Scope of JIS G3141
JIS G3141 is the Japanese Industrial Standard for cold-reduced carbon steel sheet and strip. It fixes chemical composition limits, mechanical properties, dimensional representation, thickness and width tolerances, mass calculation, surface appearance and the sampling and test methods used to verify them. The standard covers cold-rolled strip in widths below 600 mm, including the mirror-finish strip supplied in coils, together with flat sheets cut from that strip. Because one document defines both the metallurgical limits and the inspection rules, a coil ordered to JIS G3141 can be reproduced consistently from heat to heat and from mill to mill.
How the Grade Designations Work
Every grade carries an SP prefix followed by a letter that indicates the forming severity the steel is intended for, with optional suffixes for temper and surface condition. SPCC is commercial quality and the general-purpose base grade. SPCD is intended for drawing, SPCE for deep drawing, SPCF for extra-deep drawing, and SPCG for the most severe drawing and ironing duties. Formability improves as carbon and residual elements fall, so the composition limits tighten in the same order. That progression is the single most useful rule when matching a grade to a part.
Chemical Composition by Grade
| Grade | C max % | Mn max % | P max % | S max % |
|---|---|---|---|---|
| SPCC | 0.15 | 0.60 | 0.100 | 0.050 |
| SPCD | 0.10 | 0.50 | 0.040 | 0.040 |
| SPCE | 0.08 | 0.45 | 0.030 | 0.030 |
| SPCF | 0.06 | 0.45 | 0.030 | 0.030 |
| SPCG | 0.02 | 0.25 | 0.020 | 0.020 |
These are maximum values for the standard thickness ranges. Residual elements such as silicon, aluminium and nitrogen are also controlled, because they raise yield strength and damage ductility if they are allowed to drift.
Mechanical Properties
SPCC: yield strength 140-280 MPa, tensile strength not less than 270 MPa, minimum elongation 34%.
SPCD: yield strength around 240 MPa, tensile strength not less than 270 MPa, minimum elongation 41%.
SPCE: yield strength around 220 MPa, tensile strength not less than 270 MPa, minimum elongation 43%.
SPCF: yield strength not more than 220 MPa, tensile strength not less than 270 MPa, minimum elongation 45%.
SPCG: yield strength not more than 210 MPa, tensile strength not less than 270 MPa, minimum elongation 45%.
Elongation limits are quoted for the commonly ordered 0.25 mm to 2.5 mm thickness band, and the requirement becomes stricter for thinner material because the gauge has less room to distribute strain. Yield strength is deliberately kept low in the drawing grades so that the sheet flows into the die instead of springing back, while tensile strength stays at a level that still carries structural duties after forming.
Dimensions, Tolerances and Surface Finish
Thickness and width tolerances are specified separately for material supplied in coil and for cut lengths, and they depend on the ordered thickness, the nominal width and whether the edges are mill edge or trimmed edge. Coils are normally supplied with a specified inside diameter, outside diameter range and maximum coil mass, and each coil must be able to pay off without kinking. Surface finish ranges from a matte finish produced by the work rolls, through a bright finish, to the highly reflective mirror finish used in strip below 600 mm. Inspection applies to freedom from scale, rust, scratches, indentations, laminations and, in the drawing grades, from stretcher strains.
Match the grade to the forming operation first: SPCC for bending and simple forming, SPCD for moderate draws, SPCE and SPCF for deep and extra-deep draws, SPCG for ironing.
State thickness, width, edge condition, coil inside diameter, coil mass and temper, because these are all order items rather than defaults.
Specify the surface finish explicitly, since a bright finish and a matte finish behave differently in painting and in visible panels.
Confirm that elongation values are quoted for the thickness band actually ordered, not for a heavier reference thickness.
Frequently Asked Questions
Q: What is the difference between SPCC and SPCD?
SPCC is commercial quality with the widest composition limits, while SPCD is a drawing grade with tighter carbon, manganese, phosphorus and sulphur limits and a higher minimum elongation, which lets it survive a real draw without cracking.
Q: Which grade should be used for deep drawing?
SPCE is the normal choice for deep drawing and SPCF for extra-deep drawing; both keep carbon and residuals low and allow more elongation than SPCC or SPCD.
Q: Does JIS G3141 cover galvanized material?
No. JIS G3141 covers cold-reduced uncoated sheet and strip. Once zinc coating is added, the relevant standard becomes JIS G3302 for hot-dip galvanized sheet, which is a separate specification with its own coating and mechanical requirements.
Q: What thickness range is normally supplied?
Most orders fall between 0.25 mm and 2.5 mm, and the standard's composition and elongation tables are built around that band, with tighter ductility requirements applied to thinner gauges.
Q: Why is a mirror-finish strip limited to widths below 600 mm?
Mirror strip is produced for narrow-strip applications and is defined in JIS G3141 as cold-rolled strip under 600 mm wide; sheets cut from that strip are covered by the same standard.
Q: How should a coil order be written?
Quote the standard, the grade, the temper, thickness, width, edge condition, surface finish, coil inside diameter and coil mass, so that the mill can confirm the tolerances that will be applied at inspection.