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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • 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

Definitions

• Stainless steels are first classified according to their structure as ferritic, martensitic and austenitic and then, within each of those classes, according to their composition.
• DIN X6Cr13 having the following composition in percent by weight C ⁇ 0,08, Si ⁇ 1,0, Mn ⁇ 1,0, P ⁇ 0,045, S ⁇ 0,030, Cr 12,0-14,0
• DIN X6Cr13 having the following composition in percent by weight C ⁇ 0,08, Si ⁇ 1,0, Mn ⁇ 1,0, P ⁇ 0,045, S ⁇ 0,030, Cr 12,0-14,0
• Another steel, DIN X6CrAl13, has the same composition, with an aluminium quantity added of 0,1-0,3 weight percent, utilised in the oil industry or in hydroelectric power plants.
• DINX20Cr13 consisting in the. addition of 0,9-1,3 % Mo and of less than 1% Ni gives another steel (DINX20CrMo13) utilised for the production of turbine blades, engine valves, overheated steam valves.
• the published Japanese patent application no. 06 08/085 refers to a ferritic stainless steel having excellent corrosion resistance in atmospheric environments, containing, inter alia, 17,5-30% Cr, 1,5-3,5 % Mo, and stabilized with Nb and Ti.
• the present invention offers a stainless steel composition which, even remaining within a known type, has a large spectrum of different properties, such as: formability, absence of ridging and roping, weldability, hot oxidation resistance, thermal shock and fatigue resistance, resistance to corrosion by acid condensates and anti-ice salts, resistance to localised corrosion (pitting, crevice) and relevant propagation, good immunity to tensiocorrosion, good attitude to polishing, very good surface appearance, absence of defects in the rolling direction.
• the steel according to present invention is, therefor, suitable for instance to the use in the automotive field, in catalysed exhaust systems and in the external exposed parts, in interiors and outdoor architecture, for white goods and ovens, for coins.
• a ferritic, monophasic Cr, Mo, Cu stainless steel, Ti and Nb stabilised having the following weight percent composition: C ⁇ 0,025, N ⁇ 0,025, Mn 0,1-1,0, Si 0,2-0,7, P ⁇ 0,025, S ⁇ 0,002, Ni 0.07 - ⁇ 0.40, Cu 0,30-0,60, Cr 17-21, Mo 1,0-1.25, Ti 0,10-0,20, Nb 0,20-0,35, B 0.045-0.060 (REM + Hf) 0.020-0.040, remaining being iron and minor impurities, in which with REM the rare-earth metals are meant.
• the steel has the following composition, in weight percent,: C 0,018-0,014, N 0,008-0,014, Si 0,25-0,40, Mn 0,30-0,45, P 0,016-0,025, S 0,008- 0,015, Ni 0,07-0,15, Cu 0,35-0,50, Cr 17,50-18,50, Mo 1,10-1,25.
• a typical composition, in weight percent, is: C 0,010, N 0,010, Si 0,30, Mn 0,40, P 0,022, S 0,001, Ni 0,10, Cu 0,45, Cr 18,30, Mo 1,20, Ti 0,15, Nb 0,25, B 0,050, (REM + Hf) 0,030.
• the chemical composition of the steel according to present invention is chosen to suitably balance the effects of the microalloying elements.
• Cu and Mo have a beneficial effect on the resistance to general and localised corrosion, particularly in chloride-containing environments.
• the rare-earth metals globulise the sulphides, thus improving ductility and hence formability.
• Ti and Nb improve weldability and enhance the, particularly intergranular, corrosion resistance.
• the above composition relationships contribute, in a not yet clear way, to enhance and uniform the above qualitative levels, for instance limiting the harmful precipitation of carbides in the welded zones.
• a secondary but nevertheless important effect in all the uses in which the appearance of the final product is important, is a specific hue of the steel, warmer than the usual bluish one of the ferritic stainless steels, which impart to the steel a much more appealing look.
• the thermal treatment consists in a continuous annealing at 900-1050 °C, preferably at 950-1000 °C, for a time comprised between 1 and 5 minutes, preferably 2 and 3 minutes.
• a steel having the following weight percent composition C 0,010, N 0,0011, Si 0,44, Mn 0,16, S 0,001, P 0,014, Cr 18,5, Mo 1,12, Cu 0,51, Ti 0,12, Nb 0,22, B 0,05, (REM + Hf) 0,025, the remaining being iron and minor impurities, was rolled into 1 mm thick strips, having no superficial defects; samples of such material were imparted an isothermal oxidation at temperatures comprised between 900 and 1000 °C for 50-200 hours; the results are shown in Table 1.
• the performance of steels qualified for use at high temperatures can be cited, which show a weight increase of about 0,5 mg/cm 2 and of 1,5 mg/cm 2 respectively at 900 and 950 °C, for a 100 hours exposure.
• Example 1 The steel of Example 1 was laboratory tested for saline corrosion in NaCl 0,05 M at 23 °C; the depassivation pH was 2,1 without crevice, and the pitting potential was 0,6 V with respect to the saturated calomel electrode.
• Example 1 The steel of Example 1, 0,4 mm thick, was laboratory tested for corrosion resistance in condensates.
• the test consists in simulating the condensation of aggressive solutions which happens into the exhaust pipe terminal parts of car mufflers.
• the solution pH varied from about 8,5 at the beginning to about 3,5 after evaporation of most of the liquid.
• test cycle consisted in heating the sample with test solution from 20 to 250 °C in 1 h, then keeping this temperature for 3 h and finally cooling the whole at 20 °C in 6 h.
• Terminal parts for exhaust pipes were also produced, tested in the same vehicles utilised for the accelerated tests of previous Example. At the end of the test, said terminal parts did not show any through-holes or extended corrosion.
• Example 1 Other steel samples of Example 1 were tested for Erichsen drawing; the Erichsen Index value was about 8,40, compared with a value of 8,10 for a corresponding known steel.
• the steel according to present invention can, thus, be utilised for any use in which at least one of the following characteristics is requested: localised and general corrosion resistance, good drawability and formability, good weldability, resistance to hot oxidation and to thermal shock, resistance to thermal fatigue, no superficial defects.
• the steel can be usefully utilised for the production of goods such as: car exhaust pipes and terminal parts, parts exposed to the flame or otherwise to high temperatures (formability, weldability, hot oxidation resistance, resistance to acid condensates), parts of stoves and ovens, pots; hub caps and car external trimmings (superficial appearance, drawability, polishing, chloride corrosion resistance); internal parts of dishwashers, cutlery, pots (drawability, superficial appearance, resistance to localised corrosion in chlorinated environment); signs, architectural coverings, internal and external furnishing (formability, drawability, superficial appearance, resistance to generalised corrosion).
• goods such as: car exhaust pipes and terminal parts, parts exposed to the flame or otherwise to high temperatures (formability, weldability, hot oxidation resistance, resistance to acid condensates), parts of stoves and ovens, pots; hub caps and car external trimmings (superficial appearance, drawability, polishing, chloride corrosion resistance); internal parts of dishwashers, cutlery, pots (drawability, superficial appearance, resistance to localised corrosion in chlor

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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 Sheet Steel (AREA)
• Heat Treatment Of Steel (AREA)
• Catalysts (AREA)

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• 1998
  • 1998-02-17 IT IT98RM000092A patent/IT1298907B1/it active IP Right Grant
• 1999
  • 1999-02-16 DE DE69907291T patent/DE69907291D1/de not_active Expired - Lifetime
  • 1999-02-16 AT AT99103043T patent/ATE239102T1/de not_active IP Right Cessation
  • 1999-02-16 EP EP99103043A patent/EP0936280B1/en not_active Expired - Lifetime

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