The material-technological modelling of the real dynamic process.

Masek, Bohuslav ; Jirkova, Hana ; Malina, Jiri 等

1. INTRODUCTION

Material-physical modelling is an intensively developing field of science which enables real processes to be modelled under laboratory conditions. Because of the small amount of test material required, low energy requirements and the use of a thermomechanical simulator this technology can be used to modify existing production processes without the need for investing large sums into testing on real production equipment.

For physical modelling it is essential to know the influences of individual parameters and according to their intensity select the parameters for the model. When suitable parameters are selected, strong agreement with real processes can be expected.

This paper introduces the wide range of possibilities offered by modern material-technology modelling using newlydeveloped, original equipment which can with very high accuracy simulate the conditions of real, complex technology chains.

2. EXPERIMENT

2.1 Selection of material

Creation of the material-technology model was tested on two steels, A and B. They are modern low-alloyed steels alloyed with only manganese and a small amount of boron.

The initial state of both modelled materials showed ferrite-pearlite structure with marked, characteristic for rolling, texture in longitudinal section.

[FIGURE 1 OMITTED]

Samples were taken directly from a real production process. They are a semi-product with diameter 23 mm with free cooling in air taken directly from the rolling mill.

The size of ferrite grains in both samples was between 8 and 9 [mu]m. No significant deviation was seen in the proportion of ferrite between longitudinal and transverse sections. Ultimate strength of steel A in initial state was 543 MPa and for steel B it was 524 MPa (Blad! Nie mozna odnalezc zrodla odwolania.).

After comparing with the modelled results, the properties of the real product were evaluated after complete treatment on the rolling mill. Ultimate strength for both steels was between 507--513 MPa, ductility [A.sub.5mm] cca. 51% and average grain size for steel A was 6.5 [mu]m and for steel B it was 6.2 [mu]m.

2.2 Material-technology model of production process

Material-technology model of the real technological process was created from data transferred from the measurements obtained from the rolling mill and the remaining data by calculation (Fig. 1). Model treatment was carried out in a thermomechanical simulator. The regimes of heat and deformation were according to time dependency programmed from the instruction table. A test sample was resistance heated with direct flow of current in the body of the sample. Temperature was measured by thermocouples welded to the surface of the sample. Cooling was in air and water.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

2.3 Results of material-technology modelling

The samples of both steels, after complete thermomechanical modelling, were first evaluated metallographically. The structure was formed of ferrite and pearlite (Fig. 2).

Ferrite grain size in steel A was 7.3[+ or -]4.9 um and for material B 7.1[+ or -]4.8 um. Hardness was found to be about 150 HV for both steels and ultimate strength was greater than 510 MPa (Tab. 3).

2.4 Model assisting creation of textures

In order to obtain a longitudinal texture similar to that found in wire from a real rolling mill, the deformation regime was further modified (Fig. 3). Two deformation regimes were designed which were introduced to the part of the model corresponding to the last rolling block with a unidirectional tension deformation of 5 mm and 10 mm respectively. So that this large unidirectional deformation could be performed without destroying the sample, a two step unidirectional compression deformation had to be carried out on the model of the penultimate block. This created a pre-tamped sample for the following intensive tension.

The 5 mm tension deformation gave rise in both cases to a lower intensity of deformation in comparison with the basic model and somewhat coarser ferrite-pearlite structure with ferrite grain size greater than 8 [mu]m (Tab. 3). The 10 mm tension deformation gave rise to a ferrite-pearlite structure with significantly elongated structures (Fig. 4.). A higher degree of deformation created finer grains. The ferrite grain size for both materials was 7.2 [mu]m (Tab. 4).

As far as mechanical properties are concerned, no fundamental differences were found between the variants. For the model with 5 mm tension deformation for material A was measured a strength of 504 MPa and ductility of [A.sub.5mm] = 44 % (Tab. 3). Material B showed after the same treatment a strength 17 MPa higher and almost the same ductility (Tab. 3).

[FIGURE 4 OMITTED]

3. CONCLUSION

The experiment was focused on verifying a complex material-technology model of a rolling mill and its similarity to the real process. The main attention was paid to the differing characteristics of the deformations used in the model. The modelled results from alternating tension-compression deformation and incremental unidirectional tension deformation were experimentally compared. By analysing the sample material and material taken from the real production process it was found that for most parameters of structural and material properties the model did not deviate more than 10% from the real process. Because of the significant difference in the character of the deformations, this method is not suitable for modelling textures, but only for structural components and mechanical, in particular, strength properties.

4. ACKNOWLEDGEMENTS

This paper includes results created within the project 1M06032 Research Centre of Forming Technology.

5. REFERENCES

Kazeminezhad, M. & Taheri A. K.; A theoretical and experimental investigation on wire flat rolling process using deformation pattern, Materials & Design, Volume 26, Issue 2, Pages 99-103, ISSN: 0261-3069, April 2005

Kazeminezhad, M. & Taheri A. K.; Calculation of the rolling pressure distribution and force in wire flat rolling process, Journal of Materials Processing Technology, Volume 171, Issue 2, Pages 253-258, ISSN: 0924-0136, January 2006

Son, I. H.; Lee. J. D.; Choi, S.; Lee. D. L.; & Im, Y.T.; Deformation behavior of the surface defects of low carbon steel in wire rod rolling, Journal of Materials Processing Technology, Volume 201, Issues 1-3, Pages 91-96, ISSN: 0924-0136, May 2008

Weichang Z., & Yazheng L., Improvement of the structure properties for special steel wire by cold-rolling technique, Journal of Materials Processing Technology, Volume 48, Issues 1-4, Pages 469-474, ISSN: 0924-0136, January 1995

Andersson, P.; Wild, M.; Leven J. & Hemming B.; (2006) Transfer of surface texture from silicon nitride rolls to stainless steel wire in cold-rolling, Journal of Materials Processing Technology, Volume 173, Issue 3, Pages 394400, ISSN: 0924-0136, April 2006

Tab. 1. Mechanical properties of material in initial state and
ferrite grain size in longitudinal section

 [R.sub.m] KCV
Material [MPa] [A.sub.5mm] [%] [J.cm-2]

A 543 50 84
B 524 49 81

 Ferrite grain
Material HV10 size [[micro]m]

A 141 8.4 [+ or -] 5.8
B 143 8.8 [+ or -] 5.5

Tab. 3. Mechanical properties of materials after unidirectional 5
mm deformation

 [R.sub.m]
Material [MPa] [A.sub.5mm] [%] [J.[cm.sup.-2]]

A 504 44 84
B 521 46 82

 Ferrite grain
Material HV1 0 size [[micro]m]

A 138 8.7 [+ or -] 5.8
B 146 8.2 [+ or -] 5.6

Tab. 4. Mechanical properties of materials after unidirectional
10 mm deformation

 [R.sub.m] KCV
Material [MPa] [A.sub.5mm] [%] [J.[cm.sup.-2]]

A 508 45 86
B 505 46 88

 Ferrite grain
Material HV10 size [[micro]m]

A 143 7.2 [+ or -] 4.3
B 150 7.2 [+ or -] 4.6