Page 11 - Кулик В.В.

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This corresponds to the statistics of the operation of real railway wheels. In this

case, the damage is definitely correlated with the cyclic fracture toughness of the

wheel steel of Mode I fracture (ΔK ) and Mode II fracture (ΔK ІІ fc ). They can be
І fc
considered the determining parameters of this damage process, in contrast to the

fatigue thresholds ΔK and ΔK ІI th .
І th
Assessment of the influence of chemical composition and structure and

phase state of the developed wheel steels on their workability should be performed

on the basis of the proposed complex of mechanical characteristics, in particular

diagrams of structural strength and operational reliability (patent of Ukraine No.

106836) and the new parameter of structural strength of materials

P = [ UTS ‧K ‧K ] (Patent of Ukraine No. 105440), taking into account the
fc
th
influence of operational factors.

In contrast to traditional wheel steels, graphite pre-eutectoid steel (wt%: 0.60

C; 0.90 Mn; 1.0 Si; 1.0 Cu; 0.15 Al) after annealing to granular perlite (its ultimate

tensile strength is ~ 800 MPa) is characterized by the lowest level of high

temperature (> 500C) plasticity. It is not susceptible to embrittlement at low

climatic temperatures (up to –40C), and the negative influence of the corrosive

environment on its fatigue crack growth resistance characteristics is absent.

However, its low cyclic fracture toughness (K < 40… 50 MPa∙√m) does not
fc
meet the requirements for promising wheel steels.

Solid-solution hardening of the wheel steel due to the increased content of

silicon (up to 0.97%) and manganese (up to 0.85%) with reduced carbon content

(up to 0.58%) contributes to the increase of its wear resistance, but causes a

decrease in its fatigue crack growth resistance and resistance to damage.

The optimum combination of strength and fatigue crack growth resistance of

the precipitation-hardened wheel steel is ensured by the content of vanadium and

4
nitrogen [V‧N]‧10 = 22% and the austenitizing temperature of 950С and the

annealing at 550С, which corresponds to the maximum value of the structural

strength parameter P of materials at lowering carbon content from 0.63 to 0.57%.