Section 4 Castings for crankshafts

4.1.1 This Section gives the requirements for carbon and carbon-manganese steel castings for semi-built crankshafts.

4.1.2 Where it is proposed to use steels of higher carbon content than is indicated in Ch 4, 4.3 Chemical composition 4.3.1, or alloy steels, particulars of the chemical composition, mechanical properties and heat treatment are to be submitted for approval. For alloy steels, the specified minimum tensile strength is not to exceed 700 N/mm².

4.2.1 The method of producing combined web and pin castings is to be approved. For this purpose, tests to demonstrate the soundness of the casting and the properties at important locations may be required.

4.4.1 Castings are to be supplied either:

1. fully annealed and cooled in the furnace to a temperature of 300°C or lower; or

2. normalised and tempered at a temperature of not less than 550°C, and cooled in the furnace to a temperature of 300°C or lower.

4.5.1 Proposals for the number of tests and the location of test material on the casting are to be submitted by the manufacturer.

4.5.2 Not less than one tensile test and three impact tests are to be made on material representing each casting. The impact tests are to be carried out at ambient temperature.

4.5.3  Table 4.4.2 Mechanical properties for acceptance purposes: carbon - manganese steel castings for crankshafts gives the minimum requirements for yield stress and elongation corresponding to different strength levels, and it is not intended that these should necessarily be regarded as specific grades. The strength levels have been given in multiples of 40 N/mm² to facilitate interpolation for intermediate values of specified minimum tensile strength.

4.5.4 Castings may be supplied to any specified minimum tensile strength selected within the general limits detailed in Table 4.4.2 Mechanical properties for acceptance purposes: carbon - manganese steel castings for crankshafts.

4.5.5 The results of all tests are to comply with the requirements of Table 4.4.2 Mechanical properties for acceptance purposes: carbon - manganese steel castings for crankshafts appropriate to the specified minimum tensile strength. For the impact tests, one individual value may be less than the required average value provided that it is not less than 70 per cent of this average value. See Ch 1, 4.6 Re-test procedures for re-test procedures.

Table 4.4.2 Mechanical properties for acceptance purposes: carbon - manganese steel castings for crankshafts

Tensile strength N/mm2	Yield stress N/mm2 minimum	Elongation on % minimum	Reduction of area % minimum	Charpy V-notch impact tests average energy J minimum (see Note)
400 – 550	200	28	45	32
440 – 590	220	26	45	28
480 – 630	240	24	40	25
520 – 670	260	22	40	20
550 – 700	275	20	35	18
Note Impact tests are to be made at ambient temperature (i.e. 23°C±5°C), which is specified in ISO 148-1.

4.6.1 Magnetic particle examination is to be carried out over all surfaces in accordance with Figure 4.4.1 Magnetic particle inspection acceptance levels.

Figure 4.4.1 Magnetic particle inspection acceptance levels

4.6.2 Each casting is to be examined by ultrasonic testing, and the extent of examination and defect acceptance criteria, using the DGS (Distance Gain Size) technique, are to be as shown in Figure 4.4.2 Ultrasonic examination acceptance levels. Alternative ultrasonic procedures may be submitted for approval.

4.7.1 The requirements of Ch 4, 1.11 Rectification and dressing of castings apply, except where amended by this Section.

4.7.2 Where castings have shallow surface defects, consideration is first to be given to removing such defects by grinding and blending or by machining the surface where there is excess metal on the Rule dimension.

4.7.3 Subject to prior agreement and submission of the detailed welding procedure for approval by LR, welding may be carried out prior to the final austenitising heat treatment.

4.7.4 Approval for welding will not be given in the following circumstances:

1. For the rectification of repetitive defects caused by improper foundry technique or practice.

2. For the building up by welding of surfaces or large shallow depressions.

3. Where the carbon content of the steel exceeds 0,30 per cent.

4. Where the carbon equivalent of the steel, given by

   

4.7.5 Provided that the Surveyors are satisfied that welding is justified, they may also authorise welding to the surfaces of crankwebs, following the final austenitising heat treatment, within the following limits:

1. In general, the volume of the largest groove which is to be welded is not to exceed 3,2t cm³, where t is the web axial thickness, in cm. The total volume of all grooves which are to be welded is not to exceed 9,6t cm³ per crankweb.

2. The welds do not extend within the cross-hatched zones marked on Figure 4.4.3 Areas of semi-built crankthrows to which weld repairs are not permitted for semi-built crankthrows.

3. Larger welds on balance weights may be permitted at the discretion of the Surveyor, provided that such repairs are wholly contained within the balance weight and do not affect the strength of the crankweb.

4.7.6 Subsequent to the final austenitising heat treatment, welding may be authorised in the surface of the bore for the journal (or pin) within the following limits:

1. In general, the welds are to be not less than 125 mm apart.

2. The welds are not to be located within circumferential bands of from the edges of the bores, nor at any position within the inner 120° arc of the bores, as cross-hatched on Figure 4.4.3 Areas of semi-built crankthrows to which weld repairs are not permitted.

3. The volume of the largest weld is to be not more than 1,1t cm³, where t is the web axial thickness at the bore, in cm, and not more than three welds are to be made in any one bore surface.

Figure 4.4.2 Ultrasonic examination acceptance levels

Figure 4.4.3 Areas of semi-built crankthrows to which weld repairs are not permitted

4.7.7 After all defective material has been removed from a region, and this has been proven in the presence of the Surveyor by magnetic particle inspection or other suitable method, the excavation is to be suitably shaped to allow good access for welding.

4.7.8 At the discretion of the Surveyor, the size of a groove may be increased beyond the limiting sizes given in Ch 4, 4.7 Rectification of defective castings 4.7.5 or Ch 4, 4.7 Rectification of defective castings 4.7.6, if the removal of further metal will facilitate welding.

4.7.9 Welding is to be carried out by approved welders using approved procedures. The welds are to be made by an electric arc process using low hydrogen type consumables which will produce a deposited metal that is not inferior in properties to the parent metal.

4.7.10 All castings are to be given a preliminary refining heat treatment prior to the commencement of welding. Before welding, the material is to be preheated in accordance with the qualified procedure. Where possible, preheating is to be carried out in a furnace. The preheat temperature is to be maintained until welding is completed, and preferably until the casting is placed in the furnace for post-weld heat treatment.

4.7.11 Where welding is carried out after the final austenitising heat treatments, a post-weld stress relieving heat treatment is to be applied at a temperature of not less than 600°C, see also Ch 4, 1.5 Heat treatment 1.5.2.

4.7.12 Welds are to be dressed smooth by grinding. The surfaces of the welds and adjacent parent steel are to be proven by magnetic particle and, where appropriate, ultrasonic inspection, see Ch 4, 1.11 Rectification and dressing of castings 1.11.15 and Ch 4, 1.11 Rectification and dressing of castings 1.11.16.