Forged steel bars
Forged steel bars are solid bars made from steel billets through a forging process. Due to the refinement of metal grains and the resulting denser structure during the forging process, they exhibit higher mechanical properties than rolled products and are widely used in fields such as machinery manufacturing, aerospace, and petrochemicals. Diameters typically range from 50 to 500 mm, with larger sizes available upon request. Materials typically used include carbon structural steel (such as 45#), alloy structural steel (such as 40Cr and 20CrMnTi), and stainless steel (such as 304 and 316). After forging and heat treatment, these different steel grades can meet diverse requirements, from common mechanical parts to high-end pressure-bearing components.
In terms of production technology, the manufacture of forged steel bars requires key steps, including billet preparation, heating, forging, heat treatment, and finishing. First, high-quality billets, such as continuous-cast billets or slabs, are selected according to product requirements. The billet diameter should be 10%-20% larger than the finished product to ensure sufficient deformation during forging. During the heating process, the billet is fed into a ring-shaped heating furnace or a trolley furnace. The heating temperature is determined by the steel type, typically 1100-1200°C for carbon steel and 1050-1150°C for alloy steel. The holding time is controlled between 1 and 4 hours, depending on the billet size, to ensure uniform billet temperature and avoid overheating or underheating. The forging process is divided into open forging and die forging. Open forging is suitable for large diameter and small-batch production. Upsetting and drawing are performed using a hydraulic press or forging hammer, with a forging ratio of 2-5. Die forging is suitable for small and medium diameter and large-batch production, using dies to achieve more precise dimensions and shapes. After forging, the bars undergo heat treatment. Carbon steel undergoes normalizing or quenching and tempering (quenching and high-temperature tempering), while alloy structural steels are often quenched and tempered to achieve a uniform tempered bainite structure and maintain stable mechanical properties. Finally, straightening, nondestructive testing (such as ultrasonic testing), and surface finishing are performed to ensure a straightness error of ≤1 mm/m and a surface roughness Ra ≤6.3 μm.
The performance advantages of forged steel bars make them occupy an important position in load-bearing components. First, high strength and toughness. After forging and tempering, 40Cr steel bars achieve a tensile strength of 800-1000 MPa and an impact energy (at -20°C) of ≥30 J, far exceeding that of rolled products of the same material, enabling them to withstand complex stresses and impact loads. Second, they possess excellent microstructure density. The forging process eliminates defects such as porosity and pores in the steel billet, resulting in a density approaching 100%, making them suitable for pressure-bearing components such as high-pressure vessel flanges and shafts. Third, they offer excellent performance uniformity. Forging streamlines the metal fibers along the part contour, avoiding anisotropy in properties. The mechanical property deviation within a batch of steel bars is ≤5%. Fourth, dimensional accuracy is controllable. The diameter tolerance of die-forged steel bars can be controlled to ±0.5 mm, and free-forged steel bars can also achieve high precision through subsequent processing, meeting the processing requirements of precision parts. Fifth, they exhibit excellent weldability and processability. Low-carbon alloy forged steel bars have low weld crack sensitivity and can be securely joined using methods such as arc welding and submerged arc welding. They are also easily machined through turning and milling.
Across various application scenarios, forged steel bars are essential materials for high-end equipment manufacturing. In mechanical manufacturing, machine tool spindles and reducer gear shafts are often made of 40Cr and 42CrMo forged steel bars with diameters of 80-200 mm, leveraging their high strength and wear resistance to ensure transmission precision. In aerospace, aircraft landing gear and engine turbine shafts utilize high-strength alloy forged steel bars such as 30CrMnSiA with diameters of 50-150 mm to withstand extreme loads. In the petrochemical industry, high-pressure valve spools and flanges utilize 316 stainless steel forged steel bars with diameters of 100-300 mm to resist corrosive media and high pressure. In power equipment, steam turbine main shafts and generator rotors utilize 25Cr2Ni4MoV forged steel bars with diameters of 300-500 mm to withstand long-term operation in high-temperature and high-pressure environments. In mold manufacturing, cold work mold bases utilize 5CrNiMo forged steel bars, heat-treated to achieve high hardness and wear resistance.
Industry trends indicate that forged steel bars are moving toward larger sizes, higher strength, and greater precision. Production capacity for large forged steel bars continues to expand, now enabling the production of ultra-large bars with diameters exceeding 1000 mm for use in equipment such as large turbine main shafts. Ultra-high-strength steel bars (such as 40CrNiMoA) have achieved tensile strengths exceeding 1200 MPa through optimized alloy composition and heat treatment processes, while maintaining excellent toughness, making them suitable for heavy-duty equipment. Precision forging technology, through processes such as isothermal forging and powder forging, allows for dimensional tolerances of steel bars to be controlled to within ±0.1 mm, reducing subsequent processing and increasing material utilization to over 85%. Furthermore, the application of green forging processes, using regenerative heating furnaces and servo presses, reduces energy consumption by over 30%. Intelligent production technologies, such as digital simulation of the forging process and online performance testing, ensure consistent product quality. In the future, with the development of the high-end equipment manufacturing industry, demand for high-performance forged steel bars will continue to grow, driving the industry to achieve greater breakthroughs in material research and development and process innovation.
