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WELDING OF TOOL STEEL This information is based on our present state of knowledge and is intended to provide general notes on our products and their uses. It should not therefore be construed as a warranty of specific properties of the products described or a warranty for fitness for a particular purpose. Classified according to EU Directive 1999/45/EC For further information see our “Material Safety Data Sheets”. Edition 6, – Revised 02.2014, not printed The latest revised edition of this brochure is the English version, SS-EN ISO 9001 which is always published on our web site www.uddeholm.com SS-EN ISO 14001 WELDING OF TOOL STEEL CONTENTS General information on welding of tool steel ................... 4 Welding methods for tool steel ............................................ 4 The welding bay ........................................................................ 6 Filler material ............................................................................. 7 Hydrogen in tool steel ............................................................ 8 Elevated working temperature .............................................. 9 Welding procedure .................................................................. 10 Het treatment after welding .................................................. 11 Guidelines for welding in – hot work tool steel ............................................................ 13 – cold work tool steel .......................................................... 14 – plastic mould steel.............................................................. 17 3 WELDING OF TOOL STEEL General informa- welding technique and weld con- sumables that are required in order Welding methods tion on welding of to weld tool steel successfully. Of for tool steel course, the skill and experience of tool steel the welder is also a vital ingredient in Shielded metal-arc welding To ol steel contain up to 2.5% carbon obtaining satisfactory results. With (SMAW or MMA) as well as alloying elements such as sufficient care, it is possible to manganese, chromium, molybdenum, achieve weld repairs or adjustments PRINCIPLE tungsten, vanadium and nickel. The which, in terms of tooling perform- An electric arc generated by a DC or main problem in welding tool steel ance, are hardly inferior to that of the AC power source is struck between stems from its high hardenability. base steel. a coated, rod-like electrode and the Welds cool quickly once the heat Welding of tooling may be required work-piece (Fig. 1). source is removed and the weld for anyone of the following reasons: The electrodes consist of a central metal and part of the heat-affected • refurbishment and repair of wire core, which is usually low- zone will harden. This transformation cracked or worn tooling carbon steel, covered with a coating generates stresses because the weld • renovation of chipped or worn of pressed powder (flux). The consti- is normally highly constrained, with a cutting edges, e.g. on blanking tools tution of this coating is complex and concomitant risk for cracking unless • adjustment of machining errors in consists of iron powder, powdered great care is exercised. tool making ferro-alloys, slag formers and a suit- In what follows, a description is • design changes able binder. The electrode is con- given of the welding equipment, sumed under the action of the arc during welding and drops of molten metal are transferred to the work- piece. Contamination by air during the transfer of molten drops from electrode to workpiece and during solidification and cooling of the weld deposit is inhibited partly by slag formed from constituents in the elec- trode coating and partly by gases created during melting of the elec- trode. The composition of the deposited weld metal is controlled via the con- stitution of the electrode coating. POWER SOURCE For MMA welding, it is possible to use either an AC or DC power source. However, whichever is used, the source must provide a voltage and current which is compatible with the electrode. Normal arc voltages are: • normal recovery electrodes: 20–30 V • high recovery electrodes: 30–50 V Uddeholm welding consumables are of normal recovery type. A suitable power source for these is a DC unit with an open voltage of 70 V and which is capable of delivering 250A/ 30V at 35% intermittence. 4 WELDING OF TOOL STEEL Gas tungsten-ARC welding minimizes heat generation and there- inert gas protection is as efficient as by any risk of melting the electrode. possible. Welding is facilitated if the (GTAW or TIG) Current is conducted to the elec- current can be increased steplessly trode via a contact inside the TIG- from zero to the optimum level. PRINCIPLE gun. Any consumables which are In MMA welding, the electrode from required during TIG-welding are fed which the arc is struck is consumed obliquely into the arc in the form of Laser Welding during welding. rod or wire. Oxidation of the weld PRINCIPLE The electrode in TIG welding is pool is prevented by an inert-gas made of tungsten or tungsten alloy shroud which streams from the TIG High power laser light is generated which has a very high melting point gun over the electrode and weld. and focused through a lens to the (about 3300°C/6000°F) and is there- welding spot. As filler material a thin fore not consumed during the proc- wire with a diameter between 0.1– ess (Fig. 2). The arc is initially struck POWER SOURCE 0.6 mm is primarily used. The welder by subjecting the electrode-work- TIG welding can be performed with a guides the wire to the area to be piece gas to a high-frequency voltage. regular MMA power source provided welded. The laser beam melt the The resulting ionization permits strik- this is complemented with a TIG wire and the base material. The mol- ing without the necessity for contact control unit. The gun should be water ten material solidifies leaving behind between electrode and workpiece. cooled and be capable of handling a a small raised area. The welder con- The tungsten electrode is always minimum current of 250 A at 100% tinues spot by spot and line by line. connected to the negative terminal of intermittence. A gas lens is also a Argon gas shields the process from a DC power source because this desirable feature in order that the oxidation (Fig.3). Core wire Electrode holder Electrode holder + Pole Cooling water Power source Coating – Pole Slag Protective gas Tungsten electrode – Pole Weld Filler material Power source Melt pool + Pole Fig. 1 Shielded Metal-Arc Welding SMAW (MMA) Fig. 2 Gas Tungsten Arc Welding GTAW (TIG) Protective gas Protective glass Laser beam Deposited material Filler wire Fusion zone Workpiece Fig. 3 Laser Welding 5 WELDING OF TOOL STEEL POWER SOURCE age of electrodes. This should be work can be positioned securely and For deposition welding normally a thermostatically controlled in the accurately. It is advantageous if the pulsed solid state laser of Nd: YAG range 50–150°C (120–300°F). The workbench is rotatable and adjust- type is used. electrodes should be removed from able vertically, since both these fea- their containers and lie loose on tures facilitate the welding operation. Typical performance: racks. For welding of tooling outside the Nominal output 150–200 W Preheating equipment Max pulse output 10–12 kW welding bay, it will also be found use- Pulse time 0.5–20 ms ful to have a portable heated con- To ol steel cannot be welded at room Frequence 0.5–20 Hz tainer in which the electrodes can be temperature without considerable Spot diameter 0.5–2.0 mm (0.1–0.5 mm) carried. risk for cracking and it is generally necessary to pre-heat the mould or die before any welding can be Workbench attempted (see later). While it is The welding bay It is particularly important during certainly possible to weld tools suc- critical welding operations, of the cessfully by preheating in a furnace, In order to be able to effect satisfac- type performed with tool steel, that the chances are that the temperature tory welding work on tool steel, the the welder enjoys a comfortable will fall excessively prior to comple- following items of equipment are to working position. Hence, the work- tion of the work. Hence, it is recom- be regarded as minimum require- bench should be stable, of the cor- mended that the tool be maintained ments. rect height a sufficiently level that the at the correct temperature using an electrical heating box supplied from a Dry cabinet current-regulated DC source. This The coated electrodes used for MMA equipment also enables the tool to welding are strongly hygroscopic and be heated at a uniform and control- should not be allowed to come into led rate. contact with anything other than dry To place the tool on a heated table air. Otherwise, the weld will be con- or plate could sometimes be suffi- taminated with hydrogen (see later). cient to maintain the temperature. For minor repairs and adjustments, Hence, the welding bay should be Electrical elements for an insulated it is acceptable that the tool is pre- equipped with a dry cabinet for stor- preheating box. heated using a propane torch. Hence, liquid propane cylinders should be available in the welding bay. Grinding machines The following should be available: • disc grinder with minimum 180 Ø x 6 mm wheel (7 Ø x 0,25”) for preparing the joint and grinding out of any defects which may occur during welding •flat grinder capable of ≥25 000 rpm for grinding of minor defects and of the finished weld • if a welded mould is subsequently to be polished or photo-etched, it may be necessary to have a grinder capable of giving a sufficiently fine finish • small rotating metal files in different shapes and sizes Preheating in an insulated box. 6 WELDING OF TOOL STEEL Filler rods are normally produced For the three main application seg- Filler material from electro-slag remelted stock. ments for tool steel (cold work, hot The chemical composition of a weld The coated electrodes are of basic work and plastic moulding), the im- deposit is determined by the compo- type, which are far superior to rutile portant weld-metal properties are: sition of the consumable (filler metal), electrodes as regards weld cleanli- COLD WORK the base steel composition and the ness.

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