3 Fundamentals of press design

Die design
Powder metal-manufactured high-speed steels demonstrate very uniform
carbide distribution and are segregation-free. This results in
improved toughness properties and extremely high compressive
strength. If a larger wear resistance is required, for example for forward
rod extrusion or ironing dies, for large-production series carbides are
also used. The carbide types used comprise tungsten carbide as a phase
in a cobalt matrix. The cobalt content which determines the characteristics
of the carbide, lies between 15 and 30%. With a rising tungsten
carbide content, hardness, compressive strength and wear resistance all
increase. However, at the same time toughness, notch impact strength,
bending and buckling resistance are reduced. The grain size exerts an
influence here: fine-grained carbides are unsuitable as a result of poor
toughness characteristics. Table 6.7.6 provides a summary of the
mechanical characteristics of carbides. The strength values apply to static
loads and must be reduced by 50% for stress cycles greater than 10 6 .
Tool steels for warm forming
The materials X40CrMoV53 (1.2367), X38CrMoV51 (1.2343), X40-
CrMoV51 (1.2344) and X60WCrCoV93 (1.2622) are currently used for
warm forming and in conjunction with the water cooling method generally
applied today; In the case of shrink rings, 55NiCrMoV6
(1.2713)/57NiCrMoV7 (1.2714) or X38CrMoV51 (1.2343)/X40CrMoV-
51 (1.2344) can be used. Due to their low thermal shock resistance, carbides,
high-speed steels and cold forming tool steel 81MoCrV4216
(1.2369) are only suitable when using water-free cooling methods
which were common in the past. On closer examination, it becomes
clear that materials for warm forging are generally those used in the
classical field of hot forging. Special materials for warm forging, which
are capable of withstanding relatively high pressure levels and relatively
high temperatures simultaneously, have not yet been developed for
implementation in series production. Developments of die materials
for warm forming are moving in the following directions:
Compared to hot forging tool steels, high-speed steels already exhibit
good wear and heat resistance properties as well as improved tempering
resistance. By a gradual reduction of the carbon content, attempts
have been made to achieve a further improvement in thermal shock
resistance of high-speed steels. With simultaneous deterioration of the
wear and heat resistance, however, the thermal shock resistance level
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