Classifications

• • 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
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires

Definitions

• the steel is hot rolled to form bars, plate and sheets with a starting rolling temperature between 2100 F.-2300 F. and a finishing rolling temperature between 1400 F.1700 F. followed by air cooling.
• This invention is concerned with low carbon, high tensile strength, alloy steel. More specifically it is concerned with low carbon, high tensile strength, alloy steel having a minimum tensile strength of about 75,000 p.s.i. in the as rolled condition.
• Low carbon, high tensile strength steels of the prior art have required heating, quenching, and tempering treatment subsequent to rolling in order to develop the desired tensile strengths and suitable ductility and toughness.
• Such treatments require multiple and uneconomical handlings, e.g., the product must be held rigidly to prevent warping while being cooled rapidly from a temperature about 1750 F., and higher, to room temperature in about 10 to 25 seconds.
• the quenching develops 100% marstenitic steel and is required to obtain desired high tensile strength. Without such quench treatment, such steels have a tensile strength of about 50,000 to 60,000 p.s.i. in the as rolled condition.
• This invention provides an alloy steel with high tensile strengths in the range of about 80,000 to about 120,- 000 p.s.i. (minimum tensile strength of 75,000 p.s.i.).
• the steel exhibits ductility and yield point elonice gation values suitable for normal fabrication of high tensile strength steels and toughness suitable to withstanding normal stresses encountered in use of such steels. Obtaining these results Without treatment subsequent to rolling is one of the highly unexpected contributions of the invention.
• the low carbon high tensile strength alloy steel of the present invention consists essentially of the following weight-percentages:
• the balance being iron with residual impurities such as are ordinarily encountered in conventional basic oxygen, open hearth, or electric furnace practice used in producing the steel.
• residual impurities such as are ordinarily encountered in conventional basic oxygen, open hearth, or electric furnace practice used in producing the steel.
• the maximum desirable values of the most common residual impurities encountered are:
• the upper limit of carbon is ordinarily not exceeded in order to maintain the good weldability of end product provided by the invention. Carbon content below the lower limit is ordinarily avoided in order to have sufiicient carbon available for providing desired tensile strength.
• the manganese is added in the furnace or the ladle. Where possible, e.g., in open hearth practice, it is added in both the furance and the ladle. Preferably, the manganese is maintained in the range of .85% to 1.0% with a specific value of .90% being desired.
• the manganese helps increase the yield point and tensile strength of the steel and aids cold formability.
• Silicon acts as a deoxidizer and ferrite strengthener. It can be added in the furnace or ladle; where possible silicon is added in both. Silicon is desirably kept in the range of .75 to with .85% being preferred.
• the chromium is added in the ladle and acts to increase both the yield point and tensile strength of the steel.
• a preferred specific value for the chromium is .65%.
• the zirconium acts to increase hardenability, refine grain structure, increase toughness and cold formability. It is added in the ladle and is preferably kept between .075% and .12%; with .08% being the specific value aimed for.
• the boron is added in the ladle. It increases hardenability of the steel and seeks out remants of nitrogen in the steel to a greater extent than other nitride formers such as chromium, zirconium, columbium.
• the titanium helps to protect the boron for this purpose because of its 3 greater affinity for oxygen than boron.
• a preferred value for the boron is .0010% and a preferred range is .0005 to .012%.
• the titanium also acts as a carbide former and is preferably kept at about .03%.
• the titanium should be added with the boron.
• MECHANICAL PROPERTIES Elong. Bars YS (p.s.i.) TS (p.s.i.) percent, in. Bend As rolled 2-4-8 110, 620 29-21-15 SB 2 /Xt 106, 930 29-21-16 SB %Xt 111, 360 24-16-11 SB 56x2 103,760 107, 180 28-17-14 SB 105, 140 30-22-16 SB 1 0.2% ofisct. 2 Short break.
• the columbium is added in the ladle, or can be added in the mold. A preferred specific value for the columbium is .035 and the preferred range is .035% to .06%.
• the ladle additions are made after degassing to minimize oxidation products and reduce possible contamination of the steel.
• the alloy steel of this invention is rolled into bars, plate or sheets which are suitable for structural uses, railway car framing, and the like.
• This steel is characterized by high tensile strength, good weldability, high energy absorption capacity, and good ductility and yield point elongation values in the as rolled condition.
• the alloy steel is provided in billet form, that is in a suitable form for rolling into bars, plates or sheets.
• the billets are heat soaked at about 2100 to 2300 F., preferably about 2150 F., prior to rolling.
• the billets are then rolled. Multiple stand rolling is carried out so that finishing rolling temperature of the product of the present invention can be about 200 to 300 lower than the finishing rolling temperatures employed with high tensile strength steels in the prior art.
• the finishing rolling temperature should be in the range of 1400 to about 1700 F.
• the product After rolling the product is allowed to cool without quenching or forced cooling. Such cooling will ordinarily take place at a rate of about to per second at least through the major portion of the cooling depending on the shape and thickness of the final product.
• Process for producing low carbon high tensile strength alloy steel bar and plate suitable for welding and characterized by minimum tensile strength of 75,000 p.s.i. in the as rolled condition without subsequent heat treatment comprising the steps of providing an alloy steel billet consisting essentially, by

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (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 Steel (AREA)

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Cited By (14)

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Citations (2)

• 1967
  • 1967-08-11 US US659885A patent/US3544393A/en not_active Expired - Lifetime
• 1968
  • 1968-08-07 GB GB1230007D patent/GB1230007A/en not_active Expired
  • 1968-08-09 FR FR1577621D patent/FR1577621A/fr not_active Expired

Patent Citations (2)

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