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Why tensile strength is more in rolling direction of plates

I'm not sure the tensile strength is higher, but the yield strength will almost certainly be higher. When youroll a plate, most of the change in dimension is in the direction of the rolling (the plate stays the samewidth, but the length grows a lot.) So there is a lot of work hardening in that direction. The grains of thesteel get long and hard in the direction of the roll, but perpendicular to that direction, they are relatively

undeformed and remain soft.

Rolling direction

Definition:

The rolling direction is parallel with the structure lines of the surface

Illustration: Alumeco 

Down below few examples:

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Example:

That means that if you were to inform about the rolling direction of below sawn sheet, then

the rolling direction is: 300mm

Illustration: Alumeco 

Secondary Steel Glossary

This Secondary Steel Glossary is authored by, and the copyrighted intellectual property of, Essex Trading Company. Its

content information has been reviewed and approved by the metallurgical staff of ISO 17025 accredited Kieh Co.,

www.kieh.org.

ABCDEFGHI J KLMNOP Q RST U VW X Y Z

 A

Age Hardening A process in which steel increases hardness and strength and ordinarily decreases ductility over time.

Special Killed (i.e., aluminum killed) prevents that condition.

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B

Blister In coated products, a defect caused by the formation of air bubbles in a zinc or aluminum coating. In uncoated,

refers to a raised spot on the steel surface evidencing inclusions and small laminations.

Bow, Longitudinal Curvature in the plane of sheet or plate in the rolling direction. Usually caused by unbalanced stresses

between the top and bottom surfaces of the rolled product.

Bow, Transverse Curvature across the rolling direction of sheet. A more severe case can result in a center buckle. Usually

caused by an unbalanced curvature of the top and bottom mill rolls during processing.

Buckle A distortion (usually repetitive) in flatness during rolling.

Buckle, Arbor Bends, creases, wrinkles, or departures from flat, occurring perpendicular to the slit edge of a coil and

which are repetitive in nature, with severity decreasing as the distance increases in the coil from the original source. Often

they are found at/near the coil ID or OD.

Buckle, Center Undulations (wavy regions) in the center of the metal.

Buckle, Edge Undulations (wavy regions) along the edge(s) of the metal.

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Edge, Damaged Sheet/coil edge that has been bent, torn or scraped by an object.

Edge Wave A condition in the band of steel where the edges (in the direction of rolling) are longer than the center.

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F

Flaking A condition in coated sheet where portions of the coating become loosened due to inadequate adhesion.

Fluting A breaking or kinking condition caused by aging or improper processing.

Friction Scratches A series of short abrasions caused by the rubbing of laps or sheets. Also called galling. Scratches are

shallow; gouges are deep.

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G

Galling Friction scratches.

Gouge A deep scratch.

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H

Heat Ridge Usually referring to Hot Rolled, a hump in the rolling direction usually resulting from a trapped center buckle

after cold reduction.

Heavy Coating Excessive amount of coating (i.e., zinc or aluminum) applied to the surface.

Hole A metal void, usually caused by a non-metallic inclusion during rolling.

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I 

Inclusions Particles of foreign material (i.e., oxides, silicates, sulfides) in steel, usually compromising physical integrity.

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K

Kink An abrupt bend or deviation from flat which is caused by localized bending during handling.

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L

Lamination (a.k.a. Segregation or Piping) Defect caused by the presence of internal blisters, seams or inclusions.

Harmful to structural integrity; could cause steel fracturing.

Lap Weld Coil ends are "lapped" over one another and welded or stitched for production purposes. As a result, the

thickness of the steel is doubled at the weld area.

Line Stop Referring to coated steels, an area of a coil where the coating line was halted. This region is usually

characterized by irregular and questionable coating integrity.

Loose Wrap A coil that is not wound tight due to insufficient tension when winding.

Lüders Lines Elongated surface markings or depressions appearing in patterns caused by localized plastic deformation

that results from a discontinuous yield and resulting yield point elongation.

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Pickup, Roll Small particles of debris trapped in the rolls and transferred to the sheet surface. Could apply to Cold Rolled

or coated sheet.

Pinchers Fern-like creases usually diagonal to the rolling direction.

Pinholes A coating defect consisting of random small round holes. The open area (pinhole) exposes the steel substrate.

Usually caused by laminations, inclusions, scratches or improper lubricant.

Piping Similar to lamination, a void in the steel's thickness.

Pitting (Rust) A severe form of oxidation causing sharp depressions in the steel surface.

Pitting (Coated) Random small depressions in the coating. Similar to pinholes, except that pitting does not reveal the

bare substrate.

Powdering A problem in which Galvannealed's iron-zinc coating dislodges from the steel substrate.

Pup Coil A coil with relatively small P.I.W., typically under 200. They often contain defects, i.e., dents, dings, scratches.

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R

Roping A rope-like appearance in the rolling direction after the metal has undergone severe deformation. This condition is

caused by the presence of irregular grains in the rolled product before being deformed.

Ragged Edges Sheet edges that are cracked, torn, ragged, split and/or otherwise damaged.

Reel Breaks Surface blemishes (indicated by kinks across the coil width) caused by the winding arbor.

Reel Kinks Horizontal creases near a coil ID (or OD if rewound).

Ridge A surface hump down the length of a sheet/coil.

Roll Grind The uniform ground finish on the work rolls which is imparted to the sheet or plate during rolling.

Rolled-in Metal An extraneous chip or particle of metal rolled into the surface of the product.

Rolled-in Scale A defect resulting from scale being rolled into the steel surface.

Roping A rope-like effect in the rolling direction after steel has been subjected to deep forming/drawing.

Rust Corrosion caused by exposure over time to atmosphere, chemicals or other injurious elements. Usually, Hot Rolled

and Cold Rolled turn orange/red. Galvanized and Aluminized turn white to black.

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S

Scale Iron oxides which form on the surface of Hot Rolled during or subsequent to rolling. Scale can be removed by

Pickling.

Scratch Scoring or indentation of varying degree in the surface. Usually caused by rollers or during handling.

Seam A surface crack sometimes caused during casting or hot-rolling.

Secondary Steel Material that does not meet the original customer's specifications in terms of thickness, width, surface,

chemistry or physical properties. Sold at a discount compared to prime steel, secondary may be quite suitable for other

applications.

Segregation A nonuniformity in chemical composition occurring during solidification. Often associated with internal

defects, i.e., lamination and piping.

Skin Lamination Seam or inclusion at surface resembling a blister. Could lead to metal fracture.

Skip An area of uncoated sheet which is frequently caused by equipment malfunction.

Sliver Thin fragments of steel which are part of the material but only partially attached. Typically caused by surface

damage or internal inclusions which are subsequently rolled.

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Smudge A dark film of debris, sometimes covering large areas, deposited on the sheet during rolling.

Snaking A series of reversing lateral bows in coil products. This condition is caused by a weaving action during an

unwinding or rewinding operation.

Spelter Referring to Galvanized or Aluminized, a severe coating buildup resulting in a non-uniform surface.

Spooled Coil A coil having edges that are turned up or down (like a spool of thread).

Stain, Oil Surface discoloration which may vary from dark brown to white and is produced during thermal treatment by

incomplete evaporation and/or oxidation of the surface by the lubricants.

Starvation Non-uniform coating application which results in absence of coating in certain areas. This condition can be

caused by mismatch of applicator roll and sheet surface velocities.

Streak, Coating A banded condition caused by non-uniform coating during the initial application process.

Streak, Dirt Surface discoloration which may vary from grey to black, is parallel to the direction of rolling, and contains

rolled in foreign debris. It is usually extraneous material from an overhead location that drops onto the rolling surface and

is shallow enough to be removed by etching or buffing.

Streak, Grinding A streak with a helical pattern appearance transferred to rolled products from the work rolls.

Streak, Leveler A streak on the sheet surface in the rolling direction caused by transfer from the leveler rolls.Streak, Roll A non-uniform surface appearance parallel to the rolling direction. It is caused by an uneven wiping action on

the upper backup roll(s) of a mill which transfers first to the work roll and then to the rolled product.

Stretcher Strains Irregular lines that develop during drawing or stretching. Also called fluting.

Striation A coating flow defect appearing as near-parallel lines.

Surface Tear Minute surface cracks on rolled products which can be caused by caster cracks.

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T

Telescoping Lateral stacking, primarily in one direction, of wraps in a coil so that the sidewall of the coil is conical rather

than flat. Usually caused by improper alignment of rolls over which the steel passes before rewinding.

Transit Rust Oxidation occurring during shipment. Typically appears most prominently on ID and OD wraps, top and

bottom sheets, and at edges. It may manifest in sporadic spots within coil or sheet bundle.

Transition Coil A coil that is partially Electrogalvanized coated and partially bare Cold Rolled.

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V

Void An internal cavity produced during the solidification process during casting.

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W

Water Stain Superficial oxidation of the surface with a water film, in the absence of circulating air, held between closely

adjacent metal surfaces such as between wraps of a coil or sheets of a stack. The appearance varies from iridescent in

mild cases to white, gray, or black in more severe instances.

Wave An out-of-flat condition relative to the order or ASTM flatness specifications. Can occur across the width or merely at

edge(s).

Weld (Coil) Area where coils have been welded together to form a single, longer length for more efficient production. The

area near the weld is typically of poor quality in terms of strength, surface and coating adhesion.

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White Rust On galvanized, corrosion that occurs when material is exposed to moisture and is unable to quickly dry, often

between adjacent wraps or sheets. Varies in severity and coverage area.

Wrap-Loose A condition in a coil due to insufficient tension which creates a small void between adjacent wraps.

Wrinkling A coating defect of small ridges or folds resembling a small prune skin.

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Y

Yield Point Elongation (YPE) Refers to a non-uniform elongation of steel and resulting susceptibility to Lüders bands

(surface strain lines, resembling crossbreaks). The deformation can be measured and while there is no accepted industry

standard, generally a YPE measurement below 0.5% would suggest an absence of strain lines during/after stamping.

Rolling (metalworking)

From Wikipedia, the free encyclopedia

Jump to: navigation, search 

"Rolling mill" redirects here. For mills that use rollers to crush grain or stone, see roller mill . 

A rolling schematic

Rolling visualization. (Click on image to view animation.)

In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to

reduce the thickness and to make the thickness uniform. Rolling is classified according to the temperature of the metal

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rolled. If the temperature of the metal is above its  recrystallization temperature, then the process is termed as hot

rolling. If the temperature of the metal is below its recrystallization temperature, the process is termed as cold rolling.

In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes

the most tonnage out of all cold working processes.[1][2] 

There are many types of rolling processes, including ring rolling, roll bending, roll forming, profile rolling, and controlled

rolling.

Hot and cold rolling[edit]

Hot rolling[edit ] 

A coil of hot-rolled steel

See also: Hot working 

Hot rolling is a metalworking process that occurs above the recrystallization temperature of the material. After the grains

deform during processing, they recrystallize, which maintains an equiaxed microstructure and prevents the metal from

work hardening. The starting material is usually large pieces of metal, like semi-finished casting products, such as slabs,

blooms, and billets. If these products came from a continuous casting operation the products are usually fed directly into

the rolling mills at the proper temperature. In smaller operations the material starts at room temperature and must be

heated. This is done in a gas- or oil-fired soaking pit for larger workpieces and for smaller workpieces induction heating is

used. As the material is worked the temperature must be monitored to make sure it remains above the recrystallization

temperature. To maintain a safety factor a finishing temperature is defined above the recrystallization temperature; this is

usually 50 to 100 °C (90 to 180 °F) above the recrystallization temperature. If the temperature does drop below this

temperature the material must be re-heated before more hot rolling.[8] 

Hot rolled metals generally have little directionality in their mechanical properties and deformation induced residual

stresses. However, in certain instances non-metallic inclusions will impart some directionality and workpieces less than

20 mm (0.79 in) thick often have some directional properties. Also, non-uniformed cooling will induce a lot of residual

stresses, which usually occurs in shapes that have a non-uniform cross-section, such as  I-beams. While the finished

product is of good quality, the surface is covered in mill scale, which is an oxide that forms at high-temperatures. It is

usually removed via pickling or the smooth clean surface process, which reveals a smooth surface.[9] Dimensional

tolerances are usually 2 to 5% of the overall dimension.[10] 

Hot rolled mild steel seems to have a wider tolerance for amount of included carbon than cold rolled, making it a bit more

problematic to use as a blacksmith. Also for similar metals, hot rolled seems to typically be less costly.[11] 

Hot rolling is used mainly to produce sheet metal or simple cross sections, such as rail tracks. Other typical uses for hot

rolled metal includes truck frames, automotive wheels, pipe and tubular, water heaters, agriculture equipment, strappings,

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stampings, compressor shells, truck frames, railcar components, wheel rims, metal buildings, railroad-hopper cars, doors,

shelving, discs, guard rails, pipe and tubular, automotive clutch plates.[12] 

Cold rolling[edit ] 

Cold rolling occurs with the metal below its recrystallization temperature (usually at room temperature), which increases

the strength via strain hardening up to 20%. It also improves the surface finish and holds tighter tolerances. Commonly

cold-rolled products include sheets, strips, bars, and rods; these products are usually smaller than the same products that

are hot rolled. Because of the smaller size of the workpieces and their greater strength, as compared to hot rolled stock,

four-high or cluster mills are used.[2] Cold rolling cannot reduce the thickness of a workpiece as much as hot rolling in a

single pass.

Cold-rolled sheets and strips come in various conditions: full-hard , half-hard , quarter-hard , and skin-rolled . Full-hard

rolling reduces the thickness by 50%, while the others involve less of a reduction.Skin-rolling, also known as a skin-pass,

involves the least amount of reduction: 0.5-1%. It is used to produce a smooth surface, a uniform thickness, and reduce

the yield point phenomenon (by preventing Lüders bands from forming in later processing). It locks dislocations at the

surface and thereby reduces the possibility of formation of Lüders bands. To avoid the formation of Lüders bands it is

necessary to create substantial density of unpinned dislocations in ferrite matrix. It is also used to breakup the  spangles in

galvanized steel. Skin-rolled stock is usually used in subsequent cold-working processes where good ductility is required.

Other shapes can be cold-rolled if the cross-section is relatively uniform and the transverse dimension is relatively small.

Cold rolling shapes requires a series of shaping operations, usually along the lines of sizing, breakdown, roughing, semi-

roughing, semi-finishing, and finishing.

If processed by a blacksmith, the smoother, more consistent, and lower levels of carbon encapsulated in the steel makes it

easier to process, but at the cost of being more expensive.[13] 

Typical uses for cold rolled steel include metal furniture, desks, filing cabinets, shelves, tables, chairs, motorcycle exhaust

pipes, computer cabinet and hardware, all home appliances and components, shelving, lighting fixtures, hinges, tubing,

steel drums, lawn mowers, electronic cabinetry, lighting fixtures, water heaters, metal containers, and a variety of

construction related products.[14]