JPH0148337B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method of manufacturing Fe-high Ni alloy slabs. The Fe-35 to 45% Ni alloy is known as a so-called invar type alloy, and is characterized by a significantly smaller coefficient of thermal expansion than other alloys. Among these alloys, the Fe-36%Ni alloy has the smallest coefficient of thermal expansion at low temperatures, and by taking advantage of this advantage,
It is used as a transportation container or storage tank (hereinafter collectively referred to as a container) for liquefied natural gas. Wide strips of material are required for these containers. On the other hand, Fe-42%Ni alloy has a small coefficient of thermal expansion at high temperatures, and taking advantage of this fact, it is often used as lead frame material for ICs. In this application as well, with the recent development of photoetching processing technology, the demand for wide coils with a width of around 500 mm is rapidly increasing to replace the conventional narrow width coils. In response to this situation, in recent years Fe-high Ni
Amber-type alloys are also required to be mass-produced using large steel ingots and to reduce costs, and strict manufacturing controls are being implemented to prevent production yields from decreasing. In order to produce Fe-high Ni gold alloy with good yield,
It is necessary to solve the problem of frequent occurrence of cracks during blooming. Since Fe-high Ni alloys solidify as a homogeneous austenite phase, segregation of impurity elements and precipitation of sulfides and oxides are likely to occur, and during hot working, cracks occur starting from these segregations and precipitates. . Therefore, it is necessary to perform heavy grinding on the slab surface to remove cracks and scratches on the slab after blooming, and in some cases, the cracks are so severe that they have to be turned into scraps, resulting in lower yields and higher costs. Taka was invited. This tendency becomes more noticeable as the ingot becomes larger, and Fe
-This was a major constraint when manufacturing high Ni amber type alloy slabs from large ingots. As a means to overcome these difficulties, the present applicant previously found that Al in this type of alloy significantly promotes hot working cracking, and by suppressing the Al content to 0.02% or less, hot working cracking can be suppressed. (Special Publication No. 55-42141). As is well known, Al is a strong deoxidizing agent and its use is essential to obtain good quality, but it is important to control the amount of Al remaining in the alloy to a trace amount, especially 0.02% or less. is technically extremely difficult, and even with strict control, this limit is often exceeded. Therefore, the method disclosed in Japanese Patent Publication No. 55-42141 is as follows:
It has been quite difficult to implement in industrial production. The present invention provides a more practical method while following the gist of the method described in Japanese Patent Publication No. 55-42141. The present inventors have found that the hot cracking properties of Fe-high Ni alloys are significantly affected by the temperature increase rate during heating prior to rolling, and it is necessary to strictly control the heating temperature increase rate during blooming rolling. This made it possible to reduce the occurrence of hot cracking and expand the allowable amount of Al. That is, according to the present invention, Fe-high Ni containing 35 to 45% Ni and the balance consisting of Fe and unavoidable impurities.
A method for producing an alloy slab, the method comprising: Al in the alloy component;
Provided is a method characterized in that the alloy ingot is heated at a temperature increase rate of 100° C. or less per hour prior to rolling. The target alloy of the present invention is so-called amber type Fe-
It is a high Ni alloy. As mentioned above, in the low temperature range,
In the high temperature region with 36% Ni, the coefficient of thermal expansion is minimum at 42% Ni, and in order to obtain low thermal expansion, the amount of Ni should be 35 ~
45%. Regarding Mn, Si, Cr, Co, P, S, N, and O, Mn is an element that is effective in reducing hot workability and welding hot cracking and does not affect the coefficient of thermal expansion.
It may be contained up to 1.2% (Japanese Patent Publication No. 56-45989).
S and O inhibit hot workability, so
It is necessary to limit it to 0.015%, 0.025% or less (Special Publication Publication No. 55-42141). In order to prevent the formation of bubbles in the steel ingot, N must be kept at 0.02% or less, preferably 0.004% or less (Japanese Patent Publication No. 55-42141). Other information regarding Si, Cr, Co, and P
It may be contained up to the range specified by ASTMA658 (36% Ni) and ASTM F30 (42% Ni). As mentioned above, Al is an element harmful to hot cracking, and it is preferable to keep it as low as possible, but it is difficult to control it. In the present invention, by controlling the heating rate to 100°C or less per hour, up to 0.04% can be tolerated. The present invention will be explained in detail below based on specific examples. Table 1 shows the chemical composition of the sample materials. Each sample material was smelted in a 40-ton electric furnace, refined in a converter, degassed, and produced into approximately 6.5-ton ingots. When blooming these ingots, each ingot is heated at a heating rate of 70℃, 100℃, and 300℃ per hour.
After heating to 1150℃ and holding it for about 3 hours, the condition of cracks was observed when the slab was produced into a slab with a thickness of 110 mm by blooming, and the yield when the cracks were removed by grinding with a slab grinder was calculated as above. observation

【table】

【table】 The results are shown in Table 2.

[Table] Regarding the rolling reduction rate during blooming rolling, the rolling reduction rate per pie should be 3% until the rolling amount reaches 40%, as previously proposed by the applicant of the present application in Japanese Patent Publication No. 57-54205.
And so. Heating of the alloy ingot during blooming has conventionally been carried out for as short a time as possible, usually at a temperature increase rate of around 300° C. per hour, in order to reduce the use of fuel (heavy oil). As shown in Table 2, in the method of the present invention, the cracks are minute and the yield is over 95%. On the other hand, when heating to a temperature increase rate of 300℃/hour according to the conventional method, coarse cracks occur unless the Al content is 0.02% or less, making it impossible to produce a product by grinding (the table shows "Ungrindable"). ”). Al amount 0.013～
Even with samples No. 3 to 5 containing 0.02%, the yield remained at 88 to 92%, and in order to obtain a yield comparable to the method of the present invention,
The amount of Al must be kept below 0.01%, but this is an extremely difficult task. If the Al content exceeds 0.04%, as seen in the example listed as a comparative method, 70
Even when the test was carried out at a heating rate of °C/hour, coarse cracking occurred. Based on the experimental results shown in Table 2, the influence of Al content on cracking in blooming rolled slabs was evaluated at heating rates of 300°C/hour, 70°C/hour, and
Figures 1 and 2 summarize the results for 100℃/hour. The ranking of crack occurrence in these figures is as follows. Cracking occurrence rank criteria A: Items with a flaw removal yield of 95% or more B: Items with a flaw removal yield of 88% to less than 95% C: Items where coarse cracks have occurred and flaw removal cannot be done by grinding These figures As can be seen in the above, when carrying out heating at a heating rate of 300℃/hour, in order to remove cracks and obtain a surface condition of rank B or higher that can be manufactured into a product, it is necessary to
It is necessary to keep the Al amount below 0.02%
42141 proposal), 0.04% or less is sufficient to obtain a surface condition of rank B or higher when the temperature is increased at a rate of 100° C./hour or less. Compared to the conventional method, the method of the present invention reduces the Al
It is extremely effective in preventing hot working cracks in Fe-high Ni amber type alloys, significantly contributing to improving manufacturing yields, and reducing the degree of cracking. The value is great.

[Brief explanation of drawings]

Figure 1 shows the relationship between the degree of blooming cracking and the Al content of the alloy when the Fe-high Ni alloy according to the present invention is heated at a heating rate of 300°C/hour during blooming. show. Figure 2 shows the degree of blooming cracking and the alloy properties when heating the same alloy during blooming at heating rates of 70°C/hour and 100°C/hour.
The relationship between Al content is shown.

Claims (1)

[Claims] 1. A method for producing a Fe-high Ni alloy slab containing 35 to 45% Ni with the balance being Fe and unavoidable impurities, including limiting Al in the alloy components to 0.04% or less, and preparing an alloy ingot prior to rolling. heating per hour
A method characterized by carrying out the heating at a rate of 100°C or less.