Materials Science Forum Vols. 539-543

Abstract: The oxidation of steels is critically influenced by its constituent alloying elements. These alter the classical three-phase model of the external oxide scales and in addition can introduce internal oxidised regions. This paper considers the oxidation of a number of nickel containing Fe based alloys of varying compositions, including stainless steel. These have been oxidised under different conditions to produce a number of scale morphologies, which have been characterised using two SEM based techniques; Electron Backscatter Diffraction (EBSD) and Energy Dispersive x-ray Spectroscopy (EDS). Results have shown that nickel promotes the formation of a fibrous internal scale, consisting of iron oxide particles (or iron/chromium oxide in the case of stainless steel) along grain boundary regions. Nickel is rejected from these oxide particles and consequently nickel content is enriched in neighbouring metallic areas.

Abstract: Charpy transition temperature TCVN and reference temperature To for 10Ni3CrMoV steel were determined using two different experimental techniques such as Charpy V-notch impact test technique and reference temperature To test technique. It was found that two methods provided different test results. The median master curve with upper and lower tolerance bounds was got from the test. The upper tolerance bound is often used for material design and application. At the same time the TCVN and To results were discussed for two kinds of heat treatment which are QT(Quenching and Temper) and QLT(Quenching, anneal and temper). JC (med ) K values calculated were 101 and 105MPam1/2 for the QT and QLT steels, respectively. These indicated that the QLT steels have the higher JC (med ) K , the lower reference temperature and lower energy (or fracture appearance) transition temperature(ETT50 or FATT50) than the QT steels. This was mainly related with the different microstructures of two kinds of heat treatment.

Abstract: In this study the effect of thermomechanical treatment on the microstructure of austenite and martensite and the mechanical properties of a medium carbon silicon chromium spring steel with different levels of impurities is investigated. Results are presented for conventional heat treatment and for thermomechanical treatment (TMT). Compared to conventionally heat treated samples austenite deformation improves strength and ductility. Thermomechanically treated samples are not prone to embrittlement by phosphorous. TMT influences the shape and distribution of carbides within the matrix and at prior austenite grain boundaries. It is shown that utilization of TMT is beneficial for increasing the ultimate tensile strength to levels above 2200 MPa and at the same time maintaining the ductility obtained at strength levels of 1500 MPa by conventional heat treatment. The endurance limit is increased and embrittlement does not occur.