1. Panimula
Welding stainless steels is routine in industry, but the how matters: every stainless group (austenitic, ferritic, duplex, martensitic, precipitation-hardening, and high-alloy grades) brings distinct metallurgical behaviours that determine process choice, filler alloy, input ng init, pre/post-treatment, and inspection regimes.
With correct process selection and controls—shielding gas, input ng init, filler match, interpass temperature and appropriate post-weld cleaning—most grades can be welded to deliver reliable strength and corrosion resistance.
Misapplied practices, gayunpaman, lead to hot cracking, sensitization, embrittlement or unacceptable corrosion performance.
2. Why Weldability Matters for Stainless Steels
Hindi kinakalawang na asero’s value lies in its unique dual promise: paglaban sa kaagnasan (from its chromium-rich oxide layer) and structural reliability (from its tailored mechanical properties).
In industries such as oil & gas, pagbuo ng kapangyarihan, pagproseso ng kemikal, konstruksiyon, and food equipment, the majority of stainless components require welding during fabrication, pag-install, or repair.
Weldability is not merely a “manufacturing convenience”—it is the linchpin that ensures this promise holds true in welded components.
Poor weldability undermines stainless steel’s core functions, leading to catastrophic failures, excessive costs, and non-compliance with industry standards.
3. Key Metallurgical Foundations of Stainless Steel Weldability
The weldability of stainless steel is fundamentally controlled by their komposisyon ng kemikal at istraktura ng kristal.
Alloying elements not only define corrosion resistance but also govern how stainless steels behave under the thermal cycles of welding.
Impluwensya ng Mga Elemento ng Alloying
| Elemento ng haluang metal | Role in Base Metal | Impact on Weldability |
| Chromium (Cr, 10.5–30%) | Forms passive Cr₂O₃ film for corrosion resistance. | High Cr increases hot cracking risk; Cr carbide (Cr₂₃C₆) precipitation causes sensitization if C > 0.03%. |
| Nikel (Ni, 0–25%) | Nagpapatatag ng austenite (Nagpapabuti ng ductility, tigas na tigas). | High Ni (>20%, hal., 310S) increases hot cracking risk; low Ni in ferritics reduces ductility in the HAZ. |
| Molibdenum (Mo, 0–6%) | Enhances pitting resistance (raises PREN values). | No direct weldability issues; maintains corrosion resistance if heat input is controlled. |
| Carbon (C, 0.01–1.2%) | Strengthens martensitic steels; affects sensitization. | >0.03% in austenitic → carbide precipitation and intergranular corrosion; >0.1% in martensitic → cold cracking risk. |
| Titanium (Ti) / Niobiyum (Nb) | Forms stable TiC/NbC instead of Cr₂₃C₆, Pag-iwas sa Sensitization. | Improves weldability of stabilized grades (hal., 321, 347); reduces HAZ degradation. |
| Nitrogen (N, 0.01–0.25%) | Strengthens austenite and duplex phases; increases pitting resistance. | Helps control ferrite balance in duplex welds; excess N (>0.25%) may cause porosity. |
Crystal Structures and Their Influence
- Austenite (FCC): Mataas na tigas, magandang ductility, at mahusay na weldability. Gayunpaman, fully austenitic compositions are prone to mainit na pag-crack due to their low solidification range.
- Ferrite (BCC): Good resistance to hot cracking but limited ductility and toughness in the heat-affected zone (HAZ). Grain growth during welding can embrittle ferritic steels.
- Martensite (BCT): Very hard and brittle, especially if high carbon is present. Welding tends to create cracks unless preheating and post-weld heat treatments are applied.
- Duplex (mixed FCC + BCC): The combination of ferrite and austenite offers both strength and corrosion resistance, but precise heat input control is critical to maintain the ~50/50 phase balance.
4. Weldability of Austenitic Stainless Steels (300 Serye)
Austenitic stainless steels—especially the 300 serye ng mga (304, 304L, 316, 316L, 321, 347)—are the most widely used stainless steels due to their mahusay na paglaban sa kaagnasan, ductility, at tigas na tigas.
They are generally the most weldable stainless family, explaining their widespread use in pagproseso ng pagkain, mga halaman ng kemikal, langis & gas, marine, and cryogenic applications.
Gayunpaman, ang kanilang fully austenitic crystal structure at high thermal expansion bring specific welding challenges that require careful control.
Key Weldability Challenges
| Hamon | Paliwanag | Mga Diskarte sa Pagpapagaan |
| Mainit na Pag-crack | Fully austenitic solidification (A-mode) creates susceptibility to solidification cracking in weld metal. | Use filler metals with small ferrite content (ER308L, ER316L); control weld pool solidification rate. |
| Pagpapadama ng Sensitization (Pag-ulan ng karbid) | Cr₂₃C₆ forms at grain boundaries between 450–850 °C if carbon >0.03%, Pagbabawas ng paglaban sa kaagnasan. | Use low-carbon grades (304L, 316L) or stabilized grades (321, 347); limit interpass temperature ≤150–200 °C. |
| Pagbaluktot & Natitirang Stress | Austenitic steels expand ~50% more than carbon steels; low thermal conductivity concentrates heat. | Balanced welding sequences, proper fixturing, low heat input. |
| Porosity | Nitrogen absorption or contamination in the weld pool may form gas pockets. | High-purity shielding gases (Ar, Ar + O Reduxine); prevent N₂ contamination. |
Welding Consumables & Filler Selection
- Common filler metals: ER308L (for 304/304L), ER316L (for 316/316L), ER347 (para sa 321/347).
- Ferrite balance: Ideal FN (ferrite number) in weld metal: 3–10 to reduce hot cracking.
- Shielding gases: Argon, or Ar + 1–2% O₂; Ar + He blends improve penetration in thicker sections.
Welding Process Suitability
| Proseso | Kaangkupan | Mga Tala |
| GTAW (TIG) | Napakahusay | Tumpak na kontrol; ideal for thin walls or critical joints. |
| GMAW (MIG) | Napakahusay | Higher productivity; requires good shielding control. |
| SMAW (Stick) | Mabuti na lang | Maraming nalalaman; gumamit ng mga electrodes na mababa ang hydrogen. |
| FCAW | Mabuti na lang | Productive for thick sections; requires careful slag removal. |
| Laser/EB | Napakahusay | Low distortion, mataas na katumpakan; used in advanced industries. |
5. Weldability of Ferritic Stainless Steels (400 Serye)
Ferritic stainless steels, primarily 400 series grades tulad ng 409, 430, at 446, are characterized by a cubic na nakasentro sa katawan (BCC) istraktura ng kristal.
They are widely used in mga sistema ng automotive exhaust, decorative architectural components, at mga kagamitang pang industriya dahil sa kanilang moderate corrosion resistance, magnetic mga katangian, and lower cost compared to austenitic grades.
While ferritic stainless steels can be welded, ang kanilang weldability is more limited compared to austenitic grades.
Ang kumbinasyon ng mababang ductility, high thermal expansion, and coarse grain growth in the heat-affected zone (HAZ) introduces specific challenges.
Key Weldability Challenges
| Hamon | Paliwanag | Mga Diskarte sa Pagpapagaan |
| Brittleness / Low Toughness | Ferritic steels are inherently less ductile; HAZ can become brittle due to grain growth. | Limit heat input, use thin sections or intermittent welding; avoid rapid cooling. |
| Pagbaluktot / Thermal Stress | Coefficient of thermal expansion ~10–12 µm/m·°C; lower than austenitic but still significant. | Pre-bend, proper fixturing, and controlled weld sequence. |
| Pag crack (Cold / Hydrogen-assisted) | Martensite-like structures may form in some high-C ferritics; hydrogen from moisture can induce cracking. | Preheat (150-200 ° C) para sa mas makapal na mga seksyon; use dry electrodes and proper shielding gases. |
| Reduced Corrosion Resistance in HAZ | Grain coarsening and depletion of alloying elements can locally reduce corrosion resistance. | Minimize heat input and avoid post-weld exposure to sensitization temperature ranges (450-850 ° C). |
Welding Consumables & Filler Selection
- Common filler metals: ER409L for 409, ER430L for 430.
- Filler selection: Match the base metal to avoid excessive ferrite or intermetallic formation in welds.
- Shielding gases: Argon or Ar + 2% O₂ for gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW).
Welding Process Suitability
| Proseso | Kaangkupan | Mga Tala |
| GTAW (TIG) | Napakaganda | Precise heat control, ideal for thin sections. |
| GMAW (MIG) | Mabuti na lang | Suitable for production; requires shielding gas optimization. |
| SMAW (Stick) | Katamtaman | Use low-hydrogen electrodes; risk of HAZ embrittlement. |
| FCAW / Laser ng laser | Limitado | May require preheating; risk of cracking in thicker sections. |
6. Weldability of Martensitic Stainless Steels (400 Serye)
Martensitic hindi kinakalawang na asero, commonly 410, 420, 431, ay mataas na lakas, hardenable alloys characterized by high carbon content and a body-centered tetragonal (BCT) martensitic structure.
These steels are widely used in mga blades ng turbine, pump shafts, cutlery, mga bahagi ng balbula, at mga bahagi ng aerospace, where strength and wear resistance are critical.
Martensitic stainless steels are considered challenging to weld dahil sa kanilang tendency to form hard, brittle microstructures in the heat-affected zone (HAZ), which increases the risk of cold cracking and reduced toughness.
Key Weldability Challenges
| Hamon | Paliwanag | Mga Diskarte sa Pagpapagaan |
| Cold Cracking / Hydrogen-Assisted Cracking | Hard martensite forms in HAZ, susceptible to cracking if hydrogen is present. | Preheat 150–300 °C; gumamit ng mga electrodes na mababa ang hydrogen; control interpass temperature. |
| Hardness in HAZ | Rapid cooling produces high hardness (HV > 400), leading to brittleness. | Post-weld tempering at 550–650 °C to restore ductility and reduce hardness. |
| Pagbaluktot & Natitirang Stress | High thermal expansion and rapid phase transformation generate residual stress. | Proper fixturing, balanced welding sequences, and controlled heat input. |
| Pagiging sensitibo sa kaagnasan | HAZ may experience reduced corrosion resistance, especially in wet or chloride-containing environments. | Select corrosion-resistant martensitic grades; avoid sensitization temperature range. |
Welding Consumables & Filler Selection
- Common filler metals: ER410, ER420, ER431, matched to base metal grade.
- Preheat and interpass: 150–300 °C depending on thickness and carbon content.
- Shielding gases: Argon or Ar + 2% He for GTAW; tuyo na, low-hydrogen electrodes for SMAW.
Welding Process Suitability
| Proseso | Kaangkupan | Mga Tala |
| GTAW (TIG) | Napakahusay | Tumpak na kontrol; recommended for critical or thin-section components. |
| GMAW (MIG) | Katamtaman | Requires low heat input; may need preheating on thicker sections. |
| SMAW (Stick) | Katamtaman | Use low-hydrogen electrodes; maintain preheat. |
| Laser ng laser / EB Welding | Napakahusay | Localized heating reduces HAZ size and cracking risk. |
Post-Weld Performance Considerations
| Performance Aspect | Observations After Proper Welding | Praktikal na Implikasyon |
| Lakas ng Mekanikal | Welds can match base metal tensile strength after post-weld tempering; as-welded HAZ may have hardness >400 HV. | Components achieve required strength and wear resistance post-tempering; avoid loading immediately after welding. |
| Ductility & Tigas na tigas | Slightly reduced in as-welded HAZ; restored after tempering. | Critical for impact-prone parts like pump shafts and valves. |
| Paglaban sa kaagnasan | Reduced locally in HAZ if not properly tempered; generally moderate for martensitic grades. | Suitable for low-to-moderate corrosion environments; use protective coatings if needed. |
| Service Life & Tibay ng buhay | Post-weld tempering ensures long-term stability; untempered welds may crack under stress or cyclic loading. | Post-weld heat treatment is mandatory for safety-critical components. |
7. Weldability of Duplex Stainless Steels (2000 Serye)
Duplex stainless steels (DSS), commonly referred to as 2000 serye ng mga (hal., 2205, 2507), ay dual-phase alloys containing approximately 50% austenite and 50% ferrite.
This combination provides mataas na lakas, mahusay na paglaban sa kaagnasan, at magandang tigas, paggawa ng mga ito ideal para sa pagproseso ng kemikal, offshore oil & gas, mga halaman ng desalination, at mga aplikasyon ng marine.
While duplex steels offer significant advantages over austenitic or ferritic grades, ang kanilang weldability is more sensitive due to the need to maintain a balanced ferrite-austenite ratio and avoid the formation of intermetallic phases (sigma, chi, or chromium nitrides).
Key Weldability Challenges
| Hamon | Paliwanag | Mga Diskarte sa Pagpapagaan |
| Ferrite–Austenite Imbalance | Excess ferrite reduces toughness; excess austenite reduces corrosion resistance. | Control heat input and interpass temperature; select appropriate filler metal with matching duplex composition. |
| Intermetallic Phase Formation | Sigma or chi phases may form at 600–1000 °C, causing embrittlement and reduced corrosion resistance. | Minimize heat input and cooling times; avoid multiple reheats; rapid post-weld cooling. |
| Hot Cracking in Weld Metal | Duplex steels solidify primarily as ferrite; small amounts of austenite required to prevent cracking. | Use filler metals designed for duplex welding (ERNiCrMo-3 or similar); maintain ferrite number (FN) 30–50. |
| Pagbaluktot & Natitirang Stress | Moderate thermal expansion; low conductivity concentrates heat in the weld zone. | Proper fixturing and balanced welding sequence; interpass temperature ≤150–250 °C. |
Welding Consumables & Filler Selection
- Common filler metals: ER2209, ER2594, or duplex-matched fillers.
- Ferrite number (FN) kontrol: FN 30–50 in weld metal for optimal toughness and corrosion resistance.
- Shielding gases: Pure argon for GTAW; Ar + small additions of N₂ (0.1–0.2%) may be used to stabilize austenite.
Welding Process Suitability
| Proseso | Kaangkupan | Mga Tala |
| GTAW (TIG) | Napakahusay | High control over heat input and phase balance; preferred for critical piping and vessels. |
| GMAW (MIG) | Napakahusay | Suitable for production; control welding speed and interpass temperature carefully. |
| SMAW (Stick) | Katamtaman | Low productivity; requires duplex-compatible low-hydrogen electrodes. |
| Laser ng laser / EB Welding | Napakahusay | Localized heating minimizes HAZ; preserves ferrite-austenite balance. |
Post-Weld Performance Considerations
| Performance Aspect | Observations After Proper Welding | Praktikal na Implikasyon |
| Lakas ng Mekanikal | Weld metal tensile strength typically 620–720 MPa; HAZ slightly lower but within 90–95% of base metal. | Allows use in high-pressure piping and structural applications; retains superior strength over austenitic steels. |
| Ductility & Tigas na tigas | Mabuti na lang, epekto tigas ng ulo >100 J at room temperature if ferrite content controlled. | Suitable for offshore and chemical plant environments; avoids brittle failure in HAZ. |
| Paglaban sa kaagnasan | Pitting and crevice corrosion resistance comparable to base metal (PREN 35–40 for 2205, 2507). | Reliable in chloride-rich and acidic environments; ensures long-term service life. |
| Service Life & Tibay ng buhay | Properly welded duplex joints resist intergranular corrosion and stress corrosion cracking. | High reliability for critical offshore, kemikal na, and desalination applications. |
8. Weldability of Precipitation-Hardening (PH) Hindi kinakalawang na asero
Precipitation-hardening stainless steels, tulad ng 17-4 PH, 15-5 PH, at 13-8 Mo, ay martensitic or semi-austenitic alloys strengthened through controlled precipitation of secondary phases (hal., tanso, niobiyum, or titanium compounds).
They combine mataas na lakas, moderate corrosion resistance, at napakahusay na katigasan, paggawa ng mga ito ideal para sa aerospace, pagtatanggol, kemikal na, and high-performance mechanical applications.
Welding PH stainless steels presents unique challenges, as the precipitation-hardening mechanism is disturbed by the thermal cycle, potentially leading to softening in the heat-affected zone (HAZ) o loss of strength in weld metal.
Key Weldability Challenges
| Hamon | Paliwanag | Mga Diskarte sa Pagpapagaan |
| HAZ Softening | Mga Precipitates (hal., Cu, Nb) dissolve during welding, reducing hardness and strength locally. | Pagkatapos ng hinang init paggamot (solusyon + pag-iipon) to restore mechanical properties. |
| Cold Cracking | Martensitic structure in HAZ may be hard and brittle; residual stresses from welding exacerbate cracking. | Preheat 150–250 °C; low-hydrogen electrodes; controlled interpass temperature. |
| Pagbaluktot & Natitirang Stress | Moderate thermal expansion; thermal cycles can induce warping and residual stress in thin sections. | Proper fixturing, low heat input, balanced weld sequence. |
| Corrosion Resistance Reduction | Local softening and altered precipitation may reduce corrosion resistance, particularly in aged or overaged zones. | Use solution treatment post-weld; control welding heat input. |
Welding Consumables & Filler Selection
- Mga metal na tagapuno: Matched to base metal (hal., ER630 for 17-4 PH).
- Preheat and interpass temperature: 150–250 °C depending on thickness and grade.
- Shielding gases: Argon or Ar + He blends for GTAW; tuyo na, low-hydrogen electrodes for SMAW.
Welding Process Suitability
| Proseso | Kaangkupan | Mga Tala |
| GTAW (TIG) | Napakahusay | Precise heat control; ideal for thin-section, critical, or aerospace components. |
| GMAW (MIG) | Napakahusay | Higher productivity; careful heat input management required. |
| SMAW (Stick) | Katamtaman | Requires low-hydrogen electrodes; limited for thin sections. |
| Laser ng laser / EB Welding | Napakahusay | Minimizes HAZ width and thermal impact; preserves base metal microstructure. |
Example Post-Weld Data:
| Grade | Weld Process | Lakas ng Paghatak (MPa) | Ang katigasan ng ulo (HRC) | Mga Tala |
| 17-4 PH | GTAW | 1150 (base: 1180) | 30–32 | Post-weld aging mandatory; HAZ softening restored. |
| 15-5 PH | GMAW | 1120 (base: 1150) | 28–31 | High toughness and corrosion resistance maintained after aging. |
| 13-8 Mo | GTAW | 1200 (base: 1220) | 32–34 | High-strength aerospace components; controlled welding critical. |
9. Comparative Weldability Summary
| Aspekto | Austenitic (300 Serye) | Ferritic (400 Serye) | Martensitiko (400 Serye) | Duplex (2000 Serye) | Pagpapatigas ng ulan (PH) |
| Representative Grades | 304, 304L, 316, 316L, 321, 347 | 409, 430, 446 | 410, 420, 431 | 2205, 2507 | 17-4 PH, 15-5 PH, 13-8 Mo |
| Mechanical Weldability | Napakahusay; HAZ retains ductility | Katamtaman; lower ductility, HAZ can be brittle | Katamtaman; high risk of cold cracking | Mabuti na lang; strength typically maintained | Moderate to challenging; HAZ softening |
| Corrosion Resistance Post-Weld | Napakahusay; low-carbon/stabilized grades prevent sensitization | Mabuti na lang; may be locally reduced if heat input excessive | Katamtaman; may be locally reduced in HAZ | Napakahusay; maintain ferrite–austenite balance | Katamtaman; restored after post-weld heat treatment |
| Mga Hamon sa Weldability | Hot cracking, pagbaluktot, porosity | Grain coarsening, pag crack na, HAZ brittleness | Hard martensitic HAZ, cold cracking | Ferrite/austenite imbalance, intermetallic phase formation | HAZ softening, natitirang stress, nabawasan ang tigas |
| Typical Post-Weld Considerations | Minimal preheat; low interpass temperature; optional solution annealing | Preheat for thick sections; controlled heat input | Preheat and low-hydrogen electrodes; mandatory post-weld tempering | Heat input control; interpass ≤150–250 °C; filler metal selection | Preheat, low-hydrogen electrodes, mandatory post-weld solution + pag-iipon |
| Mga Aplikasyon | Pagkain, Pharma, mga halaman ng kemikal, marine, cryogenics | Automotive exhausts, architectural panels, high-temp industrial components | Valve components, mga shaft, pump parts, aerospace | Malayo sa pampang, mga halaman ng kemikal, desalination, marine | Aerospace, pagtatanggol, high-performance pumps, kirurhiko instrumento |
Key Observations:
- Austenitic hindi kinakalawang na asero are the most forgiving, pag aalay ng excellent weldability with minimal precautions.
- Ferritic grades are more sensitive to brittleness and grain growth, requiring careful heat input management.
- Martensitic steels need preheating and post-weld tempering to prevent cold cracking and restore toughness.
- Duplex steels nangangailangan ng precise phase control to avoid ferrite-rich or brittle welds while maintaining corrosion resistance.
- PH hindi kinakalawang na asero must undergo post-weld solution treatment and aging to restore strength and hardness.
10. Pangwakas na Salita
The weldability of stainless steel spans a spectrum—from highly weldable austenitic grades to challenging martensitic and PH steels.
Habang most grades can be welded successfully, success hinges on understanding the metallurgical behavior, applying appropriate welding procedures, and performing necessary pre- or post-weld heat treatments.
For engineers and fabricators, weldability is not just about joining—it is about preserving corrosion resistance, lakas ng loob, at buhay ng serbisyo.
Careful filler selection, heat input management, and adherence to codes ensure stainless steel components meet both design and lifecycle expectations.
Mga FAQ
Why is 316L more weldable than 316 hindi kinakalawang na asero?
316L has a lower carbon content (C ≤0.03% vs. C ≤0.08% for 316), which drastically reduces sensitization risk.
Sa panahon ng hinang, 316’s higher carbon forms Cr₂₃C₆ carbides at grain boundaries (depleting Cr), leading to intergranular corrosion.
316L’s low carbon prevents this, na may isang 95% pass rate in ASTM A262 IGC testing vs. 50% para sa 316.
Do ferritic stainless steels require preheating?
No—ferritic stainless steels (409, 430) have low carbon content, so preheating is not needed to prevent cold cracking.
Gayunpaman, post-weld annealing (700–800°C) is recommended to recrystallize large HAZ grains, restoring ductility and toughness (increases impact energy by 40–50%).
Maaari bang 17-4 PH stainless steel be welded without post-weld heat treatment?
Technically yes, but the HAZ will be significantly softened (tensile strength drops from 1,150 MPa sa 750 MPa for H900 temper).
For load-bearing applications (hal., aerospace brackets), Post-weld solusyon pagsusubo (1,050°C) + re-aging (480°C) is mandatory to reform copper precipitates, restoring 95% of the base metal’s strength.
Which welding process is best for thin austenitic stainless steel (1-3 mm)?
GTAW (TIG) is ideal—its low heat input (0.5-1.5 kJ / mm) minimizes HAZ size and sensitization risk, while its precise arc control produces high-quality, low-porosity welds.
Use a 1–2 mm tungsten electrode, argon shielding gas (99.99% puro na lang), and travel speed 100–150 mm/min for optimal results.
