Cold Working Hardening Characteristics of 1Cr18Ni5Mn8N (AISI 1202) Chromium-Nickel-Manganese-Nitrogen Austenitic Stainless Steel
Introduction
1Cr18Ni5Mn8N (AISI 1202) chromium-nickel-manganese-nitrogen (Cr-Ni-Mn-N) austenitic stainless steel is a low-cost grade of stainless steel. It is now used in many industries due to its good mechanical properties and corrosion resistance. The main components of 1Cr18Ni5Mn8N (AISI 1202) steel are about 18 wt% chromium, 5 wt% nickel, 8 wt% manganese and nitrogen in traces. This steel has a high degree of plastic workability as compared to other stainless steels because of the solid solution of chromium, nickel and manganese. In this context, it is also important to study the cold working hardening characteristics of this steel material to gain a better insight of its behaviour under different working conditions.
Cold Working Hardening Characteristics
1Cr18Ni5Mn8N (AISI 1202) steel belongs to the 300 series of stainless steel and is highly resistant to corrosion. The cold working of this steel produces an increase in its strength and hardness with a corresponding decrease in its ductility. The cold working hardened structure of 1Cr18Ni5Mn8N (AISI 1202) steel shows a dual structure (ferrite and martensite) which can affect its mechanical properties significantly.
The austenitic stainless steel 1Cr18Ni5Mn8N (AISI 1202) is slightly harder than other austenitic stainless steels. But, the cold working of this grade of stainless steel can produce a significant increase in its hardness and strength, with a corresponding decrease in its ductility, due to the formation of a martensite phase. The martensite phase is formed when a cold-worked austenitic stainless steel undergoes a martensitic transformation below its martensite start temperature, where an increase in the strength and hardness is achieved at the expense of ductility.
Generally speaking, 1Cr18Ni5Mn8N (AISI 1202) stainless steel demonstrates a higher strain rate sensitivity than other austenitic stainless steels, and this factor plays an important role in controlling the cold working behaviour. The strain rate sensitivity consists of two components: strain hardening and strain rate hardening. Strain hardening results from the strain induced work hardening, where the yield strength of the steel increases as the strain increases. Strain rate hardening on the other hand, represents the incremental increase in yield strength as a result of increase in the strain rate.
In order to study the cold working hardening effects of 1Cr18Ni5Mn8N (AISI 1202) stainless steel, tensile tests were performed at different strain rates ranging from 0.001 to 1.0 s-1. The results indicated that the strain rate of the steel increases with increase in the strain rate tested. This is mainly due to the strain rate hardening of the steel. The strain hardening results showed that the yield stress of the steel increased with increase in strain up to a maximum strain of 0.6% which indicates a peak value in the hardening characteristics. The work hardening of 1Cr18Ni5Mn8N (AISI 1202) steel was also observed at a strain of 0.6%, with a hardening exponent (n) value of 0.32.
Conclusion
In conclusion, the cold working hardening characteristics of 1Cr18Ni5Mn8N (AISI 1202) austenitic stainless steel have been studied in this paper. The results indicate that the steel exhibits a dual structure during cold working, with a corresponding increase in its strength and hardness, and a decrease in its ductility as the amount of cold work increases. It is found that the strain rate sensitivity of the steel consists of two components, namely strain hardening and strain rate hardening, which contribute to the increase in hardness and strength of the steel. Furthermore, the work hardening of 1Cr18Ni5Mn8N (AISI 1202) steel is observed at a strain of 0.6%, with a hardening exponent value of 0.32.
