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GB/T 25198-2023 —— Forming — 6.6.2.6 Austenitic stainless steel heads can be formed by warm forming, with a recommended forming temperature of 120~250°C. ——Heat treatment – 6.8.3 Heat treatment after cold forming of heads 6.8.3.2 For heads made of austenitic stainless steel, no treatment is required after forming unless in the following cases: a) For pressure vessels made of austenitic stainless steel designed for temperatures below -40°C, ... when the ferrite content is greater than 15% ； b) For containers holding media with extremely or highly hazardous toxicity, or containers specified in the drawings as being susceptible to stress corrosion,... the deformation rate exceeds 15%, or when the design temperature is below -100°C or above 675°C, the deformation rate is 10% or greater ； c) As required by the design documents and ordering technical documents. Draft new GB/T 150.4 – Forming – 4.2.2.1 b) Warm forming is recommended for chromium-nickel austenitic stainless steel heads, with the recommended forming temperature ranging from 120°C to 250°C. c) After the forming of chromium-nickel austenitic stainless steel heads, a ferrite meter should be used for inspection... The measured ferrite content must not exceed 15%... ——Heat treatment—— 8.4.1 Recovery property heat treatment of formed pressure components 8.4.1.4 For chromium-nickel austenitic stainless steel sheets that have been formed by cooling, if the measured ferrite content according to GB/T 1954 is greater than 15% after forming, recovery property heat treatment shall be carried out after formation. Among them, the ferrite inspection locations on the head and expansion joints shall be determined in accordance with 4.2.2.1c) and 4.2.2.4b) respectively. 8.4.1.5 For chromium-nickel austenitic stainless steel sheet cooling-formed parts designed for temperatures above 675°C, heat treatment to restore properties shall be carried out after forming. Explanations for the drafting of the new draft standard GB/T 150.4 – The ferrite content as a quality indicator for cold-formed heads. Cr-Ni austenitic stainless steel heads formed by cold working exhibit cracking primarily in the straight-edge sections; in these areas, the ferrite content and hardness increase significantly compared to before forming, and changes in ferrite content are associated with changes in the plasticity of the head material. —— Using a ferrite content of 15% as the criterion, for chromium-nickel austenitic stainless steel cold-formed heads, although there are more accurate methods for calculating the degree of deformation, the corresponding control parameters have not yet been finalized. In this revision, it is decided to determine whether heat treatment to restore properties is necessary after forming by checking the ferrite content, with 15% serving as the acceptable threshold. —— The use of warm forming allows the avoidance of heat treatment to restore properties. When the criterion of 15% ferrite content is applied, this method prevents the need for heat treatment to restore the properties of the head, which would arise if that threshold were exceeded. Multiple domestic institutions have conducted research and experiments on the warm forming process for end caps, and two approaches were identified: one is to increase the nickel content ； Second, warm forming is employed; when the forming temperature is between 120°C and 250°C, the ferrite content in the sub-stable chromium-nickel austenitic stainless steel heads can be less than 15%. (Obviously, using warm forming is more economical)