UNS N08926,25-6Mo,1.4529,6Mo Super Austenitic Stainless Steel
UNS N08926/1.4529 is a high corrosion resistant stainless steel with high contents of chromium and molybdenum, and provides excellent corrosion resistance under severe environments such as high temperature seawater and flue gas desulfurization plants. Depending on the environment, it is a highly economical stainless steel with corrosion resistance comparable to that of Nickel alloy and pure titanium.
Composition:
20Cr-25Ni-6Mo-1Cu-0.2N
Workability:
Cold and hot workability are approximately equal to those of Type 304, 316, and other standard austenitic stainless steels. However, care is necessary for both cold and hot worked materials because they have high strength.
Weldability:
Possible welding methods include shielded metal arc welding, TIG welding, and plasma welding, in the same manner as with standard austenitic stainless steels. As welding consumables, Alloy 276 should be used. Preheating and post-welding heat treatment are not necessary.
Machinability:
As a distinctive feature of high Ni stainless steels, machinability is difficult in comparison with the austenitic stainless steels, but is easier than with Ni-based alloys. Use of a superhard tool whenever possible, together with a slow feed speed and large cut depth, is advised.
Heat Treatment:
Because UNS N08926/1.4529 is an austenitic stainless steel, heat treatment also conforms to that of standard austenitic stainless steels. The heat treatment conditions normally used with this material are as follows:
Solution heat treatment: 1125~1175℃; Water cooling
Pickling:
A mixture of nitric acid and hydrofluoric acid is used in pickling. However, due to the high corrosion resistance of UNS N08926/1.4529, scale is somewhat difficult to remove in comparison with Type 304. Therefore, the material should be immersed in an alkaline solution before pickling, or if possible, shot blasting is extremely effective.
Applications:
Uses of the superaustenitic 25%Ni20%Cr6.5%MoCu-N steels include:
Condenser and cooling-water piping for power stations and other installations requiring resistance to
seawater.
Seawater and product piping systems on offshore platforms.
Duct liners and components for flue gas desulphurization plant.
Plate or frame heat-exchangers.
Chloride-contaminated phosphoric and sulphuric acid solutions.
Salt concentration and crystallization.
Pulp and paper plant.
Reverse osmosis high pressure piping.
Four similar specifications for 6%Mo superaustenitics:
X NiCrMoCuN 25 20 6 (1.4529), UNS NO8367, UNS NO8925 and UNS NO8926. Each has controlled compositions with nominally 21%Cr 25%Ni 6.5%Mo 0.2%N with some variations (notably Cu and N) between specifications. Compared with common austenitic steels, they are considerably strengthened by the nitrogen addition, and their higher nickel content provides good resistance to chloride stress-corrosion cracking plus less potential to form deleterious phases, eg. sigma. Good resistance to pitting and crevice corrosion in seawater (PRENs average 44-46). Formable and weldable. Design stresses at temperatures up to 400C are given for some types in ASME II.
Similiar Specifications:
ASTM UNS N08367
20-22%Cr, 23.5-25.5%Ni, 6-7%Mo, 0.18-0.25%N, <2%Mn, <0.03%C <0.75%Cu
ASTM UNS N08925
19-21%Cr, 24-26%Ni, 6-7%Mo, 0.10-0.20%N, <1%Mn, <0.02%C, 0.8-1.5%Cu
ASTM UNS N08926
20-21%Cr, 24.5-25.5%Ni, 6.0-6.8%Mo, 0.15-0.25%N, <1%Mn, <0.02%C, 0.8-1.0%Cu
DIN/SEW X1 NiCrMoCuN 25 20 6 1.4529
19-21%Cr, 24-26%Ni, 6-7%Mo, 0.10-0.25%N, <2%Mn, <0.02%C, 0.5-1.5%Cu |
