Micro-mechanism of central damage formation during cross wedge rolling

Yang, Ce; Dong, Hongbiao; Zheng-huan, HU

doi:10.1016/j.jmatprotec.2017.09.041

Cited by 53 publications

(39 citation statements)

References 24 publications

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“…Pater et al [3] compared nine fracture criteria to find the one most suitable for the prediction of central crack formation. Yang et al [4] studied central crack formation on a microstructural scale and revealed the ductile fracture mechanism of steels at high temperature. Zhou et al [5] considered the combined effects of the shear and normal stress and proposed a novel fracture criterion, which was validated quantitively.…”

Section: Introductionmentioning

confidence: 99%

Microstructural effects on central crack formation in hot cross-wedge-rolled high-strength steel parts

et al. 2020

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Central cracking in cross-wedge-rolled workpieces results in high wastage and economic loss. Recent cross-wedge rolling tests on two batches of steel showed that one batch formed central cracks, while the other was crack-free. The batches were both nominally of the same chemical composition and thermomechanical treatment history. In addition, both batches had passed all the standard quality assessments set for conventional forging processes. It was suspected that the different cracking behaviours were due to differences in microstructure between the two as-received steel billets, and the material in cross-wedge rolling (CWR) was more sensitive to the initial microstructure compared with other forging processes due to its specific loading condition including ostensibly compression and large plastic strain. Nevertheless, no previous study of this important problem could be identified. The aim of this study is, therefore, to identify the key microstructural features determining the central crack formation behaviour in CWR. The hot workability of the as-received billets was studied under uniaxial tensile conditions using a Gleeble 3800 test machine. Scanning electron microscope with energy-dispersive X-ray spectroscopy and electron backscatter diffraction was applied to characterise, quantitatively analyse, and compare the chemical composition, phase, grain, and inclusions in these two billets, both at room temperature and also at the CWR temperature (1080°C). Non-metallic inclusions (oxides, sulphides, and silicates) in the billets were determined to be the main cause of the reported central cracking problem. The ductility of the steels at both room and elevated temperatures deteriorated markedly in the presence of the large volumes of inclusions. Grain boundary embrittlement occurred at the CWR temperature due to the aggregation of inclusions along the grain boundaries. It is suggested that a standard on specifying the inclusion quantity and size in CWR billets be established to produce crack-free products.

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Section: Introductionmentioning

confidence: 99%

Microstructural effects on central crack formation in hot cross-wedge-rolled high-strength steel parts

et al. 2020

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“…When α = 35 • , the total length was 1215 mm, which is a little smaller than that of α = 25 • . As such, the cyclic number of shear deformation decreased [23]. Smaller shear stress and the less frequent cycles of shear stress led to a better central quality at a larger forming angle.…”

Section: Referencesmentioning

confidence: 91%

“…Central quality is another concern of the CWR process. Central cavity is a serious defect in the solid products of cross wedge rolling, which weakens the mechanical strength of the workpiece and eventually results in product failure [23]. Many works had been done to reveal the formation of central cavity during the CWR process.…”

Section: Central Qualitymentioning

confidence: 99%

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Experimental Study on Cross Wedge Rolling of 21-4N Heat Resistant Steel

Zheng

2019

Metals

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21-4N is a typical heat resistant steel used as the material of exhaust valves. The application of cross wedge rolling to manufacture preform for valves has the advantages of higher efficiency and better quality. In this study, cross wedge rolling of 21-4N with an area reduction ratio of 65% was experimentally studied. Twelve groups of different tool parameters of cross wedge rolling tests were carried out. It is found that a larger stretching angle or a smaller forming angle is better for surface quality. When the stretching angle is 7° and the forming angle is less than 25°, a smooth surface can be obtained. Furthermore, the influence of stretching angle on central quality is not obvious, but a greater forming angle is prone to get a better central quality. When the forming angle is larger than 30°, no central damage was found in the workpieces. Considering the balance of surface quality and central quality, a stretching angle of 7° and a forming angle of 30° is a suitable combination for cross wedge rolling of 21-4N with an area reduction ratio of 65%.

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“…The nucleation of microcracks is related to plastic deformation and stress concentration, while their propagation depends on the geometry and deformation mode of the specimen. In the cross-wedge rolling of steel, cavities in the center of the workpiece originated around non-metallic inclusions and grew along the shear and tensile stress directions, causing significant shear and tensile deformations [8]. Katani et al [9] used the Gurson-Tvergaard-Needleman (GTN) model [10] to simulate cavity failure of Ti-6Al-4V, and they found that a large amount of cavities nucleation related to local changes of stress and strain occurred near the two-phase boundary at the low-strength side, which controlled the cracking.…”

Section: Introductionmentioning

confidence: 99%

Study on Grinding and Deformation Fracture Control of Cold Rolled Titanium Strip

Zhang

Dong

et al. 2020

Metals

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Surface defects of titanium strip need to be removed by local grinding, but local cracking or band breaking then occurs during subsequent cold rolling. Tensile properties and deformation resistance of 3 mm thick commercially pure titanium strip with grinding pits on the surface were simulated by a finite-element method using a multi-pass cold-rolling deformation process. The stress and strain of grinding pits with depths of 0.25–2 mm were analyzed. During cold-rolling deformation, the stress and strain in the center of a grinding pit were larger than at the edge region. The strip was first subjected to tensile stress in the rolling direction, which then decreased and gradually changed to compressive stress. Partial stress was larger in the rolling direction than in the transverse direction. When the tensile stress and true strain both exceeded the stress and strain limits during second-pass rolling, the strip with a grinding depth of 2 mm cracked, but shallower grinding pits were repaired. The criterion for cracking during rolling after grinding is that the maximum tensile strain at the bottom of the pit must be less than the critical strain of the material: ln ( 1 + h / H ) ≤ ε C r . Results of numerical simulation were verified by the data for cold-rolling tests.

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Micro-mechanism of central damage formation during cross wedge rolling

Cited by 53 publications

References 24 publications

Microstructural effects on central crack formation in hot cross-wedge-rolled high-strength steel parts

Microstructural effects on central crack formation in hot cross-wedge-rolled high-strength steel parts

Experimental Study on Cross Wedge Rolling of 21-4N Heat Resistant Steel

Study on Grinding and Deformation Fracture Control of Cold Rolled Titanium Strip

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