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S770 Seamless CHS, RHS, SHS, Elliptical Hollow Sections

Beverly Steel, a major S770 high strength and S770 extra high strength steel seamless hollow sections supplier for engineering applications where the critical factors are weight control and high stress resistance. S770 high strength and S770 extra high strength hollow sections are in low temperature of -40 degree C and -50degree C, suitable applied in lifting and load handling systems and as components of lift arms (batten and tower mast) in mobile cranes, marine cranes, sea port cranes, rocket and spaceship launch tower and other super structural engineering in the extreme environmental conditions.

For these applications, high-performance steels (fine-grain and high-strength steels) with excellent strength resistance and resilience values are used, which means that the stress resistance of the systems can be increased, thus also guaranteeing their use in extreme environmental conditions.

Furthermore, the chemical composition of our seamless steel tubes is carefully controlled in order to guarantee good weldability, a fundamental issue for structures made of tubular components welded together. High-strength and extra high strength seamless steel hollow sections are also used in steel constructions for civil engineering purposes where the relationship between mass and space occupied is especially critical.

Nearest Equivalent Grade : EN10210 Hot Finished BQ800

Regular Hollow Section Profiles : Rectangular(RHS), Square(SHS), Circular (CHS), Elliptical,

Half-Elliptical, Flat-Oval, Octagonal, Hexagonal and Triangular

Weldability

The steel grades indicated in the specification are weldable with traditional welding procedures, given observance of the generally accepted technical rules. It is important to define a welding procedure that takes into account the following conditions :

- Thickness of the based material

- Specific heat input (specially for HAZ)

- Design requirements

- Welding method

- Welded material characteristics

Particular precautions should be taken towards crack susceptibility, which is more likely to happen with high thickness and high resistance. This phenomenon is connected mainly to the following factors :

- Chemical analysis (by means of CEV)

- The amount of diffusible hydrogen in the welded material

- Tensile stress concentrations at the welded joint

CEV - Carbon Equivalent Value

The maximum CEV (Carbon Equivalent Valued) is determined, based on the cast analysis, by the following formula : CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

The CEV shall comply with valued stated in the table

MAXIMUM CEV VALUES

Grade

Wall Thickness (mm)

CEV (%) (max)

S770

Wt ≤ 12,5mm

0.55

Wt > 12,5mm

0.61

Options : other calculation methods like PCM/CET may be agreed

Mechanical Properties

In order to meet tensile requirements, the tensile test shall be carried out at room temperature in longitudinal direction in accordance with EN ISO 6892-1.

Yield strength shall be reported as Rp 0.2% proof stress (0.2% permanent offset).

Minimum Yield Strength (MPa)

Tensile Strength (MPa)

Min. Elong. Long%

Min. Elong. Transv%

Grade

WT (mm) →

≤ 12

> 12

≤ 20

> 20

≤ 40

> 40

≤ 50

≤ 20

> 20

≤ 40

> 40

≤ 50*

ALL

ALL

S770

770

750

700

670

820-990

750-920

720-890

15

13

S770 Extra

High Strength

770

740

700

820-990

800-970

740-910

15

13


(*)Note that for 40 < wt ≤ 50mm chemistry should be different from what reported in “CHEMICAL ANALYSIS” table at below.

Chemical Analysis

CHEMICAL ANALYSIS %

Grade

C

Mn

Si

P

S

Ni

Cu

V

Cr

Mo

S770

≤ 0.18

≤ 1.70

0.20-0.50

≤ 0.020

≤ 0.007

≤ 0.3

≤ 0.20

≤ 0.10

≤ 0.50

≤ 0.50

S770 Extra

High Strength

≤ 0.18

≤ 1.70

0.20-0.50

≤ 0.020

≤ 0.007

≤ 0.3

≤ 0.20

≤ 0.10

≤ 0.50

≤ 0.50

Other elements like Nb and Ti may be added in order to increase hardenability and improve mechanical properties up to a total combined of 0.10% max. Boron shall not be intentionally added. Non-specified residual elements shall not exceed 0.05% each.

Impact Toughness

Impact tests shall be carried out in accordance with ENISO 148-1 for 10 X 10mm full size specimens in the longitudinal

direction at temperatures -40 degree C and -50 degree C(**).

Energy values for Charpy-V notch test for each grade are indicated below :

IMPACT TEST PROPERTIES IN LONGITUDINAL DIRECTION

Grade

WT (mm)

Test temp. (ºC)

Min. Ave. Energy (J)

S770

≤ 40

-40

45

> 40

≤ 50

40

S770 Extra High Strength

≤ 40

-50

45

> 40

≤ 50

40

Transversal direction impact test could be carried out upon additional request

IMPACT TEST PROPERTIES IN TRANSVERSAL DIRECTION

Grade

WT (mm)

Test temp. (ºC)

Min. Ave. Energy (J)

S770

≤ 40

-40

30

> 40

≤ 50

-40

27

S770 Extra High Strength

≤ 40

-50

30

> 40

≤ 50

27

(**) Other test temperature may be performed upon agreement.

When tube dimension do not allow full size testing, sub-size specimens shall be used according to PSP00148.

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