Comparison of 321 and 321H Stainless Steel: Standard vs High-Carbon Titanium-Stabilized Grade

321 and 321H are titanium-stabilized austenitic stainless steels, with the core difference being carbon content. 321H is the high-carbon variant of 321, which improves high-temperature creep strength, while 321 has better toughness and intergranular corrosion resistance. Both avoid intergranular corrosion through titanium stabilization, suitable for high-temperature welding components.

Core Parameter Comparison

Parameter	321 Stainless Steel	321H Stainless Steel
Chemical Composition (wt%)	C≤0.08, Cr=17.00-19.00, Ni=9.00-12.00, Ti=0.10-0.30, Fe=Balance	C=0.04-0.10, Cr=17.00-19.00, Ni=9.00-12.00, Ti=0.10-0.30, Fe=Balance
Mechanical Properties (Annealed)	Tensile Strength ≥520MPa, Yield Strength ≥205MPa, Elongation ≥40%, Hardness ≤201HB	Tensile Strength ≥520MPa, Yield Strength ≥205MPa, Elongation ≥40%, Hardness ≤201HB
Service Temperature	400℃ to 900℃ (continuous service)	500℃ to 900℃ (continuous service)
Equivalent Grades	SUS321 (JIS), EN 1.4541, UNS S32100	SUS321H (JIS), EN 1.4542, UNS S32109

Key Performance Differences: 1. High-temperature strength: 321H has higher creep strength than 321 at 500-900℃, creep rate 1/3 of 321 at 600℃. 2. Toughness: 321 has better low-temperature toughness than 321H, impact toughness ≥80J at -196℃, while 321H is ≥60J. 3. Intergranular corrosion resistance: Both have excellent performance, but 321 has slightly better resistance due to lower carbon content.

Applicable Scenario Distinction: 321 is suitable for high-temperature welding components requiring good toughness, such as automotive exhaust manifolds, chemical heat exchanger tubes, and low-temperature high-temperature alternating components. 321H is suitable for high-temperature stress-bearing components, such as boiler superheater tubes, nuclear power plant secondary circuit pipelines, and petrochemical catalytic cracking unit internals.

Practical Q&A

Q1: What is the role of titanium in 321 and 321H? A1: Titanium preferentially combines with carbon to form TiC, avoiding chromium carbide precipitation at grain boundaries, fundamentally solving intergranular corrosion problem; thermal simulation shows that 321 has less chromium carbide precipitation than 304 after 650℃ holding.

Q2: Can 321H be used in low-temperature environments? A2: It can be used at -196℃, but its low-temperature toughness is worse than 321; for low-temperature high-temperature alternating components, 321 is recommended.

Q3: What welding materials are suitable for 321 and 321H? A3: Both match ER321 welding wire, ensuring titanium content in the weld to maintain stabilization effect; avoid using ER308L wire, which will reduce corrosion resistance.

Q4: What is the cost difference between 321 and 321H? A4: 321H is 8-12% more expensive than 321, due to stricter carbon content control and higher requirements for high-temperature performance in production.

Q5: How to maintain 321/321H high-temperature components? A5: Regularly remove surface oxide scale with sandblasting; avoid rapid cooling after high-temperature service to prevent thermal shock; conduct annual non-destructive testing on welds.