JPS5891159A - Nonmagnetic steel roll for continuous casting and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the titled roll with superior strength, toughness and stress corrosion cracking resistance at a low cost by hot working a low carbon steel contg. Ni and/or Cu as well as Si, Al, Mn, Cr, P and S at a high reduction rate of area. CONSTITUTION:A steel consisting of, by weight, <=0.15% C, <=1.0% Si, <=0.10% sol. Al, 17.0-25.0% Mn, 10.0-15.0% Cr, <=0.03% P, <=0.010% S, <=3.0% in total of 1.0-3.0% Ni and/or 1.0-3.0% Cu and the balance essentially Fe is hot worked at >=60% reduction of area and optionally treated under heating by holding at about 900-1,180 deg.C for about 30min-15hr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention enables electromagnetic force to be effectively applied to the slab and provides a strong stirring force when applying electromagnetic stirring to the unsolidified molten metal inside the slab during solidification to improve the quality of the slab. The present invention relates to a non-magnetic steel roll for continuous casting and a method for manufacturing the same.

In continuous casting, molten steel injected from a ladle into a tundish is usually distributed and supplied to multiple molds, where it is cooled and a solidified shell grows around it, but unsolidified molten steel remains inside. In this state, the slab is pulled out by a group of support rolls following the mold, and while passing between the support rolls, it is cooled by water from a spray nozzle interposed in the group of support rolls, and becomes a completely solidified slab. In this case, the distance that the slab moves from when the molten steel is poured into the mold until it completely solidifies, that is, the distance from the molten metal surface in the mold to the complete solidification point located between the support roll group is 10 to 15
Therefore, there is an extremely elongated region of unsolidified molten steel inside the slab from the mold until it reaches the complete solidification point. This caused quality defects such as center segregation and shaft center cracks.

In recent years, in order to improve these problems, the adoption of electromagnetic stirring technology has become common, and this has resulted in significant improvements in the quality of slabs. This electromagnetic stirring is achieved by placing an electromagnetic coil facing the side of the slab at an appropriate position between the end of the mold on the upstream side of the support roll group and the complete solidification point of the slab on the downstream side. A device that applies an electromagnetic force to the unsolidified molten steel inside the slab in the horizontal or vertical direction along the side of the slab to stir it, thereby improving the solidified structure in the center of the slab and reducing center segregation, axial cracking, etc. It is.

In order to effectively perform this electromagnetic stirring, the material of the roll near the electromagnetic coil installation position should be made non-magnetic.
It is necessary to ensure that the electromagnetic force is not blocked by the rolls and is effectively applied to the unsolidified molten steel in the slab, but it is necessary to use a conventionally known non-magnetic steel material (hereinafter referred to as non-magnetic steel). However, when a support role was configured using a support role, there were the following difficulties. That is, 1) Generally, non-magnetic steel has an austenitic structure, but steel materials with this structure have a low yield point, and if the ingot is processed into rolls, the rolls will bend and deform during continuous casting operations. A situation occurs in which it becomes impossible to support the slab, making it impossible to continue the operation.

11) Cold working is a method of increasing the strength of steel cables, but due to the nature of cold working, this cannot be applied to rolls with large cross sections.

1ii) In addition, as a precipitation-strengthened steel material, A
The STM standard A-286 is known, but this is N1
It contains a large amount of , is extremely expensive, and is not practical.

iV) Furthermore, steel materials with an austenitic structure are susceptible to stress corrosion cracking in industrial materials that contain large amounts of chlorine ions, and this is due to the fact that steel materials with an austenitic structure are susceptible to stress corrosion cracking in industrial applications that contain large amounts of chlorine ions. This is extremely inconvenient when used as a support role. Cold working to increase strength as mentioned above not only further increases the susceptibility to stress corrosion cracking, but also increases the surface temperature of the roll when it comes into contact with the hot slab, causing stress corrosion cracking. Become more sensitive to this.

(2) In the process of using this steel material as a support roll, carbides precipitate at the grain boundaries, reducing toughness, and there is a risk of cracking due to thermal stress caused by contact with the slab.

vi) Furthermore, since the steel material with an austenitic structure has a low thermal conductivity and a high coefficient of thermal expansion, the thermal stress that occurs frequently during the same thermal history is greater than that of a steel material with a non-austenitic structure. In this respect as well, it is disadvantageous as a support roll material.

As described above, rolls made of conventionally known non-magnetic steel have various drawbacks and are not suitable for use as support rolls near the electromagnetic coil installation position. Like the rolls, it is currently necessary to use a ferromagnetic steel roll having a tempered martensitic structure or ferrite structure for the support roll near the position where the electromagnetic coil is installed. Therefore, the electromagnetic force is blocked by the rolls, making it impossible to obtain sufficient stirring force for the unsolidified molten steel in the slab, which has a low effect on improving the quality of the slab.In addition, it requires a large amount of electric power to apply the electromagnetic force to the slab. It has not yet been possible to avoid the inconveniences such as the need for

From the above-mentioned viewpoints, the present inventors have developed a product that has sufficient strength to support the slab, has excellent stress corrosion cracking resistance and toughness, and is capable of providing strong electromagnetic stirring to the slab. As a result of various studies conducted in order to obtain a non-magnetic steel roll for continuous casting that can apply force, the following findings (a) to (f) were obtained.

That is, a) In order to prevent the roll from bending deformation when used as a support roll for supporting slabs, the strength of the roll constituent material must be 0.2% proof stress, and the sleeve in the sleeve cooling method must have a strength of 0.2% proof stress. 35 kgt/xi or more, and 40 kg for sleeve cooling type arbor or integral roll.
C, Si, soL, and AI in the steel.

If the range of the compositional components of P, S, Mn, Cr, Ni, and Cu is adjusted to specific values and the roll is melted, a high-strength nonmagnetic steel roll that can be used as a support roll for continuous casting can be obtained. Furthermore, by appropriately setting the hot working conditions, it is possible to economically reduce the yield stress to 0,2
% yield strength, tensile strength, etc. can be obtained.

b) By keeping the amount of C component in the steel as low as possible and by appropriately setting each condition for hot working and subsequent heat treatment, precipitation of carbides is suppressed, resulting in a steel with high stress corrosion cracking resistance. A magnetic steel roll can be obtained.

C) In addition, by suppressing the amount of C component to a low value, the precipitation of carbides at the austenite grain boundaries due to the rise in roll surface temperature due to the thermal history associated with the use of the roll is suppressed, and this suppresses the precipitation of carbides at the austenite grain boundaries. Deterioration of toughness due to use is prevented, and roll cracks do not occur or propagate.

d) As mentioned above, from the viewpoint of stress corrosion cracking resistance and suppression of toughness deterioration due to roll use, if the C content in the steel is reduced to a low value, the austenite structure will become unstable. But this is Mn.

This can be sufficiently prevented by adjusting the content of component elements such as Hi and Cu. Furthermore, by blending a large amount of cheap Mn into each of these component elements, expensive N
i. The content of Cu can be suppressed as much as possible and economical efficiency can be ensured.

e) When a steel material whose composition has been adjusted in this way is subjected to hot working such as hot forging or hot rolling, the strength will improve as mentioned above, as well as ductility, toughness, and stress corrosion cracking resistance. To be able to further improve.

f) Furthermore, if the above-mentioned hot working is followed by a suitable heat treatment, the cracking susceptibility of the rolls is further reduced.

Therefore, the present invention has been made based on the above findings, and the present invention has been made based on the above findings, in which a roll for continuous casting has a carbon content of 0.15% by weight.
Below, Sl: 1.0% by weight or less, 5oL-Al: 0.10% by weight or less, Mn: 17
．． 0 to 25.0% by weight, cr: 10.0 to 15.0% by weight, P: 0.03% by weight or less, 3: 0.010% by weight or less, and further contains Ni: 1. O to 3.0% by weight, Cl: 1.0 to 3.0% by weight, or both in a range where the sum of both is 3.0% by weight or less, Fe and inevitable impurities: residual By being composed of a component composition consisting of A non-magnetic steel roll suitable as a continuous casting roll is produced by hot working at a rate of 60% or more or by subsequent heat treatment consisting of holding at a temperature of 900 to 1180°C for 30 minutes to 15 hours. It is characterized by the fact that it is made to do so.

The above-mentioned non-magnetic steel rolls of the present invention include not only integral cast rolls or forged rolls, but also ordinary sleeve/arbor type rolls, rolls with water cooling between the sleeve and the arbor, etc. , it goes without saying that it refers to all kinds of continuous casting rolls.

However, the required characteristics differ depending on the type of each roll mentioned above and the materials of parts such as sleeves and arbor, so it is desirable to select the optimal conditions for processing and heat treatment methods according to each type. .

Next, in the nonmagnetic steel roll for continuous casting and the manufacturing method thereof of the present invention, the amount of each component constituting the roll, the area reduction rate during hot working, and the range of heat treatment temperature and holding time are limited as described above. Explain why.

a) C If the content of the C component exceeds 0.15% by weight, carbides will precipitate at the grain boundaries of the austenite structure due to the thermal history received during use of the roll, which will reduce the toughness of the roll and cause stress. Susceptibility to corrosion damage also increases. Moreover, an increase in C content deteriorates the machinability of the steel material, making it difficult to form a roll. Because of this, the C content was limited to 0.15% by weight or less.

B) Sl and M Sl and At components are added to molten steel during the refining process as deoxidizing agents, but the S1 content or Bc) L and A1 content is 1.0% by weight or 0.10% by weight, respectively. Even if it is added in an amount exceeding 20% by weight, no further improvement in the deoxidizing effect is observed, and on the contrary, non-metallic inclusions increase, deteriorating the cleanliness of the roll and reducing its toughness. This also causes roll cracking.

For this reason, the Si content, sot content, and AA content were limited to 1.0% by weight or less and 0.10% by weight or less, respectively.

, T) Mn The Mn component has the effect of stabilizing the austenite structure at low cost, and is an element necessary to make the roll non-magnetic, like Ni and CU.

Since the non-magnetic roll of this invention suppresses the C content to a low value, no austenite stabilizing effect due to C can be expected.
It is necessary to contain a large amount of Mn, and in order to obtain a sufficient austenite stabilizing effect, the Mn content must be 17.0
The power of being more than % by weight! is necessary. When the Mn content is less than 17.0% by weight, the magnetic permeability μ of the roll increases,
Non-magnetic properties; they become damaged. On the other hand, if the Mn content exceeds 25.0% by weight, there is a risk of stress corrosion cracking.
It was limited to 7.0 to 25.0% by weight.

0r Cr component is an effective element for solid solution strengthening of the steel that constitutes the roll, and is added to increase the strength of the roll, but its content should not exceed 7% or 15.0% by weight. Even if the above effect is not further improved (75), on the contrary, a δ-ferrite structure is generated in the place of the austenite structure, the magnetic permeability μ force increases, and the magnetic force is impaired, and The toughness also deteriorates.On the other hand, when the content is less than 11.5% by weight, especially 10.0% by weight.
If the content is below , the corrosion rate of the roll circumferential surface E-f will not increase in industrial water, and the smoothness of the roll circumferential surface will increase. The content was limited to 10.0 to 15.0% by weight because the content would be adversely affected and the required 0.2 inch proof stress could not be obtained.

e) Ni and Cu N1 and Cu components are elements that can stabilize the austenite structure of the steel that constitutes the roll and improve corrosion resistance, but as mentioned above, it is important to keep the C content at 0.15% by weight or less. When the Mn content is increased to 17.0 to 25.0% by weight, the Ni and Cu contents are both reduced to 3.0% by weight.
By setting the content to % by weight or less, the austenite structure can be sufficiently stabilized, and the roll can be made non-magnetic. In addition, if the Cu content exceeds 3.0% by weight, the hot workability of the steel material will deteriorate.
It is appropriate to suppress the u content to 3.0% by weight or less.

and.

If the sum of the N1 and CU contents exceeds 3.0% by weight, the corrosion resistance of the roll will improve, but the stress corrosion cracking resistance will deteriorate, which is undesirable. It is necessary to make it less than 3.0 weight. On the other hand, when the Ni and CU contents are each less than 1.0 weight,
Austenite becomes unstable, magnetic permeability increases, and toughness deteriorates, so Ni and C
The content of u is 1.0 to 3°01. Even if both Ni and CU were contained together, the sum of their contents was limited to 3.0 weight or less.

If the content exceeds 0.03% by weight, the toughness will deteriorate significantly, especially when subjected to the heat history associated with roll use. The content was limited to 0.03% by weight or less. By suppressing the P content to such a low level, a good continuous casting roll can be obtained.

Although it is an element, if its content is suppressed to 0.010% by weight or less, extremely good hot ductility can be obtained, and the hot workability of the steel material improves, making it possible to strengthen it. Therefore, the content was limited to 0.010% by weight or less.

Note that the steel constituting the roll of this invention may contain up to 0.03% by weight of N as an impurity, but within this range, N is not necessary for a non-magnetic roll. It has no adverse effect on various properties.

ri) Area reduction rate of 60% during hot working In order to obtain high ductility and toughness while also taking into consideration the aperture or integral roll in sleeve cooling type rolls, and ensuring correspondingly high strength, Since it is necessary that the area reduction rate during hot working be 60% or more, the degree of working was limited to this range.

In addition, it is preferable that the finishing temperature in hot working is 900° C. or higher. This is to further increase the ductility and toughness of the roll, as well as improve stress corrosion cracking resistance.If the finishing temperature is less than 900℃, carbides or nitrides may precipitate during hot working. This is because it may encourage the occurrence of stress corrosion cracking.

i) Heat treatment temperature: 900 to 1180℃ Heat treatment of the steel material after hot working is a method suitable for manufacturing sleeves for sleeve cooling type rolls.
In particular, cracking sensitivity is reduced. The heat treatment temperature in this case is 9
If the temperature is below 00°C, the stress corrosion cracking resistance of the roll will be low and good toughness values will not be obtained;
If the temperature exceeds 180°C, the strength will decrease and the roll will bend, so the temperature should be adjusted to 900-1180°C.
It was limited to ℃. As mentioned above, even if the finishing temperature during hot working is less than 900°C and the stress corrosion cracking resistance has deteriorated, steel materials should be heat treated at 900°C or higher after hot working. Carbides or nitrides precipitated during hot working are dissolved in the base material, resulting in a roll with good stress corrosion cracking resistance.

e) Heating time: 30 minutes to 15 hours If the heating time during heat treatment is less than 30 minutes, it will be difficult to raise the temperature sufficiently to the center of the roll, and the effect of improving stress corrosion cracking resistance due to heat treatment will be reduced. I can't get it. On the other hand, even if it exceeded 15 hours, no further improvement in the effect was observed, and on the contrary, the strength of the roll decreased, so the holding time was limited to 30 minutes to 15 hours.

Next, the present invention will be explained by comparing examples and comparative examples.

Table 1 shows the chemical compositions of the steel materials A-- of the continuous casting roll of the present invention and the conventionally known non-magnetic steels LU. For these steel cables A- and L-U, Table 2 "Hot working conditions"
Hot forging was performed under the conditions as described in the column, and some of them were subsequently heat treated under the conditions described in the "Heat treatment" column of Table 2. The steel materials A to U that were hot forged or heat-treated after hot forging were tested for strength such as 0.2% proof stress and tensile strength, ductility such as elongation and drawing/shielding, and Charpy impact. In the test, we measured the toughness based on absorbed energy and the magnetic permeability μ to determine the degree of non-magnetism, and also conducted a stress corrosion cracking resistance test. These results are also listed in Table 2.

In addition, in measuring absorbed energy by the Charpy impact test, in addition to steel materials that have undergone hot forging as described above, steel materials that have been heated to 600°C after hot forging or heat treatment, assuming the thermal history that will be received during roll use, are used. Absorbed energy was also measured for steel materials that had been aged for 100 hours, and the deterioration of toughness after use of rolls was investigated. Also,
The stress corrosion cracking resistance test was conducted by immersing the steel material bent into a U-shape in an aqueous solution at 50° C. containing 500 ppm of chloride ions for one month (720 hours).

In the "Stress Corrosion Cracking Resistance" column of Table 2, ○ marks indicate cases where stress corrosion cracking occurred or did not occur, and X marks indicate cases where stress corrosion cracking occurred.

From the results shown in Table 2, the chemical composition, hot forging conditions,
The steel materials of Samples A1 to 13 according to the present invention, in which the heat treatment conditions are limited to the above-mentioned predetermined ranges, have 0 and 2% yield strength and tensile strength, which are indicators of the strength of resistance to roll bending deformation. 35, 9f/l+111 or more and 70kgf/+111 or more, respectively, which clearly indicate that the material has sufficient strength to suppress the occurrence of bending deformation, and also has good ductility and toughness. It is clear that no stress corrosion cracking occurred in the stress corrosion cracking resistance test. In addition, the magnetic permeability μ is also
As with conventional non-magnetic steel, it shows a sufficiently low value of 1.02 or less. Furthermore, it was also confirmed that even when the material was aged at 600° C. for 100 hours, the deterioration in toughness was slight and good toughness was still maintained.

On the other hand, compared to the steel according to the present invention, the C content is higher or the C content is higher than that of the steel according to the present invention.
Samples AI6 to 25 using conventional steel whose r, Mn, Ni, and CU contents are outside the specified ranges are 0.
．． Either the 2% yield strength is low, cracks have occurred in the stress corrosion cracking test, the magnetic permeability has increased to more than 102 and non-magnetism has been impaired, or sample A16
After aging at 600°C for 100 hours, the toughness deteriorates significantly, and when used as a non-magnetic support roll, bends and cracks become large, resulting in a shortened life span and the product becoming unusable. Recognize.

Even though the chemical composition is the same as the roll of the present invention, sample A14, which has a small area reduction rate during hot working, is inferior in 0.2 inch proof stress and tensile strength, and also has a lower toughness value. Sample A1 that does not show good values and has a low heat treatment temperature
It was confirmed that stress corrosion cracking occurred in sample No. 5.

As described above, according to the present invention, it is possible to obtain a non-magnetic steel roll for continuous casting at a low cost, which has sufficient strength and toughness, has little toughness deterioration during roll use, and has high stress corrosion cracking resistance. It also has no adverse effect on the electromagnetic stirring operation of continuously cast slabs. This brings about industrially useful effects, such as making it possible to manufacture slabs of excellent quality without imparting .

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo

Claims (3)

[Claims] (1) C: 0.15 cm or less, Sl: 1.0% or less, 5oL-AQ: 0.10% or less, Mn: 1'7.0 to 25.0%, Cr: 10
．． 0 to 15.0%, p: 0.03% or less, S: 0.010% or less, and further contains NIHI, 0 to 3.0%, Cu: 1.0 to 3.0%. , or both in a range of 13.0% or less of the combined strength of both, with the remainder consisting of Fe and unavoidable impurities (not less than % by weight). Non-magnetic steel roll. (2) c: 0.15 cm or less, Si: 1.0% or less, sOl, Al! : 0.10% or less, Mn: 1
'1. O~25.0%, Cr:10.0~15.0
%, P: 0.03% or less, S: 0.010% or less, and further contains any of the following: Ni: 1.0 to 3.0%, Cu: 1.0 to 3.0%. A steel material containing one or both of them in a range where the sum of both is 3.0q6 or less, and the remainder consisting of Fe and unavoidable impurities (at least % by weight) is hot-worked at a reduction in area of 60 inches or more. A manufacturing method for non-magnetic steel rolls for continuous casting. (3) C: 0.15% or less, 3i: 10% or less, 5ol-AJI: (110% day, bottom, Mn:
l 7.0-25.0%, Cr: 10.0
~15.0%, P: 0.03 or less, j3:o, 010% or less, and further contains Ni: 1. O~3.0q6, Qu: 1.0~3.0%, containing either one or both of the following in a range where the sum of both is 3.0% or less, Fe and unavoidable impurities: Remaining (or more) A steel material consisting of
A method for manufacturing a non-magnetic steel roll for continuous casting, characterized in that a heat treatment is performed by holding the roll for 0 minutes to 15 hours.