UNS N06455 Corrosion Resistant Alloys Forging / Wire For Chemical Process

Corrosion resistant alloy C-4 (N06455) forging, wire, ring, bar and tube etc for chemical process

1 PRODUCT

Corrosion resistant alloy C-4 (UNS N06455) for chemical process environments at ambient and higher temperatures.

Product forms available as pipe, tube, sheet, strip, plate, round bar, flat bar, forging, forging stock, hexagon and wire etc.

2 EQUIVALENT DESIGNATION

NS335, W.Nr. 2.4610, NiMo16Cr16Ti(DIN), NiMo16Cr16Ti(ISO), Hastelloy® C-4, VDM® alloy C-4 (Nicrofer 6616 hMo)

3 APPLICATION

Alloy C-4 finds application in the chemical industry in a wide range of chemical process environments at ambient and higher temperatures.

Typical applications are:

● Flue gas desulphurisation equipment

● Pickling baths and acid regeneration

● Acetic acid production and agrochemicals production

● Titanium dioxide production (chloride route)

● Electrolytic galvanizing rolls

● Heat exchanger

● Reactor

4 OVERVIEW

Alloy C-4 is a veratile austenitic low-carbon Ni-Cr-Mo alloy with extremely high resistance to HAZ sensitization.

Alloy C-4 is the most (microstructurally) stable of the widely used nickel-chromium-molybdenum materials, which are well known for their resistance to many aggressive chemicals, in particular hydrochloric acid, sulfuric acid, and chlorides. This stability means that the alloy can be welded without fear of sensitization, i.e. the nucleation and growth of deleterious, second phase precipitates in the grain boundaries of the weld heat-affected zone (HAZ).

Like other nickel alloys, it is ductile, easy to form and weld, and possesses exceptional resistance to stress corrosion cracking in chloride-bearing solutions (a form of degradation to which the austenitic stainless steels are prone). With its high chromium and molybdenum contents, it is able to withstand both oxidizing and non-oxidizing acids, and is resistant to pitting and crevice attack in the presence of chlorides and other halides.

The main difference between Alloy C-4 and other alloys of similar composition developed earlier, is its reduced carbon, silicon, iron and tungsten contents. This composition shows greater stability during extended exposure to temperatures in the range 650–1040°C (1200–1900°F). As a result, resistance to intergranular corrosion is improved.

5 CHEMICAL COMPOSITION

6 PHYSICAL PROPERTIES

Density: 8.7 g/cm³ (0.314lb/in³)

Melting range: 1335-1380°C (2435-2515°F)

7 MECHANICAL PROPERTIES

The following properties are applicable to Alloy C-4 in the solution-annealed condition and indicated size ranges. Specified properties of materials outside these size ranges are subject to special enquiry. All minimum values are valid for longitudinal and transverse specimens.

Table 3 Minimum mechanical properties at room temperature according to VdTÜV data sheet 424.

^* Hardness for information only

8 CORROSION RESISTANCE

Its high chromium and molybdenum contents make Alloy C-4 exceptionally resistant to a variety of chemical media, including reducing contaminated mineral acids such as phosphoric, hydrochloric and sulphuric acids, chlorides and organic and inorganic chloride-contaminated media.

Due to its high nickel content, Alloy C-4 is virtually immune to chloride-induced stress-corrosion cracking, even in hot chloride solutions.

Resistance to pitting and crevice corrosion

Alloy C-4 alloy exhibits high resistance to chloride-induced pitting and crevice attack, forms of corrosion to which the austenitic stainless steels are particularly prone. To assess the resistance of alloys to pitting and crevice attack, it is customary to measure their Critical Pitting Temperatures and Critical Crevice Temperatures in acidified 6 wt.% ferric chloride, in accordance with the procedures defined in ASTM Standard G 48. These values represent the lowest temperatures at which pitting and crevice attack are encountered in this solution, within 72 hours.

For comparison, the values for 316L, 254SMO, 625, and C-4 alloys are as follows:

Resistance to stress corrosion cracking

One of the chief attributes of the nickel alloys is their resistance to chloride-induced stress corrosion cracking. A common solution for assessing the resistance of materials to this extremely destructive form of attack is boiling 45% magnesium chloride (ASTM Standard G 36), typically with stressed U-bend samples. As is evident from the following results, the two nickel alloys, Alloy C-4 and Alloy 625, are much more resistant to this form of attack than the comparative, austenitic stainless steels. The tests were stopped after 1008 hours (six weeks).

9 METALLURGICAL STRUCTURE

Alloy C-4 has a face-centered-cubic structure. Its balanced chemical composition gives this alloy good metallurgical stability and high resistance to sensitization.

10 WORKING INSTRUCTION

Alloy C-4 can be hot forged, hot rolled, hot upset, hot extruded and hot formed. However, it is more sensitive to strain and strain rates than the austenitic stainless steels, and the hot working temperature range is quite narrow. For example, the recommended start temperature for hot forging is 1177°C (2150°F) and the recommended finish temperature is 954°C (1750°F). Moderate reductions and frequent re-heating provide the best results.

Hot working

Alloy C-4 may be hot worked in the temperature range 1177 to 954°C (2150 to 1750°F), followed by water quenching or rapid air cooling.

For heating up, workpieces may be charged into the furnace at maximum working temperature. When the furnace has returned to temperature, the workpieces should be soaked for 60 minutes per 100 mm (4 in.) of thickness. At the end of this period it should be withdraw immediately and worked within the above temperature range. If the metal temperature falls below the minimum hot working temperature, it must be reheated.

Heat treatment after hot working is required in order to achieve optimum properties and to ensure maximum corrosion resistance.

Cold working

For cold working the material should be in the annealed condition. Alloy C-4 has a higher work-hardening rate than austenitic stainless steels. This should be taken into account when selecting forming equipment.

Interstage annealing may be necessary with high degrees of cold forming. After cold working with more than 15% deformation solution annealing is required before use.

The alloy is stiffer than most austenitic stainless steels, and more energy is required during cold forming. Also, Alloy C-4 alloy work hardens more readily than most austenitic stainless steels, and may require several stages of cold work, with intermediate anneals.

While cold work does not usually affect the resistance of Alloy C-4 to general corrosion, and to chloride-induced pitting and crevice attack, it can affect resistance to stress corrosion cracking. For optimum corrosion performance, therefore, the re-annealing of cold worked parts (following an outer fiber elongation of 7% or more) is important.

Heat treatment

Solution heat treatment should be carried out in the temperature range 1050 to 1100°C (1920 to 2010°F). Water quenching or rapid air cooling is recommended for thicknesses above 1.5 mm (0.06 in.) and is essential for maximum corrosion resistance.

For any thermal treatment the material should be charged into the furnace at maximum working temperature. Also for any thermal treatment operation the precautions concerning cleanliness mentioned earlier under ’Heating’ must be observed.

Machining

Alloy C-4 should be machined in the solution-treated condition. As the alloy exhibits a high work-hardening rate only low cutting speeds should be used compared with low-alloyed standard austenitic stainless steels. Tools should be engaged at all times. An adequate depth of cut is important in order to cut below the previously formed work-hardened zone.

11 STANDARD SPECIFICATION

Chemical composition

DIN 17744

VdTÜV 424

Seamless tube and pipe

DIN 17751

VdTÜV 424

ASTM B622 / ASME SB622

Welded tube and pipe

ASTM B619 / ASTM B626 / ASME SB619 / ASME SB626

Plate, sheet and strip

DIN 17750

VdTÜV 424

ASTM B575 / ASME SB575

Rod and bar

DIN 17752

VdTÜV 424

ASTM B574 / ASME SB574

Forgings

VdTÜV 424

Fittings

ASTM B366 / ASTM SB366

Coated electrodes

SFA 5.11/A 5.11 (ENiCrMo-7)

DIN 2.4612 (EL-NiMo15Cr15Ti)

F= 43

Bare welding rods & wire

SFA 5.14/ A 5.14 (ERNiCrMo-7)

DIN 2.4611 (SG-NiMo16Cr16Ti)

F= 43

TÜV

Werkstoffblatt 424

Kennblatt 2666

Kennblatt 2667

Kennblatt 2665

Others

NACE MR0175 / ISO 15156

12 COMPETITIVE ADVANTAGE:

(1) More than 50 years experience of research and develop in high temperature alloy, corrosion resistance alloy, precision alloy, refractory alloy, rare metal and precious metal material and products.
(2) 6 state key laboratories and calibration center.
(3) Patented technologies.
(4) Ultra-purity smelting process VIM + IG-ESR + VAR.

(5) High performance material.

13 BUSINESS TERM