JIS G3141 Cold-Rolled Steel Sheet Grade Guide: SPCC, SPCD, SPCE, SPCF, SPCG

JIS G3141 is the Japanese Industrial Standard for cold-rolled carbon steel sheets and strips. It covers five formability grades — SPCC, SPCD, SPCE, SPCF, and SPCG — ranging from general-purpose commercial steel to interstitial-free (IF) steel for extreme deep drawing. The standard defines each grade by chemical composition limits and minimum elongation; only SPCE and above carry an r-value (Lankford coefficient) specification that quantifies actual deep-drawing capability. This guide covers all five grades in a single reference, including the composition logic, the mechanical property requirements, the surface finish suffix system, and the ASTM A1008 / EN 10130 / ISO 3574 equivalent designations.

1. Standard Scope and Form

JIS G3141:2021 covers cold-rolled carbon steel sheet and strip for general use. Key scope parameters:

• Thickness: 0.25–3.2 mm (thinner material is covered by JIS G3141 but practical commercial availability starts at 0.3 mm for most grades)
• Width: Coil or cut-to-length sheet; widths from 600 mm to 1800 mm are standard commercially
• Carbon maximum: 0.15% (SPCC) to 0.02% (SPCG) — all grades are low-carbon; none are hardenable by quenching
• Delivery condition: Annealed and temper-rolled; surface may be dull (-D), bright (-B), or standard; may include skin-pass (-SB/-SD) designation

2. Composition Logic: Why Each Grade Is Different

Moving from SPCC to SPCG, the chemistry becomes systematically cleaner. The four elements controlled — C, Mn, P, S — each affect formability through different mechanisms:

• Carbon (C): Dissolved C in ferrite pins dislocations (interstitial hardening), raises yield strength, reduces elongation. Also forms Fe₃C carbides that act as void nucleation sites during forming. Reduced from 0.15% (SPCC) to 0.02% (SPCG — essentially interstitial-free after Ti/Nb additions)
• Phosphorus (P): Segregates to grain boundaries, embrittles ferrite, reduces impact toughness and deep-draw ductility. The single biggest composition difference between SPCC (0.100%) and SPCD/SPCE (0.030–0.040%). High P in SPCC is acceptable for commercial use but incompatible with demanding draws
• Manganese (Mn): Solid-solution hardener; also combines with S to form MnS inclusions (which are less harmful than FeS but still act as void nucleation sites). Reduced progressively from 0.60% to 0.25% (SPCG)
• Sulfur (S): Forms inclusions (MnS when Mn is present). Stringy MnS inclusions cause anisotropic properties and reduce deep-draw uniformity. Controlled to low levels in all grades, most stringently in SPCG (0.020%)

3. Full Composition Table

Source: JIS G3141:2021. SPCF and SPCG require Ti or Nb microalloying additions to fix dissolved interstitial C and N. For SPCF, the Ti/Nb addition provides non-aging without full IF chemistry. For SPCG, the addition is sufficient to produce full IF steel where essentially all interstitial C and N are tied up as TiC, TiN, NbC, or NbN precipitates — leaving a ferritic matrix with maximum dislocation mobility and r-value.

4. Mechanical Properties Table

5. The r-Value Specification — What It Means in Practice

The r-value (Lankford coefficient) is only specified for SPCE and above. For SPCC and SPCD, the standard guarantees composition and elongation but provides no r-value floor. This matters because:

• Two SPCD coils from different heats can have r̄ values of 1.1 and 1.35 and both pass SPCD specification
• In a draw where r̄ = 1.35 is marginal and r̄ = 1.1 causes fracture, the variable r̄ in SPCD produces variable yield rates
• SPCE’s r̄ ≥ 1.4 specification eliminates this variability — every SPCE coil delivered must meet this floor

The r̄ is the average of r-values measured in three directions: r̄ = (r₀° + 2·r₄₅° + r₉₀°) / 4. The planar anisotropy Δr = (r₀° – 2·r₄₅° + r₉₀°) / 2 determines earing tendency in drawn cups. High Δr causes uneven cup height (earing); IF steels (SPCG) are produced to minimize Δr as well as maximize r̄.

6. Surface Finish and Temper Suffixes

7. ASTM A1008 / EN 10130 / ISO 3574 Cross-Reference

The most significant cross-standard difference is SPCC vs DC01: JIS SPCC allows P up to 0.100%, while EN DC01 limits P to 0.045% and ASTM A1008 CS limits to 0.030%. SPCC is a distinctly less controlled grade than its Western equivalents in terms of phosphorus. When substituting SPCC for A1008 CS in a global supply chain, the phosphorus difference must be evaluated against the application’s sensitivity to grain boundary embrittlement.

8. Grade Selection Decision Table

9. FAQ

Q: Can JIS G3141 steel be through-hardened?

No. All JIS G3141 grades are low-carbon (0.02–0.15% C) — below the carbon content needed for martensite formation by quenching. These steels cannot be meaningfully hardened by heat treatment. For applications requiring surface hardness, specify a carburizing grade (SCM415, SCM420) or a higher-carbon material and a different form (plate rather than sheet).

Q: What does “normal annealing” vs “bright annealing” mean on a JIS G3141 certificate?

Normal (open coil) annealing in a controlled atmosphere furnace produces a clean surface but with some slight oxidation at very high temperatures. Bright annealing in a pure hydrogen or nitrogen-hydrogen atmosphere furnace produces a mirror-clean surface with zero oxidation — the “bright” in SPCC-SB refers to the surface condition after skin-passing, not specifically to the annealing atmosphere. For stainless steels, bright annealing has a specific meaning (inert atmosphere); for carbon steel, “bright surface” SPCC refers to the skin-pass finish.