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
  • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • 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
  • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys

Definitions

• This processing enables the stainless steel, upon cold work, to transform the austenite to martensite' at a much higher rate than in unconditioned stainless steel so that much higher tensile strengths may be achieved with much lower amounts of cold work.
• a method of producing a type 18-8 stainless steel with a tensile strength of over 325,000 psi. at about a 60% cold work level is achieved.
• Field of the Invention is in the field of high strength stainless steel, and more particularly in the field of making high strength Type 18-8 stainless steel by more economical means.
• Type l8-8 variety of stainless steel has for many years been the primary material used when corrosion, was a problem because this material has been proven to be the best all around stainless steel when other qualities, such as formability, strength, ductility, hardness, etc., were also considered as parameters.
• One of the primary factors that has limited the use of Type l88 stainless steel is that in order to get high strength levels, such as over 350,000 psi, or high hardness levels such as over Rockwell C-55, the material must be subjected to more than 90% cold reduction, Such a high tensile strength l8-8 stainless and a method of achieving such a strength is taught in my US Pat. No. 3,698,963.
• this invention contemplates a method of providing a conditioned Type 18-8 stainless steel that can be processed by less than 75% cold work and yet achieve tensile strengths in excess of 350,000 psi.
• the invention contemplates a new process- Warm deformation must take place in a temperaturerange of [50F to 500F above the M temperature, and preferably 200F to 400F, (explained hereinafter).
• the warm deforming highly strains the austenite, conditioning it for a very rapid transformation to martensite when cold deformed.
• the cold deforming is performed at ambient or room temperature ranging from about 50F to 100F. This conditioning operation gives the material an inherent capability of achieving high tensile strengths with a low amount of cold work.
• Type 18-8 stainless steel For a given chemical composition of Type 18-8 stainless steel that has been annealed, at least 85% cold deformation at room temperature is required to obtain a strength level of about 325,000 psi. Yet, for the same chemical composition of a Type 18-8 stainless steel that is both annealed and conditioned as contemplated by this invention, only 60% cold deformation at room temperature is required to achieve the same strength level. For example, in general wire drawing technology, 60% working or reduction in area requires four Brown and Sharpe die passes while 85% working or reduction in area requires eight Brown and Sharpe die passes. The 85% reduction level requires more machine time and causes an increase in labor and tooling costs as compared to the 60% reduction level. Thus, it is obvious that much less energy is required to increase strength of the material and therefore an economic savings can easily be realized.
• the material can be shipped to a fabricator who then subjects the material to cold deformation in manufacturing the final product.
• the strength of this final product can now be approximately 60,000 psi to 100,000 psi greater than unconditioned material without any increase in manufacturing costs.
• the conditioning step requires deformation or working the material at a temperature range of 150F to 500F above the M temperature.
• T. Angel in his article entitled Formation of Martensite in Austenitic Stainless Stainless Steel, Journal of the Iron and Steel Institute, Volume 177 (1954) developed an equation that alleges to predict the metastable characteristics (or stability) by chemical composition of Type 18-8 stainless steel materials.
• Angel defines the temperature at which 26% deformation work, which equals a strain of 0.3, will produce 50% martensite in a particular chemical composition of material. Since a tensile test does not truly reflect mechanical working deformation such as defined above, the formula for the M temperature was modified by emperical data obtained from actual working conditions with the new formula for the M temperature being:
• This modified formula has been found very accurate for wire drawing and it is fully contemplated that minor modifications or adjustments may be made thereto for other types of deformation operations such as rolling, extruding, etc.
• the specific M temperature for a specific composition of Type l8-8 stainless the temperature at which the conditioning operation of warm deforming takes place is between 150F and 500F above the calculated M temperature.
• EXAMPLE I A type of 302 stainless steel wire having an approximate chemical analysisby weight of:
• EXAMPLE ll The same wire material as Example 1 was solution annealed at l, 950F and then cold worked at room temperature by wire drawing. This material exhibited a tensile strength of 252,000 psi at a 60% cold work level. The material was further wire drawn to a 90% cold work level wherein it exhibited a tensile strength of 354,000 psi. The intermediate cold work levels and tensile strengths at these cold work levels are reflected in Table 1.
• EXAMPLE Ill The same wire material as Example 1 was annealed at a temperature of about 1,800F. The wire was then heated to a temperature of 212P, which was 257F above the M temperature of Example I, and deformed by warm wire drawing to a reduction of 75% of its original size.
• the ma- EXAMPLE VI The same material as Example V was solution anterial was found to have 7.4% martensite. The material nealed at about 1,950F and then cold worked at room was then cold worked at room temperature to about a temperature by wire drawing. This material exhibited 60% level wherein it exhibited a tensile strength of apa tensile strength of 258,000 psi at a 60% cold work proximately 322,000 psi.
• the material was further cold level.
• the material was further wire drawn to a 90% worked to a 90% level wherein it exhibited a tensile cold work level wherein it exhibited a tensile strength strength of about 420,000 psi.
• the intermediate stages 10 of 370,000 psi.
• the intermediate cold work levels and of cold work levels and tensile strength are shown on tensile strengths at these cold work levels are reflected Table I. in Table I.
• EXAMPLE V A type of 302 stainless wire, having an approximate chemical analysis by weight of:
• the low level, under 15%, of martensite developed during the annealing step and the conditioning step, is an indicator that the processing was performed properly; otherwise, the martensite content would be much higher. This can easily be determined by known magnetic measuring techniques. It has been found that the chemical composition of different types of 18-8 stainless may be altered to raise or lower the tensile strength of the material. However, it has been found to be a general rule that the conditioning process contemplated herein provides a material that will yield at least 50,000
• the conditioned material can readily be used in the fabrication or wire, strings, fasteners, etc. to provide better material.
• a process for conditioning Type 18-8 stainless steel for subsequent cold deforming comprising the steps of:
• a process for conditioning type 18-8 stainless steel for subsequent cold deforming comprising the steps of:
• a process for strengthening Type l8-8 stainless steel comprising the steps of:
• annealing the material in a temperature range of from about l,500F to about 2,l0OF.
• a high strength l8-8 stainless steel having a tensile strength of at least 325,000 psi made by the process of

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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)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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Cited By (14)

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Citations (3)

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• 1972
  • 1972-11-29 US US310222A patent/US3871925A/en not_active Expired - Lifetime
• 1973
  • 1973-11-21 CA CA186,397A patent/CA1004578A/en not_active Expired
  • 1973-11-23 GB GB5456173A patent/GB1456527A/en not_active Expired
  • 1973-11-28 NL NL7316263A patent/NL7316263A/xx not_active Application Discontinuation
  • 1973-11-28 SE SE7316068A patent/SE410980B/sv unknown
  • 1973-11-28 FR FR7342420A patent/FR2207992B1/fr not_active Expired
  • 1973-11-29 BR BR9387/73A patent/BR7309387D0/pt unknown
  • 1973-11-29 DE DE2359551A patent/DE2359551A1/de not_active Withdrawn
  • 1973-11-29 BE BE138324A patent/BE807990A/xx unknown
  • 1973-11-29 JP JP48133926A patent/JPS49115929A/ja active Pending
  • 1973-11-29 ES ES420974A patent/ES420974A1/es not_active Expired

Patent Citations (3)

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