Toward Eliminating Discontinuous Yielding Behavior of the EA4T Steel

Cold-rolled EA4T steel was heat-treated by inter-critical holding at 755 °C for 90 s, 120 s, 180 s, and 240 s, respectively, and then quenching in water. The tensile testing results of the EA4T specimens show an evident transition from the discontinuous yielding to the continuous yielding of the steel specimens by prolonging the holding time. A novel relationship between the discontinuous yielding behavior of tensile-deformed steel specimens and the carbide size was proposed based on experimental results and Cottrell’s theory. The model may provide a new clue for avoiding discontinuous yielding and improving mechanical properties of metals with static strain aging behaviors.

Effect of carbides on the wear resistance of white cast iron alloyed with 12.7 wt.-% Cr and nickel

White cast iron with about 12.7 wt.-% chromium was alloyed with Ni, W and Mo for heat treatment applications. Heat treatments were performed at a range of 850-1050 °C for 1 h in order to distribute M7C3 carbides homogeneously in an environment of high wear resistance. The contents of the C, Cr, Ni, Mo, Mn and Si elements selected for the alloys were similar, though a 6 wt.-% nickel concentration was chosen. Microstructural changes in the specimens were examined by scanning electron microscopy (SEM) and optical microscopy (OM). Macro-hardness, average carbide size and volume fraction were analyzed. Wear tests were carried out under different loads of 10, 20 and 30 N. It was seen that heat treatment changed the carbide size and homogeneous distribution of the carbides. Moreover, the addition of nickel to HCrWCI increased fracture toughness and reduced the wear rate.

Effect of Precipitation State on Strength and Toughness of Precipitation Hardened Hot Rolled Steel Sheet

In this work, to clarify the effect of carbide precipitation state on strength and toughness, Ti,V alloyed precipitation hardened ferrite single phase steel sheets with different carbide size were investigated. In order to change the precipitated particle size, cooling conditions after hot rolling were changed. Under condition A, steel sheets were cooled to 873K by water spray (for fine precipitation). Under condition B, steel sheets were air-cooled from 1053K for 20sec, then cooled by water spray to 873K (for coarse precipitation). The experimental results were following. The balance of tensile strength and Charpy absorbed energy was better in condition B. (Ti,V)C were observed in both conditions, but the size of (Ti,V)C were larger in condition B. From the above, it was suggested that as the carbide size become larger, the decrease in toughness per strengthening amount becomes smaller.

Structure Refinement of Spring Steel 51Crv4 after Accelerated Spheroidisation

Material research of the spring steels tries to meet requirements of the industry, which are mainly higher yield and tensile strength. Steel 51CrV4 is widely used for spring production. Optimization of its properties lies in tensile and yield strength enhancement without decrease in ductility in quenched and tempered state. This can be accomplished by structural refinement. One possible way to refine final quenched and tempered structure is refinement of the soft annealed structure before quenching. The article is devoted to accelerated carbide spheroidisation and refinement (ASR) and subsequent hardening of the 51CrV4 spring steel. Samples with different carbide size were prepared by conventional soft annealing in atmosphere furnace and ASR process by induction heating. Influence of the structural refinement on the properties of quenched and tempered state was studied.

Influence of Carbides on Stress Rupture Property of a Ni-Base Superalloy

This study aims to explore the influence of morphology and distribution characteristic of carbides on stress rupture property at high temperature. The stress rupture life at 850°C/325MPa was tested. Meanwhile, microstructure and fracture morphology of stress rupture specimens were observed by scanning electron microscopy. The types of carbides were identified and the carbide size was also measured. The results show that the alloys with small size, uniformly distribution and moderate number of carbides present a high stress rupture performance.