JPS6254019A - Manufacture of 80kg class ultrathick high tensile steel plate superior in weldability and low temperature toughness - Google Patents

Abstract

PURPOSE:To obtain the titled steel plate, by rolling low C equivalent steel considering weldability in which ppt. hardening of Cu in a specified compsn. is utilized for high strength under a specified condition for preventing toughness deterioration due to ppt. hardening treatment and improving low temp. toughness. CONSTITUTION:Steel slab contg. by weight 0.01-0.10% C, 0.05-0.60% Si, 0.5-2.0% Mn, <=1.0% Cr, 0.1-1.0% Mo, 0.010-0.100% Nb, 0.0005-0.0020% B, 0.7-2.0% Cu, 0.010-0.100% Al, if necessary, <=0.0100% Ca and the balance Fe is prepd. This is hot rolled by >=30% draft at 900-700 deg.C range, successively cooled to room temp. by >=1 deg.C/sec average rate and directly quenched, or once cooled then reheated to 800-950 deg.C and quenched. Thereafter, it is heated to 500-650 deg.C and Cu ppt. treated, thence the titled steel plate is obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to large industrial machines, welded steel pipes, marine structures, FA
The present invention relates to a method for producing an extremely thick (U50+U+) high-strength steel plate with excellent weldability and low-temperature toughness for use as a material for beams and pressure vessels.

(Prior art) Conventional high-strength steel plates have a high carbon content (6
), and as a result they are usually highly susceptible to weldability cracking. In addition, there are high-strength steel sheets with low C and improved cracking susceptibility, but 60 kg class steel (tensile strength 6
The limit was 0 to 70 kg f/m+#).

Additionally, ASTM-A 710. There are steels standardized by A73B and those proposed in U.S. Patent No. 3,692,514 that utilize precipitation hardening of C0 to achieve high strength, but these are steels that take weldability into consideration. It is a component system with a low carbon equivalent, and with this component system alone, 50
It is difficult to obtain high-strength steel with a tensile strength of 30 kgf/- or more using an extremely thick steel plate of mm or more.

(Problems to be Solved by the Invention) In other words, in the above-mentioned known high-strength steel plates, for example, in the case of steel equivalent to A710A specified in the ASTM standard, the A steel plate shown in Table 1.2 described in Shun. , B steel plates have good weldability and weldability, but lack strength. Further, steel plate E in the same table is a known example in which B is added to increase the strength, but the strength is still insufficient for extremely thick materials of 100 mm or more.

Generally speaking, there are other known examples of steel plates, such as C steel plate, C steel plate, and F steel plate, which have higher strength than 114 plate by higher alloying, but TS: 80 kg like DI plate.
f/md is achieved, but the weldability deteriorates, or conversely, when the addition of alloying elements is suppressed compared to the C steel plate, such as C#A plate and F steel plate, to compensate for the weldability, T.S.
: It is difficult to obtain high-strength steel with a strength of 80 kgf/v or more.

Furthermore, in the conventional rolling method, when an extra-thick steel plate of 50 mm or more is rolled, the rolling finish temperature exceeds 900° C., so high toughness at low temperatures cannot be obtained.

As is clear from the above, in the case of conventional 80kg steel (C steel plate), although it has high strength and toughness,
It has high cracking susceptibility during welding, has a high cracking inhibition temperature of 75°C in the groove weld cracking test (J■5Z3158), and has high hardenability in the weld heat affected zone. On the other hand, A 710A 3 steels (A and B steel plates), which are rated as A S T M M, have low weld cracking susceptibility and high toughness, but extremely thick materials with a plate thickness of 50 i+m or more have a rating of 60 The strength of Ki0 spell is the limit.

The present invention provides excellent weldability and low-temperature toughness, and high strength (TS:
The purpose of the present invention is to provide a C1 precipitation hardening type high tensile strength steel that can achieve a hardening of 80++gf/md).

(Means for Solving the Problems) Therefore, in the present invention, (1) Weldability of high-strength and high-toughness steel is improved, Cm is reduced to 0.01 to 0.10 Wt%, and ( 2) In order to ensure high strength, 0.7 to 2.0 wt% of Cuff1 is contained with the aim of Cu precipitation hardening, and roughly 0.5 to 2.0 wt% of Mnff1.

The amount of Mo is 0.1-1.0★t% and 0.0005
(3) Under the above Cu content, controlled rolling is performed to prevent toughness deterioration resulting from precipitation hardening treatment and improve low temperature toughness. We decided to adopt the following measures.

That is, as the first means, C: 0.01 to 0.10
wt%, 3i: 0.05-0.60wt%,
Mn: 0.5 to 2.0 wt%, Cr: 1.
0wt% or less, Mo: 0.1-1.0wt%, N
b: 0.010-0.100wt%, 3: 0.0
005-0.0020wt%, Cu: 0.7-2
．． A steel slab containing 0 wt%, Al: 0.010 to 0.100 wt% and, if necessary, Ca: 0.0100 wt% or less, with the balance being substantially l”e, was heated to 900°C.
Hot rolling is performed so that the temperature range of ~700°C has a rolling reduction of 30% or more, and then an average cooling rate of 1. ℃/380
Directly quenched by cooling to room temperature above,
A method for producing an 80 kg class extra-thick high tensile strength steel plate with excellent weldability and low temperature toughness, characterized in that the steel plate is then heated to a temperature range of 500°C to 650°C and subjected to Cu precipitation treatment, and as a second means. , C:0.01~0.10Wt%, 3i:
0.05 to 0.60 wt%, Mn: 0.
5 to 2.0 wt%, Cr: 1.0 wt% or less, Mo:
0.1-1.0wt%, Nb:o, oio~0.
100wt%, B: 0,0005 to 0.00
20wt%, CLI: 0.7-2.0wt
%. A steel slab containing A°C: 0.010 to 0,100wt% and, if necessary, Ca: 0.0100wt% or less, and the balance being substantially Fe, is heated in a temperature range of 900°C to 700°C with a temperature range of 30% or more. Hot rolled to achieve the rolling reduction ratio,
It has excellent weldability and low-temperature toughness, as it is once cooled, then reheated to a temperature range of 800 to 950°C for quenching, and then heated to a temperature range of 500 to 650°C to undergo CLI precipitation treatment. We decided to adopt a manufacturing method for 80 kg class extra-thick high-strength steel plates.

The reason why the method of the present invention is specified as described above will be specifically described below.

Reasons for limiting the chemical composition range; ■ The C content is
o wt% or less is preferable, but from the viewpoint of steel sheet strength, 0.01 wt% or more is essential, and 0.01 to 0.
It was set to 10 wt%.

However, the optimum condition is C: 0.03 to 0.07 wt%.

■ Sl is reduced to 0 in order to increase the toughness and strength of the steel plate.
．． It is necessary to add 0.05 wt% or more (particularly if it is less than 0.05 wt%, the toughness deteriorates). But that M is 0
．． If it exceeds 60 wt%, weldability and toughness of the welded joint will deteriorate.

Therefore, the range of 3i was set to 0.05 to 0.60 wt%.

(2) Mnff1 is an element that increases the strength and toughness of steel sheets, and it is essential to add 0.5 wt% or more, and as the thickness of the product sheet increases from 50 mm to 200 mm, the amount of Mnff1 added needs to be increased. However, if it exceeds 2.0 wt%, weldability will be impaired, so the addition range of Mn was set to 0.5 to 2.0 wt%.

(2) Cu is an essential element for achieving high strength through precipitation hardening, and its m must be added in an amount of at least 0.7 wt%.

On the other hand, if it exceeds 2.0%, low-temperature toughness is impaired, so the addition range is set at 0.1 to 2.0 wt%.

(2) Cr is an effective element for increasing strength, but if its content exceeds 1.0 wt%, it is undesirable as it leads to deterioration of weldability and low-temperature toughness.

(2) Mo, like Cr, is effective as a high-strength element and is an essential element.

The effect of adding Mo is particularly large when it is about 0.3 to 0.4 wt%, and the effect becomes small when it is added other than that. Furthermore, even if Mo is contained at 1.0 wt% or more, the low-temperature toughness slightly deteriorates, but no deterioration of weld joint toughness or weldability is observed.
The following was made. On the other hand, if the amount of Mo added is less than 0.1 wt%, the strength decreases significantly, so the range of Moffl addition was set at 0.10 to 1.0 wt%.

■ Nb is an element that has the effect of grain refining through controlled rolling, and if the amount added is less than 0.010 wt%, the effect will be lost, and if it is more than 0.10 wt%, it will cause deterioration of the weld joint toughness. . Therefore, the Nb addition level is 0.01 to 0.10
'wt%.

■ 8β is an element necessary for deoxidation and grain refinement of austenite, and at least o, oi.

Addition of wt% is necessary. Moreover, if it exceeds 0.10 wt%, the cleanliness in the steel will be impaired, which is not preferable. Therefore, the amount of A° C. was set to 0.010 to 0.100 wt%.

■ B is an essential element for obtaining the steel of the present invention,
It is necessary to add 0.0005 wt% or more to increase the strength. However, addition of 0.0020 wt% or more causes deterioration of low temperature toughness. Therefore, B suspension is 0.0005~
It was set to 0.0020wt%.

■ Ca can be added as an element to control the shape of inclusions as needed to improve low-temperature toughness, but
Addition of 100 wt% or more causes deterioration of low-temperature toughness, so the content is set to 0.0100 wt% or less.

Next, specific details regarding the rolling conditions and heat treatment conditions of the method of the present invention will be described.

■ Finishing temperature during hot rolling shall be 900°C or less.

At temperatures exceeding 900°C, grains become coarse and toughness deteriorates. Furthermore, if the hot rolling finishing temperature is lower than 700°C, toughness will be impaired, so 700°C was set as the lower limit. As is clear from Figure 1, which shows the relationship between the fracture surface transition temperature (vTrs) and the reduction rate in the Charpy impact test, in order to obtain a reduction rate superior to that of the conventional technology in this temperature range, it is necessary to From Figure 1, 30% or more is required, and if it is less than 30%, a sufficient fine grain structure cannot be obtained.

■ Heating temperature for Cu precipitation treatment is 500 to 65
It is carried out at a temperature of 0°C. The reason why the temperature is limited to 500 to 650°C is that the precipitation hardening effect of Cu is impaired outside this temperature range.

■ When reheating and quenching is performed after controlled rolling performed prior to this Cu precipitation treatment (second invention method), the heating temperature is 800 to 950°C and rapid cooling is performed in order to refine the composition after quenching. is necessary. Further, when direct quenching is performed immediately after controlled rolling (first invention method), the cooling rate is set to 1.0° C./380° C. or more. As is clear from Figure 2, this cooling rate varies depending on the thickness of the plate, but for an extremely thick plate of 100 mm, the cooling rate is 2
．． 0℃/380 or more, plate thickness 200mm T' 1.0
A cooling rate of ℃/380 or higher is required.

Regarding the limitations of implementing the method of the present invention, the plate thickness was limited to 50 mm or more, but this is because plate thicknesses of 50 mm or less can be sufficiently manufactured by applying conventional techniques.

(Example) Table 1 shows the chemical compositions of the first invention steel, second invention steel, and comparative steel manufactured according to the method of the present invention.

Further, the manufacturing conditions and material properties of each of these test steel sheets are shown in Table 2.

The key feature of this invention is all austenitic steel (1180℃
) and reduce the rolling reduction rate at 900°C to 800°C to 50°C.
~75% was ensured, and rolling to product dimensions was completed at a finishing temperature of 800°C. After that, H, J, L.

Regarding M and N steels (first invention steel), H1M steel with a product plate thickness of 50 mm after rolling is 8.6°C/5eC1 product plate thickness 1
00am J and N steels were cooled at 2.1°C, '5ec1 and L steels with a product plate thickness of 200mm were cooled at 1.2°C/sec.

After that, at 570℃ for 3.5 hours for H and M steels, and for 6 hours for J and N steels.
．． The Cu precipitation treatment was performed for 5 hours, and for [1] for 10 hours.

Further, G of the steel corresponding to the second invention, 1. and KM are reheated to 930°C and quickly water cooled (quenched), and further heated to 570°C.
3.5 hours for G31il and 6.5 hours for III at °C.
The K steel was subjected to Cu precipitation treatment for 10 hours.

As is clear from Tables 1 and 2, it can be seen that excellent strength, toughness, and weldability can be obtained by the first and second inventions. That is, Ga4.1 steel and II
In I, high Mn, high Cu,
High strength was achieved by achieving high Mn and low Cr. Also 9
High toughness is achieved by ensuring a rolling reduction of 30% or more in the temperature range of 00°C to 700°C.

In general, 8w4, J steel and Lli! steel have the same composition as G steel, I steel, and Ni steel, respectively. By manufacturing by direct quenching method (first invention), a steel plate with even higher strength and toughness than the reheated material (second invention) was obtained.

In addition, for M steel with a plate thickness of 50++ on, 80 kg class steel was obtained by directly quenching the conventional steel (A steel) with the addition of B and an increased amount of Mo. Further, in the present invention, it is understood that high toughness can be obtained even with N1g4 in which no Ni is added.

(Effects of the Invention) As explained above, according to the present invention, steel in which the added alloying elements are adjusted according to the plate thickness within the chemical composition range of the above-mentioned composition is
After rolling to a rolling reduction of 30% or more in the temperature range of 00 to 700°C, the average cooling rate is 1.0°C/s.
By directly quenching to room temperature at ec or above,
High strength and high toughness 1A (first invention) can be provided. Also, after finishing rolling and cooling by -8'', the temperature is 950 to 800.
Reheat and quench to a range of 500°C to 65°C.
By performing the CIJ precipitation treatment at 0° C., it is possible to provide an extremely thick steel plate with a thickness of 50 to 200 m+, which has excellent weldability, and has high strength and high toughness (second invention).

[Brief explanation of the drawing]

Figure 1 shows the effect on v'rrS from 900°C to 700°C.
Figure 2 is a graph showing the influence of the rolling reduction rate on ℃ paralysis. Figure 2 is a graph showing the influence of the average cooling rate on the tensile strength in directly quenched materials. TS Imaina-vTrs (”C)

Claims (1)

[Claims] 1. C: 0.01-0.10wt%, Si: 0.05-0.05%
0.60wt%, Mn: 0.5-2.0wt%, Cr:
1.0 wt% or less, Mo: 0.1 to 1.0 wt%, Nb
:0.010~0.100wt%, B:0.0005~
0.0020wt%, Cu: 0.7-2.0wt%, A
l: 0.010-0.100wt% and C as necessary
a: Contains 0.0100wt% or less, the remainder being substantially F
The temperature range of 900°C to 700°C is 3.
Hot rolled to a rolling reduction of 0% or more, then directly quenched by cooling to room temperature at an average cooling rate of 1.0°C/sec or more, then 500°C to 650°C
A method for producing an 80 kg class extra-thick high tensile strength steel plate having excellent weldability and low-temperature toughness, the method comprising heating to a temperature range of 100 to 100 ml and subjecting it to Cu precipitation treatment. 2, C: 0.01~0.10wt%, Si: 0.05~
0.60wt%, Mn: 0.5-2.0wt%, Cr:
1.0 wt% or less, Mo: 0.1 to 1.0 wt%, Nb
:0.010~0.100wt%, B:0.0005~
0.0020 wt%, Cu: 0.7 to 2.0 wt%. A
l: 0.010-0.100wt% and C as necessary
a: Contains 0.0100wt% or less, the remainder being substantially F
The temperature range of 900°C to 700°C is 3.
Hot rolled to a rolling reduction of 0% or more, cooled once, reheated to a temperature range of 800 to 950°C and quenched, then heated to a temperature range of 500 to 650°C to form a C
A method for producing an 80 kg class extra-thick high tensile strength steel plate having excellent weldability and low-temperature toughness, characterized by subjecting it to u-precipitation treatment.