Super Austenitic Stainless Steel Alloy 27-7MO / UNS S31277 For Power Generating

Super austenitic stainless steel Alloy 27-7MO (UNS S31277) semi-products for clean energy and power generating

1 PRODUCT

Super austenitic stainless steel Alloy 27-7MO (UNS S31277) semi-products for clean energy and power generating.

Alloy 27-7MO standard semi-product forms include sheet, strip, plate, round bar, flat bar, forging, hexagon, ring, disc, wire and fastener etc.

2 EQUIVALENT DESIGNATION

UNS S31277, Incoloy ® alloy 27-7MO

3 APPLICATION

Applications for Alloy 27-7MO are found in the pollution control, power, marine, chemical processing, pulp and paper and oil and gas industries. The alloy offers a unique combination of corrosion resistance, high strength and ease of fabrication at an economical price.

4 OVERVIEW

Alloy 27-7MO is an advanced super austenitic stainless steel offering corrosion resistance in most environments superior to 6% molybdenum super austenitic stainless steels. In many environments alloy 27-7MO offers resistance approaching that of much more highly alloyed and expensive materials such as Alloys 625, 622, and C-276.

Alloy 27-7MO products typically contain 27% nickel, 22% chromium, 7.2% molybdenum, and 0.34% nitrogen. The alloy's content of nickel and nitrogen produce a stable austenitic structure. By virtue of its content of molybdenum, chromium, and nitrogen, alloy 27-7MO offers excellent resistance to pitting and crevice corrosion. The nickel, nitrogen, and molybdenum provide resistance to reducing media while a high content of chromium offers resistance to oxidizing media. Alloy 27-7MO performs well in mixed acid environments, especially those containing oxidizing and reducing acids. The alloy's contents of nickel and nitrogen result in resistance to stress corrosion cracking and attack by caustic media. Alloy 27-7MO offers excellent resistance to corrosion in seawater and brine. It is resistant to the aggressive media encountered in air pollution control systems such as flue gas desulfurization equipment for high-sulfur coal-fired electric power utilities.

5 CHEMICAL COMPOSITION (wt%):

Table 1 (wt%) as per ASTM A240

6 MECHANICAL PROPERTIES

Alloy 27-7MO exhibits an optimum combination of strength and ductility. Typical mechanical properties of alloy 27-7MO products are compared with those of similar alloys in Table 2. Alloy 27-7MO is normally supplied in the annealed condition.

Table 2 Typical mechanical properties at room temperature

7 CORROSION RESISTANCE

Pitting corrosion resistance

PRENs for alloy 27-7MO and similar materials are seen in Table 3. Based on these values of PREN, alloy 27-7MO would be predicted to offer significantly better corrosion resistance than alloy 25-6MO (and similar grades of super-austenitic stainless steel) and even superior performance to alloy 625, a significantly more highly alloyed (and costly) material. Alloy 27-7MO's resistance approaches that of alloy C-276.

Table 3 Pitting resistance equivalency numbers (PREN)*

*PREN = %Cr + 1.5 (%Mo + %W + %Nb) + 30 (%N)

8 WORKING INSTRUCTION

Alloy 27-7MO is readily fabricated, formed, and joined utilizing conventional equipment, techniques, and products. Forming can either be hot or cold.

Heating

Stagnant oxidizing conditions must be avoided, particularly when heating the alloy above 1700°F (925°C), to prevent catastrophic oxidation. For example, attack can occur at crevice points when flat rolled products are stacked or laid against each other in a heat treating furnace. Forced gas and air flow are recommended. Prolonged exposure to temperatures between 950 and 1560°F (510 to 850°C) during heating or cooling can cause precipitation of undesirable phases such as sigma. It can also cause sensitization which may lead to intergranular attack or increased susceptibility to stress corrosion cracking.

Hot forming

Alloy 27-7MO is best hot worked in the temperature range of 1800 to 2100°F (980 to 1150°C).

Cold forming

The work hardening rate of alloy 27-7MO is similar to that of Alloy 600 or grade 316 or 317 stainless steel. Equipment used to form austenitic (300 series) stainless steels and nickel-based alloys will normally be suitable for forming alloy 27-7MO. The effect of cold work on the mechanical properties of Alloy 27- 7MO and similar products is shown in Table 4.

Table 4 Typical room temperature mechanical properties of cold worked sheet

Annealing

Annealing is done at 2100°F (1150°C). Cooling after heat treatment should be by rapid air cool or water quench.

Machining

The machining characteristics of alloy 27- 7MO are similar to those of other austenitic alloys. Products are readily machined in the annealed condition.

9 STANDARD SPECIFICATION

ASTM A213 / ASME SA213 Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes

ASTM A240 / ASME SA240 Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications

ASTM A249 / ASME SA249 Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes

ASTM A312 / ASME SA312 Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes

ASTM A580 Stainless Steel Wire

ASTM B625 / ASME SB625 Plate, strip

ASTM B649 / ASME SB649 Bars

ASTM B677 / ASME SB677 Seamless pipe

ASTM B673 / ASME SB673 Welded pipe

ASTM B674 / ASME SB674 Welded pipe

ASME Code Case 2458

10 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) Excellent high performance.

11 BUSINESS TERM