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Introducing reliable stainless steel materials of different grades and characteristics
Introducing reliable stainless steel materials with different classifications and characteristics
The core of stainless steel classification lies in its microstructure, i.e., its crystal structure. Based on the stable microstructure at room temperature, international standards classify it into five major series, each with unique characteristics and strengths. Specifically, they are divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel, and precipitation-hardening stainless steel.
Austenitic Stainless Steel
1. What are the characteristics of austenitic stainless steel?
It is characterized by being non-magnetic (usually), having excellent corrosion resistance, good plasticity and toughness, and good weldability, but relatively low strength and hardness. It cannot be hardened by heat treatment, but can be strengthened by cold working.
2. What are the main alloying elements of austenitic stainless steel?
Main alloying elements: high chromium (Cr, ≥18%), high nickel (Ni, ≥8%), i.e., the common "18-8" stainless steel.
3. What are some common grades of austenitic stainless steel?
Common grades: 304 / 06Cr19Ni10: The most common and general-purpose grade, used for tableware, kitchenware, architectural decoration, and industrial equipment; 304L (low carbon): Better resistance to intergranular corrosion after welding; 316 / 06Cr17Ni12Mo2: Added molybdenum (Mo), significantly better resistance to chloride ion corrosion (such as seawater and brine) than 304, used in marine environments, chemical plants, and medical equipment; 316L (low carbon): Used for welded parts and applications requiring higher corrosion resistance; 321: Added titanium (Ti), improving resistance to intergranular corrosion.
Introducing reliable stainless steel materials with different classifications and characteristics
Ferritic Stainless Steel
1. What are the characteristics of ferritic stainless steel?
Characteristics: Magnetic, moderate corrosion resistance (better than martensitic, usually less than austenitic), good resistance to chloride stress corrosion cracking, good thermal conductivity, low coefficient of thermal expansion. Cannot be hardened by heat treatment.
2. What are the main alloying elements of ferritic stainless steel?
Main alloying elements: Primarily chromium (Cr) (usually 12%-30%), with very little or no nickel (Ni).
Common grades: 430 / 10Cr17: General purpose, used in household appliances (such as washing machine inner drums), decoration, nitric acid equipment; 409: One of the cheapest types of stainless steel, used in automotive exhaust pipes; 444: High chromium and high molybdenum, corrosion resistance and rust resistance are close to 316, used in hot water tanks, solar energy equipment.
Martensitic Stainless Steel
1. What are the characteristics of martensitic stainless steel?
Characteristics: Magnetic, strength and hardness can be significantly improved through heat treatment (quenching, tempering), but plasticity and weldability are poor. Corrosion resistance is generally low (lower than austenitic and ferritic).
2. What are the main alloying elements of martensitic stainless steel?
Main alloying elements: Medium to high chromium (Cr, 12-18%), low or high carbon, low nickel content.
3. What are some common grades of martensitic stainless steel?
Common grades: 410 / 12Cr13: General purpose, used for knives, bearings, and valve parts; 420 / 20Cr13: Higher carbon content, higher hardness, used for surgical knives, cutting tools, and wear-resistant parts; 440C / 68Cr17: High carbon and high chromium, achieving extremely high hardness, a top-grade stainless steel material for knives.
Duplex Stainless Steel
1. What are the characteristics of duplex stainless steel?
Characteristics: The microstructure consists of approximately 50% austenite and 50% ferrite. It combines the advantages of both: its strength is about twice that of austenitic stainless steel, excellent resistance to chloride stress corrosion cracking, good weldability and toughness. It is magnetic.
2. What are the main alloying elements in duplex stainless steel?
Main alloying elements: High chromium (Cr, 21-26%), medium nickel (Ni, 1.5-8%), added molybdenum (Mo), nitrogen (N).
3. What are some common grades of duplex stainless steel?
Common grades: 2205 / S32205 / 022Cr22Ni5Mo3N: The most commonly used duplex steel, widely used in offshore oil platforms, chemical industry, pressure vessels, and pipelines.
Precipitation Hardening Stainless Steel
1. What are the characteristics of precipitation hardening stainless steel?
Characteristics: Through a special "precipitation hardening" heat treatment, it can maintain good toughness while maintaining high strength. It has a wide range of adjustable mechanical properties, and its corrosion resistance is better than martensitic steel and close to austenitic steel.
Common grades: 17-4PH / 05Cr17Ni4Cu4Nb: The most famous precipitation hardening stainless steel, used in aerospace, high-stress parts, gears, and shafts.
Classification by Properties
Heat-resistant Stainless Steel: Possesses oxidation resistance and sufficient strength at high temperatures (e.g., 309, 310 series).
Nitrogen-containing stainless steel: Added nitrogen (N) to improve strength and corrosion resistance (e.g., some grades of the 200 series, 316N).
Super stainless steel: Contains higher levels of chromium, nickel, molybdenum, nitrogen, etc., exhibiting extreme corrosion resistance, suitable for harsh environments. Super austenitic: such as 904L (high molybdenum, high nickel), 254SMO (6% molybdenum). Super duplex steel: such as 2507 (S32750). Super ferritic: such as 447 (29Cr-4Mo).
Application Recommendations:
1. Everyday household use, general decorative: 304 is the first choice.
2. Knives, tools requiring high hardness: Choose martensitic 420, 440C or precipitation hardening 17-4PH.
3. Coastal environments, chemical industries: Consider 316/316L. 4. Appliance casings and automotive exhaust systems: Ferritic 430 and 409 are commonly used.
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