JPS6035981B2 - High-strength, high-toughness rolled steel for pressure vessels - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rolled steel material having high strength, high toughness, and excellent acid solubility, particularly for use in the manufacture of pressure vessels.

Conventionally, for the manufacture of pressure vessels such as boiler drums in chemical plants, JIS SB 49 (ASTM
515Gr 70) and the same SGV49 (the same A51 r7)
Rolled steel materials such as 0) are used, and these rolled steel materials have a structure of ferrite + layered pearlite. Therefore, in order to increase the room temperature strength of these rolled steel materials, increase the C content to increase the C:
0.25 to 0.35%, thereby increasing the proportion of layered pearlite, and furthermore, for example, when the operating temperature of the rolling container is 300 to 3500 C, the safety factor is 4 for the allowable design stress (4 for the high temperature design allowable stress). Even when trying to obtain strength (tensile strength) at 300 to 350°C to ensure the During welding, problems such as cracking occur even if the temperature of the weld is raised to 200 to 300°C, and even if welding can be carried out without problems such as cracking, The stress-relieving leech dulling carried out after welding at a temperature of about 620 qo lowered the graininess, and this decrease in ruttability was more pronounced for grains with a higher C content. Furthermore, when putting these rolled steel materials into practical use, thermal power generation technical standards require that, for example, 0
A low temperature toughness of 2.8k9-m at ℃ is required. On the other hand, a method of increasing strength by subjecting low-carbon boron-added steel to a ferrite-bainite structure is known, such as in Japanese Patent Application Laid-Open No. 54-25211 (Hakama Kosho 57-2373). Since the method (2) is also the key to low carbon, the content of alloying elements is high in order to guarantee strength due to the low C content, which has the disadvantage of being unnecessarily expensive.

From the Tsurumi point mentioned above, the present inventors conducted research in order to obtain a rolled steel material that has high strength and high quality, and has excellent weldability, especially suitable for use in the manufacture of pressure vessels. As a result, we found that when we compare a steel material with improved hardenability by containing a certain amount of Mo, the structure becomes mainly composed of ferrite and fine grains with a lower C content. Pseudo pearlite (degenerate pearlite, Degenra)
tePearli), and this structure provides high strength.

'b- Unlike the coarse pseudo-barrite that precipitates from coarse-grained austenite after high-temperature finish rolling, the pseudo-barrite in 'a-a' above does not deteriorate in rut quality because it is finely dispersed, and it remains the same as conventional ferrite.・Achieves the same level of toughness as barlite steel, and improves the toughness of the steel by tempering it, as well as reducing stress relief annealing (SR) sulfidation and weldability due to the lower C content. In particular, it has good elongation properties and high strength required for pressure vessels, and it also has excellent weldability.

(c- The strength is further improved by containing one or more of Cu, Ni, Cr, V, and Nb as alloying elements.

As described above, we have obtained the knowledge shown in {al~'c.

This invention was made based on the above knowledge, and C: 0.13 to 0.30%, Sj: 0.1 to 1.0%.
, Mn: 0.5-2.0%, Mo: 0.03-0.35
%, B: 0.00015-0.0009% (1.5pp
m~masupm), sol. AI: 0.005-0.10%
, P: 0.020% or less, S: 0.010% or less, N:
Contains 0.015% or less, 0:0.010 or less, and further Cu: 0.08 to 0.50%, Ni: 0 as necessary.
．． 05-1.0%, Cr: 0.05-0.90%, V:
0.005-0.10%, and Nb: 0.005-0
．． Contains one or more of 05, and the rest is F.
Composition consisting of e and unavoidable impurities other than the above (weight%
(hereinafter, % means weight %), and is characterized by a rolled steel material that has a structure mainly consisting of ferrite and fine pseudo-barrite, and has high strength, high toughness, and excellent weldability. be. The above-mentioned structure in the steel material of the present invention can be obtained by raising the temperature to just above the Ac3 transformation V point and cooling at a cooling rate of 1 to 100°C/min, and by processing after heating to just above the Ac3 transformation V point. A similar structure can be obtained in the hot working process, and the same structure can be obtained in the tempering process to improve toughness, as long as the temperature is the same, in the so-called SR treatment after welding, which involves long-term heating and slow cooling. Therefore, for steel materials subjected to SR treatment during hot working, it is not necessarily necessary to perform normalizing or normalizing and tempering after rolling, and the steel of the present invention can be produced by the following five methods.

That is, {1) Normalizing.

{2' normalized and 10 tempered.

(3- Normalizing (Ar as necessary, warm working and cold working below the transformation point) 10 Stress Relief Hammer (SR).

■ Hot processing at a heating temperature above the Ac3 transformation point. {5'
Hot-processed at heating temperatures above Ac3 transformation point and stress-relieving inscription. Next, the reason why the composition range of the rolled steel material of the present invention is limited as described above will be explained.

(a} CIn order to ensure the desired high strength, the minimum
A C content of 3% is required, but if the content exceeds 0.30%, weldability and marring resistance will deteriorate, so the content is set at 0.13 to 0.30%. Ta.

In addition, each has a board thickness: low pine and has a C component of 0.1
The rolled steel sheet of the present invention has a composition shown in Table A, with other components being kept almost constant, and the C component, which is also shown in Table A, is 0.20 to 0. Conventional rolled steel sheet (J
IS・SB49), the tensile strength (T. S), yield point (Y.P), and impact value (vE
o) are shown in Figures 1 and 2, respectively. As shown in FIGS. 1 and 2, the rolled steel sheet of the present invention has relatively high strength compared to conventionally rolled steel sheets, and if stress relief damping is performed after normalization, the ruts will be removed. It is clear that the properties of the rolled sardine steel material are further improved, which indicates that the sardine rolled steel material of the present invention has a relatively low C content, high strength, and high toughness. Table A'b - Si Si must be contained in an amount of 0.1% or more for deoxidation, but if it is contained in excess of 1.0%, the sardine quality will decrease, so its content is The amount is 0.1-1.0%
It was determined that

'c} Mn Mn must be contained at 0.5% or more to ensure hardenability, but if it is contained in excess of 2.0%, toughness will deteriorate, so the content should be reduced to 0. ．．
It was set at 5 to 2.0%.

(d) Mo M has the effect of improving hardenability in coexistence with B, but if its content is less than 0.03%, the desired hardenability cannot be secured, whereas if it exceeds 0.35%, Even if it is contained, no further improvement effect on hardenability appears,
Considering economic efficiency, the content was determined to be 0.03 to 0.35%.

[e'B As mentioned above, B has the effect of increasing hardenability when coexisting with Mo, but its content is 0.00015% (1.
If the content is less than 5 ppm), the desired hardenability cannot be secured, while if the content exceeds 0.0009% (sapm), the strength, grainability, and weldability will decrease. Content 0.00015-0.0009
It was determined that

{f) sol. al sol. Al has the effect of fixing N and refining the structure, but if the content is less than 0.005%, the desired effect cannot be obtained; on the other hand, if the content is more than 0.10%, the desired effect cannot be obtained. Since this can cause surface cracking of steel ingots, its content has been set at 0.005 to 0.10%.

(g) If the NN content exceeds 0.015%, the weldability and hot workability of the weld bond will deteriorate, so the upper limit should be set at 0.015%, and preferably , the content is preferably 0.006% or less.

(h) If the ○○ content exceeds 0.010%, the amount of oxide-based nonmetallic inclusions will increase and the ductility will deteriorate, so the content should be reduced to 0.010% or less, preferably 0.
It is necessary to keep it below 0.005%.

(i) P When the P content exceeds 0.020%, the susceptibility to deformation increases and the toughness and weldability deteriorate. (more desirable).

(j) SS If the S content exceeds 0.010%, the anisotropy of ductility increases due to Mns stretched in the rolling direction, so the upper limit was set at 0.010%.

(k) KCu Ni, Cr, V, and Nb Cu, Ni, Cr, V, and Nb have the same effect of further improving strength, so they can be used as needed when higher strength is required. contained, but each Cu:0
．． Less than 0.08%, Ni: less than 0.05%, Cr: 0.05
%, V: less than 0.005%, and Nb: 0.00
If the content is less than 5%, the desired strength cannot be improved.

By the way, if Cu' is contained in excess of 0.50%, it will cause surface roughness on the slab, and if Ni is contained in excess of 1.0%.
Even if the content exceeds 1.0%, no further improvement effect will be obtained, and therefore the content exceeding 1.0% is economically unnecessary.
For V, if the content exceeds 0.10%, rice grain quality decreases, and for Cr and Nb, the content exceeds Cr: 0.90% and Nb: 0.05%, respectively. Therefore, the respective contents were changed to Cu: 0.08 to 0.50%, Ni: 0.
05-1.0%, Cr: 0.05-0.90%, V: 0
．． 005% to 0.10%, and Nb: 0.005% to
It was set at 0.05%. Next, the rolled steel material of the present invention will be explained using Examples while comparing with Comparative Examples.

In each of the examples, molten steel having the composition shown in Table 1 was melted, cast, and forged to form a slab with a thickness of 20 mm or 22 mm. Hot rolling was carried out under the conditions shown in Table 1 to obtain a hot-rolled plate with a low thickness, and each of the resulting hot-rolled plates was
After conditioning by holding at 900℃ for 1 hour (indicated by N in Table 1), after conditioning with phosphorus by holding at 900℃ for 1 hour, the stress of furnace cooling was maintained at 900℃ for 1 hour. Removed Akatsuki (displayed as N + SR in Table 1), [C} If you don't want to hold it at 90pC for 1 hour, Q. Invention steel plates 1 to 34 and comparative steel plate 1
-6 were produced, respectively.

Note that none of the comparative steel plates 1 to 6 contain the B component (indicated by *), and the comparative steel plates 3 and 4 do not contain Mo (also indicated by *). Next, the obtained steel plates 1 to 34 of the present invention and comparative steel plates 1 to 6 were subjected to a pull test (using a mystery piece of a side sail of 6 skins in diameter x 30 in parallel length).
Welding heat input: 700A x 40V x 32 skins/
A welding test was conducted under the conditions of min (5 miscellaneous J/■) to measure the ballability (impact value) of the bond at the welded joint, and JI
An oblique Y-shaped welding test (heat input: 17,000 J/h, hydrogen amount: 38 cc/100 g) was conducted in accordance with S.Z 3158, and the heat temperature of the Y-joint restrained preventive element was measured. These test results are summarized in Table 2. From the results shown in Table 2, the steel plates 1 to 34 of the present invention in Table 2 all have high strength and high plowing properties, as well as excellent acid solubility, whereas steel sheets B or B and Mo
Comparative steel sheets 1 to 6, which do not contain , have almost the same high strength as the steel sheets of the present invention, but are significantly inferior in terms of grade and weldability.

Further, microstructure photographs (10 As is clear from the results, steel sheets 1 and 2 of the present invention have a structure in which fine pseudo barlite exists, whereas comparative steel sheet 1.2 has a structure in which layered pearlite or no layered pearlite exists. It is understood that such structural differences lead to the remarkable differences in properties as described above.

As mentioned above, the rolled steel material of the present invention has high strength, high rut resistance, and excellent weldability, so when used in the manufacture of pressure vessels that require these properties, this Sho melting vessel is suitable. It has industrially useful properties, such as being able to stably exhibit excellent performance over an extremely long period of time.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing the relationship between mechanical properties and C-containing leather in the aged condition and phosphorus conditioned ten stress relief annealing condition regarding the rolled steel material of the present invention and the comparative rolled steel material; FIGS. 3 and 4 are photographs showing the metallographic structure of the steel sheet of the present invention under a microscope, and FIGS. 5 and 6 are photographs showing the metallographic structure of the Rasame steel sheet under a microscope. Figure 6 Figure 3 Figure 3 Figure 2 Figure 5

Claims (1)

[Claims] 1 C: 0.13-0.30%, Si: 0.1-1.0
%, Mn: 0.5-2.0%, Mo: 0.03-0.3
5%, B: 0.00015-0.0009% (1.5p
pm to 9 ppm), sol. Al: 0.005-0.1
0%, P: 0.020% or less, S: 0.010% or less,
A composition containing N: 0.015% or less, O: 0.010% or less, and the remainder consisting of Fe and unavoidable impurities other than the above (
% by weight) and has a structure mainly consisting of ferrite and fine pseudo-barrite. 2C: 0.13-0.30%, Si: 0.1-1.0
%, Mn: 0.5-2.0%, Mo: 0.03-0.3
5%, B: 0.00015-0.0009% (1.5p
pm to 9 ppm), sol. Al: 0.005-0.1
0%, P: 0.020% or less, S: 0.010% or less,
Contains N: 0.015% or less, O: 0.010% or less, and furthermore, Cu: 0.08 to 0.50%, Ni: 0.0
5-1.0%, Cr: 0.05-0.90%, V: 0.
005-0.10%, and Nb: 0.005-0.0
5%, one or more of the following, and the rest is F.
Composition consisting of e and unavoidable impurities other than the above (weight%
) and has a structure mainly consisting of ferrite and fine pseudo-barrite.