1.4935

The steel designated X20CrMoWV12-1 and material number 1.4935 belongs to the group of heat‑resistant, ferritic‑martensitic chromium‑molybdenum‑vanadium alloys. It was developed for service at elevated temperatures where high mechanical strength, oxidation resistance and acceptable creep resistance are required simultaneously. In practice it is used where thermal and mechanical conditions occur together — for example in components of steam boilers, exhaust ducts, headers and turbine parts.

Basic properties and definition of heat‑resistant steel

Heat‑resistant steel is a type of alloy whose constructional and chemical features provide resistance to temperatures higher than typical structural service conditions. Unlike ordinary structural steels, heat‑resistant alloys retain useful mechanical properties (strength, hardness, creep resistance) at temperatures of several hundred degrees Celsius. In the case of X20CrMoWV12-1 the key distinguishing features are:

• chromium content providing passivation and oxidation resistance,
• molybdenum and vanadium shaping creep resistance and structural stability at high temperatures,
• moderate carbon content allowing attainment of a harder, martensitic microstructure after quenching and tempering.

History and development of the X20CrMoWV12-1 1.4935 grade

The X20CrMoWV12-1 grade emerged in the second half of the 20th century as the power industry responded to increasing operating temperature and efficiency requirements for steam boilers. Development of power technology and the need to raise process parameters — higher steam pressures and temperatures — forced adoption of alloys with better creep resistance than traditional low‑alloy steels. Over time compositions were optimised: chromium content was increased to improve oxidation resistance and micro‑alloying elements (V, W, Mo) were added to stabilise the matrix and improve mechanical properties at service temperatures. As a result of these studies a standard material designated in European standards as 1.4935 was established and has seen wide use in power generation and heavy industry.

The exact chemical composition is the result of many years of research into the compromise between ductility, strength and high‑temperature corrosion resistance. Below are typical percentage ranges of the alloying elements present in this grade.

Alloying elements and their functions

• Carbon (C) 0.17–0.24% — responsible for the possibility of producing a strong, quenched and tempered martensitic microstructure. The optimal carbon content is a compromise between hardness and ductility; excessive amounts increase brittleness.
• Silicon (Si) 0.20–0.60% — beneficial to strength; also acts as a deoxidiser in melting.
• Manganese (Mn) 0.30–0.80% — improves strength and hardenability, acts stabilising with respect to sulphur.
• Chromium (Cr) 11.0–13.0% — main element providing oxidation resistance and some types of high‑temperature corrosion resistance; a chromium oxide layer protects the material in an oxygen atmosphere.
• Molybdenum (Mo) 1.5–2.5% — increases creep resistance and improves strength at elevated temperatures; stabilises the structure.
• Vanadium (V) 0.15–0.50% — strengthens by forming carbides and improves resistance to high‑temperature fatigue.
• Tungsten (W) 0.15–0.80% — like molybdenum, supports creep resistance and structural stability at higher temperatures.
• Phosphorus (P) ≤0.025% and sulphur (S) ≤0.020% — undesirable elements, controlled at low levels because they worsen ductility and welding properties.
• Nitrogen (N) and other microelements — usually at very low levels, may be intentionally used in minimal amounts to improve mechanical properties.

Influence of elements on mechanical and thermal properties

Each alloying element performs a specific function:

• Chromium forms a stable chromium oxide layer that protects the surface from further oxidation. In practice, up to a certain limit, the more chromium the better the oxidation resistance.
• Molybdenum and tungsten increase solubility in carbides and form barriers in the crystal lattice, which slow the creep process. Their presence is crucial in applications where the material works long‑term under stress and at temperatures around 500–650°C.
• Vanadium forms strong carbides and stabilises the microstructure by limiting grain growth during heat treatment, which translates into improved resistance to shrinkage and cracking.
• Carbon determines the amount of cementite and carbides dissolved in the alloy; an appropriate concentration enables the required hardenability and mechanical stability after heat treatment.

Balancing these elements yields a steel that is resistant to oxidation and creep under industrial service conditions while maintaining acceptable weldability and machinability.

The mechanical characteristics of 1.4935 depend on the delivery condition (e.g. normalised, annealed, quenched and tempered). Below are typical values and behaviour of the material under various conditions.

Tensile strength and hardness

• Typical yield strength Rp0.2 in the quenched and tempered condition: approximately 450–600 MPa, depending on the degree of tempering and carbon content.
• Tensile strength Rm usually falls in the range 600–800 MPa for suitably hardened and tempered material.
• Hardness after quenching and tempering typically reaches values of about 200–300 HB, which corresponds to a good compromise between wear resistance and toughness.

These parameters make 1.4935 useful where strength must be maintained at relatively high temperatures.

High‑temperature resistance and corrosion

• X20CrMoWV12-1 is designed for service temperatures in the range 500–650°C. In this range the material retains a favourable strength‑to‑density ratio and good oxidation resistance.
• Degradation mechanisms include surface oxidation, grain growth and creep. Thanks to the presence of critical alloying elements (Cr, Mo, W, V) these processes are significantly slowed compared with plain carbon steels.
• In chemically aggressive atmospheres (sulphur, chlorine compounds) resistance decreases and additional protective measures or more resistant grades are required.

Ductility and fracture resistance

• Ductility of 1.4935 after appropriate tempering is sufficient for forming and machining. However, in a heavily hardened state the steel becomes more brittle.
• Fatigue and impact fracture resistance at room temperature is good, but decreases at higher temperatures. Therefore it is important to select appropriate heat treatment parameters and control welds in welded components.
• To prevent cracking, preheating and post‑weld heat treatment (PWHT) are used to reduce residual stresses and improve ductility of the heat‑affected zone.

Production and processing of this steel grade require control of thermal and mechanical parameters to achieve the desired service properties.

Rolling and forging methods

• Forging and hot rolling are standard processing stages for the produced alloy. The hot‑rolling temperature should be maintained in a range that allows good plastic deformation while avoiding excessive grain growth (typically 1000–1150°C).
• After rolling, controlled cooling and normalising follow, which stabilise the structure and improve the material’s mechanics. Normalising produces a homogeneous microstructure, and subsequent tempering reduces stresses and imparts the desired hardness.

Quenching and tempering – optimising the structure

• A typical heat‑treatment cycle for X20CrMoWV12-1 includes quenching (austenitisation) at around 980–1020°C, followed by cooling (usually slower than for high‑carbon steels to avoid cracking).
• Tempering is carried out at temperatures of about 600–700°C to reduce brittleness and achieve the required strength and ductility. Tempering time and the number of cycles influence final hardness and crack resistance.
• These processes are optimised depending on application: components exposed to creep usually require specific tempering to stabilise carbides and limit grain growth.

Machining and weldability

• Machining is relatively straightforward when appropriate tools and cutting parameters are used, although high hardness after heat treatment requires sharp tools and cooling.
• Weldability of 1.4935 is moderate. Required measures include:

– preheating to avoid rapid cooling and formation of brittle structures,
– control of heat input, and
– mandatory post‑weld heat treatment (PWHT) to reduce residual stresses and restore uniformity of the martensitic structure.

• Electrodes and welding wires should be appropriately chosen for composition to ensure chemical and mechanical compatibility in the weld.

Steel 1.4935 is used wherever service at elevated temperatures combined with mechanical loading is required.

Power industry – boiler and turbine components

• The most obvious application is components of steam boilers: reheater tubes, headers, superheater elements and steam outlets. This material is used in sections where steam and flue gas temperatures require creep and oxidation resistance.
• In turbines, parts made from this grade can be found where a combination of strength and heat resistance is needed at relatively moderate temperatures (lower than those requiring nickel‑chromium alloys).

Chemical and petrochemical industry

• In process installations where elevated temperatures and aggressive atmospheres occur (particularly where there are no strongly chlorinated corrosive components), 1.4935 is used for heat exchangers, headers and process piping.
• Where exposure is mainly to oxidation and high‑temperature effects, the material can be a good compromise between cost and performance.

Manufacture of high‑temperature machine components

• Hubs, bushings, housings and machine components working near heat sources benefit from the strength properties of this steel. Where precision machining and resistance to deformation at elevated temperatures are required, X20CrMoWV12-1 performs well.

Comparisons help to understand the strengths and weaknesses of a particular grade in the context of alternatives.

Composition and property differences compared with X10CrMoVNb9-1

• X10CrMoVNb9-1 (often used in conventional boilers) typically contains a lower chromium content (around 9%) and also includes niobium (Nb), which stabilises carbides and improves creep resistance.
• X20CrMoWV12-1 has a higher chromium content (around 12%) and usually greater amounts of molybdenum and tungsten, which translates into better oxidation resistance and higher usable temperature.
• In practice: X20CrMoWV12-1 offers better resistance at higher temperatures, while X10CrMoVNb9-1 is valued for a good combination of machinability, weldability and properties at lower service temperatures.

Advantages and limitations compared with 1.4848 (AISI 310)

• 1.4848 (AISI 310) is an austenitic steel with high chromium and nickel content, characterised by excellent oxidation and corrosion resistance at higher temperatures (even up to 1100°C).
• X20CrMoWV12-1 surpasses AISI 310 in mechanical strength and creep resistance at temperatures around 500–650°C. Conversely, AISI 310 copes better in strongly oxidising and very high‑temperature environments and where good ductility and weldability are required without concerns about martensitic transformations.
• The choice between them is a compromise: 1.4935 for mechanical loading and operation at intermediate temperatures; 1.4848 for maximum chemical resistance and higher static temperatures.

Service durability of the steel results from the interaction of thermal, mechanical and chemical factors. Understanding their influence allows extension of component life.

Thermal and mechanical factors affecting degradation

• Service temperature: long‑term exposure near the upper range of allowable temperatures causes grain growth, carbide dissolution and reduced creep resistance.
• Mechanical stresses: constant or cyclic loads at elevated temperatures accelerate creep and can initiate fatigue cracks.
• Temperature variability (thermal cycles): repeated heating and cooling leads to thermal fatigue and can cause crack formation at grain boundaries or in welds.

Preventive actions include appropriate component design (minimising stress concentrators), controlled heating and cooling and regular inspections.

High‑temperature corrosion and ways to minimise it

• Oxidation is the principal corrosion mechanism in oxygen containing atmospheres. Protection is provided by high chromium content, but also by using ceramic coatings or oxide barrier layers that slow mass loss.
• Carburisation and carbon‑nitrogen corrosion: in the presence of hydrocarbons and reducing gases the surface may undergo carbon ingress, which alters the microstructure and weakens the material. Protective atmospheres, insulation and barrier materials reduce this effect.
• Sulphurous environments: presence of sulphur oxides can significantly accelerate degradation; in these conditions special materials or coatings are required.

Monitoring surface condition, using inhibitors and correct component design are basic methods to limit degradation.

Compliance with standards ensures repeatability of properties and enables use of the material in pressure and power structures.

European and international requirements

• The material is described in German and European standards under the material number 1.4935. In commercial documentation the DIN/EN designation is often used.
• Typical applicable standards include requirements for mechanical testing, chemical composition control and manufacturing methods (e.g. EN 10028 for steels for pressure vessels, EN 10216/10217 for pipes, EN ISO 5817 for weld quality, although specific numbers may differ depending on application).
• For boiler and pressure components material certificates in accordance with EN 10204 (2.1, 2.2, 3.1, 3.2) are usually required, where 3.1 or 3.2 confirm properties via an independent laboratory.

Quality tests and technological documentation

• Standard tests include: chemical analysis, tensile test, hardness testing, impact tests (depending on requirements), as well as metallographic examinations and creep tests at specified temperatures and stresses.
• Technological documentation should include the heat‑treatment record, results of ultrasonic or radiographic inspections for critical components and declarations of conformity with relevant standards.
• Certification and quality control procedures matter not only when purchasing the material but also during its later use in critical installations.

Material availability and formats have practical significance for production and repair.

Available formats: bars, plates, pipes

• 1.4935 steel is commercially available in the following forms:

– pipes (seamless and welded) used in boiler installations,
– plates and strips for structures and casings,
– bars and sections for machine parts and forgings,
– forgings and formed parts for applications requiring specific shapes and strength.

• Typical delivery condition: normalised or quenched and tempered — depending on customer requirements.

Logistics and storage aspects

• Storage requires protection against moisture and contamination to limit initial oxidation and surface corrosion. Dry, ventilated warehouses and anti‑corrosion protection are recommended for prolonged storage.
• For orders of critical components it is important to specify requirements regarding material condition, certificates and heat‑treatment history. Deliveries with correct documentation shorten the time to install components in critical systems.

Development of heat‑resistant materials is under constant evolution, driven by the needs of high‑efficiency power generation, emissions limitations and new manufacturing technologies.

Innovations in composition and processing

• In response to rising demands for higher temperatures and better creep resistance, compositional modifications with micro‑alloying and stabilisers (e.g. controlled additions of Nb, Ti) and optimisation of W and Mo contents are being developed.
• Microstructure control technologies, such as precise multi‑stage tempering, micro‑alloying and carbide management, allow improvement of durability without significant increases in material cost.
• Protective coatings and oxide barrier technologies (e.g. ceramic sprays, ODS — oxide‑dispersion strengthened coatings) offer additional protection against oxidation and carburisation.

Applications in new industry sectors

• The growing importance of renewable energy sources and hybrid cogeneration systems creates demand for materials combining thermal resistance with cost efficiency.
• Additive manufacturing techniques open possibilities for producing complex components from high‑temperature materials; research into powder‑bed production of X20CrMoWV12-1 and its modifications is ongoing and may in future change production practices for complex geometry parts.

• X20CrMoWV12-1 (1.4935) is a chromium‑molybdenum‑vanadium heat‑resistant steel designed for service at approximately 500–650°C, combining oxidation resistance with good mechanical strength.
• Key alloying elements (Cr, Mo, W, V) work together to limit creep and grain growth while providing surface protection in oxygen atmospheres.
• Typical heat treatments include austenitisation, quenching and tempering; control of these stages is essential to achieve the required balance of hardness and ductility.
• The material is primarily used in power generation (boilers, headers, turbine parts), the chemical industry and in machine structures operating at elevated temperatures.
• Compared with other steel grades, 1.4935 offers better creep resistance than some older ferritic‑martensitic grades and higher strength than high‑alloy austenitic steels in the temperature ranges typical for steam boilers.
• Meeting standard requirements, appropriate quality testing, correct welding procedures and storage are critical for long‑term, trouble‑free operation.
• Future trends include micro‑alloy optimisation, protective coatings and integration with additive manufacturing technologies, which will extend applications and improve service properties.