Tin-Free Steel (TFS) – Introduction

Tin-Free Steel (TFS) is a type of steel sheet that is coated with a layer of chromium or chromium oxide as an alternative to traditional tinplate (steel coated with a layer of tin). The primary purpose of this coating is to protect the steel from corrosion, especially in applications where the steel will come into contact with food or other liquids, like in the production of cans, packaging, and containers. While tinplate has traditionally been used in food packaging, TFS offers similar corrosion resistance and formability but with several advantages, including a different environmental impact and ease of recycling.

Composition and Coating

• Base Material: The substrate material is typically cold-rolled steel or galvanized steel.
• Coating: The steel is coated with a layer of chromium or chromium oxide. This coating provides corrosion resistance and acts as a barrier to protect the underlying steel.
• The chromium layer can be applied through electroplating or other surface treatment methods.

Key Characteristics of Tin-Free Steel (TFS)

1. Corrosion Resistance: The chromium or chromium oxide coating gives TFS excellent resistance to corrosion, particularly in acidic and humid environments, which makes it suitable for use in food and beverage cans, as well as other containers that require long-lasting protection.
2. Environmental Friendliness: TFS is considered more environmentally friendly than tinplate because chromium is more abundant and recyclable than tin. Chromium coatings are less likely to pose environmental risks compared to tin, which can be toxic in large amounts.
3. Non-Toxic: Like tinplate, TFS is designed to be non-toxic and safe for food and beverage storage, making it a suitable material for the food industry.
4. Formability: TFS has excellent formability, making it suitable for deep drawing, stamping, and other shaping processes used in can manufacturing and other packaging applications.
5. Durability: TFS provides a strong, durable surface that resists wear and scratching, ensuring the product remains intact through handling, transportation, and storage.
6. Cost-Effectiveness: While TFS may be more expensive than some other steel types, it is often a more costeffective solution compared to tinplate when considering the long-term environmental benefits and corrosion protection it offers.

Applications of Tin-Free Steel

• Food and Beverage Packaging: Cans, especially for beverages like soda, beer, and food items like soups and vegetables.
• Chemical Containers: Packaging for chemical or pharmaceutical products, where corrosion resistance is important.
• Electronics Enclosures: Sometimes used in electronic devices that require durable, corrosion-resistant casings.
• Automotive Parts: Certain automotive applications where lightweight and corrosion-resistant steel is necessary.

Mechanical Characteristics of Tin-Free Steel (TFS)

The mechanical properties of TFS are critical to its performance in industrial applications, especially in packaging and deep drawing. Below are the typical mechanical characteristics of TFS:

1. Yield Strength
   • Definition: The yield strength is the stress at which a material begins to deform plastically (permanently).
   • Typical Value: For TFS, the yield strength typically ranges between 200 to 400 MPa (depending on the grade and thickness). This is important because it determines the material's ability to withstand forming operations without permanent deformation or failure.
2. Tensile Strength
   • Definition: The tensile strength is the maximum amount of stress that a material can endure before it breaks or fractures.
   • Typical Value: For TFS, tensile strength typically ranges from 350 to 500 MPa. A higher tensile strength allows the material to handle more stress during forming without tearing.
3. Elongation
   • Definition: Elongation is a measure of the material's ability to stretch before breaking. It is an important property for materials that undergo forming processes like deep drawing.
   • Typical Value: TFS typically has an elongation of 30% to 50%, meaning it can stretch significantly before failure, making it suitable for applications requiring complex shapes.
4. Hardness
   • Definition: Hardness refers to a material's resistance to surface indentation or scratching. For tinplate, this is important for maintaining the integrity of the surface in packaging and handling.
   • Typical Value: The hardness of TFS is typically 70 to 100 HRB (Rockwell B scale). This property determines how resistant the material is to surface deformation, scratches, or indentations, which is important in packaging and handling applications.
5. Formability
   • Definition: The n-value (strain hardening exponent) measures the material’s ability to undergo deformation without failing. A higher n-value indicates better formability.
   • Typical Value: TFS usually has a relatively high n-value (often around 0.2 to 0.3), which means it is suitable for deep drawing and other processes that require the material to stretch without cracking.
6. Modulus of Elasticity
   • Definition: The modulus of elasticity (also known as the elastic modulus) is a measure of a material's stiffness—how much it will stretch or compress under a given force.
   • Typical Value: TFS typically has a modulus of elasticity (E) around 200 to 210 GPa. This indicates how stiff the material is, and how much it will deform under a given load. This property is crucial for applications where the steel needs to maintain its shape under stress.
7. Impact Toughness
   • Definition: Impact toughness measures a material's ability to absorb sudden impacts without fracturing.
   • Typical Value: TFS generally has good impact toughness, meaning it can absorb energy and resist brittle fracture, which is important in preventing failure during sudden shocks or impacts.
8. Bendability
   • Definition: Bendability refers to the material's ability to bend without cracking or breaking, important for applications such as can making.
   • Typical Value: The ability of TFS to withstand bending without cracking is an important mechanical property for many applications. This property allows it to be used in both shallow and deep-drawing processes without compromising the integrity of the material.

Summary of Key Mechanical Properties of TFS

Schematic Image

Product standard code

Coating weight(unit : mg/m²)

Oil Weight(unit : mg/m²)

Base Steel Standard Code

Classification by Type of Steel

Classification by Temper

Classification by Surface Finish