JPH03166345A - Manufacture of ni-base alloy thin sheet - Google Patents

Abstract

PURPOSE:To manufacture the thin sheet of good quality by short time heat treatment, at the time of manufacturing the thin sheet of an alloy called 'HastelloyB(R)', by subjecting the thin sheet obtd. by using a twin roll-type continuous casting machine to heat treatment under specified conditions and thereafter subjecting it to cold rolling. CONSTITUTION:At the time of manufacturing the thin sheet of an Ni-base alloy contg., by weight, 26 to 29% Mo and 4 to 7% Fe, a pouring basin of the alloy is formed in contact with the circumference of a pair of internal cooling rolls disposed to face oppositely and rotating in the opposite direction each other. Then, the solidified shell of the alloy formed on the circumference of a pair of rolls from the molten metal of the pouring basin is subjected to continuous casting into a thin sheet of <=5mm through the gap of a pair of rolls. Next, the obtd. thin sheet is subjected to heat treatment at 1150 to 1300 deg.C for >=0.5hr and is thereafter cold-rolled into an objective sheet thickness. By this method, the thin sheet having same quality as that by a conventional technique can be obtd. with long time heat treatment before hot rolling and the hot rolling stage itself obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is based on the present invention, in which 26 to 29% by weight of Mo and 4 to 4% by weight of Mo in Nl are
This invention relates to a method for manufacturing a thin plate of a Ni-based alloy containing 7% by weight of Fe. [Prior art] Ni-based alloy containing 26-29% by weight of Mo and 4-7% by weight of Fe in Ni, specifically Ni:66
~68% by weight, Mo: 26-29% by weight, Fe
: Ni-based alloy consisting essentially of 4 to 7% by weight belongs to the alloy called Hastelloy B (trade name). Co as necessary
．． Cr. Elements such as SLMn are also added within a range of 2.5% by weight. This alloy has excellent heat resistance and corrosion resistance, and can withstand harsh corrosion conditions such as high temperature and high pressure environments containing halogen compounds.
Since tTi is useful as an environmental material, it is used, for example, as an equipment material for various chemical industry plants. Conventionally, in order to manufacture thin sheets of Hastelloy B, a method has been adopted in which an ingot is first produced by casting, and this ingot is repeatedly hot rolled. Japanese Patent Publication No. 62-18750
In the publication. It teaches that it is beneficial to perform a long heat treatment before hot rolling. [Problems to be Solved by the Invention] The following problems have been associated with the manufacturing technology of Hastelloy B thin plates.

Hastelloy B has excellent heat resistance, but in other words, this means that it has high high temperature strength5, and the hot workability of this alloy itself is extremely poor. Furthermore, during casting of Hastelloy B, coarse precipitates (
intermetallic compounds) are likely to grow. This causes embrittlement, which tends to cause cracks such as edge cracks to occur during hot rolling. In this way, this alloy has high high-temperature strength and is susceptible to edge cracking. It is not possible to increase the rolling reduction during hot rolling. Therefore, in order to obtain an El plate from an ingot, hot rolling must be repeated many times at a small rolling reduction. Additionally, since the temperature of the material decreases during rolling, the material must be returned to the heating furnace after each rolling cycle. Requiring a large number of rolling cycles means that the number of times the steel must be returned to the heating furnace also increases.

For this reason, when conventionally manufacturing thin sheets of Hastelloy B from ingots by hot rolling, an extremely large number of steps and a large amount of energy are required, leading to high manufacturing costs.

The purpose of this invention is. In order to solve these problems in Hastelloy B thin sheet manufacturing technology, we will omit the long-term heat treatment before hot rolling and the hot rolling process itself, and even with this omission, we will be able to manufacture thin sheets with the same quality as the conventional technology. That is.

[Means for Solving the Problems] The gist of the present invention, which aims to achieve the above object, is to provide a Ni-based alloy containing 26-29% by weight of Mo and 4-7% by weight of Fe in Ni. When manufacturing thin sheets of... A pool of the alloy is formed in contact with the circumferential surfaces of a pair of internal cooling rolls that are arranged opposite to each other and rotate in opposite directions, and the molten metal in this pool is formed on the circumferential surfaces of the pair of rolls. The solidified shell of the alloy is continuously cast into a thin plate of 5 mm or less through the gap between the pair of rolls. The obtained thin plate was 115
It is characterized by heat treatment at 0 to 1300"C for 0.5 hours or more, and then cold rolling to the target thickness. At that time, when casting with a pair of rolls, the casting temperature is lowered to the center of the thickness of the slab. The temperature is controlled to produce columnar crystals, and the plate width L (lI
The load P (kgf) per Il1〉 is 1 0 (kgf/
The load applied to the slab by both rolls is controlled so that the load is less than ffim).

[Detailed description of the invention]

Up to now, much research has been conducted and improvements have been made regarding the prevention of cracks that occur during hot working of Hastelloy B. but. There are no reports on the direct production of thin sheets of Hastelloy B by casting, and therefore no research studies have been found regarding the quality of the sheets obtained in this case.

The inventors etc. An attempt was made to directly produce thin sheets of Hastelloy B using a so-called twin-roll continuous caster. the result,
We obtained a number of findings as described below.

The twin roll continuous casting machine is well known. A pair of internal cooling rolls that rotate in opposite directions are placed facing each other with their axes parallel to each other with a predetermined gap, and a pair of side dams that are perpendicular to the roll axis are usually placed on both sides of the pair of rolls to create a roll circle. A pool space is formed on the circumference, and molten metal is continuously injected into this pool space. This injected molten metal is cooled on the circumferential surface of rotating rolls, and the solidified shell formed on the circumferential surface is compressed and rolled in the gap between a pair of rolls, thereby directly manufacturing a thin plate. Although various proposals have been made regarding the details, the idea remains that the solidified shell formed on the circumferential surface of the twin rolls is continuously pressed and rolled in the narrowest gap between the twin rolls.

The present inventors have repeatedly conducted casting experiments of Hastelloy B using such a twin-roll continuous caster. Although efforts were made to improve the quality of cast plates. It was found that it is impossible to produce slabs with completely suppressed segregation even with this twin roll method. In other words. Segregation occurs in this alloy when the molten alloy in the pool is cooled on the circumferential surface of the rolls to form a solidified shell, and furthermore, when the solidified shell is cooled and rolled by cooling rolls in the gap between the rolls. easy. The degree of this segregation is also related to the cooling rate. It was found that precipitates (intermetallic compounds) caused by segregation grow in the center of the thickness of the thin plate when the cooling rate is slow. However, although this segregation may occur. It was confirmed that thin sheets of Hastelloy B can be produced directly using a twin-roll continuous caster.

Therefore, in order to reduce the precipitates in thin sheets produced using this twin-roll continuous caster through heat treatment, we investigated the effects of heat treatment conditions on the precipitates. The representative results are shown in Figures 1 and 2.
Shown in the figure. Both figures use the twin-roll continuous casting machine shown in the example below, and the slab thickness is 21 and the casting degree is 30+w/+i.
n, Ni at a casting temperature of 1450°C! ;67%,
Mo! ;28%, Fe! ; 5% Hastelloy B (the same alloy was used as the test material in Figures 3 and 4 below) was continuously cast, and the resulting slab was heated at the heat treatment temperature (Figure 1) and heat treatment time (Figure 1). Figure 2) shows the area ratio of precipitates when heat treatment is performed with different values.From Figures 1 and 2, 115
If heat treated for 0.5 hours or more at a heat treatment temperature of 0°C or higher.
It can be seen that most of the precipitates can be eliminated.
Therefore, if a thin plate obtained by casting Hastelloy B with a twin-roll continuous caster is heat-treated under conditions of a degree of 1l50°C or higher and a time of 0.5 hours or more, the precipitates disappear. However, heating at a high temperature exceeding 1300°C for a long period of time is undesirable as it may generate oxide scale, so it is practical to heat the material in a temperature range of 1150 to 1300°C for 0.5 hours or more.

moreover. As a result of investigating the relationship between the solidification structure of thin sheets obtained by casting and the amount of precipitates, an interesting fact was discovered. In other words, when equiaxed crystals grow in the center of the plate thickness, there are few precipitates in areas where the width of the equiaxed product is wide (width in the thickness direction), and if the width of the equiaxed product is narrow or In regions where there are almost no equiaxed crystals, there are an extremely large number of precipitates. On the other hand, when the columnar crystals extended to the center of the plate thickness, the uneven distribution of precipitates was not observed, as was observed in the center of the plate with equiaxed crystals. This means that the non-uniformity of precipitates can be avoided by adopting casting conditions that allow the columnar crystals to lengthen to the center of the sheet thickness, and by casting conditions that prevent the formation of equiaxed crystals. This can be achieved by controlling the casting temperature. Figure 3 shows the microstructure at the center of the thickness of a thin plate obtained by changing the molten metal temperature (casting temperature) in the tundish when this alloy is continuously injected from the tundish into the tundish of a twin-roll continuous caster. a The results of investigating the number of hard shell bite defects are shown.

The marks in Figure 3 indicate cases where equiaxed crystals appear in the center of the plate thickness in addition to columnar crystals, and the ○ marks indicate cases where substantially no equiaxed crystals appear, leaving only columnar crystals. There is.

This result shows that a columnar crystal structure is obtained when the casting temperature is 1450°C or higher. On the other hand, in a twin-roll continuous caster, the lower the casting temperature of the molten metal, the more solidified shells will form on the inner surface of the side dam. The solidified shell is irregularly bitten by the surface of the healthy slab growing on the circumferential surface of the roll, and surface defects are likely to occur due to this. Figure 3 also shows the relationship between casting temperature and the number of solidified shell bite defects. Solidified shell bite defect is 1450°C
This temperature almost coincides with the starting temperature of equiaxed crystals. In other words. Casting temperature 1450°C
It can be seen that if the above conditions are maintained, solidified shell biting defects are prevented and the slab structure becomes columnar crystals, so that non-uniformity of precipitates can be avoided.

Figure 4 is. When the rolling load applied when both solidified shells formed by the circumferential surfaces of twin rolls pass through the gap between the twin rolls is changed (the rolling load of the solidified shell by the twin rolls is changed, and the rolling load is measured by a load cell). This shows the results of investigating the surface cracking condition based on the cooling unevenness (patterns formed on the surface of the thin plate due to the plate not being cooled uniformly) that occur on the surface of the obtained thin plate. be. From Figure 4, we can see that the load P (kg) per plate width L (mm)
If casting is performed by controlling the load applied to the slab by both rolls so that f) is 10 (kgf/ms) or less. It can be seen that cracks caused by uneven cooling can be almost completely suppressed.
In this way. According to the present invention, it has become clear that thin sheets of Hastelloy alloy can be produced directly from molten metal, and that non-uniformity of precipitates and uneven cooling can be avoided by appropriately controlling the molten metal temperature and rolling load. If a thin plate with a thickness of 5+III1 or less is directly produced using a twin-roll continuous casting machine, there is no longer a need to reduce the plate thickness significantly, and the precipitates will disappear from the thin plate after the heat treatment. Because of this, cold rolling is possible. It is possible to reduce the plate thickness to the target plate thickness and produce thin plate products with good product dimensions and surface properties.

〔Example〕

Rotating in opposite directions to each other Diameter 400++m, Width 300m
Two water-cooled copper rolls with a diameter of 2 mm are placed facing each other with their axes parallel and horizontal, and a pair of side dams made of refractory material are placed on both sides of this pair of rolls, and the circumferential surface of the rolls is surrounded by these side dams. The space where the melt is formed is the pool space, the roll gap is 2.0 mm, the amount of molten metal is 300 kg, the casting speed is 30 s/min, the casting temperature and the rolling load (P
/L) was controlled as shown in Table 1 to perform continuous casting of Hastelloy B. Match gold string or Ni'; 67%, M
o#28% and Fe#5%.

The obtained thin plate was heat treated at the temperature and time shown in Table 1, and the quality of the thin plate before cold rolling was investigated.The results are also listed in Table 1. ~50 According to the present invention, a thin plate of Hastelloy B of good quality was obtained without hot rolling. On the other hand, in Comparative Example 6 where the heat treatment temperature was low, the amount of residual precipitates was large, and in Comparative Example 7 where the casting temperature was low.
In Comparative Example 8, where the rolling load was high, the number of uneven cooling cracks was large.

Hee again} No. Figure 9 shows an example of the conventional method using the ingot making method. 300 kg of Hastelloy B molten metal was poured into a flat mold with an ingot thickness of 120 mm, and the obtained ingot was soaked at 1200°C for 2 hours, then the surface was ground and hot rolled. Hastelloy B has extremely high hot deformation resistance, so 2. After rolling to a thickness of OLIII, 60 baths were required. Furthermore, in order to compensate for the heat during that time, 1 part of the material was placed in a heating furnace maintained at 1250°C.
It was necessary to return to 0 times. The obtained thin plate was in good condition except for some edge cracking. As above. According to the present invention, Hastelloy alloy, which is a material with difficult hot workability, can be used. It is possible to produce high-quality thin sheets by omitting the hot rolling process, saving equipment. Energy and labor savings have been achieved,
We can make a significant contribution to this field.

[Brief explanation of the drawing]

Figure 1 is a diagram of the relationship between heat treatment temperature and area ratio of precipitates for a Hastelloy thin plate manufactured using a twin-roll continuous caster, and Figure 2 is a diagram of the relationship between heat treatment time and area ratio of precipitates. Figure 3 shows the relationship between casting temperature, slab structure, and number of solidified shell bite defects in a twin-roll continuous caster, and Figure 4 shows the relationship between casting temperature, slab structure, and number of solidified shell bite defects. This is a relationship diagram between the value P/L obtained by dividing the rolling load by the sheet width in a twin-roll continuous caster and uneven cooling cracking.

Claims (3)

[Claims] (1) In manufacturing a thin plate of Ni-based alloy containing 26-29% by weight of Mo and 4-7% by weight of Fe in Ni, a pair of internal cooling rolls are arranged to face each other and rotate in opposite directions. A pool of the alloy is formed in contact with the circumferential surface of the molten metal, and a solidified shell of the alloy is formed on the circumferential surface of the pair of rolls from the molten metal in the pool through a gap of 5 mm or less. Continuously cast into a thin plate of 115
1. A method for producing a Ni-based alloy thin plate, which comprises heat-treating the thin plate at 0 to 1300°C for 0.5 hours or more, and then cold rolling to a target thickness. (2) The method for manufacturing a thin plate according to claim 1, wherein the casting using the pair of rolls is carried out by controlling the casting temperature to a temperature at which columnar crystals are formed up to the center of the thickness of the slab. (3) Casting using a pair of rolls is performed while controlling the load applied to the slab by both rolls so that the load P (kgf) per plate width L (mm) is 10 (kgf/mm) or less. Item 2. A method for manufacturing a thin plate according to item 1 or 2.