JP2548942B2 - Method for preventing cracking during rapid solidification of Fe-Ni based alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is a so-called synchronous continuous casting method in which there is no relative speed difference between a cast piece and a mold in the production of an alloy product mainly composed of Fe-Ni base, The present invention relates to a method for producing a thin plate, a wire rod or the like by casting in a shape as close to the product size as possible and omitting hot rolling as much as possible.

(Prior art) Conventionally, in the production of various thin plates, thick cast slabs with a thickness of 100 mm or more were produced by vibrating the mold in continuous casting, and surface tampering was performed, and long-term heating to a high temperature of 1000 ° C or higher in a heating furnace After heating for a period of time, it was continuously hot-rolled by a group of hot-rolling mills consisting of multiple stands to manufacture thin steel sheets and raw materials for wire rods. From the viewpoint of mass production, the method of using large continuous cast slabs and performing hot rolling with a large, high-efficiency hot rolling mill group is considered to be one technical system, but expensive hot rolling mills and other It can be said that the method is expensive in terms of heating fuel and electric power.

In addition, it is likely to cause scale cracking due to long-term heating at high temperature or strong hot rolling, resulting in ear cracking. Depending on the steel type, hot rolling calcination annealing may be required before cold rolling, or front coil grinding process may be required. The result is that it is not always an ideal manufacturing method.

Fe is known for its unique characteristics such as a small coefficient of thermal expansion
Fe-Ni such as -42% Ni alloy (42 alloy), 36% Ni alloy (Invar alloy), and permalloy known for high magnetic permeability.
The situation is exactly the same for base-based alloys.
In particular, the problem of the current manufacturing technology of Fe-Ni-based alloys is a big problem because when they are heated at a high temperature for a long time in a heating furnace, scales grow and internal oxidation accompanied by grain boundary oxidation easily occurs. Especially when hot rolling with a powerful hot rolling mill, edge cracks are likely to occur from the grain boundary oxidized portion, and internal oxidation and grain boundary oxidized portions remain as surface defects even after pickling after hot rolling, so surface grinding It is a point that these surface defects cannot be removed unless the above is sufficiently performed. In order to solve such problems, at present, measures to reduce S, P, etc. in alloys to improve hot workability (iron and steel, 82, S496, 84-S650) and heating in a heating furnace We are dealing with the method of lowering the temperature, etc., in the direction of sufficiently grinding the coil surface.

However, due to the original characteristics of the Fe-Ni-based alloy, grain boundary oxidation in a heating furnace is unavoidable, and the current manufacturing method is not always satisfactory.

(Problems to be solved by the invention) As a new technology drastically different from the conventional method, the hot rolling process can be greatly simplified if it can be cast in a shape close to the product size as much as possible in the continuous casting stage. It is thought that this could be a technology that will radically change the steel manufacturing process. The thin steel billet manufacturing technology, which is currently the focus, is being actively researched in various countries, but in Japan as well, it is discussed in detail in a special feature in "Iron and Steel"85'A197 to 85'A256. ing. Thus, depending on the size of the slab, for example, the Twin roll method with
The twin belt method, the so-called synchronous continuous casting method, has progressed with a thickness of about 50 mm. In the future, the progress of these thin casting equipment, especially the technology for expanding the width of the slab is necessary. In addition, the development of a consistent manufacturing technology for various steel materials is left by making full use of the characteristics of these thin slabs. If the manufacturing method of these thin slabs progresses, it will be possible to solve all the problems related to the current method by applying it to the manufacturing method of Fe-Ni based alloy.

That is, cast a thin slab as close to the product size as possible,
If hot rolling is simplified as much as possible without going through a heating furnace,
It is presumed that internal oxidation due to heating could be prevented and the coil grinding process could be greatly simplified. Also, since hot rolling can be simplified, it is presumed that the problem of surface defects due to scale can be more easily solved by omitting the hot rolled sheet annealing step.

Thus, by casting in a shape close to the product size as much as possible, the rational manufacturing process of Fe-Ni-based alloys, that is, without passing through a heating furnace, simplifying hot rolling as much as possible, omitting hot rolling anneal, and pickling. It is considered possible to provide a method in which heavy grinding of the plate is omitted and a surface defect does not occur, but a major problem is cracking of the surface of the slab that occurs in thin casting. Solidification rate of the above-mentioned as a conventional thick continuous slab of about 10 ⁰ ° C. / sec to about 10 ² ° C. / sec greatly becomes fragile greater solidification contraction in twin roll method or the like while it is. Further, according to the conventional method, the surface flaws of the cast piece can be removed manually, but if the cast surface of the cast piece that is cast so as to be as close as possible to the product shape is provided, the area is large and it is not economically feasible.

Therefore, it is an object of the new process to provide a method for preventing cracks in a slab during casting which accompanies the new casting method.
Of course, measures for preventing cracks are being advanced in terms of casting machines and casting methods, but in the present invention, the alloy composition was examined to find a component system that hardly causes cracks even just below the melting point.

(Means for Solving Problems) In the twin-roll casting in which an Fe-Ni-based alloy is cast to a thickness of about 3 mm, surface vertical cracks may occur during casting. In particular, if the casting width is widened, vertical cracks are likely to occur, but even microscopic cracks are unacceptable in terms of product performance. It was found that the vertical cracking during casting is related to the high temperature ductility of the alloy immediately after casting, especially the high temperature ductility in the low temperature region of 30 to 50 ° C just below the melting point. In the above-mentioned iron and steel 82, S496, the hot deformation characteristics of the cooling process from the melting zone are described as the so-called I region, and it is shown that S adversely affects the melting point of other impurities. The effect at 50 ° C directly below is not shown.

The present inventors have used the melt greeble test method, as a result of a detailed study by quenching after melting, found that intergranular cracking occurs in these zones, and S, O, P, N, C in order. It turned out to be an adverse effect. Moreover, the influence of these components is additive, and the influence of S is particularly large. In this way, the influence of impurities was judged, and C <0.03%, S <0.001%, N <0.003%, P
<0.006%, O <0.005%, the lower the better, and it is necessary to regulate P + O + N + 10 × S <0.02% especially when the width of the slab becomes wide. In order to mitigate the harmful effects of S, Ca
1 or 2 in the range of <0.005%, Al <0.03%, Ti <0.03%
More than one species can be added.

In addition to the above impurity regulation, it was found that the alloy compositions of Si and Mn had a great influence on the ductility just below the melting point. Ie Si
Is lower than 0.3%, and the Mn is lower than 0.5%, the hot ductility just below the melting point is improved. Therefore, when the slab width is wide, it is necessary to regulate Si + Mn <0.7%.

Of course, for Fe-Ni based alloys, Cr ≤ 10 depending on the purpose of use.
%, Mo ≦ 10%, Nb ≦ 10%, Ti ≦ 2%, V ≦ 2%, Ta ≦ 20%,
One or more kinds can be selectively added within the range of W ≦ 10%.

It is desirable that the high temperature portion of the cast slab after cooling is cooled as rapidly as possible to prevent the formation of scale. Then, depending on the required characteristics, the product is made into a product by one or more processes of hot rolling, warm rolling, cold rolling, and if necessary, heat treatment is performed to obtain predetermined characteristics. If minute cracks occur on the surface during the casting stage, omitting the coil grinding process,
During hot rolling, warm rolling, or cold rolling, many cracks become apparent and the product cannot be obtained. Therefore, it is extremely important to obtain an alloy composition in which cracking is suppressed as much as possible in the casting stage.

 The present invention will be described below with reference to examples.

Example 1 A 42% Ni alloy was melted by an electric furnace-AOD method in the usual manner. Impurities were reduced in terms of manufacturability and characteristics, and inclusions were sufficiently floated and removed.

Impurities and main components are in weight percent, C 0.015%,
Si 0.02%, Mn 0.31%, P 0.003%, S 0.0003%, Ni 41.35
%, Cr 0.10%, Co 0.12%, Al 0.001%, N 0.0014%, O 0.0
It was 030%. Thus, in this alloy, P + in weight [%]
O + N + 10 × S = 0.0104% and Si + Mn = 0.51%.

This melted alloy was cast into a 700 mm wide and 2.0 mm thick slab by a twin roll casting machine consisting of an internal water-cooled drum.
The solidification rate is ~ 10 ⁴ ° C / sec. From the solidification to 1000 ° C, the atmosphere was set to the atmosphere and the roll was cooled to cool it in 25 to 30 seconds. The shape was corrected by applying a 20% reduction at about 950 ° C, followed by water cooling and winding at 600 ° C or lower. The scale generated on the surface of the coil was thin, the internal oxide layer was about 5 μm, and the γ grains were also fine grains. After that, omit coil annealing,
Descaling was carried out with a slight mechanical and pickling, the coil grinding step was omitted, cold rolling was carried out, and thereafter, the product was subjected to annealing, pickling and pressure adjusting steps as usual.

In the above examples, no surface crack was observed in the products.

In this alloy, it is important to control the components, and in particular, the next charge after the trace components were removed went through the same process, but if the coil grinding process was omitted, very small vertical cracks appeared on the coil surface after cold rolling. That is, Si 0.33%,
Mn 0.46%, P 0.007%, S 0.0005%, N 0.0025%, O 0.007
%, And other components were almost the same. In this component system, Si + Mn = 0.79%, P + O + N + 10 × S = 0.0215%, and the result of a microscopic examination of the slab revealed that micro vertical cracks were present after casting.

Example 2 An Fe-70% Ni alloy was melted by an electric furnace-AOD method in the usual manner. A high-purity, high-cleanness alloy was prepared except that it contained 4% of Mo. Al was deoxidized using Ca, and then inclusions were floated. The components are C 0.005%, Si 0.10%, Mn 0.30%, P 0.003%,
S 0.0002%, Cu 0.003%, Ni 71.3%, Cr 0.08%, Mo 4.2
%, N 0.0021%, O 0.0010%, Al 0.0011%, Ca 0.0010%
Met. By the way, Si + Mn = 0.40%, P + O + N + 10 ×
S = 0.0081%.

The melted alloy was cast in a twin roll caster with a thickness of 3.0 mm and a width of 700 mm while controlling Δt at 40 ° C or less. 10 after coagulation
It was cooled to 00 ° C. with N ₂ -enriched air and cooled in 30 seconds.

After that, hot rolling was performed at a temperature of 1000 to 950 ° C to reduce the temperature by 40%, water cooling was performed, and the coil was wound at 670 ° C. The internal oxide layer was about 6μ and the μ particle size was fine. With the alloy of the present invention, ear cracking did not occur even when a reduction of 40% was applied.

On the other hand, in the component system, Si 0.10%, Mn 0.56%, P 0.003
%, S 0.0006%, N 0.007%, O 0.006%, with almost the same composition of charge, ear cracking occurred at the stage of pressing down the slab by 40%.

By the way, P + O + N + 10 × S = 0.02 with this charge
It was 2%.

(Effect of the invention) According to the present invention, since it is possible to prevent cracking during rapid solidification of the Fe-Ni-based alloy, the occurrence of surface defects when casting the Fe-Ni-based alloy in a shape close to the product size The remarkable effect that the problem can be solved is exhibited.

Claims (1)

(57) [Claims] 1. A Fe-Ni-based alloy containing 10% by weight or more of Ni in weight% is cast by a rapid solidification-synchronous continuous casting method in which there is no relative speed difference between a mold and a slab, and hot rolling, After making the final plate thickness by one or more combinations of warm rolling and cold rolling, and finally annealing to make a product, Si in the alloy components is 0.3% or less and Mn is 0.5% or less. And C <0.03%, S <0.001%, P <0.006%, N <0.00
A method for preventing cracking during rapid solidification of an Fe-Ni based alloy, characterized in that 3% and O <0.005%.