GB/T 37559-2019Normalizing and annealing of heavy steel forgings (English PDF)

5.1.2 Determination method of effective heating zone of the heat treatment

furnace shall meet the requirements of GB/T 9452 or GB/T 30824.

5.2 Temperature measurement and control system

5.2.1 The type and technical requirements of the heat treatment furnace instrument system shall not be lower than the requirements of Class-D of GB/T 30825-2014.

5.2.2 The accuracy and calibration period of the instrument shall meet the requirements of Class-IV equipment in GB/T 32541-2016.

5.2.3 The selection and use of the temperature sensor shall comply with the provisions of GB/T 30825-2014.

5.2.4 The load thermocouple that is used to measure the temperature of the workpiece shall be in close contact with the workpiece; the load thermocouple shall be protected from furnace temperature radiation and furnace atmosphere.

5.3 Cooling equipment

The normalizing of heavy steel forgings is generally cooled in still air; simple cooling equipment such as fans and sprays can also be used. The cooling equipment shall uniformly cool the workpiece that is placed in the strong flowing air in all directions as far as possible; the wind speed and air volume shall meet the cooling rate that is required by the process.

6.1 Normalizing

6.1.3.1 The workpiece shall hold a sufficient period of time when it is heated to the normalizing temperature, so as to ensure that the structure is completely transformed into austenite. The holding time shall include two processes, namely soaking and austenitizing.

6.1.3.2 The soaking time is generally estimated by half of the austenitizing holding time. If necessary, a thermocouple can be added at the thickest section of the workpiece. After the thermocouple temperature reaches the normalizing temperature, the soaking process ends. When multiple thermocouples are added to the surface of the workpiece, the soaking process shall be completed when the temperature of all thermocouples reaches the normalizing temperature.

6.1.1 Use

6.1.1.1 For large medium-low carbon steel and low-alloy forged steel parts, normalizing destressing and refinement structure are generally adopted; for […]

6.1.3.3

Under normal circumstances, for ordinary carbon steels and alloy steel forgings whose effective thickness is 100 mm, the austenitizing holding time is estimated to be 0.8 h ~ 1.8 h; for medium-high alloy steels or martensitic stainless steel forgings whose effective thickness is 100 mm, it can be estimated to be 1 h ~ 2 h.

6.1.4 Cooling

6.1.4.1 Normalizing cooling of heavy steel forgings is generally carried out in air; for heavy steel forgings whose alloy content is low, methods such as blasting, spraying may be used to adjust the cooling rate.

6.1.4.2 During the normalizing cooling of heavy steel forgings, control the final cooling temperature. The final cooling temperature shall ensure that the austenite is fully transformed during the cooling process; however, it shall not be too low to avoid cracking and white spots on the workpiece.

6.1.4.3 After the workpiece is cooled to the final cooling temperature, it shall be tempered in time. The tempering parameters can be determined by reference to the quenching and tempering of heavy steel forgings.

6.2 Annealing

The classification, process parameters, effects and applications of the common annealing processes for heavy steel forgings are shown in Table 2. For annealing heating, refer to 6.1.2.

6.3.3 Record

6.3.3.1 Record the used production equipment, temperature record, workpiece placement position and lifting method in detail during production.

6.3.3.2 All records shall be signed and confirmed by relevant operators at the end of the operation.

6.3.3.3 All records shall be retained, so as to ensure traceability of the quality of the workpiece.

7.1 Inspection items and methods

7.1.1 Surface inspection

After the heat treatment, the surface of the workpiece shall be visually inspected, so as to ensure that the surface is free from cracks and scratches. If necessary, carry out infiltration, magnetic powder or ultrasonic flaw detection according to relevant standards.

7.1.2 Surface hardness

If the purchaser has regulations, the surface hardness of the workpiece shall meet the requirements of the technical documents. The detection location, test methods and acceptance requirements of surface hardness shall be indicated in the technical documents. The surface hardness test of the workpiece shall be carried out in accordance with the requirements of GB/T 231.1 or GB/T 17394.1.

7.1.3 Size inspection

After heat treatment, use corresponding instrument and gauge to measure the workpiece size. The workpiece size must meet the final delivery size of the workpiece.

7.1.4 Non-destructive testing