Investigations of Microstructures and Erosion–Corrosion Performance of Cast Boron-Bearing Stainless Steel

The microstructures and erosion–corrosion properties of boron-bearing stainless steel were researched by an erosion–corrosion tester, energy dispersive X–ray spectrometry, scanning electron microscope and X-ray diffraction analysis. The microstructures of as-cast, boron-bearing stainless steel contain M7(B,C)3, M2(B,C) borocarbides and the martensite matrix; the matrix has less chromium and more nickel than those in the M2(B,C) and M7(B,C)3. The microstructures in heat-treated, boron-bearing stainless steel consist of M7(B,C)3, M2(B,C) and M23(B,C)6 borocarbides and ferrite, and the Rockwell hardness of heat-treated, boron-bearing stainless steel is lower than that of as-cast steel. For Cr28 white cast iron and boron-bearing stainless steel, the mixing wheel with higher rotating speed leads to a higher erosion–corrosion weight loss, and as the impingement angle increases, the erosion–corrosion weight loss increases first, and then decreases. For any erosion–corrosion experiment conditions, the erosion–corrosion resistance of boron-bearing stainless steel is better than that of Cr28 white cast iron.

Improvement in the Resistance to Wear of Work-Rolls Used in Finishing Stands of the Hot Strip Mills

Work-rolls manufactured through the Indefinite Chill Double Poured (ICDP) method present an exterior work layer manufactured in a martensitic white cast iron alloyed with 4.5 %Ni, 1.7 %Cr, and 0.7 %Nb (wt.%). In its microstructure, there are abundant carbides of the type M3C and MC, which give high resistance to wear, and graphite particles which improve the service behaviour of the rolls against thermal cycling. The core of the rolls is manufactured in grey cast iron of pearlitic matrix and spheroidal graphite. These work-rolls are used in the finishing stands in Hot Strip Mills for rolling slabs proceeding from continuous casting at 1200 °C. Through the application of a Design of Experiments (DoE), an attempt has been made to identify those manufacturing factors which have a significant effect on resistance to wear of these rolls and to find an optimal combination of levels of these factors which allow for improvement in resistance to wear. To increase resistance to wear, it is recommended to situate, simultaneously, the liquidus temperature and the percentage of Si in the respective ranges of 1250–1255 °C and 1.1–1.15 (wt.%). Higher liquidus temperatures favour the presence of the pro-eutectic constituent rather than the eutectic constituent. The outer zone of the work layer, in contact with the metal sheet, which is being rolled, does not show the graphitising effect of Si (0.8–1.15 wt.%). On the contrary, it confirms the hardening effect of the Si in solid solution of the ferrite. The addition of 0.02% of Mg (wt.%) and the inoculation of 6 kg/T of FeB tend to eliminate the graphitising effect of the Si, thus favouring that the undissolved carbon in the austenite is found to form carbides in contrast to the majority formation of graphite.

Development and properties of austempered low alloyed white cast iron

This study examined the response of low-alloy white cast iron to austempering heat treatment. In addition, it investigated the microstructure and mechanical properties of austempered low-alloy white cast iron. The low-alloy white cast iron specimens were austenitized at 900 °C, followed by quick quenching into a salt bath at 375 °C, and held there for 15 to 120 minutes for austempering heat treatment. Microstructural features were studied by optical, scanning electron microscopes, and XRD analysis. The mechanical properties were determined by hardness and unnotched Charpy impact toughness tests. As a function of those austempering times, a microstructural map was constructed to show how the transformation products develop, quantitatively. The experimental results showed that the austempering heat treatment produced a microstructure consisting of eutectic carbides + ausferritic structure in low-alloy white cast iron. It can be concluded that the low-alloy white cast iron can be austempered, similar to ductile cast irons. Improved hardness and impact toughness values have been obtained in austempered low-alloy white cast iron.

Friction welding of high Cr white cast iron to AISI 1030 steel with Ni interlayer

In this study, the effect of friction time on microstructure and weldability of AISI 1030 steel with nickel interlayer and high chromium white cast iron welded by the friction welding method were investigated experimentally. The weld joints were produced with 2000 rpm rotational speed, under 80 MPa friction pressure, 150 MPa forging pressure, for 8 s forging time and 8, 10 and 12 s friction times. After the friction welding process, the microstructures of the weld interfaces were analyzed by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, elemental mapping and X-ray diffraction analysis. The results were lateron compared theoretically and experimentally. The increasing friction time led to high frictional heat input. The results indicated that friction time plays a vital role on the microstructure and weldability.