Iron Alloy

Iron alloys can be described as alloys which have iron as the principal component. Iron is used as a constituent in majority of the commercial alloys. For example, iron is the major component of wrought and cast iron and wrought and cast steel. Iron can also be alloyed with manganese, silicon, vanadium, chromium, molybdenum, niobium, selenium, titanium, phosphorus, or other elements for commercial applications. Some iron alloys are also used as addition agents in the process of steel-making. There are special-purpose iron alloys which demonstrate superior characteristics, like - magnetic properties, electrical resistance, thermal expansion, corrosion resistance, and heat resistance, etc.

Iron Alloy Castings

Iron castings are produced by molding iron alloys or molten iron. Gray iron is possibly one of the oldest worked metals used for casting. The metal is also one of the most abundant and least expensive materials.

Gray iron was the original cast iron, though it has recently been replaced in various applications by other iron-carbon alloys which have higher tensile strength. Ductile iron, as the name suggests, has high ductility than traditional iron materials, such as gray iron. These materials incline to be brittle and are prone to fracture under high tensile stress.

Iron is cast as like any other metal. It is poured into a mold and extracted after cools down. There are various types of casting methods, through which iron can be molded; some of these methods include shell molding, green sand molding, and centrifugal molding. The procedure through which the iron is caste can affect the mechanical properties of the metal, especially in regard to its cooling rate. Iron castings are used in a wide array of applications, including:

·         Automotive

·         Appliance

·         Agriculture

·         Machinery industries

Cast iron components are also used for pump housings, engine blocks, electrical boxes, decorative castings, and more.

Related pages

·         Steel Alloy

·         Grey Iron

·         Ductile Iron

Cast Iron Alloy

The term Cast Iron can be described as a large family of ferrous alloy. These alloys contain 2-4% carbon, along with silicon, manganese. Cast irons are manufactured and produced in specified shapes for processing by machining, heat treating, or assembly. Sometimes, to meet specific requirement it can be forged or rolled. Casts iron are produced by melting pig iron and then combining it with steel or scrap iron.

Normally, cast iron contains silicon up to 3%. Though this composition may vary while making special compositions, such as:

·         Silal: Silicon up to 6%

·         Duriron: Silicon up to 12%

One can purchase cast iron in several commercial grades, such as gray iron, chilled iron, mottled iron, white iron, malleable iron, ductile iron, spheroidal graphite iron, nodular iron, and austenitic cast iron.

Production Process

Cast iron is produced by melting pig iron. Often, this melting is done along with scrap steel and scrap iron. It also involves a several steps which lead to the removal of undesirable elements (phosphorus and sulfur).

·         The main objective of this processing is to reduce carbon and silicon content to the desired levels. Then, the addition of other elements to the melt takes place.

·         A small blast furnace known as a cupola is used to melt iron.

·         After melting is complete, the molten iron is removed from the forehearth of the blast furnace.

·         The final form is made by casting.

During solidification, the major proportion of the carbon precipitates in the form of graphite or cementite. When solidification is just complete, the precipitated phase is embedded in a matrix of austenite that has an equilibrium carbon concentration of about 2 wt%. On further cooling, the carbon concentration of the austenite decreases as more cementite or graphite precipitates from solid solution. For conventional cast irons, the austenite then decomposes into pearlite at the eutectoid temperature. However, in grey cast irons, if the cooling rate through the eutectoid temperature is sufficiently slow, then a completely ferritic matrix is obtained with the excess carbon being deposited on the already existing graphite.

Types of Cast Irons

Given below is a list of different types of cast irons and their properties:

·         White Cast Iron: White cast iron is hard to be machined as it's tough and brittle.

·         Grey Cast Iron: Due to the presence of microstructure of graphite in transformed-austenite and cementite matrix, grey cast irons are softer.

·         Spheroidal Graphite Cast Iron: The chemical composition of the cast iron is similar to that of the grey cast iron but with 0.05 wt% of magnesium.

·         Ductile Cast Iron: One of the most popular alloys used in casting. It has variety of applications including automobile components, industrial machinery, wind turbine electrical energy generation, valves, air conditioning machinery, lawn and garden equipment and agricultural products.

·         Spheroidal Graphite Cast Iron: Spheroidal graphite cast iron is known for its excellent toughness and has many applications, e.g. crankshafts.

Cast Iron Alloy Castings

Cast iron alloys have found wide usage in casting applications for their characteristics, such as strength, good strength to weigh ratio, economical price, and availability in abundance, capability to produce complex geometries. The cast iron castings are used in a multitude of applications, such as automotive, agriculture, appliance, and more.

Advantages in Casting:

·         A family of materials which is capable to meet a variety of engineering and manufacturing application requirements (the "family", includes - gray iron, ductile iron, compacted graphite iron, malleable iron, and white iron).

·         Capability of casting with inserts of other materials.

·         Capability to manufacture and design highly complex geometries and sections in various sizes.

·         Possibility to cast intricate shapes as well as very thin to very thick section sizes.

·         Good strength to weight ratio.

·         Generally economical than competing materials and relatively low cost per unit of strength than other materials.

·         Superior damping capacity, especially in Gray Irons.

·         Capability of redesigning and combining two or more parts from other materials into a single casting, thereby reducing assembly time and cost.

·         Different types of casting processes for low, medium or high production.

·         Variety of iron castings can be used without heat treatment (as cast) however, in case if required, they can be heat treated to enhance the overall properties or specific properties such as surface hardness.

Ferrous Alloys

Ferrous alloys are iron based alloys which have found extensive usage in wide range of industries because of its flexibility to meet strength, toughness, and impact of diverse industrial applications. This flexibility depends on the heat treatment processes and methods, which modifies the final micro-structure. Examples of ferrous alloys include carbon steels, stainless steels, alloy steels, tool steels, cast steel, cast iron, maraging steel, and specialty or proprietary iron-based alloys.

These days, many alloy manufacturers are trying to meet the compositional standards of the Unified Numbering System (UNS). Unified Numbering System (UNS), jointly developed by American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE), offers an overall designation system for thousands of metals and alloys in commercial use.

In UNS, metals and alloys are assigned a lettered prefix followed by a five-digit number. For example, carbon steels and alloy steels are categorized under the UNS G category and carry designations, such as UNS G10950.

Other Specifications for Ferrous Metals and Alloys

·         AISI-SAE

·         European Norm (EN)

·         Casting grades

·         U.S. Military specifications (MIL-SPEC)

Types of Ferrous Alloys

There are different types of ferrous alloys available in the market, which include – carbon steels, alloy steel, stainless steel, cast iron, cast steel alloy grades, cast iron alloy and iron alloy. Brief descriptions of these ferrous alloys are given below:

·         Carbon steels are ferrous alloys which contain carbon and small levels of other alloying elements, such as manganese or aluminum.

·         Alloy steels contain low to high levels of elements such as chromium, molybdenum, vanadium and nickel.

·         Stainless steels are highly corrosion resistant, ferrous alloys which contain chromium and/or nickel additions.

·         Cast iron, a ferrous alloy, contains high amounts of carbon. Ductile iron, gray iron and white cast iron grades are different cast iron types.

·         Cast steel alloy grades are made by pouring molten iron into a mold.

·         Cast Iron Alloy and Iron Alloy are 2 major ferrous alloys used in most industrial applications.

Material suppliers provide ferrous metals and alloys in many shapes and forms:

·         Semi-finished stock shapes are used for part fabrication. They are also suitable as feedstock for casting, forging, spinning and other forming processes.

·         Common stock shapes include bars, rods, tubes, plates, strips, shims, spheres, foil, wire, billets, slabs, and blooms.

·         Materials are also available as ingots, powders, fillers, and reinforcements.

Ferrous Alloys Casting

Companies often specialize in casting of ferrous alloys due to the requirement of specialized equipment for melting and pouring ferrous materials. Casting of ferrous materials is typically achieved through means of shell casting, sand casting, or to a lesser extent investment casting.

In ferrous casting, the most commonly used metal materials are cast iron alloys and iron alloys that include grey iron casting, ductile iron casting and steel iron casting.

Buying Tips

Before choosing ferrous metals and alloys for specific usages, a buyer must analyze the followings:

·         Dimensions: Outer diameter (OD), inner diameter (ID) overall length, and overall thickness are important dimensions.

·         Production processes: Most materials are cast, wrought, extruded, forged, cold-finished, hot-rolled, or formed by compacting powdered metals or alloys. Electric arc furnaces are used to produce very clean metals and alloys with fewer inclusions and lower variability.

·         Features: For improved weldability and the corrosion resistance Low carbon steels are used. For compressive strength, cold-worked steels are suitable.