Materials Science - Hot Rolling

8/9/2019 Materials Science - Hot Rolling

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Problem 1:

The hot-rolling of steel is a process that puts steel through plastic deformation at really

high temperatures to reduce its thickness and obtain large sheets of steel that can later be

processed into other materials, like long plates. The hot-rolling process consists of several stages.

In the first stage, the steel is sent to a reheating furnace where it is heated to a very high

temperature. Then, it goes through a process called millscale cleansingwhere the surface is

cleansed to remove any oxygen particles that may have reacted with the surface of the steel.

After that, the steel is passed through a rolling mill where its thickness is reduced from about 22

cm to about cm. The steel is then cleansed again. !ollowing that, the material passes through a

vertical rolling mill where the width of the material is ad"usted to the desired dimension. Then,

the deformed specimen enters a coil box which coils the sheet up to minimi#e space. Then the

material enters a finishing mill which reduces the thickness further to between $.% and $& mm.

Also, while reducing the thickness it also passes through an uplooper which measures, ad"usts

and controls the profile and the flatness of the material. 'astly, each strip is cooled with an

appropriate cooling rate. After going through hot rolling, the steel is either sent to the market or

sent for cold-rolling.

(ot rolling increases the ductility of materials and allows them to be easily deformed.

Temperature control is critical to the properties of the final product during hot rolling. The

temperature while rolling always has to remain above the recrystalli#ation temperature to allow

the deformation of the grains. Also, the cooling rate critically affects the strength of the

materials. If the cooling rate was too fast, the grains would not grow enough before re-combining

and would make the material too brittle. )imilarly, the cooling rate was too slow, the material

will be too ductile. *+eferenceshttpen.wikipedia.orgwiki+olling*metalworking/0(otrolling/
http://en.wikipedia.org/wiki/Rolling_(metalworking)#Hot_rolling)http://en.wikipedia.org/wiki/Rolling_(metalworking)#Hot_rolling)http://en.wikipedia.org/wiki/Rolling_(metalworking)#Hot_rolling)


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Problem 2:

In several electronic and optical applications, the grain boundaries of a polycrystalline

material is considered a downside to the properties of a material since they stand in the way of

conduction of electricity and optical properties. )cientists thought that to optimi#e the

performance of several applications, single crystal materials would allow for the wanted

properties to be maximi#ed. 1onocrystalline )ilicon is probably the most important single

crystal in the electrical industry. Its single-crystal nature allows for the maximi#ation of optimal

semiconductor properties in locali#ed areas in the circuit. Another ma"or advancement in

technology, is the use of single-crystal turbine blades to optimi#e the mechanical properties of

blades under high temperatures. The absence of the grain boundary decreases the yield strength

of the materials. (owever, it also decreases the amount of creep which may happen on the blade

which is critical since the blade operates at high temperatures and is sub"ect to creep. An

example of such a material is ickel-3ased superalloy single-crystal.

1any mechanisms have developed today for the growth of single-crystal materials. An

example of two common methods are the 3ridgman and 4#ochralski processes. The 3ridgman

techni5ue involves heating a material above its melting temperature and then cooling it slowly

from one edge to the other *hori#ontally or vertically/. This division in cooling allows one single

crystal to grow throughout the whole material. In the 4#ochralski process, a single crystal in the

form of a rod is dipped into the molten material and then slowly pulled out while rotating. The

rate at which it is pulled out and rotated makes it possible to extract one single crystal out of the

material. *List of references is provided on the next page/


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Problem 2 References:

- The )cience and 6ngineering of 1aterials &thedition *Textbook/ by Askeland, !ulay,

and 7right.

- httpen.wikipedia.orgwiki+olling*metalworking/0(otrolling- httpen.wikipedia.orgwiki)inglecrystal0citenote-spt-$

- httpwww.appropedia.org)ingle4rystalTurbine3lades

- httpen.wikipedia.orgwiki3ridgman8628%98:)tockbargertechni5ue- httpen.wikipedia.orgwiki4#ochralskiprocess0;roductionof4#ochralskisilicon
http://en.wikipedia.org/wiki/Rolling_(metalworking)#Hot_rollinghttp://en.wikipedia.org/wiki/Single_crystal#cite_note-spt-1http://www.appropedia.org/Single_Crystal_Turbine_Bladeshttp://en.wikipedia.org/wiki/Bridgman%E2%80%93Stockbarger_techniquehttp://en.wikipedia.org/wiki/Czochralski_process#Production_of_Czochralski_siliconhttp://en.wikipedia.org/wiki/Rolling_(metalworking)#Hot_rollinghttp://en.wikipedia.org/wiki/Single_crystal#cite_note-spt-1http://www.appropedia.org/Single_Crystal_Turbine_Bladeshttp://en.wikipedia.org/wiki/Bridgman%E2%80%93Stockbarger_techniquehttp://en.wikipedia.org/wiki/Czochralski_process#Production_of_Czochralski_silicon

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Materials Science - Hot Rolling