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
  • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • 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
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• the present invention relates to a ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance.
• Mn-based sulfide such as mainly MnS in these materials, they are arranged to improve the stress concentration effect when forming chips against sulfide, and machinability and grindability due to lubricating action between a tool and chips.
• the objective of the invention is to provide a ferritic free-cutting stainless steel excellent in surface roughness, corrosion resistance and outgass resistance while having an excellent machinability.
• a ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance comprising:
• Equation (3) the amount of Ti contained in sulfide produced in the texture of the steel is represented by WTi, that of Cr is represented by WCr and that of Mn is represented by WMn.
• A-based sulfide used herein refers to sulfide for which the component (element) contained in the sulfide at the highest ratio in weight is “A” among the components bonding with S. That is, in Ti-based sulfide, more Ti bonds with S compared to other elements (such as Mn).
• the upper limit is 0.06% and the preferable range is 0.03% or less. More preferably, the range is 0.015% or less.
• Si(Silicon) 0.05 to 1.0%
• Si is added as a deoxidizer for steel.
• 0.05% or more of Si is necessary.
• the upper limit is 1.0%.
• a preferable range emphasizing the hot workability is 0.05 to 0.5%.
• Mn is added as a deoxidizer for steel and, in addition, has an effect of improving machinability since it produces Mn-based sulfide (MnS).
• MnS Mn-based sulfide
• the upper limit of the amount is 2.0%.
• the range of the amount is 1.0% or less. More preferably, it is 0.5% or less.
• the range of the amount of P contained is desirably 0.050% or less. Preferably, it is 0.030% or less.
• S is a constituent element of sulfide, that improves the machinability and 0.05% of S is necessary to obtain this effect.
• the upper limit is 0.50%.
• the range of the amount of S contained is desirably 0.15 to 0.40% taking into consideration the balance between the improvement of machinability and the degradation of hot workability.
• Cu may be added when necessary since Cu is effective for improving the corrosion resistance, especially the corrosion resistance in a reducing acid environment. However, since excessive addition of Cu degrades the hot workability, the upper limit is 2.0%. It is desirably 1.0% or less.
• Ni is an element necessary for supplementing the corrosion resistance that is insufficient when only Cr is contained.
• the upper limit is 2.0%.
• the amount of Ni contained is desirably 1.0% or less taking into consideration the balance between the efficient corrosion resistance and the blending cost.
• Cr is an element which improves the corrosion resistance, and 9.0% or more of Cr should be contained in order to obtain the effect.
• the upper limit is 25.0%.
• the range of the amount of Cr contained may desirably be 13.0 to 21.0% taking into consideration the balance between the efficient corrosion resistance and the blending cost.
• Mo Mo (Molybdenum): 4.0% or Less
• Mo can further improve the corrosion resistance and strength. However, since excessive addition of Mo degrades the hot workability and, in addition, causes increase of cost, the upper limit is 4.0%.
• the range of the Mo contained is desirably 1.5% or less taking into account the increase of cost.
• Ti is an element necessary for producing Ti-based sulfide that improves the machinability, and 0.065% or more of Ti is necessary in order to obtain this effect.
• the upper limit of the amount of Ti contained is 2.0%.
• the range of the amount of Ti contained may desirably be 0.075 to 2.0% in order to obtain further sufficient machinability.
• the upper limit of the amount of O contained is 0.0150% since O bonds with Ti which is a constituent element of a compound effective for improving machinability and forms oxide which does not contribute to improvement of the machinability.
• the range of the amount of O contained may be desirably 0.0080% or less, and is further desirably 0.0050% taking into consideration of. manufacturing cost and in order to secure the effective amount of Ti necessary for forming Ti-based sulfide.
• the upper limit of the amount of N contained is 0.020% since N bonds with Ti which is a constituent element of a compound effective for improving machinability and forms nitride which does not contribute to improvement of the machinability.
• the range of the amount of N contained may be desirably 0.010% or less and is further desirably 0.006% or less taking into consideration of manufacturing cost and in order to secure the effective amount of Ti necessary for forming Ti-based sulfide.
• Al is added as a deoxidizer for the steel.
• the upper limit of the amount of Al contained is 0.100% since oxide harmful to machinability is formed when the amount of Al contained is excessive.
• the range of the amount of Al contained is desirably 0.050% or less.
• the amount of Ti contained is 1.3 times as much the amount of S contained or more in order to suppress the production of Mn-based sulfide (MnS) that degrades the corrosion resistance and the outgass resistance and to fix all S in the texture of the steel onto Ti. More desirably, [Ti] ⁇ 1.5 ⁇ [S], that is, the amount of Ti contained may be 1.5 times as much the amount of S contained or more. [ ] indicates the amount of a component contained in the steel. [Mn]/[Ti] ⁇ 3 Equation (2)
• the amount of Mn contained is three times as much the amount of Ti contained or less in order to suppress the production of Mn-based sulfide (MnS) that degrades the corrosion resistance and the outgass resistance, and (in order to decrease the amount of Mn contained and to increase the amount of Ti contained in the sulfide) to cause Ti-based sulfide to be produced.
• MnS Mn-based sulfide
• WTi+WCr >2 ⁇ WMn Equation (3)
• the sum of the amount of Ti contained and the amount of Cr contained exceeds the double of the amount of Mn contained.
• W indicates the amount of a component following it contained in the sulfide.
• the steel may further contain in addition to the components described above, in weight percentage any one or more selected from the group consisting of 0.01 to 0.30% of Pb, 0.01 to 0.30% of Se, 0.10% or less of Te and 0.01 to 0.30% of Bi.
• Pb (lead), Se (selenium), Te (tellurium) and Bi (bismuth) can improve the machinability furthermore, they can be added as necessary. However, since excessive addition of them degrades the hot workability, the upper limit of the amount to be added for each of them is respectively 0.3% for Pb, 0.30% for Se, 0.10% for Te and 0.30% for Bi. In order to obtain sufficiently the effect of improving the machinability, it is desirable to add 0.01% or more of each of the above components respectively.
• the steel may further contain in addition to the components described above, in weight percentage any one or more selected from the group consisting of 0.05% or less of Ca, 0.02% or less of Mg, 0.02% or less of B, 0.02% or less of REM, 0.50% or less of V, 0.50% or less of Nb, 2.0% or less of W and 0.50% or less of Ta.
• Ca calcium
• Mg magnesium
• B boron
• REM one or more of rare-earth elements
• W tungsten
• the upper limit of the amount to be added is 2.0%.
• Nb (niobium), V (vanadium) and Ta (tantalum) have the effect of improving toughness by forming carbon nitride and making the crystal grain in the steel very fine, each of them can be added respectively in the range of 0.50% or less.
• Machinability was evaluated by evaluating the variation of the outer diameter of the works after machining, the surface roughness and the shape of chips.
• Machining was performed under the following conditions using Carbide tool in insoluble oil: 100 mm/min. of cutting speed; 0.10 mm of depth of cut, and; 0.01 mm/rev of feed amount for one rotation. Machining was performed to 50 samples and the outer diameter of the test pieces and the wear of the tool after machining were measured.
• the variation of the outer diameter is the variation from that of an initial work.
• the criterion for judging the variation was determined as “small” for the case where the wear of the lateral relief is less than 50 ⁇ m and “intermediate” for the case where it is 50 ⁇ m or more and 100 ⁇ m or less, and “large” for the case where it exceeds 100 ⁇ m.
• the surface roughness is the arithmetic mean (Ra: ⁇ m) of the work surface after machining, measured in a method designated in JIS-B0601.
• the shape of the chips was visual-inspected and the chip of the size of approximately 10 mm or less, having a good fragmenting property were evaluated and represented as “good” and other chips that were not separated from each other were evaluated and represented as “bad”.
• the corrosion resistance evaluation test was performed in the form of wet-type test.
• As the test pieces those having a cylindrical shape, the diameter of 10 mm and the height of 50 mm were used and their surface was polished to the count number 400 with emery paper and was washed to degrease. Thereafter, these pieces were stored in a high-temperature and high-humidity atmosphere at 50° C. of temperature and 98% RH of humidity for 98 hours. Then, whether or not there is rust on the pieces was evaluated by visual inspection of their appearance.
• the evaluation of the outgass resistance was performed by determining the amount of S generated. More specifically, test pieces having a shape of rectangular parallelepiped and dimensions of 15 mm in height, 3 mm in width and 25 mm in depth, of which the entire surface has been polished with emery paper of count number 400 were used. Then, the test pieces, a sheet of silver foil (dimensions: 0.1 mm in height, 5 mm in width and 10 mm in depth; and purity: 99.9% or higher) and 0.5 cc of pure water were put in a sealed container having the volume of 250 cc. Then, the temperature inside the container was maintained at 85° C. for 20 hours.
• the sheet of silver foil acts as the getter when gas containing S is generated and the surface of the sheet of the silver foil turns black due to production of silver sulfide when S component adsorbed by the sheet of the silver foil becomes excessive. Then, the change of the color of the silver foil surface was checked by visual inspection and the outgass resistance was evaluated in three (3) ranks in which those without any change of the color were evaluated as “A”, those with a little change of the color were evaluated as “B” and those with apparent change of the color were evaluated as “C”. Those that obtained the evaluation result of A or B were judged as excellent in outgass resistance.
• any type of the steel according to the invention has excellent machinability and surface roughness as well as is excellent in the corrosion resistance and the outgass resistance.

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• 2003
  • 2003-11-10 JP JP2003379633A patent/JP4305137B2/ja not_active Expired - Fee Related
• 2004
  • 2004-11-04 EP EP04105518A patent/EP1541703A3/en not_active Withdrawn
  • 2004-11-08 CN CNA2004100907119A patent/CN1616701A/zh active Pending
  • 2004-11-09 US US10/983,709 patent/US20050098240A1/en not_active Abandoned

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