The samples for nondestructive testing are 24 cast steel joints randomly selected from the cast steel joints of civil engineering structures produced by a steel casting plant from March 2020 to may 2020. The size range of 24 samples is 0.6m ~ 4m, and the wall thickness distribution range is 40mm ~ 60mm.
| Element (%) | C | Mn | Si | S | P | Ni |
| Requirement | 0.17～0.23 | 1.00～1.60 | ≤0.60 | ≤0.020 | ≤0.020 | ≤0.80 |
The engineering structures of cast steel joints include: high-speed railway station roof truss structure, gymnasium roof truss structure, library roof truss structure, etc. All cast steel materials are g20mn5qt. The chemical composition and mechanical properties of the material are shown in Table 1 and table 2.
| Yield strength (MPa) | Tensile strength (MPa) | Elongation | Impact energy J (room temperature) |
| ≥300 | 480～620 | ≥20% | ≥50 |