JP2751582B2 - Method for producing Fe-Ni alloy hot-rolled steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a hot-rolled steel strip made of an Fe—Ni alloy containing 35 to 55% Ni. In this specification,%
"%" Means% by weight unless otherwise specified.

[Conventional technology]

Fe- (35-55%) Ni alloy or Fe-7% or less Cr-
(35-55%) Fe-Ni alloys such as Ni alloys are widely used as materials for various electronic parts because of their low coefficient of thermal expansion and excellent sealing properties with glass and ceramics.
For example, a 36% Fe-Ni alloy has the lowest coefficient of thermal expansion, and is used as a shadow mask material for television receivers and as a 42% Fe-Ni alloy.
Ni alloy has a coefficient of thermal expansion of about 4 × 10 ^-6 / ° C around room temperature, and has excellent sealing properties with IC packages, good plating properties and good solderability. ing. A thin coil having a thickness of 0.25 to 0.15 mm used for such a material as a shadow mask or an IC lead frame is obtained by cold rolling a hot-rolled steel sheet of an Fe-Ni alloy.

By the way, as a method for efficiently producing a hot-rolled steel sheet of an Fe-Ni alloy, a method in which a continuously cast slab is hot-rolled by a mill having a continuous hot rolling mill to form a hot-rolled steel strip is generally used. is there. For slab heating in hot rolling, a walking beam type heating furnace is used in many cases from the viewpoint of production efficiency and quality improvement. However, the Fe-Ni alloy has a problem that ear cracks are easily generated during hot working, and a hot-rolled steel sheet cannot be manufactured with good yield. In particular, the edge cracks generated in the hot-rolled steel strip obtained from the continuous casting slab are generated on the front and back surfaces of the edge portion up to about 50 mm from the side end of the rolling agent, and remain as uneven flaws even after cold rolling. Therefore, it is necessary to perform a plurality of passes through a so-called coil grinder for grinding the surface of the steel strip with a grinding belt after hot rolling, and this causes a reduction in yield and an increase in operation cost.

Therefore, various measures for preventing edge cracks in a hot-rolled Fe-Ni alloy strip have been conventionally proposed. For example, as a rolling method, "per pass until the total rolling rate exceeds 50%
Method of rolling at a rolling reduction of 10% or more to prevent ear cracks "
62-3801), “70 ° C when the surface temperature of the ingot is between 300 and 500 ° C
A method of preventing surface cracking by heating at a rate of not more than / hr and forging at a rolling reduction of 1% or less in one pass "
227127) and the like, "Ca
For adding 0.001-0.01% "(JP-A-61-87851).

[Problems to be solved by the invention]

However, these measures for preventing ear cracks have various problems. For example, in the method disclosed in Japanese Patent Application Laid-Open No. 61-227127, the efficiency of hot rolling is reduced at the same time as the heating time is prolonged, and there is a problem in efficiently producing a hot-rolled steel sheet of an Fe-Ni alloy. In the method disclosed in Japanese Patent Application Laid-Open No. 61-87851, a C-based (hard) Ca-based inclusion is easily generated as a deoxidation product, which adversely affects the plating property in manufacturing an electronic component. There is a problem in actually adopting it.

And, above all, the effect of preventing ear cracks was not sufficient, and in the method of directly hot rolling a continuous cast slab in order to increase production efficiency, ear cracks were particularly likely to occur.

An object of the present invention is to provide a high effect of preventing cracks from ears, and furthermore, a Fe-Ni alloy that does not adversely affect rolling efficiency, plating property, and the like.
An object of the present invention is to provide a method for manufacturing a hot-rolled alloy strip.

[Means for solving the problem]

The various ear crack prevention measures exemplified above mainly require the lack of hot deformability of the Fe-Ni alloy as a cause of the ear cracks of the hot rolled steel sheet of the Fe-Ni alloy. When hot working an alloy having poor hot deformability, it is often considered effective to limit the rolling reduction (strain amount) per pass to a small extent.
The method of -227127 is one example. However, Fe-Ni
It is known that in an alloy, the hot deformability (evaluation based on the sectional drawing ratio in a tensile test) at the strain rate (approximately 1 to 10 / s) in actual hot rolling improves as the strain rate increases. The strain rate in hot rolling increases in proportion to the square root of the rolling reduction per pass. Therefore, it can be considered that as the rolling reduction / pass is larger, the strain rate is higher and the deformability is higher, and the workability is improved. From such a viewpoint, a method disclosed in Japanese Patent Application Laid-Open No. 62-3801 is proposed, which is inconsistent with the previous example.

On the other hand, it is disclosed in Japanese Patent Application Laid-Open No. 61-227127 to improve the surface cracking during hot rolling of an Fe-Ni alloy by taking measures against the heating rate during ingot heating, which is not directly related to hot deformability. is there. Here, the reason that the surface cracks are improved is described as "It is not clear, but it may be related to the behavior of the Fe-Ni intermetallic compound between 300 ° C and 500 ° C". It has been included.

As described above, there are some problems and questions in the way of thinking about the cause of ear cracks and surface flaws that occur during hot rolling of Fe-Ni alloys, and how to take countermeasures. Seems to be separate. Therefore, the present inventors felt that it was necessary to reexamine in detail the cause of the edge cracks occurring in the Fe-Ni alloy hot-rolled steel strip obtained by hot rolling a continuous cast slab, and Detailed observation of cracks in the steel strip,
Actual machine test in which the rolling conditions of hot-rolled steel strip, slab heating conditions, etc. were changed, measurement of deformability under a wide range of strain rates mainly for 42% Ni alloy as a representative of Fe-Ni alloy, small-scale rolling experiment And so on. Then, based on the inferences made as a result, tests were performed on several countermeasure plans, and as a result, the present invention was completed. The findings and ideas that led to the completion of the present invention are as follows.

FIG. 1 is a table showing the relationship between the cross-sectional drawing ratio and the strain rate of Fe-42% Ni alloy at 800 ° C., and FIG. 2 is 1 × 10 ⁻³ / s and 5.5 × 10 ⁻¹ of Fe-42% Ni alloy. 4 is a table showing a relationship between a sectional drawing ratio and a temperature under each strain rate of / s.

The strain rate due to thermal stress during heating is 10 ^-3 to 10 ^-4 / s, but the hot deformability under such a very small strain rate deformation (evaluation based on the cross-sectional drawing rate of the hot tensile test) Is
It becomes extremely low between 600 and 1000 ° C. Therefore, in this temperature range, applying a thermal stress strain creates a starting point for cracking.

In a walking beam type continuous heating furnace, which has recently become the mainstream, a slab is heated while being placed on a fixed beam. The fixed beam consists of a beam body and a skid button that actually contacts the slab. In the vicinity of the fixed beam of the slab, the radiant heat is blocked by the fixed beam and the conduction heat is deprived by the skid button, so that the slab is hardly heated, and thermal stress due to uneven heating is generated here. Therefore, reducing the thermal stress due to uneven heating of the slab from 600 ° C. to 1000 ° C. is effective in preventing the edge crack of the hot-rolled steel strip.

In order to prevent ear cracks, it is necessary to secure the temperature inside the slab. From this viewpoint, it is necessary to further reduce the heating rate in the region from 1000 ° C. to the soaking temperature.

The hot deformability at a strain rate deformation of about 1 to 10 / S, which corresponds to hot rolling, slightly decreases below 900 ° C, but overall, SUS3 with little cracking of ears is not a problem.
It is about the same as 04 steel, and its deformation resistance is smaller than SUS304 steel. By taking advantage of the hot deformability under this good large strain rate deformation, if the first pass rolling of hot rolling is performed at a temperature of 900 ° C. or more and a reduction of 15% or more, the effect of recrystallization to refine the crystal grains As a result, the hot deformability at 900 ° C. or lower is further improved, so that even a continuous cast slab having a brittle solidified structure can be rolled once, and edge cracks can be suppressed.

The present invention has been completed based on the above findings and ideas, and contains Fe and Ni as main components, Ni
A continuously cast slab of Fe-Ni alloy having a content of 35 to 55% and a Cr content of 0 or 7% by weight or less is heated by a heating furnace and hot-rolled to produce a hot-rolled steel strip. In the method, the temperature of the slab is raised at a rate of 15 ° C./min or less from 600 ° C. to 1000 ° C., and further at a rate of 3 ° C./min or less from 1000 ° C. to the soaking temperature. Temperature, and the first pass rolling in hot rolling at a temperature of 900 ° C or more,
The gist of the present invention is a method for producing a hot-rolled steel strip of Fe-Ni alloy, which is performed at a rolling reduction of 15% or more.

[Action]

The Fe-Ni alloy in the present invention is mainly composed of Fe and Ni.
Is a high Ni alloy containing 35 to 55% of Ni. In addition to Fe and Ni, deoxidizing elements such as Si, Mn and Al, C, P,
It contains unavoidable impurities such as S, N, and O, and may further contain Cr, Co, and the like as alloying elements. However, the content of Cr is set to 7% or less, which is the level of the above-mentioned Fe-7% or less Cr- (35 to 55%) Ni alloy, in order to reduce the coefficient of thermal expansion.

A continuous cast slab is a slab having a size that can be directly hot-rolled by a continuous hot-rolling machine, for example, having a thickness of about 100 mm to 200 mm cast by a continuous caster, Not included. The crystal grains of the slab obtained by the slab rolling are refined by recrystallization, and the susceptibility to cracking is low, so that the occurrence of edge cracking is unlikely.

The heating furnace refers to a continuous or discontinuous furnace used for heating a slab prior to hot rolling. A heating furnace (continuous heating furnace) that can continuously heat and extract a slab is usually composed of zones called pre-tropical zone, heating zone, and solitary zone from the entrance. The slab placed on the fixed beam is lifted by the walking beam and advanced little by little to the higher-temperature zone for heat extraction.

It is specified that the surface temperature of the slab is raised at a rate of 15 ° C./min or less from 600 ° C. to 1000 ° C.,
This temperature range is the embrittlement temperature range associated with the low strain rate deformation peculiar to the Fe-Ni alloy, and as shown in FIG. 3, continuous casting during heating is controlled by controlling the temperature rise rate to 15 ° C./min or less. This is because thermal stress generated in the slab can be reduced and internal cracks can be prevented, and edge cracks in the hot-rolled steel strip can be reduced. The reason that the surface temperature of the slab is to be increased at a rate of 3 ° C./min or less between the temperature of 1000 ° C. and the soaking temperature is to sufficiently increase the internal temperature of the slab (close to the soaking temperature). Even if the slab surface is heated at a rate exceeding 3 ° C./min in a temperature range of 1000 ° C. or more, the internal temperature of the slab cannot follow and the hot rolling temperature cannot be ensured, so as shown in FIG. The generation of ear cracks cannot be avoided.

In the continuous heating furnace, the regulation of the heating rate is usually performed by lowering the moving speed of the slab in the furnace or by stopping the slab in the furnace.

Note that the lower limit of the heating rate is not particularly limited, and a speed that does not significantly lower the working efficiency in actual operation may be selected.

In the hot rolling performed on the slab heated under the regulation of the heating rate, the first pass rolling secures a temperature of 900 ° C. or more and a draft of 15% or more. By doing so, the large reduction does not lead to cracking, and the hot-deformability in rolling after the large reduction is also improved due to the crystal grain refinement effect accompanying the large reduction. As a result, as shown in FIG. Cracks are greatly suppressed.

〔Example〕

20Ton electric furnace-scoured by VOD (vacuum scouring furnace)
Fe-42% Ni alloy (typical component is 0.005% C-0.25% Si-
0.5% Mn-0.01% P-0.004% S-0.02% Cu-41.5% Ni-
0.05% Cr-0.05% Co-0.002% SolAl-0.002% N-0.002
% O) was cast into a continuous casting slab having a thickness of 150 mm × 1190 mm width × length (approximately 7 m), subjected to surface grinder grinding, and then coated with an antioxidant. The reason for applying the antioxidant is Fe
This is for the purpose of preventing surface flaws caused by grain boundary oxidation during slab heating specific to -Ni alloy. The slab was heated and hot-rolled under the conditions shown in Table 1 to check for cracks in the hot-rolled steel strip.

Ear cracks were evaluated by a grinding index using a coil grinder (CG). The grinding care index is the average number of passes required to grind and remove flaws such as ear cracks generated on the coil surface by a coil grinder (a belt grinder in which paper is mounted on a roll).

As is clear from Table 1, the surface temperature of the slab was 600
The rate during heating up to ~ 1000 ° C is 15 ° C / min or less,
By setting the rate during the temperature rise from 1000 ° C. to the soaking temperature to 3 ° C./min or less, ear cracks tend to be reduced, and in addition to the heating rate regulation, 900 ° C. in the first pass of hot rolling. By performing the large pressure reduction described above, it is possible to greatly reduce ear cracks.

[Effects of the Invention] As described above, according to the present invention, the edge cracks of the Fe-Ni alloy hot-rolled steel strip can be significantly reduced by a simple method, and the yield can be significantly improved. There is no concern about lowering the efficiency and plating properties, and its industrial value is very large.

[Brief description of the drawings]

FIG. 1 is a table showing the relationship between the cross-sectional drawing ratio and the strain rate at 800 ° C. of an Fe-42% Ni alloy, and FIG.
FIGS. 3 and 4 show the relationship between the cross-sectional drawing ratio and the temperature under each of the strain rates of × 10 ^-3 / s and 5.5 × 10 ^-1 / s.
Figure 5 shows the relationship between the index of grinding required to remove edge cracks in the hot-rolled 42% Ni alloy strip and the surface heating rate of the continuously cast slab in a heating furnace. 3 is a table showing the relationship between the index of grinding required for removing edge cracks of a hot rolled Ni alloy strip and the rolling reduction at 900 ° C. or higher in hot rolling.

────────────────────────────────────────────────── ⁶ Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C22C 38/00 302 B21B 37/00 BBL (56) References JP-A-62-286605 (JP, A) JP-A-1-122606 (JP, A) Tokiko Hei 1-48337 (JP, B2)

Claims (1)

(57) [Claims] (1) Fe and Ni as main components having a Ni content of 35 to
A method for producing a hot-rolled steel strip by heating a continuous cast slab of an Fe-Ni alloy having a Cr content of 0 or 7% by weight or less by a heating furnace and hot-rolling the slab. Raise the temperature of the slab from 600 ° C to 1000 ° C at a rate of 15 ° C / min or less, and raise it from 1000 ° C to the soaking temperature at a rate of 3 ° C / min or less. And a first pass rolling in hot rolling is performed at a temperature of 900 ° C. or more and a rolling reduction of 15% or more.