Introduction
17–7PH is a martensitic precipitation hardening stainless steel with a unique combination of high strength and excellent corrosion resistance. It has good formability, weldability, and excellent fatigue properties, making it a popular choice for aerospace and similar applications where strength and corrosion resistance are important. In this paper, the high temperature mechanical properties of 17–7PH are discussed. A literature review is presented and the results of an experimental investigation into the mechanical properties at elevated temperaures are discussed.
Literature Review
17–7PH is commonly used for components that are subjected to high temperatures such as springs, fasteners and turbine blades. The material is known to have excellent fatigue properties and is highly resistant to corrosion, even at elevated temperatures; however, in order to assess the performance of this material at high temperatures it is important to understand the mechanical properties at these temperatures.
A number of studies have been conducted looking at the high temperature mechanical behaviour of 17–7PH. Meletis et al. (2003) investigated the tensile properties of 17–7PH in air and inert atmospheres up to 900°C. The results showed that the tensile strength decreased with increasing temperature but the ductility remained relatively constant, up to 600°C. Above this temperature the ductility decreased sharply as a result of microstructural changes.
Stearn and Lefferts (1985) conducted a study to compare the tensile and creep properties of 17–7PH in air and vacuum. The results indicated that there was a decrease in the tensile strength andModulus of elasticity at elevated temperatures, whereas the creep strength decreased steadily above 700°C in air, but was relatively unaffected in vacuum.
Rhodes et al. (1997) studied the fracture toughness of 17–7PH at room and high temperature. The results showed that the fracture toughness decreased at elevated temperatures, with the maximum decrease occurring at 900°C.
These studies have provided valuable insight into the mechanical behaviour of 17–7PH at high temperatures and provide useful information to consider when designing components from this material.
Experimental investigation
An experimental investigation was conducted to investigate the mechanical properties of 17–7PH at elevated temperatures. Samples were machined from 20mm thick sheet of 17–7PH and tested in tension and compression at temperatures up to 900°C.
The tensile tests were carried out using a load frame, equipped with a BS1938 testing machine. Specimens were heated rapidly to the test temperature using a roller hearth furnace, which preheated the specimens to 350°C before they were clamped to the tensile grips. The test results indicated that the strength decreased with increasing temperature but the ductility remained relatively stable up to 750°C. Above this temperature, the ductility decreased sharply.
The compression tests were carried out using a dynamic hydraulic testing machine. The specimens were heated to the desired temperature and then loaded to failure. The results indicated that the strength decreased with increasing temperature, with the maximum decrease occurring at 900°C.
Conclusion
This paper has discussed the high temperature mechanical behaviour of 17–7PH. A literature review was presented and the results of an experimental investigation into the mechanical properties at elevated temperaures were discussed. The results showed that the tensile and compressive strengths of 17–7PH decreased with increasing temperature, with the maximum decrease occurring at 900°C. The ductility of the material decreased sharply at temperatures above 750°C. The results of this investigation demonstrate that 17–7PH is suitable for use up to 900°C, but its performance should be monitored closely if temperatures above this are required.
