For the control of phosphorus (P) and sulfur (S) content in SAE 1541 seamless steel pipes, it is necessary to optimize the whole process to achieve effective reduction of impurity elements. Combining metallurgical principles and industrial practice, the following is an analysis of key process technologies:
1. Raw material pretreatment process
Hot metal pre-desulfurization
Using the KR method (mechanical stirring method) or the injection method, adding CaO-based desulfurizer to the hot metal can reduce the initial sulfur content from 0.050% to below 0.005%. For example:
After 20 minutes of treatment by the KR method, the sulfur content can be reduced to 0.003%
The magnesium-based composite injection process is more efficient, and the desulfurization rate can reach more than 95%
Scrap steel sorting control
Through electromagnetic sorting + spectral detection, high-quality scrap steel with P≤0.020% and S≤0.015% is screened to reduce the introduction of impurities from the source.
2. Optimization of steelmaking process
Dynamic dephosphorization of converter
Double slag method operation:
Preliminary high basicity slag (CaO/SiO₂=3.5-4.0) promotes phosphorus oxidation
End point control temperature ≤1650℃, final slag FeO content ≤15%, phosphorus content ≤0.010%.
Out-of-furnace refining and strengthening
Application of LF+RH dual process:
LF furnace absorbs sulfur through white slag refining (CaO-Al₂O₃-SiO₂ system), and the sulfur content can be reduced to 0.005% after 40 minutes of treatment
RH vacuum degassing (vacuum degree ≤67Pa) promotes the discharge of gas inclusions and reduces the risk of phosphorus segregation.
3. Desulfurizer and inclusion control
Calcium treatment technology
Feeding CaSi wire (Ca/S=1.2-1.5) to transform MnS inclusions into spherical CaS and reduce the harmfulness of sulfur:
After the sulfide morphology is controlled, the transverse impact toughness is increased by 40%
Calcium treatment can stably control the sulfur content at 0.008%-0.012%.
Rare earth microalloying
Add 0.02%-0.05% rare earth elements (such as Ce, La):
Rare earth sulfides (Ce₂S₃) have a higher melting point (＞1600℃), avoiding hot working cracking
Phosphorus grain boundary segregation is reduced by 50%, and low-temperature toughness is significantly improved.
4. Continuous casting process improvement
Electromagnetic stirring technology
Apply an alternating magnetic field in the crystallizer and the secondary cooling zone:
The proportion of equiaxed crystals is increased from 25% to 50%, reducing center segregation
The sulfur segregation index at the center of the ingot is reduced from 1.8 to 1.25.
Light reduction process
The reduction amount is 0.8-1.2mm/m at the end of solidification:
Central shrinkage elimination rate>90%
The macro segregation of phosphorus is reduced by 30%.
V. Synergy of rolling and heat treatment
High temperature diffusion annealing
The billet is heated to 1250℃ and kept warm for 4-6 hours:
Sulfur dendrite segregation is reduced by 60%
Phosphorus micro segregation is reduced by 40%.
Controlled rolling and controlled cooling process (TMCP)
Two-stage rolling is adopted:
Rough rolling temperature ≥1000℃ to promote dynamic recrystallization and grain refinement
Rapid cooling after finishing rolling (≥15℃/s) to inhibit sulfide aggregation.
VI. Comparison of typical process effects
Process stage Sulfur content of traditional process Sulfur content of optimized process Reduction
Hot metal pretreatment 0.040% 0.003% 92.5%
After refining outside the furnace 0.020% 0.006% 70%
Finished steel pipe 0.015% 0.008% 46.7%
Future technology direction
Intelligent smelting system
Develop a phosphorus and sulfur prediction model based on machine learning to achieve dynamic composition control.
Ultra-low oxygen refining
Control the oxygen content in steel below 5ppm to reduce the interference of oxide inclusions on sulfur and phosphorus distribution.
Hydrogen metallurgy technology
Test hydrogen-based direct reduction process to inhibit sulfur and phosphorus generation from the reduction stage.
Through the above process integration, the phosphorus and sulfur content of SAE 1541 steel pipe can be stably controlled at P≤0.015% and S≤0.008%, meeting the stringent requirements of high-end application scenarios such as automotive transmission shafts and hydraulic cylinders.
