SPCC·SECC·SUS304 차이: 판금 소재별 가공성·내식성·비용 선택 기준

Material Architecture and Selection Logic

SPCC SECC SUS304 comparison is not a simple ranking of strength or corrosion resistance. SPCC is a commercial-quality cold-reduced carbon steel sheet. SECC is an electrogalvanized product built from a cold-rolled steel substrate, a controlled zinc coating and an optional chemical conversion or oil treatment. SUS304 is an austenitic Cr-Ni stainless steel whose corrosion resistance comes from the bulk alloy and its self-repairing passive film.

Because their protection mechanisms are different, the three materials react differently to punching, bending, cutting, scratches and cut edges. A technically valid choice connects material specification, forming severity, exposed environment, finishing route, production volume and total manufacturing cost. Nominal grade and thickness alone are not sufficient.

SPCC Cold-Rolled Carbon Steel

SPCC provides accurate thickness, a consistent surface and economical processing for brackets, covers, chassis, washers and shallow stampings that will normally be painted or plated. Dull finishes can retain lubricant and support paint adhesion, while bright finishes are selected for smoother appearance or decorative finishing. Storage oil is temporary corrosion protection and must be removed through a controlled pretreatment before coating.

Commercial SPCC should not automatically be treated as a deep-drawing grade. Severe draw depth, high stretch concentration or tight corner radii may require SPCD, SPCE or another forming-quality sheet. Plain SPCC also does not guarantee a fixed tensile strength merely from the grade symbol; tensile-test designation, temper and thickness range must be included when mechanical properties are contractual.

SECC Electrogalvanized Steel

SECC is not a separate bulk alloy. It is an electrogalvanized steel product whose performance depends on the substrate grade, coating mass on each face, zinc or zinc-alloy system, conversion treatment and oil condition. These variables control friction, paint adhesion, conductivity, fingerprint resistance and storage corrosion. A purchase order that states only “SECC” can therefore leave critical surface requirements undefined.

The zinc layer protects broad surfaces sacrificially, but punched and laser-cut edges expose the steel substrate. Dry indoor service may be acceptable, while condensation, chlorides and crevices can require sealing, painting or a more robust coating system. Forming must also be checked for coating cracking, powdering and die contamination.

SUS304 Austenitic Stainless Steel

SUS304 combines good ductility, formability and general atmospheric corrosion resistance with a wide range of surface finishes. Its high work-hardening rate is a major manufacturing characteristic: forming load, springback and tool-galling risk increase as deformation progresses. Dies require suitable radii, rigidity, wear-resistant surfaces and lubricants compatible with the subsequent cleaning process.

Solution-annealed 304 is essentially non-magnetic, but cold forming can generate strain-induced martensite and measurable magnetism. A magnet test alone cannot identify or reject 304. When low permeability is functional, the requirement must be measured on the finished part. SUS304 is also not universally immune to corrosion; chlorides, stagnant crevices, iron contamination and damage to the passive film can initiate localized attack. Grade 316, improved drainage, surface restoration or passivation may be necessary.

Punching, Laser Cutting and Edge Quality

A punched edge contains rollover, a burnished shear zone, a fracture zone and an exit burr. Clearance that is too small raises load and wear, while excessive clearance increases burr and dimensional error. SPCC is usually stable under conventional tooling. SECC adds coating friction and exposed-edge considerations. SUS304 requires careful clearance, sharp wear-resistant tooling and galling control because of its high work hardening.

Fiber laser cutting offers flexible geometry without hard tooling, but heat-affected condition, dross, oxide or nitrogen-cut surfaces, film condition and zinc vapor must be evaluated. Neither laser nor NCT is universally superior. The correct process depends on geometry, repeat volume, required edge condition, secondary operations and sheet utilization.

Bending, Stamping and Springback

Bend angle and radius depend on actual yield behavior, thickness, rolling direction, die opening, friction and tooling alignment. SPCC generally needs lower force, but hard temper and tight radii can crack. SECC behaves according to its substrate while adding coating friction and surface-damage limits. SUS304 normally requires greater force, more springback compensation and stronger galling control.

In a coil-fed stamping line, the uncoiler, straightener and servo feeder determine strip flatness and pitch stability before the die closes. Coil set, unstable tension or incorrect feed height can disturb pilot entry and simultaneously affect burr, hole position, camber and formed angle. Approval trials should therefore use production-representative coils, lubrication and feeding conditions.

Surface, Cut-Edge and Bend Quality

SPCC-SD has a fine low-gloss cold-rolled texture, while its exposed carbon-steel cut edge requires burr control and a defined pretreatment and coating scope. SECC has a bright, uniform electrogalvanized surface without the coarse spangle of hot-dip zinc sheet, but punching, shearing and laser cutting expose the steel core at the edge. Edge protection must therefore be specified for condensation, salt and crevice-prone environments.

SUS304 2B has a smooth, slightly reflective silver surface and a stainless cut edge through the full sheet thickness. Forming control focuses on work hardening, springback, bend-surface marking and cosmetic-face protection. Because yield behavior and surface condition differ among the three materials, minimum bend radius, flat-pattern allowance and over-bend compensation must be validated with production-representative material rather than copied as common values.

Total Manufacturing Cost

Raw sheet prices commonly trend from SPCC to SECC to SUS304, but the finished-part comparison must include nesting or strip yield, press load, cycle time, tool wear, lubricant and cleaning, deburring, painting or plating, masking, inspection, rejects, maintenance and expected service life. SPCC can carry significant downstream finishing cost. SECC can remove a separate plating step for suitable indoor parts. SUS304 may offset higher material and forming cost through coating elimination, hygiene, long service and residual scrap value.

Drawing, Quotation and Quality Acceptance

A complete drawing defines the applicable standard and edition, tensile-test requirement, temper, thickness tolerance, rolling direction, surface finish and oil condition. SECC additionally needs coating mass on each side, coating system and chemical treatment. SUS304 needs solution-annealed or cold-worked condition and a finish such as 2B, BA or No.4. Functional datums, burr direction, minimum bend radius, cosmetic faces, surface-protection criteria, corrosion environment and required tests must be unambiguous.

Incoming control may include material certificates, thickness, hardness or specified tensile properties, coating mass and surface condition. Process control connects burr height, hole geometry, bend angle, flatness, coating damage, dimensional stability and appearance to tool wear and lot traceability. Corrosion or cleaning tests must define specimen edges, scratches, pretreatment and acceptance criteria; a test duration by itself is not a service-life prediction.