Structural Steel for Ships

---

Shapes and bars are normally available as Grades A, AH32, or AH36. Other grades may be furnished by agreement between the purchaser and the manufacturer.

When the steel is to be welded, it is presupposed that a welding procedure suitable for the grade of steel and intended use or service will be utilized.

Applicable Documents

• ASTM A6M Specification for General Requirements for Delivery of Rolled Steel Plates, Shapes, Sheet Piling, and Bars for Structural Use
• ASTM A 370 Methods and Definitions for Mechanical Testing of Steel Products
• ASTM E 112 Method of Determining the Average Grain Size

Manufacture

The steel may be made by any of the following processes: open-hearth, basic-oxygen, electric-furnace, vacuum arc remelt (VAR), or electroslag remelt (ESR).

Except for Grade A steel up to and including 12.5 mm in thickness, rimming-type steels shall not be applied.

Grades AH32 and AH36 shapes through 426 lb/ft, and plates up to 12.5 mm in thickness may be semi-killed, in which case the 0.10 % minimum silicon does not apply.

Besides few exceptions Grades D, DS, CS, E, DH32, DH36, EH32, and EH36 shall be made using a fine grain practice. For ordinary strength grades, aluminum shall be used to obtain grain refinement. For high strength grades, aluminum, vanadium, or columbium (niobium) may be used for grain refinement.

Grade D material 35 mm and under in thickness, at the option of the manufacturer, may be semi-killed and exempt from the fine austenitic grain size.

Heat Treatment

Plates in all thicknesses ordered to Grades CS and E shall be normalized. Plates over 35 mm in thickness ordered to Grade D shall be normalized. When Grade D steel is furnished semi-killed, it shall be normalized over 25 mm in thickness. Upon agreement between the purchaser and the manufacturer, control rolling of Grade D steel may be substituted for normalizing, in which case impact tests are required for each 25 tons [25 Mg] of material in the heat.

Plates in all thicknesses ordered to Grades EH32 and EH36 shall be normalized. Grades AH32, AH36, DH32, and DH36 shall be normalized when so specified. Upon agreement between the purchaser and the manufacturer, control rolling of Grade DH may be substituted for normalizing, in which case impact tests are required on each plate.

In the case of shapes, the thicknesses referred to are those of the flange.

Metallurgical Structure

Fine grain practice for ordinary strength grades shall be met using aluminum. For higher strength grades, aluminum, vanadium, or columbium may be used as grain refining elements.

Grain size shall be determined on each heat by the Mc-Quaid-Ehn Method of Method E 112. The grain size so determined shall be No. 5 or finer in 70 % of the area examined.

As an alternative to the McQuaid-Ehn test, a fine grain practice requirement may be met by a minimum acid-soluble aluminum content of 0.015 % or minimum total aluminum content of 0.020 % for each heat.

For Grades DH32, DH36, EH32, and EH36 the fine grain practice requirement may also be met by the following:

• Minimum columbium (niobium) content of 0.020 % or minimum vanadium content of 0.050 % for each heat, or
• When vanadium and aluminum are used in combination, minimum vanadium content of 0.030 % and minimum acid-soluble aluminum content of 0.010 % or minimum total aluminum content of 0.015%.

Mechanical Requirements

Tension Tests. Except as specified in the following paragraphs the material as represented by the test specimens shall conform to the prescribed tensile requirements.

Unless a specific orientation is called for on the purchase order, tension test specimens may be taken parallel or transverse to the final direction of rolling at the option of the steel manufacturer.

Shapes less than 645 mm2 in cross section, and bars, other than flats, less than 12.5mm in thickness or diameter need not be subjected to tension tests by the manufacturer. For material under 8 mm in thickness or diameter, a deduction from the percentage of elongation in 200 mm of 1.25 percentage points shall be made for each decrease of 0.8 mm of the specified thickness or diameter below 8 mm.

Toughness Tests (material 50 mm and less in thickness). Except as permitted bellow, Charpy V-notch tests shall be made on Grade B material over 25 mm in thickness and on material of Grades D, E, AH32, AH36, DH32, DH36, EH32, and EH36.

Toughness tests are not required: (a) on Grade D normalized material made fully killed and having a fine austenitic grain size, (b) on Grades AH32 and AH36 when normalized, or when 12.5 mm or less in thickness when treated with vanadium or columbium (niobium) or 35 mm or less in thickness when treated with aluminum, and (c) on Grades DH32 and DH36 material when normalized or when 12.5 mm or less in thickness when treated with vanadium or columbium (niobium) or less in thickness when treated with aluminum, and on Grades DH32 and DH36 material when normalized.

For plate material, when required, one set of three impact specimens shall be made from the thickest material in each 50 tons [45 Mg] of each heat of Grades B, D, AH32, AH36, DH32, and DH36 steels and from each rolled product of normalized Grades E, EH32, and EH36 steels. When heat testing is called for, a set of three specimens shall be tested for each 50 tons [45 Mg] of the same type of product produced on the same mill from each heat of steel. The set of impact specimens shall be taken from different as-rolled or heat-treated pieces of the heaviest gage produced. An as-rolled piece refers to the product rolled from a slab, billet, bloom, or directly from an ingot.

For flats, rounds, and shapes, one set of three impact tests shall be taken from each 25 tons [25 Mg] of each heat for Grade E, EH32, or EH36 and, when required, from each 50 tons [45 Mg] of each heat of Grade B, D, AH32, AH36, DH32, or DH36 material. Where the maximum thickness or diameter of various sections differs by 10 mm or more, one set of impacts shall be made from both the thickest and the thinnest material rolled regardless of the weight represented.

The specimens for plates shall be taken from a corner of the material and the specimens from shapes shall be taken from the end of a shape at a point one-third the distance from the outer edge of the flange or leg to the web or heel of the shape.

Specimens for bars shall be in accordance with Specification A 6M. The center longitudinal axis of the specimens shall be located as near as practical midway between the surface and the center of the material and the length of the notch shall be perpendicular to the rolled surface. Unless a specific orientation is called for on the purchase order, the longitudinal axis of the specimens may be parallel or transverse to the final direction of rolling of the material at the option of the steel manufacturer.

Each impact test shall constitute the average value of three specimens taken from a single test location.

After heat treatment or reheat treatment a set of three specimens shall be tested and evaluated in the same manner as for the original material.

Toughness Tests (material over 50 mm thick). Charpy V-notch tests are required for all grades of steel over 50 mm thick, except for Grade A that is produced killed, using a fine grain practice and normalized. For plate material one set of three impact specimens shall be made from the thickest material in each 50 tons [45 Mg] of each heat of Grades A, B, D, DS, AH32, AH36, DH32, and DH36, and from each rolled product of Grades CS, E, EH32, and EH36. For flats, rounds, and shapes, one set of three impact tests shall be taken from each 25 tons [25 Mg] of each heat for Grades CS, E, EH32, and EH36, and from each 50 tons of each heat of Grades A, B, D, DS, AH32, AH36, DH32, and DH36 material.

Rivet Steel and Rivets. For rivet steel a sulfur print requirement shall be met when other than killed or semi-killed steel is applied, in order to confirm that its core is free of concentrations of sulfur segregates and other nonmetallic substances. Test specimens for rivet bars that have been cold drawn shall be normalized before testing. Finished rivets are to be selected as sample specimens from each diameter and tested hot and cold by bending and crushing in the following manner: the shank must stand being doubled together cold, and the head being flattened hot to a diameter 2.5 times the diameter of the shank, both without fracture.