Acta Microscopica, Volume 12, Supplement C, September 2003 XIX Congress of the Brazilian Society for Microscopy and Microanalysis

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MICROSTRUCTURAL ANALYSIS OF THE HEAT AFFECTED ZONE OF THE ASTM 1045 STEEL RECOVERED BY WELDING

Farias, J.P.1; De Azevedo, A.G.L.1; Marcelino Neto, M.A.1,*; Silva, C.C.1

1Universidade Federal do Ceará Centro de Tecnologia, Departamento de Engenharia Mecânica e de Produção,

Campus do Pici, Bloco 715, Laboratório de Soldagem(Engesolda), Fortaleza –Ce Cep: 60488-760

E-mail: moisesneto@bol.com.br

The welding process with covered electrode constitutes a viable alternative for the recovery of pieces that suffered wear or faults in service [1]. However, in some steels the generated thermal cycle is enough to cause significant alterations in the microstructure of the heat affected zone (HAZ) causing changes in the mechanical properties [2-3].

The Double Layer Technique is employed in the welding of several steels of the petroleum and gas industry like ASTM 4140 and 4340 [4-5]. The principal purpose of this work is to estimate the application of this technique for ASTM 1045 steel, employing the welding process with covered electrode, contributing to advance in the welding and recovery of C-Mn and low-alloy steels.

In this study, Double Layer Technique was applied in the welding of the ASTM 1045 steel with covered AWS E7018-1 electrode, trying to obtain an appropriate overlap of the cycles causing refining and tempering of the HAZ of the first layer.

It was realized the welding in semi-v joints using five energy ratios (5/5; 5/10; 10/5; 10/10; 10/16 kJ/cm). The microstructure of the HAZ of the first layer was analyzed using optic microscopy to evaluate the refining of the grains. It was determined the cross section HAZ microhardness profile of the first layer of the buttering for each semi-v joint to verify the occurrence of the tempering.

It can be observed for 5/5 energy ratio a refined microstructure in the HAZ of the first layer (figure 1.a) but the refining was not total (figure1.b) because it was observed in the interpasses region a bainitic microstructure [4]. However the hardness was smaller than 300 HV (figure 2.b) in these interpasses region. In the microhardness profile we can see the maximum hardness in the HAZ of the first layer (figure 2.a). In the figure 3 we can see the bainitic microconstituent for 10/5 energy ratio.

With the results obtained in this work, it was possible to detach the following conclusions. The used energy ratios provided considerable levels of refining of the HAZ, however they were not enough to assure a uniform refining in the interpasses region.

Due to the low hardenability of the ASTM 1045 steel it was possible to obtain significant results of tempering for all employed energy ratios. Acknowledgements: The authors thank CEFET-CE, PETROBRÁS, ENGESOLDA-UFC, ANP, CNPq and FUNCAP. References: [1] Still, J.R.; Welding of AISI 4140 and Steel for Drilling Systems. Welding Journal, Jun/1997. [2] Ninõ, C.E.B.; Corrêa, J.A.; Buschinelli, A.J.A. Técnicas de Reparo por Soldagem em Aços 5Cr-0,5Mo. Soldagem e Materiais, vol. 4 n2, 1992, p.28-33. [3] Farias, J.P.; Azevedo, A.G.L.; Silva, C.C. Efeito da Técnica da Dupla Camada Sobre a Tenacidade de Peças de Aço ABNT 1045. 2º Congresso Brasileiro de Engenharia de Fabricação. Uberlândia-MG, 2003. [4] Aguiar, W.M. Soldagem do Aço ABNT 4140 sem Tratamento Térmico Posterior. Dissertação de Mestrado. Fortaleza-CE, Universidade Federal do Ceará, 2001, 85p. [5] Arraes Jr., R. M. Avaliação da Tenacidade da ZAC na Soldagem do Aço ABNT 4340 sem Tratamento Térmico Posterior. Dissertação de Mestrado. Fortaleza-CE, Universidade Federal do Ceará, 2001, 76p.

Acta Microscopica, Volume 12, Supplement C, September 2003 XIX Congress of the Brazilian Society for Microscopy and Microanalysis

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Figure1 – 5/5 Energy Ratio. a) Regions of the test specimen, 13X ; b) Amplified detail. HAZ not much refined, 200X. Nital attack 2%.

Microhardness Profile 5/5 Energy Ratio

Distance of the fusion line (mm)

Har

dnes

s (H

V)

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Reference line

Microhardness Profile 5/5 Energy Ratio

Distance of the fusion line (mm)

Har

dnes

s (H

V)

100

150

200

250

300

350

400

450

500

0 0.2 0.4 0.6 0.8 1 1.2

Reference line

Figure 2 – Microhardness graphic: a) In the HAZ of the first layer; b) In the interpasses region.

Bainita

Figure 3 – 10/5 Energy ratio: a) Regions of the test specimen,13X ; b) Amplified detail. Bainitic microconstituents, 200X. Nital attack 2%.

a) b)

1038 µm FG-HAZ

CG-HAZ

2nd HAZ

1st HAZ

80 µm

a)

b)

Bainite

Weld metal

2nd HAZ

1st HAZ

1038 µm 87,5 µm

a) b)