HAYNES^® HR-235^®

Principal Features

HAYNES^® HR-235^® alloy (UNS N06235) is a nickel-chromium-molybdenum-copper material with outstanding resistance to metal dusting. It has no deliberate addition of iron, an element which is detrimental to the performance of alloys under metal dusting conditions. It is resistant to creep-rupture at temperatures under which metal dusting is normally encountered. Having a low silicon and aluminum content, HR-235^® alloy is resistant to weld solidification and strain-age cracking. This is an improvement over other alloys intended for metal dusting resistance. It is also available as a filler wire with matching composition.

*Please contact our technical support team if you have technical questions about this alloy.

Nominal Composition

Metal Dusting

HAYNES^® HR-235^® alloy has been tested alongside competitive materials in a controlled atmosphere, thermal cycling rig. The reaction gas was H₂ + 68% CO + 6% H₂O, the carbon activity of which was 2.9 at the reaction temperature. The cycling operation, which was controlled automatically, comprised 45 minutes at the reaction temperature of 1256°F (680°C), followed by a cooling period of 15 minutes, during which the samples rapidly reached a temperature of about 194°F (90°C). The samples were tested for 1,200 (one hour) cycles, with the following results. The formation of filamentary carbon deposits with metallic nanoparticles (coking) is an indicator of the onset of surface damage (pitting).

Carburization Resistance

In addition to its high resistance to metal dusting, HAYNES^® HR-235^® alloy also withstands carburization, a degradation process which occurs at lower carbon activities and which negatively affects many metallic materials, as shown in the following chart. The test involved a gas mixture of Ar – 5% H₂ – 2% C₃H₆ at 1800°F (982°C), with a carbon activity of 1; the test duration was 215 h.

Internal Carburization in Ar– 5% H2 – 2% C3H6 at 1800°F (982ºC)

The samples for 800HT, X, and 556^® alloys experienced through thickness carburization, hence the values for these three materials would have been greater, had the samples been thicker.

Oxidation Resistance

HAYNES^® HR-235^® alloy also exhibits good oxidation resistance, as indicated in the following chart. The test was performed in flowing air (55.5 cm³/s) for 1,008 h, with an air cool to room temperature every 168 h.

Measurement of High Temperature Corrosion Attack

To assess the extent of attack (internal and external) of materials caused by oxidation, the following measurements are taken, using metallographic techniques, where A is the original thickness of the sample.

Weld Solidification Cracking Resistance

HAYNES^® HR-235^® alloy is resistant to weld solidification cracking, as measured by the VARESTRAINT weldability test. Materials with significant silicon contents, such as HR-160^® alloy, are prone to this form of cracking, as a result of their wider melting ranges. Having a low silicon and aluminum content, HR-235^® alloy is resistant to weld solidification and strain-age cracking. This is an improvement over other alloys intended for metal dusting resistance.  It is also available as a filler wire with matching composition. For more information, visit our Welding and Fabrication Brochure.

Physical Properties

Tensile Properties

HAYNES^® HR-235^® Solution Annealed Plate

Creep and Stress Rupture Strength

HR-235^® Solution Annealed Plate*

*Preliminary data

Hardness and Grain Size

HAYNES^® HR-235^® Alloy

HRBW = Hardness Rockwell “B”, Tungsten Indentor.

Heat Treatment

Wrought HAYNES^® HR-235^® alloy is furnished in the solution heat treated condition, unless otherwise specified. The alloy is normally solution heat-treated at 2050-2150°F (1121-1177°C) at a time to commensurate with thickness and rapidly cooled or water quenched for optimal properties.

Welding

HAYNES^® HR-235^® alloy is readily weldable by Gas Tungsten Arc (GTAW) and Gas Metal Arc (GMAW) welding processes. For sheet welds and plate root passes, GTAW is suggested. For plate welds, GMAW is preferred. For GMAW, the pulsed spray transfer mode (GMAW-P) is highly suggested. The GMAW-P transfer mode is a stable, low spatter spray transfer at average current levels significantly below that for conventional spray transfer. This results in low-to-moderate weld heat input, which is important to maintain the material properties of Ni-base alloys.  Submerged arc welding (SAW) is not recommended as this process is characterized by high heat input to the base metal and slow cooling of the weld. The welding characteristics of HR-235^® alloy are comparable to the highly weldable “C-type” alloys and the same general welding guidelines apply. Compared to other metal dusting resistant Ni-base alloys, HR-235^® alloy exhibits excellent weldability. For further welding details, please click here for the Welding and Fabrication guide, which contains general welding guidelines applicable to HR-235^® alloy.

Heat Treatment

Wrought forms of HR-235^® alloy are furnished in the solution annealed condition, unless otherwise specified, and should be welded in this condition. Welding of cold-worked materials is strongly discouraged, since it accelerates precipitation of secondary phases and induces residual stresses. As such, a full solution anneal in the range of 2100-2150°F (1149-1177°C), depending on specific requirements, followed by rapid air cool or water quench is suggested. Water quenching is recommended when annealing heavy section components and cold-worked structures prior to welding.

Base Metal Preparation

The joint surface and adjacent area should be thoroughly cleaned before welding. All grease, oil, crayon marks, sulfur compounds, and other foreign matter should be removed. Contact with copper or copper-bearing materials in the joint area should be avoided. It is preferable, but not necessary, that the alloy be in the solution-annealed condition when welded.

Filler Metal Selection

For GTAW and GMAW, HR-235^® bare filler wire is suggested. For dissimilar metal welds involving HR-235^® alloy, please consult with Haynes International for suggested filler metals.

Preheating, Interpass Temperatures, and Postweld Heat Treatment

Preheat is not required and is generally specified as room temperature. Preheat should not be used if the base metal to be welded is above 32°F (0°C). To minimize the precipitation of second phases in regions affected by the heat of welding, a maximum interpass temperature of 200°F (93°C) is recommended for HR-235^® alloy. Auxiliary cooling methods may be used between weld passes, as needed, providing that such methods do not introduce contaminants. Post-weld heat treatment is not normally required or suggested for HR-235^® alloy. Heat treatment of welded fabrications may be required for other reasons, such as stress relief.

Tensile Properties of Welded Material
Transverse Tensile – GTAW Welded Sheet

Transverse Tensile – GTAW Welded Plate

AWM (All Weld Metal) Tensile – GTAW

Specifications and Codes

Specifications

Codes

¹ASME Code Case 3058: Plate, Sheet, Strip, Bar, Rod, Fittings, Seamless Pipe/Tube, Welded Pipe/Tube

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