JPH08301B2 - Welding method of low alloy steel with flux cored wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a welding method capable of obtaining good crack resistance when welding a low alloy steel using a flux-cored wire by automatic and semi-automatic welding. It is a thing.

(Prior art and problems to be solved) Low alloy steels are used in a wide range of fields depending on their properties.

For example, low alloy high strength steel takes advantage of its strength characteristics,
It is used in steel frames, bridges, tanks, marine structures, etc., and low alloy heat resistant steel is used in chemical industry plants, high temperature and high pressure boilers, nuclear equipment, etc. due to its heat resistance and corrosion resistance.

When used in these fields, various welding methods are applied, and the use of flux-cored wires having the advantages of good welding workability and high efficiency is expanding.

However, low alloy steel has various properties by adding alloy elements such as Ni, Cr, Mo, etc., so its strength is higher than that of general mild steel and 50 kg class high strength steel. Cold cracking sensitivity is also high.

Therefore, conventionally, when welding a low alloy steel using a flux-cored wire, there is a problem that sufficient heat management (preheating, heat between passes, immediately after heating) is required, and applicable steel types are limited. However, it has been desired to solve these problems.

The present invention has been made in order to meet such a demand, and an object of the present invention is to provide a welding method having low susceptibility to cold cracking by hydrogen regardless of the type of low alloy steel.

(Means for Solving Problems) In order to achieve the above-mentioned object, the present inventor changed various conditions variously, and particularly the wire protrusion length of the flux-cored wire for low alloy steel having various levels of potential hydrogen content. When the relationship between the low temperature crack resistance and the resistance to cold cracking was investigated by finding that there was a certain relationship between them, the present invention was made here.

That is, the present invention is characterized in that when welding a low alloy steel using a flux-cored wire, the welding is performed under conditions satisfying the following equation.

Here, (H) _W is a representation of the potential amount of hydrogen flux cored wires were measured by inert gas melting method in ppm, E _X is a a representation of the extension length of the flux cored wire in mm As shown in FIG. 2, the wire protrusion length indicates the distance between the tip of the flux-cored wire 1 and the tip of the contact tip 2, and the arc length 4 is subtracted from the distance between the contact tip 2 and the base material. Equal to the length

 The present invention will be described in more detail below.

First, the potential amount of hydrogen in the flux cored wire (H) and _W and wire extension described ratio of length E _X.

Various methods have been developed for measuring hydrogen contained in the wire itself, but the inert gas melting method was adopted here from the viewpoint of simplicity, universality, and accuracy.
This method melts a sample at high temperature and measures the amount of hydrogen released at that time. Knowing the total amount of hydrogen contained in the surface deposits on the flux-cored wire, the hoop material itself, and the built-in flux. You can Of course, it goes without saying that it may be measured by another method and converted into this method.

When the present inventor measured the amount of potential hydrogen of various flux-cored wires by the above-mentioned inert gas melting method, various values were obtained depending on the steel type of the wire and the manufacturing method thereof.
Therefore, using these wires, varying the protruding length of the wire, and welding the base materials of various steel types,
When a restraint cracking test was conducted on the welded portion and the presence or absence of cracking was confirmed, the results shown in FIG. 1 were obtained. From this test result, prevent cracking due to hydrogen, the [H] _W / E _X 4
The following restrictions have proved effective. Of course, if the ratio exceeds 4, cracking occurs in the welded portion and the low temperature cracking resistance deteriorates, which is not preferable.

When carrying out the method of the present invention, it is preferable to appropriately control the electric resistance and the cast diameter of the wire, as described below.

The phenomenon that the diffusible hydrogen is reduced by increasing the protruding length of the wire is considered to be because the wire is heated by Joule heat between the contact tip and the arc point, which causes dehydrogenation (moisture). .

The calorific value per unit time due to Joule heat is expressed by the following equation.

H = KI ² R Here, K: constant I: current R: resistance From this equation, it is understood that the amount of heat generation is proportional to the resistance value when compared at the same current value. Therefore, we manufactured and confirmed flux-cored wires using various hoops with different resistance values, and found that the value obtained by multiplying the electrical resistance per 1 m by the actual cross-sectional area of the wire was less than 1.0 × 10 ^-3 Ωcm ^2. Since the wire does not generate sufficient heat, it is less effective, and conversely, if it exceeds 15 × 10 ^-3 Ωcm ² , the heat generation becomes excessive and welding workability deteriorates. Since the problem that a sufficient welding current cannot be obtained, the above value is (1.0-1
5) It is preferable to use one having a density of × 10 ⁻³ Ω · cm ² .

The substantial cross-sectional area means the hoop portion in the wire cross-sectional area.

Of course, the resistance value of the flux-cored wire is heated to a high temperature during welding, so the resistance value also rises, so it is considered that it should be specified by the resistance value during actual use. Since the mild steel and the low alloy steel hoop materials have almost the same temperature coefficient of electric resistance (rate of change in resistance value due to temperature change), there is no problem in defining the electric resistance value at room temperature.

Furthermore, in order to obtain a more stable effect, it is preferable that a stable energization be performed between the wire and the contact tip. If stable energization is not performed, not only the welding workability will deteriorate, but there may be welds with high diffusible hydrogen due to insufficient Joule heat generation, which causes problems with the integrity of the joints. . As a result of studying this point, it was found that it is effective to control the wire casting within the range of 300 to 1000 mm. In other words, it was found that when the cast was less than 300 mm, the wire was difficult to pass through the conduit or the tip, impairing the stability of the arc, and when the cast was more than 1000 mm, the energization of the contact tip was unstable. Therefore, cast
It is preferably in the range of 300 to 1000 mm.

As the shield gas used in this welding method, mixed gas of CO ₂ and O ₂ in Argon even CO ₂ 100% also can be used is not particularly limited.

Further, other conditions regarding the flux-cored wire, such as hoop material, flux material, and flux filling rate, are not particularly limited, and various shapes can be adopted for the cross-sectional shape of the wire as long as there is no problem in welding. It is possible to make a distinction between so-called seamless and with a seal.

Needless to say, various types of steel can be applied as the low alloy steel of the base material.

 Next, examples of the present invention will be described.

(Example) Using the flux-cored wires having various characteristics shown in Tables 1 and 2, the base materials of various steel types shown in the same table were welded under the conditions shown in the table and the welding conditions shown in Table 3. .

The hoop materials used were various components ranging from extremely mild steel close to pure iron to alloy steel. The built-in flux has a general composition (alloying element + slag-forming agent), and in order to change the amount of hydrogen in the wire variously, the drying conditions are changed, water-containing minerals are added, and other measures are taken. The alloy composition was also adjusted according to the material steel type and the hoop composition used.
All the wires were drawn to 1.2 mmφ and the cast was controlled during rewinding.

Weldability and restraint crack tests were conducted according to the test procedure shown in Table 3. The results are also shown in Tables 1 and 2. In addition,
Weldability is evaluated by marking with ○ (good) and × (bad).
When marked with X, welding was stopped. The presence or absence of cracks is marked with a circle (no crack) and a cross (crack).

As shown in Tables 1 and 2, it can be seen that, in the case of the welding method according to the present invention, extremely low temperature crack resistance is exhibited in welding of various low alloy steels, and weldability is also good. In that case, it is preferable to appropriately control the electric resistance and the cast of the wire as shown in the example of the reference wire with parentheses in No. in the table.

(Effect of the Invention) As described in detail above, according to the present invention, when welding a low alloy steel using a flux-cored wire, the relationship between the potential hydrogen amount of the wire and the wire protrusion length is regulated. Very good cold crack resistance can be obtained, and weldability is also good.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of potential hydrogen in the flux-cored wire and the wire protrusion length, FIG. 2 is a diagram for explaining the wire protrusion length, and FIG. 3 is the shape of the test plate used in the examples. FIG. 4 is a plan view showing dimensions (mm), and FIG. 4 is a sectional view taken along the line AA ′ in FIG. 1 ... Flux-cored wire, 2 ... Contact tip, 3 ... Base metal, 4 ... Arc length.

Claims (3)

[Claims] 1. When welding a low alloy steel using a flux-cored wire, However, [H] _W: potential amount of hydrogen in the wire (ppm) E _X: Welding method low alloy steel by the flux cored wire, wherein the welding is performed under a condition satisfying wire protruding length a (mm). 2. A value obtained by multiplying the electrical resistance per 1 m by the substantial cross-sectional area of the wire as the flux-cored wire is (1.0 to 1).
5) The method according to claim 1, which uses x10 ^-3 Ω · cm ² . 3. The method according to claim 1 or 2, wherein the flux cored wire has a cast diameter of 300 to 1000 mm.