分别对球化退火态GCr15高碳铬轴承钢进行常规马氏体淬回火、马贝复相淬火和冷轧-马氏体预淬火复相淬火处理.通过扫描电镜、透射电镜和X射线衍射仪表征最终GCr15组织,同时对最终材料的硬度、冲击韧性与抗拉强度进行检测.结果表明,马氏体淬回火试样由马氏体、未溶碳化物以及残余奥氏体组成,具有较高的硬度与强度,但是冲击韧性较低.马贝复相淬火组织由马氏体、下贝氏体、未溶碳化物以及残余奥氏体组成,韧性有明显提高,但是硬度与强度很低.冷轧-马氏体预淬火复相淬火组织由预淬火马氏体、下贝氏体、二次淬火马氏体、未溶解碳化物以及残余奥氏体组成,在冷轧变形与马氏体预淬火复相淬火协同作用下,奥氏体晶粒得到明显细化,同时下贝氏体与马氏体也得到明显细化,因此最终组织不仅韧性得到了显著提升,硬度与强度也能满足服役要求.

In this work, the effects on dry wear behavior of cold ring rolling (CRR) of GCr15 bearing steel, after quenching and tempering (QT) heat treatment are investigated. The effects on steel microstructures and wear mechanisms of CRR with different austenitizing times are also discussed. The results show that, with a short austenitizing time of 10 min, CRR can increase the retained austenite content, decrease the undissolved carbide content and improve the hardness of the specimen, thus reducing ploughing and fatigue flaking, and decreasing the wear loss of the CRR specimen. With the longer austenitizing time of 20 min, the retained austenite content increases, the undissolved carbide content decreases, and the hardness increases significantly, both in specimens with and without CRR, so that ploughing, fatigue flaking, and wear loss can all be decreased. However, with an austenitizing time of less than 20 min, the effects of CRR on retained austenite content, undissolved carbide content, and hardness are not significant. Thus, CRR of less than 20 min cannot further improve wear morphology or decrease wear loss.

For the problems of exceeding taper angel and serious warping degree existing in the single cold rolled outer ring of conical roller bearing, in order to improve its rolling accuracy, the methods of blank design and optimization in cold rolling process of outer ring were studied by the integrated application of theoretical analysis, finite element simulation and experiment verification, and the reasonable blank of cold rolling was designed.The evolution of plastic deformation and geometrical shape during the cold rolling process of single conical roller bearing outer ring was investigated to verify the reasonability and feasibility of the blank design.The results show that the horizontal cross-sectional area distribution of blank along the axial direction has an important influence on the cold rolling precise of outer ring.Meanwhile, the axial force acting on the shaft during the rolling process was analyzed.The result presents that the axial force is lower at the initial stage of rolling process, and the axial force increases with the increasing of plastic deformation degree and reaches the maximum value at the final stage of rolling process.

This study investigates the correlation between the residual stress and distortion behavior of a cold-rolled ring from the annealing to quenching-tempering (QT) process. Due to the cold-rolled process, the external periphery of the bearing ring experiences a compressive residual stress. To relieve the residual stress, cold-rolled rings are annealed at 700 °C which is higher than the starting temperature of recrystallization. When cold-rolled rings are annealed at 700 °C for 15 min, the compressive residual stress is reduced to zero and the outer diameter of the annealed ring becomes larger than that of a non-annealed sample, which is unrelated to annealing time. Simultaneously, the roundness and taper deviation do not obviously change compared with those of non-annealed sample. The stress relaxation during the annealing process was attributed to the recovery and recrystallization of ferrite. Annealing has a genetic influence on the following QT heat treatment, wherein the lowest residual stress is in the non-annealed cold-rolled ring. From the annealing to QT process, the deviation of the outer diameter, roundness, and taper increased with annealing time, a large extend than that of non-annealed samples.

Restricted by the working principles, the traditional ring rolling technologies are only fit for fabricating concentric rings while it is difficult for them to fabricate eccentric rings. So this study is devoted to put forward an innovative eccentric ring rolling (ERR) method for fabricating eccentric rings. Firstly, to guarantee ERR successfully, the technological design principles and methods for the rolls, ring workpiece and objective eccentric ring are presented and the rolling conditions in ERR are correspondingly determined. Then, the deforming mechanisms and rolling defects in ERR are analyzed through FE simulations. Finally, to eliminate the rolling defects of uneven axial height distribution of the rolled eccentric ring, the optimization design methods for the ring workpiece and the corresponding rolling conditions are presented. Through simulations and experiments, it is illustrated that qualified eccentric rings with even axial height distribution and highly accurate thickness distribution along the tangential direction can be rolled by ERR and thus the presented ERR method is promising in fabricating eccentric rings.

The influences of deformation degrees on the microstructure evolution of GCr15 steel in cold ring rolling and following heat treatment (quenching and temper) are investigated in this paper. As the deformation is uneven, microstructure at the outer surface, middle place and inner surface on the cross-section of the ring is selected for the study. The microstructure is characterised by scanning electron microscopy, optical microscopy and X-ray diffraction. The [Formula: see text] transformation is studied with differential scanning calorimetry, and the hardness is examined by Vickers hardness tester. The results show that the deformation is severe on the outer surface but slight on the middle place and inner surface. A large degree of deformation leads to the acceleration of carbide dissolution, the grain refinement and the increase of hardness. In addition, the deformation results in the decrease of [Formula: see text] transformation temperature according to the differential scanning calorimetry data.

The cold ring rolling process of high carbon steel during large deformations was investi-gated herein.The deformation behaviour of the cold ring rolling process was analyzed by the finite ele-ment simulation method.The instruments like optical microscope and scanning electron microscope were employed to characterize the microstructure evolution of the cold rolled rings under large de-formations.Results indicate that under smaller deformations,both of the outer and the inner sides of the ring exhibites higher plastic strain than that on the middle part and deformation firstly occurres in the outer side.It is observed that the most severe deformations occurre in the inner surface of the ring,the less severe deformations in the outer surface and the least deformation in the middle part dur-ing the cold ring rolling process.With the deformation increasing,the inner side shows higher strain than that of the outer surface,and the location with the least strain shiftes to the peripheral layers. The ferrite matrix shows a clear direction along the rolling direction,and the distribution of cementite is more homogeneous with reduced carbide particles amount.Meanwhile,the shedding of the carbide particles is aggravated.When the deformations reach to 62·5%,the cold rolled ring reaches plastic limit with cracks firstly happening on the inner surface of the cold rolled ring.

During the conventional ring rolling process, the ring mainly produces the incremental deformation of wall-thickness reduction and diameter expansion, which makes it difficult to manufacture the cylindrical ring with small diameter and large height. In this paper, a new method for manufacturing the cylindrical ring using a ring blank with smaller height, i.e. cylindrical ring rolling, is proposed and its feasibility is verified. For evaluating the cylindrical ring rolling process and to better understanding its deformation characteristics, a 3D elastic-plastic FE model of cylindrical ring rolling is first established. Then, the comparison between conventional ring rolling and cylindrical ring rolling is investigated using this 3D FE model. Finally, the effects of the process parameters, such as the feed rate of the idle roll, diameter of the idle roll and friction coefficient between the rolls and ring, on cylindrical ring rolling are numerically revealed. The experiment is carried out on a vertical NC ring rolling machine and the good agreements between the experimental and simulation results verify the validity of the established 3D FE model of the cylindrical ring rolling. (C) 2014 Elsevier B.V. All rights reserved.

In conventional ring rolling, it is difficult to achieve a large increase in the ring height. This paper proposes a new combined radial and axial ring rolling process, which can achieve a large increase in both the ring diameter and height. During the proposed process, the geometry of the ring blank is of great importance because it determines the distribution of the radial ring rolling process and the subsequent axial ring rolling process. Therefore, this paper is aimed to reveal the effect of the geometry of the ring blank on the combined radial and axial ring rolling process. Using the finite element (FE) method, the deformation characteristics of the ring are first investigated. Then, the effect of the geometry of the ring blank, axial height H (0), outer diameter D (0), and thickness t (0), on the geometry development and inhomogeneous deformation of the final rolled ring, is revealed. The results of this research provide an important basis for the design and optimization of the ring blank in the new combined radial and axial ring rolling process.

Ring rolling is an advanced incremental metal forming technology used to manufacture precise seamless rings. Generally, it is classified as two types. One is pure radial ring rolling in which the ring mainly produces the deformation of thickness reduction and diameter expansion and its height basically remains unchanged. The other is radial–axial ring rolling in which the ring produces the deformation of thickness reduction, diameter expansion and height reduction. Obviously, it is difficult for the above two types of ring rolling processes to achieve a large increase in the ring height. Therefore, this paper proposes a new cylindrical ring rolling process which can achieve a large increase in both the ring diameter and height. For evaluating the proposed process, a 3D elastic–plastic FE model of cylindrical ring rolling is first established and its validity is verified by the experiment carried out on a vertical NC ring rolling machine. Then, some fundamental forming characteristics, such as the geometry evolution and strain distribution of the ring, contact characteristics between the rolls and ring and power parameters, are investigated based on this reliable 3D FE model. Finally, the effect of a critical process parameter, axial rolling ratio (circumferential rolling ratio), on the cylindrical ring rolling process is revealed numerically. Through the above analysis, three highlights of the proposed process can be summarized as follows: (1) The stability and final roundness of the deformed ring can be guaranteed easily by the inner surface of the constraint roll without the guide rolls and complicated control schedule. (2) The proposed process can achieve a large increase in both the ring diameter and height. (3) Under the constant radial deformation, different axial and circumferential deformation distribution can be achieved by changing the axial rolling ratio (circumferential rolling ratio).

The invention relates to a precise roll forming method for bimetallic rings. The method comprises: S1, obtaining an outer ring blank and an inner ring blank; S2, assembling the outer ring blank and the inner ring blank; S3, placing a core roller in the inner ring blank; S4, placing a drive roller outside the outer ring blank; S5, driving the drive roller to rotate through a drive device and driving the core roller to perform linear feed movement radially, wherein the outer ring blank and the inner ring blank are attached closely constantly to produce continuous local plastic deformation with the wall thickness reducing and the diameter expanding; and S6, stopping feed of the core roller and getting the core roller back when the outer diameter of the outer ring blank reaches a preset value of the outer diameter of a bimetallic ring. According to the precise roll forming method, the bimetallic ring is formed integrally through one step through continuous local plastic deformation, so that the method has the advantage that energy and materials are saved, the production cost is reduced, and the yield is improved. The bimetallic ring interface contact quality is good, the connection strength is high, and requirements of service performances and service lives of high-performance bimetallic rings can be met.