JPS58163594A - Method for improving low temperature cracking resistance in weld zone of steel material - Google Patents

Abstract

PURPOSE:To prevent the generation of low temp. cracking in the weld heat affected zone in the stage of welding steel material of high carbon equiv., by incorporating a specific small amt. of Zn powder in a flux for welding. CONSTITUTION:In the stage of welding steel material of high carbon equiv. having high strength and high toughness, 0.5-2.0wt% Zn powder is incorporated in a coating flux of a welding electrode for submerged arc welding or in the flux contained in a composite wire for submerged arc welding. Zn of a low m.p. is evaporated by the effect of the high temp. of the arc in the stage of welding, and the partial pressure of H2 in the arc atmosphere is decreased, whereby the amt. of the diffusible hydrogen in the weld metal is decreased without giving any adverse influence on the arc, and the low temp. cracking resistance in the weld heat affected zone by the hydrogen is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method for improving the cold cracking resistance of a steel weld.

In general, it is known that when steel materials with high carbon equivalents are welded using different welding methods, cold cracks are likely to occur in the weld heat affected zone. Possible causes of cold cracking include hardening of the heat-affected zone, the presence of diffusible hydrogen, and restraint conditions of the welded parts, but it is known that the amount of diffusible hydrogen has a particularly large effect.

In this way, cold cracking in the weld heat affected zone or weld metal that occurs when there is a large amount of hydrogen in the weld metal is determined by the structure and hydrogen content of the weld heat affected zone or weld metal. When welding high-strength and high-toughness steel, welding is performed on the heat-affected zone in small heat welding parts such as manual welding, and in high-heat-input welding such as salamage arc welding and MIG welding to improve toughness. Cracks tend to occur in welded parts containing hardenability-improving elements. Most of the hydrogen itself comes from the decomposition of crystallized water and adsorbed water in the flux, and some water vapor in the atmosphere also causes an increase in hydrogen during times of high temperature and humidity. Crystallization water in flux can be minimized by replacing a substance with crystallization water with a substance without crystallization water or by baking, but adhering water is retained by moisture absorption after flux production, and its Although they are dried before use, fluxes for submerged arc welding and coated arc welding rods have the problem of being susceptible to re-absorption of moisture because they are still exposed to the outside air.

However, the presence of hygroscopic water makes it difficult to dry even by heating, and this also tends to cause low-temperature cracking due to hydrogen.

As a method to reduce the 82 partial pressure in the arc atmosphere, H2
Methods of increasing the partial pressure of other harmless gases have been considered, and a method of adding a component that generates a large amount of gas, such as CaF2, to the flux or coating agent is also commonly used. However, since CaF2 itself is highly hygroscopic, it tends to create a high H2 atmosphere and often makes it difficult to obtain low hydrogen. Therefore, when using CaF2, it is more important to dry the 7lux and coating material. Moreover, the arc force increases due to the high gas pressure generated during use, which inevitably narrows the selection range of welding conditions and deteriorates workability.

From the above-mentioned viewpoint, the present inventors have proposed that prior drying treatment of the welding material may be necessary when welding materials with high carbon equivalents where cold cracking is a problem, such as high-strength and high-toughness members. As a result of repeated research to find a welding method that can easily and reliably suppress the amount of diffusible hydrogen and prevent cold cracking, we found that when welding is carried out with Zn powder contained in welding flux, Zn Since the boiling point is 907°C, Zn powder evaporates into gas in the arc atmosphere, which reduces the 82 partial pressure in the arc atmosphere, reduces the amount of diffusible hydrogen, and has no adverse effect on the arc. We have come to the conclusion that there is no adverse effect.

Therefore, the present invention was made based on the above knowledge, and the present invention is based on the above-mentioned findings.
This method is characterized in that the cold cracking resistance of the welded part of the steel material is improved by welding with Zn powder contained therein.

In the method of this invention, the content of Zn powder is from 0.5 to
The reason for limiting the range to 2.0% by weight is that the content is 0.
If the hydrogen content is less than 1% by weight, the hydrogen reduction effect will be small, and if the hydrogen content exceeds 0.5%, the effect will be significantly improved.On the other hand, if the hydrogen content exceeds 20%, the pressure of the gas generated will cause welding. This is because the metal is blown off, causing the misaligned beat 1.

Other components of the flux are not particularly affected by the addition of Zri. In particular, there is almost no mutual influence with the CaF2 component, which is also a gas generation source, and if these components are also contained within the normal range, the present invention can be applied without any inconvenience. Can be done.

The built-in Franks head of composite wire for submerged arc welding usually contains Fe powder, C aF2 to reduce Oi in the weld metal and improve toughness, and T as arc stabilization uniformity.
In addition, the hoop is made of ordinary low-C, low-Mn cold-rolled steel plate, and is made of Si, Mll, etc. as the main component.

Although the necessary elemental force I is added to weld metals such as Mo and B, the method of the present invention can be applied to welding using any of these (as mentioned above, in particular, This is effective in welding where the base metal is high-strength steel and the weld metal contains M''L and B, making it a high-strength, high-toughness weld metal.In this case, MO and B is preferably contained mainly in the required amount in the wire, and when a composite wire is used, it may be added as a flux component in the wire.

Zn powder is added to the built-in flux of composite wire for MAG.
Similarly good results can be obtained by adding it.

By the way, the built-in flux of the composite wire for MAG includes arc stabilizers such as Ti○, sio, etc. as essential components, and CaF2. Materials made of Fe powder and alloying elements are used, such as CaFl, Ti○71.5i0
The composition range of No. 2 is about 1 to 60%.

In the case of shielded arc welding, the cooling rate after welding is large because the heat input is small, and martensite precipitates in the heat affected zone of the melt and liquid in high-strength steels with a tensile strength of 75C50Y/- class or higher. However, since it is more likely to cause damage than welded metal,
Cold cracking force in the heat-affected zone: This is a problem. Therefore, it is more effective to prevent cold cracking if high tensile strength steel of 1-450 kg class or higher is used as the base material, and a low hydrogen welding rod for high tensile steel is used as the weld metal. The flux that is the coating material has CaCO3 as its main component, and C'a
F2 and TiO2 are included as an essential component, but even high-strength steels and relatively thin low-PCM steels contain TiO2 as a main component, such as illuminite and titania-based steels.
A material containing low hydrogen by adding Zn powder to υ11 can be effectively used.

Therefore, Mo, B, etc. are not used in coating materials that must contain CaCO3, CaF2, and TiO2 in amounts of 1 to 6 and 0, respectively, and in normal covered arc welding. In such products, CaC
If each of O3゛, CaF, , TiO2, and 5in2 is less than 1%, the arc stabilizing effect cannot be obtained, and if it exceeds 60%, defects such as undercuts may occur, or the amount of slag is too large and the bead shape cannot be obtained. It may worsen the situation, so each
The content range in flux is usually 1 to 60%.

As described above, the present invention can be applied to each type of welding to obtain good effects, and will be explained more specifically with reference to examples.

First, a welding flux having a general composition as shown in Table 1, and a steel plate and a welding wire having a composition as shown in Table 2 were prepared.

Table 1 Table 2 Next, as shown in Table 3, wire and flux are combined, Zn powder is added to the flux as appropriate, and for composite wires other than C, solid wire is used as a core wire. Each was coated with flux to form a coated welding rod.

Using this, a single electrode.

Current: 600A, voltage: 45V, welding speed: 60crI
Welding was performed under welding conditions of L/ml. In addition, in test number 7 using composite wire C, welding was performed using granular flux in combination. Diffusible hydrogen content and oxygen content of the weld metal thus obtained.

Measure the Charpy impact value (vE-go)+ of the weld zone and the limit welding speed at which undercut will not occur.

It is also listed in Table 3. In addition, the measurement of the limit welding speed that does not cause undercut is current: 600A, voltage:
The test was carried out under the condition of 45v.

The results shown in Table 3 also show that the welding method of the present invention has a low amount of diffusible hydrogen, good low-temperature toughness, and a good welding speed, resulting in highly reliable and workable welding. It turns out that it can be implemented.

As described above, the present invention brings about industrially useful effects such as being able to improve the cold cracking resistance of steel welds at low cost without requiring complicated and time-consuming processes. It is.

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo

Claims (1)

[Claims] The cold cracking resistance of steel welds is evaluated by welding with the coated flux of a coated arc welding rod, the built-in flame fart of a composite wire, and 0.5 to 2.0% by weight of Zn powder. How to improve.