JPS61133363A - 60kg/mm2 high tension steel having superior plating crack resistance in weld heat-affected zone - Google Patents

Abstract

PURPOSE:To improve considerably the crack resistance by establishing certain relations among the alloying elements. CONSTITUTION:The composition of a high tension steel is composed of, by weight, 0.11-0.2% C, <0.3% Si, 0.6-2% Mn, <0.06% S, <0.1% Al, <0.014% N and the balance Fe with inevitable impurities, and relations represented by equations I, II are simultaneously established among the alloying elements. The composition may further contain one or more among <2% each of Cu and Ni, <0.5% each of Cr and Mo, <0.12% each of V and Nb, <0.03% each of Ti and Zr, and <0.001% each of Ba and Ca.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a welding heat-affected zone with excellent plating resistance.
/ About 2 high tension wires.

(Prior art) Conventionally, anti-rust coatings made of K.1 materials have been used to plate Zn etc. on steel Q relics from the et point.

These platings are extremely effective in anti-corruption, or the br of steel;
i,,'M Depending on the shape of the artifact and the method of immersion in the plating bath, cracks may occur in the weld heat affected zone, which is considered a problem. This current house has been known for a long time as a MK gold metal carcass, but in recent years, as artifacts have become larger and the steel used has become stronger, cracks have been occurring frequently, and various efforts have been made to improve this. Research is progressing and some results have been published.

For example, You and Copper, March 1982 (vot 69, Ma 5)
On page 364 of , there is a review of embrittlement of molten zinc in the heat-affected zone of layer contact entitled ``Hot-dip zinc embrittlement in the bath contact zone''. According to this, the susceptibility to bath molten Zn has a good correlation with the hardness of the weld heat-affected zone, and in order to reduce this, it is effective to reduce the hardness of the weld heat-affected zone. That is clear.

On the other hand, the present inventors have so far reported in Japanese Unexamined Patent Application Publication No. 58-849 regarding steel materials with excellent resistance to welding heat-affected zone cracking.
Proposals have been made in Publication No. 59, Japanese Patent Application Laid-Open No. 59-50157, etc. However, in all of these proposed techniques, the C content is in a relatively low range of 0.04 to 0.11 inches.

However, the embrittlement of molten Zn that occurs in the weld heat-affected zone is frequently observed even in steels with a C content of 0.11 to 0.20%, and preventive measures have not yet been established. .

(An unsuccessful means to solve the problem) As a result of extensive experiments and research, the present inventors succeeded in quantifying the influence of various alloying elements on the mating resistance. By satisfying certain relationships,
Based on the embrittlement of heat-affected zone of copper, we have discovered a new technology not previously known that has made it possible to dramatically improve resistance to metal cracking, and completed the present invention. This is what I did.

That is, the first invention of the present invention has C: 0.11 to 0 in weight%.
．． 20%, Si 20, 30% or less, Seed: 0.6-2.0
%, S: 0.06% or less, Al: 0.10% or less, N:
0.014 or less, the balance consists of Fe and unavoidable impurities, and C+ Si/30 +i&in/10-8/2
<: 0.36 and N-Al/19.5 > 0.0
It is a 5Q iq/rtm2 high-performance dynamo with excellent resistance to cracking in the V section of the d heat shadow, which is characterized by satisfying 042 at the same time. In addition, the second uninvented invention is C in electric 'Jk%
: 0.11 to 0.20%, Si: 0.30% or less,
1VIn: 0.6 to 2.0%, S: 0.06% or less, Al: 0.10 width or less, N: 0.014% or less,
Furthermore, Cu and Ni are each contained at 2% or less, -Cr, M
o is 0.015% or less, v and Nb are each 0.1
2% or less, Ti and Zr each 0.03% or less, B,
Contains one or more types of Ca, each containing 0.0010 cm or less, the remainder consisting of Fe and inevitable impurities, and
+ Si/30 +i:vin/10- S/2 +
Cr/10 +i&fo/20 +V/3 +Nb/
3 + T i15 + 3 B <0.36 and N
-Ti/6.85-Al/19.5〉0.0042 is added at the same time to 5 Q Kg/wn” high tensile strength steel with excellent crack resistance in the weld heat affected zone. However, the element symbols in each of the above formulas represent the content (weight %) of each element.

The present invention will be explained in detail below.

First of all, in the present invention, 60 to 9/Tlm2 high tensile strength steel refers to steel with a tensile strength of 60 to 9/Tlm2 corresponding to 45 specified in WES 3001,
The reason why the object of the present invention is limited to such planes is that high-strength steel is prone to cracking and there is a strong desire to improve this problem.

Next, a buried field is prepared in which the content of each element is limited to the ranges described above.

C is an essential element to ensure strength, and from the viewpoint of superiority to inexpensive high-strength materials, it was set at 0.11% or more, but 0.20%
%, the bath weldability will be impaired and the resistance to cracking will be significantly reduced, so the upper limit was set at 0.20 inches.

SL is added as a deoxidizing element and to ensure strength, but if it exceeds 0.30%, it impairs plating properties, so 0.
, limited to 30% or less.

Seed is an important element in improving the mechanical properties of steel materials, but if it is less than 0.6%, its effect will not be fully apparent.
In addition, if it exceeds 25 g, the bath weldability and resistance to cracking will be significantly impaired, so the content is limited to 0.6 to 2.0%.

S is an effective element for the steel of the present invention in terms of improving galling resistance, but if it exceeds 0.060%, the toughness of the base metal will deteriorate significantly, making it unsuitable for use as a structural steel.
0.060% or less.

Al is essential as an enemy-repellent element, but if it exceeds 0.10%, it will cause deterioration of cleanliness and impair workability and cold weldability.
．． It was limited to 10% or less.

If N exceeds 0.014%, mechanical properties, #
Since it seriously deteriorates the liquid properties, it was limited to 0.014% or less.

In addition, in the present invention, the strength of the base metal and the welded hot-form w part,
Cu, Ni, Cr, M to improve toughness
It can also contain one or more of o, ■, Nb, 'f'i, Zr, B, and Ca. First, Cu, N
Although i is effective as an element for improving the strength and integrity of steel without impairing plating resistance, addition of more than 2% impairs bath weldability, so it was limited to 2.0% or less. .

Cr and Mo are effective elements for improving hardenability and strength and toughness of the base metal, but if added in excess of 0.5%, they seriously impair bath weldability and galling resistance. Therefore, 0.5%
Limited to the following.

■, Nb is added to the tetracrystalline Tl11. ＃l,
It is effective in improving toughness and is expected to have the effect of increasing strength through precipitation hardening, but when added in excess of 0.12%,
Since it impairs bath weldability and resistance to cracking, it is limited to 0.12- or less.

'Il'i, Zr is effective as an element for improving the toughness of the bath heat-affected zone, but if it is added in excess of 0.03%, the toughness of the bath heat-affected zone will deteriorate. In addition, the content was limited to 0.03% or less because it impairs the cracking resistance.

B is effective in improving hardenability and ensuring strength when added in small amounts, but the effect is saturated even if added in excess of 0.0010%, and the cracking resistance is significantly impaired. , 0.00
It was limited to 10% or less.

Ca controls the form of nonmetallic inclusions in steel and is effective in improving toughness, but if it is contained in excess of 0.0010%,
0.0.
0010% or less.

Further, in the present invention, in addition to the above-mentioned component limitations, in order to maintain the plating resistance of the weld heat affected zone, a certain relationship is established between the contents of each component: C+ Si/30+1 Vin/10- S/2 < 0
．． 36 and N-Al/19.5.20.0042 or C+ Si/30+fvin/10- S/2 +
Cr/10 +Mo/20 +V/3 +Nb/3
+ Ti15 + 3 B <0.36 and N −Ti/
It is necessary to simultaneously satisfy any combination of 6.85-Al/19.5≧0.0042, and this is based on the knowledge obtained from the following experiment.

That is, first, from the leaf material shown in Table 1, the length 17011LI
11. Process a round bar with a diameter of 10 g, and the heat input is 1700.
H
Temporary reproduction of AZ, angle 60', notch tip radius 0.5
11! Im, a depth of 2IIIIII is processed by the sun, Zn plating is applied, and then heat treatment as shown in Fig. 1 is performed.
By applying stress cycles and reproducing actual plating conditions,
The correlation between fracture strength and fracture time was determined when a simulation test was conducted.

An example of the test results is shown in Figure 2. In the figure, the horizontal axis is the rupture time, the vertical axis A is the rupture strength of the specimen without Zn plating, and Z
It is calculated by dividing the breaking strength of the n-plated specimen.

Now, in Figure 2, horizontal m4oo seconds:! In this case, the corresponding im of A (denoted as K) can be found for each steel. In this case, 40
The reason why 0 seconds was used as the standard was based on the actual plating time.
The standard is set at 400 seconds.

The values are listed in Table 1. Table 1 also shows the restrained joint test results, direct quenching, quenching resetting,
Base material strength under various manufacturing conditions such as normalizing and controlled rolling is also listed.

This restrained joint test is a test method in which a test piece is prepared as shown in FIG. 3, then immersed in a Zn bath at 470° C. and plated, and then cracks are generated in the toe portion of the test bead 1.

In the figure, 1 is a test bead, 2 is a restraining bead, and 3 is a restraining bead.
is a test plate, each dimension is t=15■, hz=
112 = ha = h4 = 501411, w =
150111. t=75 seaweed, the number of restraining beads 2 is 20.

The reason why the restraint bead was set to 20 passes is that this restraint bead can impart a high residual stress equivalent to the yield stress of the material to the test bead tow insertion, and if no cracking occurs under this condition, the Based on the autopsy, we naturally concluded that there was no occurrence of me.

The resistance to cracking of the material was evaluated based on the above two test properties. That is, a large number of KIK values are determined in this way, and the correlation between the KIK values and the chemical composition is analyzed by multiple regression analysis, and the carbon equivalent formula related to the susceptibility to plating cracking C+ Si/3 is calculated.
0 +Mn/10- S/2 + Cr/10 +Mo
/20+V/3+Nb/3+Ti15+34=T was obtained. In addition, in the same formula, if it does not contain Cr or less,
T=C+Si/30+1Qfn/10-S/2. After that, the relationship between the composition of the sample steel in Table 1 and the value calculated using the same equation (hereinafter referred to as kT value) with 1 shift is calculated as 1. It is shown in Figure 4. In the figure, the O mark indicates that no cracking occurred in the restrained joint test conducted at the same time, and the 0 mark indicates that cracking occurred.

It can be seen that there is a fairly good correlation between the T value and the value, but even at the same T value, scratches may or may not occur, so it is difficult to judge the likelihood of scratches based on this T value alone. It is not appropriate to do so. As a result of further detailed analysis and examination of these data, the present inventors discovered the limitations of each ridge component as described above, and found that the amount of free N has a large influence on the characteristics, and as a limit cover, 0 .0042%
It has been found that if it is more than that, it is effective in improving resistance to cracking.

Here, the amount of free N refers to the amount of free N in the heat-affected zone of the bath.
This refers to the amount of N, which is calculated by subtracting the amount of N chemically bonded to Al and Ti after applying a thermal cycle equivalent to a heat input of 17,000 JJ/unit from the total N amount, and N - Ti/
It is expressed by the relational expression 6.85-Al/19.5. J211, if the 7 Li N amount expressed by this formula is 0.0042% or more, T (iii( is 0.3
It has been found that cracking can be completely prevented in a restrained joint test if the thickness is 6 or less.

Therefore, the data in Fig. 4 is further classified into steels that are not in the limited combination in terms of composition, and further into N-Ti/6.85-Al/1
9.5:20.0042 or N-Al/195
〉0.0042, and it is shown in Fig. 5. In the figure, the black marks indicate those where cracks occurred in the restrained joint test.

As is clear from the figure (within the range of the desludging components of the present invention, C+Si/30+Mn/10-8/2 <0.36
and N-Al/19.5 〉0.0042, or C
+ Si/30 +4vln/10- S/2 + C
r/10 +Fvfo/20 +V/3 +Nb/3
+ T i15 + 3 B <0.36 and N −T
It is clear that Zn plating cracking can be completely prevented by simultaneously satisfying any combination of i/6.85-Al/19.5≧0.0042.

Note that N-Al/19.5 or N-Ti/6.85
- The value of Al/19.5 is also listed in Table 1 as a Q value.

The effects of the present invention will be shown below in more detail through Examples.

(Example) After melting steel with the composition shown in Table 2 in a 50-meter vacuum melting furnace,
Controlled rolling and normal rolling followed by direct quenching or quenching and tempering were conducted to obtain a 60 Kf/ag 2nd class steel plate.

These steel plates were processed to reduce the thickness from one side to produce 22 restrained joint specimens shown in FIG. 3, and two repeated experiments were conducted.

The dimensions in Figure 3 are t=15cm, h+=ht=h
a, = h4 = 501ml, w = 15QW, t =
It is 75+m. In addition, the constraint path formula was set to 2o in total.

After completion of welding, the restrained joint specimen was placed in a Zn bath at 470℃ for 10 minutes.
After immersion plating for a minute, the test bead was placed face down using magnetic flaw detection to determine the presence or absence of cracks.

I, Yuki Shinkaya, have also listed it in Table 2. As is clear from these results, C, Si, &In, S, Al, N or even Cu, Ni, Cr, Mo, V,
Limit the content of lN1r, Ti, Zr, B, Ca, and C+ Si/30 + Fiin/10- S/2
<0.36 and N-ktA 9.5 >0.0042,
Or C+ Si/30 + 1Mn/10- S/2
°+Cr/10 + 1yio/20 + V/3 +
Nb/3 + Ti15 + 3 B < 0.36 and N - Ti/6.85 - Al/19.5 > 0.00
By limiting the ingredients to satisfy any of the combinations of 42 at the same time, it is possible to completely prevent plating cracking in the heat-affected zone exposed to the bath.

(Effects of the Invention) As shown in the above embodiments, according to the present invention, the resistance to plating cracking of the weld heat-affected zone, which has been considered a problem in structures that are plated from the viewpoint of rust prevention of steel, has been improved. Excellent 5
It becomes possible to provide QKq/rtrm2 steel, and the industrial effects are extremely significant.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the stress and thermal cycle of the notched round bar tensile test, Figure 2 is a diagram showing an example of the notched round bar tensile test results, and Figures 3 (a) and (b) are restraint joint test methods. A diagram showing
Figure 4 is a chart showing the correlation between values and T values and the correspondence between restrained joint test results. Figure 5 shows the influence of jK value, T value, Q value, and alloying element content on restrained joint test results. This is a chart showing the following. 1...Test bead 2...Restriction bead 3...
・Sadan board Fig. 1 Fig. 2 Epithelium @ dark space (Senin Fig. 3. (b) Fig. 4 Fig. 5

Claims (1)

[Claims] 1% by weight: C: 0.11-0.20% Si: 0.30% or less Mn: 0.6-2.0% S: 0.06% or less Al: 0.10% The following N: 0.014% or less, the balance consists of Fe and unavoidable impurities, and C+Si/
30+Mn/10-S/2≦0.36 and N-Al/
19.5≧0.0042 A 60Kg/mm^2 high-strength steel having excellent resistance to welding heat-affected zone cracking. 2% by weight C: 0.11-0.20% Si: 0.30% or less Mn: 0.6-2.0% S: 0.06% or less Al: 0.10% or less N: 0.014 Furthermore, Cu and Ni are each 2.0% or less, Cr and Mo are each 0.5% or less, V, Nb are each 0.12% or less, Ti and Zr are each 0.03% or less, B and Ca are each 0. 0010% or less of one or more kinds, the balance consists of Fe and unavoidable impurities, and C+Si/30+Mn/10-S/2+Cr/10+M
o/20+V/3+Nb/3+Ti/5+3B≦0.3
6 and N-Ti/6.85-Al/19.5≧0.0
A 60Kg/mm^2 high-strength steel having excellent resistance to welding and cracking in the heat-affected zone of welding, which satisfies the requirements of 042 at the same time.