Applying the Masteralloy Concept for Manufacturing of Sinter Hardening PM Steel Grades

Sinter hardening is a powder metallurgy processing route that combines the sintering and the heat treating processes in one step by gas quenching the components immediately after they have left the high temperature zone of the furnace. It is both economically attractive and ecologically beneficial since it renders deoiling processes unnecessary. The slower cooling rates associated with gas compared to oil quenching however requires special alloy concepts different to those known from wrought steels. In the present study it is shown that by admixing atomized masteralloy powders consisting of suitable combinations of Mn, Cr, Si, Fe and C to base iron or pre-alloyed steel powders, sinter hardening PM steel grades can be produced that transform to martensitic microstructure at cooling rates of 2-3 K/s as typical for industrial sinter hardening. This is confirmed by CCT diagrams and hardness measurements. However, metallographic investigations are also necessary because in sintered steels, the cores of the largest base powder particles are alloyed very slowly during sintering and therefore tend to result in soft spots in the sinter hardened microstructure which are mostly not discernible in the CCT diagrams. Here, even slight pre-alloying of the base powder with Mo and/or Cr is helpful, both increasing the hardenability of the steels compared to base plain iron and avoiding soft spots in the microstructure.

Effect of CO2 Laser Fluence on Cladding Geometrical Dimensions Alternations

Geometrical dimensions could play a potential role in the function of laser cladding of nickel-base powder on the cold-rolled carbon steel substrate. The geometrical dimensions and their impact on the efficiency of the process of laser cladding of nickel-base powder (Ni -10wt% Al) on cold rolled 0.2% carbon steel substrate was investigated. This work focused on the effect of laser-specific energy input of CO2laser. The geometrical dimensions of cladding regions are including cladding width, cladding height, depth of dilution, contact angle, dilution area, cladding area, and heat-affected zone dimensions determinations. The laser power (1.8 kW) was used at different traverse speeds (1.5, 3.6, 5, 7.1, 8.6, 12.5 mm/s) with (3mm) laser beam diameter. The feed rate was kept constant after many preliminary claddings at approximately 11 g/min. Fluence values ranged from (48-400J/mm2), and the power density value was (255W/mm2). A minimum dilution percentage (25%) was obtained at the highest fluence value (400 J/mm2). Observations were measured using an optical microscope, scanning electron microscopy, and Image software. Obtained results indicated that the increase in the fluence leads to an increase in height of cladding, HAZ region but lower depth of dilution

Diffusion-alloying sintering of Cr–Mo pre-alloyed iron powders with carbon: The effect of the carbon introduction method on the sinter’s properties

The influence of the carbon introduction method on the microstructure and the mechanical properties of sinters produced from iron-based powders by diffusion-alloying sintering has been studied. Two methods of carbon introduction were tested: (1) Premixing of the base powder with graphite, and (2) Coating of the base powder with a carbon-containing substance. The results obtained could be summarized as (1) The microstructure and the mechanical properties depend on the method of carbon introduction; (2) The sinters produced from coated powders possess finer micro-structure, improved homogeneity, and in two out of three of the studied compositions, better mechanical properties. Based on the results obtained, a reasonable assumption was made that the method of carbon introduction affects the dissolution rate of the carbon additive, thus affecting the micro-structure and the mechanical properties of the sinter.