Each alloy has its own unique composition. As for a material such as steel, it is known that it contains iron and carbon in certain proportions. Each steel grade has its own unique name, in which its chemical composition and physical characteristics are encrypted. Steel 45 is no exception. In this article, we will consider this popular alloy in more detail.
Chemical composition
Everyone who deals with alloys knows that the elements that make up their composition affect their performance. Steel 45 - structural carbon quality. From the name it becomes clear that its composition includes carbon - 0.45%. The majority, of course, is iron - 97%. The remaining 2.55% includes such chemical elements as manganese (0.7%), silicon (0.2-0.3%), nickel (0.25%), chromium (0.25%), copper (0.25%), arsenic (0.08), sulfur (0.04) and phosphorus (0.035%). Each of the alloying elements affects the performance of steel 45. For example, manganese is present in almost all steel grades. It removes oxygen from it and reduces the sulfur content. Silicon affects the hardenability of steel. In addition, it increases the yield strength and elasticity.
Carbon and its effect on the properties of steel
One of the most important components that strengthens this alloy and gives it hardness is carbon. In addition, it reduces ductility and toughness. The effect of carbon on the performance of steel 45 is clearly visible in the state diagram. From the structure of the alloy and will overhang its properties. So, for example, with a pearlite structure, steel is more amenable to processing and welding. The ferritic structure is characterized by low hardness and high ductility. Austenite in steels is always liquid, and when it cools, the position of carbon grains in the crystal lattice can significantly change.
Steel structure 45
So, cementite is a chemical compound Fe 3 C, and besides it, ferrite (C) is also present in steel. Together they form another structure - perlite. Since the carbon content is below 0.8%, such steel is considered to be hypereutectoid. And in order to improve its properties, it must be hardened or annealed. This is achieved by heating it, in which it goes into an austenitic state. Critical points for this alloy: AC 1 = 725 ° C, AC 3 = 770 ° C. When it is heated to 700 ° C, no noticeable changes will occur.
Consider the state diagram of steel 45 in more detail.
So, since 0.45% carbon is present in the alloy, on the lower horizontal line, it is necessary to find this value. Rising, up from it you can trace all the transformations in steel. So, when heated above the AC line, the alloy will be in a liquid state.
Then, with decreasing temperature, the atomic lattice of iron is rearranged from face-centered to body-centered and, accordingly, ferrite will prevail in it. A large amount of carbon will be gradually converted from austenite to perlite. The final structure of the alloy will depend on how the steel was cooled after quenching.
Heat treatment
If this alloy is not subjected to heat treatment, cementite and ferrite prevail in its structure, which means that it cannot be machined. The internal voltage between the atoms of this alloy will be so high that it will crack when milling and turning. In order to avoid this, heat treatment is used. It can consist of several processes: annealing, normalization, hardening, tempering. The heat treatment itself will depend on the type of product (forging, rolling) and on its technical purpose.
Looking again at the state diagram, we can conclude that 850 ° C is the optimum temperature for quenching. At this point, for steel with a carbon content of 0.45%, the transition to the austenitic state occurs.
Therefore, most often, steel 45 is quenched at a temperature of 850 ° C, and tempering is 550 ° C. In this case, the alloy will have a tensile strength of 900 MPa, a yield strength of 800 MPa, a toughness of 1.2 MJ / m2, a relative narrowing of 65% and a hardness of 260. If the tempering temperature is increased, the tensile strength, yield strength and hardness will decrease , and the remaining values, on the contrary, will increase.
Physical properties
As mentioned earlier, the characteristics of the alloy as a whole will depend on the hardening of steel 45. Ferrite itself is soft and fairly ductile, and perlite is hard, but more brittle. So, the pearlite structure looks like puff pastry. Soft ferrite crystals alternate with hard cementite. The latter, give perlite wear resistance and hardness. Based on this, it can be concluded that with an increase in carbon content, the volume occupied by perlite also increases and, of course, the properties of the alloy are improved.
In general terms, it can be said that steel 45 is quite strong, hardy and lends itself well to machining. Among the disadvantages, poor weldability and susceptibility to corrosion can be distinguished. Parts made of steel 45 are resistant to wear and can withstand temperature extremes from 200 to 600 ° C. More detailed information on physical and mechanical properties can be seen in the following table.
As for any other steel, for this before machining, it is necessary to calculate the cutting conditions. They must be sure to choose the right cutting tool, the spindle speed and, of course, calculate the feed. Despite the fact that steel 45 lends itself well to mechanical processing, with the wrong choice of cutting conditions, problems such as too hot flying off chips, arbitrary reduction in spindle speed are possible. In addition, for this type of machining such as turning, it is recommended to use coolant for this alloy.
Of great importance is the choice of cutting tools. It must be selected according to the hardness of steel 45. For example, the T15K6 cutter and others with similar properties are perfect.
Area of use
Based on the characteristics of steel 45, it can be concluded that the alloy is widely used in the metallurgical industry. So, spindles, cylinders, cams and a wide variety of shafts are made from it. It is these parts that must have increased strength. Various enterprises produce the form, assortment and sizes, which are determined by state standards. Steel 45 refers to difficult to weld alloys, so most of the range is made as seamless pipes.