Fe-Cr-Ni-Mo ALLOY AND METHOD FOR PRODUCING THE SAME

Abstract

FeCrNiMo alloy having superior surface properties and a method for producing the same using a commonly used apparatus at low cost. The FeCrNiMo alloy has (% indicates mass %): C: 0.03%, Si: 0.15 to 0.5%, Mn: 0.1 to 1%, P: 0.03%, S: 0.002%, Ni: 20 to 32%, Cr: 20 to 26%, Mo: 0.5 to 2.5%, Al: 0.1 to 0.5%, Ti: 0.1 to 0.5%, Mg: 0.0002 to 0.01%, Ca: 0.0002 to 0.01%, N: 0.02%, O: 0.0001 to 0.01%, freely contained components of Co: 0.05 to 2% and Cu: 0.01 to 0.5%, Fe as a remainder, and inevitable impurities, wherein MgO, MgO.Al.sub.2O.sub.3 spinel type, and CaOAl.sub.2O.sub.3MgO type are contained as oxide type non-metallic inclusions, ratio of number of MgO.Al.sub.2O.sub.3 spinel type to all oxide type non-metallic inclusions is 50%, and CaOAl.sub.2O.sub.3MgO type contains CaO: 30 to 70%, Al.sub.2O.sub.3: 5 to 60%, MgO: 1 to 30%, SiO.sub.2: 8%, and TiO.sub.2: 10%.

Claims

1. An FeCrNiMo alloy comprising, % indicating mass %: C: 0.03% or less, Si: 0.15 to 0.5%, Mn: 0.1 to 1%, P: 0.03% or less, S: 0.002% or less, Ni: 20 to 32%, Cr: 20 to 26%, Mo: 0.5 to 2.5%, Al: 0.1 to 0.5%, Ti: 0.1 to 0.5%, Mg: 0.0002 to 0.01%, Ca: 0.0002 to 0.01%, N: 0.02% or less, O: 0.0001 to 0.01%, Co: 0.05 to 2% and Cu: 0.01 to 0.5% as freely contained components, Fe as a remainder, and inevitable impurities, wherein MgO, MgO.Al.sub.2O.sub.3 spinel type, and CaOAl.sub.2O.sub.3MgO type are contained as oxide type non-metallic inclusions, ratio of number of the MgO.Al.sub.2O.sub.3 spinel type to all oxide type non-metallic inclusions is 50% or less, and the CaOAl.sub.2O.sub.3MgO type comprises CaO: 30 to 70%, Al.sub.2O.sub.3: 5 to 60%, MgO: 1 to 30%, SiO.sub.2: 8% or less, and TiO.sub.2: 10% or less.

2. The FeCrNiMo alloy according to claim 1, wherein as oxide type non-metallic inclusions, composition range of the MgO.Al.sub.2O.sub.3 spinel type is MgO: 15 to 35% and Al.sub.2O.sub.3: 65 to 85%.

3. The FeCrNiMo alloy according to claim 1, wherein the number of oxide type non-metallic inclusions of 5 m or more is 50/cm.sup.2 or less and the number of oxide type non-metallic inclusions of 100 m or more is 5/cm.sup.2 or less, in the case in which the number of the inclusions is measured at a freely selected cross section of a sample collected in a tundish of a continuous casting apparatus.

4. The FeCrNiMo alloy according to claim 1, wherein the number of oxide type non-metallic inclusions of 5 m or more is 48/cm.sup.2 or less and the number of oxide type non-metallic inclusions of 100 m or more is 3/cm.sup.2 or less in the case in which the number of the inclusions is measured at a freely selected cross section of a sample collected in a tundish of a continuous casting apparatus.

5. The FeCrNiMo alloy according to claim 1, wherein SiO.sub.2 and TiO.sub.2 contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions is 2 mass % or less and 6 mass % or less, respectively.

6. The FeCrNiMo alloy according to claim 1, wherein no SiO.sub.2 and TiO.sub.2 are contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions.

7. The FeCrNiMo alloy according to claim 2, wherein the number of oxide type non-metallic inclusions of 5 m or more is 50/cm.sup.2 or less and the number of oxide type non-metallic inclusions of 100 m or more is 5/cm.sup.2 or less, in the case in which the number of inclusions is measured at a freely selected cross section of a sample collected in a tundish of a continuous casting apparatus.

8. The FeCrNiMo alloy according to claim 2, wherein the number of oxide type non-metallic inclusions of 5 m or more is 48/cm.sup.2 or less and the number of oxide type non-metallic inclusions of 100 m or more is 3/cm.sup.2 or less in the case in which the number of the inclusions is measured at a freely selected cross section of a sample collected in a tundish of a continuous casting apparatus.

9. The FeCrNiMo alloy according to claim 2, wherein SiO.sub.2 and TiO.sub.2 contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions is 2 mass % or less and 6 mass % or less, respectively.

10. The FeCrNiMo alloy according to claim 3, wherein SiO.sub.2 and TiO.sub.2 contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions is 2 mass % or less and 6 mass % or less, respectively.

11. The FeCrNiMo alloy according to claim 7, wherein SiO.sub.2 and TiO.sub.2 contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions is 2 mass % or less and 6 mass % or less, respectively.

12. The FeCrNiMo alloy according to claim 4, wherein SiO.sub.2 and TiO.sub.2 contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions is 2 mass % or less and 6 mass % or less, respectively.

13. The FeCrNiMo alloy according to claim 8, wherein SiO.sub.2 and TiO.sub.2 contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions is 2 mass % or less and 6 mass % or less, respectively.

14. The FeCrNiMo alloy according to claim 2, wherein no SiO.sub.2 and TiO.sub.2 are contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions.

15. The FeCrNiMo alloy according to claim 3, wherein no SiO.sub.2 and TiO.sub.2 are contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions.

16. The FeCrNiMo alloy according to claim 7, wherein no SiO.sub.2 and TiO.sub.2 are contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions.

17. The FeCrNiMo alloy according to claim 4, wherein no SiO.sub.2 and TiO.sub.2 are contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions.

18. The FeCrNiMo alloy according to claim 8, wherein no SiO.sub.2 and TiO.sub.2 are contained in the CaOAl.sub.2O.sub.3MgO type as oxide type non-metallic inclusions.

19. A method for production of the FeCrNiMo alloy according to claim 1, comprising steps of: melting raw materials so as to melt FeCrNiMo alloy containing Ni: 20 to 32%, Cr: 20 to 26%, Mo: 0.5 to 2.5%, decarburizing in AOD and/or VOD, adding lime, fluorite, ferrosilicon alloy, and Al so as to form CaOSiO.sub.2Al.sub.2O.sub.3MgOF type slag having CaO/SiO.sub.2 1.5 to less than 4, and preparing FeCrNiMo melt alloy comprising C: 0.03% or less, Si: 0.15 to 0.5%, Mn: 0.1 to 1%, P: 0.03% or less, S: 0.002% or less, Al: 0.1 to 0.5%, Ti: 0.1 to 0.5%, Mg: 0.0002 to 0.01%, Ca: 0.0002 to 0.01%, N: 0.02% or less, O: 0.0001 to 0.01%, freely contained components of Co: 0.05 to 2% and Cu: 0.01 to 0.5%, Fe as a remainder, and inevitable impurities.

Description

EXAMPLES

[0038] The effect of the present invention is explained by way of Examples. First, raw materials such as stainless steel scrap, iron scrap, nickel, ferronickel, and molybdenum were melted in a 60 t electric furnace. Then, oxygen was blown (oxidizing refining) in order to remove C in AOD and/or VOD so as to decarburize. Cr reduction was performed. After that, lime, fluorite, light-burned dolomite, ferrosilicon alloy and Al were added, and deoxidized by forming CaOSiO.sub.2Al.sub.2O.sub.3MgOF type slag. Subsequently, Ar stirring was performed to promote desulfurizing. It should be noted that magnesia-chrome brick lining was performed in AOD and VOD. Next, the chemical composition was adjusted in ladle refining, and slabs were produced by the continuous casting apparatus.

[0039] The surface of a slab produced was ground, heated at 1200 C., and hot rolled so as to produce a hot strip having a thickness of 6 mm. Then, the strip was annealed and acid-washed so as to remove scale on the surface. Finally, cold rolling was performed so as to obtain a cold rolled coil having a thickness 1 mm, width 1 in, and length 1000 in. Table 1 shows chemical composition of alloy and slag composition in Examples and Comparative Example, and Table 2 shows results of analysis of inclusions in the alloy. It should be noted that value in brackets [ ] means it is out of the range of the present invention.

TABLE-US-00001 TABLE 1 Chemical composition (remainder Fe) mass % No. C Si Mn P S Ni Cr Mo Cu Co Al Ti Examples 1 0.021 0.21 0.65 0.015 0.0001 21.2 21.2 0.85 0.45 0.28 2 0.028 0.16 0.25 0.012 0.0012 28.4 25.3 2.45 0.02 0.42 0.35 0.18 3 0.015 0.34 0.45 0.019 0.0002 25.1 23.6 1.21 0.05 0.27 0.36 4 0.008 0.35 0.15 0.012 0.0015 20.5 20.3 0.63 0.84 0.33 0.25 5 0.017 0.48 0.95 0.025 0.0008 31.5 22.3 0.58 1.51 0.16 0.24 6 0.025 0.24 0.53 0.025 0.0008 26.3 23.7 0.68 0.35 1.23 0.17 0.17 7 0.025 0.18 0.57 0.021 0.0018 26.3 23.7 0.65 0.15 0.16 0.23 8 0.025 0.25 0.57 0.018 0.0005 24.5 23.7 0.65 0.51 0.16 0.23 Comparative 9 0.015 [0.68] 0.45 0.019 0.0002 25.1 23.6 0.98 0.27 0.45 Examples 10 0.028 [0.05] 0.25 0.012 0.0012 28.4 25.3 [0.25] 0.45 0.42 [0.08] [0.05] 11 0.021 [0.71] 0.65 0.015 0.0001 21.2 21.2 0.85 0.48 [0.85] [0.65] 12 0.025 [0.05] 0.57 0.021 0.0018 26.3 23.7 0.65 0.51 [0.05] 0.23 13 0.021 [1.52] [1.23] 0.015 0.0001 21.2 21.2 0.85 [1.85] 0.47 Chemical composition (remainder Fe) Slag composition mass % mass % No. Mg Ca N O CaO SiO.sub.2 Al.sub.2O.sub.3 MgO F C/S Examples 1 0.0075 0.0052 0.013 0.0002 62.3 15.9 7.5 6.8 7.5 3.9 2 0.0023 0.0012 0.015 0.0021 48.3 20.5 13.5 13.2 4.5 2.4 3 0.0045 0.0005 0.009 0.0005 55.2 21.3 7.2 12.3 4.0 2.6 4 0.0035 0.0025 0.009 0.0014 53.2 21.3 6.5 12.3 6.7 2.5 5 0.0015 0.0003 0.013 0.0051 44.3 23.5 10.3 14.5 7.4 1.9 6 0.0005 0.0002 0.008 0.0075 40.1 23.5 9.5 17.9 9.0 1.7 7 0.0004 0.0003 0.012 0.0052 42.8 22.8 10.5 17.9 6.0 1.9 8 0.0004 0.0003 0.011 0.0012 42.8 22.8 10.5 17.9 6.0 1.9 Comparative 9 0.0045 0.0005 [0.025] 0.0005 55.2 21.3 7.2 12.3 4.0 2.6 Examples 10 [0] [0] 0.015 [0.0157] 25.3 35.8 13.5 16.7 8.7 [0.7] 11 0.0075 [0.0125] 0.013 0.0002 78.9 3.5 6.5 4.3 6.8 [22.5] 12 0.0002 [0] 0.012 0.0087 42.8 22.8 10.5 17.9 6.0 1.9 13 [0.0151] [0.0123] 0.018 [0.00005] 76.3 6.3 6.5 3.8 7.1 [12.1]

TABLE-US-00002 TABLE 2 Number of oxide type inclusions Oxide type non-metallic inclusions composition (mass %) (number/cm.sup.2) 20 points analyzed by EDS 5 m 100 m Magnesia Spinel type CaOAl.sub.2O.sub.3MgO type No. or more or more n MgO n MgO Al.sub.2O.sub.3 n CaO Al.sub.2O.sub.3 MgO Examples 1 12 0 13 100 0 7 64.3 8.1 27.6 2 38 0 6 100 0 14 42.1 55.2 2.7 3 25 0 5 100 0 15 50.3 25.2 24.5 4 28 0 0 0 20 58.7 15.2 26.1 5 45 1 0 3 25.3 74.7 17 30.2 45.3 18.2 6 48 0 0 7 24.5 75.5 13 31.5 55.6 12.9 7 43 1 5 100 9 25.6 74.4 6 30.9 54.3 8.1 8 36 0 12 100 8 29.5 70.5 0 Comparative 9 25 0 5 100 0 15 50.3 25.2 24.5 Examples 10 [152] [12] 0 0 [7] [0] [68.8] [0] 11 25 [5] 0 0 [13] [71.2] [1.2] [15.3] 12 [102] [7] 2 100 [13] [25.6] [74.4] [5] [0] [60.3] [10.1] 13 34 [5] 1 100 0 [9] [75.3] [3.5] [6.0] Oxide type non-metallic inclusions composition (mass %) 20 points analyzed by EDS Quality evaluation CaO (number/coil) Al.sub.2O.sub.3 Spinel Defects Defects MgO type CaO Alumina ratio by by oxide No. SiO.sub.2 TiO.sub.2 n CaO n Al.sub.2O.sub.3 % TiN inclusions Examples 1 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 5 1.1 5.2 0 0 15 0 5 6 0 0 0 0 35 0 4 7 6.7 0 0 0 45 0 8 8 0 0 40 0 7 Comparative 9 0 0 0 0 0 251 0 Examples 10 [10.8] [20.4] 0 [13] [100] 0 0 567 11 [0] [12.3] [7] [100] 0 0 15 284 12 [19.3] [10.3] 0 0 [65] 0 189 13 [0] [15.2] [10] [100] 0 0 13 432

[0040] The chemical composition, slag composition, number of non-metallic inclusions, condition of inclusions, and surface defects of coils shown in Tables 1 and 2 are evaluated as follows.

1) Chemical composition of alloy and slag composition: Quantitative analysis was performed by using an X-ray fluorescent spectrometer. Quantitative analysis of oxygen and nitrogen concentration of alloy was performed by an inert gas impulse melting IR absorption method.
2) Number of inclusions of 5 m or more: Sample (diameter: 35 mmthickness 15 mm) was collected in a tundish of a continuous casting apparatus, the sample was cut, mirror polishing was performed, and number of inclusions was counted at a freely selected cross section. It should be noted that the number of oxide type inclusions was counted here.
3) Non-metallic inclusion composition: The above sample, which was used to count the number of inclusions, was used and analyzed. By using SEM-EDS, 20 pieces of oxide type inclusions having a size 5 m or more were measured at random.
4) Number ratio of spinel inclusions: The number ratio was calculated from the measured result of the above 3).
5) Quality evaluation: Surface of the cold rolled plate produced by rolling was visually observed, and the number of defects occurred by TiN and defects occurred by oxide type inclusions were counted. The defects by TiN were observed to be stringy and the defects by oxide type inclusions were observed to be linear, and they were separated and counted.

[0041] Examples and Comparative Examples shown in Table 1 were explained. Here, Example 6 was produced by using VOD as a refining furnace, Example 8 was produced by combining AOD and VOD. The other Examples were produced by using AOD in refining.

[0042] In Examples 1 to 8, since they satisfy the range of the present invention, the number of oxide type inclusions of 5 m or more was 50/cm.sup.2 or less, number of oxide type inclusions of 100 m or more was 5/cm.sup.2 or less, and there was no or almost no (8 or less) defects on the surface of final product, which was of superior quality. It should be noted that if the number of oxide type inclusions of 100 m or more is 5/cm.sup.2 or less, it can be sufficiently used as a product. The reason for generating 1/cm.sup.2 inclusions in Examples 5 and 8 is that SiO.sub.2 and TiO.sub.2 were contained in the allowable range of the present invention. Furthermore, if the number of defects is 8 or less, it can be sufficiently used as a product. The reason for generating a few defects in Examples 5 and 8 is that spinel inclusions were generated at 50% or less.

[0043] On the other hand, since Comparative Examples were out of the range of the present invention, surface defects were generated. Hereinafter, each Comparative Examples is explained.

[0044] Si concentration was 0.68% and N concentration was 0.025% which are high values in Comparative Example 9, and many defects were caused by TiN.

[0045] Si concentration, Mo concentration, and Al concentration were low and slag basicity C/S was 0.7, which was a low value in Comparative Example 10, deoxidizing by Si and Al was insufficient, and oxygen concentration was 0.0157%, which is a high value. As a result, the number of the inclusions of 5 m or more was 152/cm.sup.2 and the number of the inclusions of 100 m or more was 12/cm.sup.2 which are high values, and compositions mainly contained alumina. As a result, many defects caused by oxide type inclusions were generated.

[0046] Si concentration and Al concentration were high and slag basicity C/S was 22.5 which was a high value in Comparative Example 11, deoxidizing reaction was strong, and Ca concentration was increased. Therefore, composition of CaOAl.sub.2O.sub.3MgO type inclusions was out of the range, inclusions mainly contained CaO, and defects caused by oxide inclusions were numerous. In addition, since the Ti concentration was also high, defects caused by TiN were also generated.

[0047] Si concentration and Al concentration were low, deoxidizing was insufficient and Ca concentration was 0 in Comparative Example 12. Since deoxidizing was insufficient, not only was the number of inclusions of 5 m or more was 102/cm.sup.2 and the number of the inclusions of 100 m or more was 7/cm.sup.2, which are high values, but also the number ratio of spinel inclusions was 65%, which is a high value, and numerous defects caused by oxide type inclusions were generated.

[0048] Si concentration, Mn concentration and Al concentration were high and slag basicity C/S was 12.1 which is a high value in Comparative Example 13, deoxidizing reaction was strong, and O concentration was decreased to outside of the range. In addition, Mg and Ca concentrations were high. Therefore, composition of CaOAl.sub.2O.sub.3MgO type inclusions was out of the range, CaO inclusions were also generated, and numerous defects caused by oxide inclusions were generated. In addition, since Si concentration was also high, which was out of the range, activity of Ti was increased and defects caused by TiN was also generated.

[0049] According to the present invention, high quality FeCrNiMo alloy for sheathed heater can be produced at low cost.