Alloy 840 (UNS S33400 / 1.4847) is a titanium- and aluminum-bearing austenitic stainless steel designed for sustained service in oxidizing and carburizing environments up to 1038°C (1900°F). The controlled addition of Ti and Al to a 20Cr-20Ni base enhances oxide scale adhesion and improves high-temperature structural stability beyond conventional 18-8 grades .

1. Product Specifications & Physical Data

ZYTC Alloy supplies UNS S33400 in mill forms suitable for heating element fabrication and furnace component manufacturing, with ISO 9001 and AS9120 certification.

• Available Forms: Sheet, plate, strip, tube (seamless/welded), rod, bar, wire, and custom forgings.

• Specifications: ASTM B409, B514, B515, B536; DIN 1.4847.

2. Operating Conditions & Selection Criteria

Alloy 840 (UNS S33400 / 1.4847)  bridges the gap between standard austenitic stainless steels and higher-cost nickel alloys for moderate-temperature oxidation service. Its primary value lies in long-term scaling resistance rather than load-bearing capacity at extreme temperatures.

• Service Temperature Range: Continuous service up to 1038°C (1900°F) in oxidizing atmospheres; suitable for cyclic conditions up to 900°C for mechanical components .

• Oxidation Resistance: Forms a dense, adherent Cr₂O₃ scale that resists spalling under thermal cycling. Performance superior to Type 304 and comparable to higher-alloyed grades up to the maximum use temperature .

• Environmental Resistance: Good resistance to carburization and sulfidation in combustion atmospheres. Titanium stabilization prevents sensitization and intergranular corrosion after welding or thermal exposure .

• Mechanical Limits: Not intended for high-stress applications above 600°C; creep strength diminishes rapidly above this range. Suitable for non-critical structural components and thin-section heating elements .

3. Fabrication & Material Comparison

Alloy 840 (UNS S33400 / 1.4847) offers excellent formability and weldability similar to standard austenitic grades, though its work-hardening rate requires consideration during severe cold forming.

• Machining: Work-hardens during cutting; machinability comparable to 304 stainless. Carbide tooling recommended with positive rake angles. Water-based coolants for high-speed operations; sulfurized oils for tapping and drilling.

• Welding: Good weldability using GTAW, SMAW, GMAW. Matching filler metals (ERNiCr-3 or similar) recommended to maintain corrosion resistance. Pre-weld cleaning essential; post-weld heat treatment not typically required .

• Forming & Heat Treatment:

  • Hot Working Range: 1000-1200°C (1832-2192°F)

  • Annealing: 1038-1121°C (1900-2050°F) followed by rapid cooling

  • Cold Working: Responds to conventional methods; intermediate annealing may be required for severe deformation .

• Material Comparison:

  • vs. Type 304: Significantly better oxidation resistance above 800°C; preferred for continuous high-temperature exposure.

  • vs. Type 310S: Lower chromium (20% vs. 25%) but comparable oxidation resistance up to 1038°C due to Ti-Al stabilization; more cost-effective where extreme creep strength not required .

  • vs. Alloy 600: Lower nickel content reduces cost; suitable where aqueous corrosion resistance not the primary driver.

Applications

• Electric heating element sheaths (rods, tubes, coils)

• Hot runner system components

• Thermocouple protection tubes

• Industrial furnace fixtures, muffles, and radiant tubes

• Automotive emission control components

• Heat treating baskets and trays

• Chemical processing tanks for water, oil, and mild acids

Contact ZYTC Alloy for certified alloy 840 materials with complete traceability, technical datasheets, and competitive pricing on standard sizes or custom-fabricated components.

Email:daisy@zytcsteel.com

WhatsApp/WeChat: +86 17335753350