Influence of the surface Influence of the surface defects concerning defects concerning

drawing processes of the drawing processes of the micro-alloyed steelmicro-alloyed steel

Stanislav RuszStanislav Rusz

IntroductionIntroduction

EEffect of the pass reduction concerning ffect of the pass reduction concerning the strain course in wires made of micro-the strain course in wires made of micro-alloyed steel, 23MnB4; namely alloyed steel, 23MnB4; namely successively investigating three particular successively investigating three particular points points before the die, before the die, in the die itself,in the die itself, at the die output section at the die output section

ExperimentsExperiments

Four variants of wire drawing reduction Four variants of wire drawing reduction have beenhave been a analysed:nalysed:

Reduction, Reduction, ØØ14 – 14 – ØØ12.1 mm; Friction 12.1 mm; Friction coefficient, 0.1 coefficient, 0.1

Reduction, Reduction, ØØ14 – 14 – ØØ12.1 mm; Friction 12.1 mm; Friction coefficient, 0.15 coefficient, 0.15

Reduction, Reduction, ØØ14 – 14 – ØØ11.8 mm; Friction 11.8 mm; Friction coefficient, 0.1coefficient, 0.1

Reduction, Reduction, ØØ12.1– 12.1– ØØ11.8 mm; Friction 11.8 mm; Friction coefficient, 0.1coefficient, 0.1

Simulation processSimulation process

Fig.1: Network – Initial condition, (a), Fig.1: Network – Initial condition, (a), Network by final drawing process (b)Network by final drawing process (b)

R R

R R

aa))

bb))

TemperaturesTemperatures s simulationimulation

Fig.2: Material deformation curves produced by Fig.2: Material deformation curves produced by upsetting tests for temperatures of 20 and 200 °C upsetting tests for temperatures of 20 and 200 °C

Drawing forceDrawing force

FFig.3: Course of drawing force – Var. aig.3: Course of drawing force – Var. a

Surface Surface sstraintrain

FFig.4: Surface strain at the cross-section locale, R-R – Var. aig.4: Surface strain at the cross-section locale, R-R – Var. a

Kalibr Odlehčení

Gauge of drawing die

Unloading

Strain condition analysis Strain condition analysis (example for reduction, (example for reduction,

ØØ1414 –– ØØ12.1 mm)12.1 mm)

Fig.5: Axial strain by drawing and after release Fig.5: Axial strain by drawing and after release [MPa] – Var. a[MPa] – Var. a

Plastic transformationPlastic transformation

Fig.6: Plastic transformation – Overview, Var. aFig.6: Plastic transformation – Overview, Var. a

ResultsResults

Significant residual pressure strains are retained Significant residual pressure strains are retained along the axis - especially as axial orientedalong the axis - especially as axial oriented

On the contrary the surface retains such values On the contrary the surface retains such values that are undesirable as regards the risks of its that are undesirable as regards the risks of its damagedamage

The plastic deformation, a very intensive The plastic deformation, a very intensive deformation takes place at the wire surface after deformation takes place at the wire surface after the passage through the die, as well as in the the passage through the die, as well as in the specimen’s centre.specimen’s centre.

The intensive deformation works on behaviour of The intensive deformation works on behaviour of surface defects. surface defects.

Axial StrainsAxial Strains

Fig.7: Axial strain course in various points of the dieFig.7: Axial strain course in various points of the die

axial comparison

-400

-200

0

200

400

600

800

0 5 10 15 20 25 30 35 40 45

axial displacement ( mm )

surf

ace

stre

ss (

MP

a )

var a

var b

var c

TThe process he process aanalysnalyse e of of the wire drawing with the wire drawing with

lengthwise defect lengthwise defect

Fig.8: Network initial Fig.8: Network initial shape for the defect shape for the defect neighbourhoodneighbourhood

Fig.Fig.99: Defect’s closing : Defect’s closing by passing through by passing through the diethe die – Detail– Detail

Perimeter movement and Perimeter movement and deformation intensitydeformation intensity

Fig.Fig.1010: Perimeter : Perimeter movementsmovements by by drawing [mm]drawing [mm]

Fig.Fig.1111: Deformation : Deformation intensity on the intensity on the defect’sdefect’s level - Detaillevel - Detail

General assessmentGeneral assessment

The results provide evidence for the fact The results provide evidence for the fact that an action of upsetting a that an action of upsetting a cylindrically shaped specimen with cylindrically shaped specimen with lengthwise defect results in a gaping lengthwise defect results in a gaping effect. effect.

This is an unfavourable condition. On This is an unfavourable condition. On the contrary, an action of drawing a the contrary, an action of drawing a sample with the same defect leads sample with the same defect leads explicitly to its closing, which is evident explicitly to its closing, which is evident in the detail of the Fig. 8 and 9.in the detail of the Fig. 8 and 9.

The value for this closing after drawing The value for this closing after drawing illustrates Fig. 10, where the blue illustrates Fig. 10, where the blue colour indicates in millimetres the colour indicates in millimetres the peripheral movement of defect edges in peripheral movement of defect edges in the direction of its closing; contrary to the direction of its closing; contrary to this, red indicates opening. this, red indicates opening.

The movement value, –0.04 mm, for The movement value, –0.04 mm, for each edge towards the centre means each edge towards the centre means that the defect does not close that the defect does not close completely, but its width decreases completely, but its width decreases from 0.1 to 0.02 mm from 0.1 to 0.02 mm

TThe material remains permanently he material remains permanently transformed to the effect of defect transformed to the effect of defect closing.closing.

TThe maximum deformation, 0.37, the he maximum deformation, 0.37, the same situation implies the value, 0.42, same situation implies the value, 0.42, for a smooth defect-free surfacefor a smooth defect-free surface. .

Further investigations will have to Further investigations will have to concentrate on experimental concentrate on experimental verifications of strain condition influence verifications of strain condition influence concerning closing of surface defects byconcerning closing of surface defects by producing high-strength boltsproducing high-strength bolts. .

Thank you for your attentionThank you for your attention