JPS5935619A - Production of high tensile steel material having excellent toughness of weld zone - Google Patents

Abstract

PURPOSE:To produce a high tensile steel material having excellent toughness of weld zones and base material at a low cost with good productivity by rolling low carbon steel having a specific Ca/S ratio and of low N content extremely low S content and high Mn content, then cooling the same under specific conditions. CONSTITUTION:The steel contg., by wt%, 0.035-0.160% C, 0.001-0.400% Si, 0.6-1.6% Mn, 0.003-0.012% Ti, 0.01-0.09% Al, 0.0001-0.0060% N, 0.0001- 0.0020% S, 0.0001-0.0100% Ca, <=0.015% P, satisfying the relation 1.0-5.0 Ca/S, contg. further >=1 kinds among 0.1-1.0% Cu, 0.1-9.5% Ni, 0.1-1.0% Cr, 0.05- 0.35% Mo, 0.008-0.030% Nb, 0.01-0.07% V, 0.0005-0.0015% B according to need, and the balance Fe, is treated in the following way: The steel is rolled after heating to 870-1,280 deg.C and is cooled at a rate of 5-50 deg.C/sec. in the temp. region from the end temp. of rolling to 450 deg.C after the completion of rolling at 800-690 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides high tensile strength with extremely excellent weld toughness, J
The present invention relates to a method for manufacturing 6ti.

In recent years, there has been an increasing demand for preparations with high strength and excellent workability as structural materials for various buildings and industrial machinery.
In order to cope with these problems, various steel materials have been developed and come into use. Recently, due to the deterioration of the energy situation, resource development in cold regions and other extremely harsh environments has become unavoidable, and in addition to improving the toughness of the steel base material itself, the corresponding embrittlement of steel welds has become necessary. Countermeasures are also becoming an important issue.

Traditionally, as a measure to improve the HA and Z (weld heat affected zone) toughness of steel materials, strength has been ensured by using high Mn steel (usually Mn: 1.3 weight coefficient or higher), and Methods such as fixing by adding NQTi to steel have been adopted.

However, in order to obtain a low carbon equivalent (low Ceq) that can suppress the occurrence of cold cracking in high Mn steel,
The C content in the steel needs to be extremely low, which makes steel manufacturing difficult, and when adding the Mn component, silicomanganese or metallic Mn must be used instead of the cheaper ferromanganese, which reduces product costs. There was a problem in that it led to a one-up increase.

If this is true, it is because ferromanganese contains a large amount of 0 min, and as Mn increases, C will inevitably increase as well.

・So, based on this, Mn: 0.90
Attempts have been made to make the HAZ part ferrite in a low Mn range below the weight coefficient, but even if ferrite is obtained in such a low Mn range, it may become fine grains, and in the end, the toughness
'1lr - It deteriorated and the desired effect could not be achieved.

On the other hand, the recent progress in steel manufacturing and refining technology is remarkable, including ultra-low S technology and low N steel melting technology.

The current state of affairs is that remarkable results that have not been achieved until now are being achieved one after another in the technology of controlling the shape of "two-eighths" in Ca treatment, and the technology of micro-controlling the amount of ``J゛''.

The present inventors have proposed the conventional weld toughness measures 41, without any particular increase in cost, from the viewpoint of ``two series''.
In order to obtain high-strength steel materials having f1 or higher and excellent weld toughness with good productivity, we have conducted research that takes into account the current state of the latest steelmaking technology, and as a result we have developed the following (a) to (C).
We came to the knowledge shown in 1. In other words, (a) Measures against embrittlement of welds in which the S content, which causes deterioration of the impact value, is usually 0.003% by weight in high-strength steel having the desired strength. In addition to reducing the N content, which causes HAZ embrittlement, to an extremely low level compared to steel, the N content, which causes HAZ embrittlement, is also reduced as much as possible, and the trace amount of S in the steel is fixed as CaS through Ca treatment and made spheroidized. The N in the steel is added to T1 to form a ferrite generation nucleus.
When the various treatments of fixation are combined, the expected effects of each treatment are organically intertwined and promoted, and as a result, a fine-grained ferrite structure can be obtained in the HAZ part even in low Mn steel. As a result, low-temperature toughness is improved more than that of conventional low-Mn steels, and on the other hand, MnS
Since there is no CaS and the amount of CaS is extremely small, the ductility and
Since extremely good impact values are obtained even in the brittle transition region, combined with the grain refinement effect of the ferrite base, it is possible to obtain superior low-temperature toughness compared to conventional high-Mn HAZ parts. In addition, if a combination of low N and extremely low S, Ti treatment and Ca treatment is applied to a high Mn preparation,
The low-temperature toughness is even better than that of conventional high-Mn materials. (C) C
By adding a predetermined amount of one or more of u, Ni, Cr, Mo, Nb, V, and B, the strength, toughness, or corrosion resistance of the steel material can be further improved. Based on knowledge, C', 0.03.5 to 0. ] -60% (Hereinafter, "F" indicates weight %).

Sj, ', 0.001-0.4.00%.

Mn: 0.6-16%.

Tj: 0.003-0012%.

Ae: OO] ~ 0.09%.

N: 00001-0.0060%.

ε: 0.0001 to 0.0020%.

(:a, :0000~00100%.

1): 0.　O], 　5% Lido.

and Ca,/S = 1.0 to 5.
6:'a is added to the relationship of 0, or in addition, C
u: O on ~: I-, 0%, Ni: 0.
1 to 9.5 b.

Cr: 0.1-1.0%, Mo: 005-0.35
%.

Nb ○008~0.030%, V:001~0
．． 07%.

13:0.0005~o, c5015 section.

1f of them! lI or more-1-, Fe and unavoidable impurities: remainder.

A steel made of By cooling in steps 5-b, a high-tensile steel material with excellent weld toughness can be obtained.

In addition, the steel to be rolled in the method of this invention may be a slab produced by subjecting a steel ingot manufactured by normal ingot casting to appropriate blooming rolling, or a slab directly produced by a continuous casting method. However, in terms of TiN fine dispersion and CaS fine dispersion, it is more preferable to form a slab by continuous casting.

Next, the reason why the chemical composition, heating temperature, rolling end temperature, and cooling conditions of the steel to be rolled are limited as described above in the method for manufacturing high-strength steel materials of the present invention will be explained.

■) Chemical composition of steel■ C The C component is the element that most economically ensures the strength of steel materials, but if its content is less than 0.5%, it may not be possible to obtain the desired effect on ensuring the strength of steel materials. 11, while O] 60%
If the content exceeds 0.035 to 0.03, the weldability and toughness of the steel material will be impaired.
It was set at 160%.

■ Sj S] component not only has the effect of improving the properties of the base material as a welded structure, but also has the deoxidizing effect of steel, but if its content is less than 0001%, the desired effect may not be achieved. On the other hand, if the content exceeds 0.400%, the toughness of the weld zone will be impaired, so the content was set at 0.901 to 0.4.00%.

■ Mn The Mn component is an element that economically ensures strength next to C, but if its content is less than 6%, the desired effect cannot be obtained; The content was set at 0.6 to 1.6% because if the content exceeds 0.2%, it would have an adverse effect on the toughness of the weld zone.

■ Tl The T1 component is a particularly effective element for improving the toughness of the weld zone. In other words, T1 is fixed as Nf:'l'i nitride in the steel, and at the same time eliminates the deterioration effect of N on the weld joint toughness, and at the same time actively promotes the effect that Ti nitride has on the weld joint toughness. It is added to utilize O and OO as a material, and its effect is therefore influenced by the amount of coexisting N. However, if the content is less than 3% of O, OO, no toughness improvement effect is brought about. 0.012%
If the content exceeds 0.2%, the toughness will deteriorate, so the content was set at 0.003% to 0.012%. Also, keeping the T1 content low in this way is one of the important points of this invention.

■ AC Ag, a component, has the effect of ensuring the toughness of the base material, but if its content is less than 0.01%, the desired effect cannot be obtained in this effect, while if it is contained in excess of 0.09%, Since the cleanliness of the steel will deteriorate, its content should be reduced to 0.00%.
It was set at 1-009%.

■ 14 Components are a type of impurity that inevitably enters steel, such as T] and Ai! It is an element that combines with to form nitrides such as TjN and A[N. And formed”]’IN
Since O has a positive effect on the toughness of the weld zone, in order to actively utilize this, the lower limit of the content was set at 1%, which is the limit at which this positive effect is recognized. On the other hand, 0.
It has also been confirmed that if the content exceeds 60% OO, the toughness of the welded joint will be extremely impaired. For the reasons mentioned above, the N content is set to f, ), 000 ] - ~ 0
．． It was set as 0060%. In addition, from the viewpoint of nitride formation, it is desirable that the ratio of 'll'', j / H is 5 to 34; It was confirmed that relatively high toughness could be obtained.

FIG. 1 is a diagram showing how the weld bond toughness changes when the N content is changed for three types of T1-added steel. Note that the welding heat input at this time was 60,000 J/cm.

It can also be seen from FIG. 1 that when the N content in the steel exceeds 0.0060%, the toughness of the weld pound portion deteriorates significantly.

In addition, as the Tl content decreased from 0.012% to 0.003%, N
You can see that the amount gradually shifts to the lower 1 inch side. The N amount exhibiting the lowest vTs is approximately 2.5 in terms of the Tl amount N ratio. It can also be seen that because the amount of T] is suppressed to a maximum of 0.012%, the degree of embrittlement in the extremely low N range is suppressed to a relatively low level.

(2) S Sl is generally contained in steel as an impurity element, but in the present invention, by achieving an extremely low S content, it was possible to significantly improve the toughness of the weld zone. This extremely low S content is achieved when the S content is O,
On the other hand, by adding Ca, S is fixed as Ca and S, which effectively reduces the anisotropy of the steel and improves the toughness of the weld zone. Since the minimum amount of S content that can effectively utilize the effect of is 0.0001%, the S content was determined to be 0,0001 to 20%.

Is the welding row in Figure 2? FIG. 3 is a diagram showing the influence of S content on the toughness of the bonded portion. In addition, the contact fever at the time of the interview was 60,000 J/cm.

It can also be seen from FIG. 2 that when the amount of S is less than 20% of O and OO, the impact absorption energy of the weld bond is significantly improved.

■ Ca The Ca component forms sulfides with S to reduce the anisotropy of the steel and improve the toughness of the welded joint ('l/
There is IJ, but if the content is less than 0.0-001%, 1) the desired effect on the action described in item 11 cannot be obtained, whereas if it is more than 0.010%, the cleanliness of the steel will deteriorate. Therefore, the content should be set at 0.0001 to 0.010.
It was set as 0%.

Like S, P is an element that cannot be avoided as an impurity in steel, and the lower its content, the better the base metal toughness, weld zone toughness, and weldability. It is preferable to suppress the content as much as possible. However, in ordinary ironmaking and steelmaking processes, special treatment is generally required to obtain low P steel;
While balancing cost increase and property improvement due to
Although it is common practice to set an upper limit for the P content, in the case of the method of the present invention, the desired weld toughness cannot be obtained especially if the P content exceeds 0.005%, so the upper limit of the P content must be set. It was set at 0.015% or less.

[Phase] Ca/S As can be understood from the above explanation, the weight ratio of the Ca component to the S component is also a factor that greatly affects the toughness of the weld bond, and in the extremely low S range, its value decreases. , that is, even if the value of Ca/S is less than 1 or 0,
Moreover, since the weld bond toughness deteriorates extremely even if the value exceeds 5.0, the value is set at 1.0 to 5.0.

Figure 3 is a diagram showing the influence of the Ca/S value on the weld pound toughness. Figure 3 also shows that in extremely low S castles, the Ca/S value ranges from 1.0 to It can be seen that only in the case of 5.0, the impact absorption energy of the weld bond is significantly improved.

(1-ONI N) Acid component [3-ONI N] without adversely affecting weldability.
Since it has the effect of significantly improving the strength and toughness of 1J, it is added as necessary especially when further improvements in matrix strength and toughness are required, but if the content is less than 0.1%, the The desired effect was not obtained, while 9.5%
Even if the content exceeds 0.01%, no further effect will be obtained, and for normal purposes, sufficient results can be obtained with addition of 95% or more. ~9.
It was set at 5%.

(i, lil C11 (:u component has almost the same effect as N1,
Since it is an element that improves environmental corrosion resistance and also has a slight strength increasing effect, it is particularly required for further matrix strength and toughness, environmental corrosion resistance, strength, etc. If the content is less than 0.1%, the desired effect cannot be obtained; on the other hand, if the content exceeds 1.0%, the hot rolling of steel Medium KCu - Since cracks occur and make steel production difficult, the content was determined to be 01 to 0.

(4Cr The Cr component is an inexpensive element that not only promotes the initization of the rolled structure and improves strength and toughness, but also improves environmental corrosion resistance. , is included as necessary when toughness and environmental corrosion resistance are required, but if the content is less than 01%, the desired effect cannot be obtained,
On the other hand, if the content exceeds 10%, it will increase the hardening of the supernatant contact area and cause a decrease in toughness and cracking resistance.Therefore, the content was set at 01 to 1.0%.

MO The Mo component has the effect of improving the strength and toughness of the base material when added in small amounts, so it is included as necessary, especially when further improvement in base material strength and toughness is required. However, if the content is less than 0.05%, the desired effect cannot be obtained;
If the content exceeds 5%, the weld toughness and weldability will be extremely deteriorated, so the content should be reduced to 0.0%.
It was set as 5 to 0.35.

Q et al) Nl) and V January) and V component are both additive elements that are included as necessary to improve the strength and toughness of the steel of the present invention, with the aim of grain refinement and precipitation hardening of the rolled structure. However, if the Nb content is less than o, oos% or the V content is less than 00]%, the desired effect on improving strength and toughness cannot be obtained;
If the Nl) content exceeds 0.030% or (■) content exceeds 0.007%, the toughness of the weld will be adversely affected, so the content should be reduced to Nb: 0.0.
08-0030%, V:00]--0.07%, respectively.

(jfj) B The B component not only improves hardenability and increases strength, but also combines with free N in the steel to form BN in the weld, improving the toughness of the weld bond. It is added as necessary, especially when further improvement of these properties is required, but if the content is O, O
If the content is less than 5% OO, the desired effect cannot be obtained, while if the content exceeds 15% 0.0 O, due to the background of Ti addition and low N content, the weld toughness will be significantly reduced. Therefore, the content is O, OO
It was set as O5 to 0.0015%.

Even if the chemical composition of the steel is limited as described above, if the hot rolling conditions are inappropriate, it will not be possible to obtain the desired excellent strength and toughness. It was limited. That is, (1) If the heating temperature of the steel subjected to heating temperature rolling is less than 870°C, there is a risk that the steel material will not be sufficiently austenitized;
On the other hand, heating above 1280°C causes γ
The heating temperature was set to 870-12 mm because the grain size becomes large and the structure after rolling becomes coarse, impairing the toughness of the matrix.
The temperature was set at 80°C. In addition, when particularly high toughness is required for the base material, the heating temperature should be adjusted to 1. It is preferable to set the limit to 1000°C.

II+) Rolling End Temperature When the rolling end temperature exceeds 800°C, the effect of refining the steel plate structure by rolling becomes insufficient, and stable high toughness cannot be obtained. Furthermore, if the transformation has not progressed sufficiently, the strength will increase and the strength variation will increase due to reasons such as gapping.

On the other hand, if rolling is performed in a temperature range below 690°C, processing will be applied to ferrite that has completed transformation, and processing distortion will remain due to low-temperature processing, resulting in loss of toughness. Therefore, the temperature at the end of the month is 800.
The temperature was set at ~690°C.

In addition, when high toughness is required depending on the matrix, it is effective to increase the amount of compression in the low temperature range, and it is recommended to set the cumulative reduction rate at 870°C or higher to 60 or more -1-. desirable.

IV) Cooling Conditions In the method for producing high-strength steel materials of the present invention, it is effective to perform accelerated cooling after the completion of rolling to increase the strength of the base material, but if the cooling rate is less than 5°C/sec. If it is 50℃/!, the strength increase will be small and the desired high strength cannot be obtained. If it exceeds ec, the strength of the base material increases but the toughness of the base material deteriorates, so the cooling rate range is from 5 to 450°C from the end of rolling temperature. However, in the temperature range below 450℃, the desired strength and toughness values can be achieved regardless of whether simple cooling or accelerated cooling is used, so the balance between the required strength and toughness of the base material is considered. However, it is better to adopt one of them. If strength is not required but high toughness is required, it is preferable to allow cooling from 450°C; conversely, if high strength is required but not so much toughness, acceleration is recommended. Preferably, cooling is continued to even lower temperatures.

Next, the present invention will be explained using examples and comparison examples.

EXAMPLE First, by a normal continuous casting method, the present invention target particles having the chemical composition shown in Table 1: [Phases] A-M
.

and comparative steel N-V/ were produced. 1st comparison @
1 (dIku~W is the point marked with * in Table 1)
) It has a composition that is outside the composition range of Zotaku j1).

Then, each of these sloughs was heated, rolled, and cooled under the conditions shown in Table 2. I got it: i(,
The mechanical property U of the +d plate and the properties of the welded part were determined.

The results are also listed in Table 2. Note that the rolling ratio during hot rolling was 50%. In addition, to measure the characteristics of the weld zone, a square groove was used, and the welding flow was 700 Δ.

Welding voltage: 37V.

Welding speed: 25 cm/Tu”.

Amount of welding personnel: 62,000 J/am.

After performing submerged arc welding under the following conditions, as shown in FIG. 4, a test piece a was taken from a depth of 1 mm from the weld surface side and tested.

On the other hand, a steel plate obtained in the same manner as described above by processing a slab having the composition of the steel A subject to the present invention shown in Table 1 under various heating, rolling, and cooling conditions as shown in Table 3. When we measured the mechanical properties and weld properties of
Similarly, the results shown in Table 3 were obtained.゛Also,
The asterisks in Table 3 indicate that conditions outside the scope of the method of the present invention were provided.

Examining the results obtained in this way, it was found that the composition of the steel used was within the scope of the present invention, and that the rolling was carried out according to the conditions of the present invention.
13. The steel plates obtained in Nos. 24 to 26 all had good base metal strength and toughness.

In addition, method 24 of the present invention had a small accelerated cooling rate of 7°C/see, and the strength of the obtained steel plate was lower than that of other method examples of the present invention. However, the base material toughness is vTs (Charpy fracture transition temperature) knee 123°C, vE-a.

(Charpy absorbed energy value at -60℃):'
34. '2, which is an extremely good value, and it is clear that the welded part also has excellent toughness.

In method 25 of the present invention, the slab heating temperature is 1150°C.
Since the accelerated cooling rate is as high as 20°C/sec, the base metal toughness of the obtained steel plate is vTs : -'i' 2
Although it is inferior to ℃, the strength is significantly improved.

Thus, this method is effective in cases where the motor power of the rolling mill is insufficient. Furthermore, method 26 of the present invention cools down to 450°C at 20°C/sec after rolling,
This is an example in which accelerated cooling is continued after that, and although the matrix toughness of the steel plate obtained by method 24 of the present invention is slightly lower, the degree of decrease in method 25 of the present invention is not large, and the strength It can be seen that this method is superior to the same extent as method 25 of the present invention.

On the other hand, steel plates manufactured by comparative examples in which the composition range of the steel used or the rolling conditions are outside the range of the present invention all have good values for the toughness of the base metal and the toughness of the welded part. It is clear that it is not shown. For example, in Comparative Method 17, the toughness of the base metal and welded part of the obtained steel plate is extremely poor because Ti is not added to the steel used, and in Comparative Method 23, the steel used contains excessive N. Therefore, it can be seen that the weld toughness is inferior.

-1- As mentioned above, according to the present invention, high-strength steel materials with significantly superior weld and matrix toughness than conventionally known weld zone toughness steels can be manufactured at low cost and with high productivity. This brings about industrially useful effects such as further expanding the scope of application of various welded structures.

[Brief explanation of drawings]

Figure 1 is a diagram showing the influence of N content on the toughness of weld bond, Figure 2 is a diagram showing the influence of S content on toughness of weld bond, and Figure 3 is a diagram showing the influence of S content on toughness of weld bond. FIG. 4 is a diagram showing the influence of the Ca/S value on toughness, and FIG. 4 is a conceptual diagram showing the state of specimen collection. Figure 1 N content (%) Nest 2 Figure S content ('/,) Frame 3 Figure 4

Claims (1)

[Claims] (1,) C2 0.035 to 0.160%
. Si, ,' 0.001-0.400%. Mn: 0.6-1.6%. Ti: 0.003-0012%. AQ: 0.01-009%. N: 0OOO1 to 0.0060%. S: 0.0001-0.0020%. Ca: O,OO01~0.0100%. P: 0.015% below. and Ca/S = 1.0 to 5.0
Satisfying the relationship, Fe and non-J' avoidable impurities remain. After heating the steel consisting of (above weight) to a temperature of 870 to 1280°C, it is rolled to a temperature of 800 to 690°C.
After finishing rolling at a temperature of 4°C,
A method for producing high tensile strength steel with excellent joint toughness in the temperature range of 50°C to 50°C. (2) C: 0.035-0.160. Si:O, 001-0400%. Mn: 0.6-1.6%. Ti: 0.003% to 0.012%. Ap: o, 01-0.09%. N: 0.0001 ~ 0.0060 Person in charge. S: 0.0001-0.0020%. Ca: 0.0001 to 0.0100%. P: 0.015% or less. and Ca/S = 1.0 to 5.0
satisfies the relationship, furthermore, Cu: 0.1 to 1.0%, Ni
2 O, 1-9. 5%. Cr: 0.1-1.0%, Mo: 0.05-0.3
5%. Nb: 0.008-0.0100. V: 0.
01 NO, 07%. B: 0O005~O, OO15%. Contains one of the following: Fe and unavoidable impurities, the remainder. (hereinafter referred to as "double cloth%") steel at 870-1280℃?
After heating to Mo, it is rolled to 800~
After finishing rolling at a temperature of 690°C, the temperature range from 1 crystallinity at the end of the rolling to 450°C is 5-b.