347H  is high-carbon niobium-stabilized austenitic heat-resistant stainless steel bright bar, high-temperature enhanced variant of standard 347. Carbon content is controlled 0.04%~0.10%, niobium ≥10×C, Cr 17.0~19.0%, Ni 9.0~13.0%, single-phase austenite and nearly non-magnetic after solution annealing.
Dual strengthening system of high carbon and niobium: Niobium preferentially combines carbon to form stable NbC, completely blocking chromium carbide precipitation at grain boundaries between 425~850℃, eliminating intergranular corrosion sensitization after long-term medium-high temperature service and welding. High carbon delivers solid-solution hardening and dispersed high-temperature carbide precipitation, greatly improving stress rupture strength and creep resistance at 500~800℃. Its allowable stress under high temperature is far superior to standard 347 and 304H, resisting creep deformation and fracture under long-term high-temperature pressure, specially designed for high-temperature high-pressure pressure parts in boilers, thermal power and petrochemical industries.
Without molybdenum, its room-temperature corrosion resistance is close to 347 and 304, only suitable for chloride-free environments such as atmosphere, fresh water and weak acid. Limitation: For thick-wall pressure parts, rapid cooling after welding leaves minor free carbon and causes local sensitization; post-weld high-temperature solution annealing is recommended to eliminate hidden risks.

Chemical element content (%)

Specification：1.00~300.00mm

Application: It is mainly used to manufacture boiler superheater & reheater mandrels, thermal power high-temperature steam pipe bolts and flanges, medium-high temperature pressure valve stems for petrochemical refining, load-bearing support shafts for medium-temperature heat exchangers, medium-high temperature pipe fasteners for waste incineration, high-temperature load-bearing tool bars for heat treatment furnaces, stressed bolts for power plant medium-temperature auxiliary machines, high-temperature hot air circulation valve bodies, high-temperature standard parts for thermal pipe networks, connectors for chloride-free high-temperature reactors, etc.
Widely applied in subcritical & supercritical thermal power units, petrochemical medium-high temperature cracking units, waste incineration waste heat boilers, HVAC medium-high temperature heat exchange systems, industrial heat treatment furnaces, thermal steam transmission pipe networks, high-temperature reactor equipment with chloride-free media and other industries.

Core Advantages Over Competitors

1. High quality stability: Full closed-loop production and online spectral non-destructive inspection strictly control key alloy elements C, Cr, Ni, Nb, carbon stably limited 0.04~0.10% with qualified Nb/C ratio. Uniform controllable austenitic grain structure ensures negligible batch fluctuation of high-temperature creep strength, anti-sensitization and mechanical properties for consistent mass production of boiler and petrochemical high-temperature pressure parts.

2. Excellent surface quality: Dedicated high-precision cold drawing & centerless grinding lines produce bars free of scale, scratches and pits with smooth flat finish. Smooth surface reduces alternating thermal stress concentration to extend fatigue life of parts under long-term high-temperature service; secondary polishing is unnecessary for most conventional machining.

3. Ultra-high dimensional accuracy: Precision cold rolling mills and automatic online dimension detectors narrow tolerance range with tiny single-bar error and strong batch uniformity. Unified part specifications during automatic mass production raise finished yield and machining precision.

4. Rich product variety: According to market demand and customer's special requirements, customized products are provided to meet the use requirements under various complex working conditions, providing customers with more choices.

5. Perfect after-sales service: The perfect after-sales service system can respond to customer needs and feedback in a timely manner. For problems encountered by customers during use, technical support and solutions are provided to customers quickly.

We mainly engage in cold heading wire, bar, peeled bar, and profiled bar; our products cover 11 series and more than 300 grades, and we continue to develop a variety of professional steels. We can provide all-round solutions such as cold heading finishing line manufacturing and high-precision bright bar customization, and provide one-stop procurement services and package procurement solutions for global customers. The website displays some grades. If you don’t have the grade you need, please contact us by phone or email.