In modern industrial production, cylinder forgings play a pivotal role, especially in energy sectors such as nuclear power, petrochemical, and hydropower, where they serve as core components of major technical equipment. These cylinder forgings often operate for long periods under harsh conditions such as high temperatures and high pressures; therefore, every stage of their manufacturing process is crucial, particularly the preparatory work before forging and the control of key process points during forging.
During the manufacturing of cylinder forgings, preparatory work before forging is a key step to ensure that subsequent forging processes proceed smoothly and that product quality meets standards. This preparation covers multiple aspects, from raw material selection to heating, each having a profound impact on the performance and reliability of the final product.
The raw materials used for cylinder forgings are diverse, including various grades of steel and high-temperature alloys as well as non-ferrous metals such as aluminum, magnesium, titanium, and copper. These materials may appear as bars and profiles processed to different sizes or as ingots of various specifications. When selecting raw materials, domestic materials suitable for national resource conditions are widely used, while foreign materials are also selected as needed. Most of the selected materials have already been included in national standards, though many newly developed materials are still at the research, trial use, or promotion stage. Product quality is closely related to raw material quality; forging personnel must possess essential metallurgical knowledge to accurately select the most appropriate materials according to process requirements.
Material calculation and cutting are key steps to improving material utilization and refining the billet. Excess material leads to waste, worsened die cavity wear, and increased energy consumption. Insufficient cutting allowance increases process adjustment difficulty and raises scrap rates. In addition, the quality of the cut end face significantly affects the forging process and final cylinder forging quality. In actual operations, the required material weight and size must be accurately calculated according to the forging's shape, dimensions, and process requirements, and the cutting method must be arranged reasonably to ensure that the billets meet subsequent forging needs while minimizing material waste.
Heating is a critical step before forging, intended to reduce deformation resistance and improve metal plasticity. However, heating also introduces issues such as oxidation, decarburization, overheating, and burning. Accurate control of initial and final forging temperatures has a major impact on product structure and properties. Common heating methods include flame-furnace heating and induction heating. Flame-furnace heating is low-cost and highly adaptable but requires long heating times, easily causes oxidation and decarburization, and demands continuous improvement of working conditions. Induction heating provides rapid heating and minimal oxidation but adapts poorly to variations in product shape, size, and material properties. When selecting a heating method, factors such as material characteristics, forging shape and size, production efficiency, and cost must all be considered. Strict control of temperature parameters throughout heating is essential to ensure heating quality.
Forging forming occurs under the action of external force; therefore, accurate calculation of deformation force is an important basis for equipment selection and die verification. Stress–strain analysis of the deformation body is also essential for optimizing the process and controlling the structural properties of cylinder forgings. The main deformation-force analysis methods include the principal stress method, slip-line method, upper-bound method, and finite element method.
The principal stress method, though not extremely rigorous, is simple and intuitive and can calculate total pressure and stress distribution on the workpiece–tool contact surface.
The slip-line method is rigorous for plane-strain problems and intuitive for solving local deformation stress distributions, but its applicability is limited.
The upper-bound method can provide overestimated loads, and upper-bound elements can also predict changes in workpiece shape during deformation.
The finite element method can provide external loads, workpiece shape changes, and internal stress–strain distributions; however, it requires extensive computer time and memory, especially for elastic–plastic finite-element calculations.
In recent years, combined analytical methods have become common, for example, using the upper-bound method for coarse calculations and the finite element method for fine analysis in critical areas. Accurate deformation-force calculation enables proper selection of forging equipment, ensuring that equipment meets load requirements without excessive or insufficient capacity, thus improving production efficiency and product quality.
Reducing friction saves energy and increases die life. More uniform deformation also improves product structural properties; therefore, friction reduction is one of the key measures during forging. Because forging methods and working temperatures vary, lubricants also differ accordingly. Glass lubricants are commonly used for high-temperature alloys and titanium alloys. For hot forging of steel, water-based graphite is widely applied. For cold forging, due to high pressures, phosphate or oxalate treatments are often required before forging. Lubrication methods and lubricants must be selected according to forging processes, material characteristics, and working temperatures to ensure smooth forging, reduce friction and wear, and improve product quality and die life.
Once preparatory work is completed, the forging stage begins, an essential phase that determines the quality and performance of cylinder forgings. Every detail of the forging process, from billet-preform design to heat treatment, directly affects the final product's performance and reliability. Therefore, precise control of forging processes is necessary for manufacturing high-quality cylinder forgings. The key points are as follows:
Material selection is crucial for cylinder forgings, as different applications require different material properties. For example, in conventional pressure vessels, carbon steel/low-alloy steel (such as SA-508 Gr.3) is widely used because of low cost and well-established processing. Stainless steels (such as 316L and duplex 2205) are suitable for corrosive environments but require attention to σ-phase precipitation. High-temperature alloys (such as Inconel 625) are used in extreme temperature and corrosion conditions. Material selection must consider mechanical properties, corrosion resistance, high-temperature performance, and cost based on application requirements.
Billet preform design is a key step in forging. For integral cylinders, the usual preform method is upsetting + piercing, with height-to-diameter ratio (H/D ≤ 2.5) controlled to avoid instability. Extra-large cylinders are forged in segments, and weld zones must have a forging ratio ≥ 3. Ring-rolling is used for ring-shaped cylinders, with rolling forces and feed speeds controlled to avoid “fish-tail” defects; dimensional accuracy requires diameter tolerance of ±1% and roundness ≤ 0.5% of diameter.
Mandrel expansion in traditional processes requires the workpiece temperature to remain above the final forging temperature by at least 50°C, with hammering every 60° of rotation to avoid ovalization.
Heating specifications must be strictly controlled:
Carbon steel: 1150–1200°C start forging, ≥850°C finish forging
Stainless steel: 1100–1180°C start forging; austenitic steel finish forging ≥900°C
Forging ratios: ≥2.5 (axial) and ≥1.5 (radial) to ensure dense microstructure.
Cooling rates: low-alloy steel slow cooling (pile cooling or pit cooling) to prevent white spots; martensitic stainless steel slow cooling + timely annealing.
Proper billet design and precise process control significantly improve cylinder-forging quality and performance.
Typical defects include wall-thickness unevenness, axial cracking, inclusion segregation, and excessive ovality.
Causes and countermeasures include:
Uneven wall thickness:
Caused by asymmetric mandrel deformation or eccentric ring rolling.
Solution: laser alignment + real-time thickness monitoring.
Axial cracks:
Caused by low final forging temperature or rapid cooling.
Solution: controlled-temperature forging + slow cooling.
Inclusion segregation:
Caused by unhealed ingot defects.
Solution: increase forging ratio + multi-direction forging.
Excessive ovality:
Caused by uneven rolling pressure.
Solution: dynamic rolling-force distribution adjustment.
Strict control and corrective measures ensure product reliability.
Dies and equipment are important components of cylinder-forging manufacturing. Ring-rolling machines must provide radial–axial combined rolling capability (e.g., D53K series). Mandrel tools use hot-work die steel (such as H13) and must be preheated to 300–400°C. Cylinders weighing over 20 tons require manipulators equipped with overturning capability. Selecting proper dies and equipment and ensuring good working conditions are critical to product quality. Regular maintenance is also required to ensure smooth production.
Heat treatment is critical and greatly influences final performance.
Carbon steel/low-alloy steel: normalizing + tempering to refine grains and eliminate banded structure.
Austenitic stainless steel: solution treatment at 1050–1100°C with water quenching to restore corrosion resistance.
Welded cylinders: stress-relief annealing at 600–650°C with slow cooling.
Proper heat treatment improves structure and reliability.
Quality control is essential for ensuring product reliability.
Ultrasonic testing (UT) using ASME SE-213 to detect internal inclusions and cracks.
Residual stress testing using X-ray diffraction or blind-hole method, with requirements: residual stress ≤ 30% of yield strength.
Dimensional inspection using full-circumference laser scanning matched to CAD models.
Strict quality control ensures compliance with design requirements and standards.
After thorough preparation and strict forging control, high-quality cylinder forgings are produced and widely applied across key industries. These application cases demonstrate not only their importance but also their excellent performance under extreme conditions.
Nuclear-power cylinders use ASME SA508 Grade 3 steel, requiring impact energy ≥ 80 J at –40°C. This material offers excellent low-temperature toughness, high strength, and irradiation resistance, meeting demanding nuclear-equipment requirements. Pressure vessels in nuclear equipment operate under high temperature, high pressure, and radiation for long periods; therefore, extremely high material performance is required. Strict material selection, process control, and inspections ensure safe and reliable operation inside reactors.
Chemical-reactor cylinders use duplex-steel forgings, requiring intergranular corrosion testing (ASTM A923). Duplex steel offers excellent corrosion resistance and high strength, meeting the demanding conditions of chemical media. Reactors operate in corrosive, high-temperature, and high-pressure environments; thus, materials must provide strong corrosion resistance, strength, and toughness. Proper material selection, forging control, and inspection ensure reliable operation in complex chemical environments.
As core components of major technical equipment in nuclear power, petrochemical, hydropower, and other energy sectors, every stage of cylinder-forging manufacturing is critical. From raw material selection, material calculation and cutting, heating, deformation-force calculation and equipment selection, lubrication methods and lubricant choice, to billet-preform design, forging-process control, defect prevention and solutions, die and equipment selection, heat treatment, and quality control, every step must be strictly controlled to ensure product quality.
