Technical Purpose and Scope
This specification defines the requirements for vacuum-degassed, quenched, and tempered carbon and alloy steel forgings. The products are intended for critical pressure vessel components, including reactor system parts. The standard covers the production of flanges, shells, tube sheets, closure heads, and support rings operated under extreme conditions.
Production Cycle and Metallurgical Requirements
Melting and Refining Process
The production of steels under this standard utilizes the basic electric-arc furnace melting process. Secondary ladle refining or remelting methods are permitted in accordance with ASTM A788/A788M requirements. A key stage is the vacuum treatment of the melt, aimed at reducing dissolved gas content (primarily hydrogen) to prevent metal embrittlement. For class 22 grades, as well as classes 4, 5, 6, and 7, it is mandatory to employ fine-grain practice (grain size 5 or finer on the austenitic grain scale).
Ingot Quality Control
During the forging process, it is mandatory to discard the top and bottom portions of the ingot in a volume sufficient to exclude zones with segregation, voids, and structural inhomogeneity.
Heat Treatment and Mechanical Properties Formation
Preliminary Preparation
After forging, the workpieces undergo preliminary heat treatment with cooling to temperatures of complete austenitic transformation. This procedure optimizes the microstructure before final quenching and improves machinability.
Final Heat Treatment
Forgings are quenched in a liquid medium (immersion or spray) after preheating to the austenitic range. For classes 4N, 1, and 3, the austenitizing temperature interval is strictly regulated between 840 °C and 895 °C.
After quenching, mandatory subcritical tempering is performed. The holding time at the tempering temperature is at least 30 minutes per inch of maximum section thickness. To achieve specific toughness and strength values, additional requirements S13 and S14 regarding cooling rates may be applied.
For classes 1, 1A, 2, 2A, 3, and 3A, multi-stage austenitizing modes are permitted, including intercritical quenching to obtain an optimal phase composition. EV Group China specialists ensure strict adherence of all products to these heat treatment protocols to guarantee equipment reliability.