The effects of Ca content on intragranular acicular ferrite nucleation in the CGHAZ of Al-Ca-Ti deoxidised shipbuilding steel

In situ observation of the formation of intragranular acicular ferrite at non-metallic inclusions in C–Mn steel

Pressure vessel steels are used in the manufacture of tanks for the storage of gases, chemical materials and oil. To meet the increasing production demands, high-wire-energy welding is widely used in the manufacture of pressure vessel steels. This means that the weldability of pressure vessel steels needs to be improved. Therefore, in order to reveal the microalloying effect of Ca in pressure vessel steel, this study took a commonly used pressure vessel steel as the research object, and three groups of experimental steels with different Ca mass fractions were prepared using vacuum metallurgy, controlled rolling and controlled cooling. Welding heat simulation technology was used to simulate the welding heat of experimental steel and the welding heat-affected zone (HAZ) was investigated. The inclusions of the welding HAZ in the experimental steels were observed by using a metallographic microscope and scanning electron microscope (SEM). The mechanism of intragranular acicular ferrite (IAF) nucleation induced by the inclusions containing Ca elements in the welding HAZ of pressure vessel steels was also discussed. The research results show that the addition of Ca increased the number density of effective inclusions in the welding HAZ of the experimental steel up to 535.60 pieces/mm2. The addition of the Ca element was beneficial for producing more pinning inclusions in the experimental steel welding HAZ under the experimental conditions, and the inclusions were mainly elliptical oxide complex inclusions of Ca-Si with a size of about 2 μm. Meanwhile, Al2O3 and MnS were precipitated. After the addition of Ca elements, Mn-poor regions appeared around the inclusions containing Ca in the welding HAZ. IAF nucleation was mainly induced by the local compositional change mechanism and supplemented by the stress–strain energy mechanism and inert interface energy mechanism. This study provides a valuable reference for optimizing the welding process of pressure vessel steels and is of great importance for understanding the IAF nucleation mechanism of Ca-containing inclusions in the welding HAZ of pressure vessel steels.

Alterations in cation homeostasis during and after recovery from myocardial ischemia may account for some of the reversible and irreversible components of myocardial cell injury. To investigate possible mechanisms involved, we exposed cultured layers of spontaneously contracting chick embryo ventricular cells to media containing 1 mM cyanide (CN) and 20 mM 2-deoxyglucose (2-DG), and zero glucose for up to 6 h, and then allowed cultured cells to recover in serum-free culture medium for 24 h. Changes in Na, K, and Ca contents, 42K uptake and efflux, ATP content, cell water content, and lactate dehydrogenase (LDH) release were measured, and compared with changes produced by exposure to 10(-3) M ouabain and severe hypoxia. Exposure to CN and 2-DG caused marked increase in cell Na (sevenfold) and Ca (fivefold) contents, and a decrease in K content (one-fifth normal), coincident with ATP depletion to one-tenth normal levels. This produced only slight cell injury, evidenced by increased LDH release. Recovery for 24 h resulted in return to near normal values (expressed in nanomoles per milligram of protein) of Na, Ca, and ATP contents. However, there was failure of cell K content to return to normal, associated with a persistent reduced net uptake of 42K, and an increase in the rate of 42K efflux. These abnormalities in K homeostasis were associated with a decrease in cell volume and water content per milligram of protein. More marked ATP depletion (to 1/100 normal values) was produced by hypoxia plus 2-DG and zero glucose, and was associated with much more severe cell injury manifested by LDH loss. Ouabain exposure resulted in a much greater Ca gain (20-30-fold), relative to increase in Na content, than did either CN and 2-DG or hypoxia; and ouabain effects were not reversible (after a 15-fold or greater increase in Ca content was produced) and were associated with significant LDH release. We conclude that these cells are resistant to cell injury caused by moderately severe Ca overload and ATP depletion produced by exposure to CN and 2-DG. However, metabolic inhibition of ATP production produces persistent abnormalities in K homeostasis, associated with functional abnormalities.

1. The membrane potential of single striated muscle fibres of toad, as modified by various Ca concentrations in Ringer fluid, was measured by means of an intracellular microelectrode.2. The resting potential rose by up to about10mV with the increase of Ca concentration and it fell by several mV with the decrease in calcium to onefifth of the normal.3. The magnitude of the action potential became greater by both 10-fold.and 30-fold increases in Ca concentration, but became smaller by 68.3-fold increase and by its decrease. The reversed potential was reduced with both the increase and decrease in Ca concentration.4. Both the rate of rise and fall of the action potential was reduced approximately in proportion to the increase in Ca concentration, and the decrease in Ca concentration also caused a reduction in both values.5. The neagtive after-potential became more prominent both with increased Ca concentration and with the rise in temperature.6. The possible mechanism of the action of Ca ions on the active membrane was discussed.

The nucleation of intragranular acicular ferrite in the welding heat-affected zone of Ti-bearing high strength low alloy steel was investigated by means of electron microscopy. It was found that intragranular acicular ferrite nucleation sites under different welding heat inputs (4.3kJ/mm and 10.0kJ/mm) are titanium complex oxides on which manganese (Mn) sulfides are precipitated. The complex compound is a Si and Mn-enriched oxide. Analysis of the oxide by means of enenrgy dispersive X-ray spectrum indicated that the oxide has higher absorption ability of Si than that of Mn.

The influences of Ti–Al complex deoxidation inclusions on nucleation of intragranular acicular ferrite (IAF) in C–Mn steel have been investigated based on four specimens with different Ti and Al contents. The inclusions of Steel 1 and Steel 2 both containing high Al are detected as Al2O3 and Ti3O5 · Al2O3, respectively. Owing to the low concentration of Mn in these inclusions, the manganese depletion zones (MDZs) which act as predominant driving force of IAF nucleation could not form easily. In Steel 3, Ti3O5–MnS is found as the main inclusion, which could be considered as potent nucleus. However, the excessive Ti leads to the aggregation of numerous inclusions less than 1 µm at grain boundaries, consequently restraining the nucleation of IAF. The main inclusions of Steel 4 containing low Al and medium Ti are found as Ti3O5 · Al2O3 · MnO, which effectively facilitate IAF nucleation. The size of inclusions mainly distributes in optimum zone corresponding to the maximum possibility of IAF nucleation. Therefore, the Al should be controlled as low as possible to ensure the nucleating effectivity of inclusion. While Ti should be appropriately controlled at medium level to distribute the inclusion size in the optimum zone to obtain well‐developed microstructures of IAF in C–Mn steel.

A study was made on both hyperpolarization and contracture which developed in the rabbit sinoatrial node cell during perfusion with Na-depleted solution. The membrane was hyperpolarized in 19 out of 27 specimens (-69.5 +/- 6.0 mV), while in the remaining 8 specimens the value of the membrane potential remained low (-39.4 +/- 2.7 mV). Slope conductance increased as the membrane was hyperpolarized in Na-depleted solution, but not when the value of the membrane potential remained at low. The amplitude of hyperpolarization increased with decrease in Na concentration, increase in Ca concentration and increase in perfusate temperature. A marked increase in diastolic tension was observed in 23 out of 29 specimens but in the 6 remaining specimens the increase in tension was small. Tension increased with decrease in Na concentration, increase in Ca concentration, and increase in perfusate temperature. Pretreatment with ouabain caused a consistent increase in contracture tension, while its effect on the membrane hyperpolarization was variable among different specimens. These results may be explained by assuming that intracellular Ca concentration increased with Na-Ca exchange in Na-depleted solution. In addition to contracture, increase in intracellular Ca concentration might have caused an increase of membrane K conductance and produced marked hyperpolarization.

Postnatal changes in calcium and amylase of rat salivary glands, including calcium changes with senescence

Effects of injection of large amounts of vitamin D3 (VD3) on the concentrations of plasma 25-hydroxyvitamin D (25OHD), 1α, 25-dihydroxyvitamin D (1, 25 (OH)2D), calcium (Ca) and inorganic phosphorus (Pi) in the lactating Holstein-Friesian cows were examined. The cows were divided into two groups, an untreated control group consisting of 4 cows and a treatment group (VD3 group) consisting of 5 cows. Each cow in the VD3 group received 10 million I.U. of VD3 intramuscularly at 7 days after parturition. Blood and milk samples were taken from 0 to 15 days after the VD3 injection. The plasma 25OHD concentration was significantly higher in the VD3 group than that in the control group throughout the experimental period, whereas the plasma 1, 25 (OH)2D concentration rose only transiently after the VD3 injection. The plasma Ca concentration was also significantly higher in the VD3 group than that in the control group throughout the experiment, while the plasma Pi concentration was higher in the VD3 group only from the 3rd to 6th day of the experiment. These results suggest that the initial increase in the plasma Ca concentration may be due to the increase in the 1, 25 (OH)2D level whereas the substained increase in the Ca concentration may be due to the increase in the plasma 25OHD concentration. Further, it seems likely that the plasma 1, 25 (OH)2D concentration is suppressed by the increase in the plasma Ca concentration in the later stage of experiment and also by the negative feedback of plasma 1, 25 (OH)2D concentration.

The effect of supplementing diets with various levels of vitamin D3 to provide 0, 0.5, 1, and 5 million IU/(steer x d) for 8 d before slaughter on the mineral content and localization of Ca in LM and muscle fragments was studied during the postmortem aging process. Twelve feedlot steers of three biological types were given access to the four levels of vitamin D for 8 d before slaughter. Differential centrifugation techniques were used to determine the concentrations of minerals relative to protein in different muscle fragments on d 3 and 21 postmortem. Electron microscopy visualization of bound Ca indicated that vitamin D3 mobilized Ca from the sarcoplasmic reticulum and transverse tubule system into the myofibrils. Bound Ca was concentrated near the Z-line at the A-band/I-band juncture within the sarcomere. Supplementing steers with 1 and 5 million IU/(steer x d) of vitamin D3 increased (P < 0.05) Ca, P, and Mg concentrations per unit of protein in the cytosol. Soluble cytosolic Ca concentrations were greater (P < 0.05) on d 21 than on d 3 postmortem only when steers were supplemented with 5 million IU/d. Concentrations of Ca, P, and Mg in isolated tissues were increased (P < 0.05) in nuclei and myofibrilar proteins by supplementing steers with 1 and 5 million IU/ (steer x d) of vitamin D3. All supplemental vitamin D3 treatments also increased (P < 0.001) Mg concentrations in the cytosol, regardless of aging treatment, and increased Mg concentrations (P < 0.04) within the mitochondria at d 3 postmortem. Thus, supplementation of feedlot steers with vitamin D3 at levels of 0.5 to 5 million IU/(steer x d) increased Ca concentrations within respiring muscle, resulting in increased bound tissue Ca concentrations. When the respiring muscle was converted to meat, the increased bound tissue Ca resulting from vitamin D3 treatment released Ca concentrations into the cytosol during aging (P < 0.05). Results of this study indicate that vitamin D3 supplementation increased total cytosolic Ca, P, and Mg concentrations in meat.

Growth of a legume in acid soils can be limited by the effects of infertility factors on the growth of the host plant per se or on nodulation and nodule function. Effects of varying solution pH (4.5, 5.0, 5.5) and external calcium (Ca) concentration (0.05, 0.5, 2.5 mM) on growth and nodulation of soybean [Glycine max (L.) Merr. cv. Fitzroy] were investigated in a solution culture experiment. Total dry matter production was not influenced by pH; however, shoot growth increased while root growth decreased with increasing solution pH. Increase in Ca concentration significantly increased shoot dry weight at pH 5.0 and 5.5. At pH 4.5, appearance of the first nodule was delayed, and nodule number and nodule dry weight per plant were lower than at higher pH. Nodule number and dry weight per plant were not affected by Ca concentration at pH 4.5 but increased significantly with increasing Ca concentration at pH 5.0. At pH 5.5, nodule number per plant decreased, but nodule dry weight increased as Ca concentration increased from 0.5 to 2.5 mM. Further experiments were conducted at pH 4.5 with 0.5 mM Ca concentration to investigate the effects of monomeric aluminum (Al) activity (∑ aA1 mono) on the growth of soybean supplied with adequate inorganic N and on growth and nodulation of plants inoculated with Bradyrhizobium japonicum. Shoot and root weights declined linearly with increase in ∑ aAl mono, with the critical ∑ aAl mono (90% of yield in Alfree treatment) ranging from 5 to 9 µM. Nodulation was totally inhibited in solutions with ∑ aAl mono ≥ 27.8 µM. The critical ∑ aA1 mono for nodule number and for nodule dry weight per plant were approximately 0.4 µM.

In total, 840 1-day-old male broiler chickens (Ross 308) were used to evaluate the effects of seven dietary calcium (Ca) concentrations (4.0, 5.5, 7.0, 8.5, 10.0, 11.5 and 13.0 g/kg, at a fixed concentration of 4.0 g/kg of non-phytate phosphorus) and two calcium sources (oyster shell and limestone) on broiler chicken Ca requirements for optimal growth rate and bone mineralisation from 1 to 21 days of age. All chickens were randomly distributed into 14 treatment groups (seven treatments of each Ca source), each being replicated four times, with 15 birds per each replicate. Results indicated that Ca source and Ca source × Ca concentration interaction had no significant (P &amp;gt; 0.05) effects on birds average feed intake, but increasing Ca concentration to &amp;gt;8.5 g/kg significantly deteriorated average feed intake. Average weight gain and feed conversion ratio were significantly influenced by Ca source × Ca concentration interaction, whereby high concentrations of Ca from oyster shell resulted in a poorer performance for both criteria than did those from limestone. Serum Ca, P and total protein were not affected by Ca source. However, increasing Ca concentrations had adverse effects on serum P concentration (P &amp;lt; 0.05). Toe ash, tibia ash and phosphorus concentrations at 21 days were not influenced by Ca source, but were depressed as dietary Ca concentration increased (P &amp;lt; 0.05). A broken-line regression analysis indicated that the Ca requirements to optimise average weight gain and tibia ash when limestone was used as a Ca source were 5.54 and 6.58 g/kg of diet respectively, and 5.80 and 6.43 g/kg of diet respectively, when oyster shell was used. In conclusion, the results indicated that Ca concentration, more than Ca source, has a significant influence on broiler chicken performance and bone mineralisation, all of which deteriorate when the dietary Ca concentration exceeds 8.5 g/kg at the constant available-phosphorus concentration of 4.0 g/kg.

The relative magnitudes and functional significance of Ca extrusion by Na-Ca exchange and by an Nao-independent mechanism were investigated in monolayer cultures of chick embryo ventricular cells. Abrupt exposure of cells in 0-Nao, nominally 0-Cao solution to 20 mM caffeine produced a large contracture (3.94 +/- 0.90 micron of cell shortening) that relaxed with a t1/2 of 8.60 +/- 1.22 s. An abrupt exposure to caffeine plus 140 mM Na resulted in a contracture that was smaller in amplitude (1.53 +/- 0.50 micron) and relaxed much more rapidly (t1/2 = 0.77 +/- 0.09 s). An abrupt exposure to caffeine in 0-Nao solutions produced an increase in 45Ca efflux that persisted for 20 s, and a net loss of Ca content, determined by atomic absorption spectroscopy (AAS), of approximately 4 nmol/mg protein, within 35 s. A comparable net loss of Ca was demonstrated in the presence of 100 microM [Ca]o. The abrupt exposure of cultured cells to 0 Nao in 1.8 mM Ca produced a Ca uptake, estimated with 45Ca, of 3.2 nmol/mg protein X 15 s, but produced no increase in cell Ca content (AAS). In cells in which a 30% increase in Nai was produced by 5 min exposure to 10(-6) M ouabain, the abrupt exposure to 0 Nao produced a Ca uptake of 6 nmol/mg protein X 15 s and an increase in Ca content (AAS) of 4 nmol/mg protein. We conclude that there is an Nao-independent mechanism for Ca extrusion in these cells, presumably a Ca-ATPase Ca pump, with a limited Ca transport capacity of no more than 2 nmol/mg protein X 15 s. This is five times smaller than the demonstrated maximum capacity of the Na-Ca exchanger in these cells. The relaxation of twitch tension in these cells seems to be dependent primarily on sarcoplasmic reticulum uptake of Ca, with a secondary role provided by the Na-Ca exchanger. The Ca pump appears to contribute little to beat-to-beat relaxation.

Understanding the impact of Ca doping on structural, morphological and low temperature transport properties of Nd2NiMnO6

The role of calcium concentration in the endocarp wall of apple fruit in the development of core rot