Technical knowledge
Welding Inconel 625 to carbon steel: buttering, filler and control
How to make a sound dissimilar joint between Inconel 625 and carbon steel: buttering sequence, filler selection, dilution control, preheat and post weld heat treatment decisions, and inspection points.
Why buttering is the standard method
When nickel filler is deposited directly onto carbon steel in one operation, iron from the steel dilutes the weld metal. The resulting composition can form a hard martensitic layer at the fusion line that is susceptible to cracking under restraint. Buttering solves this by putting a nickel rich layer on the steel first, so the final joint is made between two nickel alloy surfaces with far less iron pickup.
A practical sequence
- Prepare and clean the carbon steel bevel to bright metal, removing mill scale, paint and oil.
- Apply the first buttering layer with ERNiCrMo-3, keeping heat input moderate and the interpass temperature controlled.
- Inspect the buttered layer with dye penetrant before proceeding.
- Machine or grind the butter to the final bevel geometry.
- Complete the joint to the Inconel 625 component with ERNiCrMo-3.
- Examine the finished weld with dye penetrant and, where specified, radiography.
Parameters and decisions
| Decision | Usual answer | Reason |
|---|---|---|
| Filler metal | ERNiCrMo-3 | Compatible with both sides and tolerant of dilution |
| Preheat | Usually none, but dry | Removes moisture without adding thermal exposure |
| Interpass temperature | Typically controlled below about 150 C | Limits grain growth and distortion |
| Post weld heat treatment | Often none; agree if required | Differential expansion makes relief complex |
| Examination | Dye penetrant, plus radiography where specified | Confirms the butter and the final joint |
What happens in service
The joint also changes the corrosion relationship. The large carbon steel surface becomes anodic relative to the nickel alloy, so in a conductive environment the steel corrodes preferentially. Where this matters, consider coating or cathodic protection on the steel side, or use an insulating joint. Thermal expansion mismatch also concentrates strain at the transition, so support the line so the weld is not the anchor point.
Questions about this topic
Do I need post weld heat treatment?
Not usually for corrosion service. Stress relief of a dissimilar joint is complicated by the different expansion coefficients and can introduce new stresses. If a code or client requires it, agree the cycle with the welding engineer before manufacture.
Can I use a stainless filler instead?
It is possible but generally not preferred for this combination. Nickel base filler handles dilution better and avoids the hard transition zone that can form with an austenitic stainless filler on carbon steel.
How do I inspect the buttered layer?
Dye penetrant examination after the buttering layer, before the final joint is made. Finding a defect at that stage costs a small repair; finding it after completion means cutting out the whole joint.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email [email protected] or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.