At what degrees does metal melt? Melting point of stainless steel and cast iron

The melting points of almost all currently widely used metals are given in Table. 1. Some rare metals are also mentioned there, the production and use of which is continuously growing. As you can see, the melting point of metals covers a very large range from -39 (mercury) to 3400 °C (tungsten).
Metals with a melting point below 500-600 °C are called fusible. Low-melting metals include zinc and all other metals listed in the table. 1 above it. It is also customary to distinguish the so-called refractory metals, classifying among them those that have a higher melting point than iron (1539 °C), i.e., according to Table. 1 is titanium and then up to tungsten.

From the data in table. 1 shows that the densities of metals at room temperature also have a very wide range. The lightest metal is lithium, which is approximately 2 times lighter than water. In technology, it is customary to distinguish a group of light metals that serve as the basis for structural metal materials in aviation and rocket science. Light metals include those whose density does not exceed 5 g/cm3. This group includes titanium, aluminum, magnesium, beryllium, and lithium.
Along with density, denoted by the letter d, the inverse value is used to describe the properties of metals - specific volume v = 1d (cm3 g).
With increasing temperature, the density of all metals in the solid state decreases, and the specific volume increases accordingly. The increase in the specific volume of a solid metal that does not experience polymorphic transformations when heated to Δt can be described quite accurately linear dependence vtvt=vtv20°C (1+βtv Δt), where βtv is the temperature coefficient of volumetric expansion. As is known from physics, βt = 3α, where α is the temperature coefficient of linear expansion in a given temperature range. For most metals, heating from room temperature to the melting point causes an increase in volume by 4-5%, so dmtmel = 0.95/0.96dm20°C.
The transition of a metal to a liquid state is accompanied in most cases by an increase in volume and a corresponding decrease in density. In table 1 this is expressed through the change in specific volumes Δv = 100 (vl - vsol)/vl, where vl and vsol are the specific volumes of liquid and solid metal at the melting temperature. It can be shown that Δv = 100 (vl - vtv)/vl = Δd = 100 (dtv - dl)/dtv. The decrease in density during melting is expressed by several percent. There are several metals and non-metals that exhibit a reverse change in density and specific volume upon melting. Gallium, bismuth, antimony, germanium, and silicon decrease in volume during melting, and therefore their Δv has a negative value. For comparison, it can be noted that for Veda Δv = -11%.
A slight change in the volume of metals during melting indicates that the distances between atoms in a liquid metal differ little from the interatomic distances in a crystal lattice. The number of nearest neighbors of each atom (the so-called coordination number) in a liquid is usually slightly less than in a crystal lattice. For metals with close-packed structures, the coordination number during melting decreases from 12 to 10-11; for metals with o. c. due to the structure, this number changes from 8 to 6. In a liquid metal near the melting point, short-range order is maintained, in which the arrangement of neighboring atoms at a distance of approximately three atomic diameters remains similar to what it was in the crystal lattice, which is known to have also in a long-range manner. When melting, metals do not experience a fundamental change in a number of properties: thermal conductivity, heat capacity; electrical conductivity remains of the same order as in the solid metal near the melting point.
An increase in the temperature of a liquid metal causes not only a gradual change in all its properties, but also leads to gradual structural rearrangements, which are expressed in a decrease in the coordination number and the gradual disappearance of short-range order in the arrangement of atoms. The increase in the specific volume of liquid metal caused by an increase in temperature can be approximately described by the linear dependence vlt = vltpl (1 + βl Δt). The temperature coefficient of volumetric expansion of liquid metal is significantly greater than that of solid metal. Typically βl = 1.5/3βsol.
Alloys, both in solid and liquid states, are generally not perfect solutions, and the fusion of two or more metals is always associated with a change in volume. As a rule, there is a decrease in the volume of the alloy compared to the total volume of pure components, taking into account their content in the alloy. However, for technical calculations, the reduction in volume during fusion can be neglected. In this case, the specific volume of the alloy can be determined by the additivity rule, i.e., by the values ​​of the specific volumes of pure components, taking into account their content in the alloy. Thus, the specific volume of the alloy, which consists of components A, B, C, ..., X, contained as a percentage by weight in the amount of a, b, c, ..., x is equal to

where vA, vB, vC, vX are the specific volumes of pure components at the temperature for which the specific volume of the alloy is calculated.
The change in the volume of liquid metal before and during crystallization predetermines the most important casting property - volumetric shrinkage, which manifests itself, as will be shown later, in the form of shrinkage cavities and porosity (looseness) in the body of the casting.
The maximum possible value of the relative volumetric shrinkage of the casting is equal to Δvmax = 100 (vлт - vтвtп)/vлt, where vлt is the specific volume of liquid metal at the pouring temperature t; ttvtmel - specific volume of solid metal at the melting temperature.
The experimentally detected volumetric shrinkage in castings is usually less than the value Δvmax. This is explained by the fact that when filling the casting mold, the melt cools and crystallization may even begin, therefore the initial state of the melt in the casting mold is not characterized by the specific volume vtl. Cooling the solidified casting to room temperature does not affect the relative volumetric shrinkage.
In castings made of metals and alloys that have negative Δv values ​​(see Table 1), not shrinkage is detected, but so-called growth - squeezing out the melt onto the surface of the castings.

The melting method of the metal and the lining material depend on the melting temperature of the metal. melting furnace or crucible and linear shape. The melting point and density of all base metals are given in Table 1.1.

The density of metals is measured by mass per unit volume. The density value is used in calculating the mass of the melt or castings according to geometric dimensions or their volumes, if the mass is known.

Of the metals listed in Table 1, the lightest is lithium, and the heaviest are tungsten and gold, having a density of more than 19 g/cm 3 . The melting point of metals covers the range from - 39 o C for mercury to 3400 o C for tungsten.

Metals with a melting point below 500 - 600 o C are called fusible. In table 1.1 low-melting metals include zinc and all other metals located before it. It is also customary to distinguish refractory metals, including those that have a higher melting point than iron, that is, according to Table 1, these are titanium and then up to tungsten.

From the table 1.1 it can be seen that the density of metals at room temperature also has a very wide range of values.

Melting point and density of metals

In technology, it is customary to distinguish a group of light metals that serve as the basis for structural metal materials. Light metals include those whose density does not exceed 5 g/cm 3, that is, this group includes titanium, aluminum, magnesium, beryllium, and lithium.

The melting point of the alloy is calculated taking into account the concentration, atomic mass and lowering the melting temperature of the base metal:

For example, melting point pure iron decreases in the presence of 1 mass%: Cu- 1 o C; V, Mo, M n - 2 o C; Al- 3.5 o C; Si- 12 o C; Ti- 18 o C; P- 28 o C; S- 30 o C; C- 73 o C; B- 90 o C.

With an increase in temperature from room temperature to the melting point, the density of most metals decreases by 3-5% due to the fact that the transition of the metal to the liquid state is accompanied by an increase in volume. The exceptions are helium, bismuth, antimony, germanium and silicon, which upon melting decrease in volume with a corresponding increase in the density of the melt.

The change in the density of the alloy during the transition from the liquid to the solid state determines volumetric shrinkage. In castings made from alloys with a positive value D With shrinkage manifests itself in the form of shrinkage cavities and small pores, and with negative value D With- in the form of growths (melt extruded onto the surface of the casting).

Along with the density ( With), to describe the properties of metals, the inverse quantity is used - specific volume V = 1/s cm 3 /G. With increasing temperature, the density of all metals in the solid state decreases, and the specific volume increases accordingly. An increase in the specific volume of a solid metal that does not experience polymorphic transformations when heated to Dt can be quite accurately described by a linear dependence. , where is the temperature coefficient of volumetric expansion. As is known from physics, the temperature coefficient of linear expansion in a given temperature range.

The transition of the metal into the liquid state is accompanied mainly by an increase in volume and a corresponding decrease in density. In table 1 this is expressed through the change in specific volumes, specific volumes of liquid and solid metal at the melting temperature. It can be shown that

A slight change in the volume of metals during melting indicates that the distance between atoms in a liquid metal differs little from the interatomic distances in a crystal lattice.

An increase in the temperature of a liquid metal causes a gradual change in its properties and leads to gradual structural rearrangements, which are expressed in a decrease in the coordination number and the gradual disappearance of short-range order in the arrangement of atoms. The increase in the specific volume of the melt caused by an increase in temperature can be approximately described by a linear dependence. The temperature coefficient of volumetric expansion of liquid metal is significantly greater than the same coefficient of solid metal. Usually.

Alloys, both in solid and liquid states, are generally not perfect solutions, and the fusion of two or more metals is always associated with a change in volume. As a rule, there is a decrease in the volume of the alloy in comparison with the total volume of pure components, taking into account their content in the alloy. However, for technical calculations, the reduction in volume during fusion can be neglected. In this case, the specific volume of the alloy can be determined by the additivity rule, that is, by the values ​​of the specific volumes of pure components, taking into account their content in the alloy. Thus, the specific volume of the alloy, which consists of components contained in percentage by weight in quantity, is correspondingly equal to

Here are the specific volumes of pure components at the same temperature for which the specific volume of the alloy is calculated. It is important to keep in mind that the specified additivity rule, as written above, is valid specifically for the specific volume of the alloy. If you replace specific volumes with densities, you get a much more complex expression, so it makes more sense to use specific volumes.

IN scientific research a quantity often used is called the atomic volume or gram-atom volume of a metal or alloy. This value is found by dividing the atomic mass by the density. For metals, the atomic volume has limits of 5 - 20 cm 3, more often 8 - 12 cm 3.

Density depends on the nature of the substance (alloy), on the complex of individual properties of the elements included in its composition, and the type of their interaction. The same substance (metal) can have different densities depending on its crystal structure, the type of crystal lattice. For example, Fe b= 768 and Fe G = 7,76; WITH alm = 3,51, WITH graph = 2,23; b quartz = 2,65, V quartz= 2.51, etc.

It is important to consider the difference between the concepts of “density” and “ specific gravity» material.

Density is the ratio of the mass of a substance to its occupied volume:

Where m- mass, g (kg); V- volume, cm 3 (m 3); With- density, g/cm 3 (kg/m 3).

Specific gravity is defined as the ratio of the weight of a substance to its occupied volume:

Where P- weight, g (kg); G- specific gravity, cm 3 (m 3).

Weight is found in relation to:

Where g- acceleration free fall; k- proportionality coefficient, depending on the choice of units of measurement included in the formula of quantities.

And therefore

In the same system of units, density and specific gravity are not numerically the same. For example, for distilled water in various systems units c and g have different meanings(Table 1.2).

The agreement between the numerical values ​​of density and specific gravity taken from different systems units of measurement is sometimes the reason for replacing one quantity with another.

Body mass- a constant value and is a measure of the gravitational and inertial properties of matter, and weight- variable quantity depending on the acceleration of free fall at the observation point. Therefore, specific gravity cannot be a reference value.

The ratio of the masses of two bodies at the same observation point is attitude weights of these bodies:

Therefore, when weighing, the mass of the body is found by comparing it with the mass of the weights. As a result of weighing, the mass of the material is determined.

In practice, density is determined to detect changes in the final metal compared to the original untreated metal. Therefore, what matters is not the fact of establishing the density, but the fact of the difference in densities, or, what is even more significant, the ratio of densities:

Methods for determining density are classified according to group criteria: weight, volume, immersion.

TO weight methods include hydrostatic weighing, micrometric method, hydrometric method of constant volume and mass, etc. These are the most common and accurate methods.

Volumetric - determining the volume of a sample by linear measurements (sample of regular shape) using gas or liquid volume meters. Volumetric methods (based on geometric dimensions) make it possible to make accurate calculations when large volumes samples.

Density balancing in a liquid is called the immersion method. It also includes the thermogradient tube method, etc.

In addition to those listed, mechanical, radiation, refractometric, analytical and other methods for determining density by indirect indicators are also used.

To ensure that the molten metal fills the mold well, surface tension and its viscosity should not interfere with the forward movement of the melt until it is completely filled. Viscosity, surface tension and diffusion affect the processes of refining, alloying, and modifying alloys.

The melting point of a metal is the minimum temperature at which it changes from solid to liquid. When melting, its volume practically does not change. Metals are classified by melting point depending on the degree of heating.

Low-melting metals

Low-melting metals have a melting point below 600°C. These are zinc, tin, bismuth. Such metals can be melted by heating them on the stove, or using a soldering iron. Low-melting metals are used in electronics and technology to connect metal elements and wires for movement electric current. The temperature is 232 degrees, and the zinc is 419.

Medium melting metals

Medium-melting metals begin to transition from solid to liquid at temperatures from 600°C to 1600°C. They are used for the manufacture of slabs, fittings, blocks and other metal structures, suitable for construction. This group of metals includes iron, copper, aluminum, and they are also part of many alloys. Copper is added to alloys precious metals such as gold, silver, platinum. 750 gold consists of 25% alloy metals, including copper, which gives it a reddish tint. The melting point of this material is 1084 °C. And aluminum begins to melt at a relatively low temperature of 660 degrees Celsius. This is a lightweight, ductile and inexpensive metal that does not oxidize or rust, therefore it is widely used in the manufacture of tableware. The temperature is 1539 degrees. This is one of the most popular and affordable metals, its use is widespread in the construction and automotive industries. But due to the fact that iron is subject to corrosion, it must be additionally processed and covered with a protective layer of paint, drying oil, or prevent moisture from entering.

Refractory metals

The temperature of refractory metals is above 1600°C. These are tungsten, titanium, platinum, chromium and others. They are used as light sources, machine parts, lubricants, and in the nuclear industry. They are used to make wires, high-voltage wires, and are used to melt other metals with a lower melting point. Platinum begins to transition from solid to liquid at a temperature of 1769 degrees, and tungsten at a temperature of 3420°C.

Mercury is the only metal that is in a liquid state at normal conditions, namely, normal atmospheric pressure and average temperature environment. The melting point of mercury is minus 39°C. This metal and its vapors are poisonous, so it is used only in closed containers or in laboratories. A common use of mercury is as a thermometer to measure body temperature.

After crystallization, it is necessary to ensure that the substance is sufficiently pure. The simplest and most effective method for identifying and determining the purity of a substance is to determine its melting point ( T pl). Melting point is the temperature range at which a solid turns into a liquid phase. All pure chemical compounds have a narrow temperature range of transition from solid to liquid. This temperature range for pure substances is a maximum of 1–2 o C. The use of melting point as a measure of the purity of a substance is based on the fact that the presence of impurities (1) lowers the melting point and (2) expands the melting temperature range. For example, a pure sample of benzoic acid melts in the range of 120-122 o C, and a slightly contaminated one - at 114-119 o C.

The use of melting points for identification is obviously subject to great uncertainty, since there are several million organic compounds and inevitably many of them have similar melting points. However, firstly, T The pl of the substance obtained in the synthesis almost always differs from T pl of the starting compounds. Secondly, the technique of “determining the melting point of a mixed sample” can be used. If T pl of a mixture of equal quantities of the test substance and a known sample does not differ from T pl of the latter, then both samples represent the same substance.

METHOD FOR DETERMINING THE MELTING TEMPERATURE. Carefully grind the test substance into a fine powder. Fill a capillary with the substance (3–5 mm in height; the capillary should be thin-walled, sealed on one side, with an internal diameter of 0.8–1 mm and a height of 3–4 cm). To do this, carefully press the capillary with its open end into the powder of the substance and periodically hit its sealed end on the table surface 5–10 times. To completely displace the powder to the sealed end of the capillary, it is dropped into a vertical glass tube (30–40 cm long and 0.5–1 cm in diameter) onto a hard surface. Insert the capillary into a metal cassette attached to the spout of the thermometer (Fig. 3.5), and place the thermometer with the cassette in the device to determine the melting point.

In the device, a thermometer with capillaries is heated by an electric coil, the voltage to which is supplied through a transformer, and the heating rate is determined by the applied voltage. First, the device is heated at a speed of 4–6 o C per minute, and 10 o C before the expected T pl is heated at a rate of 1–2 o C per minute. The melting temperature is taken to be the interval from the softening of the crystals (wetting the substance) to their complete melting.

The obtained data are recorded in a laboratory journal.

1. Distillation

Distillation is an important and widely used method for purifying organic liquids and separating liquid mixtures. This method involves boiling and evaporating a liquid and then condensing the vapor into a distillate. The separation of two liquids with a difference in boiling point of 50–70 o C or more can be accomplished by simple distillation. If the difference is smaller, it is necessary to use fractional distillation on a more complex device. Some liquids with high boiling points decompose during distillation. However, as the pressure decreases, the boiling point decreases, allowing high-boiling liquids to be distilled without decomposition in a vacuum.

Steel is an alloy of iron to which carbon is mixed. Its main benefit in construction is strength, because it is a substance long time retains volume and shape. The whole point is that the particles of the body are in a position of equilibrium. In this case, the attractive and repulsive forces between the particles are equal. The particles are in a clearly defined order.

There are four types of this material: regular, alloy, low-alloy, high-alloy steel. They differ in the number of additives in their composition. The usual one contains a small amount, and then increases. The following additives are used:

• Manganese.
• Nickel.
• Chromium.
• Vanadium.
• Molybdenum.

Melting temperatures of steel

Under certain conditions solids melt, that is, turn into a liquid state. Each substance does this at a certain temperature.

• Melting is the process of transition of a substance from a solid to a liquid state.
• Melting point is the temperature at which a crystalline solid melts and turns into a liquid state. Denoted by t.

Physicists use a specific table of melting and crystallization, which is given below:

Based on the table, we can safely say that the melting point of steel is 1400 °C.

Stainless steel is one of the many iron alloys found in steel. It contains Chromium from 15 to 30%, which makes it rust-resistant, creating a protective layer of oxide on the surface, and carbon. The most popular brands of this steel are foreign. These are the 300th and 400th series. They are distinguished by their strength, resistance to adverse conditions and ductility. The 200 series is of lower quality, but cheaper. This is a beneficial factor for the manufacturer. Its composition was first noticed in 1913 by Harry Brearley, who conducted many different experiments on steel.

At the moment, stainless steel is divided into three groups:

• Heat resistant- at high temperatures has a high mechanical strength and sustainability. The parts that are made from it are used in the pharmaceutical, rocketry, and textile industries.
• Rust-resistant- has great resistance to rusting processes. It is used in household and medical devices, as well as in mechanical engineering for the manufacture of parts.
• Heat resistant- is resistant to corrosion at high temperatures, suitable for use in chemical plants.

The melting point of stainless steel varies depending on its grade and the number of alloys from approximately 1300 °C to 1400 °C.

Cast iron is an alloy of carbon and iron, it contains impurities of manganese, silicon, sulfur and phosphorus. Withstands low voltages and loads. One of its many advantages is its low cost for consumers. There are four types of cast iron:

The melting points of steel and cast iron are different, as stated in the table above. Steel has higher strength and resistance to high temperatures than cast iron, temperatures differ by as much as 200 degrees. For cast iron, this number ranges from approximately 1100 to 1200 degrees, depending on the impurities it contains.