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Eternal
Valves in petrochemical, thermal power, and nuclear power units often work for long periods at 450°C to 800°C. This range falls right in the sensitization temperature window of austenitic stainless steel. In regular 304 stainless steel at this temperature, carbon combines with chromium to form chromium carbide. The carbide precipitates along grain boundaries. This leaves grain boundary areas short of chromium. This is called “intergranular chromium depletion.” The medium then attacks along the grain boundaries. The valve body breaks in a brittle way without clear plastic deformation.
Real cases show how serious this problem is. In a refinery and chemical company, a bypass valve of a control valve on the recycle hydrogen line of a hydrocracking unit had a working pressure of 17.0 MPa and an operating temperature of 340°C. The main pipe material was TP321. The valve body cracked. This shows that even when 321 material is used, if forging and heat treatment are not good enough, high-temperature failure risk still exists.
The solution for 321 stainless steel is its titanium stabilization mechanism. The added titanium combines with carbon first to form stable titanium carbide. In this way, it “locks” the carbon and prevents it from forming chromium carbide at grain boundaries. The material can still keep excellent resistance to intergranular corrosion in the sensitization temperature range. But adding titanium also brings new challenges. Titanium easily forms inclusions, so the forging billet must be much cleaner. If smelting and forging processes are not good enough, they may instead create new sources of defects. Jiangyin Eternal Heavy Industry Co., Ltd. has mastered the forging and heat treatment process for 321 stainless steel through many years of stainless steel forging practice.
Standard | Grade |
ASTM/ASME | ASTM A182 F321 / UNS S32100 |
GB | 06Cr18Ni11Ti（ S32168） |
JIS | SUS321 |
DIN/EN | 1.4541 / X6CrNiTi18-10 |
ISO | X6CrNiTi18-10 |
SS | 2337 |
GOST | 12X18H10T (or 08Kh18N10T) |
KS | STS321 |
Chemical composition (%):
C | Si | Mn | P | S | Cr | Ni | Ti |
≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 17.0~19.0 | 9.0~12.0 | ≥5×C |
Key Control Index — Titanium-to-Carbon Ratio (Ti/C):
The Ti/C ratio is the core parameter that decides the intergranular corrosion resistance of 321 stainless steel. Studies show that when Ti/C > 10, the chance of intergranular stress corrosion cracking near the welded joint of 321 stainless steel is very low. Jiangyin Eternal Heavy Industry Co., Ltd. strictly controls Ti/C ≥ 5.5 for every batch of raw material (the minimum requirement of ASTM A182). For valve body products used in long-term high-temperature service (>500°C), it is recommended that Ti/C ≥ 8.0.
Smelting Process: Jiangyin Eternal Heavy Industry Co., Ltd. uses the process route of electric arc furnace primary melting + AOD refining + LF furnace titanium alloying + VD vacuum degassing. The 321 stainless steel produced by this process contains only fine Type B/D inclusions, and the rating level can reach 0.5. This ensures the high cleanliness of the forging billet from the source.
Item | standard request | Our typical value |
tensile strength (MPa) | ≥515 | 550~620 |
yield strength (MPa) | ≥205 | 230~280 |
elongation (%) | ≥40 | 45~55 |
reduction of area (%) | ≥50 | 55~65 |
Hardness (HBW) | ≤223 | 160~190 |
321 stainless steel has excellent oxidation resistance and creep strength in the temperature range of 1000°F to 1600°F (about 540°C to 870°C). It is one of the preferred materials for forged valve bodies and pump bodies in high-temperature service.
In academic research, low-cycle fatigue tests on SUS321 forged material at 550°C and 600°C show that its fatigue life is much better than that of the heat transfer tube base metal of the same material. The creep rate and rupture life data of 321 stainless steel at 540°C–650°C and 100–400 MPa have been systematically measured. This provides a reliable basis for the design and selection of high-temperature valves.
A 2024 comparative study on the forging process of 321 stainless steel for nuclear valves compared one-heat forging and two-heat forging, and reached the following important conclusions:
After heat treatment at 1050°C for 30–120 minutes, both processes can meet the standard.
Compared with one-heat forging, two-heat forged 321 stainless steel billets have a smaller grain size and higher yield strength.
This study directly provides a technical reference for choosing the forging process for nuclear valve bodies. It also confirms the scientific basis of the multi-heat forging strategy used by Jiangyin Eternal Heavy Industry Co., Ltd.
321 forged valve bodies are widely used in high-pressure and high-temperature valves for hydrogenation reactors, ethylene cracking units, and catalytic cracking units. In high-temperature environments of 430°C–860°C, 321 stainless steel still maintains good mechanical properties. It can withstand corrosive media in crude oil cracking and synthetic ammonia production. In cracking furnace tube fittings of ethylene units, the service life of 321 stainless steel is 3–5 times longer than that of ordinary 304 stainless steel.
In China, forged 321 stainless steel is often used as the valve body material for nuclear valves because of its stable mechanical properties and good corrosion resistance. In international nuclear power projects, 321 stainless steel is used for the valve body and bellows assembly of nuclear-grade bellows globe valves, with a design cycle life of 2,000–5,000 cycles.
Key European case in 2026: The ammonium nitrate plant expansion project of Poland’s ANWIL S.A. had a total contract value of more than EUR 1 million. It purchased more than 1,500 sets of high-pressure forged valves and pipe fittings. The working pressure ratings cover PN 16 to PN 250. 321 stainless steel (EN 1.4541) was listed as one of the core austenitic stainless steel materials, used for high-temperature corrosive service conditions in nitric acid synthesis and ammonium salt production.
Forged 321 valve bodies are suitable for valves used in boiler furnace roller shafts, kiln drive main shafts, high-temperature steam pipelines, and similar locations. In thermal power, 321H heat-resistant alloy is suitable for valves in high-temperature boiler sections. In the energy and power industry (including thermal power and nuclear power), demand for such materials is growing at an average annual rate of more than 20%.
321 forgings are used in engine exhaust pipes, combustion chamber components, and high-temperature fasteners, and comply with aerospace material standards such as AMS 5645.
The 321 stainless steel forged valve bodies produced by Jiangyin Eternal Heavy Industry Co., Ltd. strictly follow the ASTM A182 / A182M standard. Key quality control steps include:
Forging ratio ≥ 3, ensuring the as-cast structure is fully broken up, with grain size reaching Grade 5 or finer.
Solution treatment: hold at 1050°C–1150°C, then rapid water cooling to quickly pass through the sensitization temperature range.
Stabilization heat treatment: for valve bodies in long-term high-temperature service, add stabilization treatment at 850°C–930°C after solution treatment, to further inhibit chromium carbide precipitation and improve intergranular corrosion resistance.
Intergranular corrosion test: performed according to ASTM A262, ensuring products meet the acceptance requirements for sensitized intergranular corrosion.
100% ultrasonic testing (UT) + liquid penetrant testing (PT).
100% positive material identification (PMI). Each batch comes with an EN 10204 3.1 material certificate.
Each valve body forging is given a unique traceability code, linked to the material warranty, heating records, forging parameters, heat treatment curves, and inspection reports, achieving full life-cycle quality traceability.
What is the maximum operating temperature for the 321 forged valve body?
The normal recommended service temperature range is -196°C to 800°C. For long-term continuous operation, the temperature is recommended not to exceed 600°C. Short-term peaks can be withstood up to 800°C. For long-term service above 600°C, 321H (the high-carbon version, UNS S32109) is recommended.
How should 321 and 304L be differentiated in high-temperature valve selection?
The intergranular corrosion resistance of 304L is mainly achieved through a low-carbon design, but it still carries a sensitization risk during long-term service at 450°C–850°C. Through its titanium stabilization mechanism, 321 has an intrinsic advantage in resisting sensitization within this temperature range. If the valve operating temperature exceeds 450°C and welding operations are involved, 321 is preferentially recommended.
The typical cycle from placing an order to delivery?
The standard-sized forged valve body blanks usually take 25 to 40 days; non-standard custom components (including complex irregular structures and special heat treatment requirements) take 35 to 55 days. Urgent orders can be negotiated for expedited production.
