JP4993327B2 - Ni-base alloy hot-rolling slab and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Ni-base alloy having excellent resistance to stress corrosion cracking and intergranular corrosion resistance. In particular, the present invention relates to a Ni-based alloy slab having few cracks and chips and good hot workability in a forging process and a subsequent hot rolling process, and a manufacturing method thereof.
[0002]
[Prior art]
Ni-base alloys are widely used in harsh conditions due to their excellent corrosion resistance and heat resistance. Recently, the reliability requirement for the safety of materials is further increased. Of the Ni-based alloys, Inconel 600 is used as a core material for nuclear reactors, and requires high stress corrosion cracking resistance and intergranular corrosion resistance. For this reason, a method of fixing a solid solution C in advance by adding a stabilizing element such as Nb is usually performed. Conventionally, in order to improve hot workability, Japanese Patent Application Laid-Open No. 63-53235 has proposed solution heat treatment of NbC. JP-A-61-84348 proposes improvement of grain boundary strength by adding B and reducing the O content.
[0003]
[Problems to be solved by the invention]
However, ingots of Ni-based alloys to which Nb is added have poor hot workability, and thus may be subject to material defects such as cracking and breakage when passed through a forging or hot rolling process. If these defects occur, scraping becomes indispensable and the manufacturing yield is significantly reduced. When manufacturing on an industrial scale, stable hot workability may not always be obtained depending on the microstructure of the ingot, and cracking may occur during processing.
[0004]
An object of the present invention is to provide a Ni-based alloy slab that solves the above-mentioned problems of Ni-based alloys containing Nb, has excellent corrosion resistance and stress corrosion resistance, and has good hot workability, and a method for producing the same. There is.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the following inventions are provided. A first aspect of the present invention, in mass%, an Ni-based alloy for hot rolling slab comprising the components set Naru及 beauty properties below. (a) C: 0.045% or less, Fe: 3-25%, Cr: 14-26%, Nb: 4% or less, N: 0.005-0.04%, Si: 1.0% or less, Al: 0.01-0.20%, P: 0.001-0.020%, Mn: 1.0% or less, S: 50ppm or less, O: 5-50ppm, the balance being Ni and inevitable impurities ,
(b) The austenite grain size number (GSNo.) is 1 or more.
[0006]
In a second aspect of the invention, the component composition is C: 0.005 to 0.045%, Nb: 2 to 4%, Al: 0.01 to 0.1 %, S: 20 ppm or less, O: 5 A slab for hot rolling of a Ni-base alloy characterized by being 20 ppm .
[0007]
A third aspect of the present invention is a method for producing a Ni-base alloy hot-rolled slab characterized by comprising the following steps in mass% . (a) Component composition is C: 0.045% or less, Fe: 3-25%, Cr: 14-26%, Nb: 4% or less, N: 0.005-0.04%, Si: 1. 0% or less, Al: 0.01-0.20%, P: 0.001-0.020%, Mn: 1.0% or less, S: 50ppm or less, O: 5-50ppm, the balance is inevitable with Ni An ingot made of mechanical impurities is prepared, and (b) the ingot is heated to a temperature range of 1050 to 1250 ° C. and upsetting forging of 5% to 20% is performed.
[0008]
According to a fourth aspect of the present invention, the composition of the ingot is C: 0.005 to 0.045%, Nb: 2 to 4%, Al: 0.01 to 0.1 %, S: 20 ppm or less, O A method for producing a Ni-base alloy hot-rolled slab characterized by being 5 to 20 ppm .
[0009]
A fifth aspect of the present invention, the ingot for before and after SL upsetting forging, further, a process until forging reduction ratio for each press and heated to 1150 to 1250 ° C. as a range of 5-15% a first stage press working step of performing one or more times, for the previous SL ingot processed first stage press, a total reduction ratio of each press while maintaining the temperature range of 800 ~ 1300 ° C. was heated to 1200 to 1300 ° C. a second stage press working step of performing a process until forging a range of 5% to 85% one or more times, for the previous SL ingot second stage press working, the total reduction ratio were heated to 1050-1,230 ° C. And a step of performing press working at 10% or more. A method for producing a Ni-base alloy hot-rolled slab .
[0010]
A sixth aspect of the present invention, the Ni-based alloy hot-rolled slab was subjected to pre-Symbol pressing a further production method of a Ni-based alloy and performing hot rolling.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The component composition of the present invention (% and ppm are based on weight) will be described below. C is a component that contributes to improving the mechanical strength of the alloy. However, if the content is too large, the corrosion resistance deteriorates, so the upper limit is made 0.045%, preferably 0.040% or less. In order to secure the strength, 0.003% or more is desirable, and more desirably 0.005% or more.
[0012]
Fe is a component that contributes to toughness. If the content is excessive, the corrosion resistance tends to deteriorate, so the upper limit is 25%. In order to secure toughness, the lower limit is 3%, preferably 5% or more.
[0013]
Cr is an essential element for exerting corrosion resistance. If the content is less than 14%, the corrosion resistance deteriorates. If it exceeds 26%, the high-temperature strength becomes high and it becomes difficult to process, so it needs to be in the range of 14 to 26%.
[0014]
Nb has the effect of improving the corrosion resistance by precipitating solute carbon (C) and solute nitrogen (N) as carbides and nitrides. However, if the content is too large, grain boundary embrittlement may occur due to excessively precipitated precipitates, so the content is made 4% or less. Further, if the content is too small, the corrosion resistance is deteriorated and the solid solution strengthening is also reduced. Therefore, the content is desirably 2% or more.
[0015]
N is effective in improving mechanical strength, corrosion resistance, and intergranular corrosion resistance. If the content exceeds 0.04%, it approaches the solid solubility limit of N and blowholes are likely to occur. In addition, in order to ensure proof stress, it is 0.005% or more, preferably 0.01% or more.
[0016]
Al is added as a deoxidizer. If the content is too large, the hot workability is impaired, so the content is made 0.2% or less. Preferably it is 0.1% or less.
[0017]
If the Si content exceeds 1.0%, the intergranular corrosion resistance deteriorates, so the content is made 1.0% or less.
[0018]
If the P content exceeds 0.030%, intergranular corrosion resistance and weldability deteriorate, so 0.030% or less.
[0019]
If the Mn content is more than 1.0%, the intergranular corrosion resistance deteriorates, so the content is made 1.0% or less .
[0020]
About S and O, if there is too much content, hot workability will be spoiled. Therefore, S is 50 ppm or less, and O is 60 ppm or less. Preferably, S is 20 ppm or less, and O is 20 ppm or less.
[0021]
The present inventors investigated the alloy which mix | blended each component. A material with poor hot workability in an ingot which is a cast structure is processed into a fine grain structure having a GS No. of 1 or more, preferably 2 or more by improving the hot forging method. As a result, hot workability such as crack prevention was improved, and the subsequent hot rolling process could be smoothly operated.
[0022]
The present invention will be described with reference to Table 1 shown in FIGS. FIG. 1 shows the forging and pressing process of the present invention. Table 1 shows an operation example for each forging and pressing step of the present invention. The above components are blended, melted and cooled and solidified, and the ingot is heated to a temperature range of 1050 ° C. to 1250 ° C. to perform upsetting forging of 5 to 20%. Upset forging is usually performed for width expansion for the purpose of widening the slab, but unlike forging, the effect of tensile stress is small, so it is effective for breaking the solidified structure while preventing hot cracking. I found it to be a method.
[0023]
It is a feature of the present invention that it is carried out to prevent hot cracking even when no width is required. The heating temperature is 1050 to 1250 ° C. The reason is that NbC precipitates during heating at 1050 ° C or lower and cracks occur during pressing, and at 1250 ° C and higher, some of the grain boundaries whose melting point is lowered due to solidification segregation liquefies and cracks occur during pressing. It is.
[0024]
After carrying out upset forging, it is reheated to a temperature in the range of 1050 to 1250 ° C., and at least one first-stage pressing with a reduction rate of 5 to 15% is performed. Next, after heating to 1200 to 1300 ° C., at least one second stage pressing is performed in the range of 1300 ° C. to 800 ° C. with a total rolling reduction of 5 to 85%. In the final stage press working, press working is performed at a heating temperature of 1050 to 1230 ° C. and a total rolling reduction of 10% or more.
[0025]
The rolling reduction in the first stage pressing was 5-15%. The reason is that if the total rolling reduction is less than 5%, recrystallization is insufficient, and if it exceeds 15%, cracking occurs during pressing.
[0026]
In the second stage pressing, the heating temperature was set to 1200 ℃ or higher in order to increase the processing rate and increase the productivity. The reason for setting the forging temperature to 1300 to 800 ° C. is that cracks occur during pressing when the temperature is 1300 ° C. or higher, and cracks occur during pressing when the temperature is 800 ° C. or lower. The total rolling reduction in the second stage pressing was set to 5% to 85%. The reason is that if the total rolling reduction is less than 5%, recrystallization in the thickness direction becomes non-uniform, and cracks are likely to occur where coarse grains are present, whereas if it exceeds 85%, cracks occur during pressing. Because.
[0027]
The reason why the heating temperature in the final stage pressing was set to 1050-1230 ° C is that NbC precipitates at the grain boundary during heating at 1050 ° C or less, and grain boundary cracking occurs at the time of pressing. This is because it hinders hot workability. Further, the total rolling reduction was set to 10% or more. The reason is that when it is 10% or less, recrystallization becomes insufficient, and coarse grains remain, which hinders the hot workability of the slab after press working.
[0028]
The hot workability of the slab was evaluated by a drawing value (%) defined by the following equation after performing a high-temperature tensile test. Aperture value (%) = (cross-sectional area of test piece before test−cross-sectional area of test piece after test) ÷ cross-sectional area before test × 100 . Also, it is shown for the same sample combined results for grain size number in FIG. The larger the grain size number, the larger the aperture value and the better the hot workability. When the grain size number is less than 1, the aperture value decreases rapidly. If the drawing value is 50% or less, cracking occurs, so hot rolling is difficult. The crystal grain size was measured in accordance with JIS G0551 (average grain size determination method).
[0029]
The Ni-based alloy hot slab thus obtained is then hot rolled to obtain a hot rolled slab.
[0030]
【Example】
The numbers 1 to 7 in Table 2 shown as FIG. 4 and Table 3 shown as FIG. 5 are examples of the present invention. The alloy was melted and cast in an electric furnace and a vacuum deoxidation furnace so as to have the composition shown in Table 2 . Although not shown in Table 2 , the Fe content is 4.0 to 12.0%. The Al content is 0.01 to 0.20%. The P content is 0.001 to 0.020%. The content of O is 5 to 50 ppm. The cooled and solidified ingot was heated to a temperature range of 1050 ° C. to 1250 ° C. to perform upsetting forging of 5 to 20%.
[0031]
After carrying out upset forging, the first stage press work was performed by reheating. The heating temperature The results in Table 3 shown as FIG. 5, the press end temperature, the total rolling reduction (mean value) is shown, respectively as a numeric value. Subsequently, the second stage press work was performed by reheating. The heating temperature The results in Table 3 shown as FIG. 5, the press end temperature, the total rolling reduction (mean value) is shown, respectively as a numeric value. Next, the final stage press working, as a result heating in Table 3 shown as FIG. 5 temperature, showing the press end temperature, the total reduction ratio respectively as a numeric value. The average value of the total rolling reduction in the first stage and the second stage is the average value of the press work performed once or more.
[0032]
The Ni-based alloy hot-rolled sheet slab after hot pressing was evaluated for the grain size number and the presence or absence of surface cracks in the hot-pressed product. Further, the slab was hot-rolled to produce a 100 mm thick plate. Evaluated for the presence or absence of surface cracks of the resulting slab are also shown in Table 3 shown as FIG.
[0033]
Reference numbers 8 to 15 in Table 2 shown as FIG. 4 and Table 3 shown as FIG. 5 are comparative examples. The alloy was melted and cast in an electric furnace and a vacuum deoxidation furnace so as to have the composition shown in Table 2 . Although not shown in Table 2 , the Fe content is 4.0 to 12.0%. Al content is 0.01 to 0.20%. The P content is 0.001 to 0.020%. The O content is 5 to 50 ppm. The cooled and solidified ingot was upset forged and pressed. The results are shown in Table 3 as heating temperature, press finishing temperature, and total rolling reduction.
[0034]
The Ni-based alloy hot-rolled sheet slab after hot pressing was evaluated for the grain size number and the presence or absence of surface cracks in the hot forged product. Furthermore, hot rolling was performed to produce a 100 mm thick plate. Evaluated for the presence or absence of surface cracks of the resulting slab are also shown in Table 3 shown as FIG. The effects of the present invention are evident from the results of the examples and comparative examples.
[0035]
【Effect of the invention】
The slab for a Ni-based alloy hot-rolled sheet according to the present invention is processed into a fine grain structure having a grain size number of GSNo. 1 or more, and the hot workability is remarkably improved by preventing cracking.
Further, according to the method of the present invention, by performing suction forging and pressing under a predetermined condition, it is possible to produce a Ni-based alloy having excellent corrosion resistance and stress corrosion cracking resistance at a high yield without generating cracks. .
[Brief description of the drawings]
FIG. 1 is a schematic view of a forging and pressing process according to the present invention.
FIG. 2 is a table summarizing operation examples of forging and pressing processes of the present invention in Table 1.
FIG. 3 is a graph showing the relationship between the crystal grain size number and hot workability.
FIG. 4 is a diagram summarizing the composition of ingredients in Table 2.
FIG. 5 is a table in which processing conditions and measurement results are organized and summarized in Table 3.

Claims (6)

By mass%, Ni based alloy for hot rolling slab comprising the components set Naru及 beauty properties below.
(a) C: 0.045% or less, Fe: 3-25%, Cr: 14-26%, Nb: 4% or less, N: 0.005-0.04%, Si: 1.0% or less, Al: 0.01-0.20%, P: 0.001-0.020%, Mn: 1.0% or less, S: 50ppm or less, O: 5-50ppm, the balance being Ni and inevitable impurities ,
(b) The austenite grain size number (GSNo.) is 1 or more.   The component composition is C: 0.005 to 0.045%, Nb: 2 to 4%, Al: 0.01 to 0.1%, S: 20 ppm or less, and O: 5 to 20 ppm. The slab for Ni-base alloy hot rolling according to claim 1. A method for producing a Ni-based alloy hot-rolled slab characterized by comprising the following steps in mass% .
(a) Component composition is C: 0.045% or less, Fe: 3-25%, Cr: 14-26%, Nb: 4% or less, N: 0.005-0.04%, Si: 1. 0% or less, Al: 0.01-0.20%, P: 0.001-0.020%, Mn: 1.0% or less, S: 50ppm or less, O: 5-50ppm, the balance is inevitable with Ni An ingot made of mechanical impurities is prepared, and (b) the ingot is heated to a temperature range of 1050 to 1250 ° C. and upsetting forging of 5% to 20% is performed.   The component composition of the ingot is C: 0.005 to 0.045%, Nb: 2 to 4%, Al: 0.01 to 0.1%, S: 20 ppm or less, and O: 5 to 20 ppm. The method for producing a Ni-based alloy hot-rolled slab according to claim 3. For the ingot after upsetting forging,
A step of a first stage press working for performing one step at least once until heating to 1150 to 1250 ° C. and forging the rolling reduction ratio for each press within a range of 5 to 15%;
About the ingot which carried out the said 1st step press process, 1 process until it forges it as the range of 5 to 85% of the total reduction rate for each press, heating at 1200-1300 degreeC and keeping the temperature range of 800-1300 degreeC. A second stage pressing process performed once or more;
For the ingot subjected to the second stage press processing, heating to 1050 to 1230 ° C. and pressing the total reduction ratio to 10% or more; and
The method for producing a Ni-based alloy hot-rolled slab according to claim 3 or 4, characterized in that   A method for producing a Ni-base alloy, wherein the Ni-base alloy hot-rolled slab subjected to press working according to claim 5 is further hot-rolled.

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