Page 14 - Кулик В.В.

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austenitizing temperature of 950С and the annealing at 550С, which corresponds

to the maximum value of the new structural strength parameter

P = [ UTS ‧K ‧K ] of materials at lowering carbon content from 0.63 to 0.57%.
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Such steel provides high resistance to damage, but low resistance to wear of the

tread surface of the model wheel.

6. It is found that the solid-solution hardening due to the increased

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

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

decrease in fatigue crack growth resistance, including after thermo-force exposure

during braking. It is established that complex alloyed steels with a combination of
solid-solution and precipitation hardening possess the optimum strength and

fatigue crack growth resistance characteristics, wear resistance as well as damage
resistance.

7. It is shown for the first time that increasing fatigue crack growth

resistance of the heat affected zone of repair tread surface of railway wheels is

achieved by the formation in this zone a mixed structure of bainite and martensite,

and by isothermal holding at temperatures between the points of onset (M ) and the
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end (M ) of the martensitic transformation. This exposure contributes to the
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increase of the fatigue threshold of the specimen with a crack by 1.6 times, the

cyclic fracture toughness by 1.8 times along with virtually unchanged strength.

This is caused by a drop of ~ 1.5 times the residual stresses of the II type in the

volume of laths of bainite and martensite. In this case, both the known and

modified Q-n-P treatments are less effective.

The practical significance of the obtained results.

1. A test stand for simulating damage of the wheel tread surface under

contact fatigue conditions is designed and manufactured. The developed

methodology and tools allow reliably predicting the workability of railway wheels

based on the results of laboratory tests of specimens made of wheel steel.

2. Based on the obtained research results, a departmental regulatory

document “Additional requirements for steels of solid-rolled high-strength railway