Section 2 Forgings for ship and other structural applications

2.1.1 This Section gives the specific requirements for carbon-manganese steel forgings intended for ship and other structural applications such as rudder stocks, pintles, etc.

2.1.2 Where it is proposed to use an alloy steel, particulars of the chemical composition, mechanical properties and heat treatment are to be submitted for approval, see Ch 5, 1.4 Chemical composition 1.4.3.

2.2.1 For forgings to which structural items are to be attached by welding or which are intended for parts of a fabricated component, or are to be weld cladded or may be subject to weld repair in service, the chemical composition of ladle samples is to comply with Table 5.2.1 Chemical composition limits for hull steel forgings:

Table 5.2.1 Chemical composition limits for hull steel forgings

Steel type	Composition in percentage mass by mass maximum unless shown as a range
	C	Si	Mn	P	S	Cr	Mo	Ni	Cu See Note 2	Total residuals
C, C-Mn	0,23 Max. See Note 1	0,45 Max.	0,30-1,50	0,035 Max	0,035 Max	0,30 Max See Note 2	0,15 Max See Note 2	0,40 Max. See Note 2	0,30 Max.	0,85 Max.
Alloy See Note 4	Note 3	0,45 Max.	Note 3	0,035 Max.	0,035 Max.	Note 3	Note 3	Note 3	0,30 Max.	-
Note 1: The carbon content may be increased above this level provided that the carbon equivalent (Ceq) is not more than 0,41%, calculated using the following formula: Note 2: Elements are considered as residual elements. Note 3: Specification is to be submitted for approval. Note 4: The contents of all alloying elements and significant impurities detailed in the specification are to be reported.

2.2.2 It is recommended that forgings for rudder stocks, pintles and rudder coupling bolts comply with Ch 5, 2.2 Chemical composition, Table 5.2.1 Chemical composition limits for hull steel forgings in order to obtain satisfactory weldability for any future repairs by welding in service.

2.2.3 For C and C-Mn steel forgings not intended for welded construction, the carbon content may be 0,65 per cent maximum.

2.2.4 Where alloy steel forgings are intended for welded constructions, the proposed chemical composition is subject to approval by LR.

For all types of steel, the tempering temperature is to be not less than 550°C.

2.3.2 The delivery condition shall meet the design and application requirements. It is the manufacturer’s responsibility to select the appropriate heat treatment method to obtain the required mechanical properties.

2.4.1 At least one tensile specimen is to be taken from each forging or batch of forgings. The Charpy V-notch impact tests are to be in accordance with the requirements of Table 5.2.2 Mechanical properties for ship and other structural applications.

2.4.2 Where a forging exceeds both 4 tonnes in mass and 3 m in length, tensile test specimens are to be taken from each end. These limits refer to the `as forged' mass and length but exclude the test material.

2.4.3 Unless otherwise agreed between the manufacturer and the Surveyor, the test specimens are to be cut in a longitudinal direction.

2.4.4 The results of all tensile tests are to comply with the requirements given in Table 5.2.2 Mechanical properties for ship and other structural applications. appropriate to the specified minimum tensile strength. Forgings may be supplied to any specified minimum tensile strength within the general limits given in Table 5.2.2 Mechanical properties for ship and other structural applications., and intermediate values may be obtained by interpolation. See Ch 5, 2.4 Mechanical tests 2.4.6 for rudder stocks, pintles, and rudder coupling keys and bolts.

2.4.5 For large forgings, where tensile tests are taken from each end, the variation in tensile strength is not to exceed 70 N/mm².

2.4.6 For rudder stocks, pintles, and rudder coupling keys and bolts, the minimum specified yield strength is not to be less than 200 N/mm², see Table 13.2.1 Rudder material factor, k in Pt 3 Ship Structures (General) of the Rules and Regulations for the Classification of Ships, July 2022.

2.5.1 Surface inspections are to be carried out by visual examination and magnetic particle testing (or liquid penetrant testing where appropriate), for the purpose of detecting relevant indications and assessing them against the accept/reject criteria stated in Ch 5, 2.5 Non-Destructive Examination 2.5.4. Personnel engaged in visual examination are to have sufficient knowledge and experience; however, they may be exempted from formal qualification requirements.

2.5.2 Surface inspections are to be carried out in Zones I and II as indicated in Figure 5.2.1 Inspection zones for magnetic particle/liquid penetrant testing on rudder stocks.

Figure 5.2.1 Inspection zones for magnetic particle/liquid penetrant testing on rudder stocks

2.5.3 For the purpose of evaluating indications, the surface is to be divided into reference areas of 225 cm². The area is to be taken in the most unfavourable location relative to the indication being evaluated.

2.5.4 The allowable number and size of indications in the reference area is given in Table 5.2.3 Steel forgings surface inspection.

2.5.5 Volumetric inspection is to be carried out by ultrasonic testing using the contact method.

2.5.6 Ultrasonic testing is to be carried out on rudder stocks having a finished diameter of 200 mm or greater.

2.5.7 Ultrasonic testing is to be carried out in the zones II and III as indicated in Figure 5.2.2 Inspection zones for ultrasonic testing on rudder stocks. Areas may be upgraded to a higher zone at the discretion of the Surveyor.

2.5.8 Ultrasonic acceptance criteria are shown in Table 5.3.3 Acceptance criteria for ultrasonic testing of shafts and machinery components – DGS Method – Normal probes and Ch 5, 3.5 Non-Destructive Examination 3.5.6.

Figure 5.2.2 Inspection zones for ultrasonic testing on rudder stocks