JP3399125B2 - Steel material with excellent toughness of weld heat affected zone - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to welding steel used in bridges, shipbuilding, construction, marine structures, etc., and to steel products for line pipes that require welding at the time of pipe manufacturing, and particularly excellent welding. The present invention relates to a steel material for welding which is effective when heat affected zone toughness is required.

[0002]

2. Description of the Related Art Generally, when a steel material is welded, in the base metal portion (welding heat affected zone, hereinafter referred to as HAZ) in contact with the weld metal, the crystal grains become coarse and the toughness deteriorates, which deteriorates the performance of the welded structure. It has been known. In particular, when high heat input welding is performed, TiN in the steel becomes coarse and the effect of suppressing γ grain growth is lost, so it is very difficult to prevent coarsening and toughness of the HAZ structure. Many attempts have been made to improve the HAZ toughness.

Among them, the high-strength steel sheet for large heat input welding disclosed in Japanese Patent Laid-Open No. 62-170459 has a promoting effect of ferrite precipitation by lowering Al, a composite addition of Ti and B, and a control of N content. It is characterized by improving the HAZ toughness in combination. In this case, while cooling B in the HAZ part, γ in the form of BN
By precipitating in the grains and making it function as a ferrite precipitation site from within the γ grains, it is possible to make the HAZ structure into a fine intragranular ferrite structure with an even grain, and super-high heat input welding in which the γ grains become significantly coarse. Also in this case, good HAZ toughness can be secured.

Further, Japanese Patent Laid-Open No. 57-51243 discloses a grain size of 5
A steel material for welding containing 0.004 to 0.06% of TiO _x having a size of μm or less is shown.

Further, the welding steel material disclosed in Japanese Patent Laid-Open No. 59-185760 has the same low Al-based component selection, T
In addition to using iN, Ti oxide or a complex of Ti oxide and MnS, etc. is dispersed in place of BN, and these dispersoids function as precipitation nuclei for ferrite, resulting in a finer HAZ structure and improved HAZ toughness. It is a high toughness steel for welding, which can be called low Al-Ti oxide dispersion steel.

Among these, Japanese Patent Laid-Open Nos. 59-185760 and Sho
61-79745, JP 61-117245, JP 2-220
The high-strength steel or its manufacturing method proposed in each of Japanese Patent No. 735, 735 is that Ti deoxidation is performed during melting and the deoxidation product is dispersed and utilized, or , TiN and MnS are compositely deposited and used as composite inclusions.

Further, the fine particle-dispersed steels disclosed in Japanese Patent Laid-Open No. 5-255801 and Japanese Patent Laid-Open No. 5-271864 are Mn.
-Si oxide or Mn-Al containing 50% or more of Mn
It is a steel in which an oxide is formed in steel, MnS is further deposited on the oxide, and is used as a ferrite nucleus.

[0008]

As mentioned above, the HAZ
It is known to utilize precipitates or inclusions in steel for improving the toughness, but when using the dispersed particles proposed so far, there are various problems as described below.

First, the high-strength steel plate for large heat input welding described in JP-A-62-170459. However, in order to secure HAZ toughness, BN is used in addition to TiN. Addition is essential, and H must be present for solid solution B unless the balance of sol.Al, Ti, N, and B contents is accurately controlled.
The difficulty exists that the AZ hardens.

Further, the steel for welding disclosed in Japanese Patent Laid-Open No. 57-51243 has a very high reactivity of oxygen of TiO _x dispersed in the steel. It is extremely difficult to stably exist in the steel, and it is very difficult to disperse the steel in the steel within the production cost of the steel allowed from the economical point of view to exert the HAZ microstructure refinement effect.

There is also a method of utilizing Ti ₂ O ₃ instead of TiO _X. It cannot be said that it is impossible to form Ti ₂ O ₃ in steel, but Ti ₂ O ₃ itself has almost no ability as a ferrite nucleus, and the HAZ toughness of steel does not improve.

Therefore, in order to impart nucleation ability to the oxide, a method has been proposed in which TiN and MnS are compositely precipitated in Ti oxide and used as ferrite nuclei. Also,
As an oxide forming a complex inclusion with MnS, Mn-
Methods using Si oxide and Mn-Al oxide have also been proposed.

However, MnS is indispensable in these methods utilizing composite inclusions of oxides and MnS, so it is essential to contain S in steel to some extent, and the cleanliness of steel is sacrificed to some extent. I have no choice but to do it. In particular, it is difficult to suppress MnS-based inclusions that cause the generation of HIC, and the applicable range is limited.

The Mn-Si oxide and the Mn-Al oxide among the above must contain a large amount of Mn in the form of MnO or other Mn oxide. Forming an oxide in steel is very difficult in actual production, and it is very difficult to economically mass-produce it.

Moreover, even if these problems are overcome and the desired oxide-MnS composite inclusions are formed in the steel, a considerable part of MnS is once converted to steel when affected by welding heat. Since it undergoes a process of forming a solid solution and reprecipitating during cooling, Mn that cannot be reprecipitated and remains as a solid solution easily occurs around the oxide. Therefore, especially when ultra-high heat input welding is performed, the concentration of solid solution Mn locally around the composite inclusions tends to be high, the local hardenability around the inclusions increases, and the inclusions often form As a result, it does not function as a ferrite nucleus sufficiently.

As described above, at present, dispersed particles having satisfactory properties as ferrite precipitation nuclei in the heat-affected zone of welding are not known, and excellent dispersed particles are required to improve HAZ toughness.

[0017]

SUMMARY OF THE INVENTION The present inventors have formed an oxide of Al, Ti, and Mn in steel with active control of the oxide composition in mind, and the performance of the steel in that case. Was conducted.

Among the alloying elements usually contained in low alloy steels, those capable of forming oxides include Si, Mn, Ti and Al. Although Ca, Mg and rare earth elements are sometimes added, the reaction is violent and it is difficult to control the oxide composition accurately. However, when added, the amount is suppressed as much as possible, Al, Ti, The ratio of the oxide particles other than Mn to the metal elements was set to 30 mol% or less of all the metal elements forming the oxide, including the mixed content from refractories, slag, and the like. Further, when Al or Ti was added to such an extent that the toughness of steel was secured, Si was hardly contained in the oxide, so the Si element was not included in the study.

For this reason, 3 of Al, Ti and Mn are used.
As a result of earnest research on oxides composed of elements, the following findings have been obtained.

1) Whether or not the oxide dispersed in the steel functions as an intragranular ferrite precipitation nucleus in the heat affected zone of welding depends strongly on the composition of each dispersed oxide.

2) When the oxide in the steel is Al oxide, Ti oxide, or Al-Ti oxide, useful effects such as HAZ structure improvement are hardly obtained.

3) Oxides effective as ferrite nuclei are high conductivity oxides, which are oxides having compositions applicable to two regions A and B in FIG. In any case of forming a body, it becomes a good ferrite / acicular ferrite nucleus.

4) In order to form the oxides corresponding to the regions A and B stably so as to withstand commercial production, A
For C and Si, which are deoxidizing elements other than 1, Mn, and Ti, it is necessary to set an upper limit for the content, and C ≦ 0.25.
%, Si ≦ 0.6%.

The present invention has been made on the basis of these findings, and the gist of the present invention is "in% by weight,
C: 0.01 to 0.25%, Si: 0.6% or less, M
n: 0.3 to 3%, P: 0.03% or less, S: 0.01
% Or less, N: 0.0005 to 0.01%, O: 0.00
1 to 0.007%, Ti: 0.003 to 0.03%, A
1: 0.02% or less, and further B: 0 to 0.00
2%, Cr: 0 to 1.5%, Mo: 0 to 1.5%, C
u: 0-2%, Ni: 0-3%, Nb: 0-0.5%,
V: 0 to 0.5%, and optionally Zr:
0.02% or less, Ca: 0.004% or less, Mg: 0.
004% or less, Hf: 0.02% or less, Y: 0.02%
Hereinafter, a rare earth element: a steel material containing at least one of 0.02% or less, the balance being Fe and unavoidable impurities, and oxide particles dispersed in the steel material. Is an oxide particle in which Ti, Mn, and Al in the oxide particle satisfy the following formula, and an oxide particle satisfying the following formula, the average dispersion density of which is 1 mm.
Steel material with excellent toughness in the weld heat-affected zone, characterized in that it is 4 or more per ² pieces.

In terms of mol ratio, (Ti + Mn + Al)> E × 0.70 ... Here, E = total metal elements constituting the oxide. In the following molar ratio when Ti + Mn + Al = 100. , (Ti + Mn) ≧ 80 mol% ・ ・ ・ ・ ・ 50 mol% ≧ Mn ≧ 7 mol% ・ ・ ・ ・ ・ (Al + Mn) ≧ 40 mol% ・ ・ ・ ・ ・ 1 ≦ (Al / Mn) ≦ 5 ... ... ".

[0026]

Next, the component composition of the steel material of the present invention, the reason for limiting the oxide particles and the function thereof will be described below.

FIG. 1 is a three-phase diagram showing the contents of Al, Mn and Ti in the oxide. In the oxide particles to be dispersed in the steel material of the present invention, Al, Mn and Ti in the oxide are (1) (Ti + Mn + Al)> E × 0.70 (mol ratio) ... where E = oxide In the following molar ratio when Ti + Mn + Al = 100, the relationship of (Ti + Mn) ≧ 80 mol% ··· 50 mol% ≧ Mn ≧ 7 mol% ··· A satisfying oxide, that is, an oxide in the region B of FIG. 1, or (2) at a molar ratio of (Ti + Mn + Al)> E × 0.70 ... It is assumed that all metallic elements are composed. In the following molar ratio when Ti + Mn + Al = 100, the relationship of (Al + Mn) ≧ 40 mol% ··· 1 ≦ (Al / Mn) ≦ 5 ··· Satisfying oxides, that is, the oxide in the area A of FIG. An oxide was complex and an oxide that.

The oxides in the regions A and B in FIG. 1 are Al + Ti + M for Al-Ti-Mn excluding the impurity elements.
The molar ratio when n = 100 shows the composition of the oxide which is effective for refining the HAZ structure.

Region A is an Al containing Galaxite (Al ₂ MnO ₄ ).
-Mn-Ti3 is an oxide containing a major element. Region B is also a three-element system oxide and includes a region having a higher proportion of Ti. Insulator A has common physical properties
It has a much higher electric conductivity than l ₂ O ₃ and Ti ₂ O ₃ . On the contrary, in the E, D and C regions, the conductivity of the oxide is low. The present inventors have found that oxides having a high conductivity composition are effective as ferrite or acicular ferrite nuclei, and therefore, the oxides in the D and C regions are excluded in the present invention.

The oxide having the composition corresponding to the region B may be dispersed alone, or may form the composite particles with the oxide corresponding to the region A. In both cases, the oxide particles function as good ferrite nuclei or acicular ferrite nuclei.

Particles corresponding to the areas E and C may be attached to the particles in the area B or the composite particles in the areas B and A, and even in this case, they function as nuclei. However, the desired effect cannot be obtained only with particles having a composition corresponding to the regions E and C.

Further, in order to form the oxide having the composition of the regions F and G in the steel, it is necessary to excessively increase the Mn addition amount and simultaneously increase the total oxygen amount in the steel. Deteriorates, and it is difficult to apply it to applications such as thick steel plates. The composite oxide having a composition corresponding to the region D is
For unknown reasons, it was difficult to form it in steel with good reproducibility. Therefore, the oxides in the regions F and G are also excluded from the scope of the present invention.

Mn, Ti, and Al have strong deoxidizing power in this order, and Ti and Mn do not form an oxide after Al is added. Therefore, in order to form a complex oxide corresponding to the regions A and B in FIG.
.About.1%, Ti.about.100 ppm, and a trace amount of Al must be controlled and supplied to the molten steel to solidify. At this time, depending on the ratio of Ti and Al amount, the regions A and B
The amount of oxide formation changes.

In addition, adding a strong deoxidizing element such as Al, Ca, Mg, Y, Zr, and Hf in the preliminary deoxidizing step on the way to the final deoxidizing is to add molten elements of these elements to the molten steel. As long as the dissolved amount is 5ppm or less and it can be kept substantially undissolved, it is acceptable.

The oxide in the region B is unstable if it does not contain Al, and it tends to be difficult to stably disperse it in the steel. For this reason, it is desirable to contain 0.5 mol% or more. However, for the refinement of the structure, Al
Since the effect is exhibited even when the ratio is less than 0.5 mol%, the lower limit of the amount of Al is not set in the invention range of the region B.

As the metal elements constituting the oxide in the steel material, there are Ca, Mg, Y, Hf, etc. in addition to Al, Ti, Mn. However, oxides other than Al, Ti, and Mn are unavoidable impurities for the oxides defined by the present invention. Therefore, even if the ratios of Al, Ti, and Mn satisfy the expressions (1) to (5), the desired effect may not be obtained when the mixing ratio of Ca, Mg, or the like increases.

In the present invention, the effect of mixing the impurity element is confirmed only up to 30 mol%. Therefore, as shown in the formula, the upper limit of the impurity mixing ratio of oxides other than Al, Ti, and Mn is 30 mol% of all metal elements constituting the oxide.

FIG. 2 shows the composition range of the present invention by plotting the amount of the impurity (metal) element mixed in the oxide at the apex of the tetrahedron.

Next, the dispersed number of oxides can be adjusted by the cooling rate during solidification, and the dispersed number tends to increase as the cooling rate increases. When casting a large steel ingot, it is difficult to increase the cooling rate and the number of dispersed particles decreases, but if 4 or more particles / mm ² are dispersed, sufficient HAZ toughness can be secured. This dispersed number can be easily achieved when cast by a continuous casting facility.

The integrated oxide in which the oxides in the regions A and B are bonded is counted as one.

The steel of the present invention can be manufactured in a laboratory scale or in an actual process. Particularly, it is desirable that the casting in the actual process is performed by the continuous casting method. This is because not only is the production efficiency higher and more economical than the ingot, but also the cooling rate during solidification is high and the oxide is easily dispersed.

The slab thus obtained is subjected to normal rolling, controlled rolling, and controlled rolling in combination with controlled cooling, and quenching / tempering or normalizing and a combination of both. However, the effect of the dispersed oxide defined by the present invention is not adversely affected.

The reasons for limiting each component will be described below.

C : 0.01 to 0.25% C is an element necessary for securing strength, and if 0.01% is not contained, steel having practical strength cannot be produced. However, since C is a deoxidizing element, when it is contained in a large amount, it affects the formation of an oxide, and particularly inhibits the formation of an oxide containing Mn. Therefore, the upper limit of C is 0.25%.

Si : 0.6% or less Si is an element effective for preliminary deoxidation of molten steel, but excessive addition not only promotes island-like martensite formation in the HAZ part, but also 0.6%. If it exceeds, it hinders the formation of an oxide containing Mn. Therefore, the upper limit is set to 0.6%.

Mn : 0.3 to 3.0% Mn is an element necessary for ensuring strength, and is also necessary for preliminary deoxidation and formation of an oxide used in the present invention. % Or more must be added. But,
Since excessive addition causes a large deterioration of HAZ toughness,
It should not be added in excess of 3.0%.

P : 0.03% or less P is an unavoidable impurity, but since it is an element that causes intergranular cracking in the HAZ portion, in the present invention, it is 0.
The upper limit is 03%.

S : 0.01% or less S is an unavoidable impurity, and when it is present in a large amount, it causes weld cracking and forms inclusions such as MnS that can be the starting point of cracking, and therefore exceeds 0.010%. Must not be included. To secure HAZ toughness, 0.005
It is preferably less than%.

N : 0.0005% to 0.01% When a large amount of N is present, the toughness of both the base metal and HAZ deteriorates. Normally, Ti is added to steel to fix it in the form of TiN to render it harmless. However, when N exceeds 0.0100% and is present in the steel, HAZ is added regardless of the amount of Ti added.
Toughness tends to deteriorate. Therefore, N is 0.0100%
Should not be contained in excess of this value, and this value is the upper limit.

Further, it is very difficult to reduce N to less than 0.0005% in actual production, and this value is set as the lower limit value in the present invention from the viewpoint of economical efficiency.

TiN suppresses the growth of γ grains in the HAZ portion and makes the HAZ structure finer. Therefore, in ordinary welding steel, N may be contained to some extent in order to secure the amount of dispersion. Many.

However, when high heat input welding is carried out as in the present invention, TiN is often exposed to high temperature and is melted and lost, thus losing its effectiveness. Moreover, in the present invention, the γ grains are substantially refined due to the precipitation of acicular ferrite.
Coarsening of the grains does not have much adverse effect, and the merit of TiN dispersion is small. Rather, in order to secure high-temperature ductility and facilitate production such as continuous casting, it is preferable that the N content be low, and even if it is 0.0005%, no problem occurs.

O : 0.0010 to 0.007% In the present invention, an oxide dispersed in steel is used, so a lower limit is required for oxygen, and 0.001% or more is contained.

On the other hand, when the oxygen content exceeds 0.007%, the cleanliness of the steel is significantly deteriorated even if the oxygen is sufficiently fixed by Al, Ti, etc., so that both the base metal and HAZ are practical. Toughness cannot be obtained.

Ti : 0.003% to 0.03% or less Ti is necessary for fixing N to secure high temperature ductility and as a constituent element of the dispersed oxide.

To obtain these effects, the Ti content needs to be 0.003% or more.

However, if Ti exceeds 0.03% and is excessively present, TiC precipitation in the HAZ increases and hardens, which deteriorates the toughness, which is not preferable. Furthermore, it is made difficult to form the conductive oxide defined in the present invention, and Ti ₂ O ₃ which does not have the effect of refining the structure is increased.
Therefore, the upper limit of the Ti content is 0.03%.

Al : 0.02 or less Al should not be added excessively because it causes the oxide in the steel to become alumina when it is contained in excess. Therefore, the content must be 0.02% or less.

B : 0.00005 to 0.002% B is an element effective for increasing the hardenability of the γ grain boundary and increasing the base metal strength even in a small amount, but in the HAZ part, the toughness is low. Since a hardened structure is formed, it is usually not preferred from the viewpoint of ensuring HAZ toughness.

However, in the present invention, the nucleation site oxide is dispersed in the steel and functions as a very effective nucleation site for acicular ferrite regardless of the presence or absence of B. Therefore, if the addition of B is acceptable and the addition amount does not exceed 0.002%, the HAZ toughness remains at an acceptable level even if it deteriorates.

Further, B selectively increases the hardenability of the γ grain boundary, and therefore increases the precipitation amount of the intragranular ferrite when an appropriate intragranular nucleation site exists. When the oxide according to the present invention is dispersed in steel, this effect is observed even when the B content is 0.0001% or less. Therefore, if necessary, a slight amount of B is controlled and contained in order to stabilize the product performance. From such a viewpoint, the lower limit of the content of B is 0.00005 %.

On the other hand, if it exceeds 0.002%, performance deterioration cannot be avoided, so this value is made the upper limit.

Cr, Mo, Cu, Ni, Nb and V These elements not only make it possible to produce a steel material having excellent strength and toughness by adding appropriate amounts, but
If the addition amount is appropriate, the hardenability is moderately increased to promote the precipitation of acicular ferrite.

However, when Cr exceeds 1.5%, Mo exceeds 1.5%, Cu exceeds 2.0%, Ni exceeds 3.0%, Nb exceeds 0.5%, and V exceeds 0.5%, The hardenability of steel is excessively increased and the HAZ toughness tends to be impaired. Therefore, it should not be contained in excess of these values.

Zr, Ca, Mg, Hf, Y and rare earths These elements can increase the number of oxides dispersed in the regions A and B by adding them to the molten steel prior to adding Al, Ti and Mn. I can. Zr, Ca, H except Mg
f, Y, and rare earth elements also have high ability to form sulfides,
It is also added for the purpose of fixing excess S.

In order to obtain such an effect, Zr of 0.
02% or less, Ca 0.004% or less, Mg 0.00
4% or less, Hf 0.02% or less, Y 0.02% or less, and rare earth 0.02% or less. As the rare earth element, Ce, Nd, or the like may be used alone.

If the content of these elements exceeds the upper limits, it becomes difficult not only to form the desired oxide in the steel specified in Fig. 1, but also to clean the steel material in some cases. The deterioration of the steel quality causes deterioration of the steel quality itself.

[0068]

EXAMPLES Steels of the present invention having the components shown in Tables 1 and 2 and comparative steels having substantially the same components as those of the present invention but having different dispersed oxides were prepared. Of these steels, Nos. 1, 3, and 6 were melted in the actual operation process, and the others were melted 180 kg test steel ingots. In the actual operation process, all castings were performed by the continuous casting method.

[0069]

[Table 1]

[0070]

[Table 2]

These cast slabs and steel ingots are rolled to have a plate thickness of 40 mm.
Steel plate.

Reproduced HA to investigate the toughness of the welded HAZ part
The investigation was conducted by a Z toughness test.

The reproduced HAZ test was conducted in the longitudinal direction of the rolled steel plate,
After obtaining the test piece material of width 11mm and length 60mm and heating it up to the maximum heating temperature of 1400 ℃, continue to 80
In order to cool to 0 ° C. and to provide cooling conditions corresponding to medium heat input to ultra-high heat input welding of thick steel plates, 800 to 500 ° C.
The cooling was performed in four different ways, namely, 30 seconds, 60 seconds, 120 seconds, and 180 seconds (this cooling time is Δt).

In this way, the test piece to which the heat history was given was JI
It processed into the No. S4 Charpy test piece and used for the impact test.

Regarding the dispersion state of the oxide, a test piece was taken from the rolled steel sheet, and a portion 10 mm from the surface was investigated. An energy dispersive X-ray analyzer (SEM-EDX) was used for counting the dispersed oxides.

In the steel of the present invention, there are various kinds of oxides in the steel and they are often dispersed as composite particles having a diameter of 0.5 to 10 μm, which are composed of oxides of 2 to 3 phases. is doing. The composition of each oxide constituting the composite particles was investigated by EDX.

When S is detected, all are MnS.
The value obtained by subtracting the S content from the measured value of Mn was taken as the amount of Mn in the oxide.

The survey results are shown in Tables 3 and 4. In the table, the oxide particle dispersion number shows an average value at 20 points.

[0079]

[Table 3]

[0080]

[Table 4]

In the steels of the present invention (1 to 8, 17 to 27), oxides having compositions corresponding to regions A and B in FIG. 1 are dispersed in the steel, and high HAZ toughness is secured.

Although oxides having a composition other than the regions A and B are found, the HAZ toughness is poor unless the oxides in the regions A and B are sufficiently dispersed, as is clear from the comparative example.

3 to 9 are No. 21, 8, 4, 18, 1
It is the figure which plotted the composition analysis result of the oxide in steel about 0, 14, 11, and FIGS. 3-6 is this invention example, FIG.
9 to 9 are comparative examples.

In FIGS. 3 to 6, oxides having a composition within the range of the present invention are sufficiently formed, and excellent HAZ toughness is obtained as shown in Tables 3 and 4.

However, in FIG. 7, since Al was added in the stage of molten steel before solidification, it was an oxide of Al center and HAZ toughness was poor. Also, FIG.
Since the Al content was too small, the oxide had a composition close to that of Ti ₂ O ₃ , which is an insulator, and the HAZ toughness was also poor. Further, FIG. 9 shows the analysis results of No. 11, and as shown in Table 1, the Ti addition amount is below the range of the present invention, and the Al amount is small, so that an oxide having an excessively high Mn amount is present. Has been formed. For this reason, this steel has a decrease in toughness due to insufficient deoxidation, and in addition, in welding HAZ,
Since the oxide does not form a ferrite nucleus, the toughness is poor.

As described above, the oxides defined by the present invention are very effective in improving the HAZ toughness, and not only in the low strength component but also in the steel containing a large amount of Mn, Nb, V, etc., the HAZ. Improves toughness.

[0087]

According to the present invention, high base metal toughness and HAZ toughness can be secured in a welding steel material. As a result, it became possible to greatly improve the welding workability of the steel for welding and the safety of the welded structure.

[Brief description of drawings]

FIG. 1 is a three-phase diagram for Al—Mn—Ti showing a composition range of metal elements constituting a dispersed oxide defined by the present invention.

FIG. 2 shows the fourth element in addition to Al-Mn-Ti.
It is a figure showing the range of the present invention when Ca, Mg, Hf, Y, and REM are added.

FIG. 3 is a three-phase diagram in which the results of composition analysis of dispersed oxides of steel type 21 are plotted.

FIG. 4 is a three-phase diagram in which the results of composition analysis of dispersed oxides of steel type 8 are plotted.

FIG. 5 is a three-phase diagram in which the composition analysis results of the dispersed oxide of steel type 4 are plotted.

FIG. 6 is a three-phase diagram in which the composition analysis results of the dispersed oxide of steel type 18 are plotted.

FIG. 7 is a three-phase diagram in which the composition analysis results of the dispersed oxide of steel type 10 are plotted.

FIG. 8 is a three-phase diagram in which the composition analysis results of the dispersed oxide of steel type 14 are plotted.

FIG. 9 is a three-phase diagram in which the composition analysis results of the dispersed oxide of steel type 11 are plotted.

Claims (5)

(57) [Claims] 1. C: 0.01 to 0.25% by weight,
Si: 0.6% or less, Mn: 0.3 to 3%, P: 0.0
3% or less, S: 0.01% or less, N: 0.00055
0.01%, O: 0.001 to 0.007%, Ti:
0.003 to 0.03%, Al: contains 0.02% or less, the remaining portion is a steel consisting of Fe and unavoidable impurities, the oxide particles are dispersed in the steel material, the oxide A steel material having excellent weld heat affected zone toughness, characterized in that Ti, Mn, and Al in the particles satisfy the following formulas to have an average dispersion density of 4 or more per 1 mm ² . In terms of mol ratio, (Ti + Mn + Al)> E × 0.70 ... Here, E = total metal elements constituting the oxide. Here, in the mol ratio when Ti + Mn + Al = 100, Ti + Mn) ≧ 80 mol% ··· 50 mol% ≧ Mn ≧ 7 mol% ··· 2. In % by weight, C: 0.01 to 0.25%,
Si: 0.6% or less, Mn: 0.3 to 3%, P: 0.0
3% or less, S: 0.01% or less, N: 0.00055
0.01%, O: 0.001 to 0.007%, Ti:
It contains 0.003 to 0.03%, Al: 0.02% or less, and further B: 0.00005 to 0.002%, Cr:
0.05 ~1.5%, Mo: 0.07 ~1.5 %, C
u: 0.02 to 2%, Ni: 0.01 to 3%, Nb:
0.014 to 0.5% and V: 0.015 to 0.5%
A steel material containing at least one of the above and the balance being Fe and unavoidable impurities, and oxide particles dispersed in the steel material. Ti, Mn, and Al in the oxide particles are shown below. A steel material having excellent toughness in the weld heat affected zone, which satisfies the expression (1) to (4) and has an average dispersion density of 4 or more per 1 mm ² . In terms of mol ratio, (Ti + Mn + Al)> E × 0.70 ... Here, E = total metal elements constituting the oxide. Here, in the mol ratio when Ti + Mn + Al = 100, Ti + Mn) ≧ 80 mol% ··· 50 mol% ≧ Mn ≧ 7 mol% ··· 3. C: 0.01 to 0.25% by weight,
Si: 0.6% or less, Mn: 0.3 to 3%, P: 0.0
3% or less, S: 0.01% or less, N: 0.00055
0.01%, O: 0.001 to 0.007%, Ti:
0.003 to 0.03%, Al: contains 0.02% or less, the remaining portion is a steel consisting of Fe and unavoidable impurities, the oxide particles are dispersed in the steel material, the oxide The particles are oxide particles in which Ti, Mn, and Al in the oxide particles satisfy the following formulas and oxide particles satisfying the following formulas, and the average dispersion density thereof is 1 m.
Steel material with excellent toughness in the weld heat affected zone, characterized in that it is 4 or more per m ² . In terms of mol ratio, (Ti + Mn + Al)> E × 0.70 ... Here, E = total metal elements constituting the oxide. Here, in the mol ratio when Ti + Mn + Al = 100, Ti + Mn) ≧ 80 mol% ··· 50 mol% ≧ Mn ≧ 7 mol% ··· (Al + Mn) ≧ 40 mol% ··· 1 ≦ (Al / Mn) ≦ 5 ·· ... 4. C: 0.01 to 0.25% by weight,
Si: 0.6% or less, Mn: 0.3 to 3%, P: 0.0
3% or less, S: 0.01% or less, N: 0.00055
0.01%, O: 0.001 to 0.007%, Ti:
It contains 0.003 to 0.03%, Al: 0.02% or less, and further B: 0.00005 to 0.002%, Cr:
0.05 ~1.5%, Mo: 0.07 ~1.5 %, C
u: 0.02 to 2%, Ni: 0.01 to 3%, Nb:
0.014 to 0.5% and V: 0.015 to 0.5%
A steel material containing at least one of the above and the balance being Fe and unavoidable impurities, and oxide particles dispersed in the steel material.
Welding heat effect, characterized in that Al is an oxide particle satisfying the formulas shown below and an oxide particle satisfying the formulas shown below, the average dispersion density of which is 4 or more per 1 mm ^2. Steel material with excellent toughness. In terms of mol ratio, (Ti + Mn + Al)> E × 0.70 ... Here, E = total metal elements constituting the oxide. Here, in the mol ratio when Ti + Mn + Al = 100, Ti + Mn) ≧ 80 mol% ··· 50 mol% ≧ Mn ≧ 7 mol% ··· (Al + Mn) ≧ 40 mol% ··· 1 ≦ (Al / Mn) ≦ 5 ·· ... 5. Further , in% by weight, Zr: 0.02% or less,
Ca: 0.004% or less, Mg: 0.004% or less, H
The welding according to any one of claims 1 to 4, which contains at least one of f: 0.02% or less, Y: 0.02% or less, and rare earth element: 0.02% or less. Heat-affected zone Steel with excellent toughness.