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If the percentage of carbon in iron is more than 2.11% it is known as cast iron. Steel is favored in industries since its advantageous traits. in addition, the raw materials necessary for the manufacture of steel are easily obtainable in the immediate surroundings. Carbon is without difficulty procurable plus Iron is an exceedingly plentiful metal in the earth's hub. Steel is used in lieu of Iron since Iron, in spite of its large quantity; it has an extremely high melting point which is almost 2773 Â°F. While the majority of engineering processes require the reshaping and molding of such resources, the employ of Iron becomes extremely expensive economically particularly bearing in mind the fiscal side of things. On the other hand, steel is low-priced to manufacture and has a lesser melting temperature in contrast to Iron; thus it's a first-class substitute.
Additionally, the out of the ordinary mechanical properties that have turn out to be linked with steel have set up a specific place in the heart of industrial users. For example steel has relatively fair yield strength, ranging usually from 200 to 300 MPa. In addition to this steel can tolerate yield stress even when it's value exceeds 1400 MPa. Furthermore steel has a fracture toughness that reaches at least 100 MPa, Another huge benefit of steel is that as well to it's extraordinary yield stress it also shows extraordinary ductility, refuse to break or crack in very stressful conditions, where normal cast iron would easily give way. These and a swarm of other extraordinary mechanical properties unite in steel thus making it an appropriate candidate where iron and other engineering materials begin to give way.
Another huge benefit of steel over regular non-alloy engineering materials like cast iron are the related microstructures that are born due to solid state phase transformation by changing the cooling rate from austenitic conditions. This treatment during steel making lends some very appealing and advantageous qualities to steel that are normally found lacking in other engineering materials. Steel is one material that has all these enviable qualities reduced in it's retiring existence. Furthermore addition of alloying elements and normal impurities adds some advantageous properties which might have been missing beforehand and thus use it's extra qualities for further engineering purposes.
Classification of Steels:
Steel is classified in different ways depending upon the sorting of Fe-C steel alloys;
Manufacturing method used
The main quality or the work required.
Oxidation practice employed
However, the most vital means used for categorization is still chemical composition.
Chemical Composition Classification:
Carbon steel: Carbon steel is also known as plain carbon steel.
Low carbon steel:
It contains carbon which is about 0.05% to 0.15%
Mild carbon steel:
It contains carbon which is about 0.16% to 0.29% carbon. Hence, it is neither brittle nor ductile.
Medium carbon steel:
It contains carbon between 0.30% and 0.59%.
High carbon steel:
It contains approximately 0.6% to 0.99% carbon.
Ultra high carbon steel:
It contains something like 1.0 to 2.0% carbon.
Alloy steels: These are steels whose properties are generally attributed to the presence of one or more elements other than carbon.
The highest quantity of alloying element exceeds one or more of the following proportion limit:
Copper: 0.6%, Silicon: 0.6%, Manganese: 1.65%.
Other than this, Aluminum, Boron, Chromium sums up to 3.99%; Cobalt, Columbium, Molybdenum, Nickel, Titanium, Tungsten, Vanadium, Zirconium, or any other element are added, steel is called alloy steel.
The foremost alloy there is 15% to 25% nickel.
In a metallurgical way, stainless steels are classified into 3 groups:
Martensitic Class: This type of stainless steel contains 4% to 10% Chromium.
Ferritic Class: In this class the chromium is12% to 28%.
Austenitic Class: This type of stainless steel contains 7% to 35% nickel.
A 242 ("COR-TEN A"): This type of steel contains 0.12% of Carbon, 0.25% to 0.75% of Silicon, 0.2 to 0.5% of Manganese, 0.07% to 0.15% of Phosphorous, 0.03% of Sulphur, 0.5% to 1.25% of Chromium, ).25% to 0.55% of Copper and 0.65% of Nickel.
A 588 ("COR-TEN B"): This type of steel contains 0.16% of Carbon, 0.3% to 0.5% of Silicon, 0.8 to 1.25% of Manganese, 0.03% of Phosphorous, 0.03% of Sulphur, 0.4% to 0.65% of Chromium, 0.25% to 0.4% of Copper,0.40% of Nickel and 0.02% to 0.1% of V.
Tool steels: With carbon content between 0.7% and 1.5%, tool steels are contrived under carefully controlled conditions to fabricate the necessary quality. The manganese content is often kept low to minimize the possibility of cracking during water quenching.
Different classes of steels:
The Society of Automotive Engineers (SAE) has customary standards for detailed study of steels. In the 10XX series, the first numeral indicates a plain carbon steel. The second numeral indicates a variation in the alloys. 10XX means that it is a plain carbon steel where the second numeral (zero) indicates that there is no variation in the alloys. The last two numerals signify the carbon content in points. For instance SAE 1040 is a carbon steel where 40 points signify 0.40 % Carbon content. Alloy steels are indicated via 2XXX, 3XXX, 4XXX, et cetera.
The American Iron and Steel Institute (AISI) in collaboration with the Society of Automotive Engineers (SAE) revised the percentages of the alloys to be used in the production of steel, retained the numbering system, and added letter prefixes to specify the technique used in steel manufacture. The letter prefixes are:
A = alloy, basic open hearth
B = carbon, acid Bessemer
C = carbon, basic open hearth
D = carbon, acid open hearth
E = electric furnace
If the prefix is absent, the steel is understood to be open hearth. Example: AISI C1050 indicates a plain carbon, basic-open hearth steel has 0.50 % Carbon content.
SAE - AISI Number
Low carbon steel: It contains 0 to 0.25% C.
Medium carbon steels: It contains 0.25-0.55 % C
High carbon steels: It contains more than 0.55% Carbon
It is 5% Nickel which increases the tensile strength of the steel without reducing its ductility.
8-12 % of Nickel increases the steels resistance to low temperature.
15-25 % of Nickel (which includes Al, Cu and Co) develops high magnetic properties.
25-35 % of Nickel creates resistance to corrosion at high temperatures.
These type of steels are ductile and tough and also exhibit high wear resistance, hardenability and high resistance to corrosion.
Molybdenum is a tough carbide former. It has a tough effect on hardenability and high temperature hardness. Molybdenum in addition increases the tensile strength of low carbon steels.
Chromium is a ferrite strengthener in low carbon steels. It increases the core toughness and the wear resistnace of the case in carburized steels.
Triple Alloy steels which include Nickel (Ni), Chromium (Cr), and Molybdenum (Mo).
These steels exhibit high strength and also high strength to weight ratio, good corrosion resistance.
Table 1.0: Classification of steels
Carbon steel: Carbon steel, also known as plain-carbon steel, is steel where the main alloy is carbon. The American Iron and Steel Institute (AISI) define carbon steel as: "Steel is considered to be carbon steel in which there is no least content specified for the alloying elements to be added for a preferred effect; when the particular least amount for copper does not exceed 0.40%; or when the maximum content set for any of the elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60."
The term "carbon steel" may also be used in place of steel which is not stainless steel; in this use carbon steel may also comprise of alloy steels. As the proportion of carbon rises, steel becomes harder and stronger, but this makes it less ductile. Higher carbon content reduces the capability of steel to be welded. In carbon steels, the higher carbon percentage also decreases the melting point of a substance.
Low carbon steel: Low carbon steel contains roughly 0.05% to 0.15% carbon fraction by mass. Low carbon steels experiences yield-point run out in which the matter has two yield points. The first yield point (the upper yield point) is upper than the second (the lower yield point) and the yield drops evidently after the upper yield point. If low carbon steel is merely stressed to some point amid the upper and lower yield point then the exterior may have Lüder bands form on it.
Medium carbon steel: Mild steel is the most often used form of steel since its cost is comparatively little whereas it provides material properties that are suitable for many applications. Mild steel contains 0.16% to 0.29% carbon; consequently, it is neither brittle nor ductile. Mild steel has a relatively low tensile strength, but it is cheap and malleable; surface hardness can be enhanced through carburizing. It is often used when vast amounts of steel are needed, for e.g. in structuring of buildings et cetra. The density of mild steel is roughly 7.85Â g/cm3 (0.284Â lb/in3) and the Young's modulus is 210,000 MPa (30,000,000 psi)
Higher carbon steels: Steels which can endure heat treatment devoid of any harm to them and have a carbon proportion by mass of 0.3%-0.17% are known as Higher carbon steels. Sulphur is in use to make the metal red-short (that is it has a higher melting point) and manganese is typically added to progress the hardenability of low carbon steels even further.
Medium carbon steel: Stabilized ductility and strength it also has substantial put on resistance, it is used for manufacturing of huge parts, forging and machinery of automotive manufacturing.
High carbon steel: It has roughly carbon content between 0.6%-0.99%. It is very hard and tough. It is used in the manufacturing of springs and high strength wires.
Ultra-high carbon steel: The carbon content is from 1%-2% by mass. Steels can be modified to vast hardness levels. Used for precise and out of the ordinary purposes not on large industry level examples include knives, axels or punches. Steel with carbon content higher than 2% is well thought-out cast iron.
Alloy steels: Alloy steel in which a diversity of rudiments used as alloys in a total quantity of between 1.0% and 50% by mass to look up its properties or to get some preferred character in one material. Alloy steels are auxiliary separated into two groups: low alloy steels and high alloy steels. The disparity between the two is a bit irrational: Smith and Hashemi categorize the dissimilarity at 4.0%, while Degarmo, et al., illustrate it at 8.0Â %. Frequently, the term "alloy steel" Is understood as "low alloy" steels. The following are a variety of superior properties in alloy steels (in contrast to carbon steels): strength, hardness, toughness, wear resistance, hardenability, and hot hardness. In order to attain a few of these finer properties the metal may need heat treating. Frequently used alloys include manganese (the most-common one), nickel, chromium, molybdenum, vanadium, silicon, and boron. rare alloys used include aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, and zirconium. A few of these find uses in deluxe and highly-demanding applications, for example in the turbine blades of jet engines, in spacecraft, and in nuclear reactors. Due to the ferromagnetic properties of iron, some steel alloys find major applications where their responses to magnetism are very vital, as in electric motors and in transformers.
Maraging steel: This particular type is carbon free (or present in a very low amount)and is ultra high strength steel that does not get its strength from carbon but from the precipitation of inter-metallic compounds, with the major alloy used being 15% to 25% nickel. Secondary alloys contain cobalt, molybdenum, and titanium which assist in the array of the inter-metallic precipitates. At first, the growth was approved out on 20-25% nickel steel in which diminutive amounts of Al, Ti and Nb were added. The most frequent grades contain 17% to 19% of nickel, 8% to 12% cobalt, 3% to 5% molybdenum, and 0.2% to 1.6% titanium. By the addition of chromium we can make stainless grades that are insolent to corrosion. This eventually increases hardenability as their requirement of nickel is small: high-chromium, high-nickel steels are usually austenitic and not capable to change to martensite when heat treated, while lower-nickel steels include the aptitude to convert into martensite. Owing to the low carbon content in Maragin steels they have fine machinability and prior to aging (heat treatment) they may be rolled upto 80% to 90% without fracture. They also have excellent weldability. Since the high alloy content these steels have an extremely elevated hardenability.
Stainless steel: Stainless steel is also called Inox steel or at times just Inox. It is definite by a lowest amount of 11% chromium proportion by weight. Stainless steel more often than not has the class of not rusting, corroding or staining as simply as normal steel but like all it is not ideal and so it is not entirely stain-proof. Also recognized as corrosion-resistant steel when the evaluation of the steel is not mentioned this is usually used in the aviation industry. There are diverse grades and surface finishes in stainless steel according to the prerequisite of surroundings it is to be used or engaged in. Major exploit of stainless steel is where there is a necessity of properties of both steel and corrosion resistance. Chief disparity in Stainless steel and carbon steel is the quantity of chromium present in both of them.