CN115852251A - Homogenization method for regulating delta ferrite content in ferrite/martensite heat-resistant steel - Google Patents
Homogenization method for regulating delta ferrite content in ferrite/martensite heat-resistant steel Download PDFInfo
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- CN115852251A CN115852251A CN202211373978.3A CN202211373978A CN115852251A CN 115852251 A CN115852251 A CN 115852251A CN 202211373978 A CN202211373978 A CN 202211373978A CN 115852251 A CN115852251 A CN 115852251A
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- 229910000859 α-Fe Inorganic materials 0.000 title claims abstract description 82
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 53
- 239000010959 steel Substances 0.000 title claims abstract description 53
- 238000000265 homogenisation Methods 0.000 title claims abstract description 40
- 229910000734 martensite Inorganic materials 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims abstract description 25
- 230000001105 regulatory effect Effects 0.000 title claims abstract description 8
- 230000008569 process Effects 0.000 claims abstract description 9
- 239000000126 substance Substances 0.000 claims abstract description 6
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 5
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 4
- 238000007599 discharging Methods 0.000 claims abstract description 4
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 4
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 3
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 3
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 3
- 238000004321 preservation Methods 0.000 claims description 12
- 230000001276 controlling effect Effects 0.000 claims description 7
- 238000010583 slow cooling Methods 0.000 claims description 4
- 229910000851 Alloy steel Inorganic materials 0.000 abstract description 13
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Abstract
The invention discloses a homogenization method for regulating delta ferrite content in ferrite/martensite heat-resistant steel, belonging to the technical field of corrosion-resistant heat-resistant alloy steel. The ferrite/martensite heat-resistant steel comprises the following chemical components: 0.08 to 0.13 percent of C, 0.70 to 1.50 percent of Si, 0.70 to 1.40 percent of Ni, 7.0 to 10.0 percent of Cr, 0.50 to 1.0 percent of Mo, 0.45 to 0.95 percent of Mn, 0.10 to 0.35 percent of V, 0.10 to 0.35 percent of Nb and the balance of Fe; the homogenizing process comprises the following steps: placing the smelted and cast steel ingot at the high temperature of 1100-1180 ℃, preserving heat for 4-48 h, homogenizing, slowly cooling at the speed of 0.2-0.5 ℃/min, and discharging and cooling when the temperature reaches below 200 ℃. After the homogenization treatment, the delta ferrite in the heat-resistant steel is completely eliminated.
Description
Technical Field
The invention relates to the technical field of corrosion-resistant heat-resistant alloy steel, in particular to a homogenization method for regulating and controlling the content of delta ferrite in ferrite/martensite heat-resistant steel.
Background
With the development of social economy and the rapid improvement of the living standard of people, the demand of the whole society on energy sources is continuously improved. With the gradual depletion of traditional coal and petroleum energy, the development of new green clean energy capable of sustainable development is urgent. The nuclear energy is a high-efficiency and low-carbon clean energy which can be relied on and is the most promising energy, wherein the lead (lead bismuth) fast reactor is one of the fourth generation reactor types which are promising, and the lead (lead bismuth) alloy has the advantages of excellent heat conduction performance, neutron performance, no radiation damage of liquid lead (lead bismuth) and the like. According to the development idea of 'first generation materials and first generation equipment', a 9-percent Cr-containing lead (lead bismuth) corrosion resistant ferrite/martensite heat-resistant steel material (named as MAlfr-41 alloy) is developed by the metal research institute of Chinese academy of sciences, and the MAlfr-41 alloy can be used for preparing structural members such as heat exchange tubes of lead (lead bismuth) fast stacks and is a key structural material required by lead (lead bismuth) cooling fast stack construction. It is noted that the MAlfr-41 alloy has an increased chromium-nickel equivalent (CNB value) due to element adjustment compared to conventional 9Cr ferrite/martensitic heat-resistant steel, increasing the tendency for precipitation of δ ferrite in the alloy, while the presence of 3-4% δ ferrite is also observed in actual steel ingots. For ferrite/martensite heat-resistant steel, the existence of such a high-temperature δ ferrite phase has a large influence on the properties (such as impact toughness, durability, etc.) of the alloy steel. How to eliminate or reduce the delta ferrite in the preparation process is a prerequisite for obtaining the MAlfr-41 alloy with excellent comprehensive properties.
Disclosure of Invention
Aiming at the problem that the content of delta ferrite in the existing MAlfr-41 heat-resistant steel cast ingot is high, the invention aims to provide a homogenization method for regulating and controlling the content of the delta ferrite in ferrite/martensite heat-resistant steel, and the MAlfr-41 cast ingot is subjected to high-temperature treatment by the homogenization method so as to completely eliminate the delta ferrite in the cast ingot, so that the MAlfr-41 heat-resistant steel with excellent comprehensive performance is obtained.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a homogenization method for regulating delta ferrite content in ferrite/martensite heat-resistant steel is characterized in that a ferrite/martensite heat-resistant steel ingot is subjected to homogenization treatment to completely eliminate delta ferrite in the ingot, so that ferrite/martensite heat-resistant steel without delta ferrite is obtained.
The chemical components of the ferrite/martensite heat-resistant steel (MAlfr-41 alloy) ingot in percentage by weight are as follows:
0.08 to 0.13 percent of C, 0.70 to 1.50 percent of Si, 0.70 to 1.40 percent of Ni, 7.0 to 10.0 percent of Cr, 0.50 to 1.0 percent of Mo, 0.45 to 0.95 percent of Mn, 0.10 to 0.35 percent of V, 0.10 to 0.35 percent of Nb, less than or equal to 0.010 percent of S, less than or equal to 0.010 percent of P, and the balance of Fe.
The homogenization treatment process comprises the following steps: and (3) carrying out heat preservation treatment on the steel ingot at the temperature of 1100-1180 ℃ for 4-48 h, carrying out slow cooling at the speed of 0.2-0.5 ℃/min after heat preservation, and discharging the steel ingot after cooling to below 200 ℃. Wherein the steel ingot is prepared by proportioning and smelting the chemical components of the ferrite/martensite heat-resistant steel and casting.
Before the homogenization treatment, the content of delta ferrite in the heat-resistant steel ingot is 3-4%, and the delta ferrite is completely eliminated after the homogenization treatment, so that the ferrite/martensite heat-resistant steel without the delta ferrite is obtained.
The design idea of the invention is as follows:
the starting points of the invention are as follows: compared with the traditional 9Cr heat-resistant steel, the MAlfr-41 alloy steel with optimized components has improved chromium-nickel equivalent, so that high-temperature delta ferrite can be precipitated in the casting solidification process. According to the invention, a large number of system experiments are carried out to obtain the relation between the re-dissolution temperature and the time of the delta ferrite, wherein the lower the homogenization temperature is, the lower the re-dissolution speed of the delta ferrite is, and the longer the required homogenization heat preservation time is. In order to improve the production efficiency, the holding time can be shortened by adopting a higher homogenization temperature. It should be noted that the homogenization temperature is not too high, otherwise the temperature range for the delta ferrite to precipitate is entered, so that the delta ferrite is not eliminated, but a larger amount of delta ferrite may precipitate, and the homogenization purpose is not achieved. In addition, because the hardenability of the MAlfr-41 alloy steel is good, if the cooling speed is high after homogenization, phase transformation can occur to cause large internal stress, and steel ingot cracking is easily caused. Therefore, after the homogenization treatment, slow cooling is needed, and the steel ingot can be taken out for air cooling after the temperature of the steel ingot is lower than the phase transition temperature. According to the test result of the thermal expansion transformation point, the temperature of the martensite phase transformation finishing point of the MAlfr-41 alloy steel is about 224 ℃, so that the steel ingot can be taken out after being homogenized and slowly cooled to be below 200 ℃. It should be noted that the steel ingot after homogenization is heated to a temperature not exceeding the complete austenitizing temperature in the subsequent hot working process, otherwise the δ ferrite is re-precipitated.
The invention has the advantages that:
1. the invention homogenizes the ferrite/martensite heat-resistant steel for resisting liquid lead (lead bismuth) corrosion, can obtain a steel ingot without delta ferrite, and thus provides guarantee for obtaining MAlfr-41 alloy steel with excellent comprehensive performance.
2. On one hand, the homogenization temperature is moderate, the highest homogenization temperature is not more than 1180 ℃, the homogenization temperature is equivalent to the annealing temperature of alloy steel, production enterprises are relatively easy to realize, and the implementation of actual production is facilitated; on the other hand, the homogenization temperature range is wider, the temperature range is 1100-1180 ℃, the wider temperature range is easy to control in actual production, and the phenomenon of separating out delta ferrite due to overtemperature cannot occur.
Drawings
FIG. 1 shows an as-cast metallographic structure of a martensitic heat-resistant steel MALfr-41 alloy according to an embodiment of the present invention.
FIG. 2 shows the metallographic structure after the homogenization treatment according to the invention; wherein: (a) keeping the temperature at 1100 ℃ for 4h; and (b) keeping the temperature at 1250 ℃ for 4h.
Detailed Description
The following examples are given to further illustrate the present invention, but not to limit the present invention, and modifications made to the present invention under the premise of the inventive concept are within the scope of the present invention.
Examples 1-8 and comparative examples 1-6:
the invention provides a homogenization method for regulating and controlling the content of delta ferrite in ferrite/martensite heat-resistant steel (MAlfr-41 alloy), wherein the complete austenitizing temperature range of the MAlfr-41 alloy is between 860 and 1200 ℃. The alloy is smelted by adopting a vacuum induction furnace, industrial pure iron and 99.9wt.% of high-purity metals such as Cr, si, ni, mn, mo, V, nb and the like are selected as raw materials, alloy steel is smelted, and the chemical components of alloy steel ingots are shown in table 1. The ingot was observed to contain 3.6% delta ferrite as shown in fig. 1. In the experiment of taking a sample from a steel ingot for homogenization treatment, different homogenization temperatures and heat preservation times are respectively selected in each example and comparative example, after heat preservation, slow cooling is carried out at the speed of 0.2-0.5 ℃/min, and the steel ingot is taken out when the steel ingot is cooled to be below 200 ℃. The observation and statistics of delta ferrite were performed for each of the examples and comparative examples. Table 2 shows the homogenization parameters and delta ferrite contents for the respective examples and comparative examples.
TABLE 1 chemical composition (in mass%) of alloy steels of examples of the invention and comparative examples
The delta ferrite content is counted by adopting a cut-point method of YB/T4402-2014 metallographic determination method of ferrite content in martensitic stainless steel, at least 3 metallographic photos are respectively selected for counting in each homogenization state, and finally the average value is taken as the delta ferrite content. As can be seen from Table 2, when the homogenization temperature is lower (e.g., 1000 ℃), the amount of delta ferrite in the alloy steel is reduced, but the rate of re-dissolution is slower, and the delta ferrite content is still 1.5% after the temperature is kept for 48 hours. It is presumed from the theoretical calculation results that, when the holding time is further increased at the temperature, the δ ferrite content gradually decreases until the δ ferrite completely disappears, but the holding time is too long, which causes difficulty in the actual production of large alloy steel pieces. When the homogenization temperature is increased to 1100 ℃, the delta ferrite content is reduced to 0.5% after 2h of heat preservation, and the delta ferrite is completely eliminated after 4h of heat preservation, as shown in fig. 2 (a). After the temperature is continuously increased, the delta ferrite can be completely eliminated after heat preservation is carried out for 2 hours, such as 1150 ℃ and 1180 ℃. It is noted that at higher temperatures, such as 1180 ℃, no delta ferrite is observed after a longer holding time, such as 48 hours, indicating that no re-precipitation of delta ferrite occurs at this temperature. When the homogenization temperature is increased to 1250 ℃, the delta ferrite is not reduced, but the delta ferrite is increased significantly, for example, the delta ferrite content is 6.8% after 4h (as shown in fig. 2 (b)), and is increased to 8.5% after 24h, which indicates that the delta ferrite is precipitated at the temperature.
TABLE 2 homogenization Process parameters of alloy steels according to the examples of the present invention and their delta ferrite content
The results of the above examples show that the purpose of completely eliminating delta ferrite in alloy steel can be achieved by adopting the optimized homogenization process of the invention, which provides guarantee for obtaining ferrite/martensite heat-resistant steel with excellent performance subsequently. It should be noted that, in the subsequent hot working process, it is necessary to ensure that the heating temperature does not exceed 1180 ℃ to ensure that the delta ferrite is not re-precipitated.
Comparative example 7:
the difference from the embodiment 1 is that: after heat preservation, slowly cooling at the speed of 1 ℃/min, and discharging when cooling to below 200 ℃. In the present example, the cooling rate is fast after homogenization, which leads to the cracking of the steel ingot.
Claims (5)
1. A homogenization method for regulating delta ferrite content in ferrite/martensite heat-resistant steel is characterized in that: the method is to homogenize a ferrite/martensite heat-resistant steel cast ingot to completely eliminate delta ferrite in the cast ingot, thereby obtaining ferrite/martensite heat-resistant steel without delta ferrite.
2. The method of homogenizing for controlling delta ferrite content in ferritic/martensitic heat resistant steel as claimed in claim 1 wherein: the ferrite/martensite heat-resistant steel ingot comprises the following chemical components in percentage by weight:
0.08 to 0.13 percent of C, 0.70 to 1.50 percent of Si, 0.70 to 1.40 percent of Ni, 7.0 to 10.0 percent of Cr, 0.50 to 1.0 percent of Mo0, 0.45 to 0.95 percent of Mn, 0.10 to 0.35 percent of V, 0.10 to 0.35 percent of Nb, less than or equal to 0.010 percent of S, less than or equal to 0.010 percent of P, and the balance of Fe.
3. The method for homogenizing of controlling delta ferrite content in ferritic/martensitic heat resistant steel as claimed in claim 1 or 2, characterized in that: the homogenization process comprises the following steps: and (3) carrying out heat preservation treatment on the steel ingot at the temperature of 1100-1180 ℃ for 4-48 h, carrying out slow cooling at the speed of 0.2-0.5 ℃/min after heat preservation, and discharging the steel ingot when the steel ingot is cooled to below 200 ℃.
4. The method of homogenizing for controlling delta ferrite content in ferritic/martensitic heat resistant steel as claimed in claim 3 wherein: in the homogenization process, the heat preservation time is 4-10 h.
5. The method of homogenizing for controlling delta ferrite content in ferritic/martensitic heat resistant steel as claimed in claim 3 wherein: after homogenization treatment, delta ferrite in the heat-resistant steel ingot is completely eliminated, and ferrite/martensite heat-resistant steel without delta ferrite is obtained.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104451073A (en) * | 2014-08-14 | 2015-03-25 | 内蒙古北方重工业集团有限公司 | Heat treatment method for removing delta ferrites in ferritic heat-resistant steel |
| CN109811246A (en) * | 2019-03-14 | 2019-05-28 | 南京玖铸新材料研究院有限公司 | High-toughness heat-resistant cast stainless steel and its manufacturing method |
| CN113528953A (en) * | 2021-06-29 | 2021-10-22 | 中国科学院金属研究所 | Ferrite/martensite heat-resistant steel resisting liquid lead (lead bismuth) corrosion and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104451073A (en) * | 2014-08-14 | 2015-03-25 | 内蒙古北方重工业集团有限公司 | Heat treatment method for removing delta ferrites in ferritic heat-resistant steel |
| CN109811246A (en) * | 2019-03-14 | 2019-05-28 | 南京玖铸新材料研究院有限公司 | High-toughness heat-resistant cast stainless steel and its manufacturing method |
| CN113528953A (en) * | 2021-06-29 | 2021-10-22 | 中国科学院金属研究所 | Ferrite/martensite heat-resistant steel resisting liquid lead (lead bismuth) corrosion and preparation method thereof |
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