COMPARATIVE ANALYSIS OF METALOGRAPHICAL CHARACTERISTICS OF A SOLDERED ASTM A131 NAVAL STEEL BOARD BY THE E7018 COATED ELECTRODE WITH VARIATION OF THE CABLE DISTANCE OF THE ELECTRODE

COMPARATIVE ANALYSIS OF METALOGRAPHICAL CHARACTERISTICS OF A SOLDERED ASTM A131 NAVAL STEEL BOARD BY THE E7018 COATED ELECTRODE WITH VARIATION OF THE CABLE DISTANCE OF THE ELECTRODE

E. Santos¹, A. Arruda¹, A. Tavares¹.

1University of Campinas, School Mechanical Engineering, São Paulo, Brazil

e-mail: [e-mail]

Abstract: Steel, is an iron-carbon alloy, is widely used in the shipbuilding industry, has been replacing wood because it has advantages such as corrosion resistance, ductility and toughness. The process of union of steel more popular is the welding, since it is the most economical, practical and common process and to which it was used in this work.

This paper presents the assay of the grains behavior in the Affected Thermally Zone in welding coated electrode. We used a continuous-current source rectifier. The steel in question, is ASTM A131 Grade A, is widely used in the marine industry to build the hulls of boats because it meets the tenacity of -40 ° C for navigation in cold regions and the electrode was the E7018 (Latest version), but has low hydrogen and considerable amounts of iron powder to give more stability to the arc. The variable to consider is the length of the electrode holder cable, ranging from three to one hundred meters. The welds were performed in a shipyard near the city of Manaus, in order to show the current welding situation in the hull of a vessel. Often welders can not move the rectifier sources to be welded and then to a solution, only change the length of the electrode holder for larger, to reach the destination without the regular welding amperage, as a result there is a deposition of variation In Fusion Zone (ZF) and, consequently, the behavior of HAZ microstructure, and where the study was made. Analysis of HAZ was made by metallographic tests in both welded joints and the results of the micrographs, was made a comparison between the welded joints with  three meters and a hundred meters.

Keywords: Welding;Electrode; coated; HAZ; microstructure; Metallography.

Introduction

The most popular process of joining steel plates is the welding, since it is the most economical, practical and common process used in this work.

Welding is the process of joining two or more parts through high energy, ensuring in the region of contact (joint) between these parts, the continuity of physical, chemical and metallurgical properties, used in the process of construction of vessels.

Metallographic evaluation of a welded joint throughout the design is critical to determining control measures and thus save time and resources on welded joints maintenance.

Experimental Procedure

In this section we present our process developed that are divided in six steps: Welding, cutting, inlay, sanding/polishing, attack, SEM analysis.
1) First Steps: Welding. The material was collected and the part cleaned, then a 45 °C bevel was made, according to norm NBR 7239. Then the part was welded following the norm NBR 13043.

2) Cutting: The plates were cut with a Bosch Disc Saw, GDC 14-40, 127V ~ 50 / 60Hz 12A 1450W.

3) Inlay: The hot-embossing occurs when the sample is embedded in thermoplastic materials by means of presses, using pressure and heating to effect the polymerization.

4) Sanding and Polishing: was done according to norm NBR 13284/1995

5) Attack: The chemical etching of the surfaces of the samples was done with the reagent Nital 2%.

Results and Discussion

It was found that the soldering done with cable from the larger electrode holder increased the process time. In plate B (100 meters of cable) a time of approximately 22 minutes was spent and 07 (seven) electrodes were consumed in the process while in plate A (03 meters of cable) was spent a time of 12 minutes and 5 (Five) electrodes, which means that in Plate A was spent almost double the time and there was a higher electrode expense.