Investigation of CGHAZ During Single and Multi Pass Submerged Arc Welding of High Strength Steel

Owing to its fine structure and high strength to weight ratio, high strength low alloy (HSLA) steel, API X80, is most preferred grade for application in oil and gas pipeline fabrication. Coarse grain heat affected zone (CGHAZ) formed during fabrication of pipelines using high heat input welding operation like submerged arc welding (SAW) is the crucial area for failure during the application of welded structure. Large detrimental changes occur in mechanical behavior and microstructural characteristics of HAZ due to thermal cycles of the welding operation. In this study, CGHAZ built during first-pass of SAW and when it gets reheated during second-pass as well as third-pass is investigated at each stage for mechanical properties (impact toughness and hardness) as well as microstructural changes. Peak temperature of CGHAZ is determined using upper critical temperature limit of steel. For identifying the lower and upper critical temperature for this steel, dilatometry tests were performed and values were found in well agreement with theoretically determined ones. Comparative analysis of mechanical properties as well as microstructure in simulated HAZ with parent material is also discussed. It is found that subsequent reheating of CGHAZ (formed during first-pass of welding) because of second and third-pass of welding has beneficial effect. Work of this study will guide the engineers to put the limit on heat input in terms of number of passes during welding of such high strength pipeline steels.

Mathematical modeling of induction surface hardening

Purpose – As far as the author knows the modeling of induction surface hardening is still a challenge. The purpose of this paper is to present both mathematical models of continuous and simultaneous hardening processes and exemplary results of computations and measurements. The upper critical temperature Ac3 is determined from the Time Temperature Austenization diagram for investigated steel. Design/methodology/approach – Computation of coupled electromagnetic, thermal and hardness fields is based on the finite element methods, while the hardness distribution is determined by means of experimental dependence derived from the continuous cooling temperature diagram for investigated steel. Findings – The presented results may be used as a theoretical background for design of inductor-sprayer systems in continual and simultaneous arrangements and a proper selection of their electromagnetic and thermal parameters. Research limitations/implications – The both models reached a quite good accuracy validated by the experiments. Next work in the field should be aimed at further improvement of numerical models in order to shorten the computation time. Practical implications – The results may be used for designing induction hardening systems and proper selection of field current and cooling parameters. Originality/value – Complete mathematical and numerical models for continuous and simultaneous surface induction hardening including dual frequency induction heating of gear wheels. Experimental validation of achieved results. Taking into account dependence of the upper critical temperature Ac3 on speed of heating.

Thermoregulation and Habitat Preference in Mountain Chickadees and Juniper Titmice

The Mountain Chickadee (Poecile gambeli) and the Juniper Titmouse (Baeolophus ridgwayi) are closely related, ecologically similar passerines sympatric in portions of their range. However, Mountain Chickadees prefer higher altitude, cooler habitats than Juniper Titmice. We measured oxygen consumption, evaporative water loss, body temperature, and thermal conductance on seasonally acclimatized individuals to determine if thermoregulatory differences correlate with habitat preference. The Mountain Chickadee's lower critical temperature was 4.2°C lower than the Juniper Titmouse's in summer and 2.4°C lower in winter. Thermal conductance decreased significantly in winter relative to summer in Mountain Chickadees but not in Juniper Titmice. The Mountain Chickadee's upper critical temperature was 4.2°C lower than the Juniper Titmouse's in summer. Also in summer, Mountain Chickadees had significantly higher body temperature above the upper critical temperature than Juniper Titmice, indicating less heat tolerance. The overall metabolic response to temperature in these two species suggests that physiology plays a role in maintaining their habitat segregation. Termo-regulación y preferencia de hábitat en Poecile gambeli y Baeolophus ridgwayi Resumen. Las aves paserinas Poecile gambeli y Baeolophus ridgwayi, cercanamente emparentadas y ecológicamente similares, se distribuyen de modo simpátrico en partes de sus rangos. Sin embrago, P. gambeli prefiere ambientes más elevados y frescos que B. ridgwayi. Medimos el consumo de oxígeno, la pérdida de agua por evaporación, la temperatura corporal y la conductancia térmica en individuos aclimatados estacionalmente para determinar si las diferencias en termo-regulación se correlacionan con la preferencia de hábitat. La temperatura crítica menor de P. gambeli fue 4.2°C más baja que la de B. ridgwayi en el verano y 2.4°C más baja en el invierno. La conductancia térmica disminuyó significativamente en el invierno en relación al verano en P. gambeli pero no en B. ridgwayi. La temperatura crítica mayor de P. gambeli fue 4.2°C más baja que la de B. ridgwayi en el verano. También en el verano, P. gambeli tuvo una temperatura corporal significativamente mayor, por arriba del límite superior de temperatura crítica, que la de B. ridgwayi, indicando menor tolerancia al calor. La respuesta metabólica global a la temperatura en estas dos especies sugiere que la fisiología juega un rol importante en mantener la segregación de sus ambientes.

A theory of the rotations of molecules in solids and of the dielectric constant of solids and liquids

It is well known that Rochelle salt, NaKC 4 H 4 O 6 . 4H 2 O, for a limited range of temperature may, for practical purposes, he said to have an infinite dielectric constant analogous to the infinite permeability of iron in its ferromagnetic state. Such states, it is now realized, occur in a number of phenomena and a common description is of value; we shall refer to them as co-operative states . The co-operative state in Rochelle salt is limited by an upper critical temperature T u (or Curie Point) such that for T > T u the susceptibility though large is finite and decreases rapidly as T increases. Unlike the corresponding magnetic substances there is also a lower critical temperature T l such that for T < T l the susceptibility is again finite and decreases as T decreases. It is agreed that these phenomena are to be explained by the orientation of polar molecules in the crystal—the polar molecules in these particular crystals being undoubtedly water molecules present as water of crystallization. The co-operative state and the upper critical temperature T u can be explained by an exact analogy of the Weiss-Langevin theory of ferromagnetism, and no difficulties are raised by the large size of the necessary molecular field. The interaction energy of electrical dipoles is so large that it supplies precisely the necessary term which it fails to do in the magnetic case. The explanation of this part of the phenomenon requires the polar water molecules to be orientating freely under the influence of the effective applied electric field. The lower critical temperature T l can and must then be explained, it is believed, by a failure of the free rotations at lower temperatures which can so cut down the efficiency of the response to the applied field that the material is no longer self- polarizing. Again the dielectric constant of ice or water is finite at all temperatures, and falls to low values even for low frequencies as the temperature is decreased below 150° K. This can only be understood, assuming that the H 2 O molecule in ice or water carries the same dipole as in steam, or even a comparable one. if its orientations are not free but severely restricted by the local Held of its neighbours, even at the highest temperatures for which the dielectric constant of water has been investigated. The water dipoles are so numerous and so strong that water and ice would be co-operative at all temperatures if the dipole carriers were even approximately free. Somewhat similar phenomena occur for other polar liquids such as some of the alcohols and nitrobenzene which arc believed to be explicable in the same way. Rochelle salt, and its variants in which ammonium replaces potassium, arc the only known substances with a co-operative state. While there is probably general agreement about these qualitative explanations, it seems that no quantitative discussion has yet been given, even of any simplified model, which really displays behaviour of the types observed. Such a discussion of a simple model will be given in this paper. The exact results for the simple model reproduce many of the features observed, but naturally the model is too much simplified to expect it to provide a faithful representation of every detail. It is, however, possible to sec the modifications necessary in the model to make it the better fit the facts, and to see. moreover, that these modifications arc physically reasonable. The need for such a quantitative theory was first brought clearly to my notice at a conference on the solid state held in Leningrad in 1932. As will appear, however, an essential feature of the theory is an application of the ideas of order and disorder in metallic alloys, where the ordered state is typically co-operative, recently put forward by Bragg and Williams.* As soon as their ideas are incorporated the theory “ goes."