JPS61106750A - Weather resistant steel plate of more than 16mm thickness having high weldability - Google Patents

Abstract

PURPOSE:To improve the weldability and hot cracking resistance of a weather resistant steel plate by regulating the C and P contents to a specified value each. CONSTITUTION:The composition of a weather resistant high-P steel plate of >=16mm thickness is composed of, by weight, 0.08-0.15% C, <1.0% Si, 0.5-2.0% Mn, 0.05-0.15% P, <0.04% S, <2.0% Cu, <2.0% Cr, <1.0% Ni, <1.0% Al, <0.008% N and the balance Fe. The composition may further contain one or more among <0.1% Nb, <0.15% V, <0.1% Ti and <1.0% Mo. The weather resistant steel plate has improved weldability and improved hot cracking resistance at a weld zone because the C and P contents are restricted as mentioned above.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application for Mold Cracking] The present invention relates to a weathering steel plate with good weldability, and is intended to improve hot cracking, which has been a problem in the past.

[Conventional technology]

In recent years, the use of unpainted weather-resistant steel has been increasing in order to save on painting costs and make it maintenance-free.

The currently used steel is Cu-N according to JIS.
i-Cr weathering steel for welded structures and high P weathering steel are standardized.

Among these, the Cu-Ni-Cr system has low P and good weldability, but is generally considered to have inferior weather resistance compared to the high-P system.On the other hand, although it has superior f'L7j weather resistance to the high-P system, Due to the high P content, there are problems with weldability, especially hot cracking.
Therefore, it is limited to relatively thin steel plates with a thickness of 16 mm or less.

Various proposals have been made in the past in order to improve the drawback of hot cracking in high P-based high weathering steel.
For example, Japanese Patent Publication No. 55-36061 and Japanese Patent Publication No. 56-95
Proposal No. 36 is known.

In the former invention of Japanese Patent Publication No. 55-36061, in order to prevent high temperature cracking, C≦0.08% and Mn/'8≧70.
On the other hand, in JP-A No. 56-9356, it is stated that high temperature cracking can be prevented by setting C≦0.07 t% and N≦0.00t%.
However, these inventions basically aim to improve hot cracking properties by lowering carbon content.

However, according to the research of the present inventors, hot cracking is more likely to occur in the above-mentioned low C region in high P-based high weathering steel, and that to prevent hot cracking j゛1 the amount of C must be increased. It has become clear that it is necessary to limit the amount within an appropriate range.

High-temperature cracking is more likely to occur in the low C region! Japanese Patent Application Publication No. 5
Although it is also stated in No. 8-58980, this invention does not relate to steel itself, but C: 0.005 to 0.
．． 01 When welding ultra-low C steel (alloy elements other than C are not mentioned), do we use high C welding wire to prevent high-temperature cracking? (C: 0.09 to 0.33%, preferably Ho, ta to 0.30%).

The C content of this wire is considerably higher than that of commonly commercially available welding wires (usually around 0.1 inch), and it is generally commercially available without using such special wire. It is desirable to use a steel material that does not cause high-temperature cracking even when welding wire is used.

[Summary of the invention]

In view of the above-mentioned points, the present invention aims to provide a weathering steel plate having a thickness of 7h and a thickness exceeding 16 snow, and having excellent high temperature resistance: 11. It is something.

As is well known, high-temperature cracking f'L during welding tends to occur in the initial layer within the groove or in the corner weld, and is caused by the solidification form or #:
T! ! Influenced by metallurgical factors such as the segregation of P and 8 during solidification and mechanical factors such as shrinkage and % deformation during solidification, the inventors used the Hv groove self-restricted first layer weld cracking test method. Main EC,
The hot cracking properties of a steel material with a plate thickness of 254 mm were investigated by varying the amount of P. The results are shown in FIG.

In this test method, initial beads are placed under various welding conditions, and the welds are generally arranged according to the shape of the core liquid bead (ratio of bead height to bead width). The harder the bead shape factor (bead height/bead width) becomes, the more likely hot cracking will occur. It is said that hot cracking is unlikely to occur below 0°. Therefore, the bead shape factor is 1.0 and the temperature is high.
If j, does not occur, it is judged that the steel is sufficiently usable as a welded structural steel, and the ratio of the crack-free and the f'L shoulders with the coefficient of 1.0 is plotted and compared.

As you can see from this graph, the hot cracking susceptibility is C, PR
In other words, whether the CJl of the weld metal is high or low, hot cracking is likely to occur, and there is an appropriate C-jlK range.

Furthermore, as the amount of P in the base metal increases, the susceptibility to hot cracking increases, and C
The appropriate range of quantity becomes narrower. Therefore′? fFJP series high weather resistance steel exceeds the weld metal C basin by 0.065%.
．． By setting the content to 12% or less, it is possible to prevent high cracking n. The amount of C in the weld metal is determined by the amount of C in the base metal and core material and the welding conditions, but assuming that a commercially available welding wire is used, the Cjlt! Approximately 0.0
The Cft of weld metals in combination with base metals with various C contents is between 7 and 0.13 cm, as shown in FIG.

Here, the amount of C in the weld metal exceeds the above 0.065 inch and is 0.12
% or less, exceed the C content of the base material by 0.08% or less by 0.1
It can be seen that it is necessary to set the number to 5 or less. That is,
Due to the high-temperature susceptibility of high-P weathering steel whose carbon content is limited to more than 0.08% and less than 0.15%, even if a commercially available welding wire is used, it can be used for general welded structures. It becomes equivalent to steel.

Therefore, in the present invention, tl and cz are limited to these ranges, and the ranges of other components are also limited as follows.

c: o, over os% but not more than 0.15%, si: x, not more than o%, Mn: 0.5-2.0%, P: 0.05
~0.15%, S: 0.04% or less, Cu: 2.0% or less, Nl: 1.0% or less, Cr: 2.0% or less, Al:
0.1 ratio or less, N: 0.008 ratio or less, balance iron and inevitable impurities.

Furthermore, in the second invention, Nb: o, 11 or less, V: o
, 1s% or less, Tt: 0.1% or less, Mo: 1.0
% or less or more than 12 kinds are added to the above components.

The reasons for limiting the ingredients will be explained below.

c: cH As mentioned above, 0.0.
It shall be more than 0.08 inch and 0.15% or less.

""' Si: 81 is effective as a deoxidizing and reinforcing element, but addition of a large amount impairs weldability and toughness, so the coefficient should be 1.0 or less.

Mn: Mn is an important element for ensuring strength, but 0.
If it is less than 5%, the effect is small (if it exceeds 2.0%, weldability decreases, so it is set at 0.5 to 2.0%).

P: If P is less than 0.05%, weather resistance decreases, and P is 0.15%.
If the content exceeds 1, the effect will be saturated and weldability will deteriorate, so the content should be set at 0.05 to 0.15%.

S: S is 0,0 because it does not reduce the base metal properties and weldability.
Must be 4 inches or less.

Cu, Cr: Cu and Cr are elemental concentrates that are effective for weather resistance.Addition of large amounts will impair weldability, so the content should be 2.0 or less.

AA: Al is effective in deoxidizing, but if it exceeds 0.1%, the effect is saturated, so it should be 0.1% or less.

N: N is o, o which does not deteriorate the main material properties and weldability.
It shall be less than or equal to oschi. ;Nb,V
, Ti, Mo: are effective as above (gt'x strength, toughness), but addition of large amounts impairs weldability. Nb: 0.1% or less, V: 0.15% or less, Ti :0
．． It is limited to 1% or less, Mo: 1.0% or less.

〔Example〕

The chemical composition of a steel plate with a thickness of 25 m is shown below in Table 1, which shows an example of the invention. mA,
B, C, and D are uninvented steel, and steel TA, F, and G.

H, I, and J are comparative steels. Table 2 shows the tensile properties and weldability of the steel plates. All of the steels of the present invention exhibited good weldability in the V-groove self-restricted first layer weld cracking test, with a bead shape ratio of a1.0 and no high-temperature cracking n occurring.

ratio'! 2. The high temperature cracking properties of f and J are good, but these are in accordance with the appropriate range for low Pt furnace (, C content or low P system). 0 showing the groove shape and bead shape of the layer weld split test

[Brief explanation of the drawing]

Figure 1 shows hot cracking resistance, P-i of base metal and cH of weld metal filling.
Graph showing the relationship between the C view of the second welding full bending and the Ct of the foil plate. Figure 3 shows the groove shape and bead shape of the V-groove constrained first layer weld crack n test. FIG. 1 person who has issued a patent Nippon Kokan Co., Ltd. Inventor Kota Hatakeyama Immediate question
Tsutomu Ikoma Agent Masu Physician Sho Yoshihara 34
Attorney Takahashi Bedo
Yoshihara Hiromu Children 1 Ct of the Zuma-bakushu groove (%) Figure 2 CG of Shioji I ('/,) Figure 3, Sword procedure amendment (1,) ++r+ pII, 59 ++/February, t ah Commissioner of the Patent Office Gu, Mr. Tadashi Manabu (Examiner of the Patent Office)
1) Indication of the incident Showa S9, Permit Application No. 22'7qtA2, 2 Name of the Invention, Voice of the Invention ΔI et al. , (d! 2) Day 2; Shu 11th Office: 4. 4. Agent 5. Date of amendment order) 14. Yu 1st supplement
Correct Content 1 At the end of the 4th line on page 3 of the specification of the present application, there is “Unexamined Japanese Patent Publication No. 56-95
36 is corrected to read ``Unexamined Japanese Patent Publication No. 56-9356.'' The following addition is made between lines 12 and 13 of page 8 of the second edition. r N (: Nl is an effective element for weather resistance, but it should be 1.096 or less in consideration of economic efficiency. "Figure 2" in the drawings attached to this application is corrected as shown in the attached sheet. Part 2 Figure (Same talent C! (%)

Claims (1)

[Claims] 1.C: more than 0.08% and 0.15% or less, Si: 1.
0% or less, Mn: 0.5-2.0%, P: 0.05-0
．． 15%, S: 0.04% or less, Cu: 2.0% or less,
Cr: 2.0% or less, Ni: 1.0% or less, Al: 0.
1% or less, N: 0.008% or less, and the balance consists of iron and unavoidable impurities, and has a thickness of more than 16 mm and has good weldability. 2, C: more than 0.08% and less than 0.15%, Si: 1.
0% or less, Mn: 0.5-2.0%, P: 0.05-0
．． 15%, S: 0.04% or less, Cu: 2.0% or less,
Cr: 2.0% or less, Ni: 1.0% or less, Al: 0.
1% or less, N: 0.008% or less, further Nb: 0.1%
Below, V: 0.15% or less, Ti: 0.1% or less, Mo
: A weather-resistant steel plate with good weldability, having a thickness of over 16 mm and containing one or more of the following: 1.0% or less, with the balance being iron and unavoidable impurities.