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

First, the hot rolling piercing process of 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 in a furnace, the solid ingot is processed into a hollow tube through the coordinated action of a piercing mill, guide plates, and mandrel. This process lays the foundation for subsequent finishing and heat treatment, and the matching degree of its process parameters directly determines the uniformity of wall thickness, roundness, surface quality, and internal microstructure of the tube. The hot rolling piercing process of carbon steel seamless pipes is divided into three stages: the biting stage (the friction of the rolls smoothly bites the steel ingot in), the piercing stage (the metal is squeezed by the rolls and pushed by the mandrel to form a hollow tube), and the leveling stage (the leveling rolls correct the wall thickness and roundness deviations). The four main parameters—heating temperature, piercing speed, mandrel extension, and guide plate spacing—work together to determine the product quality.

Second, the influence mechanism of key parameters in the hot rolling piercing process of carbon steel seamless pipes on quality.

(I) Heating temperature in the hot rolling piercing process of carbon steel seamless pipes.

The temperature of the carbon steel seamless pipe directly determines its plasticity, deformation resistance, and microstructure. If the temperature is too low, the plasticity is insufficient, the deformation resistance is high, and it easily leads to slippage, uneven wall thickness, eccentricity, and surface cracks (especially in 45# steel). If the temperature is too high, grain coarsening leads to a decrease in mechanical properties, and surface oxidation is accelerated, forming pits and depressions, which can even cause delamination defects in severe cases. Reasonable range: 950~1050℃ for 20# steel, 980~1080℃ for 45# steel.

(II) Piercing speed in the hot rolling piercing process of carbon steel seamless pipes.

The piercing speed in the hot rolling piercing process of carbon steel seamless pipes 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 in the hot rolling piercing process of carbon steel seamless pipes results in insufficient plastic deformation, causing stress concentration, surface cracks, and inward folding. Simultaneously, unstable biting leads to eccentricity and exacerbates mandrel wear. Reasonable range: 1.2~2.0 m/s (1.5~2.0 m/s for 20# steel, 1.2~1.7 m/s for 45# steel).

(III) Mandrel Extension in the Hot Rolling Piercing Process of Carbon Steel Seamless Pipes.

The mandrel extension in the hot rolling piercing process of carbon steel seamless pipes is the offset between the mandrel head and the roll centerline, determining the penetration position and stress state. Too small an extension results in insufficient thrust, excessive radial deformation leading to thicker wall thickness, inward folding, and biting deviation; too large an extension 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 Rolling Piercing Process of Carbon Steel Seamless Pipes.

The spacing between the guide plates and the rolls in the hot rolling piercing process of carbon steel seamless pipes serves a guiding and positioning function. Too small a spacing leads to excessive extrusion pressure, causing surface scratches, wall thickness deviations, roundness errors, and equipment wear; too large a spacing weakens the guiding function, resulting in deviation, eccentricity, and localized bulges and depressions. A reasonable range is 1.02 to 1.05 times the outer diameter.

Third, the optimization effect and implementation guarantee of the hot rolling piercing process for seamless carbon steel pipes

(I) Implementation effect of the hot rolling piercing process for seamless carbon steel pipes

After three months of batch production verification by a certain enterprise, the following results were obtained after adopting optimized parameters:

Defect rate: 20# steel within 0.8%, 45# steel within 0.9%, a decrease of more than 76% compared to before optimization

Wall thickness uniformity: The compliance rate increased from 75% to over 99%

Production efficiency: Increased from 80 pieces/hour to 92 pieces/hour, with a cost reduction of 12%

Subsequent processing: Finishing time was shortened by 20%, resulting in significant economic and social benefits.

(II) Guarantee measures for the hot rolling piercing process for seamless carbon steel pipes

Temperature intelligent control measures: Adopting an intelligent temperature control system for real-time monitoring, with fluctuations ≤ ±10℃, and regular calibration

Speed digital control measures: Precisely setting the roll linear speed to maintain stability and avoid fluctuations. Regular maintenance measures: Check the mandrel extension and guide plate spacing, adjust promptly, and regularly replace worn parts.

Parameter ledger management measures: Establish an optimal parameter database for different steel grades and specifications, and regularly analyze and fine-tune.

Personnel professional training measures: Improve operational skills and ensure strict adherence to optimized parameters.

Fourth, Optimal parameter combination and conclusions for the hot rolling piercing process of carbon steel seamless 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 carbon steel seamless 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, surface treatment technology can be optimized to reduce oxidation and promote the industry to develop towards refinement and efficiency.