What are the production processes for 16MnDG seamless steel pipes in industrial projects

Hot rolling process of 16MnDG seamless steel pipes:

(1) Billet preparation and inspection: Select steel billets that meet the chemical composition and quality requirements, and strictly inspect their surface quality and dimensional accuracy. Remove surface defects such as cracks and scabs to ensure the billet quality is qualified.

(2) Billet heating: Send the qualified billet into a heating furnace and heat it to a suitable temperature range, generally around 1200℃-1250℃, so that the billet has good plasticity and machinability.

(3) Piercing: The heated billet is sent to a piercing mill for piercing operation. Through the mechanical force and heat of piercing, a cavity is formed in the center of the billet, forming a rough tube. During the piercing process, the billet rotates and advances continuously, gradually forming the prototype of a seamless steel pipe under the action of the rolls and mandrel.

(4) Rolling: The billet is then sent to a rolling mill for rolling. Through multiple rolling passes, the wall thickness of the steel pipe is further reduced, improving its dimensional accuracy and surface quality, so that the shape and size of the steel pipe gradually approach the finished product requirements.

(5) Reheating: After rolling, the steel pipe may experience increased hardness and decreased plasticity due to work hardening and other reasons. It needs to be reheated to improve its microstructure and properties, preparing it for subsequent sizing and other processes.

(6) Sizing (Reduction): The reheated steel pipe enters a sizing or reducing mill. Through the squeezing action of the rolls, the outer diameter of the steel pipe is precisely controlled to reach the specified dimensional tolerance range, obtaining the required outer diameter accuracy and surface finish.

(7) Heat Treatment: After sizing. The steel pipes undergo heat treatment, generally normalizing, to refine the grains, improve the uniformity of the microstructure, eliminate internal stress, and enhance the overall mechanical properties of the steel pipes, enabling them to meet the requirements for use in low-temperature environments.

(8) Straightening of finished pipes: After heat treatment, the steel pipes may exhibit a certain degree of bending deformation, requiring straightening by a straightening machine to ensure the straightness of the steel pipes meets standard requirements, guaranteeing the appearance quality and performance of the steel pipes.

(9) Finishing: The straightened steel pipes undergo surface treatment, such as pickling and phosphating, to remove impurities such as oxide scale and rust from the surface of the steel pipes, improving the surface quality. Simultaneously, the ends of the steel pipes are cut and chamfered to make the end faces flat and smooth, facilitating subsequent installation and use.

(10) Inspection: A comprehensive quality inspection is conducted on the finished steel pipes, including non-destructive testing, physical and chemical property testing, and dimensional accuracy testing. Non-destructive testing mainly uses methods such as ultrasonic testing and eddy current testing to check for defects such as cracks and pores inside the steel pipe; physical and chemical performance testing analyzes and tests the chemical composition and mechanical properties of the steel pipe to ensure that it meets relevant standards and technical requirements; dimensional accuracy testing mainly checks whether the outer diameter, wall thickness, length and other dimensions of the steel pipe are within the specified tolerance range. Only qualified steel pipes can be put into storage or delivered for use as finished products.

Cold Rolling (Drawing) Process of 16MnDG Seamless Steel Pipe

(1) Billet Preparation: Select suitable hot-rolled billets or steel pipes that have undergone pickling, annealing, and other pretreatments as billets, and check the dimensional accuracy and surface quality of the billets to ensure that they meet the requirements of the cold rolling (drawing) process.

(2) Pickling and Lubrication: In order to remove the oxide scale and oil stains on the surface of the billet, improve the surface quality of the steel pipe, and increase the service life of the cold rolling (drawing) die, the billet needs to be pickled. After pickling, a lubricant is applied to the surface of the billet to reduce friction during cold rolling (drawing) and prevent scratches on the steel pipe surface and wear on the mold.

(3) Cold Rolling (Drawing): The pickled and lubricated billet is processed in a cold rolling mill or cold drawing mill. Cold rolling is the process of plastic deformation of the steel pipe at room temperature through the squeezing action of the rolls, thereby reducing the wall thickness and improving dimensional accuracy and surface quality; cold drawing is the process of drawing the steel pipe through a mold to reduce its cross-sectional area and increase its length to achieve the required size specifications. During the cold rolling (drawing) process, it is necessary to reasonably select the rolling or drawing passes, deformation amount, and other process parameters according to the material, specifications, and finished product requirements of the steel pipe to ensure the performance and quality of the steel pipe.

(4) Heat Treatment: Due to work hardening, the steel pipe after cold rolling (drawing) has high strength and hardness, but low plasticity and toughness, and needs to be heat-treated to improve its structure and properties. Annealing or tempering is generally used. Annealing can eliminate work hardening and restore the plasticity and toughness of the steel pipe, while tempering can further improve the toughness and stability of the steel pipe while maintaining a certain strength.

(5) Straightening: Similar to the hot rolling process, cold-rolled (drawn) steel pipes after heat treatment also need to be straightened to ensure that their straightness meets the requirements.

(6) Finishing: The straightened steel pipes undergo surface treatment, such as pickling, phosphating, shot blasting, etc., to remove surface oxide scale, oil stains, and other impurities, improving the surface finish of the steel pipes. At the same time, the two ends of the steel pipes are cut and chamfered to meet dimensional accuracy and appearance quality requirements.

(7) Inspection: A comprehensive quality inspection is carried out on the finished cold-rolled (drawn) steel pipes, including non-destructive testing, physical and chemical property testing, and dimensional accuracy testing, to ensure that the quality of the steel pipes meets relevant standards and user requirements before they can be put into storage or delivered for use.