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.

Improving the quality of bars from special alloy of the copper—nickel—silicon system

Possibilities of improving the quality of a special wear-resistant and heat-resistant alloy Cu—Ni—Si of the copper — nickel — silicon system used in the production of special-purpose electro-vacuum devices are analyzed.

Research on Vacuum Consumable Arc Remelting Furnace Control System with Drop Short Pulses Testing

Stable and Reliable automatic control system of Vacuum Consumable Arc Remelting (VAR) furnace is the key to smelt successfully special alloy metal and high temperature alloy metal, which is related to special properties of remelting ingot directly. This paper makes a deep study for drop short pulse testing and controlling system, and digital signal processing is used to obtain drop short pulse value with different frequency ranges. Firstly, basic theory analysis of drop short pulse measuring and controlling is researched. Secondly, high-speed digital signal processing technology is adopted to sample furnace voltage signal real-timely, band pass filter group is designed directly to process and calculate the amount of drop short pulses in different frequency ranges, Finally, the relationship between drop short pulse frequency and special alloy materials is analyzed, fuzzy PID control method is used to adjust electrode gap and control arc length. Field experiment results show the effectiveness of the whole drop short pulse testing and controlling system.

Strength of Alloyed Metal Castings Using Multiphase Models and Non-Linear FEM

High chromium cast iron material 1.4405 GX4CrNiMo 16-5-1 is successfully used in chemical process industry components loaded with hot, highly corrosive and abrasive at high pressures. Overheating test made a discontinuous yielding knee to appear caused probably by dissolution of carbon containing smaller phases but the overall strength and ductility are not affected. Microstructures are studied by optical and SEM microscopy and hardness measurements. This alloy has three main phases appearing as a mixture of rounded and lamellar phases. The work hardening behaviour is studied by analytical composite phase models and 2D FEM models with individual bilinear hardening phase models. The results agreed reasonably. FEM models showed the weak points of the alloy. Fit to test data was better with rounded phase than lamellar phase model. Combination of these tools is useful for innovative special alloy developments.