Tool Steels

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Chapter 15

• Tool Steels

Tool Steels
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• The portion of the iron-carbon diagram in which
  most tool steels are found is the range of 0.6 C
  to 1.3 C.

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• Tool steels are identified by UNS designations,
  manufacturers trade names, and AISI designations.

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• Tool steel families are designated by a letter
  that stands for a key characteristic of those
  steels, which may be the method of hardening, a
  significant mechanical feature, or a major
  alloying element.

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• Diversification of properties and characteristics
  influence the number and types of uses of tool
  steels.

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• Toughness of group W steels initially increases
  with tempering temperature but falls rapidly to a
  minimum.

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• The hardness of group O tool steels is
  progressively reduced as the tempering
  temperature is increased.

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• After annealing at 845C (1550F), the
  microstructure of A2 tool steel consists of
  massive carbide and fine spheroidal carbide
  particles in a ferrite matrix. After
  austenitizing at 955C (1750F), air cooling, and
  tempering at 150C (300F), the microstructure of
  A2 tool steel consists of spheroidal carbide
  particles in a matrix of tempered martensite.

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• Group D steels show a secondary hardening effect
  when tempered in the range of 450C to 550C
  (840F to 1020F).

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• Microstructure of S1 tool steel annealed at 790C
  (1450F) consists of a dispersion of fine carbide
  particles in a ferrite matrix. After
  austenitizing at 1040C (1900F), oil quenching,
  and tempering at 425C (800F), the
  microstructure of S1 tool steel consists of
  tempered martensite and spheroidal carbide
  particles.

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• Group H steels resist softening during continued
  exposure to temperatures up to 540C (1000F).

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• The microstructure of T1 steel annealed at 900C
  (1650F) consists of large and small spheroidal
  carbide particles in a ferrite matrix. After
  austenitizing at 1280C (2335F), salt quenching
  to 605C (1125F), and air cooling, the
  microstructure of T1 tool steel consists of
  undissolved carbide particles in an untempered
  martensite matrix. After tempering the same
  sample at 540C (1000F), the microstructure of
  T1 tool steel consists of undissolved carbide
  particles in an austenite matrix.

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• Group M steels have high resistance to softening
  at elevated temperatures compared to other tool
  steels. Like group T steels, group M steels are
  tempered on the high side of their tempering
  curve.

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• Many similar P/M tool steel alloys are known by
  their trade names.

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• The binder material and grain size can influence
  the properties of cemented carbides and reduce
  failure in applications such as knives, plastic
  extrusion dies, wear guides, and seal rings.