Effect Of High Heat Treatment Research Articles

Effect of high heat treatment on the mechanical properties and the crack resistance of steel 38KhN3MFA

1. Raising the temperature of preliminary homogenization of blanks produced by electroslag remelting of steel 38KhN3MFA from 1100 to 1180°C and extending it from 5 to 20 h causes, after double austenizing with tempering, an increase of impact toughness and crack resistance. The maximal values of a1 and at are attained after homogenization at 1800°C 20 h, and values close to them are attained with 1180°C 5 h. 2. To refine the austenitic grain in castings of ESR steel 38KhN3MFA, which had grown in high-temperature treatment, it is necessary and sufficient to apply double austenizing at 880–950 and 860–880°C. 3. Preliminary high-temperature treatment has a greater effect on the subcritical characteristics (maximal ductility, energy of crack nucleation) than on the supercritical ones (energy of crack propagation, stress intensity factor). Such treatment has practically no effect on the parameters of fatigue crack resistance. 4. The increase of ductility and energy content of fracture of steel under preliminary high-temperature treatment is accompanied by a substantial reduction of the proportion of intergranular fracture. The change in the nature of fracture is connected with the change of the morphology of the highly disperse sulfide phase, in particular with its coagulation in the process of holding at a high temperature.

Effects of High-Heat Treatment on Stability of Calcium Caseinate Aggregates in Milk

Under standard conditions of centrifugation, the concentration and composition of the nonsedimenting nitrogen content of heated milks are found to vary. It decreases in concentration with increasing temperature to between 103 and 110C, where its concentration increased again with temperature. Below 103C the nonsedimenting nitrogen fraction was found to consist of whey proteins and the proteosepeptone fraction; at 110C and above the nonsedimenting nitrogen fraction consisted predominantly of caseinate. The amounts of nonsedimenting nitrogen produced above 110C was dependent on the temperature of heating, the concentration of milk solids, and on the phosphate and citrate concentrations. It has been reported by others, and also found in this investigation, that the soluble calcium and phosphate concentrations of milk decreased during heating, whereas those of citrate remained constant. Soon after heating, the soluble calcium concentration of milk returned to its former value. Formation of dissociated caseinate at temperatures of 110C and above may be attributed to removal of calcium from caseinate aggregates by the free citrate ion. Since the citrate concentration was not changed by heating, its formation of a soluble calcium citrate complex also returns the soluble calcium concentration to its value before heating.

Effect of High Heat Treatment on the Viscosity of Model Milk Systems

Summary Previous heat treatment had no effect on the viscosity of a 5% lactose solution, a 15% sucrose solution, a synthetic milk salts system, and a sodium caseinate dispersion. A slight increase was found in the viscosity of skimmilk as a result of previous heat treatment. Somewhat greater effects of heat were observed in whole milk, systems containing 16% milk solids-not-fat, and other more concentrated systems. Viscosity values were related to concentration by means of the Arrhenius equation. The assumption that the viscosity of a mixture should be the sum of the viscosities of its components, was true in a number of systems. Deviations were interpreted as indications of interaction between the components, which were found in heated systems containing sugar and milk solids-not-fat. Difficulties arise in evaluating the contribution of fat to the total viscosity, but indirect evidence showed an interaction between fat and other milk constituents. Increases in viscosity which cannot be predicted from consideration of the Arrhenius equation are believed to be of practical importance in a number of dairy products.

Relationships of Heat Treatment, Solids-Not-Fat, and Calcium Chloride to the Curd Tension of Skimmilk

Summary The effect of high-heat treatments in reducing the curd tension of milk has been further demonstrated. It has also been shown that the curd tension of milk heated as high as 165° F. for 30min. could be restored, i.e., raised to approximately 54g. (an average value for milk containing 9% solids-not-fat and heated at 143° F. for 30min.) by the addition of solids-not-fat and calcium chloride. Calcium chloride concentrations as high as 0.08% gave no detectable off-flavor to the heated skimmilk.