No abstract

The main problem of near‐net‐shape cast high speed steel toolings is the bad toughness due to the presence of relatively coarse structure and eutectic brittle carbide network. To overcome this problem intensive secondary cooling in oil immediately after casting was achieved, however special standard tool steels with high amount of austenite stabilizing elements were selected to give austenite + carbide in as‐cast condition. This eliminates the risk of martensitic transformation during intensive secondary cooling. Prespherodisation heat treatment at different temperatures was applied to improve the carbide morphology in cast structures of these steels. This is because traditional hardening of high speed (TS‐1 and TS‐2) cast steels showed severe deterioration in carbide morphology and increased noncoherency with the matrix. In this case, skeleton brittle carbide morphologies were detected in such steels. Impact toughness of prespherodised hardened high speed cast steel (TS‐2) was more or less higher than that of the normally heat treated steel, especially at section sizes lower than 20 mm. Meanwhile the prespherodised steel showed lower toughness at section sizes of more than 20 mm. The hot hardness for the same thickness and test temperature of normally hardened high speed steels was higher to some extent than that for prespherodised and hardened ones. However, the hot hardness increases as the size of sample increases, due to the gross of eutectic and secondary carbide.

A series of six Cr‐, Cr + Mo‐, Cr + Mo + V cold work cast tool steels were produced and investigated for microstructure, impact toughness and both experimental and industrial abrasive wear. Grain refinement of the steel matrix even in as‐cast condition was obtained on using 2.3 % Mo + 0.9 % V and that ensured increasing impact toughness and abrasion resistance. An optimum impact toughness of about 85 J‐cm−2 was obtained in air quenched (970°C) and tempered (450°C) Mo + V containing steels in which area fraction of carbides reached 38 %. The abrasion resistance improved in case of steels tempered at 250°C and had fine grain structure.

High chromium cast steel alloys are being used extensively in many industrial services where dry or wet abrasion resistance is required. Such steel castings are demanded for cement, stoneware pipes, and earth moving industries. In this research, five steel heats were prepared in 100 kg and one-ton medium frequency induction furnaces and then sand cast in both Y-block and final impact arm spare parts, respectively. Vanadium (0.5-2.5%) and boron (120-150 ppm) were added to the 18Cr-1.9C-0.5Mo steel heats to examine their effects on the steel microstructure, mechanical properties especially impact, fracture toughness and abrasion resistance. Changes in the phase transformation after heat treatment were examined using inverted, SEM-EDX microscopy; however, the abrasion resistance was measured in dry basis using the real tonnage of crushed and milled stoneware clay to less than 0.1 mm size distribution.

Iron-base superalloys are well known materials having excellent high temperature properties .They are used in turbo superchargers and turbine engines required for aerospace and power plants. In this investigation precipitation hardenable X5NiCrTi26-15 was used to study the influence of microstructural changes on the creep behavior at different conditions . Different creep cycles were applied for both base alloy and laser beam welded alloy (6kW CO2 ) namely at 600 , 625 and 650C at applied controlled creep stresses of 400 and 450 MPa . The base material sheet was used in as solution annealed state ( 30 min, 960 C, WQ ).The specimens were hardened in two steps (24h,760 C, FC and 16 h, 705 C,AC ) before being investigated . The microstructural changes due to grain boundary sliding, intergranual fracture perpendicular to the metal flow axis , and the type ,morphology of different secondary carbides were measured and discussed . To examine the changes in microstructure Philips EM 400 TEM with an acceleration voltage of 120KV, and SEM as well as light microscopy were used . It was found that , laser beam welded structure investigated after creep deformation at temperatures lower than 650C and at controlled stress of 400 and 450 MPa , showed a textured weld metal zone with dendrite having lower hardness combined with a higher creep resistance than that for base material .It was found also that creeping at 650C at the same stress values offsets any gain in creep resistance of welded joints as compared with that for the base material at the same conditions.