What is the difference between cast iron and How to distinguish cast iron from steel at home without special tools

Ferrous metallurgy products are widely used in many sectors of the national economy, and ferrous metal is always in demand in construction and engineering. Metallurgy has been successfully developing for a long time, thanks to its high technical potential. The most commonly used in production and in everyday life are cast iron and steel products.

Cast iron and steel both belong to the group of ferrous metals, these materials are alloys of iron and carbon that are unique in their properties. What are the differences between steel and cast iron, their main properties and characteristics?

Steel and its main characteristics

Steel is deformed alloy of iron and carbon, which is always up to a maximum of 2%, as well as other elements. Carbon is an important component, since it gives strength to iron alloys, as well as hardness, due to this, softness and ductility are reduced. Alloying elements are often added to the alloy, which ultimately gives alloyed and high-alloyed steel, when the composition is not less than 45% iron and not more than 2% carbon, the remaining 53% are additives.

Steel is the most important material in many industries, it is used in construction, and as the technical and economic level of the country grows, so does the scale of steel production. In ancient times, craftsmen used crucible melting to produce cast steel, and such a process was inefficient and laborious, but the steel was of high quality.

Over time, the processes of obtaining steel changed, the crucible was replaced by Bessemer and open-hearth method obtaining steel, which made it possible to establish mass production of cast steel. Then they began to smelt steel in electric furnaces, after which the oxygen-converter process was introduced, it made it possible to obtain especially pure metal. From the number and types of binding components, steel can be:

• low alloy
• medium alloyed
• Highly alloyed

Depending on the carbon content it happens:

• low carbon
• medium carbon
• High carbon.

The composition of the metal often includes non-metallic compounds - oxides, phosphides, sulfides, their content differs on the quality of steel, there is a certain quality classification.

Steel density is 7700-7900 kg/m3, A General characteristics steels are made up of indicators such as strength, hardness, wear resistance and suitability for processing different kind. Compared to cast iron, steel has greater ductility, strength and hardness. Due to its ductility, it is easy to process, the steel has a higher thermal conductivity, and its quality is improved by hardening.

Elements such as nickel, chromium and molybdenum are alloying components, each of which gives the steel its own characteristics. Thanks to chromium, steel becomes stronger and harder, and its wear resistance increases. Nickel also imparts strength, as well as toughness and hardness, increases its anti-corrosion properties and hardenability. Silicon reduces toughness, while manganese improves weldability and annealing.

All existing species steel have melting point from 1450 to 1520оС and are strong wear-resistant and deformation-resistant metal alloys.

Cast iron and its main characteristics

The basis for the production of cast iron is also iron and carbon, but unlike steel, it contains more carbon, as well as other impurities in the form of alloying metals. It is brittle and breaks without visible deformation. Carbon here acts as graphite or cementite, and due to the content of other elements cast iron is divided into the following varieties:

The melting temperature of cast iron depends on the carbon content in it, the more it is in the composition of the alloy, the lower the temperature, and also its fluidity increases when heated. This makes the metal non-plastic fluid, as well as brittle and difficult to machine. Its melting point is from 1160 to 1250оС.

The anti-corrosion properties of cast iron are higher because it undergoes dry rusting during use, this is called chemical corrosion. Wet corrosion also attacks cast iron more slowly than steel. These qualities led to the fact that a discovery was made in metallurgy - steel with a high chromium content began to be smelted. This is where stainless steel came from.

We draw a conclusion

Based on their many characteristics, the following can be said about cast iron and steel, what is their difference:

It can be concluded that steel and cast iron are united by the content of carbon and iron in them, but their characteristics are different and each of the alloys has its own characteristics.

Many people know about such material as cast iron and its strength characteristics. Today we will deepen this knowledge and find out what cast iron is, what it consists of, what types it happens and how it is produced.

Compound

What is cast iron? It is an alloy of iron, carbon and various impurities, thanks to which it acquires the necessary properties. The material must contain at least 2.14% carbon. Otherwise, it will be steel, not cast iron. It is thanks to carbon that cast iron has increased hardness. At the same time, this element reduces the ductility and malleability of the material, making it brittle.

In addition to carbon, the composition of cast iron in without fail includes: manganese, silicon, phosphorus and sulfur. Some brands also add additional additives to give the material specific properties. Commonly used alloying elements include chromium, vanadium, nickel and aluminium.

The material has a density of 7.2 g/cm 3 . For metals and their alloys, this is a fairly high figure. Cast iron is well suited for the production of all kinds of products by casting. In this regard, it surpasses all iron alloys except for some steel grades.

The melting point of cast iron is 1200 degrees. For steel, this figure is 250-300 degrees higher. The reason for this lies in the increased content of carbon in cast iron, which causes less close bonds between iron atoms. During the smelting of cast iron and its subsequent crystallization, carbon does not have time to fully penetrate into the structure of iron. Therefore, the material is brittle. The structure of cast iron does not allow it to be used for the production of products that are constantly subjected to dynamic loads. But what cast iron is ideal for is for parts that must have increased strength.

Receipt

Obtaining cast iron is a very costly and material-intensive process. To get one ton of alloy, you need 550 kg of coke and 900 liters of water. As for the ore, its amount depends on the content of iron in it. As a rule, ore with a mass fraction of iron of at least 70% is used. The processing of less rich ores is not economically feasible.

Before going to the smelter, the material is enriched. Pig iron production in 98% of cases takes place in blast furnaces.

The technological process includes several stages. First, ore is loaded into the blast furnace, which includes magnetic iron ore (a compound of two- and three-valent iron oxide). Ores containing hydrous iron oxide or its salts can also be used. In addition to raw materials, coking coals are placed in the furnace, which are necessary to create and maintain a high temperature. Combustion products of coals as iron reducing agents are also involved in chemical reactions.

Additionally, a flux is supplied to the furnace, which plays the role of a catalyst. It accelerates the process of melting rocks and releasing iron. It is important to note that before entering the furnace, the ore must undergo special processing. Since small parts melt better, it is pre-crushed in a crushing plant. The ore is then washed to get rid of non-metal impurities. Then the raw material is dried and fired in kilns. Thanks to roasting, sulfur and other foreign elements are removed from it.

After the furnace is fully loaded, the second stage of production begins. When the burners are started, the coke gradually heats up the feedstock. This releases carbon, which reacts with oxygen and forms an oxide. The latter takes an active part in the reduction of iron from the compounds in the ore. The more gas accumulates in the furnace, the slower the reaction proceeds. When desired proportion reached, the reaction stops altogether. Excess gases further serve as fuel to maintain the required temperature in the furnace. This method has several strengths. Firstly, it allows you to reduce fuel costs, which reduces the cost of manufacturing process. And, secondly, combustion products do not enter the atmosphere, polluting it, but continue to participate in production.

Excess carbon is mixed with the melt and absorbed by iron. This is how cast iron is made. Impurities that have not melted float to the surface of the mixture and are removed. They are called slag. Slag finds use in the production of certain materials. When all excess particles are removed from the melt, special additives are added to it.

Varieties

What is cast iron and how it is obtained, we have already found out, now we will deal with the classification of this material. In the way described above, conversion and foundry iron is obtained.

Pig iron is used in the production of steel via the BOF route. This type is characterized by a low content of silicon and manganese in the alloy. Foundry iron is used in the production of all kinds of products. It is divided into five types, each of which will be considered separately.

White

This alloy is distinguished by the content of excess carbon in the form of carbide or cementite. This species was named after White color at the site of the break. The carbon content of such cast iron is typically greater than 3%. White cast iron is highly brittle and brittle, so it is used to a limited extent. This type is used for the production of parts of a simple configuration that perform static functions and do not carry heavy loads.

By adding alloying additives to the composition of white cast iron, it is possible to increase technical specifications material. For this purpose, chromium or nickel is most often used, less often vanadium or aluminum. A brand with this kind of additives was called "sormite". It is used in various devices How a heating element. "Sormite" has a high resistivity, and works well at temperatures not higher than 900 degrees. The most common use of white cast iron is in the production of domestic bathtubs.

Grey

This is the most common type of cast iron. It has found application in various areas of the national economy. In gray cast iron, carbon is present in the form of pearlite, graphite, or ferrite pearlite. In such an alloy, the carbon content is about 2.5%. As for cast iron, this material has high strength, so it is used in the manufacture of parts that receive cyclic loading. Gray cast iron is used to make bushings, brackets, gears and industrial equipment cases.

Thanks to graphite, gray cast iron reduces friction and improves the performance of lubricants. Therefore, parts made of gray cast iron have high durability To this species wear. When operating in particularly aggressive environments, additional additives are introduced into the material, which make it possible to level negative impact. These include: molybdenum, nickel, chromium, boron, copper and antimony. These elements protect gray cast iron from corrosion. In addition, some of them increase the graphitization of free carbon in the alloy. This creates a protective barrier that prevents damaging elements from reaching the surface of the cast iron.

half-hearted

An intermediate material between the first two varieties is half cast iron. The carbon contained in it is presented in the form of graphite and carbide in approximately equal proportions. In addition, small amounts of leadburite (no more than 3%) and cementite (no more than 1%) may be present in such an alloy. The total carbon content of cast iron ranges from 3.5 to 4.2%. This variety is used for the production of parts that are operated in conditions of constant friction. These include automotive brake pads, as well as rolls for grinding machines. All kinds of additives are added to the alloy to further increase wear resistance.

Malleable

This alloy is a kind of white cast iron, which is subjected to special firing in order to graphitize free carbon. Compared to steel, such cast iron has improved damping properties. In addition, it is not as sensitive to notches and performs well in conditions low temperatures. In such cast iron, the mass fraction of carbon is not more than 3.5%. In the alloy, it is presented in the form of ferrite, granular pearlite containing inclusions of graphite or ferrite pearlite. Malleable cast iron, like half cast iron, is mainly used in the production of parts operating under conditions of continuous friction. For increase performance characteristics magnesium, tellurium and boron are added to the alloy.

high strength

This type of cast iron is obtained due to the formation of graphite inclusions in the metal lattice. spherical shape. Because of this metal base the crystal lattice is weakened, and the alloy acquires improved mechanical properties. The formation of nodular graphite occurs due to the introduction of magnesium, yttrium, calcium and cerium into the material. Ductile iron is close in its parameters to high-carbon steel. It lends itself well to casting and can completely replace steel parts mechanisms. Due to the high thermal conductivity given material can be used for the manufacture of pipelines and heating appliances.

Industry difficulties

Today, cast iron casting has dubious prospects. The point is that due to high level costs and a large number waste, industrialists are increasingly abandoning cast iron in favor of cheaper substitutes. Thanks to the rapid development of science, it has long been possible to obtain more quality materials at lower cost. Defense plays an important role in this matter. environment, which does not accept the use of blast furnaces. In order to completely transfer iron smelting to electric ovens It takes years, if not decades. Why so long? Because it is very expensive, and not every state can afford it. Therefore, it remains only to wait until the mass production of new alloys is established. Of course, stop completely. industrial application cast iron will not work in the near future. But it is obvious that the scale of its production will fall every year. This trend started 5-7 years ago.

Conclusion

Having dealt with the question: “What is cast iron?”, We can draw several conclusions. First, cast iron is an alloy of iron, carbon and additives. Secondly, it has six kinds. Thirdly, cast iron is very useful and versatile material, so for a long time its expensive production was expedient. Fourthly, today cast iron is already considered a relic of the past, and is gradually losing its position to more reliable and cheaper materials.

Cast iron is an alloy of iron and carbon. The percentage of iron contains more than 90%. The amount of carbon varies between 2.14-6.67%. Due to this element, the material has high hardness, but fragility appears. This leads to deterioration of ductility and ductility. In some types, alloying elements are added to improve performance: aluminum, chromium, vanadium, nickel.

Characteristics of the types of carbon metal

The iron-carbon diagram shows what iron is made of. In addition to iron, carbon is present in the form of graphite and cementite.

The composition of the cast iron alloy has varieties:

Individual metal properties

The material is characterized by certain characteristics. These include:

Depending on the presence of impurities, there is a difference in the properties of the material.

These elements include sulfur, phosphorus, silicon, manganese:

• Sulfur reduces the fluidity of the metal.
• Phosphorus reduces strength, but allows the manufacture of products of complex shape.
• Silicon increases the fluidity of a material by lowering its melting point.
• Manganese gives strength, but reduces fluidity.

Differences between cast iron and steel

To understand the difference between steel and cast iron, you need to consider their characteristics. Distinctive feature cast iron is the amount of carbon. Its minimum content is 2.14%. This is the main indicator by which this material can be distinguished from steel.

The percentage of impurities can only be determined chemical analysis. If we compare the melting point of cast iron and steel, then for cast iron it is lower and amounts to 1150-1250 degrees. Steel is around 1500.

To distinguish the material, you need to do the following:

• The product is lowered into the water and the volume of displaced water is determined. Cast iron is less dense. It is 7.2 g/cm3. For steel - 7.7-7.9 g / cm3.
• A magnet is applied to the surface, which is attracted to steel better.
• Using a grinder or file, chips are rubbed. Then she gathers in paper and wipes herself on it. Steel will leave no marks.

Pros and cons of the material

Like any material, cast iron has positive and the negative side. TO positive qualities relate:

Cast iron and steel - two types of compounds of iron with carbon - are widely used in a wide variety of industries. But sometimes it becomes necessary to distinguish cast iron from steel, for example, during repairs, because these alloys have different properties and, accordingly, require different handling.

Methods for determining cast iron

You can identify cast iron by the density of the product. Weigh the object, and then determine how much water it displaces. Thus, you will calculate its density and draw a conclusion about the material. The fact is that the density of the main steel grades lies in the range of 7.7 - 7.9 grams / cm ^ 3, while the density of the most common gray cast iron does not exceed 7.2 grams / cm ^ 3. But this method is unreliable, since there is more white cast iron, whose density fluctuates between 7.6 and 7.8 grams/cm^3. Therefore, it can only be used if you are firmly convinced that the product is made of either steel or gray cast iron.

Therefore, it is more reliable to use one of the following methods: to determine cast iron using the type of sawdust or chips formed, as well as using a grinder. Take a file with a fine notch, swipe several times over the surface of the product. Try to collect the resulting smallest sawdust on a piece of paper. Fold the paper in half and rub vigorously. If it is cast iron, then the paper will be noticeably dirty, if it is steel, there will be practically no traces left.

You can also drill the product a little thin drill(of course, not on the front side, but in a place that is not conspicuous). In this case, no a large number of shavings. According to her appearance and properties can accurately determine what material the part is made of. If it is cast iron, the chips will literally crumble in your fingers, turning into dust. If it's steel, the shavings will look like a coiled spring and may even scratch your fingers if you try to break them.

If in doubt, it is better to use pieces of cast iron and steel as standards and compare the shape and properties of sawdust (chips), as well as the type of sparks formed, with what is obtained when processing these samples.

Cookware for induction hob

There is China and China. In IKEA, all stainless steel is made in China, but the holders of the brand (the Swedes, and now - it seems - the Dutch) tightly control production. As a result, it seems to me that the price / quality ratio of very unpretentious IKEA pots and pans is one of the best on our market. On induction hob All work, if stated.

Most of the world's BRANDED electronics are made in China. From another "household" garbage, I can name some knife manufacturers. It is worse when the brand itself is Chinese, but here too there is rapid progress: there are things
(for example, in electronics, in the production of buses) that the Chinese, under state control, began to do very well. But when our business sharks come into play, creating “German” brands and sticking Western-style labels on the products of Chinese unknown and uncontrolled artisans, then hold on.

I heard that in the days of perestroika cooperatives in Odessa, it was not the fake sneakers under the branded Addidas that was considered the highest chic, but their crafts under the Chinese fake Addidas. This style has been preserved for all those rising from their knees - everywhere. Trash and cattle, robbing their own.

Hospadi! Yes, when will this notorious "magnet" disappear from the culinary communities. The classic "food stainless steel" - steel "18/10" - is not attracted by any "permanent magnets", but it is perfectly suited for induction cookers.

how to distinguish cast iron from steel.

• City: Ukraine
• Name: Sergey Savelyevich

how to distinguish cast iron from steel.

Look closely at the crankshaft, cast iron is cast, steel is usually forged from a single piece of steel. It can be almost unmistakably determined by appearance. By the way, what engine is the crankshaft from? And once again, by the way, the vast majority of crankshafts are cast iron. Obviously casting is cheaper and easier than forging.

#16 Sergey19

• City: Barnaul
• Name: Sergey

how to distinguish cast iron from steel.

How? They stick the same way.

#17 Vladimir_V

• Voronezh city

how to distinguish cast iron from steel.

The magnet sticks much worse to cast iron than to steel.

No, to durable cast irons also.
You can drill in a secluded place with a small drill. Remove a milligram. Cast iron does not form chips - in general, it is drilled in a completely different way than steel. To fill the eye, it is enough to drill any known cast iron.

#18 Khatru

• Moscow city
• Name: Dmitry

how to distinguish cast iron from steel.

Cast iron does not form chips

thought so too. and recently I drilled the body of an old Soviet hydraulic motor. still spiral chips, though short - 20-30. although it is definitely cast iron. seems to depend on the brand etc.

#19 Vladimir_V

• Voronezh city

how to distinguish cast iron from steel.

the same spiral shavings,

Maybe shavings - but she rubs her fingers into dust. And the steel drain is like a wire, you won’t break it.

#20 Khatru

• Moscow city
• Name: Dmitry

how to distinguish cast iron from steel.

Maybe shavings - but she rubs her fingers into dust

May be. hence the short one. I haven't tried it with my fingers. and you won’t understand from a milligram - it’s much less than a cubic mm 🙂

You can identify cast iron by the density of the product. Weigh the object, and then determine how much water it displaces. Thus, you will calculate its density and draw a conclusion about the material. The fact is that the density of the main steel grades lies in the range of 7.7 - 7.9 grams / cm ^ 3, while the density of the most common gray cast iron does not exceed 7.2 grams / cm ^ 3. But this method is unreliable, since there is also white cast iron, the density of which varies between 7.6 and 7.8 grams / cm ^ 3. Therefore, it can only be used if you are firmly convinced that the product is made of either steel or gray cast iron.

You can use a magnet. It adheres worse to cast iron than to steel. But even this method cannot be called accurate, since some types of alloyed steels with a high nickel content almost do not attract a magnet.

Therefore, it is more reliable to use one of the following methods: to determine cast iron using the type of sawdust or chips formed, as well as using a grinder. Take a file with a fine notch, swipe several times over the surface of the product. Try to collect the resulting smallest sawdust on a sheet of paper. Fold the paper in half and rub vigorously. If it is cast iron, then the paper will be noticeably dirty, if it is steel, there will be practically no traces left.

You can also drill the product a little with a thin drill (of course, not from the front side, but in a place that is not conspicuous). This produces a small amount of chips. By its appearance and properties, you can accurately determine what material the part is made of. If it is cast iron, the chips will literally crumble in your fingers, turning into dust. If it's steel, the shavings will look like a coiled spring and may even scratch your fingers if you try to break them.

Finally, one can judge the material by the size, shape and color of the sparks formed when grinder. The higher the carbon content, the brighter and stronger the sheaf of light yellow sparks will be. And the carbon content in cast iron is much higher than in steel.

If in doubt, it is better to use pieces of cast iron and steel as standards and compare the shape and properties of sawdust (chips), as well as the type of sparks formed, with what is obtained when processing these samples.

In our lives, we often have to deal with the use of various products from cast iron. which in its structure is a rather brittle alloy, but with good thermal conductivity. In accordance with this, the question often arises, how to cook it, because cast iron, due to the high content of carbon, sulfur and phosphorus in it, belongs to the group of poorly weldable metals?

Omitting subtleties chemical composition cast iron, chemical and other processes occurring during welding, let's figure it out: how to weld cast iron? The industry of our country produces gray and white cast iron, which differ greatly in their composition and characteristics. Accordingly, the welding methods for them are different. It must be remembered here that to weld cast iron products that have been exposed to high temperatures from 300 degrees and above, as well as products that have worked for a long time in direct contact with various oils, it is practically not possible.

The most acceptable method of welding cast iron in our domestic environment is welding using an electric welding machine. So, when electric welding, carry out a V-shaped groove of the edges to be welded and carefully clean them of oil, rust and dirt with a brush.

Purchase electrodes coated with UONI-13/45 (welding with these electrodes is carried out at direct current of reverse polarity).

Place the welding seam separate sections(in breakdown), this will help you avoid uneven heating of the part (separately directed sections of the weld should be no more than 10 cm). When welding products with a thickness of more than 5 mm, do not forget to strengthen the seam by a length equal to the thickness of the part being welded.

During welding, do not forget to let the separately deposited areas cool down to 60-80 degrees. low-carbon steel studs (the angle of the edges of the parts to be welded must be 90 degrees).

Insert studs of larger diameter into the groove. Perform welding with electrodes with a protective alloying coating of the E42 (42A) or E50 (50A) brand at a constant or alternating current, while the thickness of the electrode is selected depending on the thickness of the workpiece to be welded.
Perform the welding itself by scalding the studs with an annular seam, and only after that fill the space between the scalded studs and the groove itself with short sections. There are other ways to weld cast iron, but we'll talk about them later.

Information, calculations, calculators,
GOSTs

Magnetic properties of cast iron

In accordance with the requirements and details, cast iron can be used as a ferromagnetic (soft magnetic) or paramagnetic material.

Magnetic properties, more than any other, depend on the structure of the metal, which determines the division of magnetic properties into primary and secondary. The primary ones are induction, saturation (4ΠI). permeability in strong fields and magnetic transformation temperature. These properties depend on the amount and composition of ferromagnetic phases and do not depend on their shape and distribution. The secondary properties include hysteresis characteristics: induction, saturation and permeability in weak and medium fields, coercive force, residual magnetism. Secondary properties depend little on the composition of the phases and are determined mainly by the shape and distribution of structural components.

The main ferromagnetic components of cast iron are ferrite and cementite, characterized by the following data (Table 1).

Table 1. Characteristics of the structural components of cast iron

Т magnetic transformation, °C

Cementite is a harder magnetic component, so gray cast iron is always used as a soft magnetic material, not white cast iron. Graphitization leads to a sharp decrease N s and intensive increase µmax especially during the decay of the last residues of carbides. In this case, the influence of graphite, as well as other nonmagnetic phases, also depends on the shape and size of the inclusions. The most favorable in this respect is the globular form. Therefore, malleable and ductile iron are characterized by greater induction and magnetic permeability and lower coercive force than gray cast iron with the same matrix (see Table 1 in the article Electric properties of cast iron).

In the same way, the enlargement of the eutectic and ferritic true and the decrease in the amount of pearlite affect. Therefore, tempering after quenching improves the soft magnetic properties.

Non-magnetic (paramagnetic) cast irons are used in cases where it is required to minimize power losses (covers oil circuit breakers, transformer end boxes, pressure rings on electrical machines, etc.) or when minimal distortion is required magnetic field(racks for magnets, etc.). In the first case, along with low magnetic permeability, high electrical resistance is required; cast iron satisfies this requirement even to a greater extent than non-ferrous alloys. In the second case, a particularly low magnetic permeability is required. Therefore, in a number of cases, it is not possible to replace non-ferrous alloys with austenitic cast irons for the second group of castings.

Depending on the composition, austenitic non-magnetic cast irons are distinguished:

• nickel type niresist with one or another amount of chromium;
• nickel-manganese type nomag with one or another content of copper and aluminum, superior to cast irons of the first group in non-magneticness, but inferior to them in heat resistance, heat resistance and corrosion resistance;
• manganese with one or another content of copper and aluminum, which are the cheapest, but have lower strength and physical properties.

Of interest are also ferritic high-alloy aluminum cast irons, which are characterized by a particularly low magnetic permeability.

Question: March 28, 2009
What is the difference between cast iron and steel, and why?

Answer:
Oddly enough, but, despite the abundance of specialized literature on this topic, we are often asked the following question: How does cast iron differ from steel? In short and in general terms, it can be said that the composition of cast iron differs from steel in a higher carbon content, in technological properties - better casting qualities and a low ability to plastic deformation. Cast iron is generally cheaper than steel.
And if in more detail, then - read the classics, dear! Many volumes are devoted to materials science and metallurgy of ferrous alloys. As an example, I cite an excerpt from the fundamental work of Gulyaev A.P. "Metal":
“Steel is an iron-carbon alloy containing less than 2.14% carbon. However, the specified limit (2.14% C) applies only to double iron-carbon alloys or alloys containing a relatively small number of impurities. The question of the boundary between steels and cast irons in high-alloy iron-carbon alloys, i.e. containing even more elements other than iron and carbon is debatable.
In the light modern technology iron-based alloys are known and have recently become widespread, in which there is very little carbon and it is even a harmful element; however, such alloys are also referred to as steels. In order to avoid terminological confusion, it is customary to consider alloys in which iron is more than 50% as steels (cast iron) and not to call them alloys, but to refer to alloys containing less than 50% iron. It's not scientifically rigorous, but it's technically clear."