Harris 630 ER630 (17-4PH) Stainless Steel TIG (GTAW) Welding Alloy — 3/32 in (2.4 mm), 10 lb Box (174PH50) — is a precipitation-hardening martensitic stainless steel filler metal classified under AWS A5.9 as ER630. This rod is the weld filler counterpart to AISI Type 630 (also known as 17-4 PH) base metal, which derives its name from its nominal composition of 17% chromium and 4% nickel, with approximately 4% copper and a small niobium addition that controls the aging precipitation response. ER630 is one of only a handful of standard AWS filler metals that produce a truly matching deposit for precipitation-hardened (PH) stainless grades, making it indispensable when weld joints must achieve the same high strength and hardness as the parent material after post-weld aging.
The 3/32 in (2.4 mm) diameter is a medium-to-large TIG rod calibrated for structural 17-4 PH weldments with wall thicknesses of 3/16 in to 1/2 in — typical dimensions in aerospace brackets, oil and gas downhole components, pump shafts, and valve bodies. Harris Products Group (a Lincoln Electric company) manufactures this alloy to the tight composition windows required for predictable aging response.
- AWS Classification: ER630 per AWS A5.9/A5.9M
- Chromium: 16.0–17.0%
- Nickel: 4.5–5.0%
- Copper: 3.25–4.00%
- Niobium + Tantalum: 0.15–0.30%
- Carbon: 0.05% max
- Manganese: 0.25–0.75%
- Silicon: 0.75% max
- Diameter: 3/32 in (2.4 mm)
- Rod Length: 36 in (914 mm)
- Package: 10 lb box
- Tensile Strength (as-welded / solution-annealed condition): ~130,000 psi (897 MPa) solution annealed; up to 190,000 psi (1,310 MPa) after H900 aging
- Yield Strength (after H900 aging at 900 °F / 482 °C): ~170,000 psi (1,172 MPa)
- Elongation (H900): ~10–14%
- Hardness (H900): ~42–46 HRC
- Aerospace Structural Components: Airframe brackets, landing gear components, fasteners, and attachment fittings fabricated in 17-4 PH bar and plate. The weld deposit after H900 or H1025 aging reaches yield strengths of 110,000–170,000 psi, supporting the strength requirements of aircraft primary structures.
- Oil and Gas Downhole Equipment: Pump shafts, valve stems, mandrels, and handling tools in 17-4 PH where corrosion resistance, high strength, and resistance to sulfide stress cracking (with appropriate heat treatment) are required. NACE MR0175/ISO 15156 governs hydrogen sulfide environments — consult applicable HRC limits.
- Defense and Military Hardware: Weapon components, sensor housings, submarine fittings, and pressure containment vessels where the high strength-to-weight ratio of 17-4 PH is combined with the need for full-penetration weld joints that match base metal strength after aging.
- Medical and Pharmaceutical Devices: Surgical instrument components, implantable device housings, and pharmaceutical processing equipment where passivated 17-4 PH surfaces combine corrosion resistance with high strength — and weld joints must maintain both properties after aging.
- Pump and Compressor Components: Impellers, diffusers, and volute casings in chemical process pumps where 17-4 PH's combination of corrosion resistance, machinability after annealing, and high post-age strength is preferred over weaker austenitic grades.
- Repair Welding of 17-4 PH Castings: Sand-cast and investment-cast 17-4 PH components (CB-7Cu-1 per ASTM A747) are repaired with ER630 TIG to restore dimensional accuracy and mechanical properties prior to re-aging the casting.
17-4 PH and ER630 filler require careful pre- and post-weld practices to achieve the specified mechanical properties:
- Base metal condition: Weld 17-4 PH in the solution-annealed (Condition A) state whenever possible. Welding in the aged condition creates a heavily overaged HAZ adjacent to the fusion boundary, significantly reducing toughness.
- Preheat: 200–300 °F (93–149 °C) for material over 1/2 in thickness. Thinner sections may be welded without preheat from room temperature.
- Cleanliness: 17-4 PH is sensitive to hydrogen-induced cracking. Degrease all faying surfaces and rod with acetone. Use dry, clean gloves. Do not allow moisture on the weld joint.
- Process: GTAW (TIG), DCEN
- Tungsten: 2% ceriated (grey) or 2% lanthanated, 1/8 in diameter preferred for 3/32 in rod
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Amperage:
- 3/16 in material: 100–150 A
- 1/4 in material: 130–175 A
- 3/8 in material: 160–220 A
- Interpass temperature: ≤300 °F (149 °C). Allow interpass cooling to prevent martensite transformation from over-tempering during welding.
- 100% Argon at 20–30 CFH. 17-4 PH is prone to oxidation of chromium in the HAZ; generous Argon shielding minimizes oxide scale.
- Back-purge pipe and tubular joints with 100% Argon at 2–5 CFH.
To restore full mechanical properties after welding, a solution anneal and re-aging cycle is required:
- Solution Anneal (Condition A): Heat to 1,900 °F (1,038 °C) ± 25 °F, hold 30 minutes per inch of thickness (1 hour minimum), cool rapidly to below 90 °F (32 °C) by air cool or oil quench on heavy sections to ensure full martensite transformation.
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Age at desired H-condition:
- H900: 900 °F (482 °C) for 1 hour — highest strength, lowest toughness
- H1025: 1,025 °F (552 °C) for 4 hours — balanced strength and toughness (most common structural choice)
- H1150: 1,150 °F (621 °C) for 4 hours — lower strength, improved toughness and corrosion resistance
- Store in original packaging at 50–100 °F (10–38 °C) below 60% RH. ER630 is a martensitic stainless wire — surface oxidation will cause arc instability and bead discoloration.
- Handle with clean dry gloves only. Hydrogen contamination from skin oils can initiate delayed cracking in the martensitic HAZ, which is more susceptible to hydrogen embrittlement than austenitic stainless or carbon steel HAZ.
- Separate from austenitic stainless rods (ER308L, ER316L) in storage. The two rod types look similar but are metallurgically incompatible for 17-4 PH applications.
Any DC TIG machine suitable for stainless steel TIG welding is appropriate for ER630. Lincoln Electric platforms commonly used in aerospace and oil and gas 17-4 PH fabrication:
- Lincoln Dynasty 280 DX and 400 (precise amperage control for sensitive PH alloys)
- Lincoln Precision TIG 275 (K2533-2)
- Lincoln Square Wave TIG 300 (DCEN mode)
- Lincoln PTA-26 and PTA-26V TIG torch packages
Primary base metals:
- AISI Type 630 / 17-4 PH stainless (all bar, plate, and tube forms)
- ASTM A564 Type 630 (aged bar)
- ASTM A693 Type 630 (plate and strip)
- ASTM A747 Grade CB-7Cu-1 (castings)
Q1: What aging heat treatment produces the highest strength with ER630 weld deposits?
A: H900 aging at 900 °F (482 °C) for 1 hour after solution anneal produces the highest tensile strength — approximately 190,000 psi (1,310 MPa) — but also the lowest toughness and impact resistance. H900-condition 17-4 PH weld joints are used in aerospace fasteners and high-load structural fittings. For applications requiring better toughness, H1025 (1,025 °F / 4 hours) or H1100 (1,100 °F / 4 hours) provide more balanced properties.
Q2: Can I weld 17-4 PH without solution-annealing after welding?
A: Direct aging of as-welded 17-4 PH is possible using the Condition A + direct aging approach (weld in Condition A, skip re-solution anneal, age directly). This produces adequate strength but the HAZ properties will be less uniform than solution-anneal + age. For critical structural applications, ASTM and AMS specifications typically require full solution anneal + age after welding. Consult the applicable material specification and design engineering before substituting direct aging.
Q3: Is ER630 the same as 17-4 PH filler — are there other trade names?
A: ER630 is the AWS classification; 17-4 PH is the common AISI/SAE designation for the base metal grade. Other designations you may encounter for this alloy family include UNS S17400, AMS 5827 (wire), AMS 5825 (bar), ASTM A693 Type 630, and various proprietary names (e.g., Custom 455 is a related but different PH grade — do not substitute). Harris ER630 rod is manufactured to AWS A5.9 ER630 and AMS 5827.
Q4: Why does 17-4 PH weld crack more easily than austenitic stainless?
A: 17-4 PH solidifies as fully ferritic/martensitic structure, not austenitic. This microstructure is more susceptible to hydrogen-induced cold cracking (HICC) and underbead cracking than austenitic alloys. Prevention: (1) minimize moisture — dehydrate all tooling and heat joint to 200–300 °F before welding; (2) use dry, clean rod; (3) allow controlled cooling after welding (do not quench below 90 °F before the martensite transformation completes); (4) conduct solution anneal promptly after welding — do not leave the weld in the as-welded martensitic state for extended periods.
Q5: Can ER630 be used for welding 15-5 PH stainless steel?
A: ER630 is often used for 15-5 PH (15Cr-5Ni-3Cu) weldments as the closest standard AWS classification match. 15-5 PH filler does not have a distinct AWS classification — most PH fabrication codes and material specifications list ER630 as the acceptable filler for both 17-4 and 15-5 PH base metals. Verify with the applicable material specification (AMS, ASTM, MIL-SPEC) before welding critical 15-5 PH structures.
Q6: What shielding gas produces the best results on 17-4 PH TIG welding?
A: 100% Argon at 20–30 CFH is strongly preferred. Helium blends are sometimes used for thicker section (over 1/2 in) to increase travel speed, but the higher heat input can cause grain growth in the HAZ and overaging of nearby metal if interpass temperature exceeds 300 °F. CO₂ additions are not used on PH stainless — CO₂ promotes carbon pickup and oxidation that disrupts the aging response.
Q7: Where does Harris ER630 fit in oil and gas NACE MR0175 requirements?
A: NACE MR0175/ISO 15156 restricts hardness in sour-service (H₂S) environments. 17-4 PH in H1150 or H1150M condition (maximum HRC 33) is included in ISO 15156-3 Table A.29 with restrictions. As-welded or H900-condition 17-4 PH typically exceeds the 33 HRC limit and is not acceptable for sour service without a conforming heat treatment. Consult the applicable NACE/ISO 15156 annex and the project's sour-service qualification documentation before specifying ER630 for downhole sour-gas equipment.