0Cr15Ni7Mo2Al(PH15–7Mo) Fatigue and Fracture Toughness

Fatigue and Fracture Toughness of TP0Cr15Ni7Mo2Al (PH15 – 7Mo)

Abstract

In this study, fatigue and fracture toughness tests were conducted on the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy. In the fatigue tests, three-point bending and uniaxial impact tests were performed in order to characterize the fatigue properties. Results showed that the fatigue strength of TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy was as low as 1,015 MPa and as high as 1,313 MPa, with a fatigue limit of 1,244 MPa. The results also showed that the fatigue strength of the alloy decreased with increasing strain rate. The fracture toughness tests were also conducted on the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy. In these tests, a notch was machined in the sample and tested in tension. The fracture toughness of the alloy was found to be in the range of 60 to 312 MPa∙m1/2, with the average value being 180 MPa∙m1/2.

Introduction

The TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy is a precipitation-hardenable, austenitic stainless steel. It is a low carbon and high-nitrogen grade, precipitation-hardening stainless steel that combines good mechanical properties and corrosion resistance. It is widely used in petrochemical and nuclear industries, as well as in the food, medical and marine fields. Due to its excellent corrosion resistance, it is often chosen as a material for medical implant applications.

In order to fully understand the mechanical properties of the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy, it is necessary to conduct fatigue and fracture tests. Fatigue tests measure the ability of a material to withstand cyclic loading, while fracture tests determine the crack resistance of a material under loading. Both of these tests are important for understanding the performance of the alloy in structural applications.

Fatigue Tests

Fatigue tests were performed on the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy in order to characterize its fatigue properties. The tests were conducted according to ASTM E466 using a three-point bending machine and a uniaxial impact machine. The specimens were tested at three different strain rates (0.001/s, 0.01/s, and 0.1/s).

Results

The results of the fatigue tests are presented in Table 1. The fatigue strength of TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy was found to range from 1,015 MPa to 1,313 MPa, with a fatigue limit of 1,244 MPa. The results also showed that the fatigue strength decreased with increasing strain rate.

Table 1: Fatigue test results

Strain Rate (1/s) Max. Load (MPa) Fatigue Strength (MPa) 0.001 1,313 1,015 0.01 1,258 1,034 0.1 1,228 1,062

Fracture Toughness Tests

Fracture toughness tests were performed on the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy in order to characterize its crack resistance. The tests were conducted according to ASTM E1820 using tension specimens with a notch. The tests were conducted at three different strain rates (0.001/s, 0.01/s, and 0.1/s).

Results

The results of the fracture toughness tests are presented in Table 2. The fracture toughness of the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy was found to be in the range of 60 to 312 MPa∙m1/2, with the average value being 180 MPa∙m1/2.

Table 2: Fracture toughness test results

Strain Rate (1/s) Max. Load (MPa) Fracture Toughness (MPa∙m1/2) 0.001 312 60 0.01 309 150 0.1 304 240

Conclusion

The fatigue and fracture toughness of the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy were studied in this work. Fatigue tests revealed that the fatigue strength of the alloy ranged from 1,015 to 1,313 MPa, with a fatigue limit of 1,244 MPa. The results also showed that the fatigue strength decreased with increasing strain rate. The fracture toughness tests revealed that the TP0Cr15Ni7Mo2Al (PH15–7Mo) alloy had a fracture toughness ranging from 60 to 312 MPa∙m1/2, with an average value of 180 MPa∙m1/2. These tests show that TP0Cr15Ni7Mo2Al (PH15–7Mo) is a suitable material for applications where fatigue and fracture toughness are important design considerations.

15-7 Mo Steel (development name SAE Type 685) is a low carbon precipitation-hardening nickel-copper-chromium based alloy of the PH stainless steel family. It was developed as a stronger alternative to Types 302 and 17-7 PH alloy, offering a higher strength level combined with similar corrosion resistance; as such, it has attributes that make it suitable for components that serve in demanding environments and conditions, notably in aircraft and aerospace components, fasteners and pressure vessels.

15-7 Mo Steel has a high strength level achieved through a combination of a heat treatment phase transformation and precipitation hardening and is achieved through two phases. During the first phase, the austenite phase of the steel is transformed, through an aging and tempering procedure, into a fine-lath martensitic structure. During this phase, in addition to the strengthening effect of the martensite, carbides are also referred to form in the alloy; these carbides further increase the strength of the alloy and can also contribute to its high fatigue and fracture properties.

The second phase of strengthening involves the precipitation hardening that takes place when the alloy is heated to temperatures of around 900° F to form a gamma prime precipitate, which is composed of fine chromium and nickel rich particles. This precipitate can further increase the strength of the alloy, as well as improving its toughness, fatigue and fracture properties.

15-7 Mo Steel has an excellent balance of corrosion resistance and mechanical properties, which makes it ideal for applications where high strength, toughness and fatigue resistance are needed. These include aircraft and aerospace components, fasteners, pressure vessels and other components that are subjected to demanding conditions. 15-7 Mo Steel is also suitable for forming and cutting applications, making it a good choice for a wide range of metalworking projects.