ASME sa-217 c12a material is a high alloy heat-resistant steel. It is a new material developed by the United States. It is a high-end product and expensive. The steel has good resistance to high-temperature oxidation and high-temperature creep, high strength, good plasticity and machinability, and good thermal strength. It can effectively reduce the self weight of valve body castings. It is used in the environment of high temperature and high pressure. It is used to manufacture critical thermal power generators, gas cylinders, high-pressure valve bodies and other key components. The physical and chemical properties of ASME sa-217 c12a alloy steel valve castings for high temperature pressure parts are as follows:
(1) See Table 1 for technical requirements of chemical composition.
| C | Mn | Si | S | P | Cr | Ni | N | Mo | Nb | V | Al |
| 0.08-0.12 | 0.30-0.60 | 0.20-0.50 | ≤0.01 | ≤0.025 | 8.00-9.50 | ≤0.40 | 0.03-0.07 | 0.85-1.05 | 0.06-0.10 | 0.18-0.25 | ≤0.02 |
(2) Mechanical properties technical requirements for mechanical properties at room temperature are shown in Table 2.
| Rm/MPa | Rp0.2/ MPa | AKV（-29℃）/ J | A（5d）（%） | HBW |
| ≥485 | ≥205 | ≥27 | ≥30 | ≤220 |
(3) With the progress of material science and technology, the user’s technical specifications are not limited to the requirements of chemical composition and mechanical properties. The user has added the following requirements: the metallographic structure is uniform tempered sorbite and a small amount of ferrite; The grain size is above grade 8; Rated oxide inclusion ≤ grade 2, no columnar dendrite and crack; [O]≤50 × 10-6、[H]≤2 × 10-6、[N]≤150 × 10-6。
C12a alloy steel valve castings are characterized by different structures at high temperature, changes in lattice volume, easy to produce cold cracks, and high repair rate and scrap rate. In order to solve this technical problem, the method is to optimize the process, study and apply advanced schemes and obtain high-quality valve castings, so as to meet the procurement technical specifications of Chinese and foreign users.