Plastic mould steels

Tools for processing plastics are mainly stressed by pressure and wear. According to the type of plastic, corrosive conditions can prevail in addition to stresses. The type of plastic and processing method define the key requirements in addition to those generally valid to hot-work steels:

• Economic machinability or cold-hobbing ability
• Smallest possible distortion upon heat treatment
• Good polishing behavior
• High compressive strength
• High wear resistance
• Sufficient corrosion resistance

• AISI-SAE tool steel grades

  Defining property	AISI-SAE grade	Significant characteristics
  Water-quenched	W	Molybdenum alloying optional
  Cold-working	O	Oil-hardening, O6-0.3% molybdenum, cold-work steel used for gauges, cutting tools, woodworking tools and knives
  	A	Air-hardening, low distortion during heat treatment, balance of wear resistance and toughness, all molybdenum alloyed – 0.15-1.8%
  	D	High carbon, high chromium, 0.9% molybdenum, very high wear resistance but not as tough as lower alloyed steels
  Hot-working	H	H1-H19 – chromium base H20-H39 – tungsten base H40-H59 – molybdenum base
  Plastic moulding	P	Low segregation: reduced alloying of silicon, manganese and chromium Through hardenability: increased molybdenum and vanadium
  High-speed	T	Tungsten base (today mostly replaced by M22)
  	M	Molybdenum base
  Shock resisting	S	Chromium-tungsten, silicon-molybdenum, silicon-manganese alloying, very high impact toughness and relatively low abrasion resistance
  Special purpose	L	Low alloy, high toughness
  	F	Carbon-tungsten alloying, substantially more wear resistant than W-type tool steel