1.4873

Heat-resistant steel is a group of alloys designed to operate under elevated temperature conditions where resistance to oxidation, dimensional stability and retention of strength on heating are critical. Grades of this type are indispensable in power generation, the petrochemical industry, boiler construction, industrial furnaces and engine components, where the material must endure aggressive thermal environments for long service periods. Z45CNW18-09, also designated 1.4873 in material catalogues, occupies a place among grades with balanced mechanical parameters and good high-temperature resistance, combining the benefits of carbon, chromium and nickel with additions such as tungsten.

Definition and basic properties of heat-resistant steel

Heat-resistant steel is defined as a alloy steel whose composition and microstructure provide resistance to oxidation and to corrosive gases at temperatures typically exceeding 500°C. The basic features of such alloys are:

• an adequate chromium content forming a passive oxide layer,
• selection of alloying additions (nickel, molybdenum, tungsten, vanadium) that influence phase stability and strength at high temperature,
• a microcrystalline structure capable of delaying surface oxidation and thermal cracking,
• the possibility of heat treatment to achieve desired mechanical properties.

Z45CNW18-09 falls into the group of grades with a moderately high carbon content, which makes it attractive where increased strength and surface hardness are required, while maintaining oxidation resistance thanks to chromium and stability at operating temperatures due to nickel and tungsten.

Origin and development history of grade Z45CNW18-09 1.4873

The origin of grades similar in composition to Z45CNW18-09 dates back to the development of alloy steels in the mid-20th century, when industry intensively sought materials resistant to rising operating temperatures of turbines, boilers and furnaces. Advances in metallurgy, improved melting techniques and understanding of the influence of microstructure on high-temperature behaviour led to the introduction of steels with increased chromium content and additions of nickel and heavy metals such as tungsten, which improved durability and resistance to oxidising agents. The designation Z45CNW18-09 is an adaptation of nomenclature used in national naming (Z = heat-resistant, 45 = approximate carbon content 0.45%, CNW = Cr, Ni, W), while the number 1.4873 comes from DIN/EN catalogues, facilitating international comparisons and material identification on global markets.

A full understanding of the behaviour of Z45CNW18-09 requires analysis of its chemical composition and the role of individual elements. This composition determines the microstructure after heat treatment and consequently the mechanical properties, corrosion resistance and susceptibility to thermal cracking.

Typical example composition (typical and indicative values, may vary depending on manufacturer and batch):

• Carbon (C): ~0.42–0.50%
• Chromium (Cr): ~17.0–19.0%
• Nickel (Ni): ~8.0–10.0%
• Tungsten (W): ~0.5–1.5%
• Manganese (Mn): up to ~1.0%
• Silicon (Si): up to ~1.0%
• Phosphorus (P), sulphur (S): minimal trace amounts (<0.03–0.04%)
• Minor additions: molybdenum (Mo), vanadium (V), niobium (Nb) – depending on variant and order.

Below is a discussion of the role of the most important components.

Carbon content and its influence on mechanical properties

Carbon is the main factor shaping steel hardness and strength through carbide formation and its influence on martensitic structure after hardening. In Z45CNW18-09, the high carbon content (approx. 0.45%) allows achieving high hardness and load-bearing capacity with appropriate heat treatment. The result is improved wear resistance and higher tensile strength, which is desirable in components exposed to heavy mechanical loads. However, higher C also increases the risk of brittleness, susceptibility to cracking during rapid heating/cooling and promotes sensitisation (precipitation of carbides at grain boundaries), which can reduce intergranular corrosion resistance under certain conditions.

To balance benefits and risks, production and heat-treatment processes must be precisely controlled, and in some applications stabilisation with additions of titanium or niobium or specific annealing procedures are used to reduce brittleness.

The role of chromium and nickel in high-temperature resistance

Chromium is the fundamental element responsible for oxidation and corrosion resistance in heat-resistant steels. In Z45CNW18-09, a chromium content of around 18% allows the formation of a stable, protective chromium oxide layer on the surface, slowing further oxidation and degradation of the material in hot gas environments. Such a passive layer is essential when operating at temperatures of several hundred degrees Celsius.

Nickel acts as an austenite stabiliser and improves ductility and resistance to cracking at elevated temperatures. In combination with chromium, nickel increases corrosion resistance in reducing and acidic environments and improves the alloy’s deformability during hot working. Practically, the presence of about 9% nickel helps minimise the brittleness that high carbon content might otherwise cause.

Importance of alloying additions: molybdenum, vanadium and other elements

Additions such as tungsten (W), molybdenum (Mo) and vanadium (V) significantly affect high-temperature properties:

• Tungsten (W) increases resistance to softening at elevated temperatures and forms stable carbides that strengthen the matrix. In Z45CNW18-09, tungsten improves durability during prolonged exposure to high temperature.
• Molybdenum strengthens resistance to chemical corrosion, particularly in chloride-containing environments, and increases strength at temperature. Its presence is beneficial in parts exposed to aggressive chemical environments.
• Vanadium promotes the formation of fine, stable carbides, which raise strength and wear resistance while maintaining good impact properties.

Minor additions of titanium or niobium may be used to stabilise carbides and prevent sensitisation (precipitation of carbides at grain boundaries), improving the intergranular resistance of welds and welded components.

Producing high-quality heat-resistant steel requires advanced melting technologies, precise control of composition and accurate heat-treatment processes. From raw material charging to final quality control, every step affects the achieved properties.

Melting methods and alloy shaping

Typical methods of producing Z45CNW18-09 include:

• Electric arc furnaces (EAF) combined with vacuum refining, allowing control of dissolved gases and impurities,
• Melting in vacuum induction furnaces (VIM) and possible further refining in vacuum arc remelting furnaces (VAR) to achieve homogeneity and reduce segregation,
• Shaping by hot and cold rolling, drawing or ingot/casting methods, depending on geometrical requirements.

Melting in controlled atmospheres and practices such as degassing and desulphurisation are key to achieving repeatable properties and minimising macro- and microstructural defects.

Heat treatment – annealing and quenching

Heat treatment of Z45CNW18-09 includes several key stages:

• Soft annealing to reduce residual stresses after plastic working and improve machinability,
• Quenching — heating to the austenitising temperature followed by rapid cooling (mainly oil or air depending on requirements), which allows obtaining a martensitic structure and high hardness,
• Quenching and tempering — after quenching the material is tempered to reduce stresses and improve impact toughness, achieving a compromise between hardness and ductility,
• Normalising in some cases to homogenise grain size and mechanical properties.

Heat-treatment parameters are selected precisely according to the intended application: higher temperatures and shorter transformation times favour higher hardness, while tempering raises resistance to cracking and impact toughness.

Quality control and strength tests

Quality control includes a wide range of tests:

• Chemical analysis (spectral) to verify element contents,
• Mechanical tests: tensile tests, hardness, impact toughness (Charpy), measurements of yield strength and elongation,
• Microstructural examinations (optical and electron microscopy) to assess carbide distribution, grain size and presence of defects,
• Corrosion resistance tests, including high-temperature oxidation tests, corrosion tests in chloride solutions and other service simulations,
• Non-destructive testing of welds and components: ultrasonic, radiographic, penetrant and magnetic inspections.

Such a broad spectrum of controls ensures that delivered material meets application requirements and quality standards.

Mechanical and physical properties define the applications and operational limits of Z45CNW18-09. Although specific values depend on heat treatment, the following are typical characteristics encountered.

High-temperature resistance and corrosion resistance

Thanks to its chromium content and the stabilising presence of nickel and tungsten, Z45CNW18-09 exhibits good resistance to oxidation and oxidative corrosion at operating temperatures typical for boilers and industrial furnaces. The forming oxide layer inhibits further degradation. In environments containing aggressive sulphur- or chloride-bearing gases, resistance may be limited, so in such applications materials with added molybdenum or special protective coatings are often used.

Tensile strength and impact toughness

Tensile strength and hardness of Z45CNW18-09 largely depend on heat treatment. After quenching and tempering, high ultimate strength values can be achieved while maintaining acceptable impact toughness. In practice, this grade provides a good compromise between hardness (wear resistance) and resistance to impact cracking, making it useful in components operating under load and at elevated temperatures.

Oxidation resistance and thermal fatigue

Oxidation resistance is one of the distinguishing features of heat-resistant steels and in the case of Z45CNW18-09 it is at a level that allows long-term service under uniform high-temperature conditions. Thermal fatigue — cracking caused by cyclic temperature changes — is, however, a challenge: the high carbon content and presence of hard carbides can promote crack initiation under intensive heating and cooling cycles. Appropriate component design, control of temperature gradients and suitable surface treatments reduce these risks.

Z45CNW18-09 is used where a combination of high strength and resistance to elevated temperature is required, often along with exposure to wear and aggressive gaseous environments.

Energy sector – boilers and turbines

In the energy sector this steel is used for manufacturing boiler components, grates, flue gas collectors, tubular parts and other components exposed to flue gases and high temperature. For gas turbines it may be applied in less critical parts or auxiliary components where thermal stability requirements are high but do not reach the level of nickel superalloys.

Chemical and petrochemical industry

In refineries and chemical plants Z45CNW18-09 is used for heat exchangers, furnace components, vessels and parts of installations that must withstand high temperatures and combustion products. Where aggressive chemicals are present, additional protection or materials with higher molybdenum content may be necessary.

Structural components in automotive and aerospace industries

In the automotive sector this steel can be used for exhaust system components, valves, high-temperature springs and other parts exposed to high temperatures and wear. In aviation, due to extreme weight and thermal requirements, Z45CNW18-09 rarely replaces specialised superalloys; however, in less critical subsystems and when producing auxiliary parts it is used as an economical solution combining good mechanical properties with temperature resistance.

Comparing grades helps to understand in which situations Z45CNW18-09 is the optimal choice and when alternatives are preferable.

Classic grades versus modern solutions

Compared with classic grades such as 1.4841 or 1.4749, Z45CNW18-09 offers higher hardness owing to its carbon content and better resistance to softening due to tungsten and nickel additions. Compared with modern nickel superalloys (e.g. Inconel, Hastelloy), Z45CNW18-09 is considerably cheaper and easier to machine, but its service limit at extremely high temperatures and its chemical resistance are limited compared with superalloys, which retain properties at temperatures exceeding 900–1000°C and in aggressive chemical media.

Compared with ferritic and austenitic steels of lower carbon content, Z45CNW18-09 has better strength and hardness at the cost of somewhat poorer weldability and a greater risk of thermal cracking.

Advantages and limitations of Z45CNW18-09 1.4873 compared with other alloys

Advantages:

• good compromise between strength and temperature resistance,
• ability to achieve high surface hardness due to carbon content,
• oxide stability thanks to high chromium content,
• favourable cost-to-performance ratio for many industrial applications.

Limitations:

• susceptibility to thermal cracking under sudden temperature cycles,
• lower resistance in extremely aggressive chemical environments compared with superalloys,
• need for caution during welding and the requirement for pre- and post-heating procedures (PWHT) in critical components.

The decision to choose Z45CNW18-09 should be based on analysis of operating conditions: temperature, presence of aggressive chemical agents, cyclic loading and requirements for durability and cost.

Understanding the symbolism and standards is crucial when purchasing and using the material to ensure specification compliance with design requirements and international standards.

PN, DIN, EN – basic quality standards

The number 1.4873 is a designation used in DIN/EN (German and European) catalogues identifying a specific grade of stainless/heat-resistant steel. In Polish industrial notation the equivalent may be the symbol Z45CNW18-09, where:

• Z – heat-resistant,
• 45 – approximate percentage carbon content (0.45%),
• C – chromium,
• N – nickel,
• W – tungsten,
• 18-09 – indication of chromium (~18%) and nickel (~9%) content.

Standards EN 10088-1/2 relate to stainless steels and their properties. Additional standards, such as EN ISO 4957, PN-EN 10204 or PN-EN 10025, may regulate test specifications, certification requirements and material documentation. When ordering material it is advisable to refer to the appropriate standards and the manufacturer’s technical specifications to ensure parameter compliance.

Interpretation of the grade designation and symbolism

Designations such as Z45CNW18-09 1.4873 combine information about intended use (heat-resistant), composition (45 — carbon; 18 — chromium; 09 — nickel) and the standard catalogue number. This allows engineers and suppliers to quickly identify materials and their applications. When specifying material, it is always necessary to consider also heat-treatment requirements, chemical and mechanical tolerances and additional processes such as surface treatment.

Appropriate storage, operation and maintenance conditions significantly extend the life of components made from heat-resistant steel and reduce the risk of failure.

Storage conditions minimising corrosion risk

Basic storage rules:

• store in dry, ventilated premises, away from sources of moisture and aggressive chemicals,
• avoid contact with materials containing chlorides or sulphates, which could promote localised corrosion,
• use protective interleaving and packaging to protect surfaces from scratching and contamination,
• for long-term storage use protective measures, e.g. protective films or light oiling of surfaces, which can be removed prior to processing.

Additionally, welded and cut parts should be properly marked and protected from atmospheric exposure until assembly.

Operating rules at high temperatures

During operation:

• avoid sudden heating and cooling cycles that promote thermal cracking; design smooth temperature transitions and thermal zones,
• consider use of protective coatings in areas most exposed to oxidation and erosion,
• in installations exposed to aggressive chemicals monitor surface condition and carry out regular non-destructive inspections,
• for welded components follow recommended welding procedures and, where necessary, perform post-weld heat treatment (PWHT) to reduce stresses and improve intergranular resistance.

Maintenance and repair procedures

Maintenance:

• periodic visual and non-destructive inspections to detect corrosion, cracks and signs of fatigue,
• cleaning of surfaces from deposits and fouling that may locally accelerate oxidation,
• prompt repair of minor damage — grinding of scratches, local brazing or welding following procedures and possible passivation of the surface after repair.

In the case of serious damage, a failure analysis should be conducted and repairs planned according to the material manufacturer’s recommendations or industry standards.

Even the best materials can degrade if not properly used. Knowledge of typical defects helps prevent failures and plan preventive measures.

Thermal cracking and its causes

Thermal cracks arise from stresses generated by sudden temperature changes or large temperature differences between material layers. Causes include:

• sudden heating and cooling without appropriate thermal procedures,
• local heating in welds or heat-affected zones leading to stress concentration,
• improper design that does not account for thermal expansion.

Prevention includes appropriate thermal design, gradual heating/cooling and procedures to reduce stresses.

Intergranular corrosion and prevention methods

Intergranular corrosion results from precipitation of chromium carbides at grain boundaries, which causes dechromisation of boundary zones and their susceptibility to corrosion. In higher-carbon steels like Z45CNW18-09, the risk of sensitisation is significant, especially when operating at temperatures favourable to carbon diffusion (approx. 400–800°C).

Preventive measures:

• use stabilisers (Ti, Nb) in the alloy composition that bind carbon into less harmful carbides,
• control residence time at temperatures promoting sensitisation,
• combine appropriate heat treatment (e.g. rapid annealing) and surface passivation processes.

Material fatigue under dynamic conditions

Thermal and mechanical fatigue manifests as crack initiation at stress concentrators and gradual crack growth under cyclic loading. Factors degrading fatigue resistance include: surface defects, inappropriate heat treatments, poor surface finish and the presence of aggressive environments.

Prevention includes design to reduce stress concentrators, surface treatments that improve fatigue strength (e.g. surface plastic deformation, shot peening) and regular non-destructive inspections.

The future of heat-resistant materials is the continued search for better properties at lower cost and greater efficiency of the production process. Z45CNW18-09 is also influenced by these trends.

New methods of strengthening and improving parameters

Modern approaches include:

• heat and thermo-mechanical processing methods optimising carbide distribution and grain size,
• composition modifications at the level of trace additions that stabilise the structure and improve corrosion resistance,
• application of thermal and protective coatings, such as ceramic coatings or oxide-based layers, which can significantly extend the life of elements exposed directly to flame and flue gases,
• surface treatment technologies, including laser surface hardening and thermal spraying, which increase wear and oxidation resistance.

Application in advanced technologies and industries

As technology develops, Z45CNW18-09 may find applications in:

• components of heat recovery systems in modern energy installations,
• parts of boilers and heat exchangers in installations using biomass and alternative fuels, where the presence of contaminants requires a combination of oxidation and wear resistance,
• structures in vehicles with alternative drivetrains (e.g. components of fuel systems exposed to high temperatures), where an economical compromise between cost and thermo-mechanical properties is important,
• production of components using 3D printing and additive techniques, which requires adaptation of welding procedures and additive processes with regard to composition and microstructure.

Ongoing research into increasing alloy purity, microstructure homogenisation and new coating techniques means that grades such as Z45CNW18-09 will evolve while retaining a favourable cost/performance ratio.

Z45CNW18-09 (1.4873) is a heat-resistant steel combining a high carbon content with significant chromium and nickel levels and additions such as tungsten. It offers a favourable combination of hardness, strength and oxidation resistance, making it useful in many industrial applications — from boilers and heat exchangers to exhaust system components and structural parts. Its properties depend heavily on precise control of composition, melting methods and heat treatment. The main challenges are the risk of thermal cracking and sensitisation; key countermeasures are composition stabilisation, appropriate welding procedures and careful operating conditions. In the dynamically developing world of materials technology Z45CNW18-09 remains an attractive compromise between cost and performance, while being subject to continuous improvements and production innovations.