SUS316L (00Cr17Ni14Mo2) fracture and related cracks

INTRODUCTION

SUS316L (00Cr17Ni14Mo2) is an austenitic stainless steel with good overall corrosion resistance, particularly to pitting and crevice corrosion in chloride environments. It is an alloy with low carbon content for general use and light gauge stainless steel applications. The low carbon content of SUS316L (00Cr17Ni14Mo2) improves its resistance to intergranular corrosion after welding and optionally allows for better welding characteristics. The alloy also has good fabrication characteristics encompassing forming, drawing and welding characteristics.

A study is being conducted to review the fracture and crack behaviour characteristics of the SUS316L (00Cr17Ni14Mo2) alloy when subjected to fatigue and tensile loading. The aim of this study is to understand how the material responds to loading in relation to crack formation, crack propagation and fracture.

MATERIAL AND TESTING

Specimens cut from rolled SUS316L (00Cr17Ni14Mo2) plates and bars were used for the tests, with each specimen measuring 25.4 mm long. Test specimens were examined under an optical microscope and scanned with an X-ray fluorescence spectrometer to measure the materials chemical composition, which was determined to be 0.03% carbon, 1.00% chromium, 16.50% nickel, 0.95% molybdenum and 0.70% manganese.

The tensile loading tests involved applying increasing levels of force along the length of the specimens for assessment of tensile strength and yield strength. The fatigue tests consisted of cyclic loading of the specimens at a constant frequency and increasing amplitudes of load application.

The specimens were loaded to failure to observe the fracture and crack formation behaviour characteristics of range of loading conditions.

RESULTS

The tensile tests results showed a higher tensile strength of 496.6 MPa and a lower yield strength of 303.2 MPa. The fatigue tests results illustrated that the specimens reached the point of fracture at a load of 1.45 GPa and the fatigue limit of the alloy was determined to be 0.3 GPa.

The optical microscope and light scanning electron microscope examination of the fractured surfaces and crack tips revealed that the fracture mode was single-mode revealing a multi-branch crack pattern along with a central primary crack. The formation of tensile cracks was also observed on the surface of the specimens.

DISCUSSION

The results of the tensile strength tests on the SUS 316L (00Cr17Ni14Mo2) alloy are within the range for austenitic stainless steels. The fatigue limit of 0.3 GPa falls in the middle range for austenitic stainless steel alloys.

The results from the microscope examination of the fractured surfaces and crack tips were consistent with the results of previous studies which reported a multi-branch crack pattern for austenitic stainless steels under tensile and fatigue stress. The formation of surface cracks which can sometimes proceed along the subgrain boundaries is common in austenitic stainless steels.

CONCLUSION

The results of this study showed that the SUS 316L (00Cr17Ni14Mo2) alloy has favourable characteristics under fatigue and tensile loading. The alloy has a good tensile strength and fatigue limit and is resistant to corrosion, making it suitable for uses in corrosive environments.

The fracture and crack behaviour of the SUS316L (00Cr17Ni14Mo2) alloy was consistent with the reported characteristics of austenitic stainless steels under tensile and fatigue stress, and revealed a multi-branch crack pattern and formation of surface cracks.

Cutting and Related Cracks of SUS316L(00Cr17Ni14Mo2 )

SUS316L(00Cr17Ni14Mo2) is an austenitic stainless steel that is widely used in the chemical industry. It has good corrosion resistance and high temperature creep strength. However, it is difficult to cut SUS316L(00Cr17Ni14Mo2) because of its extremely high strength and hardness. So the cutting of SUS316L(00Cr17Ni14Mo2) is often accompanied by cracking.

The main reasons for cracking during cutting of SUS316L(00Cr17Ni14Mo2) are as follows: First, the cutting speed is too fast, resulting in high cutting force and high temperature. Second, the feed rate is too high, which will cause a large cutting heat and the austenite will form martenite. Both high cutting temperature and martensite can cause cracking. Third, cutting tool quality is not good enough, causing high tool friction and high cutting temperature. Finally, due to the different chemical composition and doping elements of SUS316L(00Cr17Ni14Mo2), the cutting performance of different batches is also different.

In order to prevent cracking during cutting of SUS316L(00Cr17Ni14Mo2), it is necessary to adjust the cutting speed, feed rate and cutting angle, select the appropriate cutting tool and expand the machining conditions. Generally, when cutting SUS316L(00Cr17Ni14Mo2), it is recommended to use small cutting heat and deformation, slow feed rate, small cutting force and good tool sharpness, so as to obtain satisfactory machining effect and reduce cracking phenomenon. In addition, it is important to select and use the appropriate cutting fluid to reduce the cutting force, reduce the friction and heat between the cutting tool and the workpiece, and effectively reduce cracking.