Temperature range for hot processing of steel. Heating during stamping
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1 kelvin [K] = 1 degree Celsius [°C]
Initial value
Converted value
kelvin degree Celsius degree Celsius (centigrade) degree Fahrenheit degree Rankine degree Reaumur
Metric system and SI
Read more about temperature difference and temperature difference converter
General information
This temperature difference converter differs from a temperature converter in that it allows you to compare the temperature range on different scales. For example, in a temperature converter, 5 °C = 41 °F, and in this temperature difference converter, an interval of 5 °C is equal to an interval of 9 °F. That is, if, for example, you increase the temperature from 0 °C to 5 °C, then on the Fahrenheit scale it will rise from 32 °F to 32 + 9 = 41 °F. A similar example: a temperature difference of 100 °C is equal to a difference of 180 °F, that is, if you raise the temperature from 0 °C to 100 °C, then on the Fahrenheit scale it will rise from 32 °F to 32 + 180 = 212 °F.
In everyday life, in nature and in science and technology, temperature differences and temperature intervals are of great importance. For example, climatology monitors changes in the difference between average annual temperatures, temperatures at certain times of the year, and other weather features. This helps identify changes in climate patterns, such as those caused by global warming. In cooking, food is cooked and the temperature ranges within which the food is heated affect the taste and whether microorganisms that are dangerous to humans can be destroyed at that temperature. In nature, temperature ranges of a substance affect its state of aggregation. These are not all examples where temperature differences play an important role, but this article describes two recent examples with cooking and states of matter.
Change in the state of aggregation of a substance
For each substance, there are temperature ranges at which it is in one of three states of aggregation - in crystalline form, in the form of liquid, or gas. The temperature at which solids turn into liquid is called melting point, and the temperature at which the liquid evaporates and turns into gas is called boiling point. The temperature range for each state of aggregation, as well as the melting point and boiling point, depend on pressure. Usually they talk about boiling and melting points for normal atmospheric pressure. In this case the boiling point is called normal boiling point, and the melting point is called normal melting point.
At sufficiently high temperatures, substances acquire special properties - liquids and gases behave in the same way in this case. This condition is called critical point.
Typically, substances in solid, liquid and gaseous states exist at certain temperature ranges and a certain pressure, but sometimes a change in the state of aggregation occurs at other temperatures. For example, liquids often evaporate at temperatures lower than their boiling point. This evaporation is a slower process compared to evaporation during the boiling process.
Pressure and boiling of water
Many people know the freezing and boiling points of water at normal atmospheric pressure. The normal melting point of ice (and freezing point of water) is 0 °C (32 °F), and the normal boiling point is 100 °C (212 °F).
When climbing peaks, climbers are often exposed to low atmospheric pressure. Under these conditions, water boils at lower temperatures. The boiling point decreases by 1°C every 285 meters (935 feet). For example, at the summit of Everest (8,848 meters or 29,029 feet), water boils at a temperature 71 °C (160 °F). At higher altitudes above sea level, you have to cook food longer or use portable pressure cookers - they reduce the cooking time, since the pressure in them artificially increases, and with it the boiling point also increases.
The boiling point of water at a certain pressure is the maximum temperature that water can reach under those conditions. That is why altitude above sea level and, accordingly, atmospheric pressure primarily affect cooking using water, for example, boiling. The maximum air temperature is not affected by pressure, so “dry” cooking methods, such as baking, are practically no different from cooking at sea level.
An increase in pressure, on the contrary, increases the boiling point of water, making it higher than 100 °C (212 °F). This significantly speeds up the cooking process. Pressure cookers work on this principle - the steam generated during the cooking process remains inside, thereby increasing the pressure and, accordingly, the temperature.
Temperature differences and temperature intervals in cooking
In cooking, temperature ranges are very important, since the choice of temperature during cooking affects its consistency and taste. Temperature has a particularly strong effect on the proteins found in foods, as proteins behave differently at different temperatures. At room temperature, the protein molecule is twisted into a ball, and holds its shape thanks to the chemical bonds inside the molecule. With increasing temperature, these bonds weaken and the molecule gradually unwinds and straightens. This affects the taste, consistency and texture of the product. This process is called denaturation or coagulation of proteins. If the temperature is raised even higher, the unwound molecules combine with other molecules and further change the structure of the protein. This is how products acquire the familiar “ready” taste. This process is affected not only by temperature, but also by cooking time. Denaturation can also occur when proteins come into contact with acidic foods.
Cooking eggs
If you boil or fry eggs at a temperature 63°C to 65°C (145°F to 150°F), then they gradually begin to thicken, as the process of denaturation of the proteins they contain begins. For some recipes, eggs are cooked at this temperature to create a semi-runny yolk and a slightly runnier white. Soft-boiled eggs, as well as the similar consistency “onsen-tamago” (from the Japanese “hot spring eggs”), are prepared this way. Onsen tamago was originally prepared in hot springs in Japan, hence its name. They are usually served for breakfast along with rice, miso soup, baked fish and pickled vegetables.
Eggs harden at temperatures between 70 °C and 73 °C (158 °F and 165 °F). If you cook them for a long time at a temperature 100 °C (212 °F) or higher, they lose their softness and become “rubbery”.
Cooking meat
The chemical reactions that occur in meat proteins during heat treatment change its color. The degree of readiness of meat can also be determined by the temperature at which it was cooked. A food thermometer is often used to determine whether meat is done. This is especially useful when cooking thick cuts of meat, such as roast beef, baked meat, or poultry. In this case, it is important to measure the temperature inside the meat and not at the surface, since the inside warms up more slowly than the outside and its temperature is always lower.
At 50°C (120°F) the meat takes on a pinkish or white tint. If you cook it at a lower temperature, from 46°C to 49°C (115°F to 120°F), you will get extra-rare, blue or bleu meat that is fried on the outside and raw on the inside. If the temperature inside the meat has reached 52°C to 55°C (130°F to 140°F), you will get rare meat, also known as rare or saignant.
As the temperature increases, the meat will brown and crisp, especially between 55°C and 60°C (130°F and 140°F). At this temperature, the meat turns out to be medium raw, that is, medium rare, or à point. The color of the meat darkens as a result of the oxidation of iron, which is contained in the proteins of muscle tissue. At this stage of cooking, the meat releases its juices and its structure begins to change.
As the meat heats up to 70°C (160°F), it becomes softer as the molecules of collagen, the substance that is responsible for the structural strength of meat, are gradually destroyed. During this process, collagen turns into gelatin. Because this is a long process, tougher meats, such as meats with muscle tissue that have been heavily used by the animal, or meat from older animals, need to be cooked longer. To make the meat softer, you can also cut it into small pieces. The temperature in the reduced piece rises faster and helps speed up the process of converting collagen into gelatin when exposed to temperature.
If you cook meat at very high temperatures 140°C to 150°C (285°F to 302°F), then a brown crust also forms, but this is not due to oxidation. In this case, a Maillard chemical reaction occurs - a reaction between amino acids and sugars. It changes the taste of meat and other foods to the familiar “fried” or “baked” taste, and turns the surface of meat and other foods brown. This reaction also occurs when baking bread, making maple syrup, cooking coffee beans, and in many other cases.
Meat can turn brown due to another reaction - caramelization. It occurs at temperatures between 110 °C and 160 °C (230 °F and 320 °F), depending on the sugars contained in the product. During this reaction, the sugars turn brown and take on a caramel-like flavor. This reaction occurs in any food containing sugar.
Food safety
Food is cooked not only to improve its taste, but also to kill bacteria in it. If foods are consumed raw (for example, fish in sushi or raw meat), then they are sometimes frozen for the same purpose. Salmonella, which is found in eggs, meat, fish, dairy products, and even some vegetables, can be killed by heating food to a temperature of 65°C to 70°C (150°F to 160°F). At 70°C (160°F) these bacteria die instantly, but at lower temperatures the cooking time must be longer. It used to be that you could get rid of salmonella in eggs by simply washing the outside of raw eggs, that is, by making the shells clean. It is now known that salmonella can also infect the inside of the egg, so heat treatment is necessary for safety.
Another microorganism dangerous to health is E. coli. It is found in raw meat, dairy products, vegetables and fruits. Heat treatment at 71°C (160°F) kills this organism.
Salmonella and E. coli can cause stomach upset, nausea, and diarrhea in humans. These symptoms disappear in many people after a week even without treatment, but in some cases the infection is quite dangerous and the patient is admitted to the hospital. In the most severe cases, death is possible. To avoid this contamination, you should follow safety rules and cook food. This is especially important if these products are intended for people at risk: children, pregnant women, the elderly, and those with weakened immune systems. There are a huge variety of ways to prepare and process meat, eggs, dairy and other products, so there is always a suitable recipe for even the most picky person, so it is better not to put your health at risk by consuming unprocessed foods.
Infection with E. coli and salmonella can also be prevented by pasteurizing food products. During this process, milk, juices and other products are heated to a certain temperature for a set period of time. For example, milk can be heated for 30 minutes at 63 °C (145 °F), 15 seconds at 72 °C (161 °F) or 2 seconds at 138 °C (280 °F). During pasteurization, denaturation of enzymes inside microorganisms occurs. In this case, the water in the bacterial cells expands and damages or destroys the walls of these cells. When exposed to high temperatures during pasteurization, the structure of proteins in bacterial cells changes, further weakening the walls of these cells. Pasteurization does not kill all bacteria, but reduces their number so much that the likelihood of infection spreading is significantly reduced. Thanks to pasteurization, milk is one of the safest foods if stored in the refrigerator and consumed before the expiration date.
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Heating the metal before pressure treatment.
At certain temperatures, plastic materials have high ductility and low resistance to deformation. These temperatures have upper and lower limits, between which lies the temperature range of pressure treatment.
During cold deformation (i.e., at temperatures for pure metals usually below 0.3 absolute melting temperature), hardening (hardening) of the deformed metal occurs. In this case, the elongation of its grains in the direction of deformation is observed, a certain crystallographic orientation of the grains (texture) is created, crystallographic lattices are distorted, additional (secondary) stresses accumulate, etc. Phenomena. The strength, yield, and hardness of the metal increase, while elongation, transverse contraction, and impact strength decrease. With increasing deformation, hardening increases, further deformation becomes difficult and, finally, impossible. Then the destruction of the deformed metal occurs.
As the deformation temperature increases, processes occur in the metal that prevent hardening, namely recovery (rest) and crystallization (softening processes).
Return, the signs of which appear at temperatures usually above 0.3 absolute melting point, is to reduce the distortion of the crystallographic lattice resulting from deformation and reduce additional stresses. However, in the presence of recovery, signs of hardening still appear, although to a lesser extent, therefore the main role in softening is played by recrystallization, the signs of which appear at temperatures usually above 0.4 melting point.
Recrystallization consists in the appearance in the deformed layer of metal of new crystallization centers and the growth around them of new grains with a new orientation of the crystallographic lattice and new boundaries between the grains. With complete recrystallization, the deformed metal has no traces of hardening.
If recrystallization does not proceed completely, then a decrease in ductility is observed. This is explained by the fact that the metal becomes inhomogeneous as a result of the presence of recrystallized and non-recrystallized grains, and often a non-single-phase state (if the temperature coincides with the temperature of phase transformations). Therefore, heating is necessary to a temperature that ensures complete recrystallization of the metal during forging or stamping. This determines the lower limit of the temperature range of hot metal forming.
The completion of the recrystallization process depends not only on temperature, but also on the rate of deformation, since recrystallization does not occur instantly. This explains the lower resistance to deformation of metal in a hot state on a press than on a hammer. With increasing temperature, plasticity increases. However, at temperatures close to the melting point, the metal melts and oxidizes along the grain boundaries, the bond between grains is broken, and the metal completely loses its ductility and strength. This phenomenon is called burnout.
Below the burnout temperature is the temperature overheating. At this temperature, a process of continuous grain growth (collective crystallization) occurs in the metal. This temperature can be called critical. At the same time, during pressure treatment the grains are destroyed. Therefore, for a number of metals, for example, for most steels, coarse grain size is not an obstacle when forging and stamping. Thus, the upper range of hot pressure treatment is either below the overheating temperature or below the burnout temperature, within the overheating temperature (depending on the type and properties of the metal).
The temperatures at the beginning and end of pressure treatment for alloys with a base fluctuate sharply depending on the content of other components in them. For example, for various wrought aluminum alloys, the upper limit is between 470 - 500˚C, the lower - between 350 - 400˚C; for copper alloys, the upper limit is between 700 - 900˚С, the lower limit is between 550 - 800˚С; for magnesium alloys, the upper one is 370 - 430˚С, the lower one is 300 - 350˚С; for titanium alloys, the upper one is 1000 - 1200˚С, the lower one is 700 - 950˚С; for steel, the upper one is 1100 - 1300˚С, the lower one is 800 - 950˚С.
If we mark on the diagram the state of the iron-carbon alloy and the temperature range of pressure treatment of carbon steels, then its upper limit will be located on the curve passing 150 - 200˚C below the solidus line. The lower limit of the temperature range for carbon steels corresponds to approximately 800˚C, i.e. approximately 75°C above the PSK line. Thus, steel containing from 0.4% to 1% C from the beginning to the end of pressure treatment is in a single-phase state (austenite). Carbon steel with a lower carbon content is finished processing in the presence of two phases: austenite and ferrite. This results in some hardening, which is easily removed by subsequent heat treatment.
Carbon steel containing more than 1% C is also finished when it contains two phases: austenite and secondary cementite. But in this case, pressure treatment, crushing the cementite network, has a beneficial effect on the structure of the steel. The temperature range for forging and stamping of non-ferrous metals and alloys is determined from the plasticity diagram, flow curves, deformation resistance diagrams, state diagrams and recrystallization diagrams.
The boiling range (distillation range) is the adjusted temperature range over which all or a specified portion of a substance is distilled at normal atmospheric pressure, when determined by the method described below.
A suitable determination apparatus consists of a distillation flask, a refrigerator, a receiver, a heat source with a protective shield, and a thermometer.
A distillation flask with a capacity of 50-60 ml should be made of heat-resistant glass. The following sizes of flasks are convenient: neck 10-12 cm long and internal diameter 14-16 mm; a side outlet 10-12 cm long and an internal diameter of about 5 mm is located in the middle of the neck of the flask and forms an angle of 70-75° with the lower part of the neck.
The refrigerator is a straight glass refrigerator made of heat-resistant glass, 55-60 cm long, with a water jacket about 40 cm long or refrigerator
another system with the same cooling capacity. The lower end of the condenser may be curved to serve as an outlet tube, or a curved tip may be attached to the condenser for this purpose.
The receiver is a measuring cylinder with a capacity of 25-50 ml with a scale division of 0.5 ml.
The heat source consists of a small gas burner, preferably a Bunsen burner, or an electric heater, providing the same heat control as a gas burner. If a gas burner is used, the base of the flask is covered with an asbestos screen. The screen is made from a sheet of asbestos 5-7 mm thick in the shape of a square with a side of 14-16 cm and a hole in the center. The diameter of the latter should be such that the part of the flask inserted into it below the upper surface of the asbestos sheet has a capacity of 3-4 ml.
It is advisable that the thermometer be calibrated for partial immersion of 100 mm as described in section A to determine the melting point and melting temperature range of the substances being ground; otherwise, a thermometer calibrated for full immersion can be used, with appropriate allowance for the protruding column. Once the thermometer is installed, the column should be positioned in the center of the neck of the flask, and the top of the ball should be directly below the base of the side outlet.
More on topic D. Determination of the boiling temperature range (distillation range):
- DETERMINATION OF MELTING POINT, MELTING RANGE, SOLIDIFICATION POINT, BOILING POINT AND BOILING RANGE
Heating a metal increases its ductility. However, heating temperatures must lie within a certain range.
Too low heating temperatures can cause hardening (hardening) of the metal. Hardening (hardening) – the phenomenon of a decrease in the plasticity margin of a material due to distortion of the crystal lattice and a change in the shape of metal grains under the influence of a power tool (stamp). Hardening can cause destruction of the original workpiece during pressure treatment due to a decrease in ductility.
Too high heating temperatures cause phenomena such as overheating and burnout.
Overheat characterized by a sharp increase in grain size, causing a decrease in the ductility of the metal. Overheating degrades the properties of the resulting products and should be avoided. In most cases, the consequences of overheating can be corrected by subsequent heat treatment (annealing), but for a number of materials such correction causes significant difficulties.
Burnout occurs at higher temperatures than overheating. Overburning is characterized by oxidation and melting of grain boundaries, which disrupts the connection between them. In case of overburning, the material cannot be processed under pressure and must be sent for remelting, since overburning is an irreparable type of defect.
The temperature interval located between the optimal temperatures of the beginning and end of hot processing of the material is called temperature range of hot pressure treatment. This interval is in the region of maximum plasticity of a particular material. Moreover, in this temperature range, the phenomena of hardening (hardening) of the metal, overheating and burnout should not occur.
The temperature range of hot forming for carbon and alloy steels is given in table 3.
The volume of subsequent mechanical processing associated with obtaining a part from a workpiece is, with a certain degree of approximation, estimated by the coefficient of use of the workpiece metal - KIMZ. The more KIMz, the lower the consumption of metal removed as waste during mechanical processing of a workpiece obtained by pressure treatment.
KIMz = Mdetails / Mforgings = Vdetails / Vforgings.
The volume of the forging (Vforging) differs from the volume of the part by the amount of stamping slopes, machining allowances, rounding radii and overlaps.
The volume of metal attributable to the radii of roundings of intersecting surfaces is calculated as half the volume of a truncated cone, the generatrix of which passes through the junction of the radius with the intersecting surfaces.
Plasticity called the ability of metal deform without breaking under load .
At tensile test Plasticity is determined by two quantities: relative elongation and relative narrowing.
In order to understand how these values are determined, the sample should be compared with the destroyed sample before testing, as is done in Fig. 22 (above). After destruction, the sample turned out to be longer, but it narrowed, especially at the necking site.
Relative extension determines the amount by which the sample has elongated after stretching relative to its original length.
This value is denoted by the letter δ (delta) and is expressed as a percentage:
· l 0- initial estimated length of the sample in mm;
· l- final value of the estimated length in mm.
The tensile strength is defined as
Relative narrowing characterizes the degree of reduction in the cross-sectional area in the neck.
This value is designated by the letter φ (psi) and is expressed as a percentage:
· F 0- initial area in mm 2;
· F-- area in the neck in mm 2.
Usually mechanical characteristics of metal at high temperatures reaching the melting point, determined on special installations, including a heating device that simulates the welding temperature cycle, and a mechanical part and equipped with recording devices.
The sample to be tested is heated to the temperature at which it is necessary to determine its properties, and loaded, recording the curves П = f(T).
In Fig. Figure 12.39 shows typical curves characterizing the change in strength and ductility of alloys at high temperatures. In the region of heating to temperatures close to the equilibrium solidus temperature (Tc), the strength and ductility of the alloys drop sharply.
Plasticity remains at a very low level in a certain temperature range, and then increases again.
Such an ambiguous change in properties can be explained by considering the process of crystallization of a metal from a liquid state.
After melting, the metal under study is cooled and, starting at a temperature T, nuclei of the solid phase are formed in it. As long as the amount of the solid phase is small, the metal is in a liquid-solid state, the plasticity of the melt is practically no different from the plasticity of the liquid, since the crystals of the solid phase move freely in the liquid, without limiting its ability to flow and take any shape (Fig. 12.40 , A). Metal is able to take on a new shape under load without collapsing.
Starting from a certain temperature, called the temperature of the upper limit of the brittleness interval (T VG), the metal passes into the stage of a solid-liquid state, characterized by such an increase in the amount of the solid phase, in which the ability of liquid to flow between solidified grains sharply decreases.
During deformation, grains jam, and further process becomes possible only in the case of plastic deformation of the grains themselves or their displacement relative to each other.
However, the strength of the crystallized solid phase during this period is much greater and therefore, if destruction occurs, it occurs along the grain boundaries, i.e., it is intercrystalline in nature.
The plasticity of a metal at this stage of solidification is very small - a fraction of a percent. The metal is capable of taking on a new shape under load with destruction along the grain boundaries, including eutectics, the strength of which is lower than the strength of the hardened grains.
With a further decrease in temperature, the strength of the interlayers increases, their volume decreases, and the number of contacts between grains increases.
At the same time, the strength of the grain boundaries themselves increases. At a certain temperature, the boundaries become so hardened that destruction begins to occur not along them, but along the body of the grains themselves (point A).
In this case, the plastic properties of the material increase, since the deformation is no longer concentrated in small layers between the grains, but is perceived by the entire aggregate quite uniformly.
