Inert gas welding ofhigh-alloy materialsProcess engineering and selectionof shielding gases

The right shielding gas for the right material

Rapid developments in base and filler metalsdemand a correspondingly wide-ranging programof shielding gases. This applies equally to TIG andto MIG/MAG welding.

TIG Welding For welding, argon is the gas predominantlyused. Hydrogen admixtures raise the perfor-mance appreciably, but Hydrogen Content > 2 %is only suitable for automated application. Forduplex steels, the addition of nitrogen may bebeneficial in order to safeguard the austenitecontent. For full austenites, too, the addition ofnitrogen can ensure compliance with low delta-ferrite limits. Hydrogen admixtures cannot beused for duplex steels.

MIG/MAG WeldingAustenitic steels are generally welded using anargon gas mix with 2.5% CO2 added. Oxygen canalso be used, but this results in a more oxidizedweld surface. Helium admixtures of 15%, forexample, also prove extremely effective in manycases. This is true, in particular, both for duplexsteels and for full austenites.

Backing gasesAs a rule, so-called forming gases, nitrogen-hydrogen mixtures, are used. The hydrogencomponent gives more protection againstresidual atmospheric oxygen. Under constructionsite conditions, higher hydrogen contents tend tobe used than in the workshop. As a result of thelatest regulations, hydrogen admixtures inbacking gas are no longer used for duplex steels.

Shielding gases for TIG welding of high-alloysteels according as DIN EN ISO 14175

Welding argon 4.6 I1 TIGWelding argon special 4.8 I1 TIGHelium 4.6 I2 TIGInoxline H2 R1 TIGInoxline H5 R1 TIGInoxline H7 R1 TIGInoxline H20 R2 Plasma cuttingInoxline H35 R2 Plasma cuttingInoxline He3 H1 R1 TIGInoxline N1 N2 TIGInoxline N2 N2 TIGInoxline He15 N1 N2 TIG

Shielding gases for MAG welding of austeniticsteels according as DIN EN ISO 14175

Inoxline He30 H2 C Z MAG MInoxline He15 C2 M12 MAG MInoxline C2 M12 MAG MInoxline C3 X1 M14 MAG MInoxline X2 M13 MAG MFerroline X4 M22 MAG M

Backing gases according as DIN EN ISO 14175

Forming Gas H5 N5Forming Gas H8 N5Forming Gas H12 N5Forming Gas H25 N5Inoxline H2 R1Welding argon I1

Materials Science BackgroundAustenites contain close to 20% chromium and about 10% nickel. As a rule, thetypical structure has a ferrite content of 5 to 8%. Materials frequently used: 1.4301,1.4541, 1.4571. Austenitic chrome-nickel steels are either stabilized againstintercrystalline corrosion by admixtures (usually titanium) or have a particularly lowcarbon content (LC qualities). Duplex steels have high corrosion resistance, especially against media containingchlorides and, at the same time, have greater mechanical strength.Most important material: 1.4462. Duplex steels have a mixed structure with a 50%ferrite content. Superduplex steels have an increased resistance to pitting.Fully austenites have a maximum ferrite content of 2%. This leads to an increasedsensitivity to hot cracking. On the other hand, fully austenites have higher resistanceto corrosion and to heat. Because of the extremely low ferrite content, thesematerials are non-magnetic. Typical materials: 1.4435 and 1.4439.Nickel base materials are used for maximum corrosion resistance requirements athigh temperatures of more than 1000 °C. They can no longer be classified as steelmaterials and are correspondingly identified by material numbers beginning with 2.When working with them, extreme cleanliness must be observed.TIG or MAG?Extremely high weld qualities can be achieved with TIG, as the non-metallicembeddings and the forming of pores are extremely small. The welding speed iscomparatively slow and the heat input high. Plasma welding, a variety of TIGwelding, guarantees constant values and is used mainly for fully automatedapplications. MAG welding is often used for fillet welds. Particularly in the case offully automated applications, it is also increasingly used for highly stressed welds.Pulse techniqueIn TIG welding, the pulse technique is used in the context of orbital technology toachieve a perfect weld, even with out-of-position welds. In MAG welding, on theother hand, the aim is low spatter or spatter free welding, even in the lower settingrange. The safety of the process with regard to the penetration is also increased.Modern power sources provide customised programs, adapted to the shieldinggases, allowing wide variation of the welding parameters. For high alloy steels,pulse welding can be generally recommended.Backing gasWhen welding high alloy steel, backshielding is necessary. As a rule, a residualoxygen content of <20 ppm is required at the root pass. The degree of tarnishpermissible depends on the purpose of the component. Small pipes are purged, thematching of the outlet aperture being important. In the case of larger pipes, thebacking gas is directed on to the weld by auxiliary devices. It is important to ensurethat the pre-purging time is long enough.Flux-cored wiresHigh alloy steels are mostly welded with solid wire electrodes. However, there arealso applications for flux-cored wires. Here, the use of the rutile slag typedominates. Because of the slag covering, very smooth welds are formed, littlepickling is necessary and there are practically no spatter problems. A distinction ismade between slowly setting slag for normal position and rapidly setting slag forvertical welding. In special cases, metal powder wires are used, for example insidecontainers where the slag would cause problems. The spray arc is reached morequickly with these wires than with solid wires.

Practical Notes

Technical centres – sources for innovationFor the development of new technologies in thefield of welding and cutting, Messer operatestechnical centres in Germany, Switzerland,Hungary and China. These facilities provide idealconditions for innovative projects as well ascustomer presentations and training courses.

Portfolio of gases – comprehensive andclear    Messer offers a spectrum of gases that extendswell beyond the standard fare: it ranges from justthe right gas for each application, and clear,application-oriented product designations to thecontinuous introduction of new gas mixturesdesigned to address current trends.

Specialised on-site consulting – right whereyou need itSpecifically in the context of your particular appli-cation, we can show you how to optimise theefficiency and quality of your processes. Alongwith process development, we support you withtroubleshooting and process development.

Cost analyses – fast and efficient  We will be glad to analyze your existingprocesses, develop optimisation proposals,

Good for you and the environmentThis brochure not only contains interesting information – it is also kind to the environment as it isprinted on 100% recycled paper. We would kindly ask you to dispose of any brochures that youhave “finished reading” or no longer require as waste paper for recycling.

® Messer Group GmbH

Messer Group GmbHGahlingspfad 31

47803 KrefeldTel. +49 2151 7811-0

Fax +49 2151 7811-503welding-technology@messergroup.com

www.messergroup.com

support process modifications and compare theresults with the original conditions – becauseyour success is also our success.

Training courses – always up to date For the optimal handling of our gases, we cantrain you on processes and how to use them. Our training courses illustrate the use of variousshielding gases for welding and explain how tohandle them safely. This also includes thestorage of the gases and the safe transport ofsmall quantities. Information and trainingmaterials for your plant are also part of theservice, of course.

You can also download this brochure andmany others from the Internet as a PDF file:www.messergroup.com  

Krefeld Dällikon Budapest Shanghai

Technical centres

Advice, Delivery, Service