FI64063B - FOERFARANDE FOER FOERBAETTRANDE AV SVETSENS INTRAENGNING OCH UTSEENDE - Google Patents

Description

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... . , (44) Date of Nihtiviksipanon et al. KuLfulkabun— rktant · och registerstyralsen AmMcmi Utlafd och utl. Moisio, Honkakatu 12, 53Ö10 Lappeenranta 8l,

Jouko Iivari Leinonen, Tapiontie 13 C Ui, 90570 Oulu 57, Finland-Finland (FI) (7U) Tapani Moisio (5U) A method for improving the penetration and appearance of a weld - Application of a method of intrusion and penetration

The invention relates to gas arc welding of high alloy steels. This method can be used to improve the shape of the weld pool, the surface tension and, in particular, the penetration and inertia of the weld.

In plasma, TIG and MIG welding methods, argon, helium or their mixtures are used as shielding gas as the main components. To change the properties of the shielding gas, small amounts of 1 to 5% hydrogen, carbon dioxide, nitrogen and oxygen can be added (Alfred B. Crichton, Metall Progress, Dec. 1975).

In welding in general, but especially in highly mechanized welding, it is often found that batches of products purchased with the same specifications, even of the same quality, but made from different smelters, are welded in different ways. Weldability variations are noted; in particular, the penetration of the weld with the same welding parameters varies.

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In order to make the required fusing with batches of poorly weldable products due to the properties of the welded joint, the welding speed must be reduced and, in general, the welding current must also be increased. The volume of the weld pool then increases and leads to melt control difficulties and usually also an unsatisfactory joint. Both the reduction of the welding speed and the unsatisfactory appearance of the joint have a strong effect on the economics of the operation.

Over the past ten years, enthusiastic efforts have been made to find out the reasons for these weldability variations. Despite the companies being measured, the reason is still unexplained. However, there are patents aimed at improving weldability.

The U.S. 3.584.187 With high-alloy steels, oxides (Cr, Fe, etc.) are introduced into the area to be welded before the welding operation as a water or acetone slurry, eg by brushing. The surface can also be oxidized in an oven at 1,400 ° F for 2 to 15 minutes in an oxidizing atmosphere. The disadvantages of the method are the separate treatment step required, the easy detachment of the dried oxide sludge from the surface before welding and the investment required for the annealing treatment.

GB 1,121,594 The shielding gas is an argon + helium (neon)> 95% mixture to which 0.8 ... 1.2% hydrogen and 3 ... 3.5% carbon dioxide have been added.

GB 1,460,140 shielding gas argon + helium + <5% SF ^ GB 1,378,091 shielding gas argon + 0.40 ... 0.60% oxygen in welding of various metals when silicon bronze is used as an additive.

The relatively high concentrations of active components used in these patents limit the welding process used to the MIG process or greatly shorten the electrode life when using plasma and TIG processes.

3 64063 The present invention is based on the finding that when welding high-alloy steel, the presence of oxides as a layer of a certain thickness at the welding point affects the welding arc. In gas arc welding, the arc is concentrated and thus its energy flow is directed to a smaller area, which in turn leads to a deeper penetration. This improves through-welding and welding speed. This phenomenon is particularly pronounced when welding poorly welded batches, but is also clear and significant in highly weldable batches. This leads to a smoothing of the weldability differences.

This invention is based on a method for improving the penetration and appearance of a weld in high alloy steels by commonly known gas arc welding methods when the shielding gas used is controlled oxidizing to form an oxide layer on the surface of the body to be welded. that the shielding gas (Ar, He) or gas mixture (Ar + He) is converted to oxidised in a controlled manner by adding 0.01 to 0.20% oxygen or 0.05 to 0.50% carbon dioxide, and that the gas mixture (Ar, He) , Ar + He) containing 1 to 5% hydrogen, the gas mixture is converted to controlled oxidation by the addition of 0.15 to 0.50% oxygen or 0.40 to 1.1% carbon dioxide.

The excellence of the invention is based on the fact that it does not require processing steps or expensive accessories. The oxide layer is formed at the welding point immediately before the welding operation and therefore cannot be detached during the previous mechanical treatment. The method can be used in all gas arc welding methods and the proportion of active components in the shielding gas is so small that they do not adversely affect the properties of the material or joint. When using the method, the weldability differences between different smelters are significantly smoothed out.

The oxide layer at the welding point is obtained by changing the shielding gas (Ar, He) or shielding gas mixture (Ar, He) used in gas arc welding.

He, H2) for controlled oxidation with oxygen or a compound thereof with carbon dioxide.

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The lower limit of oxidizability is determined by the surface tension factor because too low an oxygen potential causes an edge wound in the weld. Too high an oxygen content in TIG and plasma methods destroys the electrode and causes unfavorable compositional changes in the weld metal by all methods. It should also be noted that hydrogen must not be used in the gas mixture if the formation of martensite during the cooling of the weld is possible.

When welding high-alloy steels, argon and helium (neon) or their mixtures are used as shielding gas. According to the present invention, oxygen is added to them in an amount of 0.01 to 0.2% to improve penetration.

The oxygen content is preferably 0.05% when using argon and 0.08% when using helium. For argon-helium alloys, the oxygen content is obtained in a corresponding ratio. If carbon dioxide is used instead of oxygen, the argon is converted to oxidation in a controlled manner by adding 0.05 to 0.50%, preferably 0.18% carbon dioxide. If hydrogen has been added to the shielding gas to increase the melting power of the arc, the concentration of the oxidizing component must be increased to achieve a controlled oxidation potential in the arc situation. If a mixture of argon and / or helium + 2% hydrogen is used, 0.2% oxygen or 0.6% carbon dioxide must be added to achieve the desired penetration increase. The corresponding additions (Ar, He) to the + 5% H 2 mixture are 0.5% or 1.1% CO 2. For other hydrogen contents, the concentrations of the oxidizing components are (0.15 + (x - 1) · 0.085)% oxygen or (0.40 + (x-1) · 0.175)% carbon dioxide, where x = hydrogen content of the gas mixture as a percentage.

An example of improving penetration. The material to be welded is the so-called stainless steel (AISI 316) plate thickness 3 mm. Welding method TIG, surface welding without additive, welding current 100 A and welding speed 33 cm / min.

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tunkeuraan

depth D width W

shielding gas nun mm D / W

lAr 0.85 3.60 0.23 2 Ar + 0.06% 02 1.30 3.10 0.42 3 50% Ar + 50% He 1.45 4.20 0.35 4 49.96% Ar + 49.96% He + 0.07% 02 1.60 4.15 0.39 5 Ar + 2% H2 + 0.5% CO2 1.85 3.60 0.51 6 Ar + 2% H2 + 0 , 65% CC> 2 1.85 3.65 0.51 7 Ar + 2% H 2 1.05 3.80 0.28

When the shielding gas of arc welding is converted to oxidizing in a controlled manner, oxidation of the surface to be welded takes place in front of the welding point in a controlled manner. The arc caused by this as well as the thermal energy it transmits are concentrated in a smaller area.

In this way, the higher penetration of the weld, and / or the higher welding speed caused by it, can be exploited. Smelting now does not require an increase in the weld melt, only its depth increases and thus the melt is easy to control. Controlled oxidation also affects the surface tension of the weld pool. Thanks to this, while the penetration is improved, a smooth connection of the fire to the base material and a beautiful and even surface for the weld is also obtained.

Claims (2)

6 64063 A method for improving the penetration and appearance of a weld in high-alloy steels by commonly known gas arc welding methods where the shielding gas used is controlled oxidizing to form an oxide layer on the surface of the part to be welded which improves weldability by that the shielding gas (Ar, He) or gas mixture (Ar + He) is converted to oxidised in a controlled manner by the addition of 0,01 to 0,20% oxygen or 0,05 to 0,50% carbon dioxide, and that the gas mixture (Ar, , He, Ar + He) containing 1 to 5% hydrogen, the gas mixture is converted to controlled oxidation by the addition of 0.15 to 0.50% oxygen or 0.40 to 1.1% carbon dioxide. Process according to Claim 1, characterized in that the hydrogen-containing gas mixture (Ar, He, Ar + He) is converted into oxidizing in a controlled manner by adding (0.15 + (x - 1) · 0.085)% oxygen or (0.40 + (x - 1) · 0,175)% of carbon dioxide when x is the percentage of hydrogen in the gas mixture.