Elsevier

Wear

Volumes 450–451, 15 June 2020, 203261
Wear

Study on the mechanism for polygonisation formation of D2 wheel steel and its effect on microstructure and properties under rolling wear conditions

https://doi.org/10.1016/j.wear.2020.203261Get rights and content

Highlights

  • Polygonisation is mainly caused by the vertical vibration of the system and wear coupled under the rolling wear.

  • The crest is gradually transformed from the adhesive wear to the oxidative wear, the trough is fatigue wear.

  • The grain refinement of pro-eutectoid ferrite is serious on the subsurface.

  • The highest hardness is on the surface, and the hardness extreme value or platform is appeared on the subsurface.

Abstract

The rolling wear experiments of D2 wheel steel were carried out on the friction and wear machine. The forming mechanism of polygonisation on the sample surface and the influence of polygonisation wear on microstructure and hardness were studied by using contour measuring instrument, acceleration sensor, SEM (with EBSD) and microhardness tester. The results indicate that the polygonisation of the sample surface is mainly caused by the vertical vibration of the system and wear coupled under the rolling wear conditions. The development process of crest surface wear is from the initial adhesive wear to oxidation wear and adhesive wear, and finally to oxidation wear with a small amount of fatigue wear. The trough surface wear is fatigue wear, which is gradually intensified. After forming the polygonisation, the surface of crest and trough will respectively produces rolling-sliding contact with different creep rate. The wear mode changes from uniform wear to severe wear, and the wear of trough is more significantly serious than that of crest. During the formation of the polygonisation, the proportion of high angle grain boundary (HAGB) in the pre-eutectoid ferrite at the subsurface of crest and trough increased obviously, the grain refinement is more serious, and the hardness extreme or platform appears. The highest hardness is always on the surface. However, the surface hardness of the crest is similar to that of the unformed polygonisation, and the surface hardness of the trough continues to increase with the development of the polygonisation.

Introduction

With the train running speed increases significantly, the wear and damage of the wheel surface (flaking, polygonisation wear, contact fatigue, etc.) are also increasingly prominent. Whether it is high-speed railway trains or subway vehicles, wheel polygonisation have become one of the main forms of damage during the wheel operation. Wheel polygonisation wear also known as wheel corrugation or wheel periodic out-of-round(OOR) wear [1]. The wheel polygonisation will cause the vibration of the vehicle to generate noise which reduces the passengers comfort, and the seriously wheel polygonisation will shorten the service life of the related structural components, resulting in wheel and rail fatigue, loose rail fasteners, broken thread studs, etc., which seriously affects the safety of the train [[2], [3], [4], [5]].

Many scholars have conducted in-depth research on wheel polygonisation. Zhao et al. established a wheelset-track system model and used transient dynamics analysis, analyzing the wheelset eccentricity in wheelset-track system. The results indicate that the wheelset eccentricity is a considerable reason affecting wheel polygonal wear [6]. Jin et al. tested the dynamic characteristics of the running subway vehicles. The results show that the main frequencies of the vertical vibration acceleration of the axlebox dominates in the axlebox operation, furthermore is close to the passing the frequency of the polygonal wheel [7]. Brommundt studied the wheel out-of-round caused by the wheelset model behavior and wheel moment of inertia. The results show that the faster the train runs, the faster the out-of-round lower harmonics develop [8]. Morys developed a vehicle-track model to describe the short-term system dynamics of the ICE-1 carriage, clarified that large wheel out-of-round conditions can also cause the large variations of normal force between the wheel and rail under high-speed conditions [9]. Liu et al. used the vehicle-track coupled dynamics model to study the wheel/rail dynamics generated by the high-speed train polygonal wheel. The results show that the wheel polygonisation will cause the wheel/rail contact force to fluctuate significantly. The influence of the wheel polygonisation on the vehicle system is mainly related to the wheelset vibration [10]. Nielsen et al. established high frequency dynamic interaction model of train and track, and analyzed the influences of rail corrugation and wheel OOR on fatigue failure of wheel, high frequency wheel/rail force and fatigue crack initiation of wheel material [11]. Literature [12] established the linear motor vehicle/track coupling dynamics model, analyzed the effects of abrasion wheels on the normal force of the wheel-rail and derailment coefficients in the ballasted track and ballastless track. Meywerk established a rolling model of flexible wheelsets on elastic rail. The results indicate that the greater phase difference between the left and right wheels, the faster wheel polygonisation appeared, and the first and second order bending modes of wheelsets played an important role in the formation of wheel polygons [13].

In summary, most of the current researches have analyzed the reasons for the formation of wheel polygonisation and the influence of wheel polygonisation on train dynamics behavior from the perspective of wheel-rail contact dynamics. However, there are few studies on the microstructure evolution of wheel polygonisation on the wheel-rail contact. In this paper, the formation mechanism of D2 wheel polygonisation is studied by analyzing the vibration and wear measured in the rolling wear experiments. The formation process of the D2 wheel polygonisation and its influence on the microstructure evolution of the surface layer and properties are analyzed.

Section snippets

Experimental materials and methods

The experiment was carried out on a GPM-30 rolling friction and wear test machine, as shown in Fig. 1(a). The machine is mainly composed of two AC motors (A, B), two rotating shaft systems for driving the rotation of upper and lower samples, hydraulic actuator for loading, hydraulic pump, the workbench, the rack, the machine shell and mat iron, etc. The load between the wheel and rail samples is loaded by the hydraulic actuator 2 and the hydraulic pump 5. In the experiment, the sample rolling

Wear curve

The mass wearing quantity of the samples with different cycles as shown in Fig. 3. It can be observed that before the wear of 2 × 105 cycles, the mass wearing quantity increases relatively slow and the sample is at the uniform wear stage. From 3 × 105 cycles to 5 × 105 cycles, the mass wearing quantity is accelerated again and entered the rapid wear stage. After 5 × 105 cycles, the mass wearing quantity increased sharply and transferred into the severe wear stage.

The macroscopic appearance of the surface

Fig. 4 exhibits the

Mechanism of the wheel polygonisation formation

During the experiment, the equipment generates a series of vibration with different frequencies, which causes the load of the sample surface to fluctuate. Therefore, the actual load on the sample surface is composed of static load and dynamic load. At the beginning of wear, the wear rate is low (Fig. 3), and the wear is uniform (Fig. 4(a) and Fig. 6(a), (b)). Therefore, the vibration amplitude of each vibration frequency is small. With the increase of the wear cycles, the wear of local surface

Conclusions

The rolling wear experiments of D2 wheel steel were carried out on the friction and wear machine, the conclusions are as follows:

  • 1.

    The polygonisation wear of D2 wheel steel sample surface under rolling wear condition is mainly caused by the vertical vibration of the system and wear coupled. After the preliminary polygonisation is formed, the vertical vibration is intensified and the polygonisation wear is more serious with the increase of wear cycles, so the crest-to-trough height difference

CRediT authorship contribution statement

Jun Hua: Conceptualization, Formal analysis, Investigation, Writing - original draft. Xiujuan Zhao: Project administration, Investigation, Resources, Writing - review & editing. Pengtao Liu: Resources, Writing - review & editing. Jinzhi Pan: Resources, Writing - review & editing. Chong Su: Writing - review & editing. Ruiming Ren: Investigation, Resources, Writing - review & editing, Project administration, Supervision.

Declaration of competing interest

The authors declared that they have no conflicts of interest to this work.

Acknowledgments

The project was supported by the National Key Basic Research Program of China (973) (2015CB654802).

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