Designation: B600 – 09
Standard Guide for
Descaling and Cleaning Titanium and Titanium Alloy
Surfaces1
This standard is issued under the fixed designation B600; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope
1.1 This guide covers a cleaning and descaling procedure
useful to producers, users, and fabricators of titanium and
titanium alloys for the removal of ordinary shop soils, oxides,
and scales resulting from heat treatment operations and foreign
substances present as surface contaminants.
1.2 It is not intended that these procedures be mandatory for
removal of any of the indicated soils but rather serve as a guide
when titanium and titanium alloys are being processed in the
wrought, cast, or fabricated form.
1.3 It is the intent that these soils be removed prior to
chemical milling, joining, plating, fabrication, and in any
situation where foreign substances interfere with the corrosion
resistance, stability, and quality of the finished product.
1.4 Acid etching may be required following cleaning when
the surface has an oxygen-contaminated layer or alpha case
present.
1.5 The values stated in inch-pound units are to be regarded
as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only
and are not considered standard.
1.6 This standard does not purport to address the safety
concerns, if any, associated with its use. It is the responsibility
of the user of this standard to consult and establish appropriate
safety and health practices and determine the applicability of
regulatory limitations prior to use.
2. Processing Soil Removal
2.1 It is recommended that grease, oil, and lubricants
employed in machining, forming, and fabricating operations on
titanium and titanium alloys be removed by alkaline or
emulsion soak-type cleaners and electrolytic alkaline cleaning
systems. In the electrolytic system the work may be either
anodic or cathodic polarity. Removal of these soils is recom-
mended prior to heat treatment or application of acid treatment
designated in 4.2. When electrolytic systems are employed, the
voltage should be controlled to prevent the occurrence of spark
discharge and subsequent pitting.
3. Blast Cleaning
3.1 Mechanical descaling methods such as sandblasting,
shot blasting, and vapor blasting may be used to remove hot
work scales and lubricants from titanium surfaces if followed
by thorough conditioning and cleaning as described in Section
4.
3.2 The sand used for blasting should be a high-grade,
washed, iron-free, silica sand. If carbon or low-alloy steel
products are sandblasted in the same facility, the sand used for
cleaning these products should not be used on titanium surfaces
and a separate sand supply should be provided.
3.3 Roughening of exposed surface areas may occur from
grit or shot if cleaning of the entire surface is accomplished by
blasting. Partial cleaning for preserving the surface finish is to
be preferred in conjunction with proper pickling procedures.
3.4 Blast cleaning that utilizes steel grit, steel shot, or sand
containing appreciable amounts of iron should be followed by
acid pickling to remove any embedded steel particles on the
surface of the titanium.
3.5 Any abrasive or shot blast cleaning may induce residual
compressive stresses in the surface of the material or titanium
structure. Warpage may occur in sections that are subsequently
chemical milled or contour machined.
3.6 In most cases, blast cleaning is not intended to eliminate
pickling procedures completely. Abrasives will not remove
surface layers contaminated with interstitial elements such as
carbon, oxygen, and nitrogen. When these elements are present
in excessive amounts, they are preferably removed by con-
trolled acid pickling in accordance with 4.3.
4. Pickling and Descaling
4.1 Recommended post treatment of shot or abrasive blasted
titanium surfaces may include acid pickling as described in
4.3.2, to ensure complete removal of metallic iron, oxide, scale,
and other surface contaminants. If the product is to be chemical
1 This guide is under the jurisdiction of ASTM Committee B10 on Reactive and
Refractory Metals and Alloys and is the direct responsibility of Subcommittee
B10.01 on Titanium.
Current edition approved Nov. 1, 2009. Published December 2009. Originally
approved in 1974. Last previous edition approved in 2002 as B600 – 91 (2002)´1.
DOI: 10.1520/B0600-09.
1
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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milled for the removal of the oxygen-contaminated layer, salt
bath conditioning may be required to avoid selectively etched
surfaces if configuration interferes with uniform blasting.
4.2 Scale and lubricant residues developed on mill, foundry,
forged, or fabricated titanium products usually require condi-
tioning by one of the following commercial methods prior to
final pickling as described in 4.3.2 to produce a completely
scale-free surface.
4.2.1 Proprietary solutions of caustic-based compounds in
tap water in accordance with the manufacturer’s recommenda-
tion.
4.2.2 Molten alkaline-based salt baths operating at 750 to
850°F (399 to 454°C) in accordance with prescribed proce-
dures.
4.2.3 Molten alkaline-based salt baths operating at 400°F
(204°C) in accordance with prescribed procedures.
4.2.4 Oxides and heat tints developed below 1100°F
(593°C) can frequently be removed by pickling in an acid
solution composed of 10 to 20 volume % (150 to 300 g/L) of
nitric acid (70 %) and 1 to 2 volume % (12 to 24 g/L) of
hydrofluoric acid (60 %) at 120°F (49°C).
4.2.5 Forged and hot-worked titanium alloys that have the
normal heat-developed scale mixed with graphitic or glass-type
lubricants may be conditioned in a molten alkaline-based salt
bath operating at 850°F (454°C) to effect complete solubility of
the complex scale. Following conditioning, the part should be
pickled as described in 4.3.2.
4.2.6 It is recommended that heat-treatable alpha beta and
beta alloys in the solution-treated condition that have been
processed at temperatures above 1100°F (593°C), with gra-
phitic and molybdenum disulfide lubricant residues mixed with
the heat-developed scale, be conditioned in a molten alkaline-
based salt bath operating at 400°F (204°C). After conditioning,
the part may be pickled in accordance with the treatment
described in 4.3.2.
4.2.7 Abrasive methods such as wheel or belt grinding,
segmented flapper wheels, and grit or shot blasting, when
available, may be used when surface configuration is such that
the scaled areas are readily accessible.
NOTE 1—Conditioning of titanium in high-temperature oxidizing salt
can generate galvanic currents where the work is contacting ferrous base
materials. Titanium is electrically positive or anodic with respect to these
ferrous materials, having an open circuit potential of approximately 0.60
V. The resulting discharge from the rack to the work piece can result in
surface over-heating and eventual ignition. This effect can be minimized
by maintaining bath temperature at or below 850°F (455°C) and by
providing titanium fixtures or aluminum insulation between the work and
the fixture.
NOTE 2—Heavily scaled forgings or hot-rolled materials can be me-
chanically abraded to remove excess surface contamination prior to salt
bath conditioning.
NOTE 3—Silicon-based protective coatings used to minimize scale
formation during hot forming or annealing of titanium alloys are soluble
in the molten salt bath. All of the coating should be removed prior to any
acid treatment.
4.3 Following mechanical abrading or chemical condition-
ing, the material may be further treated to completely clean the
surface in one of the following solutions:
4.3.1 After salt bath conditioning and water rinse, the
titanium or titanium alloy may be immersed in a sulfuric acid
solution to remove the converted scale product. It is recom-
mended that the acid solution be maintained at 150°F (66°C)
and a concentration of 10 to 40 volume % of sulfuric acid
(95 % solution by weight). Final brightening may be accom-
plished by a short immersion in the acid solution of 4.3.2.
4.3.2 Material that has been mechanically abraded in accor-
dance with 3.1 or chemically conditioned in accordance with
4.2.1, 4.2.2, or 4.2.3 may be finish cleaned by immersion in an
acid solution composed of 10 to 30 volume % (150 to 450 g/L)
of nitric acid (70 %) and 1 to 3 volume % (12 to 36 g/L) of
hydrofluoric acid (60 %) at 120°F (49°C), maintaining a ratio
of 10 parts nitric acid to 1 part hydrofluoric acid.
NOTE 4—Hot-formed or heat-treated titanium fabrications or assem-
blies that have a mixed surface contamination consisting of graphite or
molybdenum disulfide with titanium oxides should be conditioned in a
molten salt bath. The 400°F (204°C) temperature is preferred for these
structures to avoid any thermally induced distortion.
NOTE 5—In salt bath or alkaline water solution conditioning, the
titanium oxides present on the surface of the metal are chemically reacted
to form sodium titanate. This material is soluble in the sulfuric and
nitric-hydrofluoric acid pickles. The sulfuric acid solutions are not
appreciably corrosive to titanium or titanium alloys and can be further
inhibited by the addition of 0.25 to 1.0 % of cupric sulfate or ferrous
sulfate.
NOTE 6—Most of the acid pickling following molten salt bath condi-
tioning is accomplished in the sulfuric or nitric-hydrofluoric acid solution.
The material is cycled through the salt bath, water rinse, and sulfuric acid
until all of the scale has been completely removed. Final brightening is
obtained by a brief cycle in the nitric-hydrofluoric solution (4.3.2).
NOTE 7—In the nitric-hydrofluoric pickling solution, the ratio of nitric
acid to hydrofluoric acid is more important than the concentration of either
of these two acids. When this ratio is maintained at 10 to 1, hydrogen
absorption during pickling is minimized.
NOTE 8—In the processing of titanium mill products and fabrications,
an oxygen-rich layer is unavoidable where there is a combined exposure
to high temperatures and an oxidizing atmosphere. In the removal of this
oxygen-rich layer or alpha case by pickling in strong solutions of nitric
and hydrofluoric acids, it is extremely important that all residual oxide and
scale has been removed to prevent preferential etching of the finished
product.
NOTE 9—Hydrogen in excess of the specified amount may be removed
by vacuum annealing of the cleaned work piece.
NOTE 10—Hydrofluoric acid at 48 % concentration can be used in place
of the 60 % concentration. If this is done, the ratio of nitric to hydrofluoric
should be 8 to 1.
NOTE 11—Turning, peeling, and centerless grinding have also been
successfully utilized as alternative descaling and cleaning methods for
round bar.
5. Inspection
5.1 Visual inspection of material cleaned in accordance with
this guide should show no evidence of paint, oil, grease, glass,
graphite lubricant, scale, abrasive, iron, or other forms of
contamination.
5.2 Hydrogen absorption during the cleaning process should
be minimized and well within tolerable limits if the procedures
outlined are followed. Periodic monitoring of the cleaning
system can be accomplished by processing samples of known
hydrogen content through the complete system followed by
chemical analyses. A hydrogen increase greater than 20 ppm
over the original product analyses may be cause for replacing
the acids or adjusting the composition to reduce the extent of
hydrogen pickup.
B600 – 09
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5.3 Additional evaluation of product cleanliness may be
obtained by chemical milling of an expendable sample test
piece. It is recommended that approximately 0.001 to 0.002 in.
(0.025 to 0.05 mm) shall be removed from each surface. After
chemical milling, the surface should be uniformly smooth and
bright with the absence of peaks indicative of residual scale or
contamination.
6. Keywords
6.1 alpha case; cleaning; descaling; pickling; titanium; tita-
nium alloy
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B600 – 09
3
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Scope
Processing Soil Removal
Blast Cleaning
Pickling and Descaling
Inspection
Keywords