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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C21D2261/00—Machining or cutting being involved
• • 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
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
  • C21D7/10—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars

Definitions

• the invention concerns an austenitic stainless steel for cold working such as cold heading.
• Steels containing a minimum of 11% chrome are called stainless and exhibit good corrosion resistance.
• Austenitic stainless steels also contain nickel, which provides valuable properties for processing, particularly cold working.
• One of the most commonly used austenitic steels has the following composition: C ⁇ 0.08, Si ⁇ 1%, Mn ⁇ 2%, S ⁇ 03%, P ⁇ 0.045%, 18 ⁇ Cr 20%, 8 ⁇ Ni ⁇ 12%.
• This steel is well suited for cold working, but has a limited forming range due to the relatively high hardening coefficient which leads to significant work hardening via the formation of hardening martensite.
• Another austenitic stainless steel is known with the following composition: C ⁇ 0.12%; Si ⁇ 1%; Mn ⁇ 2%; S ⁇ 0.03%; P ⁇ 0.045%; 17 ⁇ Cr ⁇ 19%; 10 ⁇ Ni ⁇ 13%, providing a solution to the hardening issue through a relatively high nickel content, which limits the formation of hardening martensite.
• the presence of nickel in such concentrations also limits the elongation properties of the steel; furthermore, this steel is costly due to the high nickel content.
• French patent 2,229,776 claims a steel with the following composition: 3 ⁇ Ni ⁇ 15%; 6% ⁇ Mn ⁇ 16%; 10% ⁇ Cr ⁇ 25%; Si>2%.
• This steel has valuable abrasion resistance properties.
• U.S. Pat. No. 3,910,788 describes a steel with the following composition: 1% ⁇ Si ⁇ 2.5%; 1.5% ⁇ Mn ⁇ 5%; 1% ⁇ Cu ⁇ 4%; 6% ⁇ Ni ⁇ 9%; 15% ⁇ Cr ⁇ 19%; N ⁇ 0.03%; C+N ⁇ 0.04%.
• This steel is suitable for cold working and die-stamping in the flat product industry and is resilient to delayed failure.
• the nickel content in the composition is relatively high; the steel also contains sensible amounts of silicon to increase the hardening coefficient.
• Japanese patents J63060051 and J63060050 both propose the following steel composition: C ⁇ 0.15%; Si ⁇ 1.5%; 0.5% ⁇ Mn ⁇ 6%; 17% ⁇ Cr ⁇ 23%; 10% ⁇ Ni ⁇ 15%; 0.1% ⁇ Cu ⁇ 3%; 0.02% ⁇ N ⁇ 0.35%; with stabilization using chemical elements Ti+Nb+V.
• the high carbon and nitrogen contents result in high hardness being rapidly attained during cold working, which disqualifies the steel for cold heading applications.
• U.S. Pat. No. 3,753,693 presents a steel composition such as: 17 ⁇ Cr ⁇ 19%; 7% ⁇ Ni ⁇ 10%; 11% ⁇ Mn ⁇ 13%; 0.01% ⁇ N ⁇ 0.07%; C ⁇ 0.06%; Si ⁇ 1%; Mo ⁇ 2%; Cu ⁇ 1.5%.
• This composition is particularly well-suited for cold heading applications where it provides a low hardening coefficient due to the very high nickel and manganese contents.
• JP 55,031,173 presents a grade with the following composition: C ⁇ 0.02%; 0.04% ⁇ N ⁇ 0.1%; 2.5% ⁇ Cu ⁇ 4%; 6% ⁇ Ni ⁇ 8%; 17% ⁇ Cr ⁇ 19% and 3% ⁇ Mn ⁇ 4%; S ⁇ 0.003%.
• the document provides a relatively high nickel content, and a very high nitrogen content. This steel is used to manufacture stainless steel rivets and screws.
• U.S. Pat. No. 4,911,883 concerns a stainless steel for cold working, with the following composition: C ⁇ 0.04%; Si ⁇ 0.6%; 6% ⁇ Ni ⁇ 8%; 2.2% ⁇ Mn ⁇ 3.8%; 17% ⁇ Cr ⁇ 19%; 2.5% ⁇ Cu ⁇ 4%; S ⁇ 0.002%; N ⁇ 0.010%.
• This composition is similar to that previously cited, but has a rather high nickel content.
• WO 00/26428 describes the following composition: 0.025% ⁇ C ⁇ 0.15%; 4% ⁇ Mn ⁇ 12%; Si ⁇ 1%; P ⁇ 0.2%; S ⁇ 0.1%; 15.5% ⁇ Cr ⁇ 17.5%; 1% ⁇ Ni ⁇ 4%; 0.25% ⁇ Mo ⁇ 1.5%; 1.5% ⁇ Cu ⁇ 4%; W ⁇ 1%; Co ⁇ 1%; 0.05% ⁇ N ⁇ 0.3%; with the conditions Cr %+Mo % ⁇ 17.75% and Cr %+3.3Mo %+13N %>20.5%.
• This composition has a low nickel content.
• JP 2001011579A presents the following composition: 0.05% ⁇ C ⁇ 0.5%; 6% ⁇ Mn ⁇ 15%; Si ⁇ 0.5%; S ⁇ 0.03%; 10% ⁇ Cr ⁇ 20%; 0.04% ⁇ Ni ⁇ 0.3%; Mo ⁇ 3%; Cu ⁇ 3%; Al ⁇ 0.1%; 0.05% ⁇ N ⁇ 0.3%, with a relatively high nitrogen+carbon content, as in the composition proposed by the previous document.
• compositions of austenitic stainless steel for cold working containing manganese may be classified in the following manner:
• the goal of the invention is to propose an austenitic stainless steel for cold forming suitable for later machining exhibiting improved mechanical properties over standard austenitic stainless steels; these properties are very valuable for cold working applications, particularly cold heading.
• the goal of the invention is an austenitic stainless steel for cold working suitable for later machining, characterized by the following composition by weight:
• the composition also comprises boron in a concentration below 50-104%;
• the ferrite rate after reheating of the raw solidification structure to 1,240° C. is below 10%, as per the following formula:
• the invention concerns an austenitic stainless steel for cold working suitable for later machining, characterized by the following composition by weight:
• the carbon content is controlled to be below 0.030% in order to limit the formation and hardening of hardening martensite.
• the combined carbon and nitrogen content must be controlled to be below 0.07%.
• the nitrogen content is controlled to a level between 0.02% ⁇ N ⁇ 0.060%, preferably 0.02% ⁇ N ⁇ 0.04%, in order to stabilize the austenite and guarantee a hot ferrite content ⁇ 15%.
• the nickel content has been lowered to between 4.55% and 7%, preferably to around 5%.
• the lower nickel content is compensated by a manganese content between 5% and 9%, preferably around 8%.
• the presence of chrome guarantees good corrosion resistance, with the content chosen between 15% and 18%.
• Copper is present in the composition to stabilize the austenite. As described in prior art, it is limited to below 4%. A content above 2% is preferred to improve stabilization of the austenite.
• Sulfur is limited to a content below 0.01% and preferably below 0.002% in order to limit the formation of manganese sulfides which are detrimental to hot workability and corrosion resistance.
• silicon content should be below 1%, preferably below 0.3%.
• the composition also contains molybdenum in a concentration below 0.8% and phosphorus in a concentration below 0.030%.
• Boron may be added in a concentration below 50 ⁇ 10 ⁇ 4 % to facilitate cold and hot working.
• the composition of a steel 1 as per the invention was compared to that of a reference sample, a standard austenitic steel with the composition presented in table 1 below: TABLE 1 % C % Si % Mn % Ni % Cr % Mo % Cu % N % S Md30 % ⁇ Steel 1 0.023 0.36 8.1 5.1 15.0 0.30 3.3 0.035 0.001 ⁇ 71.6 Ref. steel 0.029 0.33 1.8 8.1 17.2 0.29 3.2 0.027 0.002 ⁇ 59.3
• the steel as per the invention exhibits improved cold workability compared to the standard reference steel.
• Cruciform impact testing shows that:
• the reference steel exhibits incipient ductile failure at the angles of the cross.
• the steel as per the invention exhibits good corrosion resistance, comparable to that of a standard 304 steel.
• the steel as per the invention is non-magnetic in annealed temper, and lightly magnetic in hard temper; has a weldability equivalent to that of a standard 304 steel; and a machinability close to that of a standard 304 steel.
• the steel as per the invention is commercially attractive seeing as it employs alloy elements which are less costly than nickel, and facilitates working at each stage of processing, particularly due to a hot structure and mechanical properties which are compatible with existing processing techniques for standard austenitic stainless steels.
• the steel as per the invention is well-suited for parts involving an initial cold heading operation followed by a finishing machining operation.
• Its field of application may include fitting products such as fasteners, bolting, nuts, threaded rods, and any particular parts manufactured by cold heading, e.g. fixtures, automobile parts such as mountings, airbags, probe support and body elements, or mass-produced connection parts such as electrical connection equipment.
• fitting products such as fasteners, bolting, nuts, threaded rods, and any particular parts manufactured by cold heading, e.g. fixtures, automobile parts such as mountings, airbags, probe support and body elements, or mass-produced connection parts such as electrical connection equipment.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Heat Treatment Of Articles (AREA)

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Cited By (14)

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• 2001
  • 2001-07-27 FR FR0110070A patent/FR2827876B1/fr not_active Expired - Fee Related
• 2002
  • 2002-07-11 TW TW091115433A patent/TW554053B/zh not_active IP Right Cessation
  • 2002-07-24 KR KR1020020043648A patent/KR20030011628A/ko not_active Application Discontinuation
  • 2002-07-24 CA CA2395628A patent/CA2395628C/fr not_active Expired - Fee Related
  • 2002-07-25 US US10/201,968 patent/US20030021716A1/en not_active Abandoned
  • 2002-07-25 ES ES02291881T patent/ES2402763T3/es not_active Expired - Lifetime
  • 2002-07-25 EP EP02291881A patent/EP1281785B1/fr not_active Expired - Lifetime
  • 2002-07-26 MX MXPA02007294A patent/MXPA02007294A/es active IP Right Grant

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