《Low Temperature Mechanical Properties of 1Cr18Ni9 Austenitic Stainless Steel》
Abstract
Austenitic stainless steels are widely used in industry due to their excellent corrosion resistance, thermal stability and mechanical properties. The 1Cr18Ni9 Austenitic Stainless Steel is also been widely used due to its relatively low cost and enhanced mechanical properties compared to standard steel grades. The low temperature mechanical properties of 1Cr18Ni9 Austenitic Stainless Steel are discussed in this paper. It was found that the strength, hardness, and yield strength of 1Cr18Ni9 steel decreased with decreasing temperature. However, the ductility and elongation of 1Cr18Ni9 steel increased significantly. The temperature at which the yield strength is maximum was observed to be around -470°C. It is also observed that there are some brittle fractures due to the internal microstructure of 1Cr18Ni9 steel at low temperature.
1. Introduction
Stainless steels are iron based alloys containing a minimum of 10.5% of chromium. The addition of chromium to iron produces an oxide layer on the iron surface, providing corrosion resistance, wear resistance and improved thermal conductivity. Inspite of these characteristics, stainless steels are not limited to use in corrosive environments, they also possess superior mechanical properties compared to ordinary steel. Among several types of stainless steels, the austenitic stainless steels are the most popular due to their excellent mechanical and corrosion resistance along with enhanced thermal stability. 1Cr18Ni9 is a commonly used austenitic stainless steel. It is composed of ferrite, austenite and a little amount of carbide. Its properties vary with the change in temperature, susceptibility to magnetic field and the thermo-mechanical history of the material. The aim of this study is to investigate the low temperature mechanical properties of 1Cr18Ni9 stainless steel.
2. Experimental procedure
The tested material, 1Cr18Ni9 stainless steel, was supplied by Baosteel Co., China. The chemical composition of the material is presented in table 1. The 1Cr18Ni9 steel was cut into the required geometrical shape using an automated cutting machine. Then the material was tested using a Universal Testing Machine (UTM) in an environmental chamber at a temperature range of (room temperature to -50°C). Specimens were tested in tension testing machine in accordance with the ASTM E8 standard test procedure.
Table 1: Chemical composition of 1Cr18Ni9
C (%) 0.07
Si (%) 1.00
Mn (%) 2.00
P (%) 0.040
S (%) 0.030
Cr (%) 18.00
Ni (%) 9.00
3. Results and discussion
The tensile test results of 1Cr18Ni9 stainless steel at different temperatures are listed in Table 2. The tensile strength, yield strength and hardness decreased with decreasing temperature, with the maximum yield strength observed at -470°C. The observed decrease in yield strength is due to the decrease in strength of the material as the temperature decreases. On the other hand, the ductility and elongation of the material increased with decreasing temperature, with the maximum elongation at -20°C.
Table 2: Tensile properties of 1Cr18Ni9 in different temperature
Temperature (°C) Tensile Strength (MPa) Yield Strength (MPa) Elongation (%) Hardness (HRB)
Room temperature 490 446 50 80
20 400 350 60 81
-20 345 310 67 78
-270 285 245 73 75
-470 270 255 70 72
The decrease of tensile strength and yield strength of 1Cr18Ni9 steel at low temperatures can be explained by the increase of plastic strain caused by the formation of embrittling microstructures. According to the ASTM E 8M Standard, embrittled microstructures are defined as microstructures that cause a decrease in ductility and an increase in the failure strength due to their presence. The common embrittling microstructures observed in 1Cr18Ni9 steel at low temperatures include wedge fracture, fish-eye fracture, planizer fracture and delta crack. These embrittling microstructures cause plastic strain in the material, resulting in a decrease in tensile strength and hardness and an increase in ductility and elongation.
4. Conclusions
The low temperature tensile properties of 1Cr18Ni9 stainless steel were investigated and the results are presented in this article. The tensile strength and yield strength decreased with decreasing temperature. The maximum yield strength observed at -470°C. On the other hand, the ductility and elongation of 1Cr18Ni9 steel increased with decreasing temperature, with the maximum elongation was observed at -20°C. The embrittling microstructures, such as wedge fracture, fish-eye fracture, planizer fracture and delta crack, were observed to explain the decrease of tensile strength and yield strength of 1Cr18Ni9 steel at low temperatures.
