Hard-facing

Hard-facing or cladding generally means applying an extra layer to a metal base material using a welding procedure with the objective of achieving a higher wear resistance against abrasion, erosion, cavitation and corrosion. The nature of the materials to be applied (e.g. hard surfacing, manganese hard steels, austenites, nickel-base alloys, inconel, cobalt-base alloys, stellites and many others) is determined by the contact media and the prevailing application conditions such as pressure and temperature.

The DURMAT® products offer a wide range of high-quality materials for the welding processes of MIG/MAG/OA (GMAW/FCAW), PTA, Oxy-acetylene Welding, Shielded Metal Arc Welding (SMAW), Laser Cladding and Submerged Arc Welding (SAW).

The various welding processes are briefly described below. If you have further questions, please do not hesitate to contact us.

Welding processes

Welding processes

MIG/MAG/OA (GMAW/FCAW)

Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt and join. By using Flux-Cored Wires the process is calling flux-core arc welding (FCAW). Hereby an externally supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the necessary protection from the atmosphere, producing both gaseous protection and liquid slag protecting the weld. The process is widely used in construction because of its high welding speed and portability.

Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from contaminants in the air. The process can be semi-automatic or automatic. A constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. There are four primary methods of metal transfer in GMAW, called globular, short-circuiting, spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations.

Typical DURUM-products:
DURMAT® NIFD, FD 60, FD 250 K, DUROLIT 6
 

Plasma-Transferred-Arc Welding (PTA)

Being a modern advanced technology, the plasma-transferred-arc welding (PTA) is used wide to coat function areas of high responsibility details with special materials, which are resistant against intensive wear, corrosion, thermal and percussive loading. The welding process employs a constricted high-energy plasma arc between a non-consumable electrode and the base material, creating a molten weld pool. For hardfacing two arcs are commonly used, which are controlled independently by separate power sources. The non-transferred arc (pilot arc) burns between the plasma electrode anda plasma nozzle. It is started by a high-frequency ignition unit (HF) and forms the foundation for ignition of the main arc. The main arc burns between the workpiece and the plasma electrode. Using strong HF ignition it is possible to dispense with the non-transferred pilot arc because hereby the arc can be ignited directly between electrode and workpiece. High-quality protective layers with diilution of less than 5 % can be produced.

Self-fluxing nickel-based alloys, e.g. NiCrBSi (DURMAT® 57-PTA) or NiBSi (DURMAT® 59-PTA), are widely used for surfacing of composite materials. In this way the danger of adhesion of powder particles is reduced in the powder nozzle due to an excessive preheating. Moreover, conventional power sources for TIG can be used to construct a PTA system.

During the PTA process the powdery filler material is inserted into the arc and is molten. Whereas solidification, a substance-to-substance bond between the filler material and the base material is created.

Typical DURUM-products:
DURMAT® 59 PTA, 61 PTA, 505 PTA, S6 PTA
 

Oxy-acetylene Welding

Oxyacetylene welding, also known as Oxy-fuel Welding (OFW), is a gas welding process in which coalescence is produced by a flame of oxygen and acetylene gases mixed together at the point of ignition. With this family of processes, the base metal and a filler rod are melted using a flame produced at the tip of a welding torch. Fuel gas and oxygen are combined in the proper proportions inside a mixing chamber in the torch. Molten metal from the plate edges and filler metal, if used, intermix in a common molten pool and join when cooling. Commonly-used fuel gases include acetylene, propylene, propane and natural gas. The equipment used in oxyacetylene welding is low in cost, usually portable, and versatile enough to be used for a variety of related operations such as bending and straightening, preheating, post-heating, surfacing, brazing, and braze welding. Among commercially available fuel gases, acetylene most closely meets the requirements for all these applications. A minimal dilution with the base material makes OFW suitable for surfacing applications. Further an advantage is that the welder can exercise precise control over heat input and temperature, independent of the addition of filler metal.

Typical DURUM-products:
DURMAT® A, B, BK, NIA, NI3, CS, 50-WSC
 

Shielded Metal Arc Welding (SMAW)

Shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or informally as stick welding, is a manual arc welding process that uses a consumable electrode covered with a flux to lay the weld.

An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined. The workpiece and the electrode melts forming a pool of molten metal (weld pool) that cools to form a joint. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.

Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's first and most popular welding processes. It dominates other welding processes in the maintenance and repair industry, and though flux-cored arc welding is growing in popularity, SMAW continues to be used extensively in the construction of heavy steel structures and in industrial fabrication.

Typical DURUM-products:
DURMAT® E, NISE
 

Laser Cladding

Laser Powder cladding produces a high quality clad having extremely low dilution, low porosity and good surface uniformity. Moreover, laser cladding transfers minimal heat input into the part which minimizes distortion and the dilution between base material and hard-facing. The typically dilution rate is less 10 %, depend on the application. The process avoids the loss of alloying elements or hardening of the base material. Laser Poeder cladding focuses and controls weld depth, offering a clean metallic bond with minimal heat affected zone and fine grain structure, which tends to improve the the resistant against corrosion and abrasion. By Laser Powder cladding a Laser beam melts slightly the surface of a metal part. Filler material as powder is fed by a gas stream towards this interaction zone of Laser and melt pool. Thereby, a metallurgically bond, pore free layer with minimal dilution is formed. Deposition rates are up to 8 kg/hour, and surfacing thickness from 0.5 to more than 4 mm.

Typical DURUM-products:
DURMAT® 114 LAS, 163 LAS, 625 LAS
 

Submerged Arc Welding (SAW)

Similar to MIG welding, SAW involves formation of an arc between a continuously-fed bare wire electrode and the workpiece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the workpiece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. As the arc is completely covered by the flux layer, heat loss is extremely low. This produces a thermal efficiency as high as 60 % (compared with 25 % for manual metal arc). There is no visible arc light, welding is spatter-free and there is no need for fume extraction.

SAW is usually operated as a fully-mechanised or automatic process, but it can be semi-automatic. Welding parameters: current, arc voltage and travel speed all affect bead shape, depth of penetration and chemical composition of the deposited weld metal. Because the operator cannot see the weld pool, greater reliance must be placed on parameter settings.

Typical DURUM-products:
DURMAT® FD 310 UP, FD 341 UP, FD 476 UP