Titanium Alloys Titanium Grade 12

 Product Data Sheet – Titanium Alloys

Titanium Grade 12  URS-R53400

Titanium Alloy Grade 12 has outstanding corrosion resistance and a combination of high strength and low density, with good ductility. Small additions of nickel and molybdenum have been made to this alloy resulting increase in corrosion resistance and high strength. It is particularly suitable for use in mildly reducing conditions, or where conditions vary from oxidising to reducing. It is particularly resistant to crevice corrosion in hot brines.

Typical Applications

Many of the applications of grade 12 titanium are in the chemical industries. The common uses in Australia are in chemical processing, where titanium grade 12 is used for reactor autoclaves, piping and fittings, valves, heat exchanges and condensers.

Chemical Composition

ASTM B265 – Titanium & titanium alloy strip, sheet & plate

Element Titanium Nitrogen Carbon Hydrogen Iron Oxygen Molybdenum Nickel Residuals (each) Residuals (total)
% Balance 0.03 max 0.08 max 0.015 max 0.30 max 0.25 max 0.2-0.4 0.6-0.9 0.1 0.4

Specified Minium Mechanical Properties

ASTM B265 – Titanium & titanium alloy strip, sheet & plate

0.2% Proof Stress Tensile Strength Elongation
MPa MPa %
Annealed 345 483 18

Description

Titanium Grade 12 is a highly corrosion resistant alloy containing small additions of nickel and molybdenum, which enhance corrosion resistance and increase the strength of the alloy to give better mechanical properties than the commercially pure grades. It is used in mildly reducing or fluctuating conditions. In particular, it is used instead of the commercial purity grades (e.g.grade 2) for better resistance to crevice corrosion in hot brines, and where the extra strength allows the use of lighter sections.

At room temperature it is an alpha alloy, and may contain minor amounts of beta phase. It transforms to beta phase at 890°C ± 15°C

Titanium is reactive, and has a very high affinity for oxygen, which forms a skin of very stable and highly adherent oxide. The skin gives excellent corrosion resistance, despite the reactivity of the metal. The oxide layer forms spontaneously and on exposure to the atmosphere. However, when new parent metal is exposed to anhydrous conditions or in the absence of air, rapid corrosion may occur. Care should also be taken if titanium is to operate in contact with hydrogen, as hydrogen embrittlement from hydride formation can increase strength, with loss of ductility.

Availability

Austral Wright Metals can supply titanium 12 as plate, sheet and strip, rod and bar, seamless and welded pipe, weld fittings, seamless and welded tube, forging billet and forgings.

Pressure Vessels

AS1210 & ASME Boiler & Pressure Vessel Code pre-qualify Titanium 12 for use in pressure vessels up to 300°C.

Corrosion Resistance

Titanium alloys are usually used in Australia for their excellent corrosion resistance, especially to chloride solutions. The small additions of nickel and molybdenum to grade 12 titanium give a more corrosion resistant metal than the commercial purity grade 2 alloy, with a marked increase in strength. The overall corrosion resistance of this grade is not as good as the palladium alloyed lean grade 7, except for resistance to crevice corrosion in hot chloride solutions. Titanium has excellent resistance to general corrosion, with loss rates of less than 0.04mm/year being typical. The Austral Wright Metals Product Data Sheet “Corrosion of Titanium and Titanium Alloys” or your local office should be consulted more details.

Environment
Typical Corrosion
Rate (mm/year)
Wet Cl2 gas
0.00089
5% NaOCI + 2% NaCl + 4% NaOH †
0.06
70% Zinc Chloride
0.005-0.0075
50% Citric Acid
0.013
10% Sulphuric Acid
11.6
45% Formic Acid
Nil
88-90% Formic Acid
0-0.56
90% Formic Acid ‡
0.56
10% Oxalic Acid
104

† no crevice corrosion in metal-to-metal or metal-to-Teflon crevices

‡ anodised specimens

Source: Metals Handbook, vol 2, ASM

Physical Properties

Density
Melting Range
Modulus of Elasticity (Tension)
Specific Heat
Mean Coefficient of Expansion
Thermal conductivity
Electrical Resistivity
kg/m3
°C
GPa
J/kg. °C
x10 -6 / °C
W / m. °C
micro-ohm.m
4,507 1668± 10 103 519 8.41 11.4 0.420

Fabrication

Titanium Grade 12 is forged conventionally, within the narrow temperature range 815 – 900°C. Titanium and its alloys are generally more difficult to forge than both aluminium and alloy steels, due to their high strain rate sensitivity and rapid increase of strength with falling temperature. Hot forging leaves a thick, hard outer layer of titanium oxide on the surface. This layer is called “Alpha Case” and is usually removed by pickling in a mixture of nitric and hydrofluoric acids. As supplied, titanium alloys are usually annealed and pickled, and can be readily cold formed in conventional machines using standard methods. In cold forming the “alpha case” does not form and further pickling is not needed, except to remove any carbon steel embedded in the surface, which can cause pitting corrosion.

Machinability

Titanium Grade 12 is readily machinable by conventional methods. Like stainless steel, titanium has a low thermal conductivity and heat dissipation is inhibited, so copious amounts of coolant should be used. Sharp carbide tools are used. Deep, continuous cuts are best.

Weldability

Titanium Grade 12 is readily weldable by GMAW (MIG) and GTAW (TIG) processes. Preheat or post weld heat treatment are not needed. The area to be welded must be CLEAN, free from all grease and shop dirt, including marking pencil marks. A trailing gas shield is used in addition to the normal welding torch gas shield, to prevent heavy oxidation during cooling. Matching filler metal to AWS specification ERTi-12 is used. The gas shield must be low in hydrogen, oxygen and nitrogen, all of which readily dissolve in titanium and cause embrittlement.

Heat Treatment

Titanium Grade 12 is normally supplied in the annealed condition. After fabrication, stress relief at 480 – 595°C, air cooled, may be required to improve dimensional stability.

ASTM Product Specifications

Specification Title
B265
Titanium and Titanium Alloy Strip, Sheet & Plate
B381
Titanium and Titanium Alloy Forgings
B348
Titanium and Titanium Alloy Bars and Billets
B337
Seamless and Welded Titanium and Titanium Alloy Pipe
B338
Seamless and Welded Titanium and Titanium Alloy Tubes for Condensers and Heat Exchangers
The technical advice and recommendations made in this Product Data Sheet should not be relied or acted upon without conducting your own further investigations, including corrosion exposure tests where needed. Please consult current editions of standards for design properties. Austral Wright Metals assumes no liability in connection with the information in this Product Data Sheet. Austral Wright Metals supplies a comprehensive range of stainless steels, copper alloys, nickel alloys and other high performance metals for challenging service conditions. Our engineers and metallurgists will be pleased to provide further data and applications advice.

 

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