What is Super Duplex Steel

Super duplex stainless steel refers to the duplex steel with PREN>40, containing 25%Cr and high molybdenum (>3.5%), high nitrogen (0.22%~0.30%), the main grades are UNS S32550 (UR52N+), S32750 (SAF 2507 ) and S32760 (Zeron 100) were developed by companies such as CLI in France, SANDVIK in Sweden and MATER+PLATT in the United Kingdom. Their deformed materials came out in about 1990 and 1991 and entered the market in recent years. The composition of these three steels is similar, the difference lies in the content of tungsten and copper

Currently in China, the main grade of super duplex steel is 2507 (S32750)

2507 (UNS S32750) duplex stainless steel has strong strength and corrosion resistance, and is mainly used in chemical processing, petrochemical and subsea equipment. It has strong resistance to chloride corrosion, high thermal conductivity and low thermal expansion coefficient. The high content of chromium, molybdenum and nitrogen makes it highly resistant to pitting, crevice corrosion and general corrosion. Its impact strength is also very high, 2507 alloy is not suitable for use in a temperature environment higher than 570 ℃, and its toughness will be reduced in such an environment for a long time. Its chemical composition and mechanical properties are shown in Tables 1 and 2.

Table 1 Chemical composition (%)

GRADE	C≤	Mn≤	Si≤	S≤	P≤	Cr	Ni	Mo	Cu≤	N
S32750（SAF2507）	0.03	1.2	0.8	0.02	0.035	24/26	6.0/8.0	3.0/5.0	0.5	0.24/0.32
00Cr25Ni7Mo4N
S31803（SAF2205）00Cr22Ni5Mo3N	0.03	2	1	0.02	0.03	21/23	4.5/6.5	2.5/3.5		0.08/0.2
S31500(3RE60)	0.03	1.2/2.0	1.4/2.0	0.03	0.03	18/19	4.25	2.5/3.0		0.05/0.1
00Cr18Ni5Mo3Si2							5.25

Table 2. Mechanical Properties

GRADE	heat treatment	σb (Mpa)	σs(Mpa)	δ%	硬度≤
	℃	≥	≥	≥
Brinell	Rockwell
S32750（SAF2507） 00Cr25Ni7Mo4N	1025-1125 water quenching	800	550	15	310	32
S31803（SAF2205） 00Cr22Ni5Mo3N	1020-1100 water quenching	620	450	25	290	30.5
S31500(3RE60) 00Cr18Ni5Mo3Si2	980-1040 water quenching	630	440	30	290	30.5

Super duplex stainless steel 2507 (S32750) has higher corrosion resistance and better mechanical properties than duplex stainless steel 2205 (S31803). Often used in special chemical environments such as offshore oil platforms (heat exchanger tubes, water treatment and water supply systems, fire protection systems, water spray systems, water stabilization systems), desalination (desalination) equipment (high pressure pipes in Ro equipment, seawater pipes) in the device. Name S32750, SAF2507, F53, GB 00Cr25Ni7Mo4N. Application fields are: oil and gas industry equipment; offshore platforms, heat exchangers, underwater equipment, fire equipment; chemical processing industry, vessel and pipeline industry; desalination plants, submarine pipelines; mechanical parts (high strength, anti-corrosion parts), Energy industry FGD system, industrial scrubbing system, absorption tower, etc.