1.4980

Heat‑resistant steel is a category of alloys that retain strength, ductility and corrosion resistance at elevated temperatures. In many industrial sectors their role is critical — from power generation to aerospace. In practice heat‑resistant steel not only “withstands heat”, but also limits the rate of oxidation, forms stable oxide scales and preserves its crystal structure during years of service under cyclic heating and cooling.

Historically, the development of heat‑resistant steels was driven by increasing technical requirements for machines and devices burning fuels at ever higher operating temperatures. A breakthrough came with the introduction of nickel‑ and chromium‑based alloys — the combination of these elements produced the first genuinely useful class of heat‑resistant steels. Further composition modifications — adding molybdenum, titanium, vanadium or boron — made it possible to obtain materials with better structural stability, increased corrosion resistance in aggressive environments and reduced incidence of brittle fracture at high temperatures.

Understanding the importance of heat‑resistant steel requires looking from three perspectives: physicochemical properties, service requirements and the economic context. Below we discuss these aspects in relation to specific grades: A‑260 and X6NiCrTiMoVB25‑15‑2, and their equivalents designated by numbers 1.4980, 1.3980 and 1.4944.

Exceptional properties of high‑temperature resistant steels

Heat‑resistant steels are distinguished by several key features:

• Stability of mechanical properties at elevated temperatures — the ability to retain yield strength and ultimate strength during prolonged heating.
• Resistance to oxidation — formation of a continuous, adherent oxide scale (e.g. Cr2O3) that protects against further oxidation.
• Resistance to high‑temperature corrosion — limiting degradation in the presence of flue gases, hydrogen sulphide and other aggressive species.
• Microstructural stability — minimal tempering, leaching or precipitation of brittle phases during service.
• Machinability and weldability — in practice a compromise is required between service properties and manufacturability/weldability.

For example, alloying elements such as chromium and nickel form continuous oxides and increase high‑temperature ductility, while molybdenum and tungsten reduce the effects of sulphur compounds and improve creep strength.

Main applications of heat‑resistant steel in industry

These steels are used where materials must operate at temperatures from several hundred up to above 800–1000°C. Key application areas:

• Power generation: boilers, supercritical piping, turbine components, heat exchangers.
• Chemical and petrochemical industry: reactors, distillation columns, feed pipes and installations subject to corrosion.
• Aviation and space: jet engine parts, turbine housings and exhaust ducts.
• Automotive: exhaust manifolds, turbochargers, components of high‑performance exhaust systems.
• Metallurgical and glass industries: moulds and channels exposed to high temperatures and erosion.

Each application places different demands: in boilers creep and oxidation resistance are crucial, whereas in aviation the strength‑to‑weight ratio and resistance to rapid temperature changes are paramount.

This section discusses specific names/grades. It should be remembered that commercial and normative designations may vary between countries and manufacturers; equivalents in EN, ASTM or UNS systems require verification against supplier documentation. Below is a description, approximate composition and typical characteristics.

Description of A‑260 steel – chemical composition and mechanical features

A‑260 — this designation appears in technical literature as a trade name or an older designation of a heat‑resistant alloy with elevated nickel and chromium content, modified with titanium and molybdenum. In practice this grade is used where high oxidation resistance and retention of strength under prolonged loads at elevated temperatures are required.

Approximate typical composition for this type of alloy:

• Carbon (C): low, typically ≤ 0.08% — minimises embrittlement and carbide‑related brittleness;
• Nickel (Ni): significant, on the order of the mid‑teens to over 20% — increases creep resistance and structural stability;
• Chromium (Cr): 15–25% — key for oxidation protection (Cr2O3 layer);
• Molybdenum (Mo): 1–3% — enhances pitting resistance and resistance to sulphur attack;
• Titanium (Ti): up to 1% — stabilises carbides, preventing deleterious tempering effects;
• Alloying additions (e.g. V, B): trace — improve recrystallisation behaviour and resistance to cracking.

Mechanical characteristics:

• Good creep strength in the operating temperature range;
• Higher ductility than many ferritic alloys;
• Good weldability provided appropriate procedures are used (control of carbides and heat‑affected zone).

A‑260 is often used in components where a combination of oxidation resistance and retention of mechanical properties at high temperature is important.

Analysis of X6NiCrTiMoVB25‑15‑2 composition and its role in heat‑resistant constructions

The designation X6NiCrTiMoVB25‑15‑2 can be interpreted according to European convention, where:

• X — high‑alloy steel,
• 6 — maximum carbon content ~0.06% (the number indicates C × 100),
• Ni, Cr, Ti, Mo, V, B denote the presence of nickel, chromium, titanium, molybdenum, vanadium and boron,
• 25‑15‑2 — most likely indicates approximate contents of the main elements: Ni ≈ 25%, Cr ≈ 15%, Mo ≈ 2% (the order may be interpreted as Ni‑Cr‑Mo).

In practice this composition suggests an alloy with high nickel content (about 25%), moderate chromium (about 15%) and molybdenum (~2%), with additions of titanium (stabilising), vanadium (improving strength and carbide stability) and boron (in trace amounts improving resistance to brittle fracture and creep).

Role of such a composition in heat‑resistant constructions:

• Nickel (≈ 25%): provides good high‑temperature strength, improves ductility and resistance to corrosion in oxidising environments.
• Chromium (≈ 15%): forms a protective chromium oxide layer, important for oxidation resistance.
• Molybdenum (~2%): enhances resistance to pitting and to corrosive action of sulphur compounds.
• Titanium and vanadium: stabilise microstructure, help control carbide precipitation and prevent degradation during welding.

Alloys with this element set are often used in components requiring both good high‑temperature behaviour and resistance to aggressive flue gases or chemical decomposition products.

Comparison of designations 1.4980, 1.3980, 1.4944 – similarities and differences

Numbers 1.4980, 1.3980 and 1.4944 are examples of so‑called material numbers (Werkstoffnummern) used in the EN/ISO system (EN 10027). These numbers identify specific steel grades and facilitate finding their technical specifications in databases and material documentation.

• 1.4980 — often assigned to heat‑resistant alloys with elevated nickel and chromium content, with titanium additions. In practice this numbering is relatively uncommon in lightweight material catalogues, so verification with material certificates is always recommended.
• 1.3980 — may refer to steel with a different microstructure (e.g. ferritic‑austenitic) or an alloy with specific additions; the number suggests a grade with particular technical characteristics.
• 1.4944 — this number may refer to steels containing additional stabilising elements, e.g. titanium or niobium, used in high‑temperature environments.

Similarities:

• All three designations point to high‑alloy steels intended for elevated temperature service.
• Each typically shows the presence of chromium and nickel as primary elements.

Differences:

• Exact composition and microstructure — the percentages of individual elements and the type of additions (Ti, V, B, Mo) determine specific properties.
• Application range — some numbers may be preferred in specific industries (e.g. aerospace), others in more chemically severe environments.

In practice: numerical designations must be checked in supplier documentation and standards. Differences on the order of 0.1–1% of alloying additions can significantly influence corrosion and creep resistance.

Understanding the role of individual alloying elements is essential for component design and predicting material behaviour in service. Below the most important elements are discussed.

The role of nickel, chromium and molybdenum in high‑temperature resistance

• Chromium (Cr): the central element in heat‑resistant steels. At contents typically above ~12% it forms a durable, adherent chromium oxide scale (Cr2O3) which inhibits further oxidation of the metal. Higher chromium contents increase oxidation resistance but may also affect hardness and brittleness if present at extreme concentrations without appropriate additions.
• Nickel (Ni): improves ductility at low and high temperatures and stabilises the austenitic crystal structure of the steel. In high‑nickel alloys nickel increases creep resistance and corrosion resistance in oxidising environments. It acts as a “stabiliser” of the structure under cyclic thermal loads.
• Molybdenum (Mo): increases resistance to pitting and crevice corrosion, particularly in the presence of chloride ions. Molybdenum also beneficially affects high‑temperature strength, reinforcing the alloy matrix.

A well‑designed alloy uses the synergistic action of Cr, Ni and Mo: chromium forms the barrier, nickel maintains ductility, and molybdenum counters localised forms of corrosion.

Importance of titanium, vanadium and boron for strength and structural stability

• Titanium (Ti): acts as a carbide stabiliser. It binds carbon to form stable TiC/TiN carbides, which prevents dissolution of chromium carbides at high temperatures and during heat treatment. This in turn protects the chromium‑rich layer and reduces the risk of intergranular corrosion after welding.
• Vanadium (V): promotes formation of fine carbides and improves creep strength. Vanadium can also increase hardness and wear resistance, important in erosive environments.
• Boron (B): even trace amounts of boron (on the order of ppm to 0.01%) can beneficially influence creep properties and weldability. Boron raises recrystallisation temperature and can improve yield strength at elevated temperatures. However, too much boron leads to embrittlement, so it is used in very controlled concentrations.

The combination of these additions allows the production of alloys with better microstructural stability and lower susceptibility to degradation phenomena at elevated temperatures.

Influence of alloying elements on anti‑corrosion properties

A material’s anticorrosion properties are the result of the synergy of several elements:

• Chromium — fundamental, creates passivation.
• Molybdenum — prevents pitting corrosion in the presence of chlorides.
• Nickel — improves resistance in acidic and alkaline environments.
• Titanium and niobium — stabilise carbides, protecting against intergranular corrosion, especially after welding.
• Copper, nitrogen — in certain amounts can enhance resistance in specific environments.

In practice the composition choice depends on the expected service environment: in the presence of high chloride and hydrogen sulphide concentrations molybdenum is critical; in oxidising atmospheres a high chromium content is essential; for applications requiring high strength under variable temperature nickel and stabilising additions are important.

Production of heat‑resistant steels is a multi‑stage process requiring strict control of composition and processing conditions. Each stage affects the microstructure and ultimately the material’s final properties.

Melting and forming stages of heat‑resistant alloys

1. Selection of raw materials — iron, stainless steel scrap, Ni, Cr, Mo concentrates and additions (Ti, V, B). Raw material quality directly influences alloy cleanliness.
2. Melting in electric or induction furnaces — temperature and composition control is key. Undesirable impurities such as sulphur or phosphorus must be reduced.
3. Vacuum induction melting (VIM) and/or refining in inert gas — removal of dissolved gases (H, O, N) and adjustment of composition.
4. Casting — continuous casting (round or plate) is often used, followed by hot rolling to obtain billets, plates or pipes.
5. Plastic forming — hot and cold rolling, forging, tube drawing. Processing parameters influence inclusion distribution and grain orientation.
6. Heat treatment (stabilising anneal) — to relieve stresses and stabilise carbide composition, annealing at specified temperatures is used, sometimes with controlled cooling.

Precise parameters are strictly specified in technological cards; small deviations can lead to unwanted phases affecting durability.

Advanced hardening and structure improvement methods

In heat‑resistant steels conventional quenching to very hard structures is rarely used; instead, focus is on:

• Stabilising annealing (e.g. in Ti‑ or Nb‑stabilised alloys) — prevents formation of chromium carbides.
• Precipitation ageing — in some alloys (e.g. austenitic) the aim is to obtain fine precipitates that increase yield strength.
• Plastic deformation + recrystallisation — rolling and controlled heat treatment affect final grain distribution and mechanical properties.
• Surface modifications: surfacing, boriding, ceramic coating deposition — used where local additional protection is required.

For critical components microstructural control is performed using metallographic techniques to detect possible irregularities.

Quality control and testing of metallurgical properties

Quality control includes chemical and mechanical testing:

• Composition analysis (spectrometry) — confirmation of alloying element contents.
• Mechanical tests — tensile tests, impact toughness (Charpy), hardness.
• Creep resistance tests — tests at operating temperatures determining time to failure under a given stress.
• Corrosion tests — tests in chloride solutions, high‑temperature oxidation tests.
• Metallographic examinations — optical and scanning microscopy, phase analysis, carbide distribution.
• Weldability tests — analysis of heat‑affected zones, tests for cracking and post‑weld corrosion.

All results must be documented in certificates supplied with the material. Using material without confirmed documentation significantly increases the risk of failure.

This section discusses how the considered grades behave in practice — under elevated temperature and aggressive environments.

Resistance to oxidation and high‑temperature corrosion

Resistance of heat‑resistant steels is often described by:

• Oxide growth rate — the lower it is, the better the protection.
• Integrity of the oxide scale — ability to form a continuous layer that does not spall under thermal stresses.
• Resistance to pitting and crevice corrosion — important in the presence of chlorides and halogens.

Grades containing 15–25% chromium and significant nickel contents form stable oxide scales, but it is also crucial to minimise impurities (e.g. sulphur) that can initiate localised corrosion.

Mechanical strength during prolonged heating

Long‑term mechanical resistance is described by creep parameters — time to reach a specified deformation at a given temperature and load. Nickel‑rich alloys show better creep properties than purely ferritic steels.

Factors influencing strength:

• Microstructure (grain size, dispersion of precipitates),
• Presence and distribution of carbides,
• Additions such as Mo, V, Ti — they improve resistance.

For structures intended to operate for decades, performing creep tests during material qualification is essential.

Ductility and resistance to thermal cracking

Ductility at high temperatures allows a material to absorb stresses from sudden temperature changes. Thermal (thermomechanical) cracking occurs when cyclic expansion and contraction induce growing stresses.

Factors reducing cracking risk:

• Appropriate alloy compositions (nickel stabilises austenite),
• Control of thickness and geometry — thin walls heat and cool faster,
• Use of insulating coatings or ceramic layers.

In practice designers should account for temperature gradients, apply safety margins and choose materials tolerant to cyclic thermal loading.

Description of applications helps illustrate where and why particular grades are chosen. Examples by industry and application follow.

Power generation — boilers, turbines and heat exchangers

In power generation heat‑resistant steels are used in components that must withstand high temperatures and flue gas corrosion:

• Supercritical and ultra‑supercritical boiler tubes,
• Furnace and flue gas collector components,
• Components of steam and gas turbines, including housings and exhaust ducts,
• Heat exchangers operating at high temperatures and thermal differentials.

Here creep resistance and stability of oxide scales over long service periods are critical.

Chemical and petrochemical industry — reactors and installations

In chemical and petrochemical plants materials are exposed to chemically aggressive conditions, high temperatures and pressures:

• Reactors and catalysts,
• Pipelines transporting hot, aggressive media (e.g. acids, salts),
• Distillation columns and regeneration sections,
• Heat exchanger components exposed to aggressive flue gases and decomposition products.

Alloys with molybdenum and nickel additions are often preferred for their resistance to pitting and crevice corrosion.

Automotive and aerospace sectors — components exposed to extreme conditions

In automotive and aerospace industries heat‑resistant steels are used where low mass and high strength at extreme temperatures are required:

• Exhaust systems and manifolds (automotive),
• Jet engine and turbine parts (aerospace),
• Components subjected to rapid temperature changes.

In these applications the strength‑to‑weight ratio and material stability under large temperature gradients matter.

Working with high‑temperature materials requires strict adherence to standards and acceptance procedures. This helps avoid failures and ensures long, safe service life.

European and international standards – EN, ASTM, ISO

Key standards and norms include:

• EN (European Norms): definitions of grades, chemical and mechanical requirements, test procedures (e.g. EN 10028, EN 10216 for pipes).
• ASTM (American Society for Testing and Materials): detailed material specifications (e.g. ASTM A213, A335 for boiler piping), test methods.
• ISO: international standards regarding quality systems, non‑destructive testing and documentation procedures.

In practice the choice of standards depends on the market and investor requirements; in international projects parallel references to EN and ASTM are often used.

Importance of designations: 1.4980, 1.3980, 1.4944 in technical documentation

These designations facilitate unambiguous identification of materials in project documents, orders and certificates. When ordering material one should require:

• Full specification (material number + grade name),
• Material certificate (3.1 or 3.2 certificate in accordance with EN),
• Test reports (chemical composition, mechanical test results, non‑destructive testing).

Without such documentation there is a risk of using an inappropriate material, which can lead to costly failures.

Acceptance procedures and conformity tests with standards

Acceptance procedures typically include:

• Verification of documentation (certificates, drawings, batch markings),
• Visual inspection and dimensional checks,
• Repeat testing where required (e.g. composition analysis by spectrometer),
• Non‑destructive testing (UT, RT, MT, PT) of critical components,
• Trial mechanical and creep tests for special requirements.

Rigorous acceptance procedures minimise the risk of material defects.

The choice of alloy is not based solely on technical properties. Cost and environmental aspects are significant over the long term.

Production and operating costs of heat‑resistant materials

• Raw material costs — high nickel and molybdenum contents significantly increase alloy price. Nickel price volatility affects final component cost.
• Processing costs — high‑alloy steels are more difficult to machine and weld, which raises manufacturing costs.
• Operating costs — longer life and fewer shutdowns often offset higher material costs. Total cost of ownership (TCO), not just material price, should be considered.

In practice choosing a more expensive but longer‑lasting alloy can be economically justified if it reduces downtime and extends maintenance intervals.

Impact on energy efficiency and equipment longevity

Better heat‑resistant materials allow operation at higher temperatures, increasing process efficiency (e.g. higher turbine inlet temperatures improve gas turbine efficiency). This in turn:

• reduces fuel consumption,
• lowers CO2 emissions per unit of energy produced,
• improves operating economics.

From a durability perspective — reduced corrosion and material degradation increases component life and lowers operating costs.

Recycling and sustainability aspects

Heat‑resistant steels contain large amounts of strategic metals (Ni, Cr, Mo) which are valuable and suitable for recycling. Key issues:

• Separation and segregation — during maintenance waste should be separated for raw material recovery.
• Energy costs of recycling — melting and refining alloys requires energy, but material recovery is often economically viable.
• Environmental footprint — choosing long‑lived materials and enabling recycling reduces overall CO2 emissions.

Companies investing in sustainability prefer solutions that minimise primary raw material use and optimise product life cycles.

Despite many advantages, heat‑resistant steel poses specific challenges for engineers, from processing to service.

Issues related to machining and welding

• Machining: high hardness and tendency to work‑harden cause rapid tool wear. Appropriate tool materials (carbides, ceramics), coolants and machining parameters are required.
• Welding: procedures controlling the heat‑affected zone are necessary and filler wires with matching composition should be used. Without stabilisers (Ti, Nb) chromium carbides may precipitate, increasing susceptibility to intergranular corrosion.
• Distortions after welding: high thermal expansion and uneven heating produce stresses; measures to reduce distortion are needed (stitch welding, post‑weld heat treatment).

Good practice and strict welding procedure control are key to preserving material properties.

Reactions to prolonged exposure to variable temperatures

Cyclic heating and cooling can cause:

• increased brittleness due to diffusion and precipitation of brittle phases,
• thermal and fatigue cracking,
• degradation of oxide scales.

Designers must allow for dimensional changes and provide thermal compensation, and use materials with good thermal tolerance.

Typical failures and methods of prevention

Typical failures include:

• weld cracking — prevented by control of filler composition and pre‑heating/post‑weld heat treatment,
• pitting corrosion — mitigated by using Mo‑containing alloys and controlling the service environment,
• creep and permanent deformation — countered by selecting materials with appropriate high‑temperature yield strength and managing loads.

Regular inspections, condition monitoring and non‑destructive testing extend component life.

Research on heat‑resistant steels today focuses on improving performance, reducing costs and lowering environmental impact. Key directions include:

Alloy composition modifications to increase performance

• Optimised Ni‑Cr‑Mo combinations with micro‑alloying (B, Zr) to improve creep and stability.
• Use of light elements, e.g. small aluminium additions, to form stronger protective oxides.
• New classes of low‑nickel alloys with other additions to maintain high‑temperature resistance — a response to rising nickel costs.

These changes are often tested first at laboratory scale and then in prototype industrial installations.

Protective coating and composite technologies

• Ceramic and oxide coatings applied by CVD/PVD increase resistance to erosion and oxidation.
• Metal‑matrix/ceramic composites (MMC) combine metal ductility with ceramic resistance.
• Multi‑layer coatings that pair an oxide barrier with a diffusion layer extend component life.

Such solutions allow use of cheaper core alloys protected by surface layers.

Prospects for applications in future industries

• Renewable energy and energy storage technologies — require materials resistant to cyclic thermal loads.
• Hydrogen industry — components for production, transport and combustion of hydrogen will need alloys resistant to hydrogen effects and high temperature.
• Space and hypersonic applications — development of new alloys for extreme dynamic conditions.

Innovations will be driven by needs for energy efficiency, environmental protection and new technological processes.

Steels designated A‑260 and X6NiCrTiMoVB25‑15‑2 represent a group of materials designed for high‑temperature service, combining the roles of nickel, chromium and molybdenum with stabilising additions such as titanium, vanadium and boron. Numerical designations 1.4980, 1.3980 and 1.4944 serve as identifiers in standards systems and require verification of specifications at purchase. Production of these alloys requires precise control of composition and processing, and their use requires careful design, welding procedures and regular inspections. Selection of a specific grade should result from technical, economic and environmental analysis, taking into account process requirements and applicable standards.