JPS59190313A - Manufacture of steel material having superior weldability - Google Patents

Abstract

PURPOSE:To manufacture a steel material having superior weldability by deoxidizing molten steel with Ti or a Ti alloy. CONSTITUTION:Molten steel predeoxidized with one or more among Si, Mn and Al as reuired is deoxidized with Ti or a Ti alloy, and one or more among Al, Ca, Mg, Zr and a rare earth element are added to the deoxidized molten steel as required. A steel material having superior weldability, especially a steel material having superior toughness at its weld heat-affected zone can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a steel material with excellent weldability, and particularly to a method of manufacturing a steel material with excellent toughness in a weld heat affected zone.

In recent years, requirements for the material properties of steel sheets for welding have become stricter, and in particular, it is desired to improve the low-temperature toughness of welded parts. Generally, when steel materials are welded, the boundary between the base metal and the weld metal (hereinafter referred to as the weld bond) and the weld heat affected zone (hereinafter referred to as HAZ) near the weld bond are formed in the weld.
Normally, the toughness of steel deteriorates the most, and the cause of this is said to be mainly due to coarsening of austenite crystal grains.

Therefore, as a measure to improve the toughness of the weld joint (IAZ), methods have been proposed to refine the structure of these parts.

One method is to precipitate fine nitrides such as TiN'p ZrN to prevent coarsening of austenite grains, but in order to effectively utilize these precipitates, it is necessary to change the steelmaking or rolling process. It was necessary to strictly control the vertical precipitates to be uniformly and finely dispersed in the steel. Furthermore, even if dispersed in this way, the precipitates will dissolve or even become coarse during welding, especially during high heat input welding, and there is a problem that the desired effect cannot be obtained at the weld bond area and HAZ.

In addition to the precipitation of TiN, rare earth elements (La.

A method has also been proposed in which γ grains are refined by adding Ce) and Ca to form fine oxides or sulfides, and ferrite is nucleated around the oxides or sulfides to refine the ferrite. ing. However, Ti
As mentioned above, N dissolves during the welding heat cycle and loses its effectiveness in preventing γ-grain formation, while the weld bond becomes brittle because it is difficult to have sufficient oxides present. It has not yet been possible to completely solve the growing problem.

In general, the use of oxides to refine the ferrite structure is superior in principle to improving the material quality of welds because oxides are thermally stable compared to nitrides, but Currently, there is no economical means to finely disperse the particles.

That is, conventionally, for example, Ti + Zr + Ca,
When adding elements that have a strong affinity for acid systems, such as Mg, to steel, it is necessary to first add AI to molten steel to sufficiently deoxidize it, and then add these elements to improve yield. It has been. In other words, in the conventional method, the oxygen butential content of molten steel is sufficiently reduced to prevent oxidative consumption of these elements while promoting the formation of nitrides (TIN, ZrN) or sulfides (CaS, Mgs).
Since the purpose is to fix N or S, it is natural that the oxides remaining in the steel are h1203.
The main products were MnOr 5i02.

In response to this, the present inventors have intensively investigated a method of finely dispersing oxides in steel to improve the toughness of the weld bond and H'AZ.If molten steel is deoxidized with T1 or T1 alloy, welding It has been found that the toughness of the bond part and HAZ is significantly improved.

That is, the present inventors deoxidized molten steel with various elements for the purpose of improving the material quality of the welded part with fine oxides, rolled and heat-treated a steel ingot containing the deoxidized products, and processed the obtained steel plate. Welded parts were welded, and the Charpy @ impact characteristics and microstructure of the welded parts were examined in detail. Table 1 shows the order of addition of elements to the steel ingot and the chemical composition of the obtained steel material. After melting steel consisting of the basic component of 0.08 C-1,4Mn in the atmosphere, a in the table shows the steel without adding any deoxidizing agent, and b shows the conventional steel! 1lA
For C, only Ti was added.
d is the one in which ferro-Ti was added after the addition of AI, e is the one in which M was added after seven steps of T1 was added, and f is the one in which Al and Si-'Ca alloy were added at the same time after the addition of Ti. g and h are those obtained by adding Ferro Zr and Mitsushi Metal, respectively, after adding 7Ero Ti. The same table also shows the amount of oxygen after adding the alloy shown in Figure 1 for reference. After adding these alloying elements, the molten steel is immediately poured into a mold and the obtained steel ingot is heated to 1200℃.
After heating for 1 hour at a finishing temperature of 900℃, the plate thickness was 12.5
The sample was rolled to a diameter of 1.5 m, and then subjected to a norm treatment of heating at 900'C for 25 minutes. Welding was performed using a welding current of 120 OA, an arc voltage of 33 V, and a speed of 40 min. λ) Heat input: 59.4
One-pass welding is performed at kJ/11n, and as shown in FIG. A Charpy impact test piece 3 was taken at a point where lff1m was entered from the HAZ 2 side to the HAZ 2 side, and the test was conducted at -30°C. The results are also shown in Table 1 for the oldest aK. As is clear from the same table, the preparation that does not contain any strong deoxidizer (a) is -
The Charpy impact value at 30°C is extremely low.

Next, as shown in Table 1, in bl where AI was added alone and d where Al was added in advance, the oxygen content of the molten steel after AI addition was 0.0005% or less, while the average Charpy impact value Although the values are relatively good, the lowest values are all below 2 kg and 6 m, and it can be seen that there is a large variation. On the other hand, Ti or Ferro T
i was added alone or in advance (! + e * f
In r g + h, the oxygen content of the molten steel after adding the Ti source is 0.0015 Ti or more, and both the average value and the minimum value of the impact value are stable at extremely high levels, compared to conventional M alone or preceding. It became clear that the toughness was significantly superior to that of additive materials.

Furthermore, we observed the HAZ microstructure of these steels in detail,
When analyzed using an X-ray microanalyzer, steel e p
It was found that a large number of fine ferrites were nucleated from the tip-containing material in e p f h g r h. However, in steel a, Mn and Fe.

In cases b and d, although there were fine oxides mainly composed of A7, there was hardly any evidence that they promoted nucleation of ferrite. In addition, based on these study results, Ca
r Mg r Zr, La r Cer Y +
The relationship between deoxidation products and ferrite nucleation was investigated by adding each of these separately, but no preferential ferrite nucleation effect was observed, and no improvement in low-temperature toughness was obtained.

The reason why nucleation of ferrite was not observed in steel a + b + d + g r h in Table 1 is because a
is essentially Mn-deoxidized steel, so λ4nO, FeO
In b, an oxide mainly based on Al2O3 was formed, and because dFi and A7, which has a stronger deoxidizing power than T1, was added first, an oxide mainly based on M2O3 was formed,
This is because oxides were not produced or were produced in extremely small quantities.

The present invention has been made based on the above findings, and its gist is as follows.

(1) A method for producing a nail material with excellent weldability, characterized by deoxidizing molten steel with Ti or a Ti alloy.

(2) Deoxidize the molten pot with Ti or Ti alloy, then k
L, Ca * Mg r Zr + about 1 or 2F of rare earth elements? A method for making fC copper material with excellent weldability, which is characterized by the addition of the above.

(3) A method for producing a silver material with excellent weldability, which comprises deoxidizing molten steel, which has been pre-deoxidized with one or more of St, 8+In, and At, with a T1 or Ti alloy.

(4) Molten steel pre-deoxidized with one or more of St, Il#n, and AA is deoxidized with Ti or a Ti alloy, and then Atr Ca Mg r Zr
+ A method for manufacturing steel materials with excellent weldability in which one or more rare earth elements or two or more types of Fi are added.

The present invention will be explained in detail below.

First of all, in the present invention, molten steel has C:0.
01-0.23 ratio, Si: 0.01-0.5 ratio.

Mn: 0.5-3.0%, P: (1,03
% or less, S: refers to O, O'3' or less, and in addition to this, Nl: 5% or less, Cr:
1% or less, Mo: 0.5% or less, Nb: 0-15
V: 0.15% or less, Cu: 2% or less, B: 0
．． 003% or less table which one type or i! :2 fi9 or more can also be contained.

Next, in the present invention, such molten steel is
As mentioned earlier, deoxidizing with an alloy allows the Ti-containing oxide, which can be used for ferrite nucleation during γ→α transformation, that is, for refining the ferrite structure, to be uniformly dispersed. This is based on the knowledge that it is possible. In this case, the oxygen level of the molten steel is n, ooo5~o,
The oxygen level necessary to finely disperse the Ti-containing 57p compound, which effectively exhibits the effect of Ti deoxidation in the range of approximately 0.005 to 0.02 os%, is 0.0010 to 0.02.
It is in the range of 0. As for the content of Ti oxide, if Ti is present in the steel in an amount of o, ooi to 0.05%, a sufficient momme effect can be obtained.

Furthermore, the Ti alloy referred to in the present invention is sponge Ti + Ti
) Guuda, Ti block and other ferro Ti + T
It refers to i-Ni alloy, Ti-Mn alloy, 'rt-ht alloy, etc., and it is also possible to use a combination of these as appropriate depending on the purpose.

In the present invention, as mentioned above, T1 or Ti
After deoxidizing the molten steel with the alloy, base metal and H
For the purpose of further improving the strength, toughness, corrosion resistance, etc. of AZ, one or more rare earth elements such as AtrCa*Mg+Zrr can be added. The amounts of these components added are as follows: At content in lead: 0.09% or less, Ca: 0.01q6JR or less, Mg: 0.01% or less,
Zr: 0.04 or less and rare earth elements 0.01 or less are suitable, and depending on the purpose, one type or two or more types can be used in combination as appropriate. In the present invention, the rare earth elements refer to lanthanoids with atomic numbers La to No. 71 and Y.

Furthermore, in the present invention, molten steel to be deoxidized with Ti or Ti alloy may be pre-deoxidized with one or more of St+Mn*At.

One of the purposes of preliminary deoxidation is to reduce the oxygen level of molten steel to the above-mentioned T content.
Oxygen level 0.00 suitable for fine dispersion of i-oxides
By training the Ti to 10% to 0.020%,
It also helps improve the yield of raw materials.

It should be noted that the steel material obtained by the present invention can be processed by ordinary rolling. f
The Tj deoxidation method has no effect even if it is rolled, rolled, controlled rolled, combined with controlled cooling, quenched, tempered, or subjected to standard heat treatment or a combination of both. It is powerful to be influenced by

Next, the effects of the present invention will be described in more detail with reference to Examples.

Table 2 shows the order of addition of alloying elements and chemical compositions of the invention examples and comparative examples. Here A, B, D, F,
H.

J is an example of the present invention, and C, E, , G, and I are comparative examples. A-C is related to LT 33 lead and is 0.08C
-1,4Mn system, D, g are related to 50 kg class high tension canisters, 0.09 C-1,3Mn system, F, C are AP
Regarding I-X70 class, 0.05C-0.3S
i-1, 55PAn system, H, I are related to 60 kg class high tensile strength steel, 0.06 C-0,3St -1Mn
The system, J, is related to an 80 kg class high tension pot and is 0.
Copper containing 09C-0,9Mn as its main component was first melted, and then deoxidizing elements were added in the order shown in Table 2. Furthermore, for E, Ni.

Cu, Nb source, Ni*M for brass F, G
o + Nb source and Mn * Cr + for H, I
Mor V+B source, Nl r for J and K
The Cr r Mor Cu LB source was finally adjusted to the desired chemical composition.

The obtained steel ingots were further rolled under the conditions shown in Table 2, and heat-treated in the molds for A-E and quenching and tempering for H- under the conditions also shown in Table 2.

Figure 3 shows the groove shape used for welding, and Figure 2 shows the sampling positions of Charpy impact test pieces. HAZ toughness and HAZ
Examine the ferrite grain size and combine the results with the welding conditions to
Shown in the table. Examples of the present invention, A, BD, F, H, and J, are HA
It can be seen that in the Charpy impact test for Z, both the average value and the minimum value exceeded 3.5 kq-m at each test hot water temperature, showing sufficiently good GI impact values. On the other hand, C, E
, G, and I have some average values exceeding 3.5 kg-m, but the lowest values are all 3.5 kg-m.
It is below m. Further, the ferrite grain size of HAZ is also A of the present invention example.

In B, D, F, H, and J, the grain size is 100μ or less in all heat inputs, but in comparative examples C, E, G, I, and K, the grain size is 150μ or less.
It can be seen that the value exceeds μ.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the sampling positions of Charpy impact test pieces, and FIG. 3 is a diagram showing the groove shape of the welded steel material used in the example. DESCRIPTION OF SYMBOLS 1... Weld metal, 2... H house, 3... Charpy impact test piece, 4... Notch position, 5, 5'... Steel material to be welded, 6... Backing material, 7 ...Welding bond part. Figure 1 Figure 2 Procedural amendment (spontaneous) June 6, 1980 Mr. Kazuo Wakasugi, Commissioner of the Patent Office■, Indication of the case 1982 Patent Application No. 062687 2, Name of the invention Excellent weldability Manufacturing method for steel materials 3, relationship with the amended person case Patent applicant 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Nippon Steel Co., Ltd. Food Coloring Representative Takeshi 1) Yutaka 4, Shikiman 〒 100 2-4-1 Marunouchi, Chiyoda-ku, Tokyo (2) On page 9, line 10, "Exhibits Ti-containing oxides" is corrected to "Exhibits Ti-containing oxides."(3> Column A7 in black f in Table 1 on page 14 [0,015
Correct J to "o, ots, J. (4) In Table 2 on page 15, the column with the symbol P "o, o05
Correct J to 0.008J.

Claims (4)

[Claims] (1) A method for producing a steel material with excellent weldability, which comprises deoxidizing molten steel with Ti 4 or a Ti alloy. (2) A method for producing a steel material with excellent weldability, which comprises deoxidizing molten steel with T1 or a Ti alloy, and then adding 1 m or more of A11 (1, Mg l Zr + rare earth elements). (3) 81, Mn, AA! A method for producing steel materials with excellent weldability, which comprises deoxidizing molten steel that has been preliminarily deoxidized with one or more of the following using Ti or T1 alloy. (4) St, Mn, A10 type 1 or 2
A steel material with excellent weldability characterized by deoxidizing molten steel pre-deoxidized with T1 or T1 alloy, and then adding one or more of AII Cal Mg I Zr I rare earth elements. Manufacturing method.