A little-informed person believes that the main structural material of our time is iron. Understanding knows that the word "iron" refers to iron-carbon alloys - steel and cast iron. It would seem that two completely different materials and they are very easy to distinguish. However, given the wide range of their types and brands, it is difficult to determine the fine line of differences in the chemical composition of some of them. It is important to have additional skills in order to know the answer to the question: how is cast iron different from steel?
Cast iron
An alloy containing iron, carbon in the amount of 2.14-6.67, sulfur, phosphorus, manganese, silicon and other additives is called cast iron. The history of smelting began in the Iron Age. An important structural material, the basis of metallurgy and the entire steelmaking industry.
Specifications:
- Grungy, having a dull gray color.
- Melting at 1000-1600 ° C depending on the composition (for industrial ones on average - 1000-1200 ° C, white and pig iron are melted at higher temperatures).
- Density: 7200-7600 kg / m 3 .
- Specific heat: 540 J / (kg˚).
- High hardness: 400-650NV.
- Low ductility, very crumbles when exposed to pressure; the highest values of elongation are ductile ductile iron δ = 6-12%.
- Low strength: 100-200 MPa, for malleable values reach 300-370 MPa, for some grades of high strength - 600-800 MPa.
- It is modeled using heat treatment, but rarely and with great care, since it is characterized by a cracking process.
- It is alloyed with auxiliary chemical elements, however, a significant degree of alloying further complicates the processing processes.
- It is characterized by satisfactory weldability, good machinability by cutting, and excellent casting properties. It is not subject to forging and stamping.
- Good wear and corrosion resistance.
Cast iron is a material for body parts, blocks, and units of machines made by casting. It is the main charge component for steelmaking.
Steel
An iron-carbon alloy containing carbon in an amount of not more than 2.14% and iron - not less than 45% is called steel. Its main characteristics:
- Smooth, has a silver color with a characteristic sheen.
- Melting within 1450˚.
- The density is from 7700 to 7900 kg / m 3 .
- Heat capacity at room temperature: 462 J / (kg˚C).
- Low hardness, an average of 120-250 HB.
- Excellent ductility: the relative elongation coefficient δ for various grades varies within 5-35%, for most - δ≥20-40%.
- The average tensile strength for structural materials is 300-450 MPa; for especially strong alloyed ones - 600-800 MPa.
- Well amenable to correction of properties using thermal and chemical-thermal treatment.
- It is actively alloyed with various chemical elements in order to change the properties and purpose.
- Qualitatively high indicators of weldability, machinability by pressure and cutting.
- It is characterized by low corrosion resistance.
Steel is the main structural alloy in modern metallurgy, mechanical engineering, instrument making and technology.
Determine the origin of the type of part
Having considered the detailed characteristics of these alloys, you can confidently use the knowledge that cast iron differs from steel. Having a metal object in front of him, doubting its origin, it is rational to immediately recall the main distinguishing technological properties. So, cast iron is a foundry material. Simple dishes, massive pipes, machine cases, engines, large objects of simple configuration are produced from it. Parts of all sizes and complexity are made of steel, since forging, stamping, drawing, rolling and other methods of metal forming are used for this . Thus, if there is a question about the origin of the reinforcement, there can be no doubt - this is steel. If you are interested in the origin of a massive cauldron - this is cast iron. If you need to find out what the engine or crankshaft housing is made of, you should resort to other recognition options, since both options are possible.
Color Features and Fragility Analysis
In order to know how to distinguish cast iron from steel by eye, you need to remember the main visual differences. Cast iron is characterized by a dull gray color and a rougher outer texture. Steel is characterized by a special silver shiny shade for it and minimal roughness.
Also important information on how to distinguish cast iron from steel visually is information on the ductility of these materials. If the studied workpieces or metal objects do not have serious value, you can test them for strength and ductility by applying impact force. Brittle cast iron will crumble into pieces, while steel is only deformed. With more serious crushing loads, the cast-iron crumbs will turn out to be of a small, various shape, and the pieces of steel will become large, of the correct configuration.
Cut and drill
How to distinguish cast iron from steel at home? It is necessary to obtain fine dust or shavings from it. Since steel has high ductility, its shavings also have a twisty character. Cast iron crumbles, during drilling, small chips of breakage are formed along with dust.
To get dust, you can use a file or a rasp and slightly sharpen the edge of the part of interest. The resulting finely divided chips should be examined on a hand or a white sheet of paper. Cast iron contains a large amount of carbon in the form of graphite inclusions. Therefore, when grinding its dust, a black graphite “trace” remains. In steels, carbon is in a bound state; therefore, a mechanical effect on dust does not give any visible results.
Heat and sparkle
How to distinguish cast iron from steel? It is necessary to operate with the necessary equipment and a small margin of patience.
In the first case, you can resort to heating, for example, using a blowtorch, having originally dressed in special protective clothing and observing safety rules in operation. The temperature must be raised before the melting of the metal. It has already been said that the melting point of cast iron is higher than that of steel. However, this applies mainly to white and pig iron. Regarding all industrial brands - they contain carbon in an amount of not more than 4.3% and melt already at 1000-1200˚. Thus, it can be melted much faster.
An informative method of obtaining information about how cast iron differs from steel is the use of an experimental sample on a grinding machine or under a sharp circle of a grinding machine. The analysis is carried out according to the characteristics of sparks. For cast iron, faint red sparks are characteristic, and for steel - bright, blinding short rays with a white-yellow hue.
How does it sound
An interesting feature is how to distinguish cast iron from steel by sound. These two alloys sound different. It is not necessary to produce musical accompaniment at existing experimental facilities. But you must have both samples or have an experienced ear in this matter. Steel is characterized by a higher density, which is reflected in its sound. When you hit it with a metal object, the sound is much more sonorous than in the same situation with cast iron.
In order to know how cast iron differs from steel, it is necessary to have a little knowledge about these materials and a certain experience. After all, an experienced professional in the field of forging, grinding, milling, drilling, turning, heat treatment or welding, a metallurgist or a technician easily distinguishes them from each other, judging only visually or by touch.