GB/T 37681-2019Heavy steel castings - General technical specification (English PDF)

5.5.3 Post-weld heat treatment and inspection

5.5.3.1 Post-weld heat treatment In principle, after the repair welding of the casting is completed, the repair welding zone shall be subjected to stress relief annealing (except for products with special materials or special requirements). The post-weld stress relief annealing temperature shall be lower than the tempering temperature during the performance heat treatment. In special cases, if the post-weld stress relief annealing temperature is higher than the tempering temperature during the performance heat treatment, the performance test bar shall be subjected to stress relief annealing with the furnace and to mechanical property testing again. The stress relief annealing holding time shall be determined according to the depth of the repair welding for the defect and the wall thickness of the product. It is recommended to keep the heat for 2 h~4 h per 100 mm. The minimum holding time is 3 h.

5.5.3.2 Post-weld inspection The repair welding position shall, according to the technical requirements of the product, be subjected to non-destructive testing and surface hardness inspection. Unless otherwise specified, the inspection shall be carried out according to the non-destructive testing requirements of the casting body at the position where the repair welding zone is located. When the hardness inspection of the repair welding position is required in the drawing or the ordering agreement, after the stress relief annealing, it shall carry out the surface hardness inspection.

5.6 Machining

5.6.1 Machining allowance Unless otherwise specified, the machining allowance shall be selected by the manufacturer itself or in accordance with the provisions of

GB/T 6414-2017. But it shall ensure that the dimensions of the casting product after machining comply with the drawings or agreements.

5.6.2 Stress relief annealing after machining purchaser shall specify the sampling position and acceptance level of each inspection. The sample for metallographic inspection shall be prepared from the test bar for mechanical properties. The preparation of the metallographic sample shall be not less than 6 mm from the surface of the test bar blank. If the purchaser requires inspection of the body metallography, the inspection position shall be agreed by both the supplier and the purchaser.

6.4 Non-destructive testing The castings shall, after dressing and finishing and machining, be subjected to non-destructive testing. However, since the shape and structure of the castings have a great influence on the internal quality assurance, the requirements for the method, area, and acceptance level, etc. of the non-destructive testing shall be in accordance with the product design or use requirements. It shall be agreed by both the supplier and the purchaser.

6.5 Appearance, shape, dimensional tolerances, and mass tolerances

6.5.1 Appearance quality requirements It shall clean up the burnt-on sand, sand inclusion, split edge, burr, and scale on the casting. The surface roughness of the casting shall be in accordance with the requirements of the drawings or the ordering agreement. There shall be no defects affecting the use on the casting surface. If there are defects, repair welding may be carried out.

6.5.2 Dimensional tolerances The dimensional tolerances of the castings shall comply with the provisions of the drawings or the ordering agreement. If there are no provisions in the drawings or the ordering agreement, the dimensional tolerances of the castings shall comply with the requirements of Grade DCTG13 to DCTG15 in GB/T 6414-2017.

6.5.3 Mass tolerances When ordering, both the supplier and the purchaser may agree on the mass tolerances of the casting. If not required by the purchaser, the mass tolerances shall meet the requirements of Grade MT13 to MT15 in GB/T 11351-2017.

6.6 Requirements for special tests When required by the purchaser, requirements for special tests (such as metallographic, tensile at elevated temperature, high-temperature short requests acceptance of the performance after the final heat treatment, it shall be specified in the ordering requirements.

7.1.4 Inspection lot

7.1.4.1 When the mass (net mass) of the casting is less than 3 t, according to the principle of double-same (same-furnace melting, same-furnace heat treatment), a set of physical and chemical inspections are carried out.

7.1.4.2 When the mass (net mass) of the casting is greater than or equal to 3 t, each product shall be subjected to a set of physical and chemical inspections.

7.1.5 Processing of sample The sample is taken from the test bar by machining, with a minimum distance of 6 mm from the casting surface and a minimum distance of 30 mm from the thermal cutting surface.

7.2 Provisions on invalid tests When the test result does not meet the requirements, if the following conditions exist, the test will be invalid. When the test is invalid, double quantity of samples may be taken again from the same test portion or from the test portion near the adjacent position of the unqualified test bar for retest. The retest data is used as the test result.

a) Improper processing of sample (There are tool marks, no chamfers, etc.);

b) Improper installation of sample or improper operation of testing machine;

c) There are defects on the sample (There are obvious cast defects such as slag inclusion, pores, and shrinkage porosity at the fracture position);

d) In the tensile test, it breaks at a position outside the gage point.

7.3 Chemical composition analysis

7.3.1 Provisions on sampling and sample preparation Sampling and sample preparation for chemical composition analysis shall be carried out in accordance with the provisions of GB/T 20066 or GB/T 5678.

7.3.2 Melting analysis The sample for chemical composition melting analysis of castings shall be sampled from the ladle during the casting process or before tapping. It shall take 1 sample per ladle. If a single casting is cast in multiple ladle, each ladle the supplier shall select at least 2 representative positions for testing. The surface roughness Ra of the test position shall be <=3.2 µm. If the hardness test tool has provisions for the test surface of the casting, it shall meet the corresponding provisions.

7.4.3.3 Brinell hardness test is carried out in accordance with the provisions of GB/T 231.1.

7.4.3.4 Unless otherwise specified, for the hardness of the same area of the same sample or body, it shall measure 3 hardness values. The average of the 3 hardness values shall comply with the regulations.

7.5 Non-destructive testing

7.5.1 Penetrant testing The casting surface may be subjected to penetrant testing, to detect the surface defects. Penetrant testing is carried out in accordance with the provisions of GB/T 9443.

7.5.2 Magnetic particle testing The casting may be subjected to magnetic particle testing, to detect the surface or near-surface defects of the casting. Magnetic particle testing is carried out in accordance with the provisions of GB/T 9444.

7.5.3 Ultrasonic testing The internal defects of the casting may be subjected to ultrasonic testing. Ultrasonic testing is carried out according to the provisions of GB/T 7233.1 or GB/T 7233.2.

7.5.4 Radiographic testing The internal defects of the casting may be also subjected to radiographic testing. Radiographic testing is carried out in accordance with the provisions of GB/T 5677.

7.6 Surface quality, shape, dimension, and mass inspection

7.6.1 Surface quality inspection The casting surface is visually inspected. The surface roughness is evaluated in accordance with the provisions of GB/T 15056.

7.6.2 Shape and dimension inspection

7.8.2 When the tensile test fails, samples may be taken from a test bar near the adjacent position of the unqualified test bar for double retest. If the 2 test results comply with the requirements of the purchaser, the tensile properties of this lot are qualified; otherwise the supplier may handle as specified in 7.9.

7.8.3 When the impact test fails, samples may be taken from a test bar near the adjacent position of the unqualified test bar for double retest. If the arithmetic mean of the test results of the retested 6 impact samples reaches the mean specified by the purchaser, and only the test results of 2 samples are allowed to be lower than the specified mean but each shall not be lower than 70% of the specified value, otherwise the supplier may handle as specified in 7.9.

7.8.4 When the hardness is unqualified, samples may be taken from a test bar near the adjacent position of the unqualified test bar for double retest. If the arithmetic mean of the retest results meets the requirements of the purchaser, the hardness of this lot is qualified; otherwise the supplier may handle as specified in 7.9.

7.8.5 If the special test fails, a retest may be conducted. The retest rules shall be agreed by the supplier and the purchaser.

7.8.6 When the retested unqualified object is a spot-check sample, and the test unit represented by the spot-check sample is composed of the same type of castings of non-double-same (same melting, same heat treatment) heat and lot, samples may be taken again from the remaining products of the unit for inspection. The sampling position and quantity shall be agreed by the supplier and the purchaser. If the test results of the re-sampling comply with the requirements of the purchaser, the performance of the remaining products of this unit shall be qualified; otherwise the supplier may handle as specified in 7.9. Samples which fail the first spot-check shall be disposed of in accordance with 7.9.

7.9 Reheat treatment When the retest result still does not meet the requirements, the casting and the test bar may be heat treated again. Without the consent of the purchaser, the reheat treatment shall not exceed 2 times (The number of tempering is not limited). After reheat treatment, it shall, according to the provisions of 7.4~7.8, carry out the testing again. The testing content and the number of samples are the same as the original regulations.