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Nickel Alloys and Weld Information

When MIG welding nickel the welder would note many similarities to welding carbon steels. Nickel has similar mechanical properties to carbon steels, its the niclel crystalline and metallurgical structure thats very different from iron.In contrast to carbon steels, when welding nickel the nickel does not undergo a crystalline / phase change up to its melt temp.To change the grain size requires cold working and annealing.

Nickel has great solubility for elements thats why we see Nickel - Chrome, Nickel Iron, - Nickel Copper - Nickel Moly and other commercial alloys. In smaller amounts carbon, manganese, silicon, aluminum and columbian are added some have a positive influence on the weld and some have a negive influence.Manganese in the range of 3 to 9 percent is added to nickel copper alloys to improve crack resistance.

Nickel alloys are very sensitive to oxidation, however in MIG welding the addition of one percent (max) CO2 to argon not only improves the arc stability it will also allow the use of higher spray transfer wire feed rate. Titanium is sometimes added to te filler metals as a deoxidizer for weld porosity reduction.

INFO ON COMMON NICKEL ALLOYS

Nickel. Solid Solution. 200 series, typically not strengthen by heat treat. Nickel 200 - 201 used food and chemical processing equipment and pipes. The 201 is used on applications over 600F. Nickel 201 99.5% nickel -

Nickel. Precipitation Hardenable. 300 series. Strengthened by heat treatment.

Nickel Copper Alloys. Solid Solution. 400 series. High strength. high toughness and great corrosion resistance. 405 is free machining.
405 = 66.% Ni - 31% Cu - 1.25% Fe - 1% Mn.

Nickel. Copper Precipitation Hardenable. 500 series. These alloys (K-500) are strengthed with Al and Ti. Used when high strength / hardness and corrosion resistance required. K500 66.5% Ni - 28% Cu - 3% Al.

Nickel Chrome. Solid Solution. 600 series.These are the commom alloys we see in use today. 600 - 601 - 625, Good corrosion resistance at high temperature.Good resistance to chloride-ion sress corrosin cracking and corrosion from high purity water. Used in reactors, power plant water wall cladding etc.Alloy 625 good MIG weldability, using pulsed or spray transfer.625 = 61% Ni - 21.5% Cr - 9% Mo - 3.65% Cb - 2.5% Fe -

Nickel Chrome. Precipitation Hardenable. 700 series. Strengthen by Al - Ti - Cb additions. Common alloys 713 c - 706 - 718 - X750 - U500 - U700 - R41 - Astoloy - Waspaloy. When Cb is used for strengthing rather than Al - Ti the weldability is improved. Gas Turbines and Aircraft parts. X750 = 73% Ni - 15.5% Cr - 7% Fe - 2.5% - Ti -0.95% Cb.

Nickel Iron Chrome. Solid Solution. 800 series. Common alloys are 800 and 825 and 20Cb. Alloy 800 is used typically in high temp applications, has good carburization / oxidation resistance. The 825 and 20 Cb in strong corrosive situations, good resitsnce to chloride-ion stress corrosion cracking and reducing acids.825 = 42% Cr - 30% Fe - 21.5% Cr - 35 Mo - 2.5% Cu - 0.9% Ti

Nickel Iron Chrome. Precipation Hardenable. 900 series. Most common 901 (Incoloy 901). Welds similar to X750, mostly used for forgings that are not welded.901 = 42.7% Ni - 34% Fe - 13.5% Cr -6.2% Mo - 2.5% Ti.

Nickel Moly Alloys. Known as Hastelloy B - N - W. Contains 16 - 28% Mo with some Chrome and iron. B used for hydrochloric acids. N for molten fluoride salts, W for dissimiler metals with good corrosion and oxidation resistance.

Nickel Chrome Moly Alloys. Known as Hastelloy. C - C276 - F - G -X. Alloy C good corrosion and high temp properties. C-276 lower carbon and silicon than C to reduce grain boundary precipitates enables the alloy to be used in as weld condition.

Nickel Silicon Alloy. Hastelloy D. This is a cast alloy with good resistance to sulfuric acid at all temperatures.

Weld Information For Nickel Alloy Welds.

Weld Note: Due to hardening potential and the formation of refractory oxides more consideration is required for Precipitation Hardenable nickel steels. With MIG welding short circuit, spray and pulsed transfer modes are available, the primary five weld differences between carbon steel MIG welds and nickel alloy welds will be;

[1] the nickel welds are much more sluggish so weld fusion is always a primary concern,

[2] the nickel welds are very sensitive to oxidation, a weld gas selection concern and pre-flow, post-flow weld gas consideration,

[3] magentic influence on the arc is much more noticable with nickel alloys,

[4] crack sensiivity is much greater with nickel alloy.

[5] Cleanliness is super critical when welding nickel alloys. Welding and post weld heating should only be carried out on nickel alloys that are clean and free of contaminates. Grinding and shot blasting are effective, wire brushing typically will not fully remove the surface oxides. Nickel alloys are sensitive to embrittlement from phosphorous, and sulfur and these elements are found in many of the materials used in metal forming. Plasma or laser cutting oxides which will have higher melting temperature than the base metal should be removed from nickel alloy plate edges that will be part of the welds. These higher temp oxides can act as a barrier against the sluggish nickel welds impeading weld fusion potential. The oxides can also create internal weld porosity and cause a reduction in the nickel mechanical properties. Due to the sluggish composition of nickel welds contaminates on the plate surface are more likely to become trapped in the weld, in contrast with carbon steels the oxides and inclusion will typically rise much faster to the weld surface. If brushes or power brushes are utilized ensure they are made of stainless steels. The sluggish nature of the nickel welds can also cause extensive lack of weld fusion particaully on MIG welded parts > 4 mm. Lack of weld penetration can cause a point for stress concentration. When welding tube or pipe or butt welds with full penetratiion treat the weld like a stainless weld and ensure the backside of the root has an argon purge.

Weld heat typically does not have a negative impact on the nickel alloys. A small amount of grain growth and annealing will occur in the welds HAZ. Short circuit will obvioulsy have a much less affected HAZ than a spray transfer weld. When you do a tensile test on a nickel welded sample, please keep in mind that the annealed part of the HAZ will be the first location to elongate. The plastic elongation will cause strain hardening which "actually increases the yield strength". The bottom line is the work hardening influence on the elongation is influenced by the size of the HAZ, and its important to remember that transverse tensile elongation or the noted transverse yield strength attained can be misleading.

With multi-pass welds be aware of the weld heat input build up, especially when welding those oxidation sensitive, precipitation hardenaable alloys which can leave an oxide surface on the weld that can impead multi-pass weld fusion potential.

Welds subject to excess weld heat may be influenced by atmospheric contamination creating a severe oxide on the weld's surface. For mult-pass welds use interpass temperature control to minimize both the heat influence on the weld HAZ and oxidation potential.

Pre-heat is typically not necessary for nickel alloys if the metals are at or above indoor shop temperature. If the metals have been stored outside or moisture is suspect to reduce the weld porosity potential, pre-heat the metals between 70 and 80F.

Post heat treatment is usually not required for the common nickel alloys after welding to attain the desired corrosion resistance. However with nickel chrome 600 alloy, stress relief is required for fused-caustic service applications and also for alloy 400 applications as used in hydrofluoric acid service. Also note the nickel molybdenum and nickel silicon alloys HAZ can lower the corrosion resistance therefore these alloys may require a postweld solution-annealing treatment to restore the corrosion resistance of the HAZ. Not sure about this stuff ask the steel supplier or contact Haynes Alloys Kokomo IN.

 

FILLER METAL SELECTION

Filler Metal Selection.As corrosion potential is the primary concern in the selection of nickel alloys the filler metal should have similar chemisty composition to the base metal to be welded. The 600 series nickel chrome and nickel- ron-chrome alloys can end up with that austenitic problem caused by carbide precipitation (CP) in the HAZ, see the stainless section. Its reported that the CP does in most cases not result in accelerated corrosion attacks. Like stainless weld consumables, additions of columbian or titanium are added to specific filler metals such as the popular Inconel 625 are used to help stabilize the welds and minimize the CP influence.

With MIG welding remember you will get greater current density (less sluggish welds) from smaller wire diameters. Under 6 mm I would recommend an 035 1 mm nickel MIG wire, >6 mm consider an 045 1.2 mm wire. You can use straight argon for those MIG welds however when using MIG spray transfer consider argon with 1% CO2, for applications 3 to 6 mm, for spray applications over 6 mm, to attain more weld energy add 40% helium to to argon 1 % CO2 mix. The one percent CO2 range should be maintained between 0.75 and 1.25%. In this range you will see an improvement in arc stability, less sensitivity to magnetic deflection, along with an increase in the allowable spray wire feed range. Note the upper limit on the CO2 content, using CO2 above this range will cause oxidation. Use the argon CO2 mix with an addaition of 30 - 40% helium if you feel you need more weld energy in those short circuit welds. Use gas flow rates in the range of 40 to 60 cuft/hr. For those of you that are considering pulsed rather than spray, remember nickel welds are sluggish going from a pulsed peak to a low background weld current does not improve a sluggish weld in contrast to traditional spray. When TIG welding use the same filler metals as MIG with straight argon, treat the nickel welds as you would stainless welds.

 

Base Alloy	AWS Filler Metals. Need more info contact Haynes alloys Kokomo IN
Nickel 200	ERNi 3
Monel 400	ERNi Cu 7
Inconel 600	ERNiCr-3 -- ERNiCrFe 6
Inconel 718	718
Inconel X-750	718
For Dissimalar applications think about minimum weld dilution	Short circuit globular and the pused mode are recommended for cladding too minimize weld dilution. For nickel chrome welds on carbon steels ERNiCr-3 is a common consumable.
Inconel 600 - 800 to steel or stainless / monel 400	ERNiCr -3 - ERNiCrFe-6

 

For those weld shops who do not have a plasma cutter you can cut nickel alloys with the GTAW process, try a 3 mm tungsten with 400 to 450 amps with an argon hydrogen mix 60 - 70 argon balance hydrogen. Cutting speeds <12 mm 30 to 60 ipm.

 

 

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[] When welding the 300 series of stainless to carbon steels the austenitic 309 filler metal and sometimes 310 are utilized. The 310 25% Cr - 20% Ni, can cause the austenitic welds to fail due to microfissuring which resulted in cracks in applications subject to thermal stresses. The weld failures were often a result of the differences of the coefficient of thermal expansion (CTE). The 309, 23% Cr - 13% Ni filler metal when used on satinless to carbon steels results in a weld with ferrite reducing the potential for mico-fissuring, however keep in mind dependind on the application chemistry, thickness, weld process and parametrs used, the dissimiler weld joints are still dilution sensitive. The 309 filler when used on stainless to steel welds still have large CTE differences therefore one should be concerned when the welds or parts are subject to temperatures over 600F in which high stresses or thermal fatique effects the ferritic / austenitic weld interface.

[] Where the 309 and 310 have problems the weld solutions are frequently found with the 600 series Ni Alloy filler metals.

 

[] The 600 series as many of you know are often called Inconel. These high Ni-alloy filler metals typically contain up to 72 nickel 15 % Chrome and 8% Fe. These filler metals have a much lower CTE than the 300 series austenitic alloys.When welding the lower CTE results in less weld thermal stresses. The Inconel alloys are also less sensitive to weld microfissuring or weld dilution concerns from dissimiler metals.

[] When parts are in service at temperatires > 700 F, welds that contain high nickel to chrome ratios can be sensitive to sulfur corrosion. This risk is reduced with filler metals that have higher chrome / moly. Alloys 625 / 671. The 671 is AWS (ERNiCr-4 rod)

[] The 625filler, EniCrMo-3 rod , mig and flux cored wire should be restricted to applications <1000F as weld embrittlement can occur.

[] For a story on how not to use Inco 625 for cladding boiler water wall tubes click

 

 

 

 

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