The tempering process of medium and high carbon steel using quenching in water as quenching medium with different tempering temperatures has been investigated. The samples were quenched to room temperature in water. The mechanical properties and corrosion rate of the quench and tempering samples were measured. The result shows that hardness value of the medium and high carbon steel increased due to formation of martensite structure which is very strong phase but it is normally very brittle, so it is necessary to modify the mechanical properties and relieve internal stresses by heat treatment in the range 100-700°C. The experimental results revealed that mechanical properties of selective alloy were significantly changed by temper treatment. By increasing the tempering temperature, hardness and ultimate tensile strength are gradually decreased and ductility was improved. Moreover, the corrosion rate has been studied and shown within multiple phase structure corrosion rate increased more than martensite structure even its stressed structure.
The aim of this work is to study the effect of austenizing time, tempering process and tempering time on corrosion rate of austenitic stainless steel in oxalic acid. The samples of typical 304 stainless steel were heated to 1050°C for 10, 20 and 30 minutes and quenched to room temperature in water, then tempered at 250°C, 400°C and 600°C for 30, 60 minutes for each tempering time. These samples were then immersed in 0.1M of oxalic acid and then their weight losses were measured after 30 days. The result obtained show that corrosion rate of all austenitic stainless steel samples decreased with an increase austenizing time, this behaviour is due to more homogenously of austenite, and the corrosion rate will be increased with increase the tempering temperature and tempering time, this behaviour is due different phases at microstructure below 400°C, and above of 400 to 600°C the corrosion rate will be increased due to formation of carbides which are non-uniform distributed at the grain boundaries and causes intergranular corrosion.
In this work, the influence of heat treatment process and quenching in different quenchant media of medium carbon steel, gray and nodular cast iron with ferrite matrix on the hardness, ductility and corrosion rate of has been investigated. During this type of operations, the specimens were Austenizing at 900°C for one hour. Therefore, the specimens were quenched in different kind of oil as quenched medium (oil 20-50, oil 40, oil 90, and water as reference). The hardness , impact energy to measure the ductility, corrosion rate and microstructures were studied. From result of steel 0.47% carbon was clear increasing in hardness and decreasing in ductility with close varying values in oil quenchant kind comparing with as received specimen and water quenched one, corrosion rate decreased with heat treatment and quenching process due to formation of single face instead of double phase before heat treatment process which created galvanic cell. For gray and nodular cast iron it is noticeable that no changing in microstructure within heating for one hour at 900°C because the matrix in both cast iron types is ferrite, therefore no changing in mechanical properties under heat treatment process with time of one hour which is not sufficient to decomposition of graphite, but with comparison the hardness of gray cast iron is more than nodular one due to distribution of graphite flacks which increase the hardness and decrease the ductility as well as increasesing the corrosion rate compared with nodular cast iron. Microstructure of both types of cast iron have been studied after subjected the specimens to heat treatment at 1000°C and for 10 hours, the microstructures shown clear diffusion of some carbon in ferrite matrix around the graphite phase and under quenched some of martensite formed.
Wear is one of the problems that occurs in moving parts, whether rolling or sliding. Since the wear resistance is closely linked to the hardness of the involved surfaces, this research studies the possibility of increasing the hardness of low carbon steel, which is used extensively because its ductility and its shock resistance and being one of the inexpensive metals. A lot of mechanical parts require an external hard surface, resistant to wear, and at the same time high resistance to shocks. The main hardening process used in this research is the increase of the carbon proportion on the external surfaces of the equipment made of low carbon steel and thus, to make the heat treatments necessary to obtain the required properties of these surfaces such as hardness and high resistance to shocks. The study of the process of carbonization by using the solid carbonization as one of the ways of hardening the surface at temperatures in the austenite range of low carbon steels give an impression about the possibility of improvement in the qualities of hardness and resistance to wear. In order to obtain a variable thickness of the carbonated layer, a carbonization process was performed at different temperatures and times to demonstrate the effect of these two important factors to the amount of diffused carbon to the surface of the solid and thus the extent of its influence to obtain the required properties of the process. The mechanical and microscopic tests conducted on samples proved the success of the carbonization process to achieve the purpose and goal of the preparation of this paper. Finally experimental results have shown good correlation between the wear resistance and mechanical properties with temperature and carbonization time. The analysis of the variance of the results in this study indicated that the best mechanical properties are achieved when one performs the process of carbonization at 975°C for 20 hours.
In this work, the investigations were carried out to study the effect of heat treatment at dual phase of austenite and ferrite on mechanical properties , microstructure and corrosion rate of low alloyed medium carbon steel. The specimens were divided into five groups, first group, specimens were heated to the duel phase region at temperature of 740°C soaked for 30 minutes and quenched in water. The second group, The specimens were heated to 740°C soaked for 30 minutes and quenched in water, then tempered to 480°C soaked for 20 minutes. The third group the specimens were heated to austenizing temperature of 840°C soaked for 30 minutes and quenched in water, then the specimens reheated to the dual phase region at 740°C, soaked for 30 minutes and quenched in water, then the specimens were tempered at temperature 480°C for 30 minutes. The forth group, the specimens were heated to austenizing temperature of 840°C soaked for 30 minutes and quenched in water, this process were repeated again before the specimens were thereafter heated to the dual phase region at temperature of 740°C, soaked for 20 minutes and quenched in water, then the specimens were tempered at temperature 480°C for 20 minutes. The fifth group, the specimens were heated to austenizing temperature of 840°C soaked for 20 minutes and quenched in water, this process were repeated two times again before the specimens were thereafter heated to the dual phase region at temperature of 740°C, soaked for 20 minutes and quenched in water, then the specimens finally tempered at temperature 480°C for 20 minutes. The results proved the hardness increase after heat treatment at first and second group, at third group the highest hardness value was due to formation of martensite and ferrite, but at fourth and fifth groups hardness decreases due to appearance of carbides particles, also corrosion rate usually increases with two phase at microstructure than stable one phase, third group have less corrosion rate than fourth and fifth due to carbides particles formation which lead to more corrosion rate due to three phases presents.
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