JPS59159972A - Steel material for chain with high strength and toughness - Google Patents

Abstract

PURPOSE:To obtain the titled steel material with favorable weldability at a low cost by providing a specified composition consisting of C, Si, Mn, Cr, Mo, sol. Al, B, P, S and Fe and having a specified carbon equiv. CONSTITUTION:A steel material for a chain of a large diameter with high strength and toughness is obtd. by providing a composition consisting of, by weight, 0.10-0.30% C, 0.15-0.50% Si, 0.50-1.90% Mn, 0.50-2.00% Cr, 0.10- 0.50% Mo, 0.01-0.06% sol. Al, <=0.01% B, <=0.04% P, <=0.04% S and the balance Fe with inevitable impurities and having 0.60-0.80% carbon equiv. (Ceq.%) represented by the equation. The composition may further contain one or more among <=0.20% each of V, Ti and Nb. The steel material has about 65-95kg f/mm.<2> tensile strength and >= about 7 and 6kg f-m Charpy impact absorption energy values at 0 deg.C at the base metal and weld zone, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention has a tensile strength of 65 to 95 Kyf/-, and Charpy impact absorption energy values of the base metal part and weld part at 0°C of 7 to 9 f-m or more and 6 Kqf, respectively.
The present invention relates to a steel material for a chain that has both high strength and high toughness of -m or more.

In recent years, with changes in the energy situation, efforts to develop new energy resources have become active in various parts of the world, and as onshore development resources are depleted, offshore oil fields are attracting attention for their trenches. As a result, efforts have been made to encourage oil drilling rigs to be used in a wide range of trenches, centered around the continent, and extending south to the North Sea.

As mentioned above, with the increase in the number of offshore structures represented by offshore oil drilling rigs, the demand for large diameter chains used to moor these structures is also increasing. Recently, offshore structures such as rigs have begun to show a tendency to become more and more dog-shaped, so the chains used to moor them are also thicker, with diameters of 60 to 160 pieces, and moreover, in terms of loading weight restrictions. Since the diameter cannot be made larger than force 1, a higher strength one 75 =
It came as requested.

By the way, large-diameter chains are manufactured by cutting hot-rolled steel bars into predetermined lengths, forming them into annular shapes, and then flash-butt welding the end faces.Then, they are heat-treated to obtain the required mechanical properties. Needless to say, the best way to obtain high strength and toughness is to quench and temper the chain after it is formed.

However, the chain for the above-mentioned rigs, etc., which requires a high tensile strength of 65 to 95 K9fl-, is made of a very thick round bar with a diameter of 160w11, compared to steel plates. must also be made martensitic, so
Compared to plate materials that require high hardenability, and which can be completely cooled from the top and bottom surfaces, chains have problems such as: ■ It is difficult to cool the chain sufficiently9, and it is difficult to obtain the desired hardened structure. There was no choice but to increase the content of alloying components needed to improve hardenability. However, increasing the content of hardenability-improving components such as carbon can lead to deterioration of toughness.Moreover, as mentioned above, chains are flash butt welded after forming steel bars, but hardenability There was a concern that if the content of the improving component was high, the risk of weld cracking would increase, which would cause a new problem. Generally, in flash butt welding, there is no weld metal, so there is no risk of cracking due to hydrogen, but it is still extremely difficult to avoid the risk of cracking if the C equivalent is high.

However, in recent years, oil drilling has become more frequent in cold regions such as offshore oil fields in the North Sea, and in such regions, even minute cracks in welds can easily become a starting point for brittle fracture. and the Charpy impact absorption energy of the welded part at 0℃ is 7Kqf-
It has high toughness of more than m and more than 5Kqf -m,
Furthermore, there was a strong desire for a chain for holding large drilling rigs of stable quality and without the occurrence of warping at the welded part 1.

Of course, J-Ko 5G310 is used as a steel material for high-strength chains.
5, S and B C70 are known,9 and similar steel materials are specified in the ship standards of each country, but these standards include C1Si, Mn, P and Only the amounts shown are Ni, Or, M
The addition of O and ■ has also been suggested, but nothing has been shown about their specific addition amounts or effects.
It has not been possible to realize a large-diameter chain that has 95 K4f,'- and also exhibits satisfactory toughness in cold regions.

The present inventors have determined that the tensile strength is 65 from the above-mentioned viewpoint.
1 at ~95' Kff/mA. Moreover, the mother at 0℃
As a result of our research to provide a steel material for large-diameter chains that has both high strength and high toughness, with Charpy impact absorption energy values of 7 Kyf-m or more and 5 Kqf-m or more for the material and welded parts, we found that the toughness and welding Specific amounts of Cr and Mo, which can increase hardenability, are added to low-C, high-Mn-based steel materials whose C content, which is harmful to physical properties, is kept to the necessary minimum. If the lack of hardenability caused by limiting the carbon equivalent is compensated for by the addition of iB, the B component increases the hardenability without MB point metal processing, thereby reducing quench cracking and delayed fracture of the flash butt weld heat-affected zone. High strength can be obtained without full reinforcement, and sufficient tempering is possible due to uniform structure, resulting in stable and good mechanical properties and good quality chains with good mechanical properties and no cracking in welded parts. They found that steel materials for industrial use could be obtained. In addition, suitable amounts of V and Ti are added to such steel materials.

It has also been found that the toughness value can be further improved by adding one or more types of Nb.

This invention was made based on the above findings,
Chain steel material: 0:0.10~0.30% (hereinafter referred to as weight ratio), S
i: 0.15-0.50%, Mn: 1.00
~1.90%.

Cr: 0.50-1.5 io%, MO: 0.
10-0.50%.

sOMM: 0.01-0.06%, B: 0
．． 01% or less.

p: 0.04% or less, S: 0.01% or less.

Contains as well as necessary V: 0.20% or less, Ti: o, 20% or less.

N’b: 0.20 or less.

also contains one or more of the following, and has a carbon equivalent represented by the formula, 0.60-0.80%,
The composition consists of Fe and other unavoidable impurities: Residue, and the tensile strength is 265 to 95. Impact absorption energy of base metal and welded part at f/d and 0°C: 7 each 4f-77z or higher and 4f-m in 6
The feature is that the above has been achieved.

It should be noted that ordinary quenching and tempering is sufficient for the thermal treatment of the chain steel material of the invention, but if quenching and tempering is performed after normalization treatment, the crystal grains that have become coarse due to flash butt welding will become finer. This is a desirable method because it further improves the weld toughness.

In addition, since chains are usually used in seawater, corrosion may be a problem, but in such cases it is effective to add one or both of Cu and N1 to the steel material. be.

Next, in the steel for chains of the present invention, the reason why the added amounts of each component element and the carbon equivalent are limited as described above will be explained.

(a) C The C component has the effect of ensuring the hardenability of the steel material and maintaining its strength and toughness, but if its content is less than 0.10% (d) it is difficult to obtain all the desired effects on the above effects. On the other hand, if the content exceeds 0.30%, the toughness will deteriorate, and
The content was set at 0.10 to 0.30% because the probability of cracking in the welded part is high.

(b) 5i The Si component has the effect of ensuring the strength of steel materials and also acts as a deoxidizing agent, but when its content is 0
．． If it is less than 15%, the desired deoxidizing effect cannot be obtained, and nonmetallic inclusions in the steel material increase, resulting in deterioration of toughness. On the other hand, if the content exceeds 0.50'%!f, it will cause deterioration of the steel toughness, so the content was set at 0.15 to 0.50%.

(c) Mn Mn is an essential component to ensure the desired hardenability, but if its content is less than 0.50%, sufficient hardenability cannot be ensured; on the other hand, if the content exceeds 1.90%, Since this would deteriorate the toughness and weldability of the steel material, the content e was determined to be 0.50 to 1.90%.

(d) 0r The Cr component has the effect of improving the toughness of the steel material to some extent and increasing the hardenability, but when the content is 0.
If it is less than 50%, it will be difficult to secure the desired hardenability for a large diameter chain. Even if the content exceeds 0.0%, the effect of improving toughness is small and the weldability deteriorates, so the content i0.50 to 2.00
%.

(e) M.

The Mo component is an extremely effective element for improving the toughness and ensuring hardenability of steel materials, but if the content is less than 0.10%, the above effects cannot be expected; on the other hand, if the content exceeds 0.50%, If it is included, the hardenability will be excessive.

If the content is -io, 10 to 0.5, the disadvantageous result is that the cost will increase.
It was set as 0%.

(f) som M s o 1. The M component has a deoxidizing effect and also has the effect of adjusting the grain size of steel materials, but when its content is 0.01
If the modulus is less than 0.06, a sufficient grain refining effect cannot be obtained, which may cause deterioration of toughness, while if it exceeds 0.06, alumina-based nonmetallic inclusions in the steel material will increase, possibly causing deterioration of toughness. ° et al., its content is 001~0.06
%.

jg) B The B component has the effect of completely improving the hardenability of the steel without changing its MS point, and this can be suppressed by limiting the amount of alloying elements added that are harmful to the occurrence of cracks in welds by carbon equivalent. Although it is an indispensable component to effectively improve the hardenability of hardenability, even if it is contained in an amount exceeding 0.01%, it not only shows an even more remarkable effect of improving hardenability, but also improves toughness. The content was set at 0.01% or less, as it may cause deterioration in some cases.

(h) P and S Both P and S are impurities that cannot be avoided in steel manufacturing, but their contents are Q and 040, respectively.
If the P and S contents exceed 0.040%, the toughness of the steel material will deteriorate beyond the allowable limit.
It was determined as follows.

(i) V, Ti, and Nb All of these components have the effect of precipitating carbides, carbonitrides, or nitrides in steel to refine the grains of steel and improve toughness. , 91 or more species are added as necessary, but the content of each is 0.20.
If the content exceeds 0.2%, the above-mentioned effect will not be obtained due to the above-mentioned action, and the cost of the steel material will increase.

(j) Carbon equivalent (Ceq,) When the carbon equivalent of the steel material exceeds 0.80%, the probability of cracking in the flash butt weld increases rapidly, making it difficult to manufacture stable chains. If the carbon equivalent is less than 1, it will not be possible to ensure substantially sufficient hardenability and the strength and toughness of the steel material will be completely deteriorated, so the carbon equivalent i was set at 0.60 to 0.80.

Next, the present invention will be explained in detail by comparing examples and comparative examples.

Example First, steel having the composition shown in Table 1 was melted by ordinary atmospheric melting, and then a round steel bar having the same diameter as shown in Table 1 was obtained by hot rolling. Next, this was cut, formed into a chain by hot bending, and then flash butt welded and organized. Then, after deburring the welded part 5-P, insert the stand, and then,
Quenching = After heating at 900°C for 3.5 hours, water cooling and tempering:
After heating at 600° C. for 4.5 hours, quenching and tempering was performed under the conditions of water cooling to produce a chain.

From each chain manufactured in this manner, the following test pieces and tensile test pieces were obtained: D=14φ, GL=5D.

Impact test piece: J Engineering S4 Charpy test piece.

were sampled and their mechanical properties were investigated.

Furthermore, separately from this, the weld crack occurrence rate was also investigated for each chain, and the results are shown in Table 2.

From the results shown in Table 2, the steel materials 1 to 11 of the present invention exhibit good mechanical properties and weldability, while the compositional component amounts or carbon equivalents (Ceq, ) are marked with *. It can be seen that Comparative Steel Materials 12 to 16, which are outside the scope of the present invention, have poor mechanical properties or weldability, and are unsuitable as steel materials for chains used under severe conditions. In addition, comparison steel material 12 is conventional steel 5AE13.
30, but it is clear that hardenability is low and sufficient strength cannot be obtained with this.Comparative steel material 13, which has a high carbon equivalent, shows good mechanical properties, but the cracking incidence in the welded part is low. It is obvious that it is expensive and not suitable for practical use.

As mentioned above, according to the present invention, extremely high strength and
It is possible to obtain steel materials for large-diameter chains that have excellent toughness and good weldability at a low cost, and provides extremely useful steel materials for resource development under harsh conditions. It brings about an effect.

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo and 1 other person

Claims (2)

[Claims] (1) C: 0.10-030%, Si: 0.15-050%, Mn: 0.50-1.90%, Cr: 050-2.00%, Mo: 0.10-0.50 %, Sol, M: 0.01-006%, B: 0.01% or less, P: 0.04% or less, El: 0.04% or less, and the carbon equivalent represented by the formula, 1. A high-strength, high-toughness steel material for a chain, characterized in that it has a component composition (weight %) of 0.60 to 0.80%, and the balance is 9: Fe and other unavoidable impurities. (2) C: , 0.10-0.30%, Si: 0.
15-0.50%, 1vln: 0.50-1.90%, Cr: 0.5
0 to 2.00%, Mo: Q, lQ to 0.50, soLM: 0.01 to 0.06%, B
: 0.01% or less, P: 0.04% or less, B: 0.04% or less, V: 0.20% or less, Ti: 0.20% or less, Nl): 0.20 % or less, the carbon equivalent represented by is 0.60 to 0.80%,
A high-strength, high-toughness steel material for chains, characterized by containing Fe and other unavoidable impurities and residues.