GB/T 26648-2026Austenitic iron castings (English PDF)

5.2 Mechanical properties

5.2.1 The room-temperature mechanical properties of the casting materials shall comply with the requirements specified in Tables 3 and 4.

5.2.2 The acceptance criteria for the mechanical properties of castings shall be agreed upon by the supplier and the purchaser. Generally.

a) Tensile strength serves as the basis for acceptance for austenitic gray cast iron and QTANi30Si5Cr5;

b) Tensile strength and elongation serve as the basis for acceptance for austenitic ductile iron.

5.2.3 Where requirements exist for yield strength, impact toughness, and hardness, these may serve as the basis for acceptance, subject to agreement between the supplier and the purchaser.

5.2.4 If mechanical properties are determined using samples taken from the casting itself, the sampling location, size, and quantity, as well as the required performance indicators, shall be agreed upon by both the supplier and the purchaser. Table 3 -- Mechanical properties of austenitic iron castings (designations for general engineering use) Table 4 -- Mechanical properties of austenitic iron castings (designations for special-purpose use)

5.3 Metallographic microstructure

5.3.1 The metallographic microstructure of the castings shall comply with the following requirements.

a) The metallographic microstructure of austenitic gray cast iron consists of austenite, a small amount of grain-boundary carbides, and flake graphite. Type A graphite constitutes >=70%, and the graphite length falls within grades 3~5.

b) The metallographic microstructure of austenitic ductile iron consists of austenite and spheroidal graphite. The spheroidization grade shall be no lower than grade 3, and the graphite size shall be within grades 5~8.A small amount of carbides is permissible. The specific content shall be agreed upon by the supplier and the purchaser.

5.3.2 Carbides in the form of bands or lumps are not permitted. Heat treatment is permitted to alter the morphology of the carbides.

5.3.3 Castings are generally supplied in the as-cast condition. When required by the purchaser, they shall be subjected to the specified heat treatment process. Recommended heat treatment processes are given in Annex C.

5.4 Geometric shapes and their dimensional tolerances The geometric shape and dimensions of the castings shall comply with the specifications in the drawings or the purchase contract. Unless otherwise specified, the dimensional tolerance grade shall meet the requirements for DCTG10 as specified in GB/T 42124.3-2025, and the geometric tolerance grade shall comply with the requirements for GCTG6 as specified in GB/T 42124.3-2025.

5.5 Weight tolerance The weight tolerance of the castings shall comply with the specifications in the drawings or the purchase contract. In the absence of special requirements, the weight tolerance grade shall comply with the grade MT10 specified in GB/T 11351-2017.

5.6 Surface quality

5.6.1 Adhering sand, oxide scale, and similar matter on the casting surfaces shall be thoroughly removed. Gating and riser remnants, scabs, flash, and burrs shall be removed; the amount of residue remaining shall comply with the specifications in the drawings or the purchase contract.

5.6.2 The surface roughness of the castings shall comply with the specifications in the drawings or the purchase contract. In the absence of specific requirements, it shall be determined by the supplier. For castings weighing less than 1000 kg per piece, the surface roughness parameter shall comply with the requirement of Ra <= 50 µm as specified in GB/T 6060.1-2018.For castings weighing 1000 kg or more per piece, the surface roughness parameter shall comply with the requirement of Ra <= 100 µm as specified in GB/T 6060.1-2018.

5.6.3 Castings may contain surface defects that can be removed by machining. The types, quantity, and extent of casting defects permitted on non-machined surfaces shall comply with the specifications in the drawings or the purchase contract.

5.7 Internal quality

5.7.1 Castings shall be free from cracks and casting defects - such as slag inclusions, sand inclusions, gas holes, shrinkage cavities, and shrinkage porosity - that impair service performance.

5.7.2 Castings are permitted to have defects that do not impair functional performance. The type, extent, quantity, and size of such defects shall be agreed upon by the supplier and the purchaser.

6.1.1 Single-cast test blocks

6.1.1.1 The shape and dimensions of the test blocks shall be agreed upon by the supplier and the purchaser. They may be selected from Figure 1 and Table 5, or Figure 2 and Table

6.The hatched areas in the figures indicate the locations from which test specimens are to be cut. If required by the purchaser, separately cast knock-off test blocks may also be used, see Figure 3.

6.4.1 Tensile test shall be conducted in accordance with GB/T 228.1.

6.4.2 The Brinell hardness test shall be conducted in accordance with GB/T 231.1. Subject to agreement between the supplier and the purchaser, the hardness test may be performed on one or more locations on the casting or the test specimen.

6.4.3 Impact test shall be conducted in accordance with GB/T 229-2020.

6.5 Metallographic structure inspection

6.5.1 Metallographic structure inspection shall be conducted in accordance with GB/T 7216 and GB/T 9441.Sampling locations and the frequency of inspection shall be agreed upon by the supplier and the purchaser.

6.5.2 Non-destructive testing methods may be used to determine the nodularity grade. Ultrasonic testing shall be conducted in accordance with JB/T 9219.In the event of a dispute, the inspection shall be adjudicated based on GB/T 9441.

6.6 Inspection of geometric and dimensional tolerances

6.6.1 For the geometric shape and dimensional tolerances of castings, measuring tools of appropriate precision or a coordinate measuring machine (CMM) shall be selected for measurement.

6.6.2 The dimensions and geometric shapes of the initial batch of castings shall be inspected individually in accordance with the drawings. Castings produced using methods that ensure dimensional stability may be subject to spot checks. The frequency and quantity of such checks shall be agreed upon by both the supplier and the purchaser.

6.7 Inspection of weight tolerance The inspection of casting weight tolerances shall be conducted in accordance with the provisions of GB/T 11351-2017.

6.8 Surface quality inspection

6.8.1 Visible surface defects on castings shall be inspected piece by piece using visual inspection methods.

6.8.2 Subsurface defects in castings may be inspected using magnetic particle testing or penetrant testing. Magnetic particle testing shall be conducted in accordance with GB/T 9444.Penetrant testing shall be conducted in accordance with GB/T 9443.

6.8.3 The surface roughness of castings shall comply with the provisions of GB/T 15056.

6.9 Internal quality inspection Internal defects in castings can be detected using methods such as radiography and ultrasonic testing. Radiographic testing shall be conducted in accordance with GB/T 5677.Ultrasonic testing shall be conducted in accordance with GB/T 34904.

7.1 Composition of sampling batches and inspection quantities

7.1.1 Composition of sampling batch Inspection batches are defined as follows:

a) Castings poured from the same ladle of molten iron constitute a batch and are designated as a single sampling lot.

b) A batch is defined as either 2000 kg of castings produced continuously or the quantity of castings produced within a 2-h period.

c) If a single casting weighs more than 2000 kg, it constitutes a sampling lot on its own.

d) If a change in furnace charge, process conditions, or required chemical composition occurs within a given time interval, the castings poured from the iron continuously melted during that period constitute a single sampling batch, regardless of how short the interval is.

e) In addition to a), a single delivery quantity may also be designated as a sampling batch, subject to agreement between the supplier and the purchaser. In such cases, the supplier's production process must incorporate continuous monitoring methods - such as pre-pour metallographic inspection or spectroscopic analysis - to reliably demonstrate process stability and compliance with requirements. Furthermore, inspection records must exist for the molten iron processed for each batch, ensuring full traceability.

f) For heat-treated castings, each furnace load constitutes a sampling batch, or castings of identical configuration within each furnace load constitute a sampling batch.

7.1.2 Number of inspection batches Testing shall be conducted for each sampling batch, unless the production quality control system allows for the consolidation of sampling batches and appropriate safeguards have been implemented in advance. The size of the sampling batches and the quantity of tests to be performed shall be agreed upon by both the supplier and the purchaser at the time the order is placed.