1.4567

Definition and basic properties of austenitic steels

Austenitic stainless steels are a group of iron alloys with high chromium and nickel contents whose microstructure in the normal state is austenite — a face-centred cubic (FCC) phase. They are characterised by:

• High ductility and formability, which eases forming and plastic working.
• Excellent weldability, often without the need for subsequent heat treatment.
• Structural stability over a wide temperature range, including low temperatures where they retain toughness.
• Corrosion resistance arising mainly from a chromium-rich passive oxide layer.

In practice, austenitic stainless steels are versatile — from chemical installations to household goods.

Advantages of acid resistance in steel

Acid resistance, understood as a material’s ability to withstand corrosion in acidic and oxidising environments, is critical in many industries. Main benefits include:

• Longer service life of components used in contact with acids and salts.
• Lower maintenance costs due to less frequent replacement and repair.
• Improved process safety, especially where corrosion could lead to leaks or contamination.
• Retention of surface appearance and properties, important in the food and architectural sectors.

For grade 1.4567, the effectiveness of acid resistance is enhanced by the presence of copper, making it an attractive choice where standard 304 is insufficient.

Corrosion resistance – mechanisms and influencing factors

Corrosion resistance in stainless steels is based on the formation of a thin, self-healing passive layer on the alloy surface. Mechanisms and influencing factors include:

• Chromium content — the key element for passive layer stability. Above approximately 10.5–12% chromium the passive layer is stable, and higher concentrations increase resistance.
• Role of nickel — stabilises austenite, improves ductility and resistance to stress corrosion cracking.
• Influence of alloying additions — copper, molybdenum, nitrogen and titanium modify resistance to specific types of corrosion (e.g. pitting, crevice corrosion).
• Environmental factors — temperature, pH, presence of chloride ions, oxidisers and oxygen concentration determine the rate and type of corrosion.
• Surface condition and heat treatment — contaminants, burrs, residual stresses and microstructure affect local degradation of corrosion resistance.

In practice, designing components from stainless steel requires considering these variables to select the appropriate grade and processing route.

Beginnings of austenitic stainless steel use

The history of stainless steels goes back to the 19th century, but the true breakthrough came in the 20th century with the development of chromium–nickel alloys. The first stainless steels containing about 18% chromium and 8–10% nickel — the 18/8 group — became hugely popular due to their excellent combination of corrosion resistance and processability. Grades such as AISI 304 became standards in the food, chemical and construction industries.

As technology developed and environmental demands increased, the need arose to modify compositions by adding other elements to meet specific challenges such as acid resistance, pitting resistance or improved impact toughness at low temperatures.

Evolution of chemistry to X3CrNiCu18-9-4

In response to rising demands, modified 304 variants with alloying additions were developed. One direction was the introduction of copper into the alloy — resulting in the grade designated 304Cu (X3CrNiCu18-9-4 in European notation, 1.4567 in the material number system). Copper, though added in small amounts, noticeably alters the steel’s properties:

• improves resistance to certain acids, especially sulphuric and phosphoric acids at low concentrations,
• favourably affects resistance to atmospheric and chemical corrosion under moderate conditions,
• can influence disinfection processes and have bacteriostatic effects in certain applications.

Thus 1.4567 was created, combining the base advantages of 304 with targeted benefits from copper.

The significance of copper in the 304Cu alloy

Copper in the steel acts on multiple fronts. Its presence:

• promotes passivation in the presence of certain oxidisers,
• can create local microstructural effects or influence diffusion during heat treatment,
• in small amounts does not significantly impair ductility or weldability, but requires attention when controlling heat treatment to avoid undesirable precipitates.

In practice copper is a functional addition — improving suitability for specific applications rather than radically changing the overall properties of 304.

The chemical composition of 1.4567 is approximately as follows (typical values; standards and deliveries may vary in detail):

• Carbon (C): low content, typically ≤ 0.07%
• Chromium (Cr): about 17–19%
• Nickel (Ni): about 8–10%
• Copper (Cu): typically ≈ 1.5–4%
• Manganese (Mn), Silicon (Si), Phosphorus (P), Sulphur (S) — in trace amounts according to standards
• Nitrogen (N) — often in very small amounts, sometimes added to improve strength

Below I discuss the roles of the main constituents.

Role of chromium and nickel in the austenitic structure

Chromium and nickel are the foundation of austenitic properties:

• Chromium: responsible for forming and stabilising the passive oxide layer. It influences resistance to general corrosion and increases resistance in acidic conditions. A content around 18% ensures good protection.
• Nickel: stabilises the austenitic structure, which translates into high ductility, toughness and good weldability. Nickel lowers the transformation temperature, preventing unwanted martensitic phases during cooling.

Together Cr and Ni form a matrix that is resistant to oxidation and allows use across a wide spectrum of conditions.

Influence of copper on mechanical properties and corrosion resistance

Copper, although added in relatively small amounts, plays a modifying role:

• Resistance to oxidising acids: copper can improve resistance to certain acids, especially at low concentrations and moderate temperatures.
• Effect on ductility: at controlled levels copper does not significantly worsen ductility and formability, which is important for processing.
• Mechanical properties: in small amounts it may contribute to a slight increase in strength, but its key function is chemical resistance rather than load-bearing capacity.
• Weldability and heat treatment: copper can influence heat distribution and local precipitations during heat treatment; welding parameters should be controlled to avoid segregation.

In practice copper is a “special-purpose” addition — improving resistance in specific environments without disrupting basic 304 characteristics.

Other elements and their functions

• Carbon (C): must be kept low to limit the formation of chromium carbides that could cause intergranular corrosion. Low-carbon grades (often marked “L”) are used where welding is needed without risk of sensitisation.
• Manganese (Mn): in moderate amounts improves ductility and helps stabilise austenite in combination with nitrogen.
• Nitrogen (N): increases strength and resistance to corrosion, especially crevice corrosion; it enhances austenite stability.
• Oxygen, phosphorus, sulphur: trace impurities that should be minimised because they negatively affect machinability and corrosion resistance.

Commercial and standardised compositions specify these values precisely, but the roles above are universal.

Below I describe key mechanical and physical properties that determine the suitability of 1.4567 for various applications.

Tensile strength and ductility

Austenitic steels, including 1.4567, are characterised by:

• Good tensile strength — typical ultimate tensile strength values for grades similar to 304 fall in the range 500–700 MPa, and yield strength may be around 200–350 MPa, depending on heat treatment and material condition.
• High ductility and toughness, which allow safe plastic deformation without brittle fracture.
• Ability to perform at low temperatures, where the austenitic structure retains ductility, unlike some ferritic grades.

In practice this means components formed, stamped and welded from 1.4567 retain good strength parameters while preserving ductility.

Fatigue resistance and temperature effects

• Fatigue: austenitic steels have moderate fatigue resistance; surface quality, presence of defects and residual stresses from welding significantly influence fatigue life. Alloying additions and process control improve fatigue performance.
• Operating temperature: 1.4567 can operate over a wide temperature range — from low to moderately high temperatures. At elevated temperatures corrosion resistance can change, and at very high temperatures control of oxidation and mechanical property changes is necessary.
• Brittle phases at elevated temperatures: copper does not promote the formation of brittle phases under normal service conditions, but long-term ageing at elevated temperatures that favours copper or carbide precipitation requires attention.

Thermal conductivity and linear expansion

• Thermal conductivity: austenitic steels have lower thermal conductivity than ferritic or carbon steels; the copper addition slightly improves conductivity, but fundamentally 1.4567 still has relatively low thermal conductivity. In practice this means larger heat-affected zones during welding and the need to control cooling.
• Coefficient of linear expansion: is higher than for carbon tool steels, which must be considered when designing joints and thermal compensation. A higher expansion coefficient means austenitic steel components may exhibit greater thermal deformation.

Understanding these parameters is key when designing systems that must account for temperature changes and heat conduction.

Shaping methods and plastic working

1.4567 retains typical formability of austenitic steels:

• Forging and rolling: possible over a wide temperature range; the austenitic structure provides good plasticity. Temperatures and cooling rates should be controlled to avoid precipitates and to maintain even copper distribution.
• Stamping and bending: good ductility allows production of thin-walled parts and complex shapes without cracking.
• Machining: due to tendency to work-harden and high ductility, machining requires optimisation of tools and cutting parameters. Austenitic steels can gall on tools, reducing tool life.

Practical approach involves careful process planning, selection of tools and coolants, and consideration of copper in the alloy.

Specifics of weldability for copper-containing steel

Weldability of 1.4567 is generally good, but copper addition introduces considerations:

• Ease of welding: similar to 304, though copper can affect weld colour and heat distribution. Conventional methods (MIG/MAG, TIG) work well, but suitable filler materials compatible with 304Cu should be used.
• Phenomena during welding: copper may migrate in the heat-affected zone, which in extreme cases leads to local microstructural changes. Controlling welding parameters and cooling minimises these effects.
• Risk of sensitisation to intergranular corrosion: keeping carbon low or using a low-carbon variant reduces the risk of chromium carbide formation during welding.

Practical experience shows that when welding recommendations are followed, 1.4567 performs well in welded structures.

Heat treatment – solution annealing, quenching and tempering

Austenitic steels do not harden in the classical sense by martensitic transformation. Heat treatment serves different purposes:

• Solution annealing: performed to remove carbides and homogenise the structure and to restore corrosion resistance after plastic working or welding. Typical temperatures: 1000–1100°C followed by rapid cooling.
• No hardening by quenching: austenitic steels are not hardened via quenching; to increase strength work hardening or nitrogen additions are used.
• Ageing and precipitations: prolonged exposure in temperature ranges that favour copper or carbide precipitation can lead to local property changes. Controlling production and service processes is important to avoid this.

In practice heat treatment should be used to restore properties after mechanical processes and welding, taking copper’s behaviour into account.

Behaviour in acidic and alkaline environments

1.4567 shows improved resistance in certain acidic environments compared with standard 304, particularly:

• Sulphuric and phosphoric acids at low concentrations: copper increases the alloy’s resistance to these acids, making 1.4567 a preferred material for systems handling diluted acids.
• Alkaline environments: resistance is similar to 304; copper additions do not significantly change behaviour in alkaline solutions.
• Oxidising environments: passivation and resistance depend on the presence of oxidisers and temperature; 1.4567 performs well under moderate conditions.

In practice selecting this steel for chemical environments requires analysis of the specific medium, concentration and temperature.

Resistance to pitting and crevice corrosion

• Pitting: resistance to pitting is determined by the presence of chloride ions and the passive potential. 1.4567 has similar pitting resistance to 304, but in critical applications grade 316 with molybdenum is preferable.
• Crevice corrosion: also depends on the environment and component geometry. For applications with stagnant zones it is worth considering additional design measures and possibly using grades with higher crevice resistance.

Copper does not replace molybdenum; it complements it by improving properties in specific conditions, but does not remove the need for other grades in strongly chlorinated environments.

Effect of temperature and environment on steel durability

Temperature plays a key role in durability:

• Elevated temperatures: can weaken passivation and accelerate local corrosion mechanisms; long-term exposure in ranges promoting copper or carbide precipitation requires ageing studies.
• Very low temperatures: the austenitic structure retains ductility, making 1.4567 suitable for cryogenic applications provided corrosion properties in the medium are not degraded.
• Aggressive industrial environments: presence of sulphides, chlorides and other contaminants affects durability and requires design precautions.

Designers should account for operating temperature and the chemical composition of the medium when assessing the suitability of 1.4567 for a given application.

1.4567 is used where a combination of 304-level corrosion resistance and enhanced performance in specific environments afforded by copper is required.

Chemical and petrochemical industry

• Components of plants processing diluted acids: tanks, pipelines and fittings operating in the presence of sulphuric or phosphoric acid at moderate concentrations.
• Heat exchangers and pressure vessels: where good ductility and corrosion resistance are needed.
• Components for urea processes and others where copper improves resistance.

Thanks to good weldability and formability, this steel is useful in parts of installations requiring complex geometries and durability.

Food and pharmaceutical industries

• Process equipment: parts of production lines that come into contact with acidic food products; where additional chemical resistance is required, 1.4567 can be preferred.
• Sanitary equipment components: owing to good surface cleanliness and ability to maintain passivity, it is suitable for devices requiring hygiene and frequent acid cleaning.

In practice choosing 1.4567 in these sectors must consider compliance with hygiene standards.

Construction and automotive sectors

• Exterior and architectural elements: where aesthetics and resistance to atmospheric corrosion are important, and copper additions can positively influence surface behaviour.
• Automotive components: in specific applications requiring resistance to chemical agents and good formability.

Although 1.4567 will not replace all grades in construction and automotive use, it finds application in parts exposed to specific chemical conditions.

Selected example structures and components

• Pipelines transporting acidic solutions in chemical plants.
• Process battery modules in the pharmaceutical industry.
• Storage tanks and mixers in the food industry.
• Architectural elements with enhanced resistance to atmospheric pollutants.

Each application requires evaluation of the specific medium, operating conditions and regulatory requirements.

Differences in composition and mechanical properties

Comparison with commonly encountered grades:

• AISI 304 (X5CrNi18-10): the base 18/8 grade. 1.4567 differs by the copper addition, which translates into better resistance in some acidic environments. Mechanical properties are similar; ductility and weldability remain good.
• AISI 316 (X5CrNiMo17-12-2): contains molybdenum, which significantly improves resistance to pitting and crevice corrosion in chloride-containing environments. 316 is superior where high chloride concentrations are present. 1.4567 outperforms 304 in resistance to certain acids, but cannot substitute for molybdenum-bearing grades where pitting is the main threat.
• Grades with nitrogen or additional molybdenum: offer higher strength and specialised corrosion resistance, at the cost of higher price and potentially more difficult processing.

Choice among these grades depends on working environment, type of corrosion and mechanical requirements.

Corrosion resistance index – comparison with 304 and 316

Corrosion resistance is not a single universal number, but in practice:

• 304 ≈ good general resistance,
• 1.4567 (304Cu) ≈ better than 304 in certain acidic environments (due to copper),
• 316 ≈ better than 304 and 304Cu in chloride-rich environments and where pitting/crevice corrosion is critical.

Designers often use comparative tables, indices and results of pitting resistance tests (e.g. PREN — Pitting Resistance Equivalent Number) to select the appropriate grade.

Adaptation to specific application requirements

1.4567 is a compromise between cost and specific chemical resistance. Main selection criteria are:

• type and concentration of the corrosive environment,
• operating temperature,
• required service life and operating conditions,
• need for weldability and formability,
• budget constraints.

In applications where pitting resistance is crucial, 316 may be a better choice; where diluted acids are the issue, 1.4567 can be optimal.

European and international quality standards

Steels such as 1.4567 are covered by European (EN), international (ISO) and industry-specific standards:

• EN 10088 — a series of standards for stainless and acid-resistant steels (composition, requirements, classification).
• AISI/ASTM — American standards defining compositions and useful properties for industry.
• Industry standards — petrochemical, food and pharmaceutical specifications set additional requirements for cleanliness, corrosion tests and documentation.

Material deliveries are typically accompanied by a material certificate (e.g. 3.1 according to EN 10204) confirming chemical analysis and mechanical test results.

Testing methods and quality control for acid-resistant steel

Quality control includes:

• Chemical analysis (spectrometry) — confirming Cr, Ni, Cu and other element contents.
• Mechanical tests — strength, tensile and impact tests.
• Corrosion tests — pitting, crevice resistance, tests in specified solutions.
• Non-destructive testing — radiography, ultrasonic testing, weld inspection.
• Microstructural examinations — assessment of precipitates, carbides and material homogeneity.

Producers’ quality systems are often audited by industrial customers to ensure compliance with requirements.

Recommendations for storage and transport

To avoid degrading steel properties:

• store in dry, well-ventilated conditions,
• avoid contact with ferrous contaminants and iron-bearing materials that can cause rust staining,
• protect from exposure to aggressive chemicals during transport,
• for long transports avoid condensation and overheating.

Good logistics practice prevents costly cleaning operations before installation.

Modern alloying technologies and their effect on durability

Research focuses on:

• Precise selection of alloying additions (e.g. nitrogen, copper, microalloying) to optimise strength and corrosion resistance.
• New production processes (e.g. vacuum melting, improved homogenisation) that reduce segregation and improve homogeneity.
• Coatings and surface treatments that increase resistance under harsh conditions.

Results translate into steels with higher specification and better cost–benefit ratios.

Environmental aspects of production and recycling

• Reducing CO2 emissions and the energy intensity of steelmaking is an important development direction.
• Recycling of stainless steel is well developed — steel is one of the most recycled materials. Increasing the share of secondary raw material reduces environmental footprint.
• Responsible sourcing of raw materials (e.g. nickel and copper) affects supply-chain sustainability.

The steel industry is developing technologies that both raise material quality and reduce environmental impact.

Trends in applications and market requirements

Trends include:

• growing demands for durability and reliability in the chemical industry,
• demand for materials easy to weld and form while resisting aggressive environments,
• cost pressure leading to search for compromise solutions like 1.4567, where copper addition gives tangible benefits without a large cost increase.

The market expects materials tailored to specific challenges — hence the development of modified grades.

• Character: 1.4567 is an austenitic stainless steel based on the 304 class with added copper, combining good ductility and weldability with improved resistance in selected acidic environments.
• Composition: dominated by chromium (~18%) and nickel (~8–10%), with copper (about 1.5–4%) playing a modifying role for chemical resistance.
• Mechanical properties: good strength and high ductility; retains toughness at low temperatures.
• Processing: easy to form and weld, with attention to controlling thermal processes because of copper.
• Corrosion resistance: better than standard 304 in dilute acidic environments; however in chloride-rich environments a molybdenum-bearing grade (316) is still preferred.
• Applications: chemical, petrochemical, food, pharmaceutical industries, architectural elements and specialised technical components.
• Standards and quality: compliance with EN and ASTM, chemical and mechanical testing requirements and NDT control are standard for deliveries.

Steel 1.4567 is a practical choice where a reasonable cost–benefit relationship is needed from added chemical resistance. Its potential use grows as expectations for installation durability and process efficiency increase.