Due to a combination of optimal properties such as great strength, high hardness, good process ability, and good mechanical properties, AISI 4340 steel is widely used in many critical industrial applications such as nuclear, military, defense, and aerospace. It is also widely used in hydraulic forged machine tools, forged automotive crankshaft systems, shafts and gears, because of their improved characteristics, and its good tribological properties. The purpose regarding this work is to check the tribological characteristics of austempered AISI 4340 steel while dry and lubricated with machinery oil of SAE 30 grade as base oil. As received, AISI 4340 steel samples have been austempered to four definitely austenitic phase temperatures (850℃, 900℃, 1000℃, and 1050℃) for 90 minutes before being immersed in a mixture of potassium nitrite and sodium nitrite at 400℃ for 45 minutes. Friction and wear tests were then performed on austempered samples. Multi-walled carbon nanotube particles were blended at weight concentrations of 0.055, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, and 0.45 with typical machinery oil of 30 grade as base lubricant oil. A pin on the disc wear configuration was used in the experimental investigation. The use of Multi-Walled Carbon Nanotube (MWCNTs) additives in the base oil resulted in a decrease in both friction coefficients and wear rates values when compared to typical base oil lubricant. The results also showed a reduction in both friction coefficients and wear rates as the sample's austempering temperatures were raised. Sliding surfaces were also photo micro graphed, and when the volume concentrations of Multi-Walled Carbon Nanotube particles in the normal base oil lubricant were increased, smoother surfaces with less damage were shown.
The current study was absorbed on corrosion of ASTM A106 grade B -02 seamless carbon steel boiler pipes. Beyond corrosion experiments in corrosive medium with varying pH values, the weight lost in addition to corrosion rate (m.p.y) values were computed. The weight loss of boiler tube specimens exposed to corrosive liquid was shown to rise as the exposure period of the specimens increased. The results of the microstructure imaging showed that a de-carburized film of 240 µm thickness was shaped on the fireside of the pipe boiler, with ferrite and a few phases of pearlite. On the water lateral side, it was revealed that boiler pipe failure begins with small rust particles that expand to greater sizes and form scales that are displaced from the boiler pipe's surface. On the surfaces of the boiler pipe water side, several pits with crevice corrosion were observed. The corrosion amounts were discovered to decrease when the specimens' exposure time to corrosive environments and hydrogen ion concentration contents increased (pH). The findings of mechanical characteristic values such as hardness, yield strength, and tensile strength revealed that the waterside had higher values than the fireside, while the middle of the pipe had reasonable values. The findings also demonstrated that at low pH values, a tiny size of rust was created on the boiler tube specimen surface. However, at high pH values of corrosive medium, big sizes of corrosion rust were observed on the specimen surfaces.
In this paper, the amount of excess weight resulting from the design of a mathematical model composed of composite materials will be calculated and compared with a mathematical model of an armored steel structure. Five different models were designed, one of which is made of steel, the other part is made of composite materials, and a section of steel and composite materials, and then tested for resistance to stresses and compared the weight of each structure with that of the steel component by taking the maximum stress as a basic criterion for weight comparison. The results showed that the best model was the second model fiberglass, where the percentage of weight loss was compared to the steel model (73.77%), in addition to the wall thickness (62 mm) and the wall thickness of the steel model with which the comparison was (60 mm), but the displacement is (7. 24 mm), and in the steel model it is (1.827 mm). The best model compared to steel in terms of resistance to maximum stress, less displacement and less weight was the model consisting of steel with carbon fiber and its thickness was (47 layers& 57 mm, 2 layer & 10 mm steel and 45 layer & 45 mm carbon fiber), and the percentage of weight loss compared to the first mathematical model (60.96%). The results of this research may be a key to obtaining alternative materials for traditional materials in the manufacture of armored hulls, aircraft and ships, and it has a lower weight.
The present investigation deals with the study of the effect of austenizing and tempering heat treatment temperatures on the fatigue resistance of carburized 16MnCr5 steel. Rotating bending fatigue specimens were machined from 16MnCr (ASTM 5117(steel rod, and pack carburized at 900°C for 2 hours soaking time. Carburized specimens were then austenized at 900°C for one hour, water quenched, reaustenized at temperatures 750°C, 800°C and 900°C for one hour, then tempered at 200°C temperature. Other carburized specimens were tempered by heating to 760°C temperature, water quenched to room temperature, then tempered at temperatures 200°C, 300°C, and 400°C for one hour. Austenized and tempered steel specimens after carburization as well as uncarburized steel specimens were then tested by rotating bending fatigue machine up to fracture under different stress levels (200, 250, 300, 350, 400) Mpa. Experimental results showed that fatigue resistance of austenized steel specimens after carburization process has been increased, and the crack length developed on the specimen surfaces was decreased with an increase in austenizing temperature up to 800°C, due to lath martensitic microstructure formation, beyond this temperature fatigue resistance was decreased and crack lengths were increased due to the grain coarsening of the lath martensite. It was also concluded that fatigue resistance of steel specimens that have been tempered after carburization process was increased, while crack lengths due to fatigue have been decreased with an increase in tempering temperatures due to the formation of tempered martensite and troostitic microstructure. The results also revealed that uncarburized steel specimens showed a lower fatigue resistance and a higher crack lengths than those austenized and tempered specimens after carburization.
Weight is of great importance in the aircraft industry. Aircraft are made of aluminum alloys that are susceptible to heat treatment, because they are light in weight and are metal strong enough for the dynamic designed loads they can face, but there are other reasons for obtaining alternative materials, and these materials are composite materials that it is lighter in weight than aircraft made of aluminum, firstly, and secondly, it can be formed into attractive shapes, eliminating welding and rivets, and thirdly, it can be formed into aerodynamic shapes. This work is based on designing a three-dimensional model consisting of aluminum alloy (AA-6061-T6) of the structure helicopter and then comparing it with five other models of different metal and composite materials to obtain a structure that has the least weight among these models. The results indicate that the best model with the lowest weight is the fourth model consisting of carbon fiber, proportions and weight of a square meter and a thickness of (28 mm) than the weight of the first model consisting of aluminum and weighing (81 kg), it was less than (22.7%). Then the fifth model, which consisted of an outer layer of aluminum with a thickness of five millimeters and another inner layer of aluminum of the same thickness, and between the inner and outer layer eighteen layers of carbon fiber, where the percentage of decrease in it compared to the first model by up to (19.2%), and worse a model in terms of weight is the second model was made of steel, which has a weight that is almost twice the weight of the first model.
Recently, in connection with the increasing use of composite materials in various fields of modern technology, interest in theories of reinforced media and new technologies for their manufacture has significantly increased. Twenty-seven models were designed from metallic materials, one from aluminum, one from steel, and the third was composed of five layers, three from Epoxy and two from Steel. As for the non-metallic models, three models were made of fiberglass with different codes and three other models of epoxy with carbon fibers and also with different codes. All models are equal in weight, height and width but different in thickness. Three types of loads were shed in the middle of the models. The results of the comparison between the different models, after analyzing the results, indicate that the best model that can withstand the loads imposed on it is the model of composite materials (CFGR-Code2), while the worst model is the model of steel. The results of the analysis also indicate the effect of the change in the overload on the models is directly proportional to the same percentage change in the overload on the models, whether the models are composed of ferrous or non-ferrous materials composite materials.