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Titanium Raw Materials Welding Method
Oct 19, 2017

Titanium and Titanium Alloy Welding Methods

1. Weldability analysis

(1) contamination of the gap caused by embrittlement

Titanium has a strong chemical activity at high temperatures. Titanium at 300 ℃ above the rapid hydrogen absorption, 600 ℃ above the rapid oxygen, 700 ℃ above the rapid nitrogen. So titanium in the welding process and after the welding process if the lack of effective protection, will inevitably lead to decreased plasticity, brittleness increased. The mass fraction of carbon in titanium is controlled below 0.1%. When the carbon exceeds its solubility, it generates hard and brittle TiC, which is distributed in a network and easily causes cracks.

(2) hot crack

Because of the low content of titanium and titanium alloy impurities, it is not easy to produce hot cracking, but if the wire quality is not qualified, especially the welding wire cracks, sandwich and other defects, there are a lot of impurities, it may cause hot welding cracks.

(3) Delayed cracking may occur in the heat affected zone

During the welding, the hydrogen in the molten metal and the low temperature zone is diffused into the heat affected zone, causing the accumulation of hydrogen in the heat affected zone to cause cracking under adverse stress conditions.

(4) Stomata

Stomata are the most common flaws in welding titanium and titanium alloys. There are generally two types of welds in the middle of the pores and fused pores. The stomata are generally located near the fusion line when the welding line energy is large. The formation of the weld stomata is mainly due to the welding area, especially due to the docking face by moisture, grease pollution caused.

2. Welding process

(1) welding method

Welding method using GTAW, the use of DC is connected, the use of high-frequency arc and arc quenching device welding machine.

(2) welding materials

The welding wire should be selected so that the tensile strength of the weld under the normal welding process is not lower than the standard tensile strength lower limit value of the base metal annealing state. The plastic and corrosion resistance of the weld after welding are not low The base material in the annealed state is equivalent to that of the base metal, and the welding performance is good, and the requirements for manufacturing and use are satisfied.

Selection of protective gas:

Soldering argon purity should not be less than 99.99%, dew point should not be higher than -40 ℃, when the bottled argon gas pressure below 0.981MPa should not be used. Argon gas protection is used in areas where the solder bath and the welded joint are inside and outside the surface temperature above 400 ° C.

(3) Preparation before welding

Should take effective measures to avoid the welding process in the steel and titanium miscible, welding site clean, avoid the use of iron tools.

Bevel processing, pipe cutting, the use of grinder grinding groove, groove angle for the unilateral 30 ° ± 2.5 °, blunt 0.5 ~ 1.5mm. Processing of the groove does not allow the parent material to produce overheating discoloration.

Groove and wire cleaning, groove and its sides on both sides of the 25mm inside and outside the surface cleaning, cleaning procedures are as follows: grinding machine grinding - sandpaper wheel polishing - acetone cleaning. The wire is also wiped with a sponge with acetone sponge, and carefully check the base metal groove near the wire and whether the cracks and sandwich, if any, after cleaning and then welding operations. After cleaning can not be directly welding operations, to be the end of the groove to dry after the operation. If it can not be welded in time, apply self-adhesive tape and plastic (9085, 180.00, 2.02%) cloth to protect the groove. Cleaning time to welding time of not more than 2 hours, welders should be clean with gloves, before use with absolute ethanol (or acetone) cleaning, to avoid the cotton fiber attached to the surface of the weldment.

Before welding, should be based on the welding process to assess the preparation of welding instructions, welders should be specified welding instructions welding.

(4) welding process parameters (see Table 2)

Welding process parameters selected to ensure that the weld shape is good, the choice of small wire energy welding, the temperature between the layers should not be higher than 200 ℃, to prevent the high temperature too long grain growth.

Welding operations should be carried out under the protection of argon: the use of torch nozzle to protect the pool, torch torch to protect the hot seam and the outer surface of the near seam, pipe argon welding and weld near the inner surface, Specific measures: the larger diameter of the pipe welding, the tube staff wearing a gas mask, hand-held protective cover on the back of the welding pool to protect the smaller diameter of the pipe or fixed port welding, the inner surface of the tube from the groove 150 ~ 300mm (according to the operability to take a larger value) at the use of soluble paper seal, and then stuffed into a group of soluble paper to prevent excessive pressure in the tube will seal the soluble paper damage, and then filled with argon to clean the air inside the tube. Before welding must be fully pre-filled argon, after welding should be delayed argon, so that the high temperature zone to fully cool to prevent surface oxidation.

3. Precautions for welding operation

(1) welding, the welding wire and the weld between the angle to keep the minimum, basically do not make horizontal toggle, when the need to swing, the frequency is low, the range should not be too fast, and wire to be smooth. The welding wire during welding should always be kept under the protection of argon. After the arc is extinguished, the wire shall not be exposed to the atmosphere immediately and shall be removed when the weld is disengaged. If the wire is contaminated, oxidative discoloration, the pollution part should be removed.

(2) shall not be in the weld surface arc or test arc; welding should ensure that the arc and arc quality; arc should be filled when the arc, multi-layer welding of the joints should be staggered from each other.

(3) In addition to special requirements, each weld should be a continuous welding, such as forced to interrupt, and then welding must be checked to confirm that no cracks before welding

(4) If the welding operation accidentally appears when the folder tungsten, should stop welding operations, with a polisher to remove tungsten, tungsten end re-polished, to meet the requirements before re-welding operations, requiring the same as the beginning of welding operations.

(5) In order to reduce the welding deformation, welding between the joint groove between the positioning welding, positioning welding should be the same with the formal welding process, positioning welding weld length should be 10 ~ 15mm, high to 2 ~ 4mm, and not More than 2/3 of the wall thickness. Positioning welding of the weld shall not have cracks and other defects, positioning welding seam at both ends, should be ground into a gentle slope.

(6) titanium tube welding environment if one of the following circumstances, and did not take protective measures should stop welding: wind speed ≥ 2m / s; relative humidity greater than 90%; rain and snow; temperature below 0 ℃.

(7) weld repair process and the original welding process the same. The same part of the number of rework should not be more than twice, if the second rework, should be issued to repair measures. Shall be carried out after approval by the welding liability engineer and shall be indicated in the construction record.

4. Welding inspection

(1) welders should be welded on the surface of the weld to clean up, requiring a good appearance. Width to cover the edge of each side of the groove 2mm is appropriate, fillet weld feet height meet the design requirements, smooth shape transition. Surface quality should meet the following requirements: not allowed to have undercut, cracks, not fused, pores, slag, splash exists; weld height: when the wall thickness is less than 5mm, 0 ~ 1.5mm; when the wall thickness is greater than 5 mm , For 1 ~ 2mm; c weld surface misalignment should not be greater than 10% of wall thickness, and not more than 1mm.

(2) the bottom of the weld should be carried out by the penetration test, the detection method according to "pressure vessel nondestructive testing" JB4730 implementation, with no cracks and any other surface defects as qualified

(3) for each weld surface color inspection, the color change is the surface oxide film at different temperatures color changes, their mechanical properties are not the same

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