Introduction to the Labyrinth of Metallurgical Nomenclature

The question "Is steel 304 the same as 1.4301?" is one of the most frequently asked in the industry, and the answer, although seemingly affirmative, contains nuances that can determine the success or catastrophic failure of an engineering project. For a simple decorative element, these differences may be negligible. However, in the case of a pressure installation in the chemical industry, a heat exchanger in a nuclear power plant, or the skin of a launch rocket, understanding the subtle differences between the American AISI, European EN, German DIN, or Russian GOST standards becomes a matter of public safety and economic efficiency.

This report constitutes a comprehensive, expert study on the topic of stainless, acid-resistant, and heat-resistant steel grades. The purpose of this document is not only to provide dry substitution tables but primarily to explain the logic behind these designations and to analyse the impact of chemical composition on the actual functional properties of the material.

Geopolitics of Standards and Marking Systems Worldwide

Understanding marking systems requires a historical and geographical perspective. Each of the main economic blocs has developed its own codification philosophy.

American AISI and ASTM System

The most recognised system worldwide, originating from the American Iron and Steel Institute. Its strength lies in simplicity and commercial recognisability. It is based on a three-digit system:

• Series 200 and 300: Austenitic steels (e.g., 304, 316). The 300 series are classic chromium-nickel grades, the 200 series are cheaper manganese substitutes.
• Series 400: Ferritic and martensitic steels (magnetic, e.g., 430, 410).

Key suffixes in the AISI system:

• L (Low Carbon): Low carbon content (max 0.03%), crucial for weldability (e.g., 316L).
• H (High Carbon): Increased carbon content for better strength at high temperatures (e.g., 304H).
• Ti: Titanium addition as a stabiliser (e.g., 316Ti).

European EN 10088 System (Numerical and Chemical)

The European Union introduced a system that is currently the most technically precise.

Numerical system (e.g., 1.4404): Each grade has a unique number (so-called Werkstoffnummer). "1" denotes steel, "44" the group of grades (acid-resistant steels with molybdenum), and "04" the chronological alloy number. This designation is unambiguous and leaves no room for interpretation.

Chemical system (e.g., X2CrNiMo17-12-2): It tells the engineer everything about the composition. "X" denotes high-alloy steel, "2" is carbon ×100 (0.02%), and the following numbers indicate the percentage content of elements (17% chromium, 12% nickel, 2% molybdenum).

Russian and Post-Soviet System (GOST)

In Eastern Europe, including Poland (due to historical reasons) and in current trade relations with eastern markets, knowledge of the GOST standard (Gosudarstwiennyj standart) is essential. This system is very logical and resembles the old Polish PN system. The designations are based on Cyrillic, where letters correspond to chemical elements.

How to read GOST? (Key to the cipher)

• Number at the beginning: Carbon content in hundredths of a percent (e.g., 12 = 0.12% C, 03 = 0.03% C).
• Х (Kh): Chromium.
• Н (N): Nickel.
• М (M): Molybdenum.
• Т (T): Titanium.
• Г (G): Manganese.
• Ф (F): Vanadium.
• Number after the letter: Average percentage content of the given element (if no number, content is about 1% or less).

Example: 08Х18Н10 (equivalent to 304). Means: 0.08% carbon, 18% chromium, 10% nickel.

Example: 03Х17Н14М3 (equivalent to 316L). Means: 0.03% carbon (L version), 17% chromium, 14% nickel, 3% molybdenum.

Familiarity with this system is indispensable for renovating old industrial installations and in trade with CIS countries.

Detailed Characteristics of Steel Grades

Below is an in-depth analysis of the most popular grades, going beyond dry tabular data.

Austenitic Steels (300 Series) – The Foundation of Industry

This is the largest group of steels, characterised by non-magnetic properties (in the delivery condition), excellent ductility, and weldability.

1. Grade 304 / 304L (1.4301 / 1.4307)

• What it is: The classic "18/8" steel (18% chromium, 8% nickel). A universal global standard.
• Specifics: The 304 (1.4301) version may have up to 0.07% carbon, which in welding thick plates risks intergranular corrosion. The 304L (1.4307) version has carbon reduced to 0.03%, eliminating this problem. Currently, most warehouses offer material with a "dual certificate" 304/304L.
• Applications: Household appliances, gastronomy, tanks in the food industry (dairies, breweries), interior architecture. Not suitable for seawater or swimming pools (risk of pitting).

2. Grade 316 / 316L (1.4401 / 1.4404)

• What it is: "Acid-resistant" steel with molybdenum addition (2-2.5%). Molybdenum drastically increases resistance to pitting corrosion caused by chlorides (salt).
• Specifics: As with 304, the "L" version is standard for welded constructions. It is the first-choice material for the pharmaceutical industry due to its purity.
• Trivia: The famous "Cloud Gate" sculpture ("The Bean") in Chicago is made of 316L to withstand the city’s salt-saturated atmosphere.

3. Grade 316Ti (1.4571)

• What it is: The German response to the problem of intergranular corrosion. Instead of reducing carbon (which was technologically difficult in the past), titanium was added to "bind" the carbon.
• Specifics: Still very popular in German-speaking countries and Poland. Technically often inferior to 316L – titanium forms hard inclusions that make mirror polishing difficult (streaks appear). However, it is mechanically stronger at elevated temperatures than 316L.

4. Grade 321 (1.4541)

• What it is: Equivalent to 304 stabilized with titanium. The old Polish symbol is 1H18N9T.
• Specifics: Used where operating temperatures range between 400-800°C (e.g. exhaust systems, manifolds, chimney installations). Titanium prevents alloy degradation at these temperatures. Not suitable for decorative polishing.

5. Grade 904L (1.4539)

• What it is: Super-austenitic with copper addition (1.5%) and high nickel content (25%) as well as molybdenum.
• Specifics: This steel is resistant to sulfuric and phosphoric acids at concentrations that would destroy 316L steel. Known for use by Rolex (called "Oystersteel"), as it polishes to a brighter, warmer shine and is completely resistant to corrosion from sweat and seawater.

Ferritic and Martensitic Steels (Series 400) – Economy and Hardness

These steels do not contain nickel (or contain it only in trace amounts), making them cheaper and magnetic.

1. Grade 430 (1.4016)

• What it is: Basic ferritic steel (17% chromium).
• Specifics: Good corrosion resistance in dry and mildly aggressive environments. Resistant to stress corrosion cracking (which affects 304/316 steels).
• Applications: Household appliance casings, car interior trims, inexpensive cutlery. Not suitable for structural welding (brittle welds).

2. Grade 420 (1.4021 / 1.4034)

• What it is: Martensitic steel with lower chromium but high carbon content.
• Specifics: The only group of stainless steels that can be hardened (heat treated) like ordinary steel.
• Applications: Kitchen knives, surgical instruments, pump shafts, brake discs. 304 steel is unsuitable for knives (does not hold sharpness), 420 is designed for this purpose.

Duplex and Super Duplex Steels – Hybrid Strength

These are modern materials with a mixed structure (50% ferrite, 50% austenite).

1. Duplex 2205 (1.4462)

• Specifics: Has twice the mechanical strength of 304/316 steel. This means lighter constructions can be built (thinner tank walls). Also has excellent resistance to stress corrosion cracking.
• Applications: Oil platforms, bridges in coastal zones, chemical tankers.

2. Super Duplex 2507 (1.4410)

• Specifics: Extremely corrosion resistant, intended for the harshest conditions (hot seawater, aggressive chemicals). Very difficult to machine.

Heat-Resistant Steels – Working in Extreme Heat

1. Grade 309 / 309S (1.4828)

• Specifics: Suitable for use up to approx. 1000°C. Higher chromium and nickel content than 304. Often used for powder coating hangers or furnace components.

2. Grade 310 / 310S (1.4845)

• Specifics: The "king" of heat resistance (25% Cr, 20% Ni). Continuous use up to 1150°C. Forms a very tight oxide scale. Used in combustion chambers, burners, and the most thermally stressed boiler components.

Substitute Tables and Technical Data

Below we present a detailed comparison of designations, enriched with GOST standards, which are key for a comprehensive market overview.

Table 1: Stainless and Acid-Resistant Steels (Austenitic)

Type of Steel / Application	AISI / ASTM (USA)	EN (Number)	EN (Chemical Name)	PN (Poland - old)	GOST (Russia)	Brief Description
Standard	304	1.4301	X5CrNi18-10	0H18N9	08Kh18N10	Basic "stainless" steel.
Weldable (Low Carbon)	304L	1.4307	X2CrNi18-9	00H18N10	03Kh18N11	For welding, no intergranular corrosion.
Acid-Resistant	316	1.4401	X5CrNiMo17-12-2	0H17N12M2T	-	With molybdenum, better for chlorides.
Acid-Resistant L	316L	1.4404	X2CrNiMo17-12-2	00H17N14M2	03Kh17N14M3	Standard for welded "acid-resistant" steel.
Stabilized Ti	316Ti	1.4571	X6CrNiMoTi17-12-2	H17N13M2T	10Kh17N13M2T	"Acid-resistant" with titanium, difficult to polish.
Heat-Resistant / Ti	321	1.4541	X6CrNiTi18-10	1H18N10T	08Kh18N10T	Resistant up to 800°C, exhaust systems.
Super-Austenitic	904L	1.4539	X1NiCrMoCu25-20-5	-	06KhN28MDT	With copper addition, resistant to sulfuric acid.

Table 2: Ferritic, Martensitic and Duplex Steels

Type of Steel	AISI / ASTM	EN (Number)	EN (Name)	PN (Poland)	GOST (Russia)	Application
Ferritic	430	1.4016	X6Cr17	H17	12Kh17	Decorations, household appliances, interiors (magnetic).
Martensitic	420	1.4021	X20Cr13	2H13	20Kh13	Shafts, machine parts, hardenable.
Cutlery (High C)	420	1.4034	X46Cr13	4H13	40Kh13	Knives, cutting tools, high hardness.
Duplex	2205	1.4462	X2CrNiMoN22-5-3	-	03Kh22N5AM3	High strength + corrosion resistance.
Super Duplex	2507	1.4410	X2CrNiMoN25-7-4	-	03Kh24N6AM3	Extreme marine and chemical conditions.

Table 3: Heat-Resistant Steels (for high-temperature applications)

Type	AISI / ASTM	EN (Number)	PN (Poland)	GOST (Russia)	Operating Temp. (air)
Heat-resistant	309 / 309S	1.4828	H20N12S2	20Kh20N14S2	up to approx. 1000°C
High heat-resistant	310S	1.4845	H23N18	20Kh23N18	up to approx. 1150°C
Ferritic heat-resistant	446	1.4762	H24JS	15Kh25T	up to approx. 1100°C (sulphur resistant)

Summary and Practical Selection Tips

The analysis of the global stainless steel designation system leads to several key conclusions for the practitioner:

1. Geographical context is key: If you receive a project from Russia or Ukraine, look for GOST designations (e.g. 08Kh18N10) and convert them to EN 1.4301. If the project is from the USA, look for AISI 304.
2. Molybdenum is safety: In Poland, due to road salting in winter, it is safer to use 316L stainless steel (acid resistant) instead of 304 for external applications (railings, facades) to avoid unsightly "rust stains" after the first winter.
3. Titanium trap: Avoid 316Ti (1.4571) and 321 (1.4541) steels if you require a high gloss finish. Titanium prevents achieving a perfect mirror. For polishing, always choose 304 or 316L versions.
4. Economy of ferritics: Do not fear 430 (1.4016) steel indoors. It is cheaper and performs excellently in dry rooms, and its magnetism is not a disadvantage but a physical characteristic.

Selecting the appropriate steel grade is always a compromise between price, corrosion resistance, and mechanical properties. Understanding the above designations allows making these decisions consciously, avoiding costly mistakes.