Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/20—Metals
  • G01N33/204—Structure thereof, e.g. crystal structure
  • G01N33/2045—Defects

Definitions

• the invention relates to a method for non-destructive detection of machining burns on stainless steels with very high resistance (abbreviated THR) to corrosion, resulting for example from the final grinding, in particular for the production of landing gear trains. aircraft.
• the steels in particular are alloys based on Cr, Ni, Mo, Al, Ti, for example the steels known under the trade names AMS 5936, MLT 1302, Ma-0650-12 and Ma0600-12.
• the invention also relates to a calibration chart for mill burns of THR steels detected with the method above.
• the present invention relates to the field of quality control of stainless steels after heat treatment and finishing machining or grinding.
• Such control is extremely useful because, during the machining of parts, the material can reach excessive temperatures compared to nominal values and be burned. However, these machining burns generate a significant variation in the mechanical properties of the material, or even possible cracking of the parts.
• Non-destructive testing techniques for low-alloy THR steels such as inspection by etching of acidic composition, such as the alcoholic solution of nitric acid known as NITAL.
• the object of the invention is to enable the detection of machining burns of stainless steels of the THR type in an efficient and industrializable manner.
• a bath of particular acid solution based on hydrofluoric acid provides an indication visual graduated according to the state of burn steels dipped in the bath.
• the subject of the present invention relates to a method for the non-destructive detection of machining burns of stainless steels THR, in which the machined steel is immersed in an aqueous solution of acids comprising acid. hydrofluoric acid and nitric acid, and wherein a calibration scale for burns of steel machining is prepared by immersing samples subjected to deliberate damage in said aqueous acid solution. The samples are classified by their level of gray resulting from the immersion and corresponding to a determined hardness. The steel is then compared to the calibrated color chart.
• the immersion time in the acid solution is at least 5 minutes
• the proportion of all the acids is less than the proportion of water in the solution
• the solution consists, by volume, of 10 to 20%, preferably 15% of hydrofluoric acid, of 10 to 20%, preferably 15% of nitric acid, and 60% to
• the solution is free of hexavalent chromium (Cr6) which is removed by any known means, in particular by exchange of anions in grafted cellulose columns or by addition of a ferric sulphate solution; Cr6 chromium is extremely toxic and its non-proliferation is therefore important for humans and the environment;
• the steel is then immersed in a nitric acid bath for removing the soot produced by the first chemical etching, the soot being formed of residues which risk degrading the reading of the machining burns;
• the acidic solution of the process according to the invention makes it possible to obtain an elemental burn indication of a THR steel corresponding to a reduction of at least 3% in the hardness of the test steel, for an immersion lasting substantially equal to 5 minutes of this steel.
• the color chart is composed of samples subject to damage voluntary, for example by variable abusive rectifications.
• the samples consist of specimen zones subjected to variable rectification of a THR steel to be tested or by pads of this steel subjected to variable overheating heat treatments.
• the same level of gray corresponds to the same level of damage suffered regardless of the type of corrections, real or simulated.
• the samples are sandblasted beforehand in order to homogenize their surface state in order to obtain a better contrast of the coloring after immersion in the acid bath;
• the soot formed is removed by immersion in a nitric acid bath before final rinsing with water.
• the invention also relates to a calibration chart of burns of machining THR steels detected with the method above.
• FIGS. 2a and 2b superior views of the pads of two stainless steels THR having undergone superheating temperatures, corresponding to differentiated simulated rectifications, using different aging temperatures ranging from the standard aging temperature to the solution temperature;
• FIG. 3 a top view of a specimen of a zone-cut THR steel which has undergone voluntary rectifications resulting in differentiated damages
• AMS 5936 Customer 465) and MLT 1302 (MLX17), hereinafter referred to as A1 and A2
• sample pads of each of these steels - respectively P1 to P10 and P1 1 to P18 - are prepared.
• the pads are machined from bars of alloys A1 and A2. These pads have a cylindrical shape, of diameter equal to 15 mm and height equal to 9 mm in the embodiment.
• the pads are first heat treated to overheat at different temperatures, to create faults simulating damage or burn resulting from excessive rectifications.
• the pads are successively introduced into a laboratory furnace at different overheating temperatures.
• the method according to the invention then consists of immersing the pads in a bath containing two strong mineral acids: hydrofluoric acid and nitric acid, in equal proportions in the preferred example.
• the solution comprises 15 ml of each acid and 70 ml of water.
• FIGS. 2a and 2b show the upper face respectively of studs P1 to P10 of alloy A1 and studs P1 1 to P18 of alloy A2 after immersion.
• the pads have different shades according to a contrast gradient of gray level.
• the upper faces have frames whose density of lines reflects the different levels of gray. The figure recalls the corresponding processing temperatures of the pads, ranging respectively from 510 to 950 and from 505 to 850 ° C.
• a top view of a steel specimen A1 is cut into zones Zi having undergone voluntary rectifications of increasing intensity, causing damage also increasing. Hardness measurements HB are made for each zone Zi and the values obtained have been shown in the figure.
• the test piece is then immersed in an acid bath of the same composition as that previously used for simulated rectification pads. Additional immersion stripping and post immersion cleaning treatments are also performed.
• the zones Zi and the plots Pi of the same level of gray bear the same index "i".
• the pads Pi and the zones Zi are classified as abscissa according to their gray level "i”, and the hardness HB of these zones and pads is plotted on the ordinate.
• the correlation of the hardness values of the zones and the plots bearing the same number "i" that is to say having undergone equivalent mechanical (real rectifications) and thermal treatments (simulated rectifications), is corroborated by this graph. A decrease of about 3% in HB hardness is observed between two successive "i" values. The gray level "i” therefore measures a precise degree of damage.
• the invention is not limited to the examples described or represented. It is for example possible to add another acid in the solution, for example hydrochloric acid, in particular in a proportion equivalent to that of other acids.
• the immersion time in the hydrofluoric / nitric acid bath can be extended beyond 5 minutes depending on the steels and the degree of burns, without however exceeding 60 minutes or equivalent for reasons of efficiency.
• Machining modes other than grinding can be used such as for example turning or milling.

Landscapes

• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Analytical Chemistry (AREA)
• General Health & Medical Sciences (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Biochemistry (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating And Analyzing Materials By Characteristic Methods (AREA)
• Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
• ing And Chemical Polishing (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=42711799

Family Applications (1)

Country Status (8)

Families Citing this family (6)

Family Cites Families (10)

• 2010
  • 2010-02-01 FR FR1050670A patent/FR2955937B1/fr active Active
• 2011
  • 2011-01-28 CN CN2011800066018A patent/CN102822668A/zh active Pending
  • 2011-01-28 RU RU2012137211/15A patent/RU2012137211A/ru not_active Application Discontinuation
  • 2011-01-28 CA CA2786421A patent/CA2786421A1/fr not_active Abandoned
  • 2011-01-28 WO PCT/FR2011/050180 patent/WO2011092438A1/fr not_active Ceased
  • 2011-01-28 EP EP11706887A patent/EP2531850A1/de not_active Withdrawn
  • 2011-01-28 US US13/574,689 patent/US20120288946A1/en not_active Abandoned
  • 2011-01-28 BR BR112012018009A patent/BR112012018009A2/pt not_active IP Right Cessation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events