Xenith Steel

The cold-die reduction process per EN 10305-1 Section 5.2:

Each pass reduces wall by 15-30%: Pass 1 = 25% reduction → closer tolerance; Pass 2 = 20% → tighter; Pass 3 = 15% → final tolerance.

Why multiple passes:

(1) Single pass over-reduces, causes splits per ASTM A1016 Section 7

(2) Intermediate anneals restore ductility per ASTM A513 Section 8.2

(3) Each pass corrects previous variation — cumulative correction algorithm

Laser measurement feedback after each pass adjusts die automatically per ISO 25178.

Result: ±0.03mm = 0.3% of 10mm wall — exceeds EN 10305-1 Class H tolerance (normally ±0.05mm for precision tube).

Cold-rolled (Pilger process) per EN 10305-1 Section 4.2:

(1) Uses rotating dies — rolling action produces smoother ID surface (Ra ≤ 0.4μm)

(2) Better for long lengths (up to 30m continuous per DIN 1630)

(3) Higher productivity but less flexible for thick walls (> 8mm)

Cold-drawn per EN 10305-2 Section 4.3:

(1) Pulls through stationary die — better OD tolerance (±0.03mm per ISO 3304)

(2) Better for thick walls (> 8mm) — reduction per pass 15-25%

(3) More common for precision applications requiring tight concentricity

Both achieve same final tolerance (±0.05mm OD, ±0.03mm WT per EN 10305-1 Table 2).

Choice depends on: length, wall thickness, surface finish required per ISO 3304 Table A.

Residual stress from cold work per ASTM A513 Section 11.2:

Drawing leaves bending moment in tube: M = E × I / R (curvature).

Straightening method per ISO 3304 Annex B:

(1) First pass: coarse correction (2-roller) — removes 80% of bend

(2) Second pass: fine correction (6-roller) — removes remaining 15%

(3) Third pass: stress equalization (straightener with 150° wrap) — removes final 5%

Each pass rotates 90° for uniform correction across circumference.

Result: ≤ 0.5mm/m straightness achievable per EN 10305-1 Table 3 (Class S1).

Technical limit per EN 10305-1 Table 1 and ISO 3304 Section 5:

Die angle α = 12-20° limits reduction per pass: minimum wall = previous wall × (1 - reduction%).

For 10mm → 8mm (20% reduction): Easy — reduction within normal range per EN 10305-1

For 1mm → 0.8mm (20% reduction): Difficult — risk of buckling at wall < 1mm

Practical minimum wall:

Seamless cold-drawn: 0.5mm per EN 10305-1 (cold-drawn seamless)

Welded cold-drawn (DOM): 0.8mm per ASTM A513 (weld integrity limits below 0.8mm)

Below 0.5mm: requires specialized processes (cold-rolled strip, welded laser tube per ISO 3304 Annex C).

Strain hardening mechanism per ASTM E8/E8M Section 6:

Cold work % = (A₀ - A₁) / A₀ × 100% (area reduction).

Each 1% cold work: +5-10 MPa yield strength per EN 10305-1 Annex C.

Example: 20% cold work = +100-200 MPa increase in yield.

Trade-off: Higher yield → lower elongation. Elongation drops ~1% per 5% cold work per ASTM A1016 Table 3.

Solution: intermediate annealing restores ductility per ASM Metals Handbook Vol 4.

Process: 680-720°C, 30 min, argon atmosphere (dew point ≤ -40°C per ASTM A1016).

Oxygen causes scale at high temperature per ASTM A1016 Section 8:

Air anneal = blue/black iron oxide (Fe₂O₃/Fe₃O₄) formation = surface roughness Ra increases from 0.2μm to > 2.0μm.

Argon benefits:

(1) Prevents oxidation — no scale formation. Oxygen content ≤ 10 ppm required per ASTM E112

(2) Faster heat transfer = uniform temp distribution (within ±5°C across 6m tube per ASME BPE)

(3) Reduces decarburization — carbon loss limited to ≤ 0.05%C from surface per ASTM A1016 Section 8.2

Process: Tube enters furnace → argon purge (10× volume) → heat to 750-850°C → cool → argon flow maintained until exit at < 150°C per EN 10305-1 Section 5.3.

Result: Ra 0.2-0.4μm achievable (mirror finish per ASTM A480).