K. J. Ducki

Quantitative description of the structure and substructure of hot - deformed Fe - Ni austenitic alloy

The paper presents the results of research concerning the influence of hot deformation parameters on the structure and substructure as well as the plastic properties of a Fe–Ni austenitic alloy. The research was performed on a torsion plastometer in the range of temperatures of 900÷1150°C, at a strain rate 0.1 and 1.0 s-1. Plastic flow curves have been drawn up and the interrelations have been determined between the process parameters and the recrystallized grain size, inhomogeneity and shape. Functional relations between the Zener-Hollomon parameter and the mean grain size after dynamic recrystallization have been developed and the hot deformation activation energy has been estimated. The examination of substructure on TEM allowed the calculation of structural parameters: the average subgrain area and the mean dislocation density. A detailed investigation has shown that the substructure is inhomogeneous, consists of dense dislocation walls, subgrains and recrystallized regions.

Precipitation and Growth of Intermatallic Phases in an Fe-Ni Superalloy during Prolonged Ageing

The influence of prolonged aging on the precipitation process of intermetallic phases, as well as carbide and boride in an Fe-Ni superalloy has been studied. The samples were subjected to a solution heat treatment at 980°C for 2 h and water quenched, and then aged at 715, 750 and 780°C for 0.5-500 h. The samples were analysed using transmission electron microscopy (TEM) and X-ray diffraction. Direct measurements on the electron micrographs allowed to calculate the mean diameter () of the γ’ phase. The growth step of the γ’ phase particles has been analysed on the basis of the LSW theory, as well as the activation energy of the γ’ phase coagulation has been estimated.

The Deformability of Fe-Ni Superalloy during High Temperature Deformation

The influence of initial soaking and parameters of plastic deformation on the deformability of A-286 superalloy have been presented. The hot-torsion tests were executed at constant strain rates of 0.1 and 1.0 s-1, at testing temperatures in the range 900-1150°C and were conducted until total fracture of the samples. Plastic properties of the alloy were characterized by worked out flow curves and the temperature relationships of flow stresses and strain limits. Activation energy for hot working Q was assessed for the alloy after two variants of previous heating, i.e. 1100°C/2 h and 1150°C/2 h.

Fatigue Behaviour of Carbide Precipitation Hardened Austenitic Steels

The paper presents the results of investigations of the microstructure and fatigue behaviour of two newly invented Cr-Ni and Cr-Ni-Mn austenitic steels of 13/13 and 12/8/8 type strengthened through carbide particle precipitation. The specimens of the investigated steels were subjected to tests after heat treatment, i.e. solution heat treatment (1200°C/0.5 h/water) and aged at a temperature of 700°C for 12 h, with cooling in air. The heat treated specimens were then subjected to low-cycle fatigue tests (LCF), carried out at room temperature and at an increased temperature of 600°C. Diagrams of fatigue characteristics of the investigated steels at room temperature as well as at elevated temperature have been worked up. It has been found that during low-cycle fatigue tests, at both temperatures, the investigated austenitic steels indicated a fatigue softening effect. The results of LCF at room temperature showed that the fatigue durability (Nt) of both austenitic steels is located in the range 0.8÷1.3×103 cycles. The results of low-cycle fatigue tests at an increased temperature 600°C indicated that the fatigue durability of the investigated steel was lower, and is located in the range Nt = 0.5÷0.6×103 cycles. It has been pointed out that the investigated austenitic steels are characterized by a stability of structure in conditions of cyclic fatigue.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Sintered Stainless Tool Steel

In the paper, the new highly alloyed Cr-V-Mo stainless tool steel produced via the powder metallurgy method was examined. The Elmax steel is a new-generation sintered tool steel characterised by high resistance to wear and corrosion and very good dimensional stability. The purpose of the paper was to analyse the influence of the rate of cooling from the temperature of austenitization and of an additional sub-zero treatment on the microstructure, phase composition and the curve of mechanical properties of steel during tempering. It has been found that a sub-zero treatment decreased the retained austenite fraction in the steel structure after hardening in oil or compressed air. The use of a sub-zero treatment on specimens after hardening had no significant effect on steel hardness after tempering, but it negatively affected the course of bending strength and impact strength of steel. Based on the obtained results it has been found that optimum mechanical properties for the Elmax steel were obtained after hardening from a temperature of 1080°C in compressed air (without a sub-zero treatment) and tempering at a temperature of 180°C.

Analysis of the Precipitation and Growth Processes of the Intermetallic Phases in an Fe-Ni Superalloy

The chapter characterizes wrought iron-base superalloys and comprises two main parts. The first describes the chemical composition, microstructure, and precipitation reactions in Fe-Ni, Ni-Fe, and Fe-Cr superalloys. The second part presents the influence of prolonged aging on the precipitation and growth processes in an Fe-Ni superalloy of A-286 type. The prepared specimens, after solution heat treatment at 980°C/2 h/water, were aged at temperatures of 715°C, 750°C, and 780°C with the holding time of 0.5-500 h. Transmission electron microscopy (TEM) and X-ray diffraction were used to examine their structures. It was found, that application of a single-stage aging causes precipitation processes of γ’ Ni3(Al,Ti), η Ni3Ti, β NiTi, G Ni16Ti6Si7, and σ Cr0.46Mo0.40Si0.14 intermetallic phases, as well as the carbide M23C6 and boride M3B2. The main phase precipitating during alloy aging was the γ’type intermetallic phase. It was found that the mean diameter of γ’ phase precipitates increases as a function of the cube root of aging time, which is consistent with the predictions based on the Lifshitz-Slyozow-Wagner (LSW) theory. The determined value of activation energy for the process of γ’ phase coagulation in the examined alloy was E = 297 kJ/mole.

TEM and X-Ray Examinations of Intermetallic Phases and Carbides Precipitation in an Fe-Ni Superalloy during Prolonged Ageing

The influence of prolonged ageing on the precipitation process of the secondary phases in an Fe-Ni superalloy of A-286 type has been studied. The samples were subjected to a solution heat treatment at 980°C for 2 h and water quenched, and then aged at temperatures of 715, 750 and 780°C at holding times from 0.5 to 500 h. Structural investigations were conducted using TEM and X-ray diffraction methods. The X-ray phase analyses performed on the isolates were obtained by anodic dissolution of the solid samples. After solution heat treatment the alloy has the structure of twinned austenite with a small amount of undissolved precipitates, such as carbide TiC, carbonitride TiC0.3N0.7, nitride TiN0.3, carbosulfide Ti4C2S2, Laves phase Ni2Si, and boride MoB. The application of ageing causes precipitation processes of γ-Ni3(Al,Ti), G (Ni16Ti6Si7), η (Ni3Ti), β (NiTi) and σ (Cr0.46Mo0.40Si0.14) intermetallic phases, as well as the carbide M23C6. It was found that the main phase precipitating during alloy ageing was the γ intermetallic phase.

The Deformability and Microstructural Aspects of Recrystallization Process in Hot-Deformed Fe-Ni Superalloy

The behaviour of metals and alloys during hot plastic working has a complex nature and it varies with the changing of such process parameters as (Zhou et al., 1994): deformation, strain rate and temperature. The high-temperature plastic deformation is coupled with dynamic recovery and recrystallization processes which influencing the structure and properties of alloys. One of crucial issues is finding the relationship between the hot plastic deformation process parameters, microstructure and properties. Since the sixties of the last century, theoretical and experimental investigations have been carried out to find those interdependence for steels and nickel alloys.

The hot-deformability and quantitative description of the microstructure of hot-deformed Fe–Ni superalloy

The paper presents the results of research concerning the influence of hot plastic forming parameters on the deformability and structure of a Fe-Ni austenitic alloy. The research was performed on a torsion plastometer in the range of temperatures of 900-1150 °C, at a strain rate 0.1 and 1.0 s-1. Plastic properties of the alloy were characterized by the worked out flow curves and the temperature relationships of flow stress and strain limit. The structural inspections were performed on microsections taken from plastometric samples after so called freezing. The stereological parameters as the recrystallized grain size, inhomogenity and grain shape have been determined. Functional relations between the Zener-Hollomon parameter and the peak stress and the mean grain size have been developed and the activation energy of the hot plastic deformation has been estimated. The examination of substructure on TEM allowed the calculation of structural parameters: the average subgrain area and the mean dislocation density. A detailed investigation has shown that the substructure is inhomogeneous, consists of dense dislocation walls, subgrains and recrystallized regions.