Nov 7 2001
Chemical Formula
Fe, <0.030% C, 24-26% Cr, 5.5-8.0% Ni, 3.0-5.0% Mo, <1.50% Mn, <0.80% Si, <0.035% P, <0.020% S, 0.5-3.0% Cu, 0.20-0.35%N
Introduction
Grade UR52N+ stainless steels belong to the group of super duplex grade steels that combines exceptional corrosion resistance and high strength. Grade UR52N+ is a registered trade mark of the Usinor group, and designated as UNS S32550 for bar products in ASTM A276M. Super duplex grades are not suitable for operations in high or low temperatures, and grade UR52N+ steels are not preferred for use at temperatures above 270°C or below -50°C, owing to the risk of reduction in toughness.
Copper addition improves the resistance of super duplex grades to strong reducing acids, such as sulphuric acid. Grade UR52N+ is also resistant to crevice or pitting corrosion and stress corrosion cracking in high chloride environments.
Key Properties
The properties of flat rolled products such as coils, plates and sheets of grade UR52N+ stainless steels covered in ASTM A240M, Grade S32520 are given below. These specifications may not be similar to products such as bars and pipes.
Composition
The following table outlines the chemical compositions of grade UR52N+ stainless steels:
Table 1. Composition ranges of grade UR52N+ stainless steels
|
Grade
|
C
|
Mn
|
Si
|
P
|
S
|
Cr
|
Mo
|
Ni
|
Cu
|
N
|
|
UR52N+
|
min.
max
|
-
0.030
|
-
1.50
|
-
0.80
|
-
0.035
|
-
0.020
|
24
26
|
3
5
|
5.5
8
|
0.5
3
|
0.20
0.35
|
Mechanical Properties
The typical mechanical properties of grade UR52N+ stainless steels are given in the table below:
Table 2. Mechanical properties of grade UR52N+ stainless steels
|
Grade
|
Tensile Strength (MPa) min
|
Yield Strength 0.2% Proof (MPa) min
|
Elongation (% in 50mm) min
|
Hardness
|
|
Rockwell C (HR C)
|
Brinell (HB) max
|
|
UR52N+
|
770
|
550
|
25
|
-
|
310
|
Physical Properties
The physical properties of grade UR52N+ stainless steels are tabulated below:
Table 3. Typical physical properties of grade UR52N+ stainless steels
|
Grade
|
Density
(kg/m3)
|
Elastic Modulus
(GPa)
|
Mean Co-eff of Thermal Expansion (µm/m/°C)
|
Thermal Conductivity
(W/m.K)
|
Specific Heat 0-100°C
(J/kg.K)
|
Elec Resistivity
(nΩ.m)
|
|
20-200°C
|
20-300°C
|
20-500°C
|
At 20°C
|
At 500°C
|
|
UR52N+
|
7810
|
205
|
13.5
|
14.0
|
14.5
|
17
|
-
|
450
|
850
|
Grade Specification Comparison
The table provides the approximate grade comparisons of UR52N+ stainless steels:
Table 4. Grade specifications of grade UR52N+ stainless steels
|
Grade
|
UNS No
|
Old British
|
Euronorm
|
Swedish SS
|
Japanese JIS
|
|
BS
|
En
|
No
|
Name
|
|
UR52N+
|
S32520
|
-
|
-
|
1.4507
|
X2CrNiMoCuN25-6-3
|
-
|
-
|
Possible Alternative Grades
The suitable alternatives to UR52N+ stainless steels are tabulated below:
Table 5. Possible alternative grades to UR52N+ stainless steels
|
Grade
|
Reasons for choosing grade UR52N+
|
|
2205
|
The lower cost and better availability of 2205 are required, and a lower corrosion resistance and strength can be accepted.
|
|
6% Mo
|
Higher ductility of this austenitic grade is needed, and the much lower strength is acceptable. Corrosion resistance is similar in many environments, but needs to be considered case by case.
|
|
Ni Alloys
|
A corrosion resistance even higher than UR52N+ is required, and a higher cost structure is acceptable.
|
Corrosion Resistance
Grade UR52N+ stainless steels have excellent corrosion resistance, higher than all kinds of stainless steels. They also offer high resistance to inter-granular corrosion and stress corrosion cracking in both sulphide and chloride environments.
Grade UR52N+ is rated to be more corrosion resistant than grade 904L, and almost similar to that of 6% molybdenum "super austenitic" grades. The crevice corrosion resistance of grade UR52N+ can be more than that of 6% molybdenum grades in certain cases. Addition of copper to the material improves its resistance to sulphuric acid and other reducing acids in the mild concentration range. This material is preferred for applications in chemical and petrochemical processing and high temperature marine environments.
Heat Resistance
Super duplex steel grades have good oxidation resistance at high temperatures. However, they are subjected to embrittlement at temperatures greater than 270°C, like any other duplex stainless steels. Embrittled steels can be modified only through full solution annealing treatment.
Heat Treatment
Grade UR52N+ stainless steel can be solution-treated at 1080 to 1120°C and then cooled rapidly. Thermal treatment does not harden super duplex and duplex steel grades.
Welding
Grade UR52N+ stainless steel can be welded using all conventional welding methods without the need for pre-heating. Nickel-based stainless steels provide welds with high corrosion resistance. The coefficient of the thermal expansion of duplex stainless steels is lower than that of austenitic grades, which minimizes residual stresses and distortion. Corrosion resistance of the welds can be improved by post-weld annealing.
Fabrication
Grade UR52N+ stainless steel is a high strength steel that requires forming forces for fabrication. The ductility of this grade is sufficient for most of the operations. However, processes such as cold-forging involves heavy deformation, and hence the steel needs to be more ductile. An intermediate solution annealing can be carried out under cases that require more than 20% cold work.
Applications
Grade UR52N+ finds application in the following:
- Pulp and paper processing industries
- Chemical processing, transport and storage
- High chloride and marine environments
- Pollution control processes, such as flue gas desulphurization
- Oil and gas processing industries