JPH0459925A - Production of hot rolled fe-ni alloy strip - Google Patents

Abstract

PURPOSE:To effectively prevent edge crack and also to produce a hot rolled Fe-Ni alloy strip without adversely affecting rolling efficiency, plating suitability, etc., by subjecting a continuously cast slab of Fe-Ni alloy to temp. rise up to soaking temp. at specific velocity and then to specific hot rolling. CONSTITUTION:A continuously cast slab of an Fe-Ni alloy containing about 35-55wt.% Ni is heated by means of a heating furnace and hot-rolled so as to be formed into a hot rolled strip. At this time, temp. is elevated at a rate of <=15 deg.C/min until surface temp. of this slab reaches 600-1000 deg.C and further elevated at a rate of <=3 deg.C/min from 1000 deg.C to soaking temp. Moreover, rolling in the first pass at the time of hot rolling is carried out at >=900 deg.C at >=15% reduction of area. By limiting temp. rise velocity in the brittle temp. region by the above procedure, reduction of thermal stress established in the slab and prevention of internal crack can be attained, and the edge crack of the hot rolled strip can be reduced. Further, by the hot rolling applied to the slab heated under controlled temp. rise rate, edge crack can be remarkably inhibited owing to the grain refining effect attendant upon heavy draft.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a hot rolled steel strip made of an Fe-Ni alloy containing 35 to 55% N1. In addition, in this specification, % represents overlapping % unless otherwise specified.

[Conventional technology]

Fe-Ni alloys such as Fe-(35-55%) Ni alloys or Fe-7% or less Cr-(35-55%) Ni alloys have a small coefficient of thermal expansion and have excellent sealing properties with glass, ceramics, etc. Because of this, it is widely used as a material for various electronic components.

For example, 36% Fe-Ni alloy has the lowest coefficient of thermal expansion and is used as a material for shadow masks in television receivers, and as a material for shadow masks in television receivers.
2% Fe-Ni alloy exhibits a coefficient of thermal expansion of about 4XIO-"/"C at room temperature, has excellent sealing properties with the IC pancake, and has good solderability and solderability, making it a suitable material for IC lead frames. is used as. Thin plate coils with a plate thickness of 0.25 to 0.15 m used as materials for these shadow masks, IC lead frames, etc. are obtained by cold rolling hot rolled Fe-Ni alloy steel plates.

By the way, as a method for efficiently manufacturing hot-rolled steel sheets of Fe-Ni alloy, a common method is to hot-roll a continuously cast slab in a mill equipped with a continuous hot rolling mill to form a hot-rolled steel strip. be. For slab heating during hot rolling, a walking beam heating furnace is often used to improve production efficiency and quality. However, Fe--Ni alloys are susceptible to edge cracking during hot working, and have a problem in that hot-rolled steel sheets cannot be manufactured with a high yield. In vf, edge cracks that occur in hot rolled** obtained from continuous casting slabs occur on the front and back surfaces of the edge part from the side edge to the 50th position, and these remain as uneven spots even after cold rolling. do. Therefore, it is necessary to use a plurality of so-called coil grinder buses for grinding the IjRIIF surface with a grinding belt after hot rolling, which causes a decrease in yield and an increase in work costs.

Therefore, various measures for preventing edge cracking in Fe--Ni alloy hot-rolled steel strips have been proposed. For example, as a rolling method, ``Method to prevent edge cracking by rolling at a reduction rate of 0% or more per 1 bath until the total rolling rate exceeds 50%'' J
(Japanese Unexamined Patent Publication No. 62-3801), "The surface temperature of the ingot is 300
A method of preventing surface cracks by heating between ~500°C at a rate of 70°C/hr or less and forging at a reduction rate of 4% or less per bath” (Japanese Patent Laid-Open No. 61-2271.27) etc., and rCa is 0.0 due to the addition of trace elements.
01 to 0.01% addition method” (JP-A-6L-87
851) etc.

[Problem to be solved by the invention]

However, these measures to prevent ear cracking have various problems. For example, in the method disclosed in Japanese Patent Application Laid-Open No. 61-227127, the heating time increases and the efficiency of hot rolling decreases, which poses a problem in efficiently manufacturing hot rolled steel sheets of Fe--Ni alloy. Also, JP-A-61-8785
The method disclosed in No. 1 uses C-based (hard) as a deoxidation product.
Since Ca-based inclusions are likely to be generated and have a negative effect on plating properties when manufactured as electronic parts, there are problems in actually adopting this method.

Above all, the effect of preventing edge cracking was insufficient, and edge cracking was particularly likely to occur in a method in which continuous casting slabs were directly hot rolled in order to increase production efficiency.

The object of the present invention is to use Fe-N which has a high effect of preventing edge cracking and which does not have a negative effect on rolling efficiency, plating property, etc.
An object of the present invention is to provide a method for producing an i-alloy hot rolled steel strip.

[Means to solve the problem]

The various measures for preventing edge cracking exemplified above are based on the fact that the cause of edge cracking in hot-rolled steel sheets made of Fe--Ni alloy is mainly due to the poor hot deformability of FeNt alloy.

When hot working alloys with poor hot deformability, it is often considered effective to limit the rolling reduction rate (amount of strain) per pass to a small value, and the method of JP-A-61227127 is an example of this. . However, in Fe-Ni alloys, hot deformability (evaluation by cross-sectional area reduction ratio in tensile tests) at strain rates (approximately 1 to 10/s) during actual hot rolling
is known to improve 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 the larger the rolling reduction/pass, the thicker the strain rate (and thus the higher the deformability, and the better the workability.From this point of view, although it contradicts the previous example, The method shown is proposed.

On the other hand, Japanese Patent Application Laid-Open No. 61-227127 proposes to improve surface cracking during hot rolling of Fe-N1 alloy by taking measures regarding heating rate during ingot heating, which is not directly related to hot deformability.
This is the method. Here, the reason why surface cracks are improved is
Although it is not clear, Fe-
It may be related to the behavior of Ni intermetallic compounds."
The explanation is that it contains some questions.

As mentioned above, there are several problems and questions regarding the concept of causes and countermeasures for edge cracks and surface defects that occur during hot rolling of Fe-Ni alloys, and there are some problems and questions regarding the exact causes of edge cracks. may be considered to be separate. Therefore, the present inventors have developed Fe-
In order to avoid the need to reexamine in detail the cause of edge cracks that occur in Ni alloy hot rolled steel strips, we conducted detailed observations of edge cracks in hot rolled steel strips, rolling conditions for hot rolled steel strips, and heating of slabs. Actual machine test with changed conditions and 42%N as a representative of Fe-Ni alloy
We conducted laboratory studies, mainly focusing on alloy J, including deformability measurements under a wide range of strain rates and small-scale rolling experiments. and,
Based on the inferences made as a result, the present invention was completed as a result of testing several countermeasures. The findings and ideas that led to the completion of the present invention are as follows.

Figure 1 is a chart showing the relationship between cross-sectional reduction ratio and strain rate at 800 °C for Fe-42%Ni alloy, and Figure 2 is for Fe-42%Ni alloy.
lXl0-”/s and 5.5X]0- of 2% Ni alloy
It is a chart showing the relationship between cross-sectional reduction ratio and temperature under each strain rate of '/s.

The strain rate due to thermal stress during heating is 101 to 10-4/S, but the hot deformability under such extremely small strain rate deformation (evaluation by cross-sectional area reduction ratio in hot tensile test)
becomes extremely low between 600 and 1000°C. Therefore, applying thermal stress strain in this temperature range creates a starting point for cracks.

In the walking beam continuous heating furnace that has become mainstream in recent years, the slab is heated while placed on a fixed beam. The fixed beam is composed of a beam body and a skin button that actually contacts the slab. The area near the fixed beam of the slab is difficult to heat because radiant heat is blocked by the fixed beam and conductive heat is taken away by the skin topot, and thermal stress is generated here due to uneven heating. Therefore, reducing the thermal stress caused by non-uniform heating of the slab from 600°C to 1000°C is effective in preventing edge cracking in the hot-rolled steel strip.

To prevent edge cracking, it is also necessary to ensure the temperature inside the slab. From this point of view, it is necessary to further reduce the temperature increase rate in the range from 1000° C. to the soaking temperature.

Although the hot deformability at strain rate deformation of about 1 to 10/S, which corresponds to hot rolling, slightly decreases below 900°C, overall, 5US304 steel has less problem with edge cracking. The deformation resistance is about the same, and the deformation resistance is 5US30
Rather smaller than the 4th rope. Taking advantage of this favorable hot deformability under large strain rate deformation, if the first bath rolling of hot rolling is performed at a temperature of 900°C or higher and a reduction rate of 15% or higher, the crystal grain refinement effect due to recrystallization can be achieved. Since the hot deformability at temperatures below 900° C. is further improved, even a continuously cast slab having a brittle solidification structure can be rolled once, and edge cracking can be suppressed.

The present invention has been completed based on the above findings and ideas, and provides a method for manufacturing hot-rolled steel strip by heating a continuously cast slab of Fe-Ni alloy in a heating furnace and hot rolling it. , the surface temperature of the slab is 600 °C
The temperature was increased at a rate of 15°C/min or less until it reached 1000°C, and then the temperature was increased for 3 times from 1000°C to the soaking temperature.
Fe-Ni alloy hot-rolled steel strip characterized in that the temperature is raised at a rate of less than ゛c/min, and the first bus of hot rolling is carried out at a temperature of 900°C or higher and a reduction rate of 15% or higher. The gist is the manufacturing method.

[Function] The Fe-Ni alloy in the present invention is an alloy whose main components are Fe and N1, and is a high-Ni alloy containing 35 to 55% Ni.
It is an alloy. In addition to FeNj, this alloy also contains Si, Mn
, including deoxidizing elements such as AN, unavoidable impurities such as CP, S, , N, O, and further contains Cr as an alloying element,
It may contain Co and the like.

Continuously cast slabs are slabs that are cast by a continuous casting machine, have a thickness of about 100 m to 200 m, and have dimensions that allow direct hot rolling by a continuous hot rolling mill, and are subjected to blooming. is not included. The crystal grains of the slab obtained by blooming are refined by recrystallization, and cracking sensitivity is reduced, so that edge cracking is less likely to be a problem.

A heating furnace is a continuous or discontinuous type used to heat a slab prior to hot rolling.

A heating furnace that can continuously heat and extract slabs (
A continuous heating furnace (continuous heating furnace) usually consists of zones called a pre-heating zone, a heating zone, and a soaking zone. Among these, in a walking beam type heating furnace, a slab placed on a fixed beam is lifted by a walking beam. It is designed to gradually advance to a higher temperature zone and heat extraction.

The reason why we specified that the surface temperature of the slab should be increased at a rate of 15°C/min or less from 600°C to 1000°C is because this temperature range is brittle due to the low strain rate deformation peculiar to Fe-Ni alloys. temperature range of 15℃ as shown in Figure 3.
This is because by regulating the temperature increase rate to less than /min, it is possible to reduce the thermal stress generated in the continuously cast slab during heating and prevent internal cracks, thereby reducing edge cracks in the hot rolled steel strip.

The reason why the slab surface temperature is specified to be raised at a rate of 3°C/min or less between 1000°C and the soaking temperature is to sufficiently raise the internal temperature of the slab (to bring it 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 higher, the internal temperature of the slab cannot follow it and the hot rolling temperature cannot be ensured, so the temperature shown in Figure 4 is As such, ear cracking cannot be avoided.

In a continuous heating furnace, the rate of temperature increase is usually controlled by reducing the moving speed of the slab in the furnace or stopping the slab midway through the furnace.

Note that there is no need to particularly limit the lower limit of the temperature increase rate, and it is sufficient to select a rate that does not significantly reduce work efficiency in actual operation.

Hot rolling performed on a heated slab under temperature increase rate regulation shall ensure a temperature of 900° C. or higher and a rolling reduction of 15% or higher in the first pass rolling.

By doing this, the large reduction does not lead to cracking, and the grain refinement effect accompanying the large reduction improves the hot deformability during rolling after the large reduction.As a result, as shown in Figure 5, the Cracking is greatly suppressed.

〔Example〕

Fe-42%N1 alloy (typical composition is 0.00
5%C-0,25%Si-0,5%Mno,01%P
-0,004%S-0,02%Cu-41°5%Ni-
0,05%Cr-0,05%Co-0,002%S o
lAl-0,002%N-0,002%O) to 150
It was cast into a continuous casting slab of 1190 mm width and length (approximately 7 m), and after surface grinding with a grinder, an antioxidant was applied. The reason for applying antioxidant is that Fe-N
This is to prevent surface flaws caused by grain boundary oxidation during slab heating, which is unique to i-alloys.

This slab was heated and hot rolled under the conditions shown in Table 1, and edge cracks in the hot rolled steel strip were investigated.

Edge cracking was evaluated using a grinding care index using a coil grinder (CC).

As is clear from Table 1, the surface temperature of the slab is 600
By keeping the rate of heating up to 1000°C to 15°C/min or less, and setting the rate of heating up to 1000°C to soaking temperature to 3°C/min or less, edge cracking tends to be reduced. 9 in the first pass of hot rolling, in addition to this temperature increase rate regulation.
By applying large pressure at temperatures above 00°C, it is possible to significantly reduce edge cracking.

[Table 1] [Effects of the Invention] As described above, according to the present invention, edge cracking in Fe-Ni alloy hot-rolled copper strips can be significantly reduced by a simple method, and the yield can be greatly improved. Moreover, there is no concern that hot rolling efficiency or plating performance will be reduced, and its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 is a chart showing the relationship between cross-sectional reduction ratio and strain rate at 800 °C for Fe-42%Ni alloy, and Figure 2 is for Fe-42%Ni alloy.
2% Ni alloy lXl0-'/s and 5.5 X 1
A chart showing the relationship between cross-sectional reduction ratio and temperature under each strain rate of 0-'/s, and Figures 3 and 4 show the grinding effort required to remove edge cracks in Fe-42%Ni alloy hot-rolled steel strip. Figure 5 is a graph showing the relationship between the surface temperature increase rate of a continuous cast slab in a heating furnace and the surface temperature increase rate of a continuously cast slab in a heating furnace. It is a chart showing the relationship between the index and the reduction rate at 900° C. or higher in hot rolling. *) CG not available, size down Diagram Strain rate (S”) Breaking temperature/l (0 Diagram Temperature increase rate from 600 to +000'c (℃/m, n) Diagram Increase from 1000@c or more Temperature rate (℃/m1n')

Claims (1)

[Claims] (1) In a method of manufacturing a hot-rolled steel strip by heating a continuously cast slab of Fe-Ni alloy in a heating furnace and hot rolling it, the surface temperature of the slab is from 600°C to 1000°C. Further to 1000°C at a rate of 15°C/min or less
The temperature is increased at a rate of 3°C/min or less between the temperature and the soaking temperature, and the first pass of hot rolling is performed at a temperature of 900°C or higher and a reduction rate of 15% or higher. A method for producing a Fe-Ni alloy hot-rolled steel strip.