Steel and Other Materials FAQCarbon Steel, Tinplate & Nickel FAQ

In the early days, tinplate was called "foreign iron" (yangtie in Chinese). Its formal name is tin-coated steel sheet. It is said that, in the middle of the Qing dynasty, it was first imported through Macao (an old Chinese name for Macao was "Makou"). That is why people commonly call it Makou iron.

The tin coating protects against corrosion, but the coating is thin and has limits. Where the steel base is exposed, it rusts easily. This can happen at cut edges, scratches, and coating defects. Rust is more likely in wet or acidic places. Store tinplate in a dry place and keep it away from moisture.

Under CNS 4155, the tin coating is shown as weight per side, in g/m². The standard coating weights are 2.8, 5.6, 8.4, and 11.2 g/m². The two sides can have equal coatings or different coatings. For example, 2.8/2.8 (also written 25/25 in the older #25 pounds-per-base-box system) means 2.8 g/m² on each side.

Temper grade is a hardness level. Under CNS 4155, it is shown with Rockwell superficial hardness, HR30T. Single cold-reduced steel has grades T-1 to T-5 (HR30T 49±5 to 65±5). Double cold reduced steel (rolled a second time) has grades DR-8 to DR-10 (HR30T 73±5 to 80±5). A bigger number means harder steel.

CNS 4155 (tinplate and the base steel for tin coating) applies to beverage cans and food cans. Whether a product is allowed to touch food (for example, the can's inner coating and hygiene rules) depends on the end use and local laws.

SPTE is a grade of electrolytic tinplate (steel coated with tin). The standard is JIS G3303 (Japanese Industrial Standards; title in English: tinplate and blackplate). The corresponding Taiwan standard is CNS 4155 (tin-coated steel sheets and base plate for tin coating). CNS is the Taiwan national standard.

SPCC is cold-rolled carbon steel sheet (JIS G3141). It has a smooth surface and tight dimensional accuracy. SPHC is hot rolled steel sheet (JIS G3131). Its surface is rougher. SECC is cold-rolled steel sheet with an electro-galvanized (zinc) coating (JIS G3313). The coating helps protect the surface from rust.

Hot rolled steel is rolled at high temperature. If it is not pickled (cleaned with acid), the surface has mill scale, which is a layer of iron oxide. Its dimensional accuracy is lower. Cold-rolled steel starts as hot rolled steel that has been pickled. It is then rolled thinner at room temperature. The surface is smooth, and the dimensional accuracy is higher.

Yes, SPCC rusts. It has no rust-proof coating. It usually ships with a light coat of rust-preventive oil, but it rusts easily when it touches moisture. We suggest you store it in a dry place and use it soon after opening. After processing, apply a surface treatment that fits the end use.

SPCC is a general-purpose grade of cold-rolled carbon steel sheet and strip. The standard is JIS G3141 (Japanese Industrial Standards; title in English: cold-reduced carbon steel sheets and strip). The corresponding Taiwan standard is CNS 9278 (cold-rolled carbon steel sheets, cut sheets, and strip). CNS is the Taiwan national standard.

Yes. They are the same grades. SK5 and SK7 are the old symbols in JIS G4401:1983 (JIS is Japanese Industrial Standards). The current JIS G4401 uses SK85 (formerly SK5) and SK65 (formerly SK7).

Both have at least 99.0% nickel (cobalt included), as listed in JIS G4902 (NW2200 and NW2201). Ni201 is a low-carbon type, with carbon of 0.020% or less. Ni200 has carbon of 0.15% or less. When used for a long time above about 315°C, Ni201 is less likely to suffer graphitization (carbon separates out as graphite and makes the metal brittle).

Yes. Pure nickel is ferromagnetic (strongly magnetic) at room temperature. Its Curie temperature is about 360°C. Above that temperature, it loses its magnetism.

Pure nickel resists corrosion very well in caustic alkalis such as sodium hydroxide, at all concentrations up to the molten state. It also does well in many non-oxidizing (reducing) environments. It is not suitable for oxidizing acids such as nitric acid. At room temperature, it can only be used in nitric acid up to about 0.5% concentration.

Pure nickel (Ni 99% or more) is a metal made mainly of nickel. Stainless steel is an iron-based alloy that contains chromium. Pure nickel is often used in batteries, electrical parts, and alkali-resistant environments. Stainless steel is mostly used for general corrosion-resistant needs.

Ni200 (pure nickel) corresponds to NW2200 in JIS G4902 (Japanese Industrial Standards), N02200 in UNS (Unified Numbering System), and 2.4066 in EN (the European standard; Nickel 99.2). The low-carbon type, Ni201, corresponds to NW2201 in JIS, N02201 in UNS, and 2.4068 in EN.