What is stainless steel?

Stainless steel is an iron-based alloy material made by adding specific alloying elements to achieve corrosion resistance. Its core characteristic is the formation of a dense, stable chromium oxide passivation layer on its surface. This layer acts as a barrier against external corrosive agents, preventing the base material from rusting—hence the name “stainless steel.” It is not completely rust-proof, but it exhibits exceptional resistance to corrosion in the vast majority of environments.

Composition of Stainless Steel

The chemical composition of stainless steel determines its properties, with core constituent elements including:

1. Base Element: Iron (Fe), comprising approximately 60%-80% of the alloy and serving as its matrix;

2. Key Element: Chromium (Cr), with a content ≥10.5% (the minimum standard for stainless steel's rust resistance), used to form a passivation film.

3. Auxiliary Alloying Elements:

· Nickel (Ni): Enhances corrosion resistance, toughness, and machinability (core element in 304, 316 series);

· Molybdenum (Mo): Improves resistance to pitting and crevice corrosion (e.g., 316 series contains Mo);

· Carbon (C): Affects strength and machinability; low-carbon (≤0.08%) or ultra-low-carbon (≤0.03%) grades offer superior corrosion resistance;

· Other elements: Manganese (Mn), Silicon (Si), Nitrogen (N), etc., used to optimize strength, weldability, and other properties.

Core Characteristics of Stainless Steel

1. Exceptional Corrosion Resistance: The protective passivation layer enables adaptation to complex environments including moisture, acids, and alkalis;

2. High/Low Temperature Resistance: Certain grades withstand temperatures exceeding 1200°C, while others maintain toughness at -270°C;

3. High Strength and Toughness: Superior mechanical strength compared to ordinary steel, with reduced susceptibility to fracture and deformation;

4. Workability: Can be processed into various forms through stamping, welding, cutting, polishing, and other techniques;

5. Aesthetic Appeal: Surfaces can be finished with mirror, brushed, or sandblasted effects, offering a clean texture without requiring additional coating;

6. Eco-Friendly and Recyclable: A 100% recyclable material aligned with green environmental principles.

Types of Stainless Steel Classified by Composition:

Based on metallographic structure (determined by composition), stainless steel is primarily divided into four major categories:

1. Austenitic Stainless Steel (Most Common, Accounting for Approximately 70%)

· Composition Characteristics: High chromium, high nickel (or nitrogen substituting part of the nickel), non-magnetic;

· Representative grades: 304 (0Cr18Ni9), 316 (0Cr17Ni12Mo2), 304L, 316L;

· Advantages: Strong corrosion resistance, good toughness, excellent weldability, suitable for most applications.

2. Ferritic Stainless Steel

· Composition Characteristics: High chromium, low nickel (or nickel-free), magnetic properties;

· Representative Grades: 430 (1Cr17), 409L;

· Advantages: Low cost, excellent stress corrosion resistance, suitable for decorative applications and appliance housings.

3. Martensitic Stainless Steel

· Composition Characteristics: Medium-to-high chromium, low nickel, relatively high carbon content, magnetic;

· Representative Grades: 410 (1Cr13), 420 (2Cr13);

· Advantages: High strength, heat treatable for hardening, suitable for cutlery, valves, mechanical components, etc.

4. Duplex Stainless Steel (Austenitic + Ferritic Dual-Phase Structure)

· Composition Characteristics: Chromium content 18%-28%, nickel content 3%-10%, contains molybdenum;

· Representative Grades: 2205, 2507;

· Advantages: Combines the corrosion resistance of austenitic steel with the strength of ferritic steel, suitable for harsh environments like chemical processing and marine engineering.

Differences Between Stainless Steel and Ordinary Steel

Core Advantages of Stainless Steel

1. Long-lasting Durability: Resistant to rust and aging, with a service life 3-5 times longer than ordinary steel;

2. Low Maintenance Costs: Requires no frequent painting or repairs, with simple cleaning (plain water or neutral detergent suffices);

3. Safe and hygienic: No harmful substance leaching, compliant with food contact and medical-grade standards;

4. Wide applicability: Suitable for everyday items to extreme environments (marine, high-temperature, strong acid);

5. Strong value retention: Recyclable with high resource value.

Typical Applications of Stainless Steel

Due to its comprehensive properties, stainless steel has permeated various industries:

1. Architectural Decoration: Railings, doors and windows, curtain walls, stair handrails, elevator cabins (commonly 304, 430);

2. Kitchen & Bath Appliances: Sinks, cookware, water heater liners, refrigerator panels (commonly 304, 316);

3. Food Processing: Storage tanks, conveying pipelines, equipment casings, tableware (commonly 304, 316L);

4. Healthcare: Surgical instruments, medical devices, hospital handrails, sterilization equipment (commonly 316L);

5. Industrial applications: Chemical reactors, oil pipelines, boilers, automotive exhaust systems (commonly 316, 2205);

6. Marine engineering: Ship decks, offshore platforms, seawater desalination equipment (commonly 316, 2507);

7. Daily life: Thermos flasks, stainless steel tableware, outdoor furniture, fitness equipment (commonly 304).