1.4310

What stainless steels are and their classification

Stainless steel is an iron-based alloy material whose ability to form a durable passive oxide film provides higher corrosion resistance than ordinary carbon steels. The basic element responsible for this resistance is chromium — at around 10.5% and above it forms a chromium oxide layer on the surface capable of self-repair after mechanical damage.

Classification of stainless steels is based on their microstructure:

• ferritic (chromium-rich, low nickel content),
• martensitic (containing carbon, amenable to heat hardening),
• austenitic (containing significant amounts of nickel or other austenite stabilisers, e.g. nitrogen),
• duplex (two-phase: austenite + ferrite),
• low-carbon and special variants (e.g. with additions of molybdenum, titanium, niobium).

Austenitic stainless steels are distinguished by the highest ductility and corrosion resistance in many environments, as well as good weldability. Their structure is stable at room temperature thanks to nickel additions that stabilise the austenite phase.

Characteristics of austenitic steels: properties and structure

Austenitic stainless steels have a face-centred cubic crystal lattice, which translates to:

• high ductility and formability — enabling complex forming and deep drawing,
• high impact resistance and good retention of properties at low temperatures,
• inability to be hardened by conventional quenching (they are not heat-hardened in the classical way to increase hardness), but significant hardening by plastic deformation (work hardening) — particularly pronounced in grades prone to strain-induced martensitic transformation (such as AISI 301),
• relatively low thermal conductivity and high thermal expansion compared with carbon steels — important when designing parts exposed to temperature changes.

On the chemical side the structure is governed mainly by chromium (Cr) and nickel (Ni), with additions of elements such as manganese (Mn), silicon (Si), nitrogen (N), and sometimes molybdenum (Mo) or titanium (Ti) to improve resistance to specific types of corrosion.

Differences between acid-resistant and stainless steel

The terms “acid-resistant” and “stainless” are often used interchangeably, but there is a practical difference:

• stainless steel — the general category covering materials capable of forming a surface passive film protecting against corrosion in moderate conditions;
• acid-resistant steel — a subgroup of stainless steels with extended resistance to aggressive chemical agents (acids, chlorides) thanks, among other things, to additions of molybdenum, nitrogen or increased chromium and nickel content.

Acid resistance depends on composition and the temperature of the environment: grades without molybdenum perform well in non-chloride environments and at neutral pH, whereas in chloride-containing environments (stress corrosion cracking, crevice corrosion) special alloys are required (e.g. AISI 316 with added Mo). In practice “acid-resistant” means a higher level of protection, but does not guarantee resistance in all conditions.

1.4310 and X10CrNi18-8 are two notations for the same steel grade in European numeric (material number) and symbolic chemical designation systems. In practice it is one of the classic representatives of the “18/8” austenitic group.

Chemical composition and microstructure of 1.4310

Typical chemical composition (approximate values):

• C: ~0.08–0.12% (the “X10” designation meaning about 0.10% C),
• Cr: ~17.0–19.0%,
• Ni: ~7.0–9.0%,
• Mn: ≤2.0%,
• Si: ≤1.0%,
• P: ≤0.045%,
• S: ≤0.03%,
• N: trace, up to 0.11%.

Microstructure: austenite predominates at room temperature; no ferritic phases in the annealed condition. With severe cold deformation part of the austenite may transform to martensite, causing significant strengthening.

Mechanical properties and corrosion resistance

Mechanical properties of 1.4310 are typical for austenitic steels: high ductility and relatively moderate strength in the annealed state. A characteristic feature is a very strong capability for strain hardening — wire, strips and springs can reach much higher strengths after cold working.

Corrosion resistance is good in air, water and mild chemical solutions. However, without molybdenum this steel has limitations in chloride environments — pitting and crevice corrosion may occur under aggressive conditions. Carbon content nearer 0.10% increases the risk of sensitisation (precipitation of chromium carbides) during prolonged exposure at approximately 500–800°C, which degrades resistance to intergranular corrosion. In practice annealing and rapid cooling procedures are used to minimise these effects.

Typical industrial applications

1.4310 is used where a good balance of ductility and corrosion resistance and the possibility of significant strengthening by mechanical processing are important. Typical applications:

• springs, spring strip, elastic elements,
• rods, wires and strips for forming automotive and household appliance parts,
• architectural and decorative elements,
• components requiring high strength after cold work, e.g. belts and clamps.

In areas with intensive chloride exposure, alloys with molybdenum or low-carbon versions of the steel are recommended.

1H18N9 is a designation encountered in documentation from several Eastern European countries and the former Soviet Union; it identifies a steel similar in character to conventional 18/8. In the national system the letter “H” denotes nickel (Nikol) in Cyrillic-based systems, and the numbers indicate approximate percentage contents.

Analysis of chemical composition of 1H18N9

Typical composition (approximate values):

• C: ≤0.12%,
• Cr: ~17–19%,
• Ni: ~8–10%,
• Mn: ≤2%,
• Si: ≤1%,
• P and S: trace according to standards,
• N: often a small addition improving strength.

This composition makes 1H18N9 suitable for general-purpose applications, with somewhat higher nickel content than 1.4310 in some variants, improving austenite stability and corrosion resistance.

Use in manufacturing and the food industry

Thanks to good corrosion resistance in neutral environments and against many food substances, 1H18N9 is often used in:

• apparatus and equipment for the food and dairy industries,
• process vessels, tanks and pipes in production lines,
• kitchen and catering elements where ease of cleaning and resistance to acidic and alkaline media under moderate conditions are key.

In food applications low-carbon grades (designated “L”) or stabilised versions (e.g. titanium-stabilised) are often chosen to avoid the risk of intergranular corrosion associated with precipitation of chromium carbides.

Comparison with other austenitic steels

Compared with 1.4310 and typical AISI grades, 1H18N9 performs similarly in terms of ductility and corrosion resistance. Practical differences often stem from permissible carbon limits, additional elements and tolerance to impurities. Compared with molybdenum-bearing alloys, 1H18N9 has lower resistance to pitting in chloride environments but is cheaper and often more economical in industrial and food applications where environmental aggressiveness is limited.

AISI 301 is a classic representative of the 18/8 austenitic steel family, particularly well known for its ability to be heavily strain-hardened.

Composition and mechanical properties of AISI 301

Approximate chemical composition:

• C: up to 0.15% (lower in some variants, depending on specification),
• Cr: 16–18%,
• Ni: 6–8%,
• Mn: ≤2%,
• Si: ≤1%,
• P, S: trace.

Mechanical properties:

• in the annealed state: moderate strength and high ductility,
• after cold working: significant increase in strength and hardness due to partial transformation of austenite to martensite (strain-induced martensite),
• elasticity and shape memory in spring applications.

This ability to cold work and simultaneously raise mechanical parameters makes AISI 301 a popular material for springs, strips and suspension components.

Corrosion resistance and high-temperature strength

AISI 301 offers good general corrosion resistance in air and water, but like other 18/8 grades it has limitations in chloride environments. Higher carbon content in standard variants increases the risk of sensitisation during prolonged heating in the 450–850°C range, so in welded constructions low-carbon materials (e.g. 301L) or process procedures minimising carbide precipitation are often used.

At elevated temperatures the steel retains mechanical properties over a certain range, but prolonged exposure to higher temperatures can lead to long-term degradation processes, including precipitation of brittle phases (e.g. sigma) under unfavourable composition and conditions.

Typical application areas for AISI 301

• flat and wire springs,
• actuating elements in the automotive industry (e.g. strips, guides),
• decorative external elements and car trim,
• parts requiring substantial strengthening by cold work (e.g. clamps, clips).

AISI 301 is used where designs require the combination of good corrosion resistance with the ability to achieve high strengths by mechanical processing.

AISI 302 is another grade from the 18/8 family, designed for better austenite stability and somewhat higher corrosion resistance than some variants of 301.

Differences in chemical composition between AISI 301 and AISI 302

The main difference is the slightly higher nickel content in AISI 302:

• AISI 301: Ni ≈ 6–8%,
• AISI 302: Ni ≈ 8–10%.

The higher nickel share stabilises the austenitic phase and reduces the tendency to martensitic transformation under deformation, which results in:

• lower susceptibility to hardening by cold forming compared with 301,
• better predictability of properties in applications requiring ductility,
• usually slightly better resistance to pitting and crevice corrosion than grades with less Ni.

Advantages of AISI 302 compared with other austenitic steels

• greater stability of the austenitic microstructure due to higher Ni,
• good weldability and ductility, facilitating forming and assembly,
• a favourable compromise between corrosion resistance and cost (higher Ni raises the price compared with 301).

Compared with 1.4310, AISI 302 will be chosen more often where greater stability of properties after cold forming and lower tendency to cracking due to hardening are required.

Specialised applications of AISI 302

• fasteners and small spring elements requiring stable ductility,
• spring wires, helical springs in applications demanding greater resistance to loss of austenite,
• medical devices, laboratory apparatus and consumer items where uniformity of material properties is important.

AISI 302 finds application where greater resistance to plastic deformation while retaining good corrosion resistance is required.

Analysis of hardness, strength and ductility

• Strength: in the annealed state, austenitic steels from the 18/8 family have moderate strength, but differences appear after plastic deformation. AISI 301 stands out with the greatest capability for cold working, which allows achieving much higher strength values than 302 or 1.4310 in the as-supplied condition.
• Hardness: depends on processing; austenitic steels are soft in the annealed state, but AISI 301 can reach high hardness after cold forming.
• Ductility and elongation: 302 and 1H18N9 typically show somewhat higher ductility compared with heavily hardened 301.

In design practice this means that grade choice depends on whether the priority is to obtain high strength by processing (choose 301) or stable ductility and predictable behaviour after forming (choose 302).

Resistance to aggressive environments and acid resistance

• All the discussed grades are resistant to oxidising environments and perform relatively well in air and water.
• In chloride-rich environments their resistance is limited — lack of molybdenum makes them susceptible to crevice and pitting corrosion. In chloride-containing conditions grades with added Mo (e.g. AISI 316) or duplex steels are recommended.
• High nickel content (AISI 302 and some variants of 1H18N9) improves the mentioned resistance, however true protection in aggressive environments is achieved by a comprehensive selection of alloy and protective technologies.

Indications for use in different industries

• Food and pharmaceutical industry: 1H18N9 and similar grades (low-carbon and stabilised variants) thanks to ease of cleaning and resistance to sanitary treatments.
• Automotive and textile industries: AISI 301 for springs and components that require high strength via cold forming.
• Construction and architecture: 1.4310 and AISI 302 for decorative elements and details where aesthetics and weather resistance matter.
• Chemical industry: where the environment is not extremely chloride-rich, the discussed grades can be used, but for aggressive conditions steels with Mo are preferred.

Weldability and joining methods for acid-resistant steels

Austenitic steels are generally well weldable. Recommended welding methods are TIG (GTAW), MIG/MAG (GMAW) and arc welding. Some practical tips:

• use appropriate filler wires and electrodes matched to the base material composition (e.g. types 308, 309 for welding 18/8 alloys),
• control the heat-affected zone temperature to minimise the risk of sensitisation (especially in higher-carbon grades),
• use low-carbon (L) or stabilised materials (e.g. with Ti, Nb) where prolonged exposure to temperatures that promote carbide precipitation is expected,
• after welding passivation of the surface and heat treatment (e.g. solution annealing and rapid cooling) can be used to restore corrosion resistance.

For mechanical joining use riveting, bolting (with appropriate measures against galvanic stresses) and resistance welding, especially in the production of thin-sheet components.

Heat treatment and its influence on material properties

Austenitic stainless steels are not hardened by quenching transformations, therefore heat treatment serves other functions:

• solution annealing — dissolving carbides and rapid cooling, restoring full corrosion resistance and ductility,
• stress-relief after plastic forming — reducing residual stresses,
• prolonged exposure at 500–900°C can lead to precipitation of brittle phases (e.g. sigma), which negatively affects corrosion resistance and toughness.

In practice solution annealing is used to restore properties after welding, and prolonged intermediate temperatures are avoided, or stabilised grades are used to prevent degradation.

Problems and challenges in shaping austenitic steels

• a high degree of hardening during cold work may lead to cracking if even distribution of deformation is not ensured,
• tendency to galling (seizure) during machining and bolted connections; friction control and use of coatings or lubricants are required,
• low thermal conductivity — welding produces local heating and distortion, requiring special welding procedures,
• requirement for larger bend radii due to high ductility and tendency for springback.

Managing these issues requires a combination of selecting the right grade, tools, processing parameters and thermal procedures.

Designation systems in Poland, Europe and the USA

There are several parallel systems:

• European system (EN/DIN): symbolic designations (e.g. X10CrNi18-8) and numeric material numbers (e.g. 1.4310) in accordance with EN 10088 standards,
• American AISI/ASTM system: designations such as AISI 301, AISI 302 etc., sometimes supplemented by ASTM numbers,
• Russian/GOST and former Eastern Bloc systems: designations like 1H18N9, where “H” corresponds to nickel and the digits indicate approximate percentage contents.

Each system has its historical justification, and equivalences are often provided in specifications, though they are not always identical in permissible composition ranges.

How to read symbols like 1.4310, AISI 301 and others

• 1.4310 — material number in accordance with EN; the first digit “1” denotes steel and the subsequent digits are a unique grade identifier;
• X10CrNi18-8 — chemical symbol: “X” (alloy steel), “10” approximate carbon content (0.10%), “CrNi18-8” denotes ~18% Cr and ~8% Ni;
• AISI 301/302 — American designations, without direct composition indication in the symbol; reference to a comparative table is necessary.

For an engineer or designer the important thing is not literal reading of the symbol but checking the full chemical and mechanical specification in the relevant standard.

The importance of EN and ASTM standards for steel quality

EN and ASTM standards define permissible ranges of chemical composition, mechanical property requirements, test methods, dimensional tolerances and quality procedures. Compliance with standards:

• ensures repeatability of supplied material quality,
• enables comparison and substitution of materials between suppliers and countries,
• is required in industrial and public procurement.

In design practice one should always refer to concrete standards and specifications, not only to general grade names.

Purchase and operating costs compared with alternative materials

The cost of austenitic steel depends mainly on nickel and molybdenum content — the more Ni and Mo, the higher the price. 18/8 grades (e.g. 1.4310, AISI 301/302) represent a compromise between cost and corrosion resistance. When selecting, consider:

• initial material costs,
• processing costs (e.g. requiring more energy, special tools),
• operating and maintenance costs (stainless steel reduces need for renovation and replacement),
• life-cycle costs — often outweighing the benefits of lower initial cost of coated carbon steel.

In many applications it often pays to invest in stainless steel due to lower maintenance costs and longer service life.

Recycling and durability of stainless steels

Stainless steels are among the most recyclable engineering materials. scrap stainless steel can be recovered and used in the production of new alloys, reducing demand for primary raw materials (especially nickel and chromium). In practice:

• a high share of recycled steel reduces production costs and the carbon footprint,
• design for disassembly facilitates material recovery,
• material durability and corrosion resistance extend service life, which is environmentally beneficial.

The importance of steel selection for sustainable development

Choosing the right grade of steel affects sustainability by:

• reducing replacements and repairs (less raw material and energy use),
• enabling recycling and reuse of materials,
• reducing the risk of failures and associated environmental costs (e.g. leaks in chemical and food industries).

From a design perspective one should balance technical needs, costs and environmental impact, using grades that meet functional requirements without excessive over-specification.

Modern production technologies and property enhancement

Trends in stainless steel development include:

• development of “lean” or low-nickel austenitic alloys that lower cost and reduce dependence on volatile nickel prices,
• increased use of nitrogen as an austenite stabiliser and strengthener, allowing lower nickel content,
• adoption of microstructure modification techniques through advanced heat treatment and controlled rolling processes,
• surface modifications (coatings, passivation, vapour deposition) improving local resistance without increasing alloy cost.

These technologies allow combining lower cost with satisfactory corrosion resistance and mechanical properties.

Trends in applications and material development

• wider use of optimised-composition materials in automotive and energy sectors where weight reduction while maintaining strength is important,
• development of special steels for marine environments and renewable energy (turbines, offshore installations),
• integration with digital technologies (material condition monitoring, corrosion prediction) enabling more precise grade selection and maintenance procedures.

Increasing ecological and economic demands steer industry toward materials offering a better ratio of properties to cost.

Steels 1.4310 (X10CrNi18-8), 1H18N9, AISI 301 and AISI 302 are versatile materials whose advantages are used where a combination of corrosion resistance, ductility and the possibility of increasing strength by mechanical processing is required. Their role is key in the production of springs, wires, structural elements and equipment for the food industry, automotive sector, household appliances and in architecture.

In design practice choosing the specific grade requires assessment of:

• corrosion conditions (presence of chlorides, pH, temperature),
• mechanical requirements (is cold working anticipated, is high ductility needed),
• technological conditions (welding, forming, machining),
• economic and environmental aspects (Ni cost, recycling).

Each of the discussed alloys has its strengths: 1.4310 and X10CrNi18-8 offer a good compromise of resistance and hardening capability; 1H18N9 is popular in the food industry for relative simplicity of use; AISI 301 stands out for extreme cold-work hardenability; AISI 302 provides greater austenite stability and predictability after processing. Their common feature is a wide range of applications in modern industry, where the material must combine durability, economy and the ability to precisely tailor properties to the intended function.