Stainless Steel Fabrication requires a more delicate and complicated skills compared to Carbon Steel.

Novelty Steel is an experienced stainless steel fabricator with its manufacturing facilities located in Turkey.

1. Fabrication of Stainless Steel

Stainless steels require care during fabrication. They are sensitive to thermal and mechanical operations, the control of which is complicated by the varying effects of different chemical combinations. To obtain the best results purchasers normally consult with the steel producer regarding the working, machining, heat treating and other operations to be employed in fabrication.

Stainless steels can be readily fabricated by conventional manufacturing methods, but heir fabrication characteristics are different from those of the carbon and alloy steels. Among the most important differences which must be recognized are the relatively high hot strengths of these alloy steels, which affect forging, the high toughness and work hardening rates of some types, which affect machining and cold forming, and the high thermal expansion of the austenitic types, which affects weldment distortion.

The two most common fabrication deficiencies which affect later service are;

• Surface contamination with carbon and alloy steels
• Improper post fabrication cleaning.

Stainless steels must have clean surfaces to provide optimum corrosion resistance. It is important to note than even minor, invisible contamination from non-stainless steels can later cause unsightly staining when exposed to moisture, and often may lead to more serious corrosion.

Such contamination can come from high pressure contact with low alloy steels, from wire brushing with non-stainless brushes, from grinding with wheels previously used for carbon steels or even from airborne particles in a shop which also fabricates carbon steel.

Contamination of stainless steel surfaces can be minimized by utilizing careful procedures, including use of covered or plated dies and corrosion resisting handling equipment, but complete prevention of contamination is very difficult in shops which fabricate a variety of non-stainless metals. It is often the best practice to provide for an acid treatment to remove any contaminating particles after fabrication when staining or corrosion in service cannot be accepted.

Post fabrication cleaning may be necessary for three basic purposes:

• To remove oxide scale resulting from welding hot working or heat treatment operations
•  To remove contaminating metallic particles
•  To remove general shop soils.

Oxide scales are most frequently removed by mechanical means (wire brushing with a stainless steel brush or blasting with clean sand or aluminium oxide grit) or by acid descaling (pickling). For faster descaling, pickling may be preceded by mechanical descaling.

Grease, oil, lubricants, paint and other soils may be removed from stainless steels by alkaline cleaners, emulsion or solvent cleaners, vapour degreasing or other suitable means, as described in the standards. Such cleaning may be required before processing steps, such as heat treatment or acid descaling, or as a final cleaning to prevent product contamination. Cleaning solutions containing chlorine or chlorides should be avoided, or used only with extreme caution. There are documented cases of serious service failures which resulted from cleaning with chloride-containing solutions.

The trend to use of clean-in-place systems is favourable if cleaning is done with good control, especially of the final rinsing operation. Failure to rinse thoroughly can lead to severe corrosion damage.

2. Forming of Stainless Steel

Stainless steels, especially austenitic grades, can be fabricated using standard techniques. They are capable of being

• Folded
• Bent
• Cold and hot forged
• Deep drawn
• Spun
• Roll formed.

Despite requiring more force than carbon steels due to high strength and work hardening rates, they are highly ductile.

Austenitic stainless steels can undergo heavy cold forming, making them suitable for various applications.

• Work Hardening
  • Austenitic stainless steels can only be strengthened through work hardening.
  • Martensitic stainless steels can be hardened via quench-and-temper treatment, similar to carbon steels.
  • Ferritic stainless steels harden solely through cold working, but their rates are low compared to austenitic grades.
• Cold Working Properties
  • Austenitic grades like 301, 302, and 304 can achieve high tensile properties through cold drawing.
  • Tensile properties in larger sections become impractical due to surface hardening.
  • Higher work hardening rates in austenitic grades result in higher magnetic permeability.
  • Ferritic and martensitic alloys have limited cold working capabilities, with martensitic grades commonly heat treated for optimization.
• Effect of Temperature
  • Work hardening decreases at higher temperatures, resulting in reduced strength and increased ductility.
  • This characteristic is utilized in certain applications such as deep drawing and warm heading.
• Forming Speed
  • More severe deformation is possible at slower forming speeds for stainless steels, unlike carbon steels.
  • Stainless steel processing is generally slower compared to carbon steel, suggesting the need to slow down for challenging forming operations.

3. Heat treatment of Stainless Steel

Stainless steels are rarely placed in service in the hot rolled or forged condition. Annealing or other forms of heat treatment are desirable to obtain the full advantages of the corrosion resistance and mechanical properties of the steels. Standard heat treating equipment may generally be used.

The 4xx series of Ferritic and martensitic stainless steels are annealed by heating to above the critical temperature followed by slow cooling below this temperature to obtain minimum hardness and maximum ductility. These steels can also be annealed by an isothermal heat treatment below the critical temperature.

Some steels of the 4xx series may be hardened by heating to above the critical temperature and rapidly cooling. This hardening operation is generally followed by a tempering or stress relieving treatment.

The 2xx and 3xx series of austenitic stainless steels are annealed by heating to a temperature sufficiently high to put the carbides into solution and rapidly cooling from that temperature to retain the carbides in solution. The austenitic types when maintained at the temperature range of 425 to 900C may cause the precipitation of chromium carbides, as a separate phase, in the grain boundaries. Associated with such carbide precipitation is a severe loss of corrosion resistance in some corrosive media.

4. Cleaning and maintenance of Stainless Steel

Routine cleaning and maintenance of stainless steel is often necessary to maintain corrosion resistance and appearance. Frequent cleaning on a routine scheduled basis is recommended to prevent initiation of crevice corrosion under deposits and hardening of deposits. Accumulated materials while fresh and soft can often be easily removed by flushing with steam, hot water or warm detergent solution. A sponge, fiber brush or cloth can assist in the removal of residues from low temperature operation. More resistant deposits, such as food residues, may require scouring with abrasive cleaning powder or fine stainless steel wool. Common steel wool, scouring pads, scrapers, wire brushes and other steel tools should never be used to clean stainless steel, because they can leave embedded iron particles which will eventually rust and stain the surface.

When stainless steel equipment is cleaned or sterilized, particular attention should be given to agents containing chlorine compounds. These compounds may decompose and release free chlorine.

5. Frequently used Stainless Steel Grades

5.1 Grade 304 (L)

UNS NO : S30400 (S30403) Euronorm : 1.4301 ( 1.4307)

Grade 304 is the most widely used austenitic, chromium-nickel stainless steel. Its corrosion resistance is somewhat higher than that of Type 302. It is essentially nonmagnetic when annealed and can become slightly magnetic when cold worked. The alloy has excellent fabricability and weldability.

This alloy serves a wide range of applications. It resists rusting in architectural applications. It is resistan to food processing environments, except for high-temperature conditions involving high acid and chloride contents and it resists organic chemicals and a wide variety of inorganic chemicals.

Type 304H is a modification of Type 304 in which the carbon content is controlled to a range of 0.04 to 0.10 to provide improved high temperature strength to parts exposed to temperatures above 425C

Corrosion Resistance of Grade 304

• 304 has excellent corrosion resistance in various environments and when in contact with different corrosive media.
• Pitting and crevice corrosion can occur in environments containing chlorides.
• Stress corrosion cracking can occur above 60°C.

Heat Resistance of Grade 304

• 304 has good resistance to oxidation in intermittent service up to 870°C and in continuous service to 925°C.
• For continuous use at 425- 860°C, 304L is recommended due to its resistance to carbide precipitation.
• Where high strength is required at temperatures above 500°C and up to 800°C grade 304H is recommended. This material will retain aqueous corrosion resistance.

Fabrication

• Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials.
• Tooling and work surfaces must be thoroughly cleaned before use.
• These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Machinability

• 304 has good machinability.
• During the machining cutting edges must be kept sharp. Dull edges cause excess work hardening.
• Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material.
• Chip breakers should be employed to assist in ensuring swarf remains clear of the work.
• Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities.

Welding

• Fusion welding performance for type 304 stainless steel is excellent both with and without fillers.
• Recommended filler rods and electrodes for stainless steel 304 is grade 308 stainless steel.
• For 304L the recommended filler is 308L.
• Heavy welded sections may require post-weld annealing.

5.2 Grade 303

UNS NO : S30300 Euronorm : 1.4305

Grade 303 stands out as the most easily machinable among all austenitic stainless steel grades, owing to the inclusion of Sulphur in its composition. While Sulphur enhances machinability, it concurrently diminishes corrosion resistance and marginally reduces toughness. In comparison to grade 304, the corrosion resistance of type 303 is inferior. However, its toughness remains superior, similar to other austenitic grades.

Corrosion Resistance

The addition of Sulphur to the composition serves as points of initiation for pitting corrosion. This consequently reduces the corrosion resistance of 303 stainless steel compared to 304. Nonetheless, its corrosion resistance remains satisfactory in mild environments.

In chloride-rich environments exceeding 60°C, 303 stainless steel is vulnerable to pitting and crevice corrosion. Therefore, it is unsuitable for applications in marine environments.

Heat Resistance

303 stainless steel demonstrates commendable resistance to oxidation when subjected to intermittent temperatures up to 760°C. Additionally, it maintains good oxidation resistance when continuously utilized up to 870°C. However, it’s important to note that continuous use within the range of 425-860°C is not advised due to the susceptibility of 303 stainless steel to carbide precipitation.

Fabrication

• Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials.
• Tooling and work surfaces must be thoroughly cleaned before use.
• These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Welding

The inclusion of Sulphur in 303 stainless steel leads to subpar weldability. In instances where welding is necessary, it is recommended to utilize filler rods or electrodes made of grades 308L and 309 stainless steels. To ensure optimal corrosion resistance, it is essential to anneal the welds.

5.3 Grade 316

UNS NO : S31600 Euronorm : 1.4401

Grade 316 holds the second position, following 304, in terms of commercial significance among austenitic grades.

The addition of molybdenum in 316 stainless steel enhances its corrosion resistance, particularly evident in combating pitting and crevice corrosion in chloride-rich environments.

316L, being the low carbon version of 316 stainless steel, is resistant to sensitization caused by grain boundary carbide precipitation, making it suitable for heavy gauge welded components, typically over 6mm thick.

For applications involving high temperatures, it is recommended to use either the high carbon variant, 316H stainless steel, or the stabilized grade 316Ti stainless steel.

The austenitic structure of 316 stainless steel ensures excellent toughness, even at extremely low temperatures.

Stainless steel grade 316Ti contains a small proportion of titanium, typically around 0.5%. Titanium atoms serve to stabilize the structure of 316 at temperatures exceeding 800°C, thereby preventing carbide precipitation along grain boundaries and safeguarding the metal against corrosion.

The primary advantage of 316Ti lies in its ability to withstand higher temperatures for extended durations without experiencing sensitization (precipitation). Moreover, 316Ti maintains physical and mechanical properties akin to standard grades of 316.

Corrosion Resistance

Grade 316 stainless steel showcases outstanding corrosion resistance when confronted with various corrosive environments and substances. Often labeled as “marine grade” stainless steel, it should be noted that it is not resistant to warm sea water. Exposure to warm chloride environments can lead to pitting and crevice corrosion in Grade 316. Moreover, Grade 316 is susceptible to stress corrosion cracking when temperatures exceed approximately 60°C.

Heat Resistance

Grade 316 exhibits commendable resistance to oxidation, capable of intermittent service up to 870°C and continuous service up to 925°C. Nonetheless, prolonged utilization within the range of 425-860°C is discouraged, especially if maintaining corrosion resistance in water is essential. In such cases, Grade 316L is preferred due to its resistance to carbide precipitation.

For applications necessitating high strength at temperatures surpassing 500°C, Grade 316H is recommended.

Fabrication

• Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials.
• Tooling and work surfaces must be thoroughly cleaned before use.
• These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Welding

The fusion welding performance of 316 stainless steel is exceptional, whether with or without fillers. Recommended filler rods and electrodes for both 316 and 316L are identical to the base metal, namely 316 and 316L, respectively. In some cases, post-weld annealing may be necessary for heavy welded sections. Grade 316Ti can serve as an alternative to 316 for heavy section welds.

However, oxyacetylene welding has not proven to be effective for joining 316 stainless steel.

5.4 Grade 321

UNS NO : S32100 Euronorm : 1.4541

Stainless steel 321 is a stabilized version of stainless steel 304. It combines an 18/8 blend of chromium and nickel with titanium to guard against intergranular corrosion following heat treatment. This alloy is designed to withstand temperatures ranging from 800 to 1500°F and exhibits high strength and resistance to various forms of corrosion, including aqueous environments.

Type 321 is commonly used in heavy welding components and dynamic environments subjected to fluctuations.

However, the inclusion of titanium imposes limitations on certain fabrication methods, as it renders the metal non-consumable for certain welding techniques. Despite this drawback, stainless steel 321 boasts excellent formability, eliminates the need for post-weld annealing, and maintains toughness across a wide temperature range.

The alloy retains its strength even when exposed to cryogenic temperatures and is often preferred over Type 304 for its enhanced resistance to creep and rupture. However, both alloys may be susceptible to stress corrosion cracking.

Corrosion Resistance

321 stainless steel (1.4541) demonstrates excellent corrosion resistance under normal temperatures but is primarily engineered for high-temperature performance. The significant titanium content, at least five times the carbon percentage (maximum 0.7%), imparts grade 321 with exceptional creep strength, resistance to chromium carbide precipitation, and robust resistance to oxidation and intergranular corrosion up to 850°C under dry air service conditions. However, exposure to other corrosive compounds such as water and sulfur compounds in hot atmospheres can notably reduce the maximum service temperature.

The overall characteristics of this material make it an outstanding and relatively cost-effective choice for numerous applications. Nonetheless, it is susceptible to pitting and crevice corrosion in warm chloride environments, as well as stress corrosion cracking above approximately 60°C. It is generally deemed resistant to potable water with chloride levels up to around 200 mg/L at ambient temperatures, decreasing to about 150 mg/L at 60°C.

Heat Resistance

These grades exhibit excellent oxidation resistance, capable of intermittent service up to 900°C and continuous service up to 925°C. They perform admirably within the 425-900°C range, especially in scenarios where subsequent aqueous corrosive conditions are encountered.

321H, distinguished by higher hot strength, is particularly well-suited for high-temperature structural applications.

Fabrication

• Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials.
• Tooling and work surfaces must be thoroughly cleaned before use.
• These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Welding

321 stainless steel exhibits excellent weldability through all standard fusion methods, whether with or without filler metals. AS 1554.6 pre-qualifies welding of 321 and 347 using Grade 347 rods or electrodes. Additionally, a high silicon version of 347 is also pre-qualified for welding of 321. Notably, a post-weld heat treatment is not required for this process.

5.5 Grade 310

UNS NO : S31000 Euronorm : 1.4845

Grade 310 Stainless Steel is categorized as an austenitic stainless steel renowned for its outstanding high temperature properties, coupled with commendable ductility and weldability. It finds prevalent use in elevated temperature applications owing to its elevated chromium and nickel content, which confer robust corrosion resistance, exceptional resistance to oxidation, and superior strength even at temperatures reaching up to 2100°F. Its high chromium and nickel content render it superior to both 304 and 309 stainless steel in most environments.

Corrosion Resistance

Grade 310 stainless steel offers excellent corrosion resistance, facilitated by its high chromium content, which enables robust resistance to aqueous corrosion. It exhibits exceptional resistance at normal temperatures and maintains good resistance even in oxidizing and carburizing atmospheres.

Heat Resistance

Grade 310 stainless steel demonstrates good resistance to oxidation, capable of intermittent service in air at temperatures up to 1040°C and continuous service up to 1150°C. It also exhibits resilience against thermal fatigue and cyclic heating. This alloy finds widespread application in environments where sulphur dioxide gas is present at elevated temperatures.

However, continuous use within the range of 425-860°C is not advisable due to potential carbide precipitation, especially if subsequent aqueous corrosion resistance is required. Typically, Grade 310 is utilized at temperatures starting from about 800 or 900°C, surpassing the effectiveness of both 304H and 321 stainless steel at higher temperatures.

Fabrication

Grade 310 stainless steel is widely utilized in the heat treatment and process industries due to its suitability for high temperatures and corrosive environments. It is frequently fabricated into intricate structures and can be easily roller-formed, stamped, and drawn. However, it is important to note that Grade 310 tends to work harden, so any severe forming operations should be followed by an annealing process to relieve stress and restore ductility.

Welding

Austenitic stainless steel is commonly acknowledged for its weldability. It is generally regarded to have weldability on par with that of 304 and 304L stainless steel grades. However, special attention should be given to compensate for its higher coefficient of thermal expansion to prevent warping and distortion during welding processes.

5.6 Grade 253 Ma

UNS NO : S31000 Euronorm : 1.4835

253MA is a grade renowned for its exceptional performance at high temperatures while maintaining ease of fabrication. It withstands oxidation at temperatures up to 1150°C and can outperform Grade 310 in atmospheres containing carbon, nitrogen, and sulphur.

One of the advantages of 253MA is its relatively low nickel content, which makes it more effective in reducing sulphide atmospheres compared to high nickel alloys and Grade 310. Additionally, the high silicon, nitrogen, and cerium contents contribute to the steel’s oxide stability, elevated temperature strength, and resistance to sigma phase precipitation.

Thanks to its austenitic structure, this grade exhibits excellent toughness, even at cryogenic temperatures.

Corrosion Resistance

While not specifically engineered for aqueous corrosion resistance, the high chromium and nitrogen content in 253MA endows the grade with pitting resistance comparable to that of 316 stainless steel. However, it’s crucial to note that 253MA contains a high carbon content, rendering it highly susceptible to sensitization from both welding and service exposure.

Heat Resistance

253MA exhibits high strength at elevated temperatures, making it a preferred choice for structural and pressure-containing applications operating at temperatures above approximately 500°C and up to about 900°C. Its strength at these elevated temperatures surpasses that of alternatives like Grade 310.

However, it’s important to note that 253MA is susceptible to sensitization within the temperature range of 425-860°C. While this isn’t typically an issue for high-temperature applications, it can lead to reduced aqueous corrosion resistance.

Fabrication

Stainless steel 253 MA can be easily fabricated using standard commercial procedures. When compared to carbon steel, stainless steels are tougher and have a tendency to work harden quickly. However, this tendency can be minimized by employing positive feeds and slow speeds, along with ample cutting fluid during the fabrication process.

Welding

253MA demonstrates excellent weldability with all standard fusion methods, utilizing matching filler metals. AS 1554.6 pre-qualifies welding of 253MA with Grade 22.12HT rods or electrodes. Alternatively, Grade 309 fillers can be employed if lower creep strength is acceptable. It is recommended to use pure argon shielding gas during the welding process.

5.7 Grade 904L

UNS NO : N08904 Euronorm : 1.4539

Grade 904L stainless steel is classified as a non-stabilized austenitic stainless steel with a low carbon content. This high-alloy stainless steel is enriched with copper to enhance its resistance to strong reducing acids, such as sulphuric acid. Additionally, it boasts resistance to stress corrosion cracking and crevice corrosion. Notably, Grade 904L is non-magnetic and offers excellent formability, toughness, and weldability.

However, it’s worth noting that Grade 904L contains high levels of costly elements like molybdenum and nickel. Consequently, many applications that historically utilized Grade 904L have transitioned to low-cost duplex stainless steel 2205.

Corrosion Resistance

Grade 904L stainless steels exhibit outstanding resistance to warm seawater and chloride attack. The exceptional resistance of grade 904L to stress corrosion cracking is attributed to its high nickel content. Furthermore, the addition of copper enhances resistance to sulphuric acid and other reducing agents, both in aggressive and mild conditions.

The corrosion resistance of grade 904L falls between super austenitic grades with a 6% molybdenum content and standard 316L austenitic grades. However, it is less resistant to nitric acid compared to grades 304L and 310L, which lack molybdenum. To achieve maximum stress corrosion cracking resistance in critical environments, grade 904L requires solution treatment after cold working.

Heat Resistance

Grade 904L stainless steels provide good oxidation resistance. However, it’s important to note that the structural stability of this grade deteriorates at elevated temperatures, especially beyond 400°C.

Fabrication

Grade 904L stainless steels are characterized by high purity and low sulphur content, making them suitable for machining using standard methods. These grades can be easily bent to a small radius under cold conditions. While subsequent annealing is generally unnecessary, it should be considered when fabrication occurs under severe stress corrosion cracking conditions.

Welding

Welding of grade 904L stainless steels can be carried out using all conventional methods. Pre-heat and post-weld heat treatments are not necessary for this grade. However, it’s important to note that grade 904L may be prone to hot cracking in constrained weldments. Grade 904L electrodes and rods are typically employed for welding grade 904L steels in accordance with AS 1554.6 standards.

6. Duplex Stainless Steels

Duplex stainless steels are highly corrosion-resistant and work-hardenable alloys. They typically contain elevated levels of chromium, ranging from 18% to 28%, and lower to moderate amounts of nickel, varying between 1.5% and 8%. The remarkable corrosion resistance and superior mechanical properties of duplex stainless steels stem from their chemical composition and balanced microstructure, which comprises approximately equal volume percentages of ferrite and austenite. This duplex nature imbues duplex stainless steels with properties characteristic of both austenitic and ferritic stainless steels.

Due to their duplex structure, duplex stainless steels are generally tougher than ferritic stainless steels. In some instances, the strength of duplex stainless steels can be double that of austenitic stainless steels.

6.1 Advantages of Duplex Steels

• Duplex Stainless Steels offer advantageous traits from ferritic and austenitic material such as elevated strength and commendable corrosion resistance.
• Their elevated chromium, molybdenum, and nitrogen contents, coupled with a duplex structure, confer numerous advantages over 300 series austenitic grades.
• Strength is notably heightened, approximately twice that of austenitics.
• They exhibit higher resistance to pitting and crevice corrosion.
• Exceptional resistance to stress-corrosion cracking.
• Demonstrates good erosion and fatigue resistance.
• Weldability is satisfactory, accompanied by enhanced heat transfer capabilities.
• Pricing stability is ensured due to lower nickel levels compared to austenitic stainless grades.

6.2 Common Applications of Duplex Steels

• Pressure vessels, reactor tanks and heat exchangers
• Desalination plants and seawater systems
• Water transmission pipes
• Rotors, impellers and shafts in industrial equipment
• Stock washers and other equipment for the pulp and paper industry
• Absorber towers, FGD systems for air pollution control
• Phosphoric acid production
• Food, oil and gas, mining and architectural applications
• Biofuels plants
• Pulp and Paper industry

6.3 Corrosion Resistance of Duplex Steels

Duplex stainless steels demonstrate a high level of corrosion resistance in most environments where standard austenitic grades are utilized. However, there are specific cases where they exhibit notably superior performance. This is primarily attributed to their elevated chromium content, which is advantageous in oxidizing acids, combined with sufficient levels of molybdenum and nickel to offer resistance in mildly reducing acid environments. Additionally, the relatively high chromium, molybdenum, and nitrogen content provide excellent resistance to chloride-induced pitting and crevice corrosion.

The duplex structure of these steels is advantageous in environments prone to chloride stress corrosion cracking. If the microstructure contains at least 30% ferrite, duplex stainless steels exhibit significantly greater resistance to chloride stress corrosion cracking than austenitic stainless steel Types 304 or 316. However, it’s important to note that ferrite is susceptible to hydrogen embrittlement. Consequently, duplex stainless steels may not exhibit high resistance in environments or applications where hydrogen can permeate the metal and cause hydrogen embrittlement.

6.4 Fabricating Duplex Steels

The processes commonly used to cut austenitic stainless steels and carbon steels can generally be applied to duplex stainless steels as well. However, adjustments in parameters may be necessary to accommodate the differences in mechanical properties and thermal response of duplex stainless steels. These adjustments help ensure optimal cutting performance and quality when working with duplex stainless steels.

• Sawing: Cutting duplex stainless steels requires adjustments in parameters due to their high strength, work hardening rate, and absence of chip-breakers. This includes using powerful machines, coarse-toothed blades, slow-to-moderate cutting speeds, heavy feeds, and generous coolant flow. Cutting speeds and feeds should be similar to those for austenitic stainless steel.
• Shearing: Shearing duplex stainless steels typically doesn’t require special adjustments, but due to their greater shear strength, the power of the shear must be increased or the sheared thickness reduced compared to austenitic stainless steels.
• Slitting: Coil slitting of duplex stainless steel requires conventional equipment, but maintaining slit edge quality is more challenging due to higher strength. Carbide or tool steel slitter knives are recommended.
• Punching: Punching duplex stainless steels is difficult due to their high strength, rapid work hardening, and resistance to tearing. It’s suggested to treat them as if they were twice the thickness of austenitic stainless steel.
• Plasma and Laser Cutting: Duplex stainless steels can be processed using standard plasma and CNC laser cutting equipment with minimal adjustments. The higher thermal conductivity and low sulphur content may marginally affect optimal parameters. The Heat Affected Zone (HAZ) from plasma cutting is narrow and can be removed during normal machining or welding preparation.
• Machining: Duplex stainless steels typically boast yield strengths approximately twice that of non-nitrogen alloyed austenitic grades, and their initial work hardening rate is generally comparable to that of common austenitic grades. However, the chips formed during machining duplex stainless steel are strong and abrasive to tooling, particularly for the more highly alloyed duplex grades. Additionally, because duplex stainless steels are produced with minimal sulfur content, there is little aid for chip breaking. Due to these factors, duplex stainless steels are typically more challenging to machine compared to 300-series austenitic stainless steels with similar corrosion resistance. Machining duplex stainless steels requires higher cutting forces, and more rapid tool wear is typical. This increased difficulty in machinability, especially noticeable when using carbide tooling, underscores the need for careful consideration and adjustments during machining operations.

6.5 Welding Duplex Steels

When encountering welding issues with austenitic stainless steels, the problems often stem from the weld metal itself, particularly the propensity for hot cracking during fully or predominantly austenitic solidification. For common austenitic stainless steels, adjusting the composition of the filler metal to introduce a significant ferrite content helps minimize these issues. However, for highly alloyed austenitic stainless steels where the use of a nickel-base filler metal is necessary and austenitic solidification cannot be avoided, the problem is managed by employing low heat input, often requiring multiple passes to build up the weld.

In contrast, duplex stainless steels exhibit very good resistance to hot cracking due to their high ferrite content, making hot cracking rarely a concern when welding these steels. Instead, the primary concerns with duplex stainless steels lie in the heat-affected zone (HAZ), rather than the weld metal itself. HAZ issues can include loss of corrosion resistance, toughness, or post-weld cracking. To mitigate these problems, welding procedures should prioritize minimizing the total time spent at temperature in the “red hot” range, rather than focusing solely on managing heat input for individual passes. Experience has demonstrated that this approach can lead to welding procedures that are both technically and economically optimal.

 

» Novelty Steel is an experienced stainless steel fabricator based in Turkey. Contact us at info@noveltystructures.com for your inquiries.