Microstructure, Substructure and Mechanical Properties of 9CrNB Steel after Tempering

This paper deals with the analysis of microstructure and substructure of 9CrNB steel, after normalization at temperature of 1070 °C and tempering at 790 °C / 240 min. The tube was second time tempered at the following temperatures and holding times: 760 °C / 30 min (A1), 760 °C / 120 min (C1), 800 °C / 30 min (G1) and 800 °C / 120 min (I1). Microstructure after tempering consists of tempered martensite and bainite with lath morphology, while inhomogeneous redistribution of precipitates is visible. Substructure analysis of state A1 and I1 show, that a relatively large number of irregular, rod-shaped and oval carbide particles, often arranged in clusters, were precipitated at the primary original austenite grain boundaries. In case of state A1, the average size of these carbide particles is 300 nm and in case of state I1 the average size is 350 nm. A relatively large number of rod-shaped and oval shaped particles were found at the interface of the tempered martensite and bainite mainly in the form of clusters and also inside the tempered bainite with higher particle distribution. In the case of the state A1, they reached an average size of 150 nm. In some regions of substructure of the state I1, the fine carbide particles with an average size of 200 nm and coarse carbide particles with an average size of 400 nm were presented within the areas of tempered bainite. Particles were identified by EDX analysis and by selection electron diffraction. The mechanical properties after tempering were evaluated and compared with properties of P91 and P92 steel.

Effects of core sand type and heat treatment on solid particle erosion of core box AISI H13 tool steel

The paper reports on investigations into the erosion, microstructural features, and material removal mechanisms of AISI H13 core boxes eroded by two types of core sand (silica and chromite). Different heat treatment operations are carried out, namely martempering, carbonitriding, quenching, and tempering, in order to vary hardness, microstructure, and surface morphology. Scanning electron microscopy inspections show that erosion is not only a function of surface hardness of the target material but also of its microstructure. Erosion of martensitic microstructure, consisting of very fine carbides with a uniform martensitic substructure, is much less severe than erosion of a material characterized by dispersed coarse carbide. Hardness effects on the erosion process are discussed in terms of material removal modes.

Effect of Structure on Wear Resistance of Co-, Fe-, and Ni-Base Alloys

Alloy characteristics that relate directly to wear resistance are much sought after, but elusive. Attempts have been made to correlate wear resistance with mechanical and physical properties, including hardness, but only with limited success. During the course of this investigation, cast, wrought, and hard facing wear alloys were processed using various casting, consolidation and deposition techniques and evaluated using laboratory sand abrasion wear tests, and metal-to-metal (adhesive) wear tests. In general, superior abrasive wear resistance was obtained with those processing conditions that produced microstructures which contained coarse carbide morphologies. No general relationship between hardness and abrasive or adhesive wear was found in this processing study. Little effect of processing, structure or hardness was observed on metal-to-metal wear. Where chemical similarity and common structural condition between the commercial alloys tested allows comment on chemical effects, carbon appeared to be the most effective variable; particularly with abrasive wear where resistance increased with increasing carbon level and volume percent of carbide phases present.