JPS59147795A - Welding method with large heat input by which welded joint having excellent toughness and bendability is obtained - Google Patents

Abstract

PURPOSE:To obtain inexpensively a welded joint having excellent toughness and bendability in welding with large heat input by adding an iron oxide in a specific amt. per unit groove gap and performing welding. CONSTITUTION:Iron oxide is added at 0.005-0.08g at each 1cm<2> of a groove gap to a weld zone and welding is performed in the stage of welding the weld zone by welding with large heat input such as electroslag welding. The crystalline grains of a weld metal are then fined and problems such as a deterioration in the toughness of the weld metal and a decrease in bendability are solved. The iron oxide consists of FeO, Fe3O4, Fe2O3, etc. and is added to the weld zone by a method of pulverizing the iron oxide and adding the powder thereof together with a flux to the weld zone or the scale formed during rolling may be kept stuck as it is in the groove.

Description

[Detailed Description of the Invention] The present invention is applicable to shipbuilding, bridge construction, etc. that require vertical welding of thick steel plates,
The present invention relates to a high-heat-input welding method that allows welding joints with excellent toughness and bendability to be obtained at low cost in welding industrial machinery or pressure vessels.

Electroslag welding, electrogas welding, etc. are mainly used for vertical welding of 40 kg or 50 kg thick steel plates. These welding methods allow for efficient welding due to large heat input, but on the other hand, due to the large heat input, the weld metal becomes coarse grained, the toughness of the weld metal deteriorates, and cracks occur in the weld metal during bending. There are problems that occur easily.

One method for solving these problems is to use a welding wire to which a large number of alloying components are added, but in this case, cost increases are unavoidable. The present invention aims to improve the above problems without increasing costs.

The present inventors investigated the toughness, structure, chemical composition, etc. of weld metal in Elec I/Loss lag welding of thick steel plates, and found that weld metal using flux containing an appropriate amount of iron oxide had finer grains. discovered that toughness and bendability were improved, and as a result of various studies, determined the appropriate amount and completed the present invention.

That is, in the present invention, FeQ, Fe30
Iron oxide consisting of 4 and Fe20z etc. 0.0 O
Welding is performed by adding 5 to 0.08 g to the welded part to refine the crystal grains of the weld metal, which solves the problem of deterioration of the toughness and low bendability of the weld metal. It is.

The iron oxide may be added by pulverizing the iron oxide and adding it to the weld together with flux, or by leaving the scale during rolling stuck in the groove as it is.

When iron oxide is added into the groove gap and high heat input welding is performed,
Spherical nonmetallic inclusions made of oxides such as Aj, Si, Mg, and Ca are formed in the molten pool. Among these nonmetallic inclusions, large ones float to the surface and turn into slag, but fine ones tend to remain in the molten metal. According to the results of various experiments conducted by the present inventors, the amount of fine nonmetallic inclusions depends on the amount of iron oxide added, and the remaining fine nonmetallic inclusions cause the molten pool to solidify. When weld metal is formed, it acts as a nucleation site and refines the crystal grains of weld metal, resulting in a welded joint with excellent toughness and bendability.

In this case, the amount of ζ iron oxide added to the groove gap is important. Figure 1 shows the relationship between the amount of iron oxide added to the groove gap and the absorbed energy in O'C of the weld metal in electroslag welding of 40 kg steel and 50 kg steel. O,OO5g per 1cm' of groove gap
By adding the above amount of iron oxide, the absorbed energy increases rapidly and gradually increases thereafter, but if more than 0.08 g of iron oxide is added per 1 cm of groove gap, the absorbed energy decreases rapidly. .

The present invention limits the amount of iron oxide added to the groove gap based on such experimental results.

The amount of iron oxide added is 0.005g per 1cm' of groove gap.
If it is less than that, the grains of the weld metal will not be sufficiently refined. Therefore, the toughness and bendability of the welded joint are not improved.

Therefore, the limit for the amount of iron oxide added was set at 0.005 g per 1 cm' of groove gap. On the other hand, as the amount of iron oxide added increases, the grains of the weld metal become finer, but the groove gap 1c
o, C18g per m', the crystal grains of the weld metal will become finer, and at the same time, a large amount of nonmetallic inclusions will be present, and nonmetallic inclusions with large grain sizes will also be present. As a result, the toughness and bendability of welded joints deteriorate. Therefore, the amount of iron oxide added was set at 0.08 g per 1 cm of the groove gap.

EXAMPLE High heat input welding was performed on a test steel plate with a groove shape shown in FIG.

The chemical composition of the test steel sheet is as follows.

(C) = 0.1'7 Weight% (Si) = 0.25 weight% (Mn) = 0.90 weight% (P) = 0.015% by weight [:5)-0,003 weight 1% [A standing) = 0.026% by weight The welding conditions were as follows.

Welding method: Consumable nozzle electroslag welding Bevel shape: As shown in Figure 2 Welding materials: Wire KW'30C Flux KFloo Consumable nozzle KUlooO Current: +480 A Voltage: 38 V Speed: 1.7 0 m/min input Heat amount +64
4 KJ/cm.

Table 1 shows the results of performance tests of welded joints when the amount of iron oxide in the groove gap was varied. In Table 1, Example 1.
2 is an example of the present invention, and Comparative Example 1.2 is an example in which the amount of iron oxide added in the groove gap is outside the range of the present invention. It is clear that by adding an amount of iron oxide within the range of the present invention into the groove gap and performing high heat input welding, a welded joint with excellent toughness, bendability, etc. can be obtained.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between the amount of iron oxide added in the groove gap and the absorbed energy in O'C of the weld metal, and Fig. 2 is a horizontal cross-sectional view showing the groove shape of the example. . 1... Base material, 2... Copper dowel, 3... Groove gap, 4
...Welding wire patent applicant Kawasaki Steel Co., Ltd. agent Patent attorney Yoshio Kosugi

Claims (1)

[Claims] 1 0.00 iron oxide per 1 cm' of groove gap during welding
A high heat input welding method characterized by welding with the addition of 5 to 0.08 g.