SS 316Ti

Stainless steel types 1.4401 and 1.4404 are also known as grades 316 and 316L respectively. Grade 316 is an austenitic grade second only to 304 in commercial importance. 316 stainless steel contains an addition of molybdenum that gives it improved corrosion resistance. This is particularly apparent for pitting and crevice corrosion in chloride environments. 316L, the low-carbon version of 316 stainless steel, is immune to grain boundary carbide precipitation (sensitisation). This makes it suited to use in heavy gauge (over about 6mm) welded components. For elevated temperature applications the high carbon variant, 316H stainless steel and the stabilised grade 316Ti stainless steel should be employed. The austenitic structure of 316 stainless steel gives excellent toughness, even at cryogenic temperatures. Property data given in this document is typical for bar products covered by EN 10088-3:2005. ASTM, EN or other standards may cover products sold. It is reasonable to expect specifications in these standards to be similar but not necessarily identical to those given in this datasheet.

Stainless steel grade 316Ti contains a small amount of titanium. Titanium content is typically only around 0.5%. The titanium atoms stabilise the structure of the 316 at temperatures over 800°C. This prevents carbide precipitation at the grain boundaries and protects the metal from corrosion. The main advantage of 316Ti is that it can be held at higher temperatures for a longer period without sensitisation (precipitation) occurring. 316Ti retains physical and mechanical properties similar to standard grades of 316.

 Difference between SS316 and SS316L

316Ti is essentially 316 with the addition of some titanium(Ti) to reduce the risk of losing corrosion resistance in the heat-affected zone. An alternative to prevent this is to reduce the carbon(C) level, which results in grade 316L. So we may conclude that these grades offer the same results with different approaches. 316ti with addition and 316L with a reduction.

One could say it makes more sense to remove an element, instead of simply adding one. However, in the early days of stainless steel making, there was no technology around to reduce the C content to the desired level. So this resulted in the development of the Ti-stabilized types. Nowadays it’s possible to abstract C from the molten steel through processes like AOD (Argon Oxygen Decarbusation) which makes 316L possible to replace 316Ti. But the 316Ti type has been traditionally specified by German engineers, and the costs of changing the specifications are keeping this grade alive.

The type of corrosion which both types prevent is intercrystalline corrosion (ICC), also known as intergranular attack. This corrosion occurs when the material is brought into a heat zone of about 450°-800°C, which could be created by welding, for example. The Chromium (Cr) reacts with the C and forms chromium-carbides of the type Cr23C6 at the grain boundaries. The Cr content in this crystal structure is very high compared to the C. This results in the formation of zones without Cr adjacent to the grain boundaries and of course, a weakening of the Cr protection on these spots where the Cr content is below 12%.

The Ti in 316Ti fights against this mechanism by forming titanium carbo-nitrides instead of chromium carbides, thus maintaining the original structure of Cr. The Ti content must be 5 times the actual C content to obtain this result. In 316L, the low C content (less than 0,03%) prevents the Cr to form an alliance with the carbon, simply because there is not enough carbon to react with.

The stabilizing element Ti has multiple other (dis)advantages. 316Ti material has an improved mechanical strength because of the higher C content. E.g. the proof strength (Rp0.2) at room temperature 210MPa for 316Ti and 190MPa for 316L. This difference rises with the temperature. This implies they are not automatically a substitute for each other when strength matters.

316Ti is sensible to a form of intergranular corrosion, named Knife Line Attack (KLA). This corrosion type occurs between the weld and the heat-affected zone (HAZ), through the precipitation of chromium carbide in this area.

This happens after slow cooling or subsequent heating of the material. This corrosion attack appears as an extremely narrow line. To solve this problem, a heat treatment above 1035°C is recommended, followed by rapid cooling.

 Specification

ASME SA-240, ASTM A240

Chemical Composition, %

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Applications of SS 316Ti

Initially developed for use in paper mills 316 stainless steel is now typically used in:

• Food processing equipment
• Brewery equipment
• Chemical and petrochemical equipment
• Coastal architectural panelling
• Coastal balustrading
• Boat fittings
• Chemical transportation containers
• Heat exchangers
• Mining screens
• Nuts and bolts
• Springs
• Medical implants

Physical Properties 

• Density:  8.0 g/cm³
• Melting Point:  1400 °C
• Thermal Expansion:  15.9 x10^-6 /K
• Modulus of Elasticity:  193 GPa
• Thermal Conductivity:  16.3 W/m.K
• Electrical Resistivity:  0.74 x10^-6 Ω .m

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Linear Coefficient of Thermal Expansion 

Coefficient of linear thermal expansion 10^-6 K-1 between 20°C and

• 100 °C: 16.5
• 200 °C: 17.5
• 300 °C: 18.0
• 400 °C: 18.5
• 500 °C: 19.0

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 Thermal Conductivity

• 8.4 Btu-in./ft.²hr.-°F (100°C)
• 14.6 W/m-K (100°C)

Electrical Resistivity 

• 28.4 μ ohm.in
• 72 μ ohm.cm

Specific Heat

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Heat Resistance of SS 316Ti

316 has good resistance to oxidation in intermittent service to 870°C and in continuous service to 925°C. However, continuous use at 425-860°C is not recommended if corrosion resistance in water is required. In this instance, 316L is recommended due to its resistance to carbide precipitation.

Hot Working of SS 316Ti

All common hot working processes can be performed on 316 stainless steel. Hot working should be avoided below 927°C. The ideal temperature range for hot working is 1149-1260°C. Post-work annealing is recommended to ensure optimum corrosion resistance.

Cold Working of SS 316Ti

Grade 316 is readily brake or roll formed into a variety of parts. It is also suited to stamping, heading and drawing but post-work annealing is recommended to relieve internal stresses. Cold working will increase both strength and hardness of 316 stainless steel.

Heat Treatment of SS 316Ti

316 stainless steel cannot be hardened by heat treatment. Solution treatment or annealing can be done by rapid cooling after heating to 1010-1120°C.

Fabrication of SS 316Ti

Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross-contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Mechanical Properties of SS 316Ti

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Corrosion Resistance of SS 316Ti

Alloy 316Ti displays better corrosion resistance in a standard range of corrosive media than 304 & 316. But shows slightly poor resistance to internal pitting & stress corrosion resistance due to titanium carbonitrides particles. SS 316Ti plays a superior role while installed at high-temperature services in contrast to 304 & 316.

 Machinability

316Ti stainless steel has good machinability. Machining can be enhanced using the following rules:

• Cutting edges must be kept sharp. Dull edges cause excess work hardening.
• Cuts should be light but deep enough to prevent work hardening by riding on the material's surface.
• Chip breakers should be employed to assist in ensuring the swarf remains clear of the work
• The low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities.

 Welding of SS 316Ti

Standard welding processes for this steel grade are:

• TIG-Welding
• MAG-Welding Solid Wire
• Arc Welding (E)
• Laser Beam Welding
• Submerged Arc Welding (SAW)

When choosing the filler metal, the corrosion stress has to be regarded, as well. The use of higher alloyed filler metal can be necessary due to the cast structure of the weld metal. Preheating is not necessary for this steel. A heat treatment after welding is normally not used. Austenitic steels only have 30% of the thermal conductivity of non-alloyed steels. Their fusion point is lower than that of non-alloyed steels therefore austenitic steels have to be welded with lower heat input than on-alloyed steels. To avoid overheating or burn-through of thinner sheets, a higher welding speed has to be applied. Copper backup plates for faster heat rejection are functional, whereas, to avoid cracks in the solder metal, it is not allowed to surface-fuse the copper backup plate. This steel has an extensively higher coefficient of thermal expansion than non-alloyed steel. In connection with a worse thermal conductivity, a greater distortion has to be expected. When welding 1.4571 all procedures, which work against this distortion (e.g. back-step sequence welding, welding alternately on opposite sides with double-V butt weld, assignment of two welders when the components are accordingly large) have to be respected notably. For product thicknesses over 12mm, the double-V butt weld has to be preferred instead of a single-V butt weld. The included angle should be 60° - 70°, when using MIG-welding about 50° is enough. An accumulation of weld seams should be avoided

Tack welds have to be affixed with relatively shorter distances from each other (significantly shorter than those of non-alloyed steels), in order to prevent strong deformation, shrinking or flaking tack welds. The tacks should be subsequently grinded or at least be free from crater cracks. 1.4571 in connection with austenitic weld metal and too high heat input the addiction to form heat cracks exists. the addiction to heat cracks can be confined if the weld metal features a lower content of ferrite (delta ferrite). Contents of ferrite up to 10% have a favourable effect and do not affect the corrosion resistance generally. The thinnest layer as possible has to be welded (stringer bead technique) because a higher cooling speed decreases the addiction to hot cracks. A preferably fast cooling has to aspired while welding as well, to avoid the vulnerability to intergranular corrosion and embrittlement. 1.4571 is very suitable for laser beam welding (weldability A in accordance with DVS bulletin 3203, part 3). With a welding groove width smaller than 0.3mm respectively, a 0.1mm product thickness the use of filler metals is not necessary. With larger welding grooves a similar metal can be used. With avoiding oxidation with the seam surface during laser beam welding by applicable backhand welding, e.g. Helium as an inert gas, the welding seam is as corrosion resistant as the base metal. A hot crack hazard for the welding seam does not exist when choosing an applicable process. 1.4571 is also suitable for laser beam fusion cutting with nitrogen or flame cutting with oxygen. The cut edges only have small heat-affected zones and are generally free of micro cracks and thus are well-formable. While choosing an applicable process the fusion cut edges can be converted directly. Especially, they can be welded without any further preparation. While processing only stainless tools like steel brushes, pneumatic picks and so on are allowed, in order to not endanger the passivation. It should be neglected to mark within the welding seam zone with oleigerous bolts or temperature-indicating crayons. The high corrosion resistance of this stainless steel is based on the formation of a homogeneous, compact passive layer on the surface. Annealing colours, scales, slag residues, tramp iron, spatters and such like have to be removed, in order to not destroy the passive layer. For cleaning the surface the processes of brushing, grinding, pickling or blasting (iron-free silica sand or glass spheres) can be applied. For brushing only stainless steel brushes can be used. Pickling of the previously brushed seam area is carried out by dipping and spraying, however, often pickling pastes or solutions are used. After pickling a careful flushing with water has to be done.