austenitic grain structure in which plate martensite with microcracks developed on cool-ing within a large amount of retained austenite. The overload fracture through this mi-crostructure followed a predominately intergranular path and effectively by-passed the retained austenite and microcracked martensite. Auger electron analysis showed that C and P were present on the intergranular fracture surfaces at concentrations above bulk, an observation consistent with literature reports of P segregation during austenitizing.

Carbide-intermetallic strengthening of nonmagnetic steels

1. Alloying with nickel (8.6–15.7%) and aluminum (3.7–6.2%) of nonmagnetic manganese steels strengthened by precipitates of dispersed particles of vanadium carbide during aging leads to further increase of the strength after aging. This increase in strength is due to additional precipitation not only of spherical vanadium carbide particles 50–150 A in diameter but lamellar particles of intermetallic phase of the (Fe, Ni, Mn)Al type with average linear dimensions of 150×600 A. 2. The physicomechanical properties are highest for steel 50G17N10Yu4F2 quenched from 1150° and aged at 650° for 8 h: σb = 160 kgf/mm2, σ0.2 = 142 kgf/mm2, δ=11%, ψ=19%, μ<1.005 G/Oe.

Microstructure and fracture of 52100 steel

The fracture behavior of 52100 steel hardened and tempered to RC62 has been investigated as a function of austenitizing over the temperature range from 800 to 1100°C. Specimens were homogenized at 1150°C and either furnace cooled or isothermally transformed at 580°C to produce a pearlitic microstructure prior to austenitizing for hardening. Furnace-cooled specimens developed a proeutectoid carbide network that did not dissolve during subsequent austenitizing below Acm. The residual proeutectoid carbides and the carbide-free martensite-austenite structure between them controlled fracture and produced KIC of 19 MPa \ m1/2, the highest determined in this investigation. The specimens isothermally transformed prior to austenitizing below Acm produced a microstructure of fine spherical carbides dispersed throughout a fine martensitic matrix and did not contain residual proeutectoid carbides. The transgranular fracture of the latter specimens by microvoid coalescence around the closely spaced spherical carbides resulted in the lowest values of fracture toughness, 14 to 16 MPa\ m1/2, determined in these experiments. Austenitizing above Acm caused solution of all carbides, a gradual coarsening of the austenitic grain size, a transition to plate martensite, and an increase in retained austenite. Fracture toughness increased slightly with increasing austenitizing temperature above Acm despite the fact that fracture propagated primarily along the austenitic grain boundaries. The improved fracture toughness, verified by scanning electron microscopy of the fatigue crack-overload fracture interface, is believed to be caused in part by transgranular crack propagation during the first stages of crack extension that are most important in determining K1C.

Nuclear Fuel Coated Particle Development in the Reactor Fuel Element Laboratories of the U.K. Atomic Energy Authority

The objectives of the coated particle development program at the Reactor Fuel Element Laboratories (RFL) have been to define the essentials of a production route for the manufacture of nuclear fuel kernels and coated particles and to identify the important process parameters that determine the particle properties and hence the irradiation performance. Detailed characterization assessments of the various components of the coated particles have enabled a number of advanced coated particle designs to be optimized. The versatility of the RFL powder agglomeration process for the fabrication of highly spherical carbide or oxide kernels is exemplified by its ability to produce virtually monosized kernels in the range from 200 to 1000 ..mu..m in diameter, with controlled porosities in the range from 5 to 20 percent and the facility with which solid fission product and oxygen getters may be incorporated. The principles of the RFL pyrocarbon (PyC) and silicon carbide (SiC) coating processes, together with the experience of coating particles on a large--kernel batch sizes up to 25 kg--have been delineated. The understanding of the important parameters controlling deposition processes has led to optimum specifications for coater design and process route such that high sphericity is maintained throughout coating with a minimummore » spread in coat properties. More recent detailed investigations of process variables have identified the factors controlling PyC microstructure and the effect that coat defects and substrate shapes have on the ability of SiC to contain the gaseous fission products released by the fuel kernel during in-reactor operation. The proportion of defective particles is reduced by establishing process specifications to minimize coating-kernel bonding and misshapen kernels.« less

The effect of carbon on 2.25 Cr-1 Mo steel: (I). Microstructure and tensile properties

The microstucture, hardness, and the tensile properties of 2.25 Cr-1 Mo steel with 0.009, 0.030, 0.120, and 0.135 wt % C were determined on steels in the annealed (furnace-cooled from 927°C), normalized (air-cooled from 927°C), and normalized-and-tempered conditions. As annealed, the microstructure was primarily proeutectoid ferrite with spherical carbides and pearlite, the amounts increasing with increasing carbon content. During normalization ( 7 8 in rods or 1 in plates were heat-treated), granular bainite formed: 1 to 2 and 15 to 20% bainite (remainder proeutectoid ferrite) for the 0.009 and 0.030 wt % C steels, respectively; the 0.120 and 0.135 wt % C steels were entirely bainite. On tempering, carbides precipitated. In all heat-treated conditions, there was little difference in the room temperature hardness of the 0.009 and 0.030 wt % C steels and between the 0.120 and 0.135 wt % C steels. Tensile tests from 25 to 565°C indicated that strength depends on microstructure, which is determined by carbon content.

Experiments with spherical tools

Spherical steel and carbide tools were scraped through the surface layers of steel, brass and aluminum specimens. Results of force measurements and records of groove shapes are presented and discussed. Force ratio ( R = ratio of tangential to radial components) was found to be related to the proportion of the spherical surface contacting the workpiece material, and to frictional resistance. Aluminum gave less side flow and higher values of R than steel or brass due to its inherently greater friction characteristics.

Studies on oil-lubricated gears of thermoplastic materials. (in German) : E. A. Cornelius, Konstruktion, 77 (11) (1965) 437–447; 28 figs., 3 tables, 15 refs.

Smooth nanocrystalline diamond coatings (NDC) have been deposited on spherical cemented carbide substrates. These coatings have been tested in dry and lubricated (water, oil) sliding against cemented carbide (CC), ball-bearing steel (BBS), stainless steel (SS), titanium (Ti) and aluminium (Al). In addition, the same types of coatings were subjected to tests against Ti and Al after polishing NDC. Comparative experiments were performed with self-mated BBS. Dry sliding conditions of as-deposited NDCs against CC, BBS, SS and lightly polished NDCs against Ti and Al gave a friction coefficient of 0.06–0.1. Lubricating the contact generally resulted in a small reduction in friction. The self-mated BBS showed a friction of 0.8, 0.4 and 0.14 when tested in dry-, water- and oil-lubricated conditions, respectively. A very low wear was detected for the NDC, and the counter surfaces displayed practically no wear at all. In dry sliding against SS, the wear resistance of the diamond was roughly 100 times higher than that of self-mated BBS tested with oil lubrication. All three test conditions of as-deposited NDCs against Ti and Al gave a high friction coefficient (0.3–0.6) and seizure except for oil-lubricated Al where the friction was 0.11.

843. Pulse measurements on thin magnetic films: H.J. Harloff and W. Kayser, Elektron Rechenanl., 3 (3), 17 Jan. 1963, 113–118. (Available as Centre Library Translation No. 649)

The influence of post ageing treatment on creep behaviour of aluminide coating prepared by low-activity high-temperature on a Ni-based single crystal superalloy was investigated. The results showed that the aluminide coating reduced the creep behaviour of Ni-based single crystal superalloy. The decrease in creep behaviour may be due to the change in microstructures after aluminizing treatment. However, the post ageing treatment at low temperature has successfully improved the creep behaviour of aluminized Ni-based single crystal superalloy. The increase in creep behaviour of aluminized Ni-based single crystal superalloy after post ageing treatment was due to the formation of fine spherical carbides which are distributed in the substrate of Ni-based single crystal superalloy. These fine spherical carbides are able to hinder the dislocation movement and suppress the amount of topologically close-packed phase.

冷間圧延用作業ロールの電子顕微鏡組織(I)

The work rolls for cold rolling mills are usually forged from high-carbon-chromium steel, spheroidized, machined and finally heat treated to secure favorable rolling properties. The electron microscopic structure at the surface layer of heat-treated roll consists of spheroidized carbides, martensite matrix and some amount of retained austenite. If considerable amount of austenite are retained and spherical carbides are few, the working character of the roll is insufficient. To obtain properly spheroidized structure after forging, several experiments by small specimens were pursued. The results show that the most effective annealing methods are likely to be the types in which phase transformation are applied. The cooling rate after holding at 780°C is quite important. The slower cooling rate produces the better carbide distributions. By repeated heatings and coolings between 700°C and 780°C, the carbides grow larger and pearlite lamellae develops remarkably.

軸受鋼の研究(V)

In this report the behavior of spherical carbide going into solution in austenite was studied quantitatively, and the behavior of hardness and fracture roughness in austenite was studied together with.The results obtained are summarized as follows;1) At each heating temperature, the hardness increases with the holding time. At 840°C temperature, the hardness increases rapidly and is saturated after 1 hour, and at 860°C temperature it is considerably high in mere 5 minutes of the holding time.2) Between SKF and Japan-made ball bearing tubes the behaviour of the carbide in austenite is very different. The carbide solution of the former is saturated in 50-60 minutes, and one of the latter in 30-50 minutes at each heating temperature. In the former the intervals of saturated carbide contents at each heating temperature are equal, but not equal in the latter. Namely, in the latter the intervals of saturated carbide contents between 780-800°C and 840-860°C temperature are considerably wide, and these between 800°C, 820°C and 840°C temperature are narrow.3) The fracture roughness don't always agree with the visual observations, and it is considered generally that the fracture roughness increases. at the point from the sliding failure to the separate one.