Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

Definitions

• the present invention resides in a novel and useful structural steel composition characterized by its high strength and low cost and in a method of treating the same to obtain optimum properties.
• So-called structural steel which is hot rolled in the form of I-beams, channels, angle irons, plates, rods, etc., constitutes a major portion of all steel used. It is a low carbon steel of minimum cost and has limited yield strength compared with the more expensive alloy steels which are of greater strength because of their capacity to be hardened by heating and quenching. It has been recognized for many years that the designs of steel structures such as buildings, bridges and the like could be improved and a saving in material realized if stronger materials were available. However, the added cost of all prior alloy steels has more than otfset their advantage from a strength standpoint when used in place of conventional structural steel, except in unusual situations.
• Another object is to provide a structural steel alloy which is capable of being age hardened at relatively low temperatures and which will, without any necessity of quenching or any other drastic heat treatment, develop a hardness and strength substantially in excess of that of conventional structural steel.
• Another object of the invention is to provide a method of producing an economical structural steel member of greater strength than those made of conventional structural steels.
• a further object of the invention is to provide a method of producing an economical structural steel member having unusually high toughness at very low temperatures.
• a low carbon steel alloy containing as essential ingredients molybdenum, copper, boron and aluminum.
• Carbon is not essential and is preferably no more than 0.10 percent but may be present in amounts up to 0.15 percent.
• Silicon and manganese may be employed in the usual fashion for deoxidization and retained amounts of 0.40 to 0.70 percent manganese and from 0.10 to 0.30 percent silicon are permissible but not essential.
• the boron, molybdenum and aluminum are essential to produce an alloy which will form a bainitic structure when air cooled in the usual manner from conventional hot working temperatures.
• only minute amounts of boron are necessary, i.e., less than 0.008 percent; but in order to insure that this small quantity of boron is not tied up with oxygen, it is necessary to incorporate aluminum in an amount in excess of that required -for deoxidization.
• the aluminum which combines 3,303,061 Patented Feb. 7, 1967" with the oxygen is acid insoluble, and any excess is acid soluble aluminum.
• the alloy must have at least 0.01 percent acid soluble aluminum and preferably has a residual acid soluble aluminum content in the range of 0.20 to 0.40 percent.
• a further essential element of the composition is copper which may be present in amounts ranging from 0.60 percent to 2.0 percent.
• alloy preferably contains nickel ranging upwardly from 0 to 1.0 percent as the copper content increases from 0.60 percent to 2.00 percent.
• Suitable alloys of the type mentioned comprise the following:
• Example 1 Example 2
• Example 3 Percent Percent Percent Carbon 0.07 O. 10 0.05 Mangane 0. 60 0. 70 0. 50 Silicon”... 0. 10 0. 20 0. 15 Molybdenum... 0. 52 0. 40 0. 60 ickel 0. 68 0. 20 0. Copper 1.16 0.80 l. 50 Boron 0. 0023 0. 003 0. 004 Aluminum (acid soluble). 0. 23 0. 07 0 30 Aluminum (acid insoluble)- 0. 04 0. 04 Sulphur 0. 02 0. 02 0.015 Phosphorus 0. 01 0. 015 Iron Balance Balance Hot worked alloys of the above type Wlll, on normal cooling, form a bainitic structure and will have a tensile yield strength (0.20 percent offset) in the order of 80,000 pounds per square inch in the hot worked condition.
• the yield strength of the hot worked structural members may be materially increased by age hardening from one to four hours at temperatures in the order of 900 to 1100 F.
• the bainitic structure of the alloys of the present invention results from their cooling from an austenitic condition following conventional hot working operations. Accordingly, the alloy should be heated prior to working to a temperature high enough to convert the alloy to austenite. The minimum temperature for this purpose will depend upon the carbon content, but will ordinarily be around 1750 F. Initial working may be conducted at or above this temperature or may be delayed until the alloy has partially cooled, but to obtain the maximum toughness at low temperatures, it is necessary to complete the hot working operation at a temperature of approximately 1200" F. Thus, for example, hammer forging may start at temperatures of 2000 F.
• the alloys may be hot rolled by the procedures conventionally employed in forming structural steel members such as I-beams, channels, angle irons, plates, etc. In this case the initial rolling operations may be conducted at conventional temperatures such as 2050 F., but again maximum toughness is obtained if the final rolling pass is carried out at a temperature in the range of 1100 F. to 1300 F. and preferably about 1200 F. i
• Low temperature toughness is also enhanced by continuing the age hardening operation beyond the point of maximum yield strength. This is shown by the following table setting forth data obtained in Charpy V- Notch impact tests on specimens cut from a hot worked 1% inch square bar having the composition of Example 1. This bar had been hammer forged in two stages, the first starting at a temperature of about 2050 F. reduced thebar from 3% inches square to 2% inches square. The second stage, which started at about 1700 F. and continued until the temperature was about 1200 F. reduced the bar to 1% inches square.
• Abainitic structural steel having from 0 to 0.15 percent carbon, from 0.35 to 0.75 percent molybdenum, from 0 to 1.0 percent nickel, from 0.60 to 2.00 percent copper, from 0.002 to 0.008 percent boron, from 0.01 to 0.40 percent acid soluble aluminum, and the balance essentially iron.
• An age hardened structural steel member having a bainitic metallurgical structure and a finely divided copper-containing precipitate dispersed through the crystal matrix and having a composition containing from 0 to 0.15 percent carbon, from 0.35 to 0.75 percent molybdenum, from 0 to 1.0 percent nickel, from 0.60 to 2.00 percent copper, from 0.002 to 0.008 percent boron, from 0.01 to 0.40 percent acid soluble aluminum, and the balance essentially iron.
• An age hardened bainitic structural steel member having a bainitic metallurgical structure and a coppercontaining precipitate dispersed through the crystal matrix .60 to 2.00 percent copper, from about .002 'to about .008
• a structural steel member which consists in Working a steel alloy containing from 0 to 0.15 percent carbon, from 0.35 to 0.75 percent molybdenum, from 0 to 1.0 percent nickel, from 0.60 to 2.00 percent copper, from 0.002 to 0.008 percent boron, from 0.01 to 0.40 percent acid soluble aluminum, and the balance essentially iron, at least a portion of said working being conducted after the alloy has been heated to a temperature suflicient to convert it to an austenite structure and the final working to form the structural member being conducted while the alloy is at a temperature in the range of 1100 'F.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

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Citations (3)

• 0
  • GB GB1054098D patent/GB1054098A/en active Active
• 1965
  • 1965-02-24 US US435064A patent/US3303061A/en not_active Expired - Lifetime
  • 1965-05-06 DE DE19651483172 patent/DE1483172B2/de active Pending
  • 1965-05-07 SE SE5992/65A patent/SE312920B/xx unknown

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