The selection of materials for hollow piston rods should comprehensively consider strength, stiffness, wear resistance, corrosion resistance, and processing performance. Common materials and characteristics are as follows:
1、 Carbon steel and alloy steel: a balance between high strength and economy
35 steel, 45 steel seamless steel pipe
Application scenarios: General hydraulic cylinders, air cylinders, shock absorbers, etc., suitable for medium load, non corrosive environments.
Performance characteristics:
After quenching and tempering treatment, the hardness of 45 steel can reach 229-285HB, and the surface hardness after high-frequency quenching can reach 45-52HRC, significantly improving its wear resistance.
35 steel has a lower cost, but its strength is slightly inferior to 45 steel, and it is commonly used in light load scenarios.
Processing technology: quenching and tempering after rough machining, chromium plating (0.03-0.05mm) on the surface to prevent rust, or high-frequency quenching to improve wear resistance.
40Cr seamless steel pipe
Application scenarios: Heavy load and high impact conditions, such as hydraulic cylinders in construction machinery and rocket launchers.
Performance characteristics:
Medium carbon quenched and tempered steel, with excellent comprehensive mechanical properties and strong impact resistance.
The hardness after quenching and tempering is 230-285HBS, and the surface hardness after high-frequency quenching reaches 50-55HRC.
Processing technology: quenching and tempering after rough machining, and surface chrome plating or polishing if necessary.

2、 Stainless steel: the preferred choice for corrosion resistance and high temperature resistance
304 and 316 seamless stainless steel pipes
Application scenarios: Corrosive environments such as chemical, marine, and food industries, such as wind power equipment spindles and battery cooling pipes.
Performance characteristics:
304 stainless steel is resistant to weak corrosive media such as air, steam, and water, while 316 stainless steel with added molybdenum element has stronger resistance to chloride corrosion.
The surface can be polished to Ra ≤ 0.2 μ m, reducing the friction coefficient and extending the service life.
Processing technology: precision cold drawing, precision grinding, high-precision polishing, no need for chrome plating to meet corrosion resistance requirements.
2Cr13 martensitic stainless steel
Application scenarios: High strength, wear-resistant scenarios, such as shock absorber piston rods.
Performance characteristics:
After stabilization treatment (insulation at 580-590 ℃ for 3-5 hours), the surface hardness reaches HRC50 or above, and the depth of the hardened layer is ≥ 1.5mm.
The sub thermal treatment technology can improve toughness by more than 10% and reduce the risk of quenching cracks.
Processing technology: high-frequency quenching+tempering, surface chrome plating or polishing.

3、 Special materials: meet the requirements of extreme working conditions
Aluminum alloy seamless steel pipe
Application scenarios: Aerospace, new energy vehicles and other fields with high demand for lightweight.
Performance characteristics: The density is only 1/3 of steel, but the strength is low and needs to be compensated through structural design.
Processing technology: High strength aluminum alloys such as 7075 and 2024 are usually used, and the surface is anodized to prevent corrosion.
Carbon fiber composite material
Application scenarios: High end sports equipment, robot joints, etc., with extremely high requirements for weight and rigidity.
Performance characteristics: The specific strength is more than 5 times that of steel, and the fatigue resistance is excellent, but the cost is high.
Processing technology: compression molding or winding technology, which requires solving the connection problem with metal parts.

4、 Core principles of material selection
Load and operating conditions:
Heavy load and high impact: 40Cr steel or 2Cr13 stainless steel are preferred.
Corrosive environment: 316 stainless steel or specially coated carbon steel must be selected.
Lightweight requirements: Aluminum alloy or carbon fiber composite materials.
Cost and lifespan:
45 steel+chrome plating is the most cost-effective universal solution, with a lifespan of over 80000 cycles.
The cost of 316 stainless steel is three times that of 45 steel, but its lifespan can be extended to over 20 years.
Feasibility of processing:
Seamless steel pipe is the mainstream form of hollow piston rod, and it is necessary to ensure that the coaxiality of the inner hole is ≤ 0.05mm.
For scenarios with high welding requirements (such as piston rods with ventilation holes), 35 steel with good welding performance should be selected.