17-4PH and 347H are different types of stainless steel, with fundamentally different core design goals and application scenarios. Their grade definitions and standard systems have clear technical orientations. HT PIPE is a 17-4PH and 347H material supplier with 15+ export experience. Contact us for more information and quotes for free!
what is stainless steel 17-4ph and 347h?
17-4PH is a martensitic precipitation-hardening stainless steel, characterized by a "martensitic matrix + copper-based precipitation strengthening." Its strength and toughness can be flexibly controlled through heat treatment to achieve a balance between "high strength and medium corrosion resistance." 347H is a niobium-stabilized austenitic heat-resistant stainless steel, characterized by an "austenitic matrix + niobium-carbon stabilization," focusing on structural stability and corrosion resistance at high temperatures.
Stainless Steel 17-4 PH Chemical Composition
| Grade | C | Mn | Si | S | Cu | Fe | Ni | Cr | Cb+Ta |
| SS 17-4 PH | 0.07 | 1.0 max | 1.0 max | 0.03 | 3.0 – 5.0 | Bal | 3.0 – 5.0 | 15.0 – 17.5 | 5 X C / 0.45 |
ASTM A240 Stainless Steel 347H Chemical Composition
| Grade | C | Ni | Si | N | S | Mn | P | Cr | Co + Ta | |
| SS 347H | min. | 0.04 | 9 | – | – | – | – | – | 17 | 8xC min |
| max. | 0.1 | 13 | 1 | – | 0.03 | 2 | 0.045 | 19 | 1.00max | |
Production Process and Control Points of 17-4PH
Smelting and Refining: An electric arc furnace is used for initial smelting + LF refining. The uniformity of copper and niobium elements is carefully controlled to avoid uneven strengthening caused by component segregation. Finally, argon-protected casting is used to reduce oxide inclusions.
Forming and Processing: Hot working temperature is controlled at 1100-1180℃, and the final forging temperature is not lower than 850℃ to ensure the formation of a uniform martensitic structure. Cold working can be carried out in the solution-treated state, where the material has good plasticity (elongation ≥20%), suitable for stamping, cutting, and other forming processes. Aging treatment is required promptly after processing.
Heat Treatment: This consists of two key steps: solution treatment and aging. Solution treatment temperature is 1020-1060℃, held for 1-2 hours, then air-cooled or oil-cooled to form a supersaturated martensitic matrix.
Aging treatment parameters are selected according to performance requirements: H900 (480℃ × 1 hour air cooling) achieves the highest hardness (≥40HRC), while H1150 (620℃ × 4 hours air cooling) balances strength and toughness (HRC 30-35). The aging temperature directly affects the size of the precipitated phase and must be precisely controlled within ±5℃ to avoid performance fluctuations.
Production Process and Control Points of 347H
Smelting and Refining: Electric furnace primary smelting + VOD refining + LF fine-tuning are employed. The core control focuses on the niobium to carbon ratio (Nb≥10×C%), while reducing harmful impurities such as sulfur to extremely low levels (≤0.001%) to improve high-temperature toughness. A protective atmosphere is used during casting to prevent secondary oxidation.
Forming and Processing: Hot working temperature is 1150-1200℃ to ensure a sufficiently uniform austenitic structure. The final rolling temperature is not lower than 900℃ to avoid the formation of ferrite phase. During cold working, due to the high work hardening index of austenite, multi-pass forming and intermediate annealing (holding at 850-900℃ followed by air cooling) are required to restore plasticity.
Heat Treatment: Only a single solution treatment is required at a temperature of 980-1150℃. The holding time is calculated based on thickness (1-2 minutes per millimeter), followed by rapid water cooling. The purpose is to dissolve all carbides, forming a single austenitic structure while ensuring uniform distribution of niobium. No additional heat treatment is required after welding.
Corrosion Resistance Comparison of ss347h and ss17-4ph
17-4PH: Corrosion resistance is close to that of 304 austenitic stainless steel and superior to conventional martensitic steel. It performs excellently in chloride environments such as air, fresh water, and seawater, exhibiting outstanding resistance to stress corrosion cracking. It shows no tendency for intergranular corrosion according to ASTM A262 C.
However, its corrosion resistance is insufficient in strong acid and high-temperature oxidizing environments, with a significantly accelerated oxidation rate above 600℃.
347H: Its core advantages are resistance to intergranular corrosion and high-temperature corrosion resistance. Niobium preferentially combines with carbon, avoiding chromium depletion at grain boundaries during welding or high-temperature service. It passes ASTM A262 E testing. It forms a stable oxide film in air at 750-800℃, with an oxidation limit of 850℃.
In 565℃ molten nitrate salt, the corrosion rate is less than 0.01 mm/a after 1000 hours, superior to similar foreign products. However, its resistance to stress corrosion in high-chloride environments is weaker than that of 17-4PH.
17-4PH application
- Aerospace: Used to manufacture structural components such as engine mounts, drive shafts, and fasteners.
- Medical Devices: Orthopedic implants (artificial joints, bone screws), surgical instruments (forceps, saw blades), its biocompatibility and high strength meet the requirements of human implantation and surgical procedures.
- Marine Engineering: Ship propeller shafts, offshore platform fasteners, its resistance to seawater corrosion and high load-bearing capacity extend service life.
- High-end Manufacturing: Precision molds, valve cores, high-pressure pump components, heat treatment deformation ≤0.1%, suitable for manufacturing precision parts.
Typical Applications of 347H
- Power Plant Energy Sector: Superheater tubes and reheater tubes in supercritical/ultra-supercritical power plant boilers, with a creep limit of 74MPa at 593℃, meeting the design conditions of 482℃/20.55MPa.
- Chemical Sector: Used in the manufacture of high-temperature reactors, heat exchanger tubes, and distillation tower internals, capable of withstanding high-temperature media above 600℃ and corrosive media such as nitric acid and acetic acid.
- Petroleum Refining Sector: High-temperature pipelines and valves in hydrocracking units; resistance to high-temperature sulfide corrosion and creep ensures long-term equipment operation.
- Other High-Temperature Applications: Furnace bottom plates and heating element supports in industrial furnaces; oxidation resistance below 800℃ reduces high-temperature losses.
