JPS59159970A - Steel material for chain with high strength and toughness - Google Patents

Abstract

PURPOSE:To obtain the titled steel material at a low cost by specifying a composition consisting of C, Si, Mn, Cr, Mo, sol.Al, N, P, S and Fe and the relation among such components and the required tensile strength of a chain. CONSTITUTION:A steel material for a chain of a large diameter with very high strength and superior toughness is obtd. at a low cost by providing a composition consisting of, by weight, 0.15-0.30% C, 0.10-0.50% Si, 1.30-2.50% Mn, 0.50-1.50% Cr, 0.10-0.60% Mo, 0.010-0.060% sol.Al, 0.003-0.020% N, <=0.040% P, <=0.040% S and the balance Fe with inevitable impurities and satisfying an equation C%+(Mn%+Cr%+2Mo%)/3>=1.25X10<-2>sigmaB+0.11 [where sigmaB is the required tensile strength (kg f/mm.<2>) of a chain]. The composition may further contain <=0.20% in total of one or more among V, Nb and Ti.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention has a tensile strength of 75 kyf/- or more, and a 7 Jarby impact absorption energy value of 5 to 7 f-m or more and 5]< 9f
The present invention relates to a steel material for a chain that has both high strength and high toughness, and has a strength 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, attention is also being focused on offshore oil fields. Now, oil drilling 11]
Development using commercial rigs has begun to take place in a wide range of areas, mainly near the continent, from the south to the North Sea.

As the number of offshore structures, typified by the above-mentioned offshore oil drilling rigs, increases, the demand for large-diameter chains used to hold them down continues to increase. Offshore structures such as drilling rigs have recently begun to show a tendency to become more and more dog-shaped, so the chains used to hold them down must be thicker, with a diameter of 60 to 160 knots, and the length of the load can be reduced. Since it is not possible to increase the diameter further due to restrictions, there has been a demand for something with even higher strength.

Incidentally, large-diameter chains are manufactured by cutting a hot-rolled steel bar to a predetermined length, forming it into an annular shape, and then welding the entire end surface in a flash butt bath.Then, it is heat-treated to obtain the required mechanical properties. It goes without saying that quenching and tempering the formed chain is the best way to obtain high strength and high toughness. Compared to steel plates, etc., the chain for stopping the above-mentioned rigs, which requires high strength, is made of a very thick center part 1 of a round bar with a diameter of 160 nm.
Since even the chain must be made into martensite, high hardening conditions are required.■ Compared to plate materials, which can be completely cooled from the top and bottom, it is difficult to cool the chain sufficiently, and the desired hardening structure cannot be achieved. However, there were problems such as difficulty in obtaining the hardenability of the steel, and it was necessary to increase the content of alloying components in order to improve the hardenability of the steel material. However, increasing the content of hardenability-enhancing components such as carbon leads to deterioration of toughness.Moreover, as mentioned above, chains are flash butt welded after forming steel bars, but increasing the content of hardenability-improving components such as carbon leads to deterioration of toughness. There was a concern that a high content would cause a new problem in that there would be an increased risk of weld cracking.

However, recently, oil drilling in cold regions such as offshore oil fields in the North Sea has increased in frequency, and in such regions even minute defects in welds can easily become a starting point for brittle fracture, so high strength is of course difficult. , the base metal part and the welding part each have 6 ky of Yarpy impact absorption energy at 0℃.
There has been a desire for a large excavation lidar holding chain having high toughness of f-m or higher and 5 to 9f-rn or higher.

Of course, JISG is used as a material for high-strength chains.
3105 with the symbol 5BC70 is known, and similar steel materials are specified in the ship standards of each country, but these standards include ClSi, Mn, P and S.
Only the component amounts of Ni, Cr, M are shown.
The addition of O and V is also suggested, but nothing is shown about their specific addition amounts or effects.
It has not been possible to realize a large-diameter chain that has more than kgf/- and also exhibits satisfactory toughness in cold regions.

From the above-mentioned viewpoint, the present inventors believe that the tensile strength is ``
”/mA or more, and at 0°C, the 7-Yarby impact absorption energy value of the base metal part and welded part is 5 and 4, respectively.
As a result of conducting research to provide steel materials for large-diameter chains that have both high strength and toughness of f-m or more and 5kyf-m or more, we have minimized the C content, which is harmful to toughness and weldability, to the necessary minimum. Is it possible to add a specific amount of Cr and H810 to low C, high Mn steel materials that can increase hardenability? In addition to achieving the desired strength, these C
It was discovered that by adjusting the amounts of alloying elements such as , Rh, Cr+, and MO, good toughness could be ensured in the welded joint.

In other words, the above-mentioned chain can be used depending on its use.
For example, tensile strength: 75 krf/- or more, 85 krf/-
Various strength levels are required, such as 95 kpf/-9, above, or 95 kpf/- or above, but by controlling the amount of the alloying elements added according to these demands, Cr, MO, etc. It has been found that this method not only increases hardenability but also extremely effectively improves toughness, and that a high-strength, high-toughness steel material with excellent hardenability and toughness can be obtained overall. Moreover, appropriate amounts of V, Ti,
They also discovered that the toughness value further increases if one or more types of Nb are added.

This invention was made based on the above findings,
The steel material for the chain is (: 0.15~0.30% (hereinafter referred to as weight), Si: 0.10~0.50%, un
: 1.3 0-2.50%.

Cr: 0.50-1.50%, Mo:
o, 10-0.60%+sot, At: 0.
010-0.060%.

N: 0.003~0.020%
.

p: 0.040 or less, s:”o, o4o% or less.

and, if necessary, one or more of V, Nb, and Ti in a total of 0.20% or less.

and the formula, [where σB: required tensile strength of the chain kgf /
mA )], and by configuring the composition with a component composition consisting of Fe and other unavoidable impurities 'JfJ: remainder, tensile strength: 75 k
pf/- or more, impact absorption energy of base metal and weld at 0°C: 5 kyf-m or more and 5 kyf-, respectively.
The feature is that it has achieved more than m.

Note that normal quenching and tempering is sufficient for the thermal treatment of the steel material for the chain of this invention, but if quenching and tempering is performed after the normalizing treatment 'fcN, the crystal grains that have become coarse due to flash butt welding will become finer. This is a desirable measure because it further improves the toughness of the weld zone.

Corrosion of broken chains, which are normally used in seawater, may be a problem, but in such cases, it is recommended to add one or both of Cu and Ni to the steel material. Effective.

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

(a) C The C component has the effect of ensuring the hardenability of steel materials to maintain strength, strength, and toughness, but when the content is 0.10
If it is less than %, the desired effect cannot be obtained in the above action,
On the other hand, if the content exceeds 0.30%, the toughness will deteriorate and the probability of cracking in the bath contact area will increase, so the content was determined to be 0.10 to 0.30%.

(b) 5i The Si component has the effect of ensuring the strength 111j' of the steel material and also acts as a deoxidizing agent, but if its content is 0. If Ft is less than 10%, the desired deoxidizing effect cannot be obtained, and non-metallic inclusions in the steel material are crucified, resulting in deterioration of toughness. On the other hand, even if the content exceeds 50% (J), it will not cause toughness deterioration.
The content of FK k was determined to be 0.10 to 0.50%.

(c) Mn base is an essential component to ensure the desired hardenability, but if its content is less than 1.30%, sufficient hardenability cannot be ensured, while if the content exceeds 2.50%, Since this may deteriorate the toughness and bath weldability of the steel material, the content was determined to be 1.30 to 2.50%.

(d) Cr The Cr component has the effect of improving the toughness of the steel material to some extent and increasing the quenching strength, but if the content is 0.
If the content is less than 50%, it will be difficult to secure the desired hardenability for large diameter chains, while if the content exceeds 1.50%, the effect of improving toughness will be small and the weld will deteriorate. From, its content H,k 0050~1.
It was set at 50%.

(e) M.

The MO acid component is an element that is extremely effective in improving the toughness and ensuring hardenability of steel materials, but if its content is less than 0.10%, the above effects cannot be expected; If the content exceeds this amount, the hardenability becomes excessively high, resulting in an increase in cost. Therefore, the total content is set at 0.10 to 0.60%.

(f) sot, A7 The Sot, At component has the effect of adjusting the grain size of steel materials in addition to its deoxidizing effect, but when the content is 0.01
If it exceeds 0.06%, alumina-based nonmetallic inclusions in the steel material increase, which also causes toughness deterioration. , its content 'eo, 01~0.0
It was set at 6%.

(g) N The N component contains At which combines with At and is effective for adjusting the crystal grain size.
It has the effect of precipitating N, but the needle containing it is 0.003
If it is less than %, the above-mentioned effect will not be achieved sufficiently, and no grain refining effect can be expected. On the other hand, if the content exceeds 0.020%, solid solution N increases and the toughness of the steel material deteriorates, so the content was set at 0.003 to 0.020%.

(h) P and S Both P and S are impurities that cannot be avoided in the construction of steel materials, but their content is 0.040% each.
If the P and S contents exceed 0.040%, the toughness of the steel material will deteriorate beyond the total 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, refining the grains of steel, and improving toughness. , one or more types may be added if necessary, but the total content of these may be 0.
If the content exceeds 20%, not only will no further effect be obtained in the above-mentioned action, but the cost of steel manufacturing will increase, so the total content was set at 0.20% or less.

Figure 1 shows a steel bar with a diameter of 84 mm obtained by hot rolling a sample steel with the composition shown in Table 1.The material is formed into a chain by hot bending, and then plated by flash butt welding. ,
Tensile strength -Ivln +Cr + 2 M of chain products obtained by deburring, stud charging, hardening and tempering at the temperatures shown in Table 1.

σB) Addition amount of 1 alloy element (C1-1.-).

FIG. 3 is a diagram showing the relationship between welding zone impact absorption energy values at 0° C. and 0° C. In addition, test steel A-D has a tensile strength of 75 to 80 kf/a through quenching and tempering treatment, and test steel E-L has a tensile strength of f85 to '95 kf/mA.
The test steel M-8 was adjusted to have a tensile strength of 'k95 kgf/- or more, and the tensile strength and weld impact absorption energy value at 0°C of each test steel A-8 are shown in Table 1. It is also shown in .

It is clear from Figure 1) that in order to ensure a good impact absorption energy value of the weld, it is important to increase the amount of alloying elements added as the strength of the steel increases. Impact absorption energy value of bath contact part at 0℃ at variable level: 5
In order to ensure kyf-m or more, it is necessary to use the formula %().

Regarding the effect of increasing the number of alloying elements, the first effect is an increase in hardenability, but in addition to this, an increase in tempering softening resistance can be an important factor.

ff1l, the usual measure to ensure high strength of steel is to lower the tempering temperature, which is not desirable as it causes a complete deterioration of toughness, but the inventors have discovered that alloying elements Adjust the amount of addition according to the required strength.
By adjusting the temperature, the tempering softening resistance is increased and high temperature tempering is possible.This also makes it possible to manufacture chains with high stiffness and high toughness. It was discovered that it is extremely effective in improving toughness.

The relationship between the amount of alloying elements added and the tempering temperature is clear from Table 1, and at each strength level, the higher the amount of alloying elements added, the higher the temperature tempering becomes possible.
It can be confirmed that high toughness can be obtained.

Note that there is no particular need to set an upper limit to the amount of alloying elements added from the viewpoint of toughness, but since excessive addition causes increased costs and deterioration of weldability, it is preferable to set the amount above or below the practical limit.

Next, the present invention will be explained in more detail through Examples and in comparison with Comparative Examples.

EXAMPLE First, steel having the composition as shown in Table 2 was melted by ordinary atmospheric melting, and then a round steel bar having the same diameter as shown in Table 2 was obtained by hot rolling. Next, this was cut, formed into a chain by hot bending, and flash butt welded to form a plate. Then, after deburring the welded part, insert the stud, and then
After quenching by heating to 0° C., holding for 3.5 hours, and cooling with water, a tempering treatment was performed at the temperature shown in Table 3 to produce a chain.

The following test pieces were prepared from each chain manufactured in this way: Tensile test piece: D=14φ, GL=5D.

Impact test piece: JIS No. 4 Charpy test piece.

was sampled and its mechanical properties were investigated.

The results shown in Table 3 also show that steel materials 1 to 13 of the present invention, in which the amount of alloying elements added is adjusted to a predetermined value according to the tensile strength, have high strength and impact absorption energy at VcO ℃ is 5. It is clear that a good weld zone toughness of 9 f-m or more is obtained, whereas comparative steel materials 14 to 19 whose compositional content is outside the range of the present invention cannot obtain the desired characteristic values. However, in cases where the amount of alloying elements is particularly insufficient, low-temperature tempering is required to ensure the desired strength, and it is clear that the impact properties of the bath contact area deteriorate.

Further, steel materials 6 to 10 of the present invention added with V, Nb, or Ti. and 13, the 0°C impact absorption energy value of the welded part is 1 to 2 compared to those without these elements added.
kyf-m increased, and the effect of its addition was also confirmed.

As mentioned above, this invention provides extremely high strength and
It is possible to obtain steel materials for large-diameter chains that have excellent toughness at a low cost, and it brings about industrially useful effects such as providing extremely useful steel materials for resource development under harsh conditions. .

[Brief explanation of drawings]

Figure 1 shows the tensile strength of steel, the amount of alloying elements added, and the
3 is a drawing showing the mutual relationship between Charpy impact absorption energies of welded parts at ℃. Applicant: Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] +11C: 0.15 to 0.30%. Si: 0.10-0.50%. ΔPongee: 1.30-2.50%. Cr: 0.50-1.50%. Mo: 0.10-0.60%. soL, AL: 0.010-0.060%. N: 0.003-0.020%. p: 0.040% or less. S: 0.040% or less. In addition to the total content, the formula is [However, σB: Required tensile strength of the chain kg f /
A) A high-strength, high-toughness copper material for a chain, which satisfies the following: Fe and other unavoidable impurities: the remainder (weight %). f21C: 0.15-0.30%. Si: 0.10-0.50%. Mn: 1.30-2.50%. Cr: 0.50-1.50%. Mo: 0.10-0.60%. sot, At: 0.010-0.060%. N: 0.003-0.020%. P: 0.040% or less. S: 0. O10% or less. Total content of one or more of v, Nb, and Ti is 0.20% in total
below. and the formula, [where σB: required tensile strength of the chain kff/m
, 4) ], and has a composition (N content % above) of Fe and other unavoidable impurities (remaining).