What are the key parameter optimization details for the hot rolling piercing process of carbon steel seamless pipes

First, an overview of the hot rolling piercing process for carbon steel seamless pipes.
Hot rolling piercing is the mainstream forming process for medium and large-sized carbon steel seamless pipes (outer diameter 80~200mm). Using round steel ingots as raw material, after heating to a plastic state, the solid ingot is processed into a hollow tube through the coordinated action of a piercing mill, guide plates, and mandrel. The hot rolling piercing process lays the foundation for subsequent finishing and heat treatment. Its parameter matching directly determines the wall thickness uniformity, roundness, surface quality, and internal microstructure of the carbon steel seamless pipe.
The process is divided into three stages: the biting stage (the roller friction smoothly bites into the steel ingot), the piercing stage (the rollers squeeze and the mandrel pushes to form a hollow tube), and the leveling stage (the leveling rollers correct wall thickness and roundness deviations). The four main parameters—heating temperature, piercing speed, mandrel extension, and guide plate spacing—work together to determine product quality.

Second, the influence mechanism of key parameters on the quality of hot-rolled piercing of carbon steel seamless pipes
(I) Heating temperature for hot-rolled piercing of carbon steel seamless pipes: The hot-rolled piercing temperature directly determines the plasticity, deformation resistance, and microstructure of the carbon steel. If the temperature is too low, insufficient plasticity leads to slippage, uneven wall thickness, eccentricity, and surface cracks (especially in 45# steel); if the temperature is too high, grain coarsening and decreased mechanical properties occur, and surface oxidation of the carbon steel seamless pipe intensifies, forming pits and craters, and in severe cases, delamination defects. Reasonable range: 950~1050℃ for 20# steel, 980~1080℃ for 45# steel.
(II) Piercing speed for hot-rolled piercing of carbon steel seamless pipes: The piercing speed determines the deformation efficiency and uniformity. Too slow a speed leads to excessive local deformation, thinner wall thickness, surface scratches, and exacerbates oxidation; too fast a speed results in insufficient plastic deformation, causing stress concentration, surface cracks, and inward folding, while unstable biting leads to eccentricity and exacerbates mandrel wear. Reasonable range: 1.2~2.0 m/s.
(III) Mandrel Forward Extension in Hot-Rolled Piercing of Carbon Steel Seamless Pipes: The forward extension in hot-rolled piercing of carbon steel seamless pipes is the offset between the mandrel head and the roll centerline, determining the piercing position and stress state. Too small a speed results in insufficient thrust, excessive radial deformation leading to thicker wall thickness, inward folding, and biting deviation; too large a speed results in excessive axial deformation leading to thinner wall thickness, outward folding, surface cracks, and exacerbates mandrel wear. Reasonable range: 8~15 mm.
(IV) Guide Plate Spacing in Hot-Rolled Piercing of Carbon Steel Seamless Pipes: The spacing between the guide plates and the rolls in hot-rolled piercing of carbon steel seamless pipes serves a guiding and positioning function. Too small a diameter results in excessive extrusion pressure, causing surface scratches, wall thickness deviations, out-of-tolerance roundness, and equipment wear; too large a diameter weakens the guiding force, leading to misalignment, eccentricity, and localized bulges and depressions. The appropriate range is 1.02 to 1.05 times the outer diameter.

Third, the optimization effect and implementation guarantee of the hot rolling piercing of carbon steel seamless pipes
(I) Implementation effect of hot rolling piercing of carbon steel seamless pipes
After three months of batch production verification by a certain enterprise, after adopting optimized parameters:
Defect rate: 20# steel within 0.8%, 45# steel within 0.9%, a decrease of more than 76% compared with before optimization
Wall thickness uniformity: The compliance rate increased from 75% to more than 99%
Production efficiency: Increased from 80 pieces/hour to 92 pieces/hour, and the cost decreased by 12%
Subsequent processing: Finishing time was shortened by 20%, with significant economic and social benefits.
(II) Guarantee measures for hot rolling piercing of carbon steel seamless pipes
Intelligent temperature control of hot rolling piercing of carbon steel seamless pipes: Adopting an intelligent temperature control system for real-time monitoring, with fluctuations ≤±10℃, and regular calibration
Digital speed control of hot rolling piercing of carbon steel seamless pipes: Precisely setting the roll linear speed to maintain stability and avoid fluctuations
Carbon steel seamless steel. Regular maintenance of tooling for hot rolling piercing of seamless carbon steel pipes: Inspect the mandrel extension and guide plate spacing, adjust promptly, and replace worn parts regularly.
Parameter management for hot rolling piercing of seamless carbon steel pipes: Establish an optimal parameter database for different steel grades and specifications, and regularly analyze and fine-tune.
Professional training for personnel involved in hot rolling and piercing of seamless carbon steel pipes: Improve operational skills and ensure strict adherence to optimized parameters.

Fourth, optimal parameter combination and conclusions for hot rolling piercing of seamless carbon steel pipes:
Steel grade 20#: Heating temperature 1000℃, piercing speed 1.7m/s, mandrel extension 11mm, guide plate spacing: 123.6mm
Steel grade 45#: Heating temperature 1030℃, piercing speed 1.4m/s, mandrel extension 11mm, guide plate spacing: 123.6mm
This parameter combination effectively solves common defects such as eccentricity, uneven wall thickness, cracks, and internal folds, and is suitable for mass production of medium and large-sized seamless carbon steel pipes. In the future, digital simulation technology can be combined to simulate the deformation law of metals and realize intelligent parameter control; at the same time, the surface treatment technology of carbon steel seamless steel pipes can be optimized to reduce oxidation and promote the industry to develop towards refinement and efficiency.