INSTITUTE OF TECHNOLOGY OF METALS

DEVEOPMENT OF THE INSTITUTE :: Laser beam hardening

        Laser beam hardening is employed to locally improve the surface properties of  components. Use of this treatment can increase wear and fatigue resistance in parts of steel and cast iron. Through a locally restricted heat treatment arises a minimum heat input, thereby minimized distortion. The associated high heating and cooling rates result in fine microstructures with good mechanical properties.

        Targets

        Optimization of surfaces through:

• Increasing wear resistance
• Improvement of the mechanical-dynamic properties.

        Process

        As in conventional hardening a hardness increase arises through martensitic transformation of the microstructure. The localized absorption of the laser beam creates a rapid increase in surface temperature to above the austenitisation temperature. A rapid cooling by conduction of heat into the relatively cool substrate generates the necessary transformation in appropriate steels. In addition, compressive stresses are generated in the hardened layer.

        Applications
        Laser beam hardening can be applied wherever localized improvement of hardness and fatigue life are required. Examples of successfully hardened components are found in general engineering (cutting knives, shafts, pump parts, guide ways, gears), power generation (turbine blades, pistons), tool in¬dustry (press, forming and injection tools) etc. Laser beam hardening can offer distinct advantages in terms of hardness, distortion, treatment speed and accu¬racy in comparison to many conventional processes.

        Advantages

• Fine microstructure with optimum mechanical properties
• Increased wear resistance
• Improved fatigue resistance
• Minimal heat affected zone and distortion through reduced heat input
• Economic treatments due to rapid process and CNC control
• Localized treatments possible
• Areas with difficult access often treatable

        Laser hardenable materials
        The range of treatable materials extends from low alloy steels, through to high alloyed tool steels and hardenable stainless steels. Various cast irons can also be easily laser hardened providing the ferrite contents are low.

        Equipment
        Ion Bond Laser technique in Nьrnberg employs different laser systems (CO2- and Nd:YAG-Laser) and Robot handling with a wide capacity and offers a wide range of treatments. Part weight: to 10 t, hardened depth: to 3 mm, length: to 5 m.

        Hardening technology using laser radiation makes it possible to carry out hardening without volume heating-up of parts. Such type of hardening is used for aluminum and aluminum alloy parts; hardening of such parts is considered as rather problematic due to its fusibility. This technology presupposes application of alloying component coating on a surface to be hardened and its subsequent laser beam remelting. Selection of alloying covering and regimes of laser treatment ensures formation of coatings with the required complex of physical and mechanical properties.
        Value of micro hardness of the hardened coating depends on saturating element and it may vary within the limits – from 2,000 to 11,000 MPa in accordance with selection of covering composition.
        Depth of the hardened coating may vary within the limits: 0.2….0.8 mm. While increasing speed of part movement relatively to laser beam a structure of the obtained coatings becomes finer.
        Wear resistance of the hardened surface is increased by 4….5 fold in comparison with an initial state without reduction of heat stability.
        Life-service increase is equal to 2…3 fold.