Section 5 Forgings for gearing

5.1.1 Provision is made in this Section for carbon-manganese and alloy steel forgings intended for use in the construction of gearing for main propulsion and for driving electric generators.

5.1.2 Gear wheel and rim forgings with a specified minimum tensile strength not exceeding 760 N/mm² (760–910 N/mm² acceptance range) may be made in carbon-manganese steel. Gear wheel or rim forgings where the specified minimum tensile strength is in excess of 760 N/mm², and all pinion or pinion sleeve forgings, are to be made in a suitable alloy steel. Specifications for alloy steel components and for quill shafts, giving chemical composition, heat treatment and mechanical properties, are to be submitted for approval.

5.1.3 Forgings for flexible couplings, quill shafts and gear wheel shafts are to comply with the requirements of Ch 5, 3 Forgings for shafting and machinery.

5.1.4 Manufacturers' test certificates for forgings may be accepted where the transmitted power does not exceed 220 kW (300 shp) for main propulsion and 100 kW (150 shp) for auxiliary drives.

5.2.1 All forgings are to be made with sufficient material to allow an adequate machining allowance on all surfaces for the removal of unsound or decarburised material.

5.2.2 The hardenabilty of the forged material is to be checked at random intervals using an end quench test complying with a National or International Standard.

5.2.3 The grain size is to be checked on a random basis in accordance with the testing and reporting procedures of ASTM E 112, or an equivalent National Standard, and is to be within the range 5 to 8.

5.2.4 The microstructure of the hardened case is to be mainly martensite, with a maximum content of 15 per cent of retained austenite.

5.3.1 The chemical composition of ladle samples is to comply with Ch 5, 3.2 Chemical composition 3.2.1 for carbon and carbon-manganese steels and Ch 5, 1.4 Chemical composition 1.4.3 for alloy steels.

5.4.1 Except as provided in Ch 5, 5.4 Heat treatment 5.4.5 and Ch 5, 5.4 Heat treatment 5.4.6, forgings may be either normalised and tempered or quenched and tempered in accordance with the approved specification. The tempering temperature is to be not less than 550°C.

5.4.2 The delivery condition shall meet the design and application requirements. It is the manufacturers responsibility to select the appropriate heat treatment method to obtain the required mechanical properties. Where forgings for gearing are not intended for surface hardening, lower tempering temperatures may be allowed.

5.4.3 Where forgings are machined prior to heat treatment, the allowance left for final machining is to be sufficient to remove the decarburised surface material, taking into account any bending or distortion which may occur.

5.4.4 When the teeth of a pinion or gear wheel are to be surface hardened, i.e. carburised, nitrided or induction hardened, the proposed specification together with details of the process and practice are to be submitted for approval. For purposes of initial approval, the gear manufacturer is required to demonstrate by test that the surface hardening of the teeth is uniform and of the required depth and that it does not impair the soundness and quality of the steel.

5.4.5 Where induction hardening of nitriding is to be carried out after machining of the gear teeth, the forgings are to be heat treated at an appropriate stage to a condition suitable for this subsequent surface hardening.

5.4.6 Forgings for gears which are to be carburised after final machining are to be supplied in either the fully annealed or the normalised and tempered condition, suitable for subsequent machining and carburising.

5.5.1 At least one tensile test specimen is to be taken from each forging in carbon or carbon-manganese steel, and at least one tensile specimen from forgings in alloy steel. Sufficient test material is to be provided for this purpose and the test specimens are to be taken as follows:

1. For pinion forgings where the finished diameter of the toothed portion exceeds 200 mm, tests are to be taken in a tangential direction and adjacent to the toothed portion (test position B in Figure 5.5.1 Test positions for forgings for gearing). Where the dimensions preclude the preparation of tests from this position, tests in a tangential direction are to be taken from the end of the journal (test position C in Figure 5.5.1 Test positions for forgings for gearing). If, however, the journal diameter is 200 mm or less, tests are to be taken in a longitudinal direction (test position A in Figure 5.5.1 Test positions for forgings for gearing). Where the finished length of the toothed portion exceeds 1250 mm, tests are to be taken from each end.

2. For small pinion forgings where the finished diameter of the toothed portion is 200 mm or less, tests are to be taken in a longitudinal direction (test position A in Figure 5.5.1 Test positions for forgings for gearing).

3. For gear wheel forgings, tests are to be taken from each forging in a tangential direction (from one of the test positions A or B in Figure 5.5.2 Test position A or B).

4. For gear wheel rim forgings, tests are to be taken in a tangential direction (from one of the test positions A in Figure 5.5.3 Test position A). Where the finished diameter exceeds 2500 mm or the mass (as heat treated but including test material) exceeds 3 tonnes, tests are to be taken from two diametrically opposite positions (test positions A in Figure 5.5.3 Test position A).

5. For pinion sleeve forgings, tests are to be taken in a tangential direction (from one of the test positions C in Figure 5.5.4 Test position C). Where the finished length exceeds 1250 mm, tests are to be taken from each end.

6. For forged rings, the directions and positions of the set of tests to be taken from each ring are to comply with the requirements of Ch 5, 3.4 Mechanical tests 3.4.4.

Figure 5.5.1 Test positions for forgings for gearing

Figure 5.5.2 Test position A or B

Figure 5.5.3 Test position A

Figure 5.5.4 Test position C

5.5.2 As an alternative to Ch 5, 5.5 Mechanical tests for through hardened, induction hardened or nitrided forgings 5.5.1, small forgings may be batch tested in accordance with Ch 5, 1.6 Test material 1.6.4 provided that, in addition, hardness tests are carried out on each forging.

5.5.3 Table 5.5.1 Mechanical properties for acceptance purposes: carbon-manganese steels for gear wheel and rim forgings to Table 5.5.3 Mechanical properties for acceptance purposes: alloy steel gear forgings - Quenched and temperedgive the minimum requirements for yield stress and elongation corresponding to different strength levels, but 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, or 50 N/mm² in the case of alloy steels, to facilitate interpolation for intermediate values of specified minimum tensile strength.

5.5.4 Forgings may be supplied to any specified minimum tensile strength selected within the general limits detailed in Table 5.5.1 Mechanical properties for acceptance purposes: carbon-manganese steels for gear wheel and rim forgings to Table 5.5.3 Mechanical properties for acceptance purposes: alloy steel gear forgings - Quenched and tempered.

5.5.5 The results of all tensile tests are to comply with the requirements of Table 5.5.1 Mechanical properties for acceptance purposes: carbon-manganese steels for gear wheel and rim forgings, Table 5.5.2 Mechanical properties for acceptance purposes: alloy steel gear wheel and rim forgings - Normalised and tempered or Table 5.5.3 Mechanical properties for acceptance purposes: alloy steel gear forgings - Quenched and tempered, appropriate to the specified minimum tensile strength. Unless otherwise agreed, the specified minimum tensile strength is to be not less than 800 N/mm² (800–950 N/mm² acceptance range) for induction hardened or nitrided gear forgings.

5.5.6 Where more than one tensile test is taken from a forging, the variation in tensile strength is not to exceed the following:

5.5.7 Hardness tests are to be carried out on all forgings after completion of heat treatment and prior to machining the gear teeth. The hardness is to be determined at four positions equally spaced around the circumference of the surface where teeth will subsequently be cut. Where the finished diameter of the toothed portion exceeds 2500 mm, the number of test positions is to be increased to eight. Where the width of a gear wheel rim forging exceeds 1250 mm, the hardness is to be determined at eight positions at each end of the forging.

Table 5.5.2 Mechanical properties for acceptance purposes: alloy steel gear wheel and rim forgings - Normalised and tempered

Tensile strength N/mm2	Yield stress N/mm2 minimum	Elongation on 5,65 % minimum		Hardness Brinell
		Rims	Wheels
600 – 750	330	18	16	175 – 215
650 – 800	355	17	15	190 – 235
700 – 850	380	16	14	205 – 245
750 – 900	405	15	13	215 – 260
800 – 950	430	14	12	235 – 275
850 – 1000	455	13	11	245 – 290
Intermediate values may be obtained by interpolation.

Table 5.5.3 Mechanical properties for acceptance purposes: alloy steel gear forgings - Quenched and tempered

Tensile strength N/mm2 (see Notes 1 and 2)	Yield stress N/mm2 minimum (see Note 2)	Elongation on 5,65 % minimum			Hardness Brinell
		A	B	C
600 – 750	420	18	16	14	175 – 215
650 – 800	450	17	15	13	190 – 235
700 – 850	480	16	14	12	205 – 245
750 – 900	530	15	13	11	215 – 260
800 – 950	590	14	12	10	235 – 275
850 – 1000	640	13	11	9	245 – 290
900 – 1050	690	13	11	9	260 – 310
950 – 1100	750	12	10	8	275 – 330
1000 – 1150	810	12	10	8	290 – 340
1050 – 1200	870	11	9	7	310 – 365
= Column A is applicable to tests from gear rims and to longitudinal tests from pinions. = Column B is applicable to tests from gear wheels and to tangential tests from pinions. = Column C is applicable to tests from pinion sleeves.
Intermediate values may be obtained by interpolation
Note 1. For gear wheel and rim forgings the specified minimum tensile strength is not to exceed 850 N/mm2. Note 2. For carburised gear forgings the requirements for minimum yield stress and maximum tensile strength are not applicable.

5.5.8 For small gear forgings which are batch tested, at least one hardness test is to be carried out on each forging.

5.5.9 The results of all hardness tests are to comply with the appropriate requirements ofTable 5.5.1 Mechanical properties for acceptance purposes: carbon-manganese steels for gear wheel and rim forgings to Table 5.5.3 Mechanical properties for acceptance purposes: alloy steel gear forgings - Quenched and tempered. The difference between the highest and lowest values on any one forging is not to exceed the following:

5.5.10 On nitrided or induction hardened components, hardness tests are also to be made on the teeth when surface hardening and grinding have been completed. The results are to comply with the approved specification.

5.6.1 Sufficient test material is to be provided for preliminary tests at the forge and for final tests after completion of carburising. For this purpose, duplicate sets of test material are to be taken from positions as detailed in Ch 5, 5.5 Mechanical tests for through hardened, induction hardened or nitrided forgings 5.5.1, except that, irrespective of the dimensions or mass of the forging, tests are required from one position only, and in the case of forgings with integral journals are to be cut in a longitudinal direction. The test material which is to be used for measurements of case depth, hardness, grain size and residual austenite as well as mechanical properties is to be machined to a coupon of diameter of or 30 mm, whichever is less, where D is the finished diameter of the toothed portion.

5.6.2 For small forgings, where a system of batch testing is adopted, the test material may be prepared from surplus steel from the same cast provided that the forging reduction approximates to that of the actual gear forgings. The test samples are to be correctly identified and heat treated with the forgings they represent.

5.6.3 For preliminary tests at the forge, one set of test material is to be given a blank carburising and heat treatment cycle simulating that which will be subsequently applied to the forgings.

5.6.4 For final acceptance tests, the second set of test material is to be blank carburised and heat treated together with the forgings which it represents.

5.6.5 At the discretion of the forgemaster or gear manufacturer, test samples of larger cross-section than in Ch 5, 5.6 Mechanical tests for carburised forgings 5.6.1 may be either carburised or blank carburised, but these are to be machined to the required diameter prior to the final quenching and stress relieving heat treatment.

5.6.6 At least one tensile specimen is to be prepared from each sample of test material.

5.6.7 Unless otherwise agreed, the specified minimum tensile strength is to be not less than 750 N/mm², and the results of all tensile tests are to comply with the requirements given in Table 5.5.3 Mechanical properties for acceptance purposes: alloy steel gear forgings - Quenched and tempered.

5.6.8 Where it is proposed to adopt alternatives to the requirements of Ch 5, 5.6 Mechanical tests for carburised forgings 5.6.1 to Ch 5, 5.6 Mechanical tests for carburised forgings 5.6.7, full details are to be submitted to the Surveyor for consideration.

5.7.1 Magnetic particle or liquid penetrant testing is to be carried out on the teeth of all surface hardened forgings. This examination may also be requested on the finished machined teeth of through hardened gear forgings.

5.7.2 The manufacturer is to carry out an ultrasonic examination of all forgings where the finished diameter of the surfaces, where teeth will be cut, is in excess of 200 mm, and is to provide the Surveyor with a signed statement that such inspection has not revealed any significant internal defects.

5.7.3 On gear forgings where the teeth have been surface hardened, additional test pieces may be required to be processed with the forgings and subsequently sectioned to determine the depth of the hardened zone. These tests are to be carried out at the discretion of the Surveyor, and for induction or carburised gearing the depth of the hardened zone is to be in accordance with the approved specification. For nitrided gearing, the full depth of the hardened zone, (i.e. depth to core hardness), is to be not less than 0,5 mm and the hardness at a depth of 0,25 mm is to be not less than 500 HV.