JPH057457B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to a method for manufacturing austenitic stainless steel that does not generate work cracks during hot rolling. (b) Prior art Since stainless steel contains large amounts of expensive Ni, Cr, Mo, Cu, etc., improving yield is the most important item for reducing manufacturing costs. Therefore, it is desired to improve the yield through continuous casting and prevention of defects in the manufacturing process. However, in terms of corrosion resistance, oxidation resistance and strength
Stainless steel containing large amounts of Ni, Cr, Mo, Cu, N, etc. has poor hot workability and cracks occur at dendrite grain boundaries during hot working, making it impossible to manufacture and requiring continuous casting. There are many high-alloy stainless steels that have not been cast continuously, and even when they are continuously cast, they produce scratches that reduce yields. First, in order to improve the hot workability of continuously cast slabs, it is necessary to further improve the grain boundary ductility of dendrites during casting, and the PV shown by equation (1) is
It was revealed that hot workability is good when δF is 30 or less and δF shown by equation (2) is −10 or more (Japanese Patent Application No. 58-58200), but hot workability is improved when δF is less than −10. Measures to improve workability were unclear. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) (c) OBJECTS OF THE INVENTION The purpose of the present invention is to improve hot workability and increase yield in the production of stainless steel. (d) Structure of the Invention The hot workability of alloys with a wide range of compositions with varying amounts of S, O, and added amounts of Ca and Ce is obtained by vacuum melting slabs and slabs continuously cast in an electric furnace (AOD). We conducted an evaluation. As shown in Figure 1, hot workability can be organized by δF and PV. It was also found that the region with good hot workability can be organized using equation (3). PV≦3δF+45…(3) In addition, the good hot workability region in Figure 1 indicates a minimum reduction of area of 60% or more at 950 to 1200℃ in a high-temperature tensile test, and a hot impact average score of 1 or less. The poor machinability area is 950~ in high temperature tensile test.
Indicates a minimum reduction of area value of less than 60% at 1200°C or a hot shock average rating of 1 or more. In FIG. 1, the ○ mark indicates a minimum aperture value of 60% or more and the hot shock average rating of 1 or less, and the ● mark indicates a minimum aperture value of less than 60% and a hot impact average rating of less than 1. δF represents the δ ferrite index in the cast structure,
PV indicates the detoxification index of S and O, and the relationship in equation (3) indicates that when the amount of δ ferrite is small, S and O must be further reduced or Ca and Ce must be added. means. δ ferrite is S
This reduces the segregation of O and O to the γ grain boundaries. Therefore, if δF is low, cracks at the γ grain boundaries will occur due to hot working unless S and O are lowered to clean the γ grain boundaries. Additionally, Ca and Ce fix O and S, prevent the formation of MnS, and greatly improve hot workability. In other words, hot workability is improved by reducing PV even with a small δF. In the present invention, the components are adjusted so as to satisfy equation (3) in a region where the ΔF value is less than 1.5. In order to reduce the PV value, in the present invention, Ca, Ce
Either reduce the S content to 0.001% or less and the O content to 0.003% or less without adding Ca, or
and Ce in a total amount of 0.03% or less, and reduce the S content to 0.003% or less and the O content to 0.004% or less. S and O
Ca and Ce have the effect of fixing S and O, which are harmful to hot workability, and improve hot workability. This is because it deteriorates the properties and corrosion resistance. The reasons for limiting the other components will be described below. C: Although C is harmful to the corrosion resistance of stainless steel, it is effective for obtaining high strength. Accordingly
Up to 0.15%. Si: Si increases the corrosion and oxidation resistance of stainless steel. However, if Si content exceeds 5%, the effect becomes saturated and hot workability deteriorates. Mn: Mn increases the solid solubility of N and is effective in stabilizing austenite in steel, and is also used as a substitute for Ni, but it deteriorates corrosion resistance, so the upper limit should be limited.
It was set at 12%. Cr: Cr is a basic component of stainless steel, and 15% or more is particularly effective; the higher the amount, the better the corrosion resistance and oxidation resistance, but if it exceeds 35%, it becomes expensive. Ni: Ni, along with Cr, is a basic component of stainless steel and heat-resistant steel. If it is less than 2%, it is difficult to maintain the austenitic structure and obtain the minimum required properties; more is more effective, but if it exceeds 40%, it becomes extremely expensive. Mo: Mo increases the corrosion resistance and strength of stainless steel,
Selectively add 5.5% or less depending on the application. If it exceeds this value, the effect will be saturated and hot workability will deteriorate. Cu: Cu increases the corrosion resistance of stainless steel and is selectively added at 5% or less depending on the application. If it exceeds 5%, hot workability deteriorates. N: N is effective in improving the hot workability, strength, and corrosion resistance of stainless steel, and can be adjusted from 0.01 to 0.01 depending on the application.
Add in a range of 0.35%. Al: Al is added at 0.1% or less as a strong deoxidizing agent. Al coexists with Ca or Ce in low S steel and O
, and reduces Si and Mn oxides, greatly improving hot workability. Ti, Nb, Zr, Ta: Ti, Nb, Zr and Ta are C
It preferentially combines with C to reduce the negative effect of C on corrosion resistance. These components can be used alone or in combination of two or more, and the total content must be at least four times the C%. However, if added in large amounts, the cleanliness and workability of the steel will deteriorate, so the upper limit can be kept to 1.5%. (e) Example Table 1 shows the melting process using the electric furnace-AOD method.
The steel composition of the present invention example and the comparative example, which were continuously cast into slabs of mm thickness x 1000 mm width and billets of 150 mm square, are shown. Furthermore, by hot rolling the slab,
Plate materials with a thickness of 3.3 to 5.0 mm and wire rods with a diameter of 5.5 to 10 mm were obtained, and the evaluation of hot workability is shown in Table 2. Continuously cast slabs made using the method of the present invention, that is, steel that satisfies PV≦3δF+45, have no hot work cracks or sagging defects, compared to comparative steel, that is, PV≦3δF+45.
Continuously cast slabs made of steel that do not satisfy the above conditions are either impossible to manufacture due to frequent cracking during hot working, or cracks occur frequently on both sides of the hot coil, resulting in increased side truncation and peeling defects in the next process. This caused a significant decrease in yield.

【table】

【table】

[Table] (f) Effect of the invention The present invention has a high content of Ni, Cr, Mo, N, etc. that require corrosion resistance, oxidation resistance, high strength, etc. By enabling continuous casting of the high-alloy stainless steel we manufacture and reducing machining crack defects caused by hot rolling,
Many effects such as significant production cost reduction and yield improvement can be obtained.

[Brief explanation of the drawing]

FIG. 1 shows regions with good hot workability and regions with poor hot workability in terms of the relationship between δF and PV.

Claims (1)

[Claims] 1 C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, S: 0.001% or less,
O: reduced to 0.003% or less, with the remainder consisting of Fe and unavoidable impurities, and the components are adjusted so that the PV value shown by equation (1) and the δF value shown by equation (2) are within the range of equation (3). A method for producing austenitic stainless steel with excellent hot workability, which comprises continuously casting molten steel and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 2 C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, S: 0.001% or less, O: 0.003%
Continuously produce molten steel whose composition has been adjusted so that the PV value shown in equation (1) and the δF value shown in equation (2) are within the range of equation (3), with the balance being Fe and unavoidable impurities. A method for producing austenitic stainless steel with excellent hot workability, which comprises casting and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 3 C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, further contains Al: 0.1% or less, S: reduced to 0.001% or less, O: reduced to 0.003% or less, the balance consisting of Fe and inevitable impurities,
The PV value shown in equation (1) and the δF value shown in equation (2) are (3)
A method for producing austenitic stainless steel with excellent hot workability, characterized by continuously casting molten steel whose composition has been adjusted to fall within the range of the formula, and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 4 C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, Al: 0.1% or less, further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, S: 0.001% or less, O: 0.003 %, the remainder consists of Fe and unavoidable impurities, and the PV value shown by equation (1) and
Hot workability characterized by continuously casting molten steel whose composition has been adjusted so that the δF value shown by equation (2) falls within the range of equation (3), and hot rolling the obtained continuously cast slab. A method of manufacturing superior austenitic stainless steel. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 5% by weight: C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, and further contains Ti, Nb, and Zr.
A total of 4x of one or more of Ta and Ta
Contains C ~ 1.5%, S: 0.001% or less, O: 0.003
%, the remainder consists of Fe and unavoidable impurities, and the composition has been adjusted so that the PV value shown by equation (1) and the δF value shown by equation (2) are within the range of equation (3). A method for producing austenitic stainless steel with excellent hot workability, which comprises continuous casting and hot rolling of the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 6 C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, Al: 0.1% or less, and further contains 4×C to 1.5% in total of one or more of Ti, Nb, Zr, and Ta, S: 0.001%
Hereinafter, O: is reduced to 0.003% or less, the remainder consists of Fe and unavoidable impurities, and the PV value shown by equation (1) and the δF value shown by equation (2) are within the range of equation (3). A method for producing austenitic stainless steel with excellent hot workability, characterized by continuously casting molten steel whose composition has been adjusted and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 7 In terms of weight%, C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, and further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, and one or more of Ti, Nb, Zr, and Ta in total. Contains 4×C ~ 1.5%,
S: reduced to 0.001% or less, O: reduced to 0.003% or less, and the remainder consists of Fe and unavoidable impurities, and the PV value shown by equation (1) and the δF value shown by equation (2) are within the range of equation (3). A method for producing austenitic stainless steel with excellent hot workability, characterized by continuously casting molten steel whose composition has been adjusted so as to have the following properties, and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 8 At weight%, C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, Al: 0.1% or less, and further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, Ti, Nb, Zr, and
Total of 1 or 2 or more types of Ta: 4 x C ~ 1.5
%, S: 0.001% or less, O: 0.003% or less, the remainder consists of Fe and unavoidable impurities, and the PV value shown by equation (1) and the δF value shown by equation (2) are ( 3) A method for producing austenitic stainless steel with excellent hot workability, characterized by continuously casting molten steel whose composition has been adjusted to fall within the range of the formula, and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 9 C: 0.15% or less, Si: 5% or less,
Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, S: 0.003% or less,
O: reduced to 0.004% or less and Ca and Ce
Contains 0.03% or less in total of one or two of the following, with the balance consisting of Fe and unavoidable impurities, and the PV value shown by formula (1) and the δF value shown by formula (2) are within the range of formula (3). A method for producing austenitic stainless steel with excellent hot workability, characterized by continuously casting molten steel whose composition has been adjusted so as to have the following properties, and hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 10% by weight: C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, S: 0.003% or less, O: 0.004%
It contains 0.03% or less of one or both of Ca and Ce in total, and the balance consists of Fe and unavoidable impurities, and the PV value shown by formula (1) and δF shown by formula (2) An austenitic stainless steel with excellent hot workability is produced by continuously casting molten steel whose composition has been adjusted so that the value falls within the range of formula (3), and hot rolling the obtained continuously cast slab. Production method. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 11 In weight%, C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, further contains Al: 0.1% or less, S: 0.003% or less, O: 0.004% or less, and one or both of Ca and Ce in total is 0.03% or less. Continuously cast molten steel whose composition is adjusted so that the PV value shown by equation (1) and the δF value shown by equation (2) fall within the range of equation (3). A method for producing austenitic stainless steel with excellent hot workability, which comprises hot rolling the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 12 C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, Al: 0.1% or less, further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, S: 0.003% or less, O: 0.004 % or less, and contains one or both of Ca and Ce in a total of 0.03% or less, with the balance consisting of Fe and unavoidable impurities, (1)
The molten steel whose composition has been adjusted so that the PV value shown by equation (2) and the δF value shown by equation (2) are within the range of equation (3) is continuously cast, and the obtained continuously cast slab is hot rolled. A manufacturing method for austenitic stainless steel with excellent hot workability. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 13 In weight%, C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, and further contains Ti, Nb, and Zr.
A total of 4x of one or more of Ta and Ta
Contains C ~ 1.5%, S: 0.003% or less, O: 0.004
% or less, and contains one or both of Ca and Ce in a total of 0.03% or less, with the balance consisting of Fe and unavoidable impurities, and is expressed by formula (1).
A hot rolling process characterized by continuous casting of molten steel whose composition has been adjusted so that the δF value shown in equation (2) is within the range of equation (3), and the obtained continuously cast slab is hot rolled. A method for manufacturing austenitic stainless steel with excellent workability. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 14 In weight%, C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, Al: 0.1% or less, and further contains 4×C to 1.5% in total of one or more of Ti, Nb, Zr, and Ta, S: 0.003%
Hereinafter, O: is reduced to 0.004% or less, and contains one or both of Ca and Ce in a total of 0.03% or less, with the balance consisting of Fe and unavoidable impurities, (1)
The molten steel whose composition has been adjusted so that the PV value shown by equation (2) and the δF value shown by equation (2) are within the range of equation (3) is continuously cast, and the obtained continuously cast slab is hot rolled. A manufacturing method for austenitic stainless steel with excellent hot workability. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 15% by weight: C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni2-40%,
Contains N: 0.01 to 0.35%, and further contains at least one selected from Mo: 5.5% or less, Cu: 5% or less, and one or more of Ti, Nb, Zr, and Ta in total. Contains 4×C ~ 1.5%,
Reduce S: 0.003% or less, O: 0.004% or less, and reduce the total content of one or both of Ca and Ce.
Molten steel containing 0.03% or less, the balance consisting of Fe and unavoidable impurities, and whose composition has been adjusted so that the PV value shown by equation (1) and the δF value shown by equation (2) are within the range of equation (3). A method for producing austenitic stainless steel with excellent hot workability, which comprises continuous casting and hot rolling of the obtained continuously cast slab. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 ...(3) 16 In weight%, C: 0.15% or less, Si: 5% or less, Mn: 12% or less, Cr: 15-35%, Ni: 2-40
%, N: 0.01 to 0.35%, Al: 0.1% or less,
Furthermore, at least one selected from Mo: 5.5% or less, Cu: 5% or less, and one or more of Ti, Nb, Zr, and Ta, in total 4 × C ~
Contains 1.5%, S: 0.003% or less, O: 0.004% or less, and contains one or both of Ca and Ce in a total of 0.03% or less, the balance consisting of Fe and inevitable impurities, (1 ) and the PV value shown by the formula
Hot workability characterized by continuously casting molten steel whose composition has been adjusted so that the δF value shown by equation (2) falls within the range of equation (3), and hot rolling the obtained continuously cast slab. A method of manufacturing superior austenitic stainless steel. PV (ppm) = S + O - 0.8Ca - 0.3Ce ... (1) δF (%) = 3 (Cr + Mo + 1.5Si) -2.8 [Ni + 0.5 (Mn + Cu) + 30 (C + N)] -19.8 ... (2) PV≦3δF + 45 …(3)