R. Colas

7006126422

Publications - 4

Extension of isothermal time-temperature parameters to non-isothermal conditions: Application to the simulation of rapid tempering

Janez Grum G. Sarmiento A. M. Deus I. Felde T. Reti R. Colas

Publication Name: Strojniski Vestnik Journal of Mechanical Engineering

Publication Date: 2010-04-28

Volume: 56

Issue: 2

Page Range: 84-92

Description:

A phenomenological method for constructing non-isothermal, generalized time-temperature parameters (GTT parameters) is presented. An analysis of the relationship between the various traditional isothermal time-temperature parameters has verified that the generalized Dorn-parameter is regarded to be the sole non-isothermal complex parameter to which a rigorous, physically well-founded interpretation is attributed. Possible applications of GTT parameters are illustrated by examples concerning the prediction of hardness change in quenched steels during rapid tempering treatments. © 2010 Journal of Mechanical Engineering. All rights reserved.

Open Access: Yes

DOI: DOI not available

Diffusion in electrodes used for resistance spot welding of galvannealed steel

Martha P. Guerrero-Mata Patricia Zambrano I. Felde Mihaly Réger Maribel De La Garza T. Reti R. Colas

Publication Name: Defect and Diffusion Forum

Publication Date: 2010-01-01

Volume: 297-301

Issue: Unknown

Page Range: 300-307

Description:

A study was carried out on Zr-Cr bearing copper electrodes used for resistance spot welding of galvannealed steel strips. One electrode exhibited a series of well-defined layers in which Zn diffused to form β- and γ-brasses; an external layer containing iron was detected in this electrode. Another electrode that exhibited a high degree of damage did not exhibited continuous Zn-diffusion layers in all places, moreover, the Fe-containing layer was either removed, or had it grown to a high extent in some places; the occurrence of Cu-rich particles embedded within the Fe containing layer was observed. Multiple cracks were observed within the γ brass layer in both electrodes. The difference in the observed behaviour of the electrodes can be attributed to a difference in the characteristics of the galvannealed coating of the strips, as the first electrode was used to weld strips in which the layer corresponding to the γ phase was well developed, whereas the second electrode was used to weld strips with only an incipient layer. It can be concluded that growth of the γ phase changes the thermophysical properties of the zinc coating, affecting the temperature profile during spot welding. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/DDF.297-301.300

On the temperature rate dependent transformation processes

L. Costa I. Czinege I. Felde T. Reti R. Colas

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 571-578

Description:

Kinetic models of new types are suggested which are designated primarily to predict the progress of non-isothermal transformations occurring during rapid heating and cooling in alloys. A common feature of each model outlined is that it takes into account not only the varying temperature but also the rate of temperature change on the transformation rate of the process. The two models represented by differential equations are generated by using the concept of virtual kinetic parameters, which can be determined from non-isothermal experiments only. A key property of the virtual parameter "p" involved in the transformation rate equations is that it quantitatively characterizes the temperature rate dependence of the non-isothermal reaction.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.571

A novel approach of quenchant evaluation by applying quality functions

I. Czinege B. Smoljan I. Felde R. Colas

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 513-518

Description:

A novel numerical approach for testing and evaluation of quenching media and quenching systems is outlined. The technique proposed is based on determination of heat transfer coefficient from temperature signals recorded and applying it as input for simulation of quenching process. The evaluation method is based on the calculated microstructural and mechanical properties of cylindrical samples.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.513