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Production process analysis of UNS N10276 pipe fittings

Standard

Standard of pipe fittings:
ASTM B366 is the latest edition of 2016.
Standard Specification for factory made nickel and nickel alloy pipe fittings.
Raw material standard:
The latest edition of ASTM B575 is 2015e.

The mechanical properties of UNS N10276 are based on the standard of mechanical properties of the material.

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20200702133145 12846 - Production process analysis of UNS N10276 pipe fittings

Chemical composition of Hastelloy C276 (UNS N10276)

Ni Mo Cr Fe W Co Mn C V P S Si
Remainder 15.0-17.0 14.5-16.5 4.0-7.0 3.0-4.5 2.5 max 1.0 max .01 max .35 max .04 max .03 max .08 max

We used to make austenitic steel (such as 316L, 304L, etc.) and duplex stainless steel (such as S32205, S32750, etc.) all belong to iron-based materials, and the main component is iron. The material N10276 (C276) produced by the 16gw477 order is nickel based, that is, its main component is nickel, which generally accounts for about 60% of the total content of the material. We all know that nickel is one of the most important elements in stainless steel. Experiments abroad have proved that nickel with purity of 99% will not produce rust marks in 20 years during normal use. N10276 has excellent resistance to pitting corrosion, crevice corrosion and stress corrosion cracking. This material is mainly used in components and catalytic systems that are exposed to chlorinated organics. It is especially suitable for high temperature, mixed with impurities of inorganic and organic acids (such as formic acid and acetic acid), seawater corrosion environment.

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Plasticity

  • Plasticity refers to the ability of metal materials to produce permanent deformation (plastic deformation) without being destroyed under the action of external load. The length and cross-sectional area of metal materials will change when they are stretched. Therefore, the plasticity of metals can be measured by the elongation of length (elongation) and the reduction of area (reduction of area).
  • The greater the elongation and reduction of area, the better the plasticity. Compared with the two methods, the reduction of area is more close to the true strain of the material.
  • N10276 has large elongation and small differential shrinkage of cross section, which has strong characteristics.

Cutting and forming

  • Cutting can be done by cold and hot cutting (sawing machine, plasma). Generally, it does not affect the subsequent processing.
  • Although N10276 has good plasticity, its work hardening rate is high. When the first cold working deformation is more than 15%, brittle fracture is very easy to occur due to hardening. This situation has been encountered in the production of general dual phase steel and super austenitic steel, but it will not be as sensitive as N10276.
  • Deformation calculation: = (force x length) / (3x elastic modulus x section secondary wheelbase)
  • Elastic modulus: when N10276 is at 0-100 ℃, 209-204 is selected
  • Section secondary wheelbase: π x (big circle diameter fourth power small circle diameter fourth power) / 64

This formula is a little complicated, and the key point is that the material at different temperatures. Its elastic modulus is different, and generally decreases with the increase of temperature.

Forming

  • Hot forming: hot forming (bending) temperature of N10276 is recommended to be above 1000 ℃. Because the sensitized area is about 1000-600 ℃, it should be avoided as far as possible to carry out thermoforming. The hot formed N10276 material should be re solution heat treated, otherwise its corrosion resistance will be affected.
  • Cold forming: we said that its work hardening rate is higher than that of austenitic stainless steel, so it should be confirmed that the workpiece (material) should be solution heat treated. The surface of the workpiece shall be protected, and the iron carbon metal shall not be directly contacted.

As mentioned above, if the cold rolling deformation is greater than 15%, a secondary solution treatment is required for the workpiece. Intermediate annealing is recommended. However, it is absolutely not allowed to use acetylene and oxygen for heating.

Heat treatment

  • N10276 standard requires heat treatment at 1121 ℃ and rapid water cooling. The hardness after heat treatment shall be determined as HRB ≤ 100, although it is noted in ASTM b575 that hardness value is only shown for information purposes and not as a basis for acceptance or rejection. However, after the subsequent processing and welding, the hardness will have a certain degree of improvement, so in order to ensure the smooth later process, the hardness after heat treatment must be within the standard range.
  • Because the material is sensitive to sulfur, phosphorus, lead and other elements in the heat treatment process, it is easy to affect the properties of the alloy, thus causing irreversible defects in the later corrosion resistance of the material. Therefore, the workpiece should be kept clean and pollution-free before and during heat treatment. It is particularly important to remove the oil stain on the surface of the workpiece. The oily marker, lubricating oil and paint should be removed first.

Pickling

After heat treatment, the oxide scale of N10276 material has strong adhesion and strong corrosion resistance, so it is very difficult to clean the oxide skin. It is suggested that polishing, sandblasting and shot blasting should be used directly and then pickling solution (hydrofluoric acid, nitric acid) should be soaked after shot blasting to achieve a very good surface gloss.

Plastic

  • N10276 products, in the shaping process, do not allow the use of oxygen, acetylene and other forms of heating percussion process. After heating, it is clear that at 600-1000 ℃, the alloy properties will be affected, mainly in corrosion resistance, and the influence on mechanical properties is relatively limited.
  • It is not allowed to knock with iron hammer, but stainless steel hammer must be used.
  • The forklift truck must be equipped with a stainless steel protective cover.

Welding

Welding material: according to ASME IV, nicrmo-4 welding material is used for N10276 material, and the welding material standard refers to AWS A5.14.
Base metal:

  • When the thickness of plate is 2.5-15mm, V-shaped groove can be used, no blunt edge can be left below 12mm, and the blunt edge within 2mm can be used if the thickness is more than 12mm.
  • When welding, because the welding turntable or bracket is made of iron carbon metal, it should be protected and isolated.

Welding environment: reduce iron ion dust in the air as far as possible, keep it clean and pay attention to crosswind.
Welding end (groove): be sure to grind clean and flat, allow no overheating fine grinding, workpiece surface is clean, at least 30mm area of welding end must be polished clean and bright.

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The physical properties of nickel base alloy are mainly low thermal conductivity and high expansion coefficient. These characteristics should be considered in the preparation of welding groove, including widening the bottom gap (1 ~ 3 mm), and due to the viscosity of molten metal, a larger groove angle of 60 ~ 70 ° should be used in butt welding to offset the shrinkage of the material.

Welding conditions

After the groove is polished, do not touch the workpiece with gloves again, put an end to the contact between harmful substances and the workpiece, and melt into the weld during welding.
Prevent contact with low melting point metals (such as lead, copper, etc.) to avoid embrittlement of unstable metals due to the increase of carbon or sulfur.
The grinding wheel should be free of iron ions and its binder should be non organic resin.
Welding parts shall not be assembled by force during assembly, which will cause local hardening of products after welding.

Welding parameters

Interlayer temperature: ≤ 100 ℃. That is to say, for multi pass welding, after one pass of welding, it shall be cooled to less than 100 ℃ before the next welding. This is to ensure the weld metal composition and weld corrosion resistance requirements.
Parameter

Material

Thickness

Current range

Welding pass

Voltage range

Welding speed

N10276

8mm

120-160

4

14-18

110-130mm/min

The parameters of 8mm plate welded before, tensile and bending tests after welding all passed.

PQR/WPS

20200702134622 50349 - Production process analysis of UNS N10276 pipe fittings

  • WPQ: GTAW welding is adopted, and welder qualification covers austenite steel, duplex stainless steel and nickel base alloy.
  • From the welding parameters, it is also similar to the welding of ordinary steel.
  • However, the fluidity of the weld pool is worse than that of the ordinary austenitic steel. When the welding current is too high, the weld surface formation is not good and the surface oxidation is fast.

Repair welding

When the product needs repair welding, the welding operation can be carried out according to the requirements of WPS 2-N pass.
It is necessary to use sand wheel to measure the bottom of the defect and ensure that the weld is clean. The defect is ground into a groove of 60-70 ° before filling and covering welding.
The welding wire of Φ 2.4 should be used with small current and low welding speed. After welding, the weld surface shall be pickled.
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Post weld heat treatment

Generally not required, N10276 can still achieve good mechanical properties after welding under strict welding process, and the hardness of HAZ will be increased. If the formed workpiece has been solution heat treated, the hardness of the product after welding should fully meet the standard limit value.
In most corrosive environments, C-276 can be used as a weldment. However, in very harsh environment, C-276 material and welding parts need solution heat treatment to obtain the best corrosion resistance.
After welding, if the temperature of the weld is too high, the oxide scale of the weld can be quickly brushed off with a wire brush. Generally, pickling is a post weld treatment process.

Thermal output value

  • ThyssenKrupp (a large manufacturer with rich production experience of N10276) recommends GTAW welding with heat output less than 8kj / cm
  • Calculation of thermal output value: kJ / cm = (60 * current * voltage) / welding speed * 1000

Machining

  • Because N10276 is sensitive to work hardening, it is suitable to use low cutting speed and re feed to machine under the surface layer of cold work hardening.
  • When clamping the workpiece, attention should be paid to protect it from direct contact with iron carbon metal, including the fixture should be well isolated before processing.

Product protection

At any time, the products should be kept away from the ground and not directly contact with iron, carbon steel and other materials.
Do not mark paint and oil marking pen on the surface of products.
The final inspection personnel shall wear dry white gloves to contact the surface of pipe fittings. Avoid secondary contamination of the workpiece by sweat on bare hands or grease on work gloves.

Source: China Hastelloy C276 Pipe Fitting Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@epowermetals.com

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  1. […] the first generation super stainless steel, and is the same as that of nickel based alloys such as UNS N10276. All welding methods can be used to weld the second generation super austenitic stainless steel […]

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