Stainless Steel, Duplex
1.4501 S32760 (F55) Super Duplex
High performance duplex steel with additions of chromium, molybdenum, and nitrogen for enhanced pitting and crevice corrosion resistance.
Superduplex UNS S32760 (F55) combines the desirable aspects of both austenitic and ferritic grades and gives significant life cycle cost advantages when used in severe and corrosive conditions.
It has exceptional resistance to pitting, crevice corrosion and to stress corrosion cracking and have high strength combined weldability.
The higher chromium, molybdenum and nitrogen contents result in a Pitting Resistance Equivalent number (PREN) of >40, providing pitting and crevice corrosion resistance superior to austenitic and duplex stainless steels in almost all corrosive media. It also provides higher strength than both austenitic and 22% Cr duplex stainless steels.
DOWNLOAD PDF
Range
| Product Form | Size Range |
| Round Bar Peeled K12 | 5⁄8" - 3" |
PLEASE NOTE
If you do not see what you are looking for, please contact your local service centre with your specific requirements.
1.4501/S32760 Stainless Steel Related Specifications
| System / Standard | Country / Region | Grade / Designation |
| UNS | International | S32760 |
| EN / W.Nr. | Europe | 1.4501 |
| EN Name (EN 10088) | Europe | X2CrNiMoCuWN25-7-4 |
| ASTM A240 | USA | S32760 (plate, sheet, strip) |
| ASTM A276 | USA | S32760 (bars, shapes) |
| ASTM A479 | USA | S32760 (bars for pressure) |
| ASTM A789 | USA | S32760 (seamless tubing) |
| ASTM A790 | USA | S32760 (seamless pipe) |
| ASTM A182 | USA | F55 (super duplex forging) |
| Trade name | International | Zeron 100 |
Properties
Chemical Composition
1.4501/S32760 Steel
| Chemical Element | % Present |
| Carbon (C) | 0.00 - 0.03 |
| Chromium (Cr) | 24.00 - 26.00 |
| Manganese (Mn) | 0.00 - 1.00 |
| Silicon (Si) | 0.00 - 1.00 |
| Phosphorous (P) | 0.00 - 0.03 |
| Sulphur (S) | 0.00 - 0.01 |
| Nickel (Ni) | 6.00 - 8.00 |
| Nitrogen (N) | 0.20 - 0.30 |
| Copper (Cu) | 0.50 - 1.00 |
| Molybdenum (Mo) | 3.00 - 4.00 |
| Tungsten (W) | 0.50 - 1.00 |
| Iron (Fe) | Balance |
Mechanical Properties
Bar & Section Up to 160mm Dia/Thickness
| Mechanical Property | Value |
| Elongation A50 mm | 25 % |
| Hardness Brinell | 270 Max HB |
| Tensile Strength | 750 N/mm2 |
| 0.2% Proof Stress | 550 N/mm2 |
General Physical Properties
| Physical Property | Value |
| Density | 7.81 g/cm³ |
| Thermal Expansion | 17.2 x10-6/K |
| Thermal Conductivity | 14.2 W/m.K |
| Electrical Resistivity | 0.8 x10-6 Ω .m |
Applications of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 (UNS S32760, often known by trade names like ZERON® 100) is a super duplex stainless steel with very high pitting resistance (PREN > 40), excellent resistance to chloride stress-corrosion cracking and yield strength roughly twice that of 304/316, making it ideal for highly aggressive chloride and mixed-process environments.
1. Offshore Oil & Gas and Subsea Production
Subsea manifolds, jumpers, flowlines and umbilical hardware exposed to cold, high-pressure seawater
Seawater injection systems, risers and topside process piping handling chlorides, CO₂ and small amounts of H₂S
Christmas trees, valves, connectors, hubs and fittings where both high strength and maximum localized-corrosion resistance are critical
2. Seawater Handling, Desalination and Marine Engineering
Seawater cooling-water systems: intake piping, pump casings, strainers and heat-exchanger components
Desalination plant high-load parts: high-pressure components, evaporator/RO hardware and brine-handling equipment
Highly exposed marine structures and hardware in splash/tidal zones where 316/2205 may pit or crevice-corrode over time
3. Chemical, Petrochemical and Refining Service
Equipment handling hot chloride-bearing, acidic or mixed chloride/acid media where 316L/2205 are borderline
Reactors, columns, heat exchangers and transfer lines in aggressive brines, chlorinated process streams and certain organic acids
Critical components where both high mechanical load and top-end localized-corrosion resistance must be combined in one alloy
4. Pulp, Paper, Mining and Minerals Processing
Bleach plant equipment (towers, washers, filtrate lines) in very aggressive chloride + oxidizing conditions
Components in strong, hot liquors where pitting, crevice corrosion and stress-corrosion cracking are severe risks
Slurry piping, pumps, mixers and flotation/processing hardware in mining and mineral-processing plants handling abrasive, chloride-containing slurries
5. Power Generation and Other High-Load Corrosive Duties
Power-plant seawater cooling systems, condensers and high-load structural hardware in coastal installations
FGD (flue-gas desulfurization) equipment where chloride-contaminated condensates and high temperatures are present
High-strength fasteners, shafts, flanges and fittings that must withstand both high stress and very aggressive wet corrosion in industrial plants
Summary
1.4501 / S32760 super duplex stainless steel is chosen for the most aggressive chloride and mixed-process environments—offshore and subsea oil & gas, seawater and desalination systems, harsh chemical and pulp-and-paper service, mining slurries and power-generation cooling—whenever designers need superior pitting/crevice resistance and chloride SCC resistance, together with very high strength, beyond what 316L or even standard duplex grades like 2205 can reliably provide.
Characteristics of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 (UNS S32760, often known under trade names like ZERON 100) is a super duplex stainless steel with a duplex (austenite + ferrite) structure, very high pitting resistance and yield strength roughly twice that of 304/316, designed for the most aggressive chloride and mixed-process environments.
1. Super Duplex Microstructure and Alloy Design
Roughly 50% ferrite / 50% austenite in the solution-annealed condition.
High alloying levels (Cr, Mo, N, often W and Cu) give a very high pitting resistance compared with standard duplex (2205) and 300-series austenitic grades.
The duplex structure provides a balance of high strength, good toughness and excellent resistance to stress-corrosion cracking.
2. Very High Strength and Structural Efficiency
Yield strength is typically about twice that of 304L/316L and higher than standard duplex 2205.
Allows designers to use:
Thinner wall thicknesses in piping and vessels
Lighter, more compact sections in structural and mechanical components
This high strength is crucial offshore and subsea, where weight reduction and compact, high-load parts are valuable.
3. Outstanding Pitting and Crevice Corrosion Resistance
High Cr + Mo + N (and often W) give a very high PREN (pitting resistance number), comfortably above standard duplex and 316L.
Excellent resistance to pitting and crevice attack in:
Natural seawater (including warm, oxygenated conditions)
Concentrated brines and chlorinated waters
Aggressive chloride/acid mixtures found in chemical and oil & gas service
This makes S32760 a “go-to” grade where 316 or even 2205 cannot deliver sufficient localized-corrosion margin.
4. Excellent Resistance to Chloride Stress-Corrosion Cracking (SCC)
Duplex microstructure gives very high resistance to chloride SCC, even at elevated temperatures and stress levels where austenitic grades fail.
Particularly suited to:
Warm seawater and high-chloride cooling systems
Offshore production, injection and process lines under high pressure
This SCC resistance is a key reason for its widespread use in offshore, subsea and desalination equipment.
5. Erosion–Corrosion and Corrosion-Fatigue Performance
High strength plus robust passive film give good resistance to erosion–corrosion in high-velocity seawater and abrasive, chloride-containing slurries.
Duplex structure provides strong corrosion-fatigue resistance under combined cyclic loading and corrosive attack.
Well suited to pumps, valves, mixers, manifolds, risers and slurry-handling components in harsh service.
6. Toughness and Temperature Capability
Toughness is lower than austenitic 316, but high for such a highly alloyed, high-strength grade when microstructure is correct.
Performs well at typical offshore and subsea temperatures, including low-temperature seawater.
Like other duplex and super duplex grades, long exposure in certain intermediate/high temperature ranges can form embrittling intermetallic phases, so fabrication heat treatments and service temperatures must respect manufacturer limits.
7. Weldability and Fabrication Considerations
Weldable, but must be welded using super duplex-specific procedures:
Carefully controlled heat input and interpass temperature
Super duplex or over-alloyed austenitic filler metals
Proper shielding and back purging to avoid oxidation and loss of corrosion resistance
Correct procedures produce welds with strength and corrosion resistance close to the base metal; poor procedures can lead to intermetallics, reduced toughness and much lower pitting resistance.
8. Mechanical and Physical Property Balance
High elastic modulus and strength give excellent stiffness and load-carrying capacity.
Lower thermal expansion than austenitic grades improves dimensional stability in temperature-cycling service.
Ferrite phase makes the alloy magnetic in all conditions (unlike annealed 304/316).
Overall, S32760 offers a strong combination of mechanical strength, toughness, fatigue resistance and top-tier localized corrosion resistance.
Summary
1.4501 / S32760 is a super duplex stainless steel that combines a duplex microstructure, very high strength, outstanding pitting/crevice and chloride SCC resistance, good erosion–corrosion and corrosion-fatigue performance, and weldability with appropriate procedures—making it a premier choice for the most demanding offshore, subsea, seawater, chemical and mining environments where both mechanical load and extreme corrosion must be handled in a single material.
Additional Information
Weldability
Weldability of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 (super duplex) is weldable, but it is much more sensitive than 304/316 or even 2205. To keep its very high strength and corrosion resistance, welding must follow strict super-duplex procedures for heat input, filler choice, shielding and post-weld cleaning.
1. General Weldability Characteristics
Can be welded with standard stainless processes, but:
Process window is narrow compared with austenitic and standard duplex grades.
Incorrect parameters quickly lead to intermetallic phases (sigma, chi) and loss of toughness and pitting resistance.
Super duplex welds must preserve:
A balanced ferrite–austenite ratio in weld metal and HAZ.
High pitting resistance and SCC resistance comparable to the base metal.
2. Suitable Welding Processes
Commonly used processes:
GTAW (TIG) – preferred for root passes and thin sections; excellent control.
GMAW (MIG/MAG) – for production welding of pipe, tube and plate.
SMAW (MMA) – for site work and repairs with super duplex electrodes.
FCAW – for shop fabrication using super duplex flux-cored wires.
Autogenous welding (no filler) is generally not recommended, except on very thin material, because filler composition is critical for phase balance and corrosion resistance.
3. Filler Metal Selection
Use matching or slightly over-alloyed super duplex fillers specifically intended for S32760-type alloys.
Filler must:
Provide PREN at least equal to, preferably higher than, the base metal.
Deliver a duplex weld metal with suitable ferrite–austenite balance after cooling.
In special cases, over-alloyed austenitic fillers may be used for dissimilar joints or to maximise toughness, but weld metal strength and corrosion resistance must still meet design requirements.
4. Heat Input, Interpass Temperature and Cooling
Tight control of heat input is critical:
Too low → excess ferrite, low toughness, reduced corrosion resistance.
Too high / too slow cooling → formation of sigma and other intermetallics, serious embrittlement and loss of pitting resistance.
Typical practice (conceptually):
Keep heat input in a narrow, moderate band recommended for super duplex.
Limit interpass temperature (often quite low), and avoid heat build-up.
Allow welds to cool in still air; no water quenching.
The goal is a refined duplex microstructure in weld and HAZ with minimal harmful phases.
5. Weld Microstructure, Mechanical Properties and Corrosion Behaviour
Correctly welded S32760 joints can achieve:
High strength close to the base metal.
Good impact toughness, including transverse toughness where required.
Pitting, crevice and SCC resistance comparable to the parent plate in seawater/brine service.
Poor welding practice leads to:
Ferrite-rich or intermetallic-containing welds/HAZ with low toughness.
Markedly reduced pitting resistance, often visible as early corrosion near the welds in seawater or brine.
6. Joint Design, Shielding and Post-Weld Cleaning
Joint design:
Avoid excessive restraint and sharp stress raisers at weld toes.
Ensure good access for torch/wire and for later cleaning and inspection.
Shielding / backing:
Use high-quality shielding and back purging (typically inert gas) on root passes to prevent oxidation and loss of corrosion resistance on the inside surface.
Post-weld cleaning:
Remove slag, spatter, heat tint and oxide scale by grinding, brushing or blasting.
Use suitable pickling and/or passivation to restore a clean, chromium-rich passive film on and near welds.
7. Post-Weld Heat Treatment (PWHT)
In most cases, no PWHT is applied to S32760; properties are controlled by welding parameters, not by tempering afterwards.
Standard carbon-steel-type stress-relief cycles are not suitable and can promote intermetallics and embrittlement.
If any PWHT is specified, it must follow strict super duplex guidance from the material standard or mill; otherwise, it can severely damage toughness and corrosion resistance.
Summary
1.4501 / S32760 super duplex stainless steel is weldable, but only with carefully controlled super-duplex procedures: use appropriate super duplex fillers, keep heat input and interpass temperature within a very narrow window, ensure excellent shielding and back purging, and thoroughly clean and passivate welds to maintain the alloy’s very high strength, toughness and top-tier pitting/SCC resistance in seawater, brines and other aggressive environments.
Fabrication
Fabrication of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 is a super duplex stainless steel with very high strength and top-tier corrosion resistance. It can be fabricated successfully, but the process window is tighter than for 304/316 or even 2205, so forming, welding and heat input must be carefully controlled.
1. General Fabrication Approach
Supplied mainly in the solution-annealed and pickled condition (plate, pipe, tube, bar, forgings).
Most forming, machining and welding should be done in this condition.
Very high yield strength means:
Higher forming and cutting forces
More spring-back in bending/rolling
Planning must integrate:
Forming sequence
Weld sequence and access
Final tolerances, residual stresses and distortion control
2. Forming and Cold Working
Cold formability is lower than 304/316 and standard duplex 2205, but still adequate for:
Rolling and bending of plate and sections
Forming shells, cones, heads and moderate profiles
Good practice:
Use larger bend radii than for 304/316 to avoid edge cracking.
Form in gradual steps with smooth tools and good lubrication to reduce galling.
Expect and compensate for increased spring-back.
Heavy cold work raises strength/hardness and introduces residual stresses; for critical parts in severe environments, very high cold strain should be followed by solution annealing.
3. Hot Working and Solution Annealing in the Route
Hot working (forging, hot bending) must follow super duplex temperature limits to avoid intermetallic phases.
After significant hot work, a full solution anneal + rapid cooling is typically required to:
Restore a balanced austenite–ferrite microstructure
Recover toughness and maximum pitting/SCC resistance
Components are normally put into service in the solution-annealed condition, with no additional PWHT after correct welding.
4. Machining
Machinability is more demanding than 304/316 and 2205 because of higher strength and work-hardening.
Recommendations:
Use rigid setups and carbide tooling designed for duplex/super duplex.
Apply moderate cutting speeds and adequate feed to cut below any work-hardened layer.
Use plenty of coolant and good chip-breaking geometries.
Typical route:
Rough machining in the solution-annealed condition.
After all welding/straightening, apply light finishing cuts or grinding to reach final size and surface finish.
5. Welding as Part of Fabrication
S32760 is weldable, but welds must follow super duplex procedures (see Weldability section):
Tight control of heat input and interpass temperature.
Correct super duplex filler metals.
High-quality shielding and back purging for roots.
Normally no PWHT is used; properties are controlled by welding parameters, not post-weld tempering.
6. Surface Cleaning, Pickling and Passivation
To achieve full corrosion performance, all fabricated surfaces and welds must be properly cleaned:
Remove slag, spatter and heat tint by grinding, brushing or blasting.
Use suitable pickling (or high-quality mechanical cleaning) followed by passivation.
Aim for smooth, defect-free surfaces, especially in seawater / brine / crevice-prone areas.
Poorly cleaned or heat-tinted areas will lose a large part of the alloy’s pitting and crevice resistance advantage.
7. Distortion, Residual Stresses and Dimensional Control
High strength and lower thermal expansion than austenitics help dimensional stability, but:
Welding and heavy cold work still introduce significant residual stresses.
Practical measures:
Use balanced weld sequences and adequate fixturing.
Avoid excessive local cold straightening in critical areas.
For precision parts, plan:
Form → Weld (with super duplex WPS) → Light straighten if needed → Finish machine / grind.
Summary
1.4501 / S32760 super duplex stainless steel can be fabricated successfully when treated as a very high-strength, narrow-window duplex alloy: do forming and machining mainly in the solution-annealed state, use super-duplex-qualified welding procedures, and always finish with thorough cleaning, pickling/passivation and light final machining or grinding to preserve its balanced duplex microstructure, very high strength and exceptional corrosion performance in the most aggressive environments.
Hot Working
Hot Working of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 super duplex stainless steel can be hot worked successfully, but it has a narrow and critical temperature window. Correct hot-working practice is essential to avoid intermetallic phases and to maintain toughness and very high corrosion resistance.
1. Recommended Hot Working Temperature Range
Typical hot-working / forging range is about 1100–1250°C.
Start deformation towards the upper part of this range for best plasticity.
Do not work below roughly 1000°C – ductility drops rapidly and the risk of cracking increases.
Avoid long holds in the 800–1000°C region, where intermetallic phases (e.g. sigma) can form.
2. Heating and Forging Practice
Heat slowly and uniformly through the full section before heavy deformation.
Use substantial, well-controlled reductions per pass, not light tapping, to refine the grain structure.
Reheat when the workpiece temperature falls near the lower working limit – do not continue to work it “too cold”.
Avoid overheating or excessive soaking at maximum temperature to limit grain growth, scale formation and property loss.
3. Cooling After Hot Working and Solution Annealing
After forging or hot forming, allow the part to cool in still air down to a safe handling temperature.
For S32760, a full solution anneal after significant hot work is normally mandatory to restore optimum properties:
Reheat to the specified solution-annealing range (per mill/specification).
Soak for full through-heating.
Rapidly cool (usually water quench, or very fast air for small/thin sections).
Avoid slow cooling through the 600–1000°C range, which promotes intermetallic phase formation and embrittlement.
4. Surface Scale, Machining Allowance and Cleaning
At hot-working temperatures, super duplex develops heavy oxide scale and may suffer some surface damage.
Leave sufficient machining/grinding allowance to remove scale and any decarburised or otherwise damaged surface layer.
After hot working and solution annealing, apply:
Mechanical cleaning (grinding, blasting, brushing) and/or
Pickling and passivation
to restore a clean metallic surface and full corrosion resistance.
5. Effect on Microstructure and Properties
Correct hot working + solution annealing gives:
A fine, well-balanced austenite–ferrite (duplex) microstructure.
High yield strength with good toughness.
Maximum pitting, crevice and SCC resistance characteristic of super duplex.
Poor control (working too cold, overheating, slow cooling, long holds in mid-temperature ranges) can:
Produce coarse grains and reduced impact toughness.
Form sigma and other intermetallic phases, severely degrading toughness and localized corrosion resistance.
6. Design, Distortion and Cracking Control
Design preforms and forgings with:
Smooth transitions, generous radii and uniform section thickness where possible.
No sharp corners or abrupt thickness changes that concentrate stress during forging or cooling.
For long shafts, rings or complex shapes:
Use proper support and handling during hot work and cooling to minimise bending and distortion.
Inspect forgings for laps, folds and surface cracks before investing in final heat treatment and machining.
Summary
Hot working of 1.4501 / S32760 super duplex stainless steel must be done in a controlled 1100–1250°C range, with substantial reductions, careful reheating, followed by obligatory solution annealing and rapid cooling plus thorough cleaning, to preserve a fine duplex microstructure, very high strength, and the exceptional corrosion resistance required in its typical offshore, subsea and other highly aggressive applications.
Heat Resistance
Heat Resistance of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 is a super duplex stainless steel designed primarily for high-strength service in aggressive, chloride-containing environments at low to moderately elevated temperatures, not as a high-temperature or creep-resistant alloy.
1. Recommended Service Temperature Range
Typically used from sub-zero temperatures up to about 250–300°C in continuous service.
Within this range it retains:
Very high yield and tensile strength compared with 304/316 and even 2205
Good toughness and excellent localized-corrosion resistance
Long-term operation significantly above this range is not recommended, especially in critical corrosive service.
2. Strength and Toughness at Elevated Temperatures
As temperature increases:
Yield and tensile strength decrease, but remain high relative to standard stainless steels.
Fatigue strength drops with temperature and cyclic loading, as with all steels.
In its intended range, S32760 provides:
A very favourable strength-to-weight ratio for pressure-containing and structural components
Adequate impact toughness where fabrication and heat treatment have been properly controlled
3. Chloride Environments and SCC Behaviour at Elevated Temperature
A key advantage of super duplex S32760 is its very high resistance to chloride stress-corrosion cracking (SCC), even at elevated temperatures where 304/316 are vulnerable.
In hot seawater, warm brines and aggressive chloride process streams:
Austenitic 300-series grades may fail by SCC.
S32760 typically maintains integrity, provided design stresses and temperature remain within recommended limits.
This makes it particularly valuable in offshore, subsea, desalination and cooling-water systems operating at elevated but not extreme temperatures.
4. Microstructural Stability and Intermetallic Phases
Like all duplex and super duplex alloys, S32760 is sensitive to intermetallic phase formation (e.g. sigma, chi) and 475°C-type embrittlement if held too long in certain temperature bands.
Extended exposure in intermediate/high ranges can:
Sharply reduce impact toughness
Lower pitting and crevice-corrosion resistance
Increase susceptibility to cracking under load
For this reason, continuous long-term service at elevated temperatures is limited, and fabrication heat cycles (welding, hot working, PWHT) must be carefully controlled.
5. Oxidation and Surface Behaviour
Chromium-rich composition gives good oxidation resistance in air and combustion-type atmospheres at moderate temperatures.
Short-term higher-temperature excursions (start-up, shutdown, cleaning cycles) are typically tolerable if total exposure time is limited.
For true high-temperature or creep-critical service (e.g. furnace internals, continuous operation at very high temperatures), dedicated heat-resistant austenitic or nickel alloys are usually required instead of super duplex.
6. Design Considerations for Elevated-Temperature Service
Treat S32760 as a high-strength, corrosion-resistant alloy for moderate temperatures, not as a primary high-temperature material.
In design, you should:
Keep continuous operating temperatures within the recommended range (≈ up to 250–300°C).
Use temperature-dependent allowable stresses reflecting strength loss with temperature.
Avoid geometries and conditions that create local hot spots or prolonged exposure in intermetallic-forming temperature ranges.
Combine material selection with good surface finish, strict welding procedures and suitable inspection intervals in hot, chloride-bearing service.
Summary
1.4501 / S32760 super duplex stainless steel offers reliable heat resistance and very high strength in aggressive, chloride-containing environments at low to moderately elevated temperatures, retaining superior SCC and localized-corrosion resistance compared with 304/316 and standard duplex grades; however, it is not intended for long-term high-temperature or creep-controlled service, where intermetallic phase formation and property degradation become significant risks and dedicated heat-resistant alloys are more appropriate.
Machinability
Machinability of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 super duplex stainless steel has relatively poor machinability compared with 304/316 and even 2205, mainly because of its very high strength, work hardening and tough duplex microstructure. It can still be machined successfully, but only with rigid setups, correct tooling and carefully chosen cutting data.
1. General Machining Behaviour
Very high yield strength → high cutting forces and tool loads.
Work hardens if feeds are too light or tools are dull, making subsequent passes harder.
Chips are tough and continuous, and can be difficult to break if parameters and chip breakers are not optimised.
Overall machinability is more demanding than 304/316 and 2205, but acceptable for critical parts with proper planning.
2. Preferred Condition for Machining
Machine in the solution-annealed, pickled condition as supplied.
Avoid heavy cold work (severe forming/straightening) just before finish machining because it:
Increases surface hardness
Accelerates tool wear
Makes dimensional control more difficult
Typical route for precision parts:
Rough machine in solution-annealed condition → weld/form (if needed) → light straightening → finish machine / grind.
3. Tooling and Cutting Parameters
Use high-quality carbide tooling designed for duplex / super duplex stainless steels.
Key points:
Positive or mildly positive rake geometry to reduce cutting forces.
Rigid toolholders and fixturing to minimise chatter.
Moderate cutting speeds, generally lower than for 304/316 and 2205.
Adequate feed and depth of cut to cut below any work-hardened layer.
Avoid very light “polishing” cuts that only rub the surface and cause rapid work hardening and tool wear.
4. Coolant and Chip Control
Super duplex generates considerable heat; coolant is essential:
Use abundant, well-directed cutting fluid/emulsion at the cutting zone.
For deep holes, ensure coolant reaches the tool tip and chips are flushed out.
S32760 tends to form tough, continuous chips:
Use inserts with effective chip breakers.
Adjust feed and depth of cut to promote reliable chip breaking.
Good chip control improves tool life, surface finish and process stability, especially in CNC production.
5. Drilling, Tapping and Threading
Drilling
Use carbide or cobalt HSS drills with robust web and suitable point geometry.
Apply steady feed; avoid dwelling at the bottom to prevent work hardening.
For deep holes, use peck drilling with chip evacuation and strong coolant flow.
Tapping / Threading
Use premium, strong taps with generous lubrication and modest speed.
Expect high torque because of material strength; avoid shock loading.
For critical or large threads, thread milling is often preferable to reduce risk of tap breakage and improve control of thread fit.
6. Surface Finish and Dimensional Control
With correct tooling and parameters, S32760 can achieve high-quality turned, milled and ground finishes suitable for sealing surfaces and precision fits.
For dimensional accuracy:
Use rigid clamping and balanced machining (remove material symmetrically where possible).
Avoid local overheating during heavy cuts or grinding to prevent residual tensile stresses and minor distortion.
For slender parts, plan multiple lighter passes rather than one very heavy cut to maintain straightness.
Summary
1.4501 / S32760 super duplex stainless steel has difficult but manageable machinability: it requires rigid setups, duplex/super-duplex-rated carbide tooling, conservative cutting speeds with adequate feed, abundant coolant and good chip-breaking strategies, plus a sensible route of roughing in the solution-annealed condition and light finishing after fabrication, to achieve accurate dimensions, good tool life and high-quality surfaces on critical high-strength, corrosion-resistant components.
Corrosion Resistance
Corrosion Resistance of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 super duplex stainless steel has outstanding corrosion resistance, especially in seawater, high-chloride brines and aggressive mixed chloride/acid environments. Its Cr + Mo + N (+ often W, Cu) alloying gives it a very high pitting resistance well above 316L and 2205.
1. General Corrosion Behaviour
Excellent resistance to uniform corrosion in many industrial, marine and process environments.
Clearly superior to 304/316 and even to standard duplex grades such as 2205 in demanding chloride service.
Designed for long service life in seawater, brines and chloride-containing process streams where conventional stainless steels pit or crack.
2. Pitting and Crevice Corrosion in Chloride Media
High levels of Cr, Mo, N and often W give S32760 a very high pitting resistance (PREN well above 40).
Provides:
Excellent resistance to pitting in natural and warm seawater.
Strong resistance to crevice corrosion under gaskets, deposits and tight joints, provided designs minimise stagnant crevices.
Widely used where 316L and even 2205 cannot provide sufficient margin against localized attack in seawater and concentrated brines.
3. Chloride Stress-Corrosion Cracking (SCC)
Duplex microstructure gives very high resistance to chloride SCC, far superior to austenitic 304/316.
In hot, aerated chlorides (e.g. warm seawater, brackish process waters, chlorinated cooling water):
304/316 often suffer SCC under tensile stress.
S32760 normally remains crack-free within its recommended temperature and stress limits.
This SCC resistance is a key reason for its use in offshore, subsea, desalination and seawater-handling systems.
4. Behaviour in Chemical and Process Environments
Good resistance in many acidic, alkaline and mixed media, especially where chlorides are present:
Aggressive bleach and oxidizing environments in pulp and paper plants.
Chloride-bearing process streams in chemical and petrochemical service.
Certain acid–chloride mixtures where 316L and 2205 are at or beyond their limits.
For extremely strong mineral acids or very reducing conditions, nickel alloys or high-molybdenum super-austenitics may still be required; S32760 is optimised for chloride-dominated environments.
5. Welds, Heat-Affected Zones and Intermetallic Phases
With correct super duplex welding procedures (controlled heat input, proper filler, limited interpass temperature), weld metal and HAZ can achieve corrosion resistance close to the base metal.
Poor welding practice can:
Leave welds ferrite-rich, reducing toughness and localized-corrosion resistance.
Form sigma and other intermetallic phases in welds/HAZ, which sharply reduce pitting resistance and impact toughness.
For critical seawater/brine service, qualified WPS/PQR and strict QC around welding are essential to maintain the alloy’s corrosion performance.
6. Surface Finish, Cleaning and Design Effects
As with all stainless steels, corrosion resistance depends strongly on surface condition:
Remove weld scale, heat tint, slag and contamination by grinding or blasting.
Follow with appropriate pickling and/or passivation to restore a clean, chromium-rich passive film.
Smooth finishes (ground, brushed, polished) resist pitting and fouling better than rough or damaged surfaces.
Good design further improves performance:
Minimise crevices, dead legs and dirt traps in seawater/brine systems.
Ensure proper drainage and access for inspection and cleaning.
Use compatible materials to avoid adverse galvanic couples in wet service.
Summary
1.4501 / S32760 super duplex stainless steel offers top-tier pitting and crevice-corrosion resistance, outstanding resistance to chloride SCC and excellent overall corrosion behaviour in seawater, brines and aggressive chloride-containing process environments; when it is correctly welded, properly cleaned and sensibly detailed, it provides a very robust, long-life solution where 304/316 and even 2205 cannot deliver enough corrosion margin.
Heat Treatment
Heat Treatment of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 is a super duplex stainless steel, and like other duplex alloys it is not hardened by quenching like martensitic steels. Heat treatment is mainly used to set and restore the correct duplex microstructure and to protect toughness and corrosion resistance by avoiding harmful intermetallic phases.
1. General Heat-Treatment Behaviour
Strength comes from high alloy content + duplex (ferrite + austenite) structure, not from martensite.
The key treatment is solution annealing with rapid cooling.
Conventional low-temperature “tempering” or carbon-steel-type stress relief is not suitable and can damage properties.
Long exposure in certain intermediate temperature ranges can form sigma and other intermetallic phases, causing embrittlement and loss of corrosion resistance.
2. Solution Annealing (Primary Heat Treatment)
Purpose
Restore a balanced austenite–ferrite microstructure after hot working or heavy cold work.
Dissolve harmful precipitates and recover toughness and top-tier pitting/SCC resistance.
Typical practice (conceptual)
Heat to a high-temperature solution-annealing range (super duplex band specified by the mill/standard).
Hold long enough for full through-heating of the section.
Rapidly cool – usually water quench (or very fast air for thin products) – to freeze in the desired duplex structure and avoid intermetallic formation.
After correct solution annealing + rapid cooling, S32760 has:
Very high yield strength for a stainless steel.
Good impact toughness.
Maximum pitting, crevice and SCC resistance for this grade.
3. Stress Relief and Post-Weld Heat Treatment (PWHT)
In most applications, no PWHT is performed; properties are controlled by the welding procedure, not by tempering after welding.
Standard carbon-steel-type stress-relief cycles (long holds in mid-temperature ranges) are dangerous for super duplex:
They can cause 475 °C embrittlement and form sigma/chi phases.
This severely reduces toughness and localized-corrosion resistance.
If any stress relief or PWHT is absolutely required by a code or client, it must:
Follow super-duplex-specific limits from the material standard or mill.
Be applied with strict control of temperature and time.
In practice, most components are used as-welded in the solution-annealed condition, with careful welding and thorough cleaning instead of PWHT.
4. Effect of Heat Treatment on Microstructure and Properties
Correct solution annealing + rapid cooling:
Produces a fine, balanced duplex structure.
Delivers very high strength with good toughness.
Restores maximum resistance to pitting, crevice corrosion and SCC.
Incorrect heat exposure (overheating, long holds, slow cooling in the 600–1000 °C range):
Promotes sigma and other intermetallic phases.
Causes sharp drops in impact toughness.
Reduces resistance to localized corrosion, especially in seawater and brine.
Repeated uncontrolled heat cycles do not increase strength and can only damage the alloy’s mechanical and corrosion performance.
5. Practical Heat-Treatment Route in Fabrication
Typical route for critical S32760 parts:
Supply from mill in solution-annealed and pickled condition.
Hot working / heavy forming (if required) → followed by solution annealing + rapid cooling.
Cold forming, machining and welding with super-duplex procedures in the solution-annealed state.
No PWHT, only:
Proper weld procedure control (heat input, interpass, filler).
Thorough post-weld cleaning, pickling and passivation to restore a clean passive surface.
Summary
For 1.4501 / S32760 super duplex stainless steel, heat treatment is centred on high-temperature solution annealing followed by rapid cooling to obtain a fine, balanced duplex microstructure with very high strength and maximum corrosion resistance; routine stress relief or tempering cycles are avoided, and prolonged exposure in intermetallic-forming temperature ranges must be strictly prevented to keep toughness and pitting/SCC resistance at super-duplex levels.
Cold Working
Cold Working of 1.4501 / S32760 Super Duplex Stainless Steel
1.4501 / S32760 is a super duplex stainless steel with very high strength and limited ductility compared with 304/316 and even 2205. It can be cold worked, but only with sensible forming limits, generous radii and good process control.
1. General Cold Workability
Much higher yield strength and lower ductility than austenitic 304/316.
Cold work is more restricted than for 2205:
Suitable for moderate bending, rolling and profiling.
Not ideal for very severe deep drawing or tight-radius bends in thick sections.
Expect significantly higher forming loads and more spring-back.
2. Bending, Rolling and Forming Practice
Use larger minimum bend radii than for 304/316 and 2205 to avoid edge cracking.
Form in multiple, gradual steps rather than one heavy hit, especially on thicker plate.
Use:
Smooth, well-polished tools
Generous lubrication to reduce friction and galling
Good alignment and support to avoid local over-strain
Always allow for extra spring-back in tooling angles and roll settings.
3. Work Hardening and Residual Stresses
S32760 work hardens strongly during cold deformation:
Deformed areas become harder, stronger and less ductile.
High residual stresses are introduced, which can affect fatigue and corrosion performance.
Heavy cold work may:
Make subsequent machining noticeably more difficult.
Increase distortion risk during and after welding.
For critical components in severe seawater or brine service, avoid very high local strain in highly stressed regions.
4. Heavy Cold Work and Solution Annealing
For light to moderate forming (typical bends, rolling shells, cones, simple profiles):
Parts are often used without further heat treatment, provided welding procedures and cleaning are correct.
For severe cold work, for example:
Tight-radius bends on thick plate
Heavy cold reduction in thickness or diameter
Large-area stretch forming or deep drawing
a full solution anneal + rapid cooling is normally recommended to:Restore a proper austenite–ferrite balance
Recover toughness and maximize pitting / crevice / SCC resistance
Remove the hard, highly strained structure created by heavy cold work.
5. Interaction with Welding and Machining
Cold-worked zones:
Are more susceptible to distortion when welded due to stored strain energy.
May respond differently in the heat-affected zone if heavily work-hardened.
Practical sequence for precision/critical parts:
Form → Weld (with super duplex procedure) → Light straightening if needed → Finish machine / grind.This keeps cold strain moderate before welding and ensures final dimensional accuracy and surface quality.
6. Design Recommendations for Cold-Worked S32760 Components
Assume very high forming forces and ensure presses/rolls are capable.
Avoid:
Sharp corners and very tight radii in highly loaded or seawater-exposed zones.
Local necking or severe thinning in critical areas.
For demanding offshore, subsea or desalination service:
Keep cold strain moderate and well distributed, not concentrated.
Consider solution annealing after extreme forming steps if maximum toughness and corrosion resistance are required.
Summary
Cold working of 1.4501 / S32760 super duplex stainless steel is possible but must be treated as high-strength, limited-ductility forming: use generous radii, gradual forming with good lubrication, expect high forming forces and spring-back, keep strains moderate in critical areas, and apply solution annealing after very heavy cold work to restore a balanced duplex microstructure and top-level toughness and corrosion resistance for severe seawater and high-chloride service.
