JPS5939494B2 - A steel for high heat input welding with a heat input of 60,000 J/cm or more and excellent notch toughness at the weld bond part. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for high heat input welding with a heat input of 60,00 oJ/cm or more, and in particular to a steel for welding a bond with a notch during single layer welding performed under such a high heat input. The purpose of this invention is to propose a welding steel that has excellent toughness and can therefore be advantageously used in applications where welding is performed with large heat input, regardless of whether it is a single layer or a multilayer weld.

Recently, when manufacturing large structures, the number of welding steps has been reduced,
In order to reduce welding costs, automatic welding using high heat input, such as single-sided single-layer submerged welding, electrogas welding, or electroslag welding, is being widely adopted.

However, when welding 50 kg to 60 kg class high-strength steel, which is conventionally used in large structures, with a large heat input of 60,000 J/cm or more, the structure of the weld heat affected zone, especially the bond part, is The result is a mixed structure of large mesh-like pro-eutectoid ferrite and coarse upper bainite, resulting in significant deterioration of toughness, which has hindered the practical application of high heat input welding.

As a result of intensive research into the characteristics of steel materials for application of high heat input welding, the inventors found that by adding an appropriate amount of Be to the composition of conventional steel, a heat input of 60. OOOJ/cm.

It was discovered that even when single-layer welding was performed with the above-mentioned high heat input, the bond structure became a mixed structure of fine ferrite and pearlite, and the toughness of the bond was significantly improved.

After conducting a rough investigation, we found that not only the as-rolled base material but also the base material that has undergone heat treatment such as normalizing or quenching and tempering, the welding bond part can be damaged under large heat input. It was found that the effect on

That is, this invention has C: 0.03 to 0.22 wt
% (hereinafter simply indicated by section), Si: 0.02 to 0.80
%, Mn: 0.40-2.00% and Be: 0.
Heat input 60,00 with excellent notch toughness of weld bond, including 0.001 to 0.1 and the remainder being essentially iron.
0J 7cm or more steel for high heat input welding (hereinafter referred to as the first invention), and in addition to the upper basic components, Vlo of 0.1 or more F, 8% or less Cr, 0.01% or less B.1
．． Among Ni with a coefficient of 0 or less and Cu with a coefficient of 0.5 or less, V,
Either Cr or B alone, B and Ni, or ■ and Ni
and one containing Cu in combination (hereinafter referred to as the second invention)
, and also 0.1% or less of At, Ti, and Zr, respectively.
and of REM, At.

Those containing Ti and Zr alone or in combination with A4 and REM (hereinafter referred to as the third invention), and furthermore, ILt, which is also a basic component, is also an essential component, and in addition to this, 0.1% or less of each is Nb, V, .

Ni with a coefficient of 1.0 or less, Cu with a coefficient of 0.5 or less, and 0.1
Of the following Ti, those containing Nb, V and Ni alone or in combination with V, Ni, Cu and TiC
The fourth invention (hereinafter referred to as the fourth invention) also achieves the same object as the first invention.

The reason for limiting the basic components of the steel to those mentioned above for each of these inventions is as follows.

First, the C content is limited to 0.03 to 0.22%.

In terms of strength as this type of structural steel, C is at least 0.03
% is necessary, and less than 0.03% is not preferable from the viewpoint of steel manufacturing.

On the other hand, the upper limit is 0.2 in terms of weld hardenability and weld crack sensitivity.
It was limited to 2%.

Si is required to be at least 0.02% for steel manufacturing purposes, and can be added up to 0.80% to provide appropriate strength, but if it exceeds this, the toughness of the base metal will be significantly impaired, so Si should be added at 0.02% or more.
It was limited to Article 0.80.

Mn is required to be 0.40% or more in order to impart ductility and strength to the base metal, but if it exceeds 2.00%, weld hardenability increases significantly, so it is limited to 0.40 to 200%.

Be significantly improves the toughness of high-heat-input welding bonds with a heat input of 60.000 J/cm or more, but if it is less than 0.001%, there is little effect, and if it exceeds 0.1%, the effect is diminished. It shows a tendency to saturate and actually decrease, so 0.
001-0.1%+c was limited.

The above are basic ingredients, but the following two groups that have the same action and effect as optional ingredients are both useful, and of course an appropriate combination of the two groups is also possible.The reasons for limiting these will be described below.

First, from the group of V, Cr, B, Ni, and Cu, any one of V, Cr, and B alone or B and N
The combination of i or ■ with Ni and Cu has in common a solid solution hardening effect for as-rolled steel and normalized steel, and a ζtun hardenability enhancement effect and precipitation hardening effect for quenched and tempered steel. This can be achieved without impairing the purpose of the invention, so it can contribute to increasing the strength of the base material.

Next, from the group of A/l, , Ti, Zr and REM, At, Ti and Zr alone or ht and REM
Commonly, these composites exert a grain refining effect on both as-rolled starved and normalized steel and quenched and tempered steel without impairing the purpose of the invention, in addition to increasing the strength of the base material. It can contribute to improving the toughness of the base material.

Furthermore, regarding the combination of both groups, A of the latter
4 as an essential component, V of the former, N in addition to NiCu
b and Ti also help improve the strength and toughness of the base metal.

Here ■ is particularly effective in increasing the strength of the base material.
．． It is effective when the ratio is less than 1%, but when it exceeds 0.1%, the notch toughness of the base metal is impaired and the susceptibility to weld cracking increases, which is not preferable.

In addition, even if the steel is for high heat input welding, it may be partially dwarf heat welded in actual use, so it is preferable that it has excellent dwarf heat weldability, and ■ is 0.1%. Normal 15,000 to 20,000 J/c below
It is also useful for improving the cracking susceptibility when performing dwarf heat welding of about 200 m.

Note that Nb in the fourth invention also functions in substantially the same manner as above.

Although Cr is an effective element for increasing strength, it increases weld hardenability and weld cracking susceptibility, so it is limited to 0.8 or less.

B is an element that is effective in improving the strength and toughness when quenching and tempering treatment is performed to significantly improve the hardenability of steel, but if it exceeds 0.01%, the toughness will deteriorate considerably. The content was limited to 0.01% or less.

In a composite with B or V and Cu, Ni is particularly used to improve both the strength and notch toughness of the base metal.Ni is an expensive element and is limited to 1.0% or less from the economical point of view of this type of steel. be done.

Here, Cu also contributes to an increase in strength, but if it exceeds 0.5%, the susceptibility to weld cracking increases, so it is limited to 0.5% or less.

Note that Cu of 0.5% or less also contributes to improving the corrosion resistance of steel.

Next, At is an effective element for improving strength and toughness through deoxidation and grain refinement, but its effect is 0.1
% or more, saturation occurs, so it is limited to 0.1 inches or less.

Here, 0.1% or less of At is useful for further enhancing the effect of Be on the toughness of the weld bond under large heat input, and is therefore an essential component in the fourth invention.

Ti is also effective not only in improving strength through deoxidation and grain refinement, but also in improving the ductility of the heat-affected zone of dwarf heat welding and improving the mechanical properties of the base metal (especially the Charpy value in the C direction). It is effective to eliminate the anisotropy of 0.1%
If it exceeds 0.1%, it will deteriorate the notch toughness of the base material.
Limited to the following.

In addition to being effective in increasing the strength of steel, Zr is useful in improving the shape of sulfides in steel, preventing coarsening of crystal grains, and improving toughness.

However, if it exceeds a coefficient of 0.1, the notch toughness of the base material will be significantly deteriorated, so it is limited to a coefficient of 0.1 or less.

In combination with Nt, REM (rare earth element) is effective in increasing the strength and reducing the anisotropy of the notch fractures in the base metal, but if it exceeds 1%, the toughness deteriorates, so 0.
．． Limited to 1 inch or less.

Almost the same as in ■, at 0.1% or less, Nb does not have disadvantages in notch toughness or weld cracking susceptibility, helps improve the strength of the base metal, improves cracking susceptibility during dwarf heat welding, and improves V
Like Ni, Be contributes effectively to increasing the strength by promoting the effect of Be in combination with At.

In addition, in this invention, unavoidable impurities contained in the normal steel manufacturing process are acceptable, and P and S are each 0.035.
It should be less than %.

This invention is a steel for adult heat welding with a heat input of 60,000 J/cm or more, and the reason for this limitation of use is as described later, especially when welding with a large heat input of 60,000 J/cm or more. Its unique property, in that the toughness of welded bond parts is significantly superior to conventional steels, can be used particularly effectively.

The method for producing steel according to the present invention can be essentially any method as long as the composition listed above can be obtained, and there is no particular limitation on the method, and conventional methods can be used. Regardless of the process, the process is exactly the same as the normal process applied to welded structural steel, except that it is necessary to add Be to the fully killed molten steel that has undergone degassing treatment. The casting (ingot-forming or continuous casting) and rolling steps after melting and, if necessary, the heat treatment step may also be carried out by conventional methods.

Next, the present invention will be explained in more detail based on examples.

A single-layer welded joint with a heat input of 230,000 J/cm is produced using a hot-rolled steel plate having the composition shown in Table 1 obtained through vacuum melting (however, steel T is quenched and tempered). Wall or heat input 230,000J/crn
A thermal cycle simulation heat treatment equivalent to that of the weld bond was performed, and the mechanical properties were tested. The transition temperature (Trs) results are listed in Table 2.

Invention with addition of Be @~, (B), (C),
CD) and (1), it can be seen that the toughness of the large heat input bond portion is significantly improved compared to the conventional steel 0.

On the other hand, the toughness of the large heat input bond part of the comparison steel blade with too little and too much Be added was considerably inferior to that of Kerr's invention steel, which was considerably superior to the conventional steel.

The addition of Naori e has a great effect on improving the stability of high heat input welded bond parts, but it is also unique in that it also considerably improves the impact toughness of the base metal.

Next, heat input of 230,000 J to conventional steel q and invention B)
Fig. 1 shows a comparison of the optical microscopic structure when a thermal cycle equivalent to a weld bond part of 1/cm is applied.

This figure shows that conventional steel has a mixed structure of large network ferrite and coarse upper bainite, whereas Be
Additive steel 1 has a fine ferrite/pearlite structure.

Thus, it can be seen that the addition of Be improves the toughness by improving the structure of the large heat input welding pound part.

This structural improvement is thought to be due to the fact that Be is a ferrite-forming element, and in addition to this, the Be compound contributes to ferrite nucleation and generates fine island-like ferrite from within the austenite grains.

This effect of f, K B e was discovered by the present inventor, and its application to steel for high heat input welding is extremely appropriate.

Next, as rolled containing selected components (but steel U).

Table 3 summarizes Examples in the case of steel plates ((2) and W (quenched and tempered)).

It can be seen that the effect of Be addition is maintained in this case as well.

Further, the steel according to the present invention generally has good toughness at the bond portion when high heat input welding is performed regardless of the heat treatment state of the base metal.

An example is shown in Table 4.

Whether as rolled, or after normalizing or quenching and tempering, the bonding part has good tenacity.

That is, the effect of adding Be is hardly affected by the pretreatment of the base material.

This is advantageous when the base material is subjected to heat treatment to improve its strength level.

Next, the toughness of the weld bond was investigated for the inventor steel and conventional steel Q when the welding heat input was varied.

The results are shown in Table 5.

In conventional steel Q, the toughness value of the bond part decreases as the heat input increases, whereas inventive steel N's toughness increases as the heat input increases, especially at 60.000 J/cyn.
The effect is remarkable at the above amount of heat input.

By using the steel of the present invention when constructing large structures using automatic high heat input welding, it is possible to effectively prevent the conventionally unavoidable weld bond from sinking even when welding a single layer. Therefore, it can significantly contribute to reducing welding work man-hours and costs and improving welding efficiency.

[Brief explanation of the drawing]

FIG. 1 is an optical micrograph showing the structure of a weld bond with a heat input of 230 KJ/cm for conventional steel Q and invention steel (4).

Claims (1)

[Claims] IC: 0.03-0.22wt% Si-0.02-0.80wt%Mn: 0
．． 4C) ~2.00 wt% and Be: 0.
A steel for adult heat welding having a heat input of 60.000 J7f:m or more and having excellent notch toughness at the weld bond, containing 0.001 to 0.1 wt%, with the remainder essentially having a composition of iron. 2C: 0.03-0.22 wt% Si: 0.02-0.80 wt% Mn:
0.40-2.00 wt% and Be: 0.00
Contains 1 to 0.1 wt %, and has less than 0.1 w Cr 0.8 wt % or less Cr 0.01 wt % or less B 1.0 wt % or less Ni and O, 5 wt % Among the following Cu, ■, Cr and B alone or B and N
A high heat input welding steel containing a composite of i1 or ■, Ni and Cu, with the remainder essentially having a composition of iron, with a heat input of 60.000 J/cmJJ and excellent notch toughness at the weld bond. . 3 C: 0.03 to 0.22 wt% Si: 0.02 to 0.80 wt% Mn: 0.40 to 2.00 wt% and Be: 0.001 to 0.1 wt%, and each o, 1wt% or less A4. Among Ti, Zr and REM, At, Ti and Zr alone or At and R
Contains BM in a composite form, with the remainder essentially having a composition of iron.
Heat input of 60,000 yen with excellent notch toughness of welded bond parts
Steel for adult heat welding of J/crn or higher. 4 C: 0.03-0.22 wt% Si: 0.02-0.80 wt% Mn: 0.40-2.00 wt% Be: 0.001-0.1 wt% and A7: 0
．． Contains 1 wt% or less, and. O, 1wt% or less of Nb 0.1wt% or less of Ni O, 5wt% or less of Cu, and 0.1wt% or less of Ti, any of Nb, V, and Ni Alone or V. A steel for high heat input welding, containing a composite of Ni, Cu, and Ti, with the remainder being essentially iron, and having a heat input of 60,000 J/cm or more and excellent notch toughness at the weld bond.