Knowledge for Cold Rolled Steel

1、Brief Introduction for Cold Rolled Steel Coil/Sheet

(1) Cold Rolled Steel Coil/Sheet is steel that has been worked below its recrystallization temperature by passing it between a pair of rollers. Recrystallization temperature is the temperature at which grains in the lattice structure of the metal have been rearranged, leaving it free of strain and deformations. In this way, cold rolling differs from hot rolling, which is used to work metal above its recrystallization temperature. There are several reasons for Cold Rolled Steel Coil/Sheet. The cold rolling process reduces the thickness of the metal worked and achieves tighter thickness tolerances than can be produced with hot rolling. Cold rolling can also produce a high quality surface finish and prepare the metal to receive a surface coating. Cold Rolled Steel Coil/Sheet is available in a variety of sizes and shapes with characteristics useful in a wide range of applications.

(2) Cold Rolled Steel Coil/Sheet is pre-treated before being cold rolled with a process known as pickling, which uses strong acids to remove scale and other impurities. The Cold Rolled Steel Coil/Sheet is then passed through rollers to reduce its thickness. Most cold rolling takes place in multiple passes and usually incorporates two stations to work the metal. One station is used for a larger initial reduction in size while the other produces a smaller finishing reduction to produce a quality surface. Due to increased hardness created by cold rolling, this process is more limited than hot rolling in the size reduction achieved with each pass.

(3) Comparison Chart for the working processes of Hot Rolled Steel Coil/Sheet and Cold Rolled Steel Coil/Sheet

Comparison-Chart-for-Hot-Rolled-Steel-and-Cold-Rolled-Steel.jpg

(4) A variety of grades of Cold Rolled Steel Coil/Sheet may be produced depending on the reduction in size of the original coil/sheet. Skin-Pass rolled steel undergoes a reduction of 0.5–1.0% and is noted for its smooth surface finish and good ductility. Other grades include quarter hard, half hard, and full hard, which can reach up to 50% reduction in size from the original steel coil/sheet.

(5) As the size of the Cold Rolled Steel Coil/Sheet is further reduced, its strength and hardness both increase, but its ductility decreases. Quarter Hard steel retains sufficient ductility that it can be bent back on itself without fracturing. Half hard steel can only be bent to 90 degrees and full hard steel can only be bent to 45 degrees without fracturing. After cold rolling, heating the metal up in a process known as annealing can restore some of its ductility. The final Cold Rolled Steel Coil/Sheet may be manufactured in the form of sheets, strips, bars, or other forms.

GradeFull Hard SteelHalf Hard SteelQuarter Hard SteelEighth Hard Steel

Annealed + Skin
Passed Steel

HRB≥ 8574 ~ 8965 ~ 8050 ~ 7185 ~ 110
HV≥ 170135 ~ 185115 ~ 15095 ~ 130/


(6) Cold Rolled Steel Coil/Sheet features a variety of attributes suitable in a wide range of applications. In addition to its high strength, Cold Rolled Steel Coil/Sheet is highly resistant to denting and exhibits useful magnetic properties. It also readily accepts surface coatings such as enamel and paint. Manufactured items made with Cold Rolled Steel Coil/Sheet range from commercial products such as appliances and bathtubs to automobiles to industrial products including motors, generators, and transformers.

2、Production Flow Chart of Cold Rolled Steel Coil/Sheet

Production-Flow-Chart-of-Cold-Rolled-Steel.jpg


3、Carbon Cold Rolled Steel Coil/Sheet

   Grades and Usage of Carbon Cold Rolled Steel Coil/Sheet
GradesUsage
SPCCCommon Usage
SPCDDrawing Usage
SPCE, SPCENElongation Usage


   Chemical Components of Carbon Cold Rolled Steel Coil/Sheet %
GradesChemical Componets
CMnPSAlta
SPCC≤0.12≤0.50≤0.035≤0.025≥0.020
SPCD≤0.10≤0.45≤0.030≤0.025≥0.020
SPCE, SPCEN≤0.08≤0.40≤0.025≤0.020≥0.020
When C≤0.01, Alt≥0.015 for all grades


   Mechanical Property of Carbon Cold Rolled Steel Coil/Sheet
GradesYield Strengtha
≤ (MPa)
Tensile Strengtha
≥ (MPa)
Elongationb (Lo=50mm b=25mm) % No Less than
(Nominal Thickness mm)
<0.250.25 ~ < 0.400.40 ~ < 0.600.60 ~ < 1.01.0 ~ < 1.6≥ 1.6
SPCC270303234363738
SPCD270323436383940
SPCE, SPCEN210270343638404142
a. When yield is not obvious, Rp0.2  is to be used. Otherwise, use ReL.
b. The tested sample is same as the P14 sample in GB/T228.


   Tensile Strain Marks of Carbon Cold Rolled Steel Coil/Sheet
GradesTensile Strain Marks
SPCCNo guarantee period
SPCDStore under the roon temperature, will be free of tensile strain marks within a guarantee period of 3 months
SPCEStore under the roon temperature, will be free of tensile strain marks within a guarantee period of 6 months
SPCENStore under the roon temperature, will be free of tensile strain marks all the time


   Surface Quality of Carbon Cold Rolled Steel Coil/Sheet
LevelSymbolFeature
Relative High Surface QualtiyFB (03)Small amount of defects such as monior scrath, indentation, pitting, roll marks, oxidation tint etc.
are tolerable on the surface. It won't affect the molding and coating adhesivity
High Surface QualtiyFC (04)Obivious defects visible to the naked eyes are unacceptable on the relatively better side,
and the other side is supposed to at least be up to the demand for the FB
Super High Surface QualtiyFD (05)Any defects who will affect the coating quality are unacceptable on the relatively better side,
and the other  side is supposed to at least be up to the demand for the FB


   Surface Quality of Carbon Cold Rolled Steel Coil/Sheet
StandardQ/BOB 402-2003BZJ491-2004JIS G 3141-1996GB/T 5213-2001Q/BOB 402-1999
GradesSPCCSPCCSPCCSPCC
SPCDSPCDSPCDSPCD
SPCESPCESPCESC1SPCE、SPCEF、
SPCEHF、SPCEZF
SPCENSPCENSPCENSC2SPCEN


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