Product Internal Metallurgical Structure & Tubular Mechanical Structure
Our high toughness alloy structural steel tube adopts full seamless integral tubular structure, completely abandoning welded pipe seam defects that easily cause stress concentration and brittle fracture under alternating load. The base metal metallurgical structure is refined tempered sorbite tissue after precise quenching & tempering heat treatment, matched with micro-alloy grain refinement system formed by Cr, Mo, Mn, Ni, Nb composite alloy elements inside steel matrix. From cross-section tubular structure, we control uniform wall thickness tolerance within ±0.7% outer diameter, wall thickness error ≤0.04mm for precision cold-drawn series; the inner and outer pipe walls adopt smooth oxide-free finishing after descaling shot blasting, no surface crack, fold, scratch or inclusion defect. The internal metal tissue achieves equiaxed grain ratio over 38%, central looseness grade controlled below Grade 1.5, extremely low internal micro-crack risk, which is the core structural foundation to realize ultra-high impact toughness at low temperature and heavy load. Different from ordinary carbon structural tube and common alloy pipe, this product designs low-carbon low-impurity chemical formula: carbon mass fraction strictly limited ≤0.28%, sulfur & phosphorus harmful impurities controlled below 0.020% respectively, effectively inhibiting grain boundary brittleness source. Alloy elements are proportioned in gradient: chromium improves oxidation resistance and hardenability, molybdenum eliminates temper brittleness under long-term alternating temperature, nickel stabilizes low-temperature plastic deformation ability, niobium & vanadium tiny particles pin grain boundary to prevent grain coarsening during high-temperature service, forming dual protection of tubular macro structure and metal micro tissue
High Toughness Performance Core Production Process High Toughness Performance
The whole production flow strictly follows vacuum smelting-hot piercing-precision rolling-controlled heat treatment-nondestructive testing closed process, every procedure targets toughness optimization:
First, raw material round billet adopts LF refining + VD vacuum degassing, removing hydrogen, oxygen gas in molten steel to avoid hydrogen-induced cracking under impact load; then 1200℃ constant temperature annular furnace heating, conical roller skew piercing to form blank tube, uniform metal flow to prevent one-sided tissue segregation; continuous rolling mill distributes deformation gradient reasonably to reduce residual rolling stress inside pipe wall.
The core procedure determining high toughness is integrated controlled heat treatment: quenching temperature 860–890℃ heat preservation, oil cooling to balance strength and plasticity; medium temperature tempering at 540–630℃ adjustable temperature, clients can select low tempering for higher tensile strength or high tempering for ultra-high low-temperature impact toughness. After heat treatment, stress relieving holding is added to eliminate internal processing stress, avoid deformation during later machining and assembly.
Structural & Process-Derived Unique Product Characteristics
Uniform overall tissue performance: No local toughness attenuation, the whole pipe can bear cyclic impact, bending, torsion composite load without brittle fracture;
Low temperature anti-brittle property: Charpy impact energy remains above 60J at -40℃, suitable for alpine, polar regional engineering structure;
Excellent deep processing adaptability: Moderate hardness HB180–230 after heat treatment, easy cutting, drilling, bending, welding without preheating complex process;
Stable dimensional structure: Small thermal expansion coefficient, no permanent deformation under long-term high pressure and temperature alternating working condition.
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