Difference between steel and cast iron pdf
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- Casting vs. Forging
- What Is the Difference Between Cast Iron And Steel?
- Difference Between Cast Iron and Steel
Casting vs. Forging
Metals have a combination of strength and plasticity that is not found in many other materials. What is the difference between cast iron and steel? The most notable difference between steel and cast iron is the carbon content.
Toughness is the ability of a material to absorb energy without fracturing. Rubber is a tough material. Toughness is a combination of ductility and strength see below. Strength is a measure of how much force is needed to bend an object. Steel and cast iron are both strong materials. Ductility is a measure of a materials ability to undergo plastic transformation without rupturing.
Gold is a ductile material. Hardness is the ability of a material to resist scratching. Diamonds are hard objects. However , the quick answer I gave above is complicated by heat treatments and alloys. Heat treatments can increase or decrease hardness assuming there is enough carbon in a metal. Some heat treatments allow you to harden parts of the material, while leaving other parts soft tough. This treatment is done by heating a metal to just below its critical transformation point, and then letting that metal cool down slowly over a long period of time.
This process can relieve internal structural stresses in the metal caused from cold working, shearing, or gas cutting. Unlike the previous treatment, the annealing process requires that the metal be heated to just above its critical point. After which, it is cooled over a long period of time inside the furnace or another heated environment. This can greatly improve the strength and ductility toughness of a metal at the expense of hardness.
The normalizing process is very similar to annealing, the primary difference is that the stock is allowed to cool outside the furnace at atmospheric temperatures. Due to the faster cool down speed, normalized metal is harder but less tough than annealed metal. Much like the softening processes above, the stock is heated to its critical temperature. After the heating, the stock is quenched in one of the following: water,brine, oil, or liquid nitrogen.
Liquid nitrogen or even blasts of cold air may be used for high-alloy materials. There are other methods for low carbon materials, which I will cover later. The basic idea of surface hardening, is that you only harden the surface that needs to be hardened.
As the name suggest, flame hardening involves using an acetylene torch to heat the part of the project that needs to be hardened. This is because you want to avoid hardening the metal at different rates throughout the stock.
This methods uses a high frequency electrical induction current to heat the metal. A quenching medium follows directly after the induction coil. This method is extremely precise and efficient, and is often used in large scale manufacturing processes. This method uses a laser to rapidly heat up a piece of metal. These lasers are incredibly precise, allowing control over the heating depth as well as the heating area.
Most processes that use laser hardening use a shallow depth heat, meaning that no quenching material is needed as the material will quench itself. If you are working with a low carbon steel, you must use a different technique like carburizing. The most common carbon rich agents are : Carbon monoxide, sodium cyanide, and barium carbonate, or hardwood charcoal.
Some of these agents are highly toxic,so be very careful in deciding whether they are even necessary. Choose safer options when at all possible, and always exercise caution when using these materials. In addition to heat treatments, there is another factor complicating my rule of thumb from earlier. Mainly, there are also many different types of steel alloys. An alloy is simply a mixture of metals. The most common elements found in steel alloys are: Iron, Carbon, Manganese, and silicon.
A number of other elements such as copper and lead can be added to some alloys. Mixing these elements allows a manufacturer to create steels with differing properties. There are also a number of undesirable elements that can sneak in during the production process, elements like sulfur and phosphorus.
Manufacturers must also keep a lookout for oxides that may form during steel manufacturing. So why did I take the time to explain all this technical stuff about heat treatment and alloys? Summed up: Heat treatment and the differing mechanical properties of alloys can make my rule of thumb stated above a little clumsy.
I think it might be useful to compare cast iron and steel on a number of different factors. As discussed earlier, these are general guidelines. As you now know, heat treatment and alloys can change the character of a metal greatly. Always look up the exact specs of your metal when doing important commercial work. If you were judging the two materials based purely on the above table, it would seem like cast iron was a clear winner.
However this is not really the case, as many real world applications require a tough non-brittle material. Hardened steel is very common in many projects as the brittleness of cast iron is real big drawback. Up until now I have tried to compare the difference between cast iron and steel from a very high level.
This is a very common form of cast iron. It has relatively few shrinkage cavities and little porosity. Gray cast iron is specified by a two-digit ASTM code. It has a graphitic microstructure and is named after the gray color graphite of the fracture it forms. It is the most widely used cast iron based on weight and has a high thermal conductivity making it great for cookware.
This is a type of graphite-rich cast iron that has much more impact and fatigue resistance. These properties come from the shape in which the embedded graphite take on. In Gray Iron, graphite takes on the form of flakes in its microstructure.
Meanwhile, In ductile iron, the graphite takes on a nodular shape. This nodular shaped microstructure makes it harder for fractures to occur. This is a type of cast iron that provides incredible hardness at the expense of toughness. This hardness comes from the fact that the carbon in the material organizes itself into cementite rather than graphite. White cast iron is too brittle for many applications, however it is incredibly handy as a wear surface and is used in the manufacture of:.
Malleable Iron is basically annealed white cast iron. During this process the cementite dissociates into iron and graphite, and takes on a microstructure of ferrite or pearlite. This transformation provides more ductility, strength, and shock resistance, hence the name malleable iron. Malleable Iron is used in the manufacture of:. Finally we have Compacted Graphite Iron. This material has mechanical and physical properties that put it somewhere in between gray and ductile iron.
This iron has damping and thermal properties that are similar to gray iron, and strength and stiffness comparable to ductile iron. Due to this strength, objects made with compacted graphite iron can be made thinner and lighter. It has better machinability than ductile iron, and is easy to cast. It is used in the manufacture of:. Taking the time to explain them in depth would make this article waaaaay too long.
For now, just take in the idea that the atoms of any given material organize themselves into shapes. These shapes greatly affect the material properties of a given material. In this article I did my best to give general guidelines that can help you figure out what the difference is between cast iron and steel.
These guidelines are crude however, as cast iron and cast steel are terms that actually refer to a bunch of a different materials. I tried to provide some detail, and to give the scientific underpinnings for the differences between the two materials.
What Is the Difference Between Cast Iron And Steel?
The matrix microstructure in austempered ductile iron can be further refined by secondary graphite if the austenitization, quench, and isothermal transformation into ausferrite are preceded by an austenitization at a slightly higher temperature followed by quench to martensite, resulting in higher carbon content than being soluble at the second austenitization temperature. Hypoeutectoid steels with high silicon contents can be rapidly graphitized, causing recrystallization of surrounding ferrite due to plastic deformation making room for less dense graphite. In rolled steels, the interface between manganese sulfide and steel matrix is the most common nucleation site. Graphitized Si-solution strengthened ferritic steels may perform similar to free-cutting steels but with improved mechanical properties. Graphite formation in iron-based materials offers increased degrees of freedom regarding a multitude of properties. So far it has mainly been utilized in iron castings where solidification shrinkage is counteracted by graphite expansion, machinability is improved since graphite both acts as lubricant and results in discontinuous chips. In steels having by definition much lower carbon contents experiences are more mixed, including decreased mechanical properties at elevated temperatures due to unwanted graphitization and uneconomically long annealing requirements when graphitization is desired.
Difference Between Cast Iron and Steel
Steel and iron are two of the most common materials used in the manufacturing industry. They are used to make a wide range of products and components. While iron and steel look similar, though, they are two unique materials with their own respective characteristics and qualities.
Carbon steel and stainless steel are both metals that are used in a wide array of commercial and consumer applications. The main difference between the two is in the components that are added to the steel to make it useful for its intended purposes. Steel is an alloy made out of iron and carbon.