JPS5913021A - Production of steel material having high strength and high toughness - Google Patents

Abstract

PURPOSE:To produce a steel material having high strength and high toughness with a compsn. having a low carbon equiv. by incorporating C, Si, Mn, Mo, Nb, B and solAl in a specific ratio in iron, and subjecting the same to heating, rolling, cooling, heating, hot working, air cooling and reheating successively under specific conditions. CONSTITUTION:The steel contg. <=0.20% C, 0.05-0.5% Si, 0.5-2.5% Mn, 0.05- 0.6% Mo, 0.01-0.1% Nb, 0.0005-0.01% B, <=0.1% solAl, contg., if necessary, 0.005-0.1% Ti, and further 1 or >=2 kinds of 0.01-0.15% V, <=0.5% Cu, <=1.0% Nb, <=1.0% Cr, and consisting of the balance iron and unavoidable impurities is heated to the austenitization temp. or above, and is sbjected to the rolling wherein cumulative draft at <=900 deg.C is kept at >=20%. After the steel is once cooled, the steel is heated to 820-980 deg.C and is air cooled with or without hot working and is then reheated to 400-700 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to improve the composition of steel materials for hot working such as fittings (hereinafter referred to as low Ceq), and its gist is 0) controlled rolling ( Control
ed Rolling Hereinafter referred to as CR, the following three points are combined: (c) Nyor fine graining, (c+) fine graining after hot working with Nb or after standardization, and (c) high strength using solid solution poron. .

By the way, 1. the above-mentioned fitting refers to the following processing step.

(1) Steel plate → hot processing → tempering: fabricator who purchased steel plate from a steel manufacturer
A (processor) heats the steel plate to an austenite region, then hot-works it and tempers it, and this hot-working may be performed not only once but several times.

(11) Steel plate → hot working → standard → tempering: This is almost the same process as the above middle process, but after fitting the material into a specified shape, standardization is performed to ensure that the material is perfect. Naturally, it is possible that the machining process is repeated several times.

(m) Steel plate → hot working → welding → stress removal annealing; A welding process may be required to form the specified shape, and in order to remove the welding residual stress generated by this welding, the entire fitting is stressed. Since it is a removal annealing process, the base metal will naturally undergo a tempering process, and standards may naturally be conducted before welding. ,,.

That is. Therefore, it can be said that the normalizing and hot working specified in the present invention are performed more often by a processing company than by a steel manufacturer. ,.

However, it goes without saying that the scope of the manufacturing method of the present invention does not apply even if the steel manufacturer processes the steel and ships it in the above-mentioned processing. , ,Recently, in the field of steel materials for hot working, the usage environment is gradually becoming more severe.1. It has been requested.

Ordinary low-alloy steel with relatively low hardenability is tempered or stress-relieving annealed (hereinafter referred to as NT) after hot working or standardization.
In this case, it is extremely difficult to satisfy high strength if the steel has a low Caq, that is, a steel with a small amount of alloy elements. In addition, in order to obtain high strength in the steel that has undergone the above treatment, it is necessary to increase the alloy components, which results in an increase in Caq.1. This will impair weldability.

On the other hand, from the viewpoint of obtaining high strength with low Ce q with emphasis on weldability, the conventional methods are 74. The method was known. However, as mentioned above (
In method 1), about 1% of Cu is contained in the steel, and by tempering after standardization, 5-Cu precipitates, resulting in a low Ceq.
Although it exhibits excellent material quality and weldability, there is a problem in that the addition of a large amount of Cu impairs hot workability. In addition, the method (11) above is based on “Jinmin Metal Vol.
, 31 N1140ct, 1979, Page
1-12, although high strength is obtained at low Ceq, in terms of toughness, the fracture surface transition temperature (vTs
) was approximately 0°C, which was unsatisfactory in this respect.

In addition, as a method for improving toughness, a method of standard treatment after controlled rolling is proposed in JP-A-53-56818 and JP-A-54.
Although there is No.-17317,
In the case of No. 818, Nb is not mentioned at all,
In the case of JP-A-54-17317, the plate thickness is as thin as 12 to 20 mm, and the strength is insufficient.

Based on the philosophy that it is essential to refine the structure at the same time, we conducted a detailed study on the Mo-Nb-B system fMK, and found that this steel was subjected to a specific controlled rolling (CR) and then NT. In this case, it was found that significantly higher toughness can be obtained than steel that does not contain Nb and steel that contains Nb but is rolled without CR.

This means that when Nb@ is OKed, the unrecrystallized austenite grains elongate, a deformation zone is introduced inside the austenite, the number of transformation nucleation sites to ferrite increases, and the structure becomes finer. Even when heated, the structure obtained in the rolled state is fine and Nb (CN 2 ) precipitates are present, so the heated austenite grains become finer and the toughness after NT becomes better.

The details of the γ-grain refinement mechanism during standard heating of Nb steel after controlled rolling are unknown, but because Nb (CN) is uniformly and finely dispersed, the inside of the Nb steel before the α→γ transformation during reheating is It is thought that this prevents the disappearance of the structure and also prevents the coarsening of the γ grains in the γ region.

The present invention provides mco, 2% or less, 8i0.05-0.5%
, Mn 0.5-2.2%, Mo 0.05-0.6%
, Nb0.01~ is heated above the austenitizing temperature, rolled with a cumulative reduction of 20% or more at 900°C or less, cooled once, then heated to 820 to 980°C, and then hot worked. Or to do it (air cooling, then 4
840 characterized by reheating to 00-700℃
, 05-0.5%, Mn 0.5-2.2%, MoQ,
05-0.6%, NbO, 01-0.1%, Bo,
0005 to 0.01%, sot, N, 0.1% or less, as well as Ti 0.005 to 0.1%, the remainder consisting of iron and unavoidable impurities, is heated above the austenitizing temperature, Rolling is performed at a cumulative reduction of 20% or more at 900°C or lower, once cooled, then heated to 820-980°C, air-cooled with or without hot working, and then SiO,05-0. 5%, Mn0.5-2.2%,
Moo, 05-0.6%, Nb0.01-0.1%, B
o, 0005% to 0.01%, sot, A10.1% or less, and ■0.01 to 0.15%, Cu0.5
% or less, Ni 1.0% or less, Cr 1.0% or less, the remainder is iron and unavoidable impurities, and the steel is heated above the austenitizing temperature to 900°C.
Rolling is performed with the following cumulative reduction of 20% or more, and once cooled.

Then, after heating to 820-980°C, hot working is carried out (8) A method for producing high-strength, high-toughness steel material characterized by air cooling without heating and then reheating to 400-700°C. . (4) CD, 20% or less, 810.05~0
．． 5%, Mn 0.5~2.2%, Mo 0.05~
0.6%, Nb0.01~0.1%, B Ooo 00
5~0.01%, 80t, A1 0.1% or less, TlO, 005~0.1%, and VD, 01~
0.15%, Cu 0.5% or less, Ni 0.1% or less, C
Steel containing one or more types of r1.0% or less, the remainder consisting of iron and unavoidable impurities, is heated to a temperature higher than the austenitizing temperature and rolled at a cumulative reduction of 20% or higher at 900°C or lower. temperature, cooled once, and then heated to 820 to 980
After heating to .degree. C., it is air-cooled with or without heat processing, and then air-cooled to 400.degree. C. Next, the reasons for limiting the chemical components of the present invention will be described.

C is an effective element for increasing strength, and is also a necessary element for obtaining carbides such as Nb. However, if it exceeds 0.20%, the toughness of the base metal deteriorates and the hardening of the weld zone becomes significant, so this was set as the upper limit.

Si, 1. This element is added for deoxidation and strength reasons, and if it is less than O,OS%, this effect cannot be sufficiently obtained, so this is set as the lower limit, and if it exceeds 0.5%, weldability deteriorates, so this is set as the lower limit. The upper limit was set.

Pigeon is an element necessary for high strength and hexagonal properties of steel materials, and if it is less than 0.5%, this effect will be small, so this is the lower limit, and if it exceeds 2.2%, weldability will be significantly impaired. Therefore, this was set as the upper limit.

Mo is an essential element for making steel materials high in strength and toughness. If it is less than 0.05%, this effect is small and the desired purpose cannot be achieved, so this is set as the lower limit, and 0.6% is also If it exceeds this, weldability will be impaired, so this is set as the upper limit.

Since the effect is small at full capacity, this is the lower limit, and 0.1
%, weldability deteriorates significantly, so this was set as the upper limit.

B has the effect of significantly improving hardenability even in a small amount, and is an essential component for increasing strength.

However, if it is less than 0.01%, the effect will be small, so this should be set as the lower limit, and if it exceeds 0.01%, the toughness of the base metal and the weld heat affected zone (HAD) will be impaired, so this should be set as the upper limit. did.

sot, A1 is necessary for deoxidizing steel, and also fixes nitrogen as AgN during normalizing and hot working, and B is free.
Ni is an essential element for exhibiting the hardenability improvement effect of B, and is contained in an amount of 0.1% or less. When Ti is not included at all, the lower limit is set at o, ois%, and in order to completely fix the chamber plate, it is preferable to add an excess of at least 6 times the elementary amount of fg. When Ill i is added, Ti has a nitrogen fixing effect, so the lower limit of sot A1 is so
tM > 3 (total N-T!/Z,, 4
) may be 0.0005%, which is necessary for deoxidation. Also, the upper limit is 0, 1 regardless of whether Ti is included or not.
%. This is because if it exceeds this, the cleanliness of the steel will be impaired and the weldability will be impaired.

N is 1. Above IQ5, if it is present in a large amount, it will combine with B to form BN, reducing the hardenability improvement of B.

Therefore, the upper limit of O.Ti must be set at 0.01%5, which was also mentioned above. N is an effective element for determining Vi1, but if it is less than 0.005%, its effect is small, so this is the lower limit, and if it exceeds 0.1%, it will damage the toughness of similar materials and welded parts. This is the upper limit.

Next, the reasons for limiting the elements to be added as necessary in the present invention will be described. ,.

■ has the effect of improving the strength and toughness of steel by 0.01
If the content is less than 0.15%, the effect will be small or non-existent, so this is set as the lower limit, and if it exceeds 0.15%, the toughness of the base material and HAZ will be significantly deteriorated, so this is set as the upper limit.

Ni has the effect of improving the strength and toughness of steel without impairing weldability, but it is economically undesirable to exceed 1.0%, so this was set as the upper limit.

Although it has approximately the same effect as C111,Ni, 1, if added in a large amount, surface flaws are likely to occur during hot rolling, so the upper limit was set at 0.5. , .

Cr has the effect of improving the strength and toughness of steel materials, but 5
．． ．． 1.0. If it exceeds %, weldability will be impaired, so this was set as the upper limit. .

Next, the reasons for the rolling and heating conditions limited in the present invention will be explained.

In the present invention, the reason why the heating temperature before rolling is limited to one austenitizing temperature or higher is 5. This is to make the structure before rolling a uniform genius-stenite structure, and to make Nb a solid solution in the steel to exhibit the effect of Nb during control and rolling.

In addition, in the present invention, the cumulative rolling reduction rate of 900°C or less is 2.
0. , % or more is limited to 5 or more as shown in FIG.

(Furthermore, in the present invention, the heating temperature for hot working or normalizing is limited to 820 to 980°C.) If the temperature is lower than this, the structure becomes non-uniform and the toughness deteriorates. This is because at temperatures exceeding this, the austenite grains become coarse and the toughness deteriorates.
゛Furthermore, in the present invention, the reheating temperature after the standard is set to 40
When the temperature is 0 to 700°C, when the hardenability is high like the steel of the present invention, the steel material becomes composed mainly of 1-bainite after normalizing, and the ductility improves by reheating. do. Furthermore, if one weld is performed, reheating is required to release residual stress. For this purpose, sufficient gelatin cannot be obtained at temperatures below 400°C, and
This range was chosen because the strength would decrease if the fore-furnace was performed at 7i and MW exceeding 00°C.

11th No. 1 shows the relationship between Nbt# and the material after NT, and FIG. 2 shows the relationship between the Crt ratio and the material in Nb steel, as described above. From Figure 1, the amount of Nb is 0.0
It can be seen that excellent toughness can be obtained when CR-N'l''tt is applied at 1% or more, and from Figure 2, even with Nb steel, the cumulative reduction rate at 900°C or less must be 20% or more. ^ It is essential that sex cannot be obtained. That is, M.O.
This is because it lowers the γ-α transformation point after CR, refines the structure after rolling, and further has the effect of partly suppressing coarsening of the structure due to precipitation of Mo carbides during reheating. In Figure 1, an example of Mo free (does not contain MO) #I4 is shown as “
Steel 4".

In this example, not only the strength but also the toughness deteriorated, and this toughness deterioration is due to the decrease after quenching and the lack of the above-mentioned effects.

Further add B. Mo, Nb, and B are all known as elements that improve hardenability, and these are added at the same time. , a synergistic effect can be obtained,
Superior strength can be obtained compared to the case of using either one or two of these. .

According to the present invention, the tensile strength is 55 IC9/, I+7,
(2) Excellent performance steel material with a temperature of 8 -40°C or less can be obtained.

Next, examples of the present invention will be shown together with comparative examples, and the explanation of the present invention will be fully supplemented.

Tables 1 and 3 show the chemical composition and roy (%) of the test steel.
) Ni (%)] Steel 2, 3 and fMl in the table
1, 12, 13.14 all satisfy the scope of the present invention in terms of their components. ! NT for 111,2,3,4
The subsequent materials are shown in Table 2 and FIGS. 1 and 2. Since this FIG. 1.2 has already been explained, it will be omitted here.

Steels 5, 6, and 7.8 in Table 3 do not contain B, and are used with planes 9 and 10 B, but N is u, T.
Since B is present in excess relative to i, the effect of improving the hardenability of B cannot be expected. Table 4 shows Mo -N, -B thread 1
The results are summarized as 1, 12, 13, and 14. It can be seen from this table that the material of the present invention has superior strength and toughness compared to the comparative material.

For example, plate Ir Gt steel 11 has a plate thickness of 45 n and Ce
qLRO037 has a high strength of 9/- compared to T858, and the toughness is gentle and excellent at vls -70°C. steel 12,1
3(D Yo'3 K CeqLRlri O,420~
0.464 To? fiy<'lx 7;), the hardenability is improved, and with a plate thickness of 45 mm, a VTR with a high strength of TS>60 kg/lj and a temperature below -40°C can be obtained.

With this steel, good material quality can be obtained even if the plate thickness is as thick as 60 mm like Steel 14. Tempering L? Regarding the liK degree, there is no problem as long as it is within the scope of the present invention.
! 1111 or board number M, ij? Safe materials such as 111 can be obtained.

On the other hand, the effect of B was not observed in the comparative materials E and F (Steel 9 and 10), and although the components were relatively high, TS Ke60 had a
Also, the TS of steel 8, written on the board, remains at 60 to 9/- or less despite its relatively high composition. In addition, board A, @5, board B, steel 6, and board C9 steel 7 are all conventional types with Ceq LR of 0.40 to 0.46 with emphasis on weldability, but the strength and toughness of each is ceqLRO. ,3
Plate number 7 is inferior to steel 11.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between Nb content and material quality, and FIG. 2 is a graph showing the influence of cR on the material quality of NT material. Agent: Patent attorney: Mitsu Kimura Term: Souji Sasaki Figure 1 Nbf (%) Figure 2 900°c)% JCR rate (%) Procedural amendment (voluntary) Commissioner of the Japan Patent Office August 16, 1981 1 , Indication of the case 1982 Patent Application No. 119859 2, Title of the invention Process for manufacturing high strength and high toughness steel material (amended name) Name (4
12) Nippon Steel Tube Co., Ltd. (name) 4. Agent 6, Subject of amendment 7, Contents of amendment (1) In the column of issuer name of the application and specification [Method of manufacturing high strength and high toughness steel materials] The text has been corrected to read "method for producing high-strength, high-toughness steel." (2) Supplement the claims section of the specification as per the attached 5 sheets (
31, page 3, line 5 from the bottom, page 5, line 5, line 6 from the bottom, page 7, line 11', page 9, line 1, line 11', page 10, line 2 Line, line 15, page 11, line 6, 10
Line 16, page 14, line 16, page 15, 4 from the bottom
In line 2 from the bottom, bottom line, page 16, line 10, ``
"High toughness" [High (4; Ni in Table 1 on page 19)
Add "2" to the blank column of "Hagane 1". (5) Page 20, Table 6, rl, 67J in the column of Tane and Steel 6
A certain j, r 1.61 J is supplemented. Attached patent claims (1100, 20% or less 48i0.05 to 0°51s%
2.2ts%MoO in MrI0.5, 05~0.6%
, NbO,0.1~0.1'16%BO,000
A steel containing 5 to 0.01 Ch, 5 OtAt 0.1- or less, the remainder consisting of iron and unavoidable impurities, is heated to a temperature above the austenitizing temperature and subjected to a cumulative reduction of 900°C or less for 20
- Perform rolling to above, cool once, and then roll to 820~
A method for producing a high-strength, high-toughness steel material, which comprises heating to 980°C, air cooling with or without hot working, and then reheating to 400 to 700°C. (2) CO, 20% or less, SiO, 05~
0.5%, Mn0.5-2.2%%Mo0.05-0,
69g, NbO, 01~0.1%, BO, 00
0.05 to 0.01 Ti, 5O1-AlO, 1% or less, and a steel containing 0.005 to 0.1% of Ti, the remainder consisting of iron and unavoidable impurities, is heated above the austenitizing temperature, Rolling is performed with a cumulative reduction of 20 inches or more at 900°C or less, once cooled, then heated to 820 to 980°C, air cooled with or without hot working, and then
A method for producing a high-strength, high-toughness steel material, which comprises reheating to 00 to 700°C. (3) C0,20q6 or less, Si 0505~0.
5%, Mn 0.5-2.2chi, Mo 0.05-0.6
%, Nb O, 01~0.1%, BO, 0005~0
．． 01%, sot, At o, i% or less, further including y O, O + ~0.15%, CuO, 5% or less,
Ni 1.0% or less, Cr 1.0% or less type 1 or 2
A steel containing at least 100% of carbon dioxide and the remainder consisting of iron and unavoidable impurities is heated to a temperature higher than the austenitizing temperature, rolled at a cumulative reduction of 20% or higher at 900°C or lower, and once cooled.
A method for producing a high-strength, high-toughness steel material, which comprises heating to 820 to 980°C, air cooling with or without hot working, and then reheating to 400 to 700°C. f41 CO, 20% or less, Si 0.05-0.
5%, Mn 0.5-2.2%-Mo 0.05-0.
6%, Nb O, 01~0.1%, B O, 0005~
0.01% 5oL-At O,I In addition to the following, it also contains TiO,005~0.1%, and further vO1
01 to 0.15%, CuO, 5% or less, Ni 1.0 or less, Cr 1.0 or less, and the remainder is iron and unavoidable impurities. Heating to above temperature, rolling with a cumulative reduction of 20 inches or more at 900°C or less, cooling once, then rolling to 820-9
A method for producing a high-strength, high-toughness steel material, which comprises heating to 80°C, air cooling with or without hot working, and then reheating to 400 to 700°C.

Claims (1)

[Claims] (1) = CD, 20% or less, 8i0.05 to 0.5
%, MnO, 5-2.2%, Mo 0.05-0.6%
, NbO, Oi is heated above the austenitizing temperature, rolled with a cumulative reduction of 20% or more at 9.00°C or lower, once cooled, and then rolled at 820 to 980°C.
After K heating, hot processing is performed. (2) 0.20% or less, SiO, 05-0.5%
, MnO, 5-2.2%, Moo, 05-0.6%,
NbO, 01-0.1%, BO, 0005-0.
01%, 5oLA 10.1% or less, as well as TiO, OD
Steel containing 5 to 0.1% and the remainder consisting of iron and unavoidable impurities is heated above the austenitizing temperature to 900%
Rolling with a cumulative reduction of 20% or more below °C is performed, once cooled, then heated to 820 to 980 °C, air cooled with or without hot working, and then (3) CD, 2
0% or less, 8i 0.05-0.5%, Mn015-2
．． 2%, MoO, 05~0.6%, NbO, 01~
0.1%, B Ooo 005~0.01%, so/,
Contains 0.1% or less of At, and further [V O,01~0.1
5%, Cu O, 5% or less, Ni 1.0% or less, Cr1
．． A steel containing 0% or less of one or more kinds, with the remainder consisting of iron and unavoidable impurities, is heated above the austenitizing temperature and rolled at 900°C or below with a cumulative reduction of 20% or more. After cooling and then heating to 820 to 980°C, hot processing or processing. (4) CO, 20% or less, 810.05-0.5%
, MnO, 5-2.2%, Mo0.05-0.6%, N
bO, 01~0.1%, Bo, 0005~0.01%
, sot, u 0.1% or less and Ti 0.00
Contains 5 to 0.1%, and further contains vo, oi to o,
i s%, Cu 0.5% or less, N 11.0% or less, C
Steel containing one or more of r1.0% or less, the remainder consisting of iron and unavoidable impurities, is heated to a temperature higher than the austenidizing temperature and rolled at a cumulative reduction of 20% or higher at 900°C or lower. temperature, cooled once, and then heated to 820-980°C
After heating to , with or without hot processing