An overview of stainless steel 174PH
As a martensitic precipitation-hardening stainless steel, 17-4PH (ASTM) is comparable to the national standard 05Cr17Ni4Cu4Nb. This kind of stainless steel is low in carbon, high in nickel and copper, and has good weldability and corrosion resistance. In addition, a high concentration of alloy elements like Cu and Nb are present in the steel. By precipitating aging hardening phases like ε-Cu, NbC, M23 C6, etc., during heat treatment, these alloy components can increase the material’s strength and hardness. Given the aforementioned benefits, the aviation, aerospace, chemical, and nuclear industries make extensive use of 17-4PH martensitic precipitation hardening stainless steel.
Composition and properties of 17-4PH stainless steel
The chemical composition (mass fraction, %) of 1.17-4PH stainless steel is: ≤0.07C, ≤1.00Mn, ≤1.00Si, ≤0.023P, ≤0.03S, 15.50~17.50Cr, 3.00~5.00Ni, 3.00~5.00Cu, 0.15~0.45Nb. Its main precipitation hardening elements are copper and niobium, and some are aluminum, titanium, etc.
17-4PH physical properties:
∙ Average density: about 7.8 g/cm³ or 7.81 g/cm³
∙ Melting point: 1400-1440℃
∙ Specific heat capacity: 502J/(kg·℃)
17-4PH mechanical properties:
∙ After heat treatment, the yield strength can reach more than 1200MPa
∙ Tensile strength: 1100 MPa
∙ Yield strength: 1000 MPa
∙ Elongation: 15%
∙ HRC hardness: >40
17-4PH Resistance to Corrosion
Comparable to 304 stainless steel, 17-4 stainless steel resists corrosion better than 400 series stainless steel. It is appropriate for usage in a range of corrosive settings and exhibits good tolerance to air, diluted acid, and salt water.
Application areas of 17-4PH stainless steel
Aerospace: Because 17-4 stainless steel can withstand high temperatures and high pressures, it is frequently used to create turbine blades, aircraft joints, and other aviation components.
Oil and Gas Industry: To prevent corrosion and wear, the material is frequently used in pump shafts, oilfield valve components, and other oil and gas equipment.
Chemical Equipment: 17-4 stainless steel is appropriate for chemical processing equipment because of its strong resistance to corrosion and ability to tolerate erosion from a range of chemical media.
Nuclear Energy: Because 17-4 stainless steel is stable and resistant to oxidation at high temperatures, it is utilized to build important components for nuclear reactors.
Paper Industry: Used in machinery used in paper mills to endure harsh chemical and high humidity conditions.
Military and Aerospace: Due to its strength and ability to withstand corrosion under harsh circumstances, the material is also utilized in missile joints and other military hardware.
General Manufacturing: Fasteners, gears, and other mechanical components made of 17-4 stainless steel are utilized in applications requiring great strength and resistance to wear.
Effect of Heat Treatment on 174PH Stainless Steel
The process of heating, maintaining, and cooling solid metal materials to alter their interior structure and characteristics is referred to as heat treatment. By regulating temperature and time, this technique maximizes the material’s mechanical qualities, including hardness, strength, toughness, and wear resistance, without altering the workpiece’s shape or general chemical makeup.
The mechanism and process of heat treatment on 174PH stainless steel
Method of Heat Treatment
1. Treatment of the Solution
For solution treatment, 17-4 PH stainless steel is heated to roughly 1025°C (1875°F) for a while in order to guarantee that the alloying components are distributed uniformly. The microstructure of the material is transformed into a completely austenitic phase during this operation, setting it up for further quenching and aging procedures.
2. Quenching
Following solution treatment, 17-4 PH stainless steel is quickly chilled to produce a martensitic structure, typically by air cooling or water quenching. High-strength, high-hardness martensite provides superior mechanical qualities. Although internal pressures may be induced concurrently, quenching greatly improves the material’s strength and hardness.
3. Tempering
Tempering is typically necessary after quenching to lower internal tensions and modify the material’s toughness and strength. The final qualities are influenced by the tempering temperature and duration; higher temperatures can enhance toughness while decreasing hardness.
4. Hardening of Precipitation
One of the main properties of 17-4 PH stainless steel is precipitation hardening. The material is aged between 480°C and 620°C during tempering, producing precipitates that are rich in copper. The strength and hardness of the material are further increased by these precipitates, which serve as a barrier to dislocation movement in the microstructure.
Mechanism of Action
- Phase Transformation and Strengthening: Through solution treatment and quenching, phase transformation in the material results in the formation of the martensite phase, which has extremely high strength and hardness. By controlling the cooling rate, different types of martensite can be obtained, which affects the final properties.
- Precipitation Strengthening: During the aging process, the formation of a copper-rich phase effectively blocks the movement of dislocations, a mechanism known as precipitation strengthening. By adjusting the aging temperature and time, the distribution and size of these precipitates can be optimized to achieve optimal performance.
- Internal Stress Management: The tempering process helps eliminate internal stresses caused by rapid cooling, while adjusting the balance between toughness and strength, making the final product both strong and impact-resistant
When heat treating 17-4 PH stainless steel, there are a number of factors to take into account in order to guarantee the end product’s functionality and quality. Here are some important things to think about:
1. Temperature of heating
Select the proper heating temperature: To guarantee that the alloying elements are completely dissolved, solution treatment is often carried out at 1025°C (1875°F). The composition of the material should determine the quenching heating temperature; hypoeutectoid alloys should be heated to 30–50°C above Ac3, while eutectoid alloys should be heated to 30–50°C above Ac113.
2. Waiting
Control the holding time: Typically, 1 to 4 minutes are needed for every millimeter of thickness. This time should be established based on the workpiece’s shape and thickness. A holding period that is too short could lead to partial phase change, while one that is too long could result in excessive oxidation or grain growth23.
3. The cooling technique
Select the proper cooling medium. Brine, oil, and water are common cooling media. Oil cools slowly and is appropriate for complexly formed workpieces to reduce deformation; water cools quickly but may result in increased internal tension.13. Prevent quenching cracks: An uneven cooling rate during the quenching process can lead to workpiece cracking, thus it’s important to use cooling techniques like single-liquid or double-liquid quenching sensibly to lower internal stress.3.
4. Treatment with tempering
Apply the proper tempering: To reduce internal stress and increase toughness, tempering should be applied after quenching. The typical tempering temperature is from 450°C to 650°C; the precise temperature must be chosen based on the material’s composition and desired qualities23.
5. Management of internal tension
Remove internal stress: Since heat treatment may produce internal tension, stress relief annealing may be a viable option to remove any remaining internal stress brought on by casting, welding, or processing.12.
6. Size and shape of the workpiece
Think about the workpiece’s dimensions and form: To avoid deformation or breaking due to uneven cooling, particular attention should be paid to the homogeneity of the cooling process for big or complicated workpieces3.
7. Observation and evaluation
Keep a close eye on the heat treatment procedure: To guarantee the uniformity and dependability of the heat treatment, make sure that variables like temperature, time, and cooling rate fulfill the specifications. To make sure the finished solution satisfies the design criteria, performance testing at critical links is advised concurrently23.
Taking these precautions can successfully enhance the performance of 17-4 PH stainless steel following heat treatment, guaranteeing its dependability and durability in demanding applications.
In summary, heat treatment changes the microstructure of 17-4 PH stainless steel by controlling the heating, cooling, and holding processes, thereby significantly improving its mechanical properties and corrosion resistance, making it suitable for a variety of demanding applications