Section 5 Embrittlement tests

5.1.1 The test material is to be heat treated in accordance with the specification except that after tempering:

1. half the material is to be water quenched;

2. the other half is to be cooled from the tempering temperature to 300°C at a rate not exceeding 10°C per minute.

5.1.2 Impact tests in accordance with Ch 2, 3 Impact tests are to be made on the material in each condition at temperatures over a range wide enough to establish the upper and lower shelf energies and temperatures, tests being made at no less than three intermediate temperatures.

5.1.3 A set of three specimens is to be tested at each temperature. The results are to be plotted separately for each condition, in the form illustrated in Figure 2.5.1 Idealized transition curve. In addition, the test temperatures, proportions of crystallinity and absorbed energies for all the specimens tested are to be reported.

5.1.4 The transition temperature for each condition is to be taken as the mid-temperature of the fracture transition zone. The difference between the two transition temperatures is to be reported.

5.2.1 The test material is to be heat treated in accordance with the specification and then subjected to five per cent strain. The test material is then to be heated to 250°C and held for one hour.

5.2.2 Impact tests in accordance with Ch 2, 5.1 Temper embrittlement tests 5.1.2 are to be made in both the strain aged and unstrained conditions.

Figure 2.5.1 Idealized transition curve

5.2.3 The tests are to comply with Ch 2, 5.1 Temper embrittlement tests 5.1.3.

5.2.4 The test results are treated in accordance with Ch 2, 5.1 Temper embrittlement tests 5.1.4.

5.3.1 Two specimens are to be tested. The specimens are to be of a diameter of 20 mm. Where this is not practicable a diameter of 14 mm may be accepted.

5.3.2 One specimen is to be tested within a maximum of 3 hours after machining. Where the specimen diameter is 14 mm, the time limit is 1,5 hours. Alternatively, the specimen may be cooled to –60°C immediately after machining and kept at that temperature for a maximum period of 5 days before being tested.

5.3.3 The other specimen is to be tested after baking at 250°C for 4 hours. Where the specimen diameter is 14 mm the baking time is to be 2 hours.

5.3.4 A strain rate not exceeding 0,0003s ^–1 is to be used during the entire test, until fracture occurs.

5.3.5 Tensile strength, elongation and reduction of area are to be reported.

5.3.6 The ratio Z ₁/Z ₂ is to be reported, where Z ₁ is the reduction in area without baking and Z ₂ the reduction in area after baking.