1. Duplex stainless steel: the coexistence phase ratio of austenite and ferrite about half and half in stainless steel, referred to as dual-phase steel. Some previously known as "double steel", also called "multiphase steels." The actual ratio of ferrite phase accounts for 45% to 55%, corresponding to 55 to 45% austenite. It combines a number of ferrite and austenite most beneficial properties, showing the unique characteristics different from the conventional stainless steel.
2. Use: generally used in medium containing Cl-, the temperature of the occasion. Urea level duplex steel have been used in the Japanese Toyo ACES urea process equipment.
3. Unique characteristics:
(1) Type 316L austenitic stainless steel compared to:
a. has good resistance to stress corrosion cracking performance.
b. with good resistance to pitting, crevice corrosion resistance.
c. high strength, low toughness.
Good (2) welding performance.
(3) low coefficient of linear thermal expansion, and carbon steel similar.
(4) presents several temperature zones embrittlement, there is σ, α, χ-phase precipitation and so on.
4. Techniques on the quirks and cold forming
Habits and Influence Strategies and Technology
A, high strength, surface stress large.
Shaping force, surface defects induced cracking; half of the ferrite phase, cold forming still has a rear directional forming a straight edge margin range.

a, cutting slightly larger in size than conventional stainless steel, polished surface for radioactivity; increased pressure side of the contact surface, the vice-cylinder pressure increase, while the blank slip block increases, book wall head drum kits easy to produce, but also to make up for molding Cutting the amount of margin deficiency caused uneven.

B, high strength, large resilience.
After forming head straight edges difficult to deform when pressure drum forming excessive camber.
b, bad material in the head area or the entire stock of small r preheat molding, preheat temperature should be controlled. After the head end of the first straight edge forming not cut, the straight cutting edge portion after heat treatment setting.
C, a strong work hardening tendency.
Forming deformation rate is limited, otherwise it will crack.
c repeatedly forming head, the intermediate heat treatment step increases, should be cleaned before the heat treatment of the workpiece.
D, 4750C or so brittle zone.
At this temperature process will make material cracking. d, 4750C embrittlement will 3500C ~ 5250C
Appears, thermoforming strictly prohibited in this temperature zone operations.
E, heat quickly, about 9500C have brittle zone.
Billet heating furnace temperature dropped rapidly, and soon reach the brittle zone.
e, billet heating and pressing force, with "sandwich" of "plywood" type of conduct, released to the press should try to shorten the time, after the head forming a release of not less than 9500C
F, thermoforming will lose each half of the equilibrium.
Corrosion Resistance.
f, should the solution heat treatment after hot forming, the maximum heating temperature limit, quenching time as short as possible, such as the head with an opening, after opening solution should be. If there is no opening should be increased exhaust devices.
G, and the linear thermal expansion coefficient similar to carbon steel. G, the equivalent carbon steel hot die clearance requirements.

5. Duplex stainless steel of the market
China has developed five kinds of dual-phase steel, all belong to the second generation of steels, only 0Cr18Ni5Mo3Si2 satisfied standard steel and mass production, the other according to factory standard production, yield little, the steel market a large number of imported foreign products.

Press duplex steel manufacturing requirements, national well-known enterprises have played their own brands such as Sweden AVESTA, SANDVIK company SAF series, Sumitomo's DP series, the French company CLI UR series cross-reference these grades in the following table.:

Standard
Series UNS DIN JIS SAF
Series DP UR series of Chinese brands
Double
Phase
Steel
Cards
No. S31500 1.4417 SAF1805 DP1 00Cr18Ni5Mo3Si2
S31260 SUS329J2L DP3 00Cr25Ni7Mo3WCuN
S31803 1.4462 SAF2205 DP8 URANUS45N 00Cr22Ni5Mo3N
S32304 1.4362 SAF2304
S32750 1.4410 SA2507
S32550 1.4507 URANUS52N
URANUS52N +
S32760 1.4501 URANUS76N

6. Usually duplex stainless steel should pay attention to matters:
(1) sheet shall be subject to solution heat treatment, warranty book, the heating temperature and cooling mode should not use the "rapid cooling" These vague words to express, it is very important to clearly explain the best "solution water quenching" foreign orders is often the case.
(2)
Ni should consider ordering up to the appropriate level of the cap. While considering Ni, N relationship, because they are austenite forming elements, if Ni, N is the upper limit of the number is too high may lead to the austenite phase, the impact resistance performance of SCC.
(3) mechanical properties, the yield point is not too high, hardness is not exceeded, otherwise difficult to cold forming.
(4) China GB150-1998 provisions elongation duplex steel should be not less than 25%.