US3155495A

US3155495A - Nitride containing ductile steel

Info

Publication number: US3155495A
Application number: US164291A
Authority: US
Inventors: Nakamura Hajime
Original assignee: IHI Corp
Current assignee: IHI Corp
Priority date: 1961-03-11
Filing date: 1962-01-04
Publication date: 1964-11-03
Anticipated expiration: 1981-11-03
Also published as: GB988704A; DE1458399A1

Description

Nov. 3, 1964 HAJIME NAKAMURA NITRIDEI CONTAINING DUCTILE STEEL Filed Jan. 4, 1962 7 Sheets-Sheet l T 1 a 1 VNQTCH CHARPY IMPACT VALUE KILLED STEEL TEST TEMPERA'IUREC 1 2| V NOTCH CHARPY IMPACT VALUE TEST TEMPERATURE C INVENTOR HAJIME NAKAMURA Y ATTO R N EY 3, 1964 HAJIME

NAKAMURA

3, 5, 5

NITRIDE CONTAINING DUCTILE STEEL Filed Jan. 4, 1962 7 Sheets-Sheet 2 Ti j- ASTM FERRITE GRAIN SIZE NUMBER N O 1 I I l x l O I 2 3 ASTM FERRITE GRAIN SIZE MJMBER CI 0 Q05 01 m5 AMOUNT OF METALLIC ALUMINUM IN SOLID SOLUTION%) INVENTOR HAJIME NAKAMURA I l l ATTORNEY Nov. 3, 1964 HAJIME NAKAMURA 3,155,495

NITRIDE CONTAINING DUCTILE STEEL v '7 Sheets-Sheet 3 Filed Jan. 4, 1962 NUMBER OF FERRlTE GRAIN IN 1mm AMOUNT OF METAL ALUMINUM IN SOLID SOLUTION (0.003- 015%) AMOUNT OF METAL ALUMlNUM lN SOLID SOLUTION (3.5- 0.36%)

m B 6 4 mum-E32 mN w 23mm mtmmwm 2.54

w 0 m 0 w 0 7 w 6 O. O mm A 4 O. 0

INVENTOR HAJIME NAKAMURA ATTO R N EY Nov. 3, 1964 HAJIME NAKAMURA 9 3 NITRIDE conmmmc DUCTILE STEEL 7 Sheets-Sheet 4 Filed Jan. 4, 1962 Photo 2 xuoo The same as in Photo 1 Photo 1 IELR o 3% Nital C8, 930C 1 hr air-cooled ASTM ferrite grain size 310. 9.5

Photo 1 x1400 The same as in Photo 3 Photo 3 C8, 930C 1 hr oil-cooled 656C 1.5 hrs air-cooled ASTM ferrite grain size No. 11

INVEN TOR. HA JIME NAKA I MR1:

Attorneys Nov. 3, 1964 HAJIME NAKAMURA 3,155,495

NITRIDE CONTAINING DUCTILE STEEL.

Filed Jan. 4, 1962 '7 Sheedas-Sheet 5 Photo 5 x100 3% Nital The same as in Photo 7 No. 80, 930C 1 hr oil-cooled 933- 0 1 hr oil-cooled 656C 1.5 hrs air-cooled 650C 1.5 hrs air-cooled Austenite grain size No. 8

No. 85, 930C 1 hr oil-cooled The same as in Photo 5 650C 1.5 hrs air-cooled 930C 1 hr oil-cooled 650C 1.5 hrs air-cooled Austenite grain size No. 6

INVENTO HAJII-E NAKAMURA Attorneys Nov. 3, 1964 HAJIME NAKAMURA 3,155,495

rumors. commune DUCTILE STEEL '7 Sheets-Sheet 6 Filed Jan. 4, 1962 Photb 9 C8, Each-action Replica.

Photo 10 m1, Extraction Replica INVENTOR. HAJIME NAKAMURA Attorneys 3, 1964 HAJIME NAKAMURA 3,155,495

NITRIDE CONTAINING DUCTILE STEEL 7 Sheets-Sheet 7 I Filed Jan. 4, 1962 Photo 11 No. 85, Extraction Replica Photo 12 No 80, Extraction Replica INVENTOR. mmaz NAKAMURA flllh 3 Attnrneys United States Patent C) M 3,155,495 NHRIDE CGNTAINENG BUCTELE STEEL Haiime Nalmmnra, Tokyo-to, Japan, assignor to lishikawajima-Harima .luhogyo Kahushilsi Kaislia, Tokyoto, lapan, a company of Japan Filed Jan. 4, 1962, Ser. No. 16 2 201 Claims priority, application .lapan, Mar. 11, 1961, Tao/8,484- 2 Claims. (Cl. 75-124) The present invention relates to a nitride containing ductile steel.

In the construction of structures in services at temperatures lower than normal environmental temperature, such as in the case of ships hulls or pressure vessels, steels have been hitherto used, which were deoxidized by both silicon and aluminum, because the notch-transition temperatures of such steels are substantially lower than those that are deoxidized by silicon only; that is to say, steels of former kind are tougher, or more ductile, at lower emperatures than the latter. Although the main reason for the use of such deoxidizers as silicon and aluminum and the attendant improvement of transition temperature characteristics is thought to be due to Le action of aluminum oxide and aluminum nitride to refine and uniformize the ferrite grains. The present invention contains evidence of the discovery that it is the precipitated aluminum nitride which contributes to the desired characteristics more effectively.

In producing steel containing precipitated aluminum nitride, however, it is almost impossible to produce a steel containing only aluminum nitride and, inevitably, a certain quantity of metallic aluminum is dissolved as in solid solution. The present invention is based on the discovery that it is impossible to get a fine grained steel, and therefore one which is ductile at low temperatures, if more than a certain quantity of metallic aluminum is contained in solid solution.

It is an object of the present invention to obtain ductile carbon-steels and low-alloy steels that have uniform and very refined grains by maintaining a quantity of precipitated aluminum nitride and dissolved metallic aluminum in the steel; and the present invention relates to ductile steels containing 0.040.25% carbon, 0.010.50% silicon, 1.00% or less than 1.00% manganese, less than 0.035% phosphorus and sulphur, 0.030.l2% aluminum nitride as precipitated and 0.003-0.15% metallic aluminum in solid solution and having a ferrite grain size of more than N0. 9 ASTM and a V notch Charpy impact value of more than 15 kg-rn/cm. at C.

Reference is made to the accompanying drawing and photos, wherein:

FIGURE 1 shows V notch Charpy-transition temperature curves of various kinds of carbon steel containing different amounts of precipitated aluminum nitride and metallic aluminum in solid solution. FIGURE 2 shows V notch Charpy-transition temperature curves of various kinds of low-alloy steels containing different amounts of precipitated aluminum nitride and metallic aluminum in solid solution. FIGURE 3 shows the relation between the quantity of metallic aluminum in solid solutionand ferrite grain size. FIGURE 4 shows the relation between the condition of heat treatment and ferrite grain size in various types of steel containing less than 0.15% metallic aluminum in solid solution. FIGURE 5 shows the relation between the quantity of metallic aluminum in solid solution and the number of ferrite grains in '1 mmfi. FIGURE 6 shows the relation between the quantity of precipitated aluminum nitride and the ferrite grain size in various types of steels contain ng different quantities of metallic aluminum in solid solution. Photo 1 and Photo 2 are photomicrographs showing the ferrite grain 3,l55,d35 Fatented Nov. 3, 1964 size when a carbon steel containing 0.09% carbon, 0.091% precipitated aluminum nitride and 0.0024% metallic aluminum is heated at 930 C. for one hour and then air-cooled. Photo 3 and Photo 4 are photomicrographs showing the ferrite grain size when the same type of steel as used in Photo 1 and Photo 2 is heated at 930 C. for one hour and oil-cooled, and reheated at 650 C. for 1.5 hours then air-cooled. Photos 5-8 are photomicrographs showing the austenite grain size of various types of lowalloy steels containing different quantities of precipitated aluminum nitride and metallic aluminum in solid solution. Photo 9 and Photo 10 are electron-micrographs showing the precipitated aluminum nitride in carbon steel. Photo 11 and Photo 12 are electronmicrographs showing the precipitated aluminum nitride in a low-alloy steel.

Table 1 shows the chemical compositions of some of the sample carbon steels used in the tests conducted.

Sample No. C Si Mn Ni Cr Cu Total Total Al N3 Sample No. AlN Met; Acid A Heat A1 Sol. Al Treatment. 7

Commercial killed steel 0.0014 As rolled. 0. 024 0. 034 0. 037 930 C/H. 0.096 0.156 0. 017 930 C/H. 1.073 1. 092 0. 032 930 (31H. 2. 657 2. 672 0. 026 930 O/H.

FIGURE 1 shows the transition temperature curves of the carbon steels shown in Table 1. The V notch Charpy-transition temperature curves of steels A41 and A51, which contain more metallic aluminum, are flatter than that of commercial killed steel which has a lower aluminum content, while the V notch Charpy-transition temperature curve of C8, containing less metallic aluminum in solid solution, considering the amount of aluminum nitride, runs steeper, and the curve of C8 which was heat treated (as to be explained later) runs even higher. The reason why the V notch Charpy-transition temperature curve of All proceeds less steep than that of C8, in spite of the fact that All and C8 contain the same quantity of aluminum nitride, is that All contains more metallic aluminum in solid solution. The result shown in FIGURE 1 is mainly due to the ferrite grain size, and

it is to be seen that the coarser the ferrite grain size, the

higher is the transition temperature.

FIGURE 3 and FIGURE 4 show the change in ferrite grain size as a function of the concentration of metallic aluminum in Solid solution for carbon steels with 0.04- 0.25% carbon. It is observed that, in order to get finer grains than ferrite grain size ASTM No. 9, the top limit of the dissolved aluminum is'0.1% for a heat treatment of heating at 930 C. for one hour and air-cooling therefrom (N); the limit is 0.36% for a heat treatment consisted of heating at 930 C. for one hour, oil-cooling therefrom, re-heating at 650 C. for 1.5 hours and aircooling therefrom (QT). Although the relationship be tween the ferrite grain size and the carbon content is not clearly definable, because, as the carbon content is increased, the amount of gaseous nitrogen whichcan be dissolved in the metal matrix, and hence the yield of aluminum nitride, is decreased thus tempting an increase of the concentration of dissolved metallic aluminum, the

graphs shown in FIGURES 3 and 4 represent relations with all these above mentioned factors considered.

The relations indicated in FIGURE 3 and FIGURE 4 are reproduced on a log-log scale in FIGURE 5, showing a linear relationship.

FIGURE 6 shows the relation between precipitated aluminum nitride and ferrite grain size in the case of various types of steel containing ditferent amounts of metallic aluminum in solid solution. Namely, in the case when the concentration of metallic aluminum in solid solution is small, the lower limit of the amount of precipitated aluminum nitride necessary for a ferrite grain size of ASTM No. 9 is above 0.035% when the steel is air-cooled after having been heated at 930 C. for 1 hour, and is above 0.0075% when the steel is oilcooled after having been heated at 930 C. for one hour and air-cooled after having been heated at 650 C. for 1.5 hours. And in the case the amount of the metallic aluminum in solid solution is large, the limit of the amount of precipitated aluminum nitride necessary for a ferrite grain size of ASTM No. 9 is more than 0.1% when Table 3.Meclzanical FIGURE 2 shows V notch Charpy-transition temperature curves of such low-alloy steels of high tensile strength. Specimen No. 80 containing metallic aluminum in solid solution rather plentifully as compared with the aluminum nitride, N0. 85 contains a large amount of aluminum nitride along with much of metallic aluminum in solid solution, and No. 82 the composition of which is intermediate between 80 and 85, are found to have different impact values at low temperatures. Especially No. 85 is found to have excellent toughness, in spite of its high tensile strength. Thus, it is to be considered demonstrated that an identical tendency is held for high tensile strength low-alloy steels as for carbon steels described earlier.

Properties of Carbon Steel Conditions Diameter Gauge Yield Tensile Elongation, Reduction Rupture Yield No. of heat of tested length, point, strength, percent of area, position rate,

treatment pieces, mm. mm. leg/r11. kg./rn. percent percent NorE.N; 930 0., 1 hour, air-cooled. 61.1; 930 (3., 1 hour, oil-cooling and 650 0., 1.5 hours, air-cooled.

Table 4.-Mechanzcal Properties of Low-Alloy Steel Conditions Diameter Gauge Yield Tensile Elongation, Reduction Rupture Yield No. of heat of tested length, point, strength, percent 01 area, position rate,

treatment pieces, mm. mm. kgJrn. kg./m. percent percent N OTE.-Q.T; 930 0., 1 hour, oil-cooled and 650 0., 1.5 hours, air-cooled.

the steel is air-cooled after having been heated at 930 C. for one hour, and is more than 0.0575 when the steel is oil-cooled after having been heated at 930 C. 50 for one hour and air-cooled after having been heated at 650 C. for 1.5 hours.

From FIGURES 36, and considering the cooling rate during the heat treatment employed in the experiments, it is evident that a fine grained steel can always be obtained by maintaining the amount of precipitated aluminum nitride between 0.030.12%, and the amount of metallic aluminum in solid solution at 0.0030.15%, respectively.

When the test results obtained on carbon steels were applied to low-alloy high tensile strength steel, the same tendency was seen as in the cases of carbon steel mentioned above. Table 2 below shows the chemical composition of a few samples chosen from various types of low-alloy steels with high tensile strength used in the test.

Table 2.-Clzemical Composition of Various Type of Low-Alloy Steel It is possible to make ferrite grain size finer by a degree of 14 ferrite grain size number than that of the as-rolled or as-forged state, if carbon steels and lowalloy steels of this invention are quenched and quenchtempered from a temperature higher than the transformation temperature of the steel where the precipitation of aluminum nitride is vigorous. And, moreover, it is possible to make ferrite grain size much more finer by a degree of 11.5 ferrite grain size number, by changing the method of cooling from air-cooling to oil-cooling or water-cooling. At the same time, it was found that the transition temperature can be improved by shifting it towards lower values. Photos 1-4 show an example of this, demonstrating clearly that the ferrite grain size being refined by a degree of 1-1.5 in ferrite grain size number. Photos 9-12 are electron-micrographs showing precipitation conditions of aluminum nitride, this effect playing a most important role in this invention, in various types of carbon steels and low-alloy steels. Photos 9 and 10 are made from carbon steels, While

Photos

11 and 12 are made of low-alloy steels. Photo 9 shows the case where the steel contains 0.091% precipitated aluminum nitride, and the square or rectangular black portions in this photo are the aluminum nitride precipitated particles. Photo 10 is the case of specimen A41 which shows a lower precipitate concentration of aluminum nitride and other non-metallic inclusions. in Photo 11, in the case of specimen the black squares or rectangles are the aluminum nitrides, and the round or rounded shapes are other non-metallic inclusions, chiefly precipitated carbide. Photo 12 of specimen 80 shows little aluminum nitride. It is to be seen clearly that the grain size can be made even more finer and uniform thus helping to improve the low temperature properties of the above mentioned aluminum nitride bearing steels with an amount of metallic aluminum in solid solution not exceeding a certain limit, by distributing the aluminum nitride in a large quantity and evenly throughout the grains.

As explained heretofore, the nitride containing ductile steel of this invention that is made to contain 0.03-0.12% precipitated aluminum nitride and is also made to contain only 0.003-0.15% metallic aluminum in solid solution has a very remarkable high ductility at low temperatures, and exhibits excellent properties as steel for use not only as a construction material in services at temperatures lower than normal atmospheric temperature conditions but also as a steel that can be used for various other structures.

What I claim is:

1. In a ductile steel composition consisting essentially of 0.040.25% carbon, 0.010.5% silicon, up to 1.0% manganese, not over 0.035% 0.035% sulphur, and 0.030.12% precipitated aluminum nitride, in addition to the iron content, the improvement which consists of metallic aluminum being present in a concentration of 0.003-0.15%, the steel having an phosphorus, not over 2 ASTM ferrite grain size number higher than 9, and a 2 mm. V-notch Charpy impact value higher than 15 kg.- fir/cm. at 0 C.

2. In a ductile steel composition consisting essentially of 0.04-0.25% carbon, 0.0l-0.5% silicon, up to 1.0% manganese, less than 0.035% phosphorus, less than 0.035% sulphur, 0.03-0.l2% precipitated aluminum nitride, and at least one of the elements nickel, chromium, molybdenum, vanadium and copper from traces up to 1.0% and boron up to 0.1%, in addition to the iron con tent, the improvement which consists of metallic aluminum being present in a concentration of 0.0030.15%, the steel having a 2 mm. V-notch Charpy impact value higher than 10 kg.-rn./cm. at 0 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,679,454 Offenhauer May 25, 1954 FOREIGN PATENTS 808,556 Great Britain Feb. 4, 1959 OTHER REFERENCES Journal of Research of the National Bureau of Standards, vol. 48, No. 3, March 1952. Research paper 2305. Pages 193 to 199.

Bullens: Steel and Its Heat Treatment, 5th edition, vol. 1, pages 63 to 66.

Claims

2. IN A DUCTILE STEEL COMPOSITION CONSISTING ESSENTIALLY OF 0.04-0.25% CARBON, 0.01-0.5% SILICON, UP TO 1.0% MANGANESE, LESS THAN 0.035% PHOSPHORUS, LESS THAN 0.035% SULPHUR, 0.03-0.12% PRECIPITATED ALUMINUM NITRIDE, AND AT LEAST ONE OF THE ELEMENTS NICKEL, CHROMIUM, MOLYBDENUM, VANADIUM AND COPPER FROM TRACES UP TO 1.0% AND BORON UP TO 0.1%, IN ADDITION TO THE IRON CONTENT, THE IMPROVEMENT WHICH CONSISTS OF METALLIC ALUMI-