JPH1096053A - Rolled or normalized high strength steel excellent in hot-dip galvanizing cracking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a cracking from the opening part of a bolt hole for joining sections at the time of plating, at the time of producing rolled or normalized high strength sections used for an iron tower for power transmission, by specifying its compsn. and adding Ti or/and Ca thereto. SOLUTION: This steel contains, by weight, 0.08 to 0.20% C, <=0.60% Si, 1.0 to 2.0% Mn, <=2.0% Cu, <=1.0% Mo and <=0.1% V, also satisfying the conditions of Nb+0.5V+Ti>=0.08, and the balance Fe with inevitable impurities. Preferably, <=0.2% Ti and/or <=0.004% Ca is furthermore incorporated therein. This steel is subjected to hot rolling to form high strength sections of a 690MPa class, and its tensile elongation percentage in a galvanizing bath shows >=20% to prevent the generation of cracking from the periphery of the bolt hole in the process of plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-heat treated high-strength steel mainly used as a steel material for a steel tower.

[0002]

2. Description of the Related Art In recent years, high-strength steel materials for the purpose of reducing the weight of steel materials used have been actively used in various fields. Such a tendency has also appeared in steel materials for power transmission towers, and steel materials having a tensile strength of 590 MPa class are currently used. In addition, large power transmission towers are often constructed in the mountains, and further higher tension is required to reduce costs in transporting materials. Steel tower steel is hot-dip galvanized after construction to make it maintenance-free. Shaped steel for steel towers (for example, equilateral equiangular angle steel)
Can be used as a steel tower without welding, so the plating crack susceptibility of the base material is regarded as important.
In a high-strength section steel of 0 MPa or more, plating cracks occur at the time of plating from a drilled portion for joining bolts of the section steel, which is a great hindrance to high strength.

[0003] With respect to high-strength steel to be hot-dip plated, Japanese Patent Application Laid-Open No. 58-84959 and Japanese Patent Application Laid-Open No. 59-113
Techniques such as No. 16 have been proposed, but all are related to steel materials that prevent cracks that occur in welds, and there is little knowledge about high-strength steel that prevents cracks from drilled holes. It is.

[0004]

SUMMARY OF THE INVENTION The present invention fundamentally solves the above-mentioned problems, and provides a non-heat treated high-strength steel excellent in hot-dip galvanizing crack resistance of a base material. Things.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve this object, and (1) C: 0.
08 to 0.20%, Si: 0.60% or less, Mn: 1.
0 to 2.0%, Cu: 2.0% or less, Ni: 2.0% or less, Cr: 1.0% or less, Mo: 1.0% or less, Nb:
0.1% or less, V: 0.1% or less, Nb + 0.5V + T
a non-heat treated high strength steel excellent in hot-dip galvanizing crack resistance characterized by i ≧ 0.08%, balance Fe and unavoidable impurities, (2) Ti: 0.2% or less by weight ratio (1) a non-heat treated high-strength steel excellent in hot-dip galvanizing cracking resistance according to (1), and (3) further containing Ca: 0.004% or less by weight ratio. It is a non-refined high-strength steel excellent in hot-dip galvanizing crack resistance described in (1) or (2).

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have prepared 0.11C-0.
Specimens of equilateral equiangular iron by hot rolling, including steels containing 25Si as basic components and varying amounts of Mn, Nb, V, and Ti and further adding Ca (see FIG. 2) The effect of the added element on the relationship between the room temperature tensile strength and the tensile elongation in the plating bath was examined.

As a result, the relationship between the two is uniquely determined by the Nb + 0.5V + Ti value, and in the case of high-strength steel in which a bolt hole is drilled, Nb + 0.5V + Ti ≧ 0.
08 has to be satisfied. (Generally, when the elongation in the hot-dip galvanizing bath is 20% or more, it is said that cracking at the bolt hole processed portion can be prevented.) That is, as shown in FIG. 1, Nb + 0.5V + Ti
When the addition amount is 0.06%, the elongation in tension in the plating bath is low, and the elongation in high-strength steel is 20% or less.
When the content exceeds 0.08%, the elongation in tension in the plating bath exceeds 20% even in high-strength steel, and it has been found that the elongation increases with the addition of Ti or Ca or Ti-Ca in combination. . (Note that elements not contained in the formula are calculated as 0.) The reasons for limiting the added components will be described below.

C: 0.08 to 0.20% C is an essential element for increasing the strength. If it is less than 0.08%, it is difficult to obtain high strength, and if it exceeds 0.20%, the toughness of the steel is significantly deteriorated.
Limited to 20% or less.

Si: 0.60% or less Si is related to the appearance after plating, and if it exceeds 0.6%, plating burn is likely to occur. Therefore, 0.
It was limited to 6% or less.

Mn: 1.0 to 2.0% Mn is an essential element in view of strength and toughness.
If it is less than 2.0%, it is difficult to obtain high strength, and if it exceeds 2.0%, hardenability is increased, coarse bainite is generated, and toughness is significantly deteriorated. Limited to. P: Inevitable impurity level P segregates at the grain boundaries and degrades toughness, but the upper limit value is not limited, since it is sufficiently reduced by the current refining technology.
Lower is more desirable. S: unavoidable impurity level S is mainly present in the form of inclusions in steel and causes deterioration of the material due to embrittlement. However, since the current refining technology has sufficiently reduced it, the upper limit is not limited. Lower is more desirable. Cu: 2.0% or less Cu is an element effective for increasing the strength of steel.
When added in excess of 0%, Cu cracks are likely to occur. Therefore, it was limited to 2.0% or less. Ni: 2.0% or less Ni is an element effective for increasing the strength and toughness of steel, but is limited to 2.0% or less in consideration of economy. Cr: 1.0% or less Cr is an element effective for increasing the strength of steel.
If added in excess of 0%, the toughness of the steel deteriorates.
It was limited to 1.0% or less. Mo: 1.0% or less Mo is an element effective for increasing the strength of steel.
If added in excess of 0%, the toughness of the steel will be significantly degraded, so it was limited to 1.0% or less. Ti: 0.2% or less Ti is an effective element because it enhances the strength of steel by precipitation strengthening with a small amount of addition and exhibits excellent properties in hot-dip galvanizing cracking resistance. If added, the precipitates become coarse and the toughness of the steel deteriorates significantly.
The following could be added as needed. Nb: V: 0.1% or less, V: 0.1% or less Nb and V are effective elements for increasing the strength of steel by precipitation strengthening when added in a small amount. Since the toughness of the steel significantly deteriorated, the content was limited to 0.1% or less. Nb + 0.5V + Ti ≧ 0.08% Ti, Nb, and V are all effective elements for increasing the strength of steel by precipitation strengthening, but have the strength as a high-strength steel and have excellent hot-dip galvanizing crack resistance. In order to exhibit the above characteristics, it is necessary to add Nb + 0.5V + Ti ≧ 0.08%. Ca: 0.004% or less Ca is an element that can significantly improve hot-dip galvanizing crack resistance by being added. However, 0.00
If it is added in excess of 4%, Ca-OS clusters are generated and the cleanliness of the steel decreases. Therefore, Ca was limited to 0.004% or less. Al: In the present invention, Al may be added for deoxidation, in which case the usual addition amount (0.005-0.
60%). Treated as unavoidable impurities in deoxidation of Si with mold steel. B: Inevitable impurity level While B significantly improves the hardenability of steel, it significantly deteriorates the hot-dip galvanizing cracking resistance of the welded portion. Therefore, when B is welded, it is controlled to 2 ppm or less. The steel of the present invention is not targeted for welding work in principle, and has a hole drilling degree, and the upper limit of B is about 5 ppm. However, lower is more desirable.

[0011]

Examples are shown in Table 1. The steel of the present invention is manufactured by hot rolling (for example, a slab heating temperature of 1100 to 1350 ° C. and a rolling end temperature of 850 ° C. or less). In Examples, all steels were rolled into equilateral equiangular angle steel. As for the presence or absence of plating cracks in the table, the rolled angle iron is pierced in a hot-dip galvanizing bath after drilling holes for joining bolts in the same manner as in actual It is the result of confirming whether or not it occurs. 1-3 has low strength because of low C. 1-12 is Nb + V + T
Since i is less than 0.08%, the intensity level is 690M
Although it is of Pa class, cracks have occurred in the drilled portion.
1-5, 1-7, 1-8, 1-9, 1-10, 1-1
1, 1-13, 1-14 and 1-15 are Si, M, respectively.
Since the added amounts of n, Cu, Ni, Cr, Mo, Ti, Nb, and V are high and the strength is too high at 810 MPa or more, cracking occurs. In No. 1-16, the amount of Ca was high, and the cleanliness of the steel was inferior. Therefore, although the strength was at a level of 690 MPa, cracks occurred. On the other hand, 1-1, 1-2, 1-6, 1-
Nos. 17, 1-18, 1-19, and 1-20 have a strength of 690 M because the components of the test steel all satisfy the range of the present invention.
It is as high as Pa or more, and generation of cracks is not recognized.

[0012]

[Table 1]

[0013]

According to the present invention, it is possible to provide a steel material capable of preventing cracks even when hot-dip galvanizing is performed after a bolt hole is formed in a steel tower, bridge, or the like.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the room temperature strength TS (MPa) of a steel material and the elongation (y) of a tensile test in a plating bath.

FIG. 2 is a view showing a tensile test piece of a base material in molten zinc.

Claims (3)

[Claims] 1. A weight ratio of C: 0.08 to 0.20%, S
i: 0.60% or less, Mn: 1.0 to 2.0%, Cu:
2.0% or less, Ni: 2.0% or less, Cr: 1.0% or less, Mo: 1.0% or less, Nb: 0.1% or less, V:
A non-refined high-strength steel excellent in hot-dip galvanizing crack resistance, characterized by being 0.1% or less, Nb + 0.5V + Ti ≧ 0.08%, the balance being Fe and unavoidable impurities. 2. The non-refined high-strength steel with excellent hot-dip galvanizing crack resistance according to claim 1, further comprising Ti: 0.2% or less by weight. 3. The non-refined high-strength steel with excellent hot-dip galvanizing crack resistance according to claim 1 or 2, further comprising Ca: 0.004% or less by weight.