Welding of Special Steels

Besides basics on special steels, this article describes techniques applicable for welding special steels, such as:
abrasion-resisting steel
free machining steels
manganese steels and
silicon steels.

Abrasion-Resisting Steel

Abrasion-resisting steel (AR) is carbon steel usually with a high-carbon analysis used as liners in material-moving systems and for construction equipment where severe abrasion and sharp hard materials are encountered. Abrasion-resisting steels are often used to line dump truck bodies for quarry service, for lining conveyors, chutes, bins, etc.

Normally the abrasion-resisting steel is not used for structural strength purposes, but only to provide lining materials for wear resistance. Various steel companies make different proprietary alloys that all have similar properties and, in general, similar compositions. Most AR steels are high-carbon steel in the 0.80-0.90% carbon range; however some are low carbon with multiple alloying elements.

These steels are strong and have hardness up to 40 HRc or 375 BHN. Abrasion-resisting bars or plates are welded to the structures and as they wear they are removed by oxygen cutting or air carbon arc and new plates installed by welding.

Low-hydrogen welding processes are required for welding abrasion-resisting steels. Local preheat of 400°F (204°C) is advisable to avoid underbead cracking of the base metal or cracking of the weld. In some cases this can be avoided by using a preheat weld bead on the carbon steel structure and filling in between the bead and the abrasion-resisting steel with a second bead in the groove provided. The first bead tends to locally preheat the abrasion-resisting steel to avoid cracking and the second bead is made having a full throat. Intermittent welds are usually made since continuous or full-length welds are usually not required. Efforts should be made to avoid deep weld penetration into the abrasion-resisting steel so as not to pick up too much carbon in the weld metal deposit. If too much carbon is picked up the weld bead will have a tendency to crack.

When using the shielded metal arc welding process the E-XX15, E-XX16, or E-XXX8 type electrodes are used. When using gas metal arc welding the low penetrating type shielding gases such as the 15% argon-25% CO2 mixture should be used. The flux-cored arc welding process is used and the self-shielding version is preferred since it does not have the deep penetrating quality as the CO2 shielded version.

During cold weather applications, it is recommended that the abrasion-resistant steel be brought up to 100°F (38°C) temperature prior to welding.

Free Machining Steels

The term free machining can apply to many metals but it is normally associated with steel and brass. Free machining is the property that makes machining easy because small cutting chips are formed. This characteristic is given to steel by sulfur and in some cases by lead. It is given to brass by lead.

Sulfur and lead are not considered alloying elements. In general, they are considered impurities in the steel. The specifications for steel show a maximum amount of sulfur as 0.040% with the actual sulfur content running lower, in the neighborhood of 0.030%. Lead is usually not mentioned in steel specifications since it is not expected and is considered a "tramp" element. Lead is sometimes purposely added to steel to give it free-machining properties.

Free-machining steels are usually specified for parts that require a considerable amount of machine tool work. The addition of the sulfur makes the steel easier to turn, drill, mill, etc., even though the hardness is the same as a steel of the same composition without the sulfur.

The sulfur content of free-machining steels will range from 0.07-0.12% as high as 0.24-0.33%. The amount of sulfur is specified in the AISI or other specifications for carbon steels. Sulfur is not added to any of the alloy steels. Leaded grades comparable to 12L14 and 11L18 are available.

Unless the correct welding procedure is used, the weld deposits on free-machining steel will always be porous and will not provide properties normally expected of a steel of the analysis but without the sulfur or lead.

The basis for establishing a welding procedure for free-machining steels is the same as that required for carbon steels of the same analysis. These steels usually run from 0.010% carbon to as high as 1.0% carbon. They may also contain manganese ranging from 0.30% to as high as 1.65%. Therefore, the procedure is based on these elements. If the steels are free-machining and contain a high percentage of sulfur the only change in procedure is to change to a low-hydrogen type weld deposit.

In the case of shielded metal arc welding this means the use of low-hydrogen type electrode of the E-XX15, E-XX16, or the E-XXX8 classification. In the case of gas metal arc welding or flux-cored arc welding the same type of filler metal is specified as is normally used since these are no-hydrogen welding processes.

Submerged arc welding would not normally be used on free-machining steels. Gas tungsten arc welding is not normally used since free-machining steels are used in thicker sections which are not usually welded with the GTAW process.

Manganese Steel

Manganese steel is sometimes called austenitic manganese steel because of its metallurgical structure. It is also called Hadfield manganese steel after its inventor. It is an extremely tough, nonmagnetic alloy. It has an extremely high tensile strength, a high percentage of ductility, and excellent wear resistance. It also has a high resistance to impact and is practically impossible to machine.

Hadfield manganese steel is probably more widely used as castings but is also available as rolled shapes. Manganese steel is popular for impact wear resistance. It is used for railroad frogs, for steel mill coupling housings, pinions, spindles, and for dipper lips of power shovels operating in quarries. It is also used for power shovel track pads, drive tumblers, and dipper racks and pinions.

The composition of austenitic manganese is from 12-14% manganese and 1-1.4% carbon. The composition of cast manganese steel would be 12% manganese and 1.2% carbon. Nickel is oftentimes added to the composition of the rolled manganese steel.

A special heat treatment is required to provide the superior properties of manganese steel. This involves heating to 1850°F (1008°C) followed by quenching in water. In view of this type of heat treatment and the material toughness, special attention must be given to welding and to any reheating of manganese steel.

Manganese steel can be welded to itself and defects can be weld repaired in manganese castings. Manganese steel can also be welded to carbon and alloy steels and weld surfacing deposits can be made on manganese steels.

Manganese steel can be prepared for welding by flame cutting; however, every effort should be made to keep the base metal as cool as possible. If the mass of the part to be cut is sufficiently large it is doubtful if much heat will build up in the part sufficient to cause embrittlement. However, if the part is small it is recommended that it be frequently cooled in water or, if possible, partially submerged in water during the flame cutting operation. For removal of cracks the air carbon arc process can be used. The base metal must be kept cool. Cracks should be completely removed to sound metal prior to rewelding. Grinding can be employed to smooth up these surfaces.

There are two types of manganese steel electrodes available. Both are similar in analysis to the base metal but with the addition of elements which maintain the toughness of the weld deposit without quenching. The EFeMn-A electrode is known as the nickel manganese electrode and contains from 3-5% nickel in addition to the 12-14% manganese. The carbon is lower than normal manganese ranging from 0.50 to 0.90%. The weld deposits of this electrode on large manganese castings will result in a tough deposit due to the rapid cooling of the weld metal.

The other electrode used is a molybdenum-manganese steel type EFeMn-B. This electrode contains 0.6-1.4% molybdenum instead of the nickel. This electrode is less often used for repair welding of manganese steel or for joining manganese steel itself or to carbon steel. The manganese nickel steel is more often used as a buildup deposit to maintain the characteristics of manganese steel when surfacing is required.

Stainless steel electrodes can also be used for welding manganese steels and for welding them to carbon and low-alloy steels. The 18-8 chrome-nickel types are popular; however, in some cases when welding to alloy steels the 29-9 nickel is sometimes used. These electrodes are considerably more expensive than the manganese steel electrode and for this reason are not popular.

Silicon Steels

Silicon steels or, as they are sometimes called, electrical steels, are steels that contain from 0.5% to almost 5% silicon but with low carbon and low sulfur and phosphorous. Silicon steel is primarily provided as sheet or strip so that it can be punched or stamped to make laminations for electrical machinery.

The silicon steels are designed to have lower hysteresis and eddy current losses than plain steel when used in magnetic circuits. This is a particular advantage when used in alternating magnetic fields. Their magnetic properties make silicon steels useful in direct current fields for most applications.

Silicon steel stampings are used in the laminations of electric motor armatures, rotors, and generators. They are widely used in transformers for the electrical power industry and for transformers, chokes, and other components in the electronics industry.

Welding is important to silicon steels since many of which are welded together. Welds are made on the edge of each sheet to hold the stack together. Welding is done instead of punching holes and riveting the laminations in order to reduce manufacturing costs. Almost all of the arc welding processes are used, submerged arc, shielded metal arc, gas metal arc, gas tungsten arc and plasma arc welding. The more popular processes are gas metal arc using CO2 for gas shielding and the gas tungsten arc process. The plasma arc process is used for some of the smaller assemblies.

When the consumable electrode processes are used the stampings are usually indented to allow for deposition of filler metal. For gas tungsten arc and plasma arc the filler metals are not used and the edges are fused. The size of the weld bead should be kept at minimum so that eddy currents are not conducted between laminations in the electrical stack.

One precaution that should be taken in welding silicon steel laminations is to make sure that the laminations are tightly pressed together and that all of the oil used for protection and used in manufacturing is at a minimum. Oil can cause porosity in the welds which might be detrimental to the lamination assembly.

July, 2006
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