Processing Technology of GH3600 Alloy Steel Pipe

 

GH3600(ASTM/ASME UNS N06600) is a high temperature and oxidation resistant nickel based alloy. It is widely used in petrochemical processing, nuclear power and aerospace industry. Aerospace GH3600 alloy tubes are mainly used for hydrogen and oxygen rocket engines of upper stage power devices of carrier rockets. At present, the United States is planning on the basis of hydrogen and oxygen rocket engine’s orbit transfer vehicle and single stage to orbit of the space shuttle, developed for landing on the moon of Saturn rocket, second, third class, the J – 2 lox/lh2 engine developed by France and other European countries Ariane rocket and Japan is developing, the carrier rocket level above all use hydrogen engine as their main power devices.

At present, forging and drilling or cross-rolling piercing technology is mainly used in the billet of Nickel-based pipes in China. Due to the limitation of forging ratio, the uneven grain size of tube billet and a waste of raw materials in the drilling process, forging and drilling process are generally only suitable for thick wall, a short length and difficult to prepare hot-processed tube billet. Although the cross-rolling piercing process has high efficiency and high yield, due to its own structural constraints, whether it is two-roll or three-roll cross-rolling piercing, the material is not subjected to three-dimensional compressive stress, which results in circular micro-cracks on the cross-section of the billet and affects the possibility of subsequent processing. GH3600 alloy pipes for aerospace use are extruded to avoid the above situation.  Operations details including:

The equipment of extrusion blank is 2.5MN horizontal extrusion press. The blank size is 125 mm x 37 mm x L. The extrusion force is 1.6-1.8MN. The extrusion parameters are heating temperature 960-980 C, holding time 90-120 min, preheating temperature 500-600 C, extrusion speed 80-100mm?S-1 and extrusion ratio 10.1.

Two different rate distribution methods were used for cold rolling of finished products. The effects of different cold rolling processes on mechanical properties of products were compared for different cold rolling processes from 15mm *1.75mm to 5.8mm *0.4mm. The annealing pass processing rate of process 1 ranges from 68.9% to 70%, and that of process 2 ranges from 51.5% to 56.9%. The results are as follows:

  • GH3600 alloy tube can be extruded to refine the microstructure obviously and improve the microstructure uniformity.
  • The cold processing rate of finished products is controlled within the range of 51% to 57%, which can not only obtain good finished product structure, but also improve the room temperature elongation and yield strength at high temperature, and obtain better performance of finished products. Elongation of 39.8% at room temperature and 900 ℃ under the Rm of 124 Mpa, Rp0.2 is 82 Mpa.

The key point of tube extrusion is the matching of extrusion ratio and extrusion temperature. High extrusion ratio is beneficial to obtain the more uniform structure, but it will increase the extrusion pressure at the same time. While high extrusion temperature reduces the extrusion pressure, it also reduces the surface quality and dimensional accuracy of the product. At the same time, the sheath and lubrication mode of the high temperature alloy extrusion also play a crucial role.

 

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