US3348980A - Process for producing non-aging steels - Google Patents

Process for producing non-aging steels Download PDF

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Publication number
US3348980A
US3348980A US438241A US43824165A US3348980A US 3348980 A US3348980 A US 3348980A US 438241 A US438241 A US 438241A US 43824165 A US43824165 A US 43824165A US 3348980 A US3348980 A US 3348980A
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steel
hydrogen
aging
nitrogen
annealing
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US438241A
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Joseph F Enrietto
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Jones and Laughlin Steel Corp
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Jones and Laughlin Steel Corp
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Priority to US438241A priority Critical patent/US3348980A/en
Priority to JP41014572A priority patent/JPS5112445B1/ja
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/08—Extraction of nitrogen

Definitions

  • HYDROGEN FLOW RATE 40 00mm. AGING INDEX AS A STRIP TH
  • This invention pertains to the production of non-aging steels, and more particularly to the production of nonaging rimmed steel by annealing in hydrogen.
  • strain aging can be defined as any change in the mechanical properties of a steel which takes place with time after the steel has been plastically deformed.
  • the deformation can be imposed by temper rolling, tension, bending, drawing or other cold work; and the changes may take the form of a return of the yield point, an increase in the flow stress or hardness, or a loss in ductility.
  • strain aging is caused by the presence f interstitial atoms of carbon or nitrogen in solid solution in sufiicient quantity to pin or lock the dislocations produced by plastic deformation so as to render them less mobile.
  • the presence of nitrogen or carbon above a'predetermined maximum limit in solid solution in a-il'On at a temperature willciently high to render the interstitial atoms mobile enough to diffuse to dislocations is a necessary condition for strain aging.
  • the second alternative to reducing the mobility of the interstitials is to remove them from solid solution altogether either by precipitating them with the addition of alloying elements or chemically taking them completely out of the steel as by decarburizing or denitriding the steel.
  • the present invention has as its primary object the provision of such a method.
  • the invention is concerned with a method for denitriding rimmed steels with the use of hydrogen in an open coil anneal, in which hydrogen forms ammonia gas in its reaction with the nitrogen in the steel.
  • the invention resides in the realization of the fact that by open coil annealing coils of low carbon rimmed steels weighing in the range of about 10,000 to 80,000 pounds within upper and lower temperature limits, the nitrogen content of the steel can be reduced to at least 0.000S% by weight and in many cases to less than 0.0002% by weight. A nitrogen content of less than 0.0005%, however, is sufficient for a commercially acceptable non-aging steel.
  • annealing the strip material in a dry hydrogen atmosphere at ordinary annealing temperatures in the range of about 1200 F. to 1300 F. the process takes an extraordinarily long time, thereby making it economically unfeasible.
  • the process can be hastened so as to make it economically practical by annealing at a lower temperature within the range of about 975 F. to 1150 F. Below about 975 F., the action will again take a long time.
  • the annealing temperature can be determined.
  • the steel in strip form is loosely coiled to permit hydrogen gas to flow along the surfaces of all the convolutionsin the coil, and the coil placed in a batch annealing furnace. Dry hydrogen gas is caused to flow through the annealing furnace and along the surfaces of the strip between successive convolutions of the coil, while the temperature of the furnace is maintained somewhere in the range between 975 F. and 1150 F., the exact optimum temperaturebeing calculated from the mass of the coil, the thickness or gage of the strip and the flow rate of hydrogen through the furnace as mentioned above. If the mass of the coil or the thickness of the sheet is increased, the optimum annealing temperature also increases. On the other hand, if the sheet thickness or coil mass is decreased, the optimum temperature also decreases. In a similar manner, if the flow rate of hydrogen through the furnace is increased, the
  • FIGURE .1 is a graph illustrating the annealing or soak time necessary to denitride coils of steel of different weights in accordance. with the teachings of the invention
  • FIG. 2 is a graph illustrating the manner in which the optimum annealing temperature varies as a function of coil mass
  • FIG. 3 comprises a graph showing the manner in which the aging index and nitrogen content of the steel vary as a function of annealing temperature.
  • Table II the effect of dry hydrogen on the aging index of steel having the composition shown in Table I is illustrated.
  • aging index is defined as the difference in flow stress after 12% prestrain between the aged and unaged sample.
  • the samples utilized to obtain the tabular results of Table II were denitrided by annealing in flowing dry hydrogen at a temperature of 1112 F. for the times indicated.
  • the results of Table II show that it is possible to produce a non-aging steel by annealing in hydrogen so as to remove only the nitrogen. Moreover,
  • FIG. 1 shows the theoretical soak time necessary to reduce the nitrogen concentration from 0.004% to 0.0002% as a function of annealing temperature for steel coils open coil annealed and weighing 40,000, 60,000 and 80,000 pounds, respectively.
  • the hydrogen flow rate under these conditions is 2500 cubic feet per hour at a sheet thickness of 0.035 inch. Note that the soak time increased for all coils beneath a temperature of 975 F., and above 1150 F. Thus, there is a critical temperature range within which annealing or soak time .is a minimum.
  • the optimum temperature depends primarily on the thickness of the sheet, the mass of the steel and the flow rate of hydrogen through the furnace. From this information, the optimum temperature can be calculated by means of the following two differential equations:
  • F The flow rate of hydrogen into the furnace.
  • M The mass of steel in the furnace.
  • [N I]1 Nitrogen concentration at the. 1 position in the s eet.
  • FIG. 2 shows how the optimum annealing temperature varies with coil size. This particular curveis applicable for hydrogen flow rates of 2000 to 5000 cubic feet per hour. If the flow rate exceeds 5000 cubic feet per hour, the curve will be slightly displaced toward higher temperatures; the exact displacement will be given by the equations previously developed. If the flow rate is less than 2000 cubic feet per hour, the curve will be dis placed toward lower temperatures. The size of these displacements will be about 50 F., depending on how much the flow rate is increased or decreased. In a similar fashion, a change in sheet thickness from the 0.036 inch upon which the curve is based will also cause a shift. For example, increasing the thickness from 0.036 inch to 0.050 inch will displace the curve about 50 F. toward higher temperatures.
  • FIG. 3 shows experimental data which supports the work cited above.
  • the data were obtained on annealed specimens with the annealing time, hydrogen flow rate, specimen gage, and specimen weight being held constant. Under these conditions the amount of nitrogen removed, as measured by the aging index, passed through a maximum with temperature, thus indicating that an optimum annealing temperature indeed exists.
  • the curve itself in FIG. 3 was drawn according to the theoretical predictions. Note how well the experimental data points conform to the predicted behavior as shown by the solid line.
  • the experimental data in FIG. 3 was derived from fifteen stacked sheets of steel having the nominal composition given above and having a total weight of 240 grams. Note that the indicated optimum annealing temperature of about 1112 F. is in the upper part of the range 975 F. to 1150 R, which confirms the data shown in FIG. 2 where the optimum annealing temperature increases as the coil mass increases.
  • the present invention thus provides a means for denitriding rimmed low carbon steels in the presence of dry hydrogen at a minimum annealing time. It is, however, important to be aware of the following factors: First, the equilibrium between the furnace atmosphere and the surface of the steel must be mainta ned at all times. Second, complete mixing of gases must take place in the furnace to prevent the accumulation of ammonia gas at the surfaces of the steel. Third, the ammonia must obey the ideal gas low; and fourth, the only chemical reaction taking place is the combination of dissolved nitrogen and gaseous hydrogen to form gaseous ammonia.
  • the first assumption merely dictates that the reaction rate of the formation of ammonia at the surface of the sheet is much faster than either the removal of ammonia from the furnace or the solid-state diffusion of nitrogen through the steel. In other words, it is not a rate controlling factor.
  • the second assumption dictates that the velocity of gas moving across the sheet is sufi'iciently high to thoroughly mix the ammonia and hydrogen, and that no short circuiting of hydrogen exists. If this were not true, the ammonia would be exhausted from the furnace at a slower rate than that predicated and the efficiency of the process would suffer accordingly.
  • the hydrogen flow rate must be at least 1500 cubic feet per minute for coil sizes in the range of 10,000 to 80,000 pounds, assuming that a conventional batch annealing furnace is employed for coils of this size.
  • the third and fourth assumptions are, of course, self-explanatory.
  • a process for producing non-aging rimmed plaincarbon steel containing above about 0.04% by weight of carbon said steel having, when cast, a nitrogen content of about 0.004%, said process consisting essentially of the steps of rapidly cooling said steel through the transformation range to cause a fine carbide distribution and then slow-cooling said steel to about 300 F. to allow precipitation so as to prevent the occurrence of carbon strain aging, and then loosely coiling said steel in strip form and annealing said strip in an enclosure in the presence of dry hydrogen in an open-coil box anneal at a temperature in the range of about 975 F. to 1150 F.
  • the flow of hydrogen through the enclosure being sufiicient to mix the ammonia gas formed at the surfaces of the strip with hydrogen and prevent any accumulation of ammonia at the surfaces from impeding the reaction of nitrogen in the steel with the hydrogen.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
US438241A 1965-03-09 1965-03-09 Process for producing non-aging steels Expired - Lifetime US3348980A (en)

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US438241A US3348980A (en) 1965-03-09 1965-03-09 Process for producing non-aging steels
JP41014572A JPS5112445B1 (enrdf_load_stackoverflow) 1965-03-09 1966-03-09

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3404047A (en) * 1965-12-20 1968-10-01 United States Steel Corp Method for producing deep-drawing low-carbon steel sheet
US3953245A (en) * 1969-01-24 1976-04-27 Ford Motor Company Process for the production of drawing steel

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2271242A (en) * 1940-05-23 1942-01-27 Great Lakes Steel Corp Method of making nonaging steel
US2360868A (en) * 1943-01-02 1944-10-24 Carnegie Illinois Steel Corp Manufacture of nonaging steel
GB942341A (en) * 1960-07-18 1963-11-20 Metallurg D Esperance Longdoz Control of atmospheres for annealing steel sheet

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2271242A (en) * 1940-05-23 1942-01-27 Great Lakes Steel Corp Method of making nonaging steel
US2360868A (en) * 1943-01-02 1944-10-24 Carnegie Illinois Steel Corp Manufacture of nonaging steel
GB942341A (en) * 1960-07-18 1963-11-20 Metallurg D Esperance Longdoz Control of atmospheres for annealing steel sheet

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3404047A (en) * 1965-12-20 1968-10-01 United States Steel Corp Method for producing deep-drawing low-carbon steel sheet
US3953245A (en) * 1969-01-24 1976-04-27 Ford Motor Company Process for the production of drawing steel

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JPS5112445B1 (enrdf_load_stackoverflow) 1976-04-20

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