EN 10031:2003

Overview

EN 10031:2003 - "Semi-finished products for forging - Tolerances on dimensions, shape and mass" is a CEN European Standard that defines dimensional, geometrical and mass tolerances for semi-finished steel products intended for hot forming by forging. It applies to blooms, slabs and billets made from general purpose steels (EN 10250‑1 to 4) and steels for pressure purposes (EN 10222‑1 to 5). It does not cover drop-forging semi-finished products (see EN 10243‑1).

Keywords: EN 10031:2003, semi-finished products for forging, tolerances on dimensions, shape and mass, blooms slabs billets, forging tolerances.

Key Topics and Requirements

• Appearance and soundness

  • Products must be free from defects (segregation, cracks, laminations). Surface defects may be dressed by chipping or grinding under strict limits.
  • Dressing limits: depression ≤ max(2% of nominal size, 3 mm); removed area width ≥ 6× depth; remaining transverse dimensions must stay within specified tolerances.

• Dimensional tolerances

  • Rectangular products: thickness t = ±4% or 3 mm (whichever greater). Width b: ≤150 mm = ±3% or ±3 mm; >150 mm = ±4.5 mm or ±2% (whichever greater).
  • Square/circular products: side or diameter ≤150 mm = ±3% or ±3 mm; >150 mm = ±4.5 mm or ±2% (whichever greater).
  • Diagonal tolerance: difference between diagonals ≤ 6% of larger diagonal for nominal width ≤ 200 mm (wider sizes by agreement).

• Length tolerances

  • Standard lengths: ±1000 mm; minimum delivered length normally ≥1000 mm.
  • Fixed lengths: Normal ±250 mm, Tightened ±100 mm, Reduced ±50 mm (class must be specified; normal applies if omitted). Options for positive/negative or special tolerances by agreement.

• Shape tolerances

  • Straightness: bending ≤ 10 mm per metre uniformly; local waviness ≤ 20 mm per metre. Special straightening (if requested) ≤ 4 mm/m.
  • Twist: square sections ≤ 4° per m (max 10° for lengths ≤6 m, 15° for greater lengths). Rectangular sections: no adverse twist; square tolerances may be applied on agreement.

• Mass tolerances

  • Billets: mass per unit length between 88% and 100% of theoretical.
  • Blooms/slabs: mass per unit length between 94% and 100% of theoretical.
  • Batch mass tolerance: ≤5 t ±10%; >5 t ±7%. Wider tolerances may be agreed.

Applications

• Used by steel mills, forging shops, material purchasers, quality and inspection engineers to specify and verify acceptable forging feedstock (blooms, slabs, billets).
• Ensures consistent starting geometry for hot forming processes, reduces scrap, and helps sizing for downstream machining and heat treatment.
• Useful for procurement contracts, technical specifications, inspection checklists and supplier compliance.

Related Standards

• EN 10250 series (open die steel forgings for general engineering)
• EN 10222 series (steel forgings for pressure purposes)
• EN 10243‑1 (drop and vertical press forgings - tolerances)
• EN 10079 (definition of steel products)

For procurement or inspection, reference EN 10031:2003 when specifying tolerances on dimensions, shape and mass for semi-finished forging products.