JPS626634B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a high-temperature, high-strength steel containing carbide-forming elements, which has significantly increased strength compared to current heat-resistant steels while maintaining workability comparable to that of ordinary austenitic stainless steel. As a heat-resistant steel used at high temperatures of 800℃ or higher,
Carbide-reinforced heat-resistant steel is known, but it contains 0.4%
There are two types of heat-resistant cast alloys that contain a large amount of C, such as those that are reinforced with Ti, Nb, etc. SCH-22 alloy is known as a typical heat-resistant cast alloy containing a large amount of C, but due to its nature as a cast alloy, this heat-resistant cast alloy has drawbacks such as limitations in shape and safety issues. be. On the other hand, those reinforced with Ti, Nb, etc. are intended to obtain high strength by forming carbides or carbonitrides during high-temperature use using these carbide-forming elements. Kosho 47-
30806 is known. However, in steels containing these carbide-forming elements, the relationship between grain size, solution treatment, and the amount added has not yet been sufficiently clarified. In addition, the above-mentioned proposed steel was designed to be used at temperatures below 700°C, and had the drawback of not being able to meet the demands for higher temperatures. The present invention was made in view of the above-mentioned drawbacks of the prior art, and was made by clarifying the relationship between crystal grain size, solution treatment, and the amount of carbide-forming elements added.
This is intended to improve tension at temperatures below 900°C. That is, in the present invention, C: 0.06-0.30%, Ni: 9-45%, Cr: 15-30
%, Si: 1.0% or less, Mn: 2.0% or less, and Nb,
Contains one or more of Ti, Zr, and Ta so as to satisfy the following conditions, furthermore, P: 0.04% or less, S:
The basic feature is that the austenite crystal grain size is JIS 3 to 5, with the content being 0.02% or less, and the remainder being iron and unavoidable impurities. Cr (%) 0.8×Ni (%) + 13 Ti% + Nb (%) + Zr (%) + Ta (%)/C
(%): 1-13 Ti (%)/C (%): 1-10 Nb (%)/C (%): 1-10 Zr (%)/C (%): 1-10 Ta (%) /C (%): 1 to 10 In the above, all percentages are by weight (the same applies below). The reasons for this limitation are explained below. C: If C is less than 0.06%, sufficient strength cannot be obtained as shown in FIG. Moreover, if it is added in an amount exceeding 0.30%, as shown in FIG. 2, it will only deteriorate workability and will not lead to an increase in strength. Ni, Cr: Ni needs to be at least 9% to form an austenite single-phase structure, and the higher the Ni content, the more it stabilizes the austenite phase and toughens the austenite, especially in the high temperature range of 700°C or higher. If the content is increased, it becomes necessary to strictly limit the S content as described below, and it becomes very expensive, so it is difficult to set the upper limit.
It was set at 45%. Cr is 15% to ensure acid resistance at high temperatures
However, if it exceeds 30%, it will not be possible to obtain an austenite single phase structure.
This is the upper limit. Further, as is well known, Cr is a ferrite-forming element and Ni is an austenite-forming element, and an austenite single-phase structure cannot be obtained unless the relationship between their contents is controlled as follows. Cr (%) 0.8 x Ni (%) + 13 ... In the above formula, when Al is included, Cr (%) + Al (%) 0.8 x Ni (%) + 13 ... must be satisfied. Si, Mn: The content of Si and Mn is similar to that of ordinary austenitic steel, that is, Si is 1.0% or less and Mn is 2.0% or less. The purpose is primarily deoxidation. Nb, Ti, Zr, Ta: These are carbide or carbonitride-forming elements that improve strength by forming carbides and carbonitrides during high-temperature use, and one or more of these elements Add.
Conventionally, the addition of large amounts of these elements, such as Ti and Nb, is often considered undesirable because the C in the steel is fixed by Ti and Nb, and the reinforcing effect of C cannot be obtained. However, by raising the solution treatment temperature, the dissolution of TiC and NbC during the solution treatment progresses, and the amount of C that precipitates as Cr ₂₃ C ₆ during subsequent use increases. Therefore, when solution treatment is performed at high temperatures (inevitably, the grain size becomes coarse), the amount of Ti, Nb, etc. added can be increased compared to when heat treatment is performed at low temperatures without sacrificing high-temperature high strength. Can be added. Furthermore, Ti, Nb, etc. added in large amounts become precipitates by themselves and are useful for strengthening. However, the upper limit of solution treatment temperature is actually 1300℃
Ti%+Nb(%)+Zr(%)+Ta(%)/C
(%) (all weight % as mentioned above) is limited to 13. Further, if it is less than 1, there is little effect of achieving high temperature and high strength, so this is set as the lower limit. Furthermore, in order to obtain even higher strength, it is necessary to set the number to 2 to 11. In addition, these elements alone are Ti (%) / C (%),
Nb (%)/C (%), Zr (%)/C (%), Ta
(%)/C (%) ratio shall satisfy the range of 1 to 10. The reason for the above limitation is shown in FIG. 3 using Nb and Ti as examples. Figure 3 shows 0.1%C-20%Cr-30%Ni-0.5%Al
The graph shows the creep rupture strength at 900℃ for 1000 hours of steel treated at 1250℃ with various Nb and/or Ti added (the crystal grain size of these materials is grain size No. 3). 5, but the higher the Nb and/or Ti content, the finer the grain size). In Figure 3, the vertical and horizontal axes show the amount of Ti (%) and the amount of Nb (%), respectively, and the numbers shown within the circles in each blot are shown at that position.
This is the creep rapture strength at 900°C x 1000 hr obtained by the steel containing Ti and Nb. Single addition of Nb or Ti, that is, Nb or Y on the X axis
On the axis, where Ti exceeds 1.0%, that is, where Nb/C or Ti/C exceeds 10 (points A and D), the creep rapture strength tends to be lower than that at points below. Even in the case of Nb/C or Ti/C
Since strength tends to be lower where the value exceeds 10 than where it is less than 10, the content of Nb or Ti is limited to a ratio of 10 or less with respect to C, respectively, as described above. In addition, there is a line on the drawing that separates areas where the creep rapture strength at 900°C for 1000 hours is 3.0 Kg/mm ² or more from those below it, and a line that indicates the creep rapture strength under the same conditions.
Lines ``'' and '' indicating the division where 3.5 Kg/mm ² or more can be obtained are also shown. That is, in the present invention, the amounts of Nb and Ti are
It is selected so that it falls within the range enclosed by ABCDEF, preferably within the range enclosed by AB'C'DE'F'. More preferably, from the same figure, Ti/C: 4.5 or less and Nb/C: 2
-7 combined additions. That is, Ti+Nb/C: 1 to 13 (preferably 2 to 11) [However, Ti/C10 Nb/C10] Note that Zr and Ta are also carbide-forming elements like Ti and Nb and may have the same effects. For example, it has been confirmed as shown in FIG. Therefore, in the present invention, as described above, one or more of Ti, Nb, Zr, and Ta are used as follows: Ti+Nb+Zr+Ta/C: 1 to 13 (preferably 2 to 11); however, Ti/C10, Nb/C10, Zr/ It is added within the range of C10 and Ta/C10. P: P does not need to be particularly limited, and there is no problem as long as it is 0.04% or less, which is allowed for ordinary austenitic steel. S: Since S deteriorates both high temperature strength and workability, its content is limited to 0.02% or less. Especially when the amount of Ni is large, the restriction becomes severe. Figure 5 shows 18%Cr-10%Ni-0.1%C-0.5%
Nb steel, 23%Cr-18%Ni-0.1%C-0.5%Nb steel and 20%Cr-28%Ni-0.1%C-0.5%Nb steel (both grain size number 3 solution treated at 1250℃)
This figure shows the effect of the amount of S on the creep rupture strength of the
It can be seen that the S content has a large influence on the S content and that the S content must be strictly limited. From the figure, it is preferable to set the upper limit of S to 0.015% when the Ni content is 18% or more, and to set the upper limit of S to 0.010% when the Ni content is 28% or more. Grain size: The austenite crystal grain size shall be adjusted to JIS No. 3 to 5 by appropriate solution treatment. As shown in FIG. 6, as the particle size number decreases (as the particles become coarser), the breaking strength increases, but on the other hand, the breaking elongation decreases. Therefore, it is necessary to select the grain size depending on the application, but if the grain size is less than 3, the strength will not increase much, and if the grain size is more than 5, the high temperature strength will be much different from that of ordinary heat-resistant steel (SUS310, Incoloy 800, etc.). It becomes something that does not exist. Therefore, the crystal grain size is limited to JIS 3 to 5. In order to obtain sufficient coarse grains through solution treatment, it is necessary to heat at 1180°C or above for 5 to 30 minutes, followed by water cooling, oil cooling, or air cooling.
It varies depending on the amount of Ti, Nb, etc. added, and the larger the amount added, the higher the temperature required to obtain the same particle size. The basic limitations of the steel of the present invention are as described above, but the effect is greater when the following elements are further added. Al: Adding Al improves oxidation resistance. However, addition of a large amount exceeding 4% lowers the creep strength as shown in FIG. 7, and furthermore, an Al content exceeding 4% is unfavorable in terms of manufacturing (melting and processing). Therefore, the upper limit is set at 4%. Note that since Al is a strong ferrite-forming element, it is necessary to satisfy Cr (%) + Al (%) 0.8 x Ni (%) + 13 as described above. N, B: Both N and B are effective for high temperature strength.
N is also an element that does not reduce workability, and therefore it is necessary to add 0.05 or more of it as an impurity.
It is preferable to contain 0.1% or more, but 0.3%
It is not possible to contain more than Therefore N
shall be 0.3% or less. As shown in FIG. 8, addition of B in excess of 0.01% is harmful to processability. Therefore, it should be 0.01% or less. Examples of the present invention are shown in the table below. This table shows that the steel of the present invention has improved strength without hindering workability.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between creep rupture strength and C%, Figure 2 is a graph showing the relationship between hot workability and C%, and Figure 3 is a graph showing the relationship between creep rupture strength and Ti and C%.
Graph showing the relationship with Nb%, Figure 4 is a graph showing the influence of Zr and Ta on Nb additives, Figure 5 is a graph showing the relationship between creep rupture strength and S%,
Figure 6 is a graph showing the relationship between creep rupture strength and elongation and grain size, Figure 7 is a graph showing the relationship between creep rupture strength and oxidation resistance, and Al%, and Figure 8 is a graph showing the relationship between creep rupture strength and B%. It is a graph showing the relationship between.

Claims (1)

[Claims] 1 C: 0.06 to 0.30%, Ni: 9 to 45%, Cr: 15 to
30%, Si: 1.0% or less, Mn: 2.0% or less, and
Contains one or more of Nb, Ti, Zr, and Ta so as to satisfy the following conditions, and further includes P: 0.04% or less,
S: A high-temperature, high-strength steel containing carbide-forming elements with an austenite crystal grain size of JIS 3 to 5, with S: 0.02% or less, the remainder consisting of iron and unavoidable impurities. Cr (%) 0.8×Ni (%) + 13 Ti% + Nb (%) + Zr (%) + Ta (%)/C
(%): 1-13 Ti (%)/C (%): 1-10 Nb (%)/C (%): 1-10 Zr (%)/C (%): 1-10 Ta (%) /C (%): 1~102C: 0.06~0.30%, Ni: 9~45%, Cr: 15~
30%, Si: 1.0% or less, Mn: 2.0% or less, and
One or more of Nb, Ti, Zr, Ta, and P:
0.04% or less, S: 0.02% or less, and Al: 4%
The following contains one or more of N: 0.3% or less and B: 0.01% or less so as to satisfy the following conditions,
A high-temperature, high-strength steel containing carbide-forming elements with an austenite crystal grain size of JIS 3 to 5, the remainder being iron and unavoidable impurities. Cr (%) + Al (%) 0.8 × Ni (%) + 13 Ti (%) + Nb (%) + Zr (%) + Ta (%) / C
(%): 1-13 Ti (%)/C (%): 1-10 Nb (%)/C (%): 1-10 Zr (%)/C (%): 1-10 Ta (%) /C (%): 1-10