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The difference of grades 1.4401/316,1.4404/316L and 1.4571/316Ti
- Sep 10, 2018 -

Stainless Steel 316 is a chromium-nickel based steel that possesses increased levels of resistance against several substances, due to the addition of molybdenum in its composition. The molybdenum allows SS 316 to be more resistance to corrosion overall, with specific resistance against chlorine pitting. SS 316 is also found to be more applicable in areas with high or elevated temperatures compared to other stainless steels. It has more heat resistance than Type 304 but otherwise possesses many of the same general characteristics.
316’s corrosion resistance is especially effective against chemicals, such as those used in the paper and textile industries. The metal finds other common applications in food processing equipment, chemical processing, nuts and bolts, and medical implants.
While the metal is pliable under hot and cold-working techniques, it cannot be work hardened with heat treatment and in general is considered to have lower weldability compared to the 304 type stainless steels. However, it is still preferred over many other stainless steel grades in terms of workability.
Stainless Steel 316L was designed to have a much lower carbon content than its 316 counterpart. As such, 316L is useful in areas where the avoidance of carbon precipitation is desired. The metal is commonly applied in weldments, where its particular carbon content combined with welding guarantees maximum resistance against general corrosion, and also in heavy gauge components.
316L is considered to be more resistant to oxidation than type 316, especially in warm marine environments. Once again, its low levels of carbon protect it against carbon precipitation. The metal also shows resistance in extremely low temperatures, even down to cryogenic levels. In regards to heat, 316L shows better resistance to creep, stress to rupture and overall strength than other stainless steel grades.
Many of the same work practices effective on type 316 may also be employed on 316L, including weldability and work hardening through cold working. In addition, 316 does not require post-work annealing to maximize its corrosion resistance, however annealing may be utilized in certain situations.

Stainless Steel 316Ti is referred to as the stabilized grade of the 316 types, and also one of the two 316 stainless steels that is recommended for higher temperature situations. This grade contains a small amount—typically only 0.5%—of titanium. While it still possesses many of the characteristics of other 316 grades, the addition of titanium allows 316Ti to be protected from precipitation at elevated temperatures, even with prolonged exposure.
316Ti also contains an addition of molybdenum in its composition. Like in other 316 grades, the molybdenum serves as increased protection against corrosion, pitting from chloride solutions and increased strength when placed in high temperature environments. However, its high temperature resistance is also compounded by its titanium content, which allows 316Ti to be immune to precipitation at these temperatures. Additionally, the metal shows resistance to acids, such as sulfuric acids, hydrochloric acids, and acid sulfates.
316Ti is commonly utilized in heat exchangers, paper mill equipment, and architectural components in marine environments.

Is 316Ti interchangeable with 316L?

Under most conditions it can be taken that the two grades are interchangeable, 316L (316S11/1.4404) being suitable for applications where 316Ti (320S31/1.4571) is specified. In aqueous corrosion media or environments at ambient temperatures, there is no practical advantage in specifying the 316Ti type in preference to the 316L. In some circumstances the 316L (1.4404 / 1.4432) grades may be better choices.

 Mechanical Properties

The presence of titanium to 1.4571 does, however, give some improvements to mechanical strength, especially, at elevated temperatures above about 600 C. and care must therefore be exercised in selecting 1.4404 as a substitute under these conditions. The 1.4571 may however have inferior impact properties at ambient temperatures, compared to the 1.4404 / 1.4432 types.

 Machinability

The machinability of 1.4571 can also be an issue as the titanium carbo-nitrides particles can result in higher tool wear and may not cold form or cold head as readily as the 1.4404 / 1.4432 types.

 Polishing

The titanium carbo-nitrides in 1.4571 can also result in problems where high standards of polished surface finish are required. The titanium carbo-nitrides particles can result in 'comet-tail' streaks on the polished surface as they are dragged out during polishing. This is similar to the 1.4541(321) grade, which was not recommended for a 'No8' bright mechanical polish in now obsolete BS1449 Pt2 (now replaced by BSEN 10088:2-1995 finish 1P/2P).

 Corrosion Resistance

There is also some evidence that the 1.4571 type may have inferior pitting and stress corrosion cracking resistance, compared to the 1.4404 / 1.4432 types, although the general corrosion resistance can be assumed to be generally similar. The titanium stabilised 1.4571 grade may also be prone to 'knife line attack' in the heat-affected zones of welds, very close to the fusion zone where the carbo-nitrides have redissolved in the solid steel matrix.

Specifications – Stainless Steel 316 / 316L / 316Ti

STANDARD

316

316L

316TI

UNS

S31600

S31603

S31635

WERKSTOFF NR.

1.4401

1.4404

1.4571

Chemical Composition – 316L / 316Ti / 316 Stainless Steel

ELEMENT

316

316L

316TI

NI

11.0 – 14.0

10.0 – 14.0

10.0 – 14.0

C

0.08 max

0.035 max

0.08 max

MN

2.0 max

2.0 max

2.0 max

P

0.045 max

0.045 max

0.045 max

S

0.30 max

0.30 max

0.30 max

SI

1.0 max

1.0 max

0.75 max

CR

16.0 – 18.0

16.0 – 18.0

16.0 – 18.0

MO

2.0 – 3.0

2.0 – 3.0

2.0 – 3.0

TI



5x(C+N) – 0.70

N



0.10 max