Alloy 255

Introduction

Alloy 32550 (super duplex 255) is a super duplex stainless steel supplied in the hot worked and annealed condition. It achieves higher strengths than most stainless steels and alternative corrosion resistant alloys, offering the potential to reduce section size and therefore weight and cost. As a 25% Cr alloy, with significant additions of copper, Alloy 32550 offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid.In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C. Excellent ductility and impact strength at both ambient and sub-zero temperatures combine with a high resistance to abrasion, erosion and cavitation erosion.

Equivalent Grades Of Alloy 255

Zeon Grade Alloy Name UNS EN / DIN / W Nr. AISI / ASTM Trademarks
Zeon51 Alloy 255 UNS S32550 1.4507 F61 Ferralium255/URANUS52N

Chemical Composition Of Alloy 255

Elements Min Max
Cr 24.50 26.50
Ni 5.50 6.50
Mo 3.10 3.80
Cu 1.50 2.00
C - 0.025
Mn 0.80 1.20
N 0.20 0.25
Si - 0.70
P - 0.025
S - 0.005
Fe - Balance

Physical Properties Of Alloy 255

Density (Kg/m3) 7810
Magnetic Permeability (20°C) 33
Young’s Modulus (kN/mm2) 199
Specific Electrical Resistance, 20°C (Ω-m) 0.80 x 10-6
Mean coefficient of thermal expansion, 20-100°C (m/m/degC) 11.1 x 10-6
Specific Heat, 20°C (J/kg.K) 475
Thermal conductivity, 20°C (W/m.K) 14.2
Fracture Toughness, KQ (MPa/m2) 98

Mechanical Properties Of Alloy 255

  Bars up to and including 4.0” (100mm) diameter or section Bars greater than 4.0” (100mm) and up to 12.0” (300mm) diameter or section Bars greater than 12.0” (300mm) diameter or section
0.2% Proof Stress 586 N/mm2 85ksi 586 N/mm2 85ksi 570 N/mm2 83ksi
Tensile Strength 790 N/mm2 114.5ksi 790 N/mm2 114.5ksi 760 N/mm2 110ksi
Elongation, 5.65√S0 and 4D 25%   25%   25%  
Reduction of Area 50%   50%   50%  
Hardness (Brinell) 220-270   220-270   220-270  
Impact Strength (Room Temp) 80J 59 ft.lb 80J 59 ft.lb 80J 59 ft.lb
Impact Strength (-46degC) 45J av (35J min) 33 ft.lb av (25.8 ft.lb min) 45J av (35J min) 33 ft.lb av (25.8 ft.lb min) 45J av (35J min) 33 ft.lb av (25.8 ft.lb min)
Corrosion Resistance Properties of Alloy 255
UNS S32550 Displays superior corrosion resistance in most media. Also, 2550 typically out performs duplex alloy 2205. It performs well in sulphuric, phosphoric, and nitric and shows excellent resistance to organic acids such as acetic and formic acid. Highly reducing media should be avoided.

Processing Alloy 255

Heat Treatment Duplex stainless steels cannot be hardened by heat treatment. They can however be work hardened. Solution treatment or annealing can be done by rapid cooling after heating to around 1100°C.
Welding Duplex stainless steels have good weldability. All standard welding processes can be used. They are not quite as easily welded as the austenitic grades but low thermal expansion in duplex grades reduces distortion and residual stresses after welding.

Applications Of Alloy 255
Oil & Gas industry pumps, valves, wellhead and subsea equipment Pollution control scrubbers, precipitators, fans and pumps Marine propellers, shafts, rudders, seals, pumps, valves
Bolts and fasteners Process industry equipment in sulphuric acid, nitric acid, phosphoric acid, PP / PVC/TiOx production, agrochemicals Grain and vegetable processing plant, sugar cane centrifuges
Pulp and paper digester blow vales, feed valves, washers, black liquor heater tubes, bleaching components Copper smelting fans, tuyere bars, wet scrubbers, leaching area precipitators Water and sewage treatment, desalination, swimming pools