The Influence Of Cobalt On 304 Stainless Steel Microstructure And Property

Austenitic stainless steel is the 70 percent of the total of the stainless steel. Nickel is widely used in the austenitic stainless steel, which is a forming element in austenite. In recent year, as the price of nickel was rising and nickel ore was mined largely, the amount of nickel ore stored in the global was sharp declined .In order to solve this problem, People pay attention to the red ore, which contain the nickel and the cobalt ,and lose sight of sulfide ore. So, to understand the effect of cobalt in stainless steel, this, which was the development of nickel-based austenitic stainless steel, is of great significance.In this paper, the influence of different mass fraction of the cobalt on cast and forging state solution heat treatment 304 stainless steel in microstructure were studied by metallographic observation .Using scanning electron microscopy, chemical immersion, tensile test and impact test, such as analytical tools study the effect of cobalt on cast 304 stainless steel for corrosion resistance, as well as the forging state solution heat treatment mechanical properties and corrosion resistance. Through experiments and analysis, the conclusions are as following:For the as-cast 304 stainless steel, the different mass fraction of cobalt inhibited the ferrite formation in the 304 stainless steel. Increasing of the quantity of cobalt, the shape of ferrite was from sticks-crystal shape to short rod-shape, and the cobalt can also be reduce the grain size in austenite. The different mass fraction of cobalt affected significantly the inter-granular corrosion resistance in the 304 stainless steel. The relationship between the rate of inter-granular corrosion and the cobalt content increased exponentially. The cobalt content could also increase the sensitivity of pitting corrosion in the304 stainless steel. When the cobalt content was less than or equal to 0.3 percentage, the rate of the pitting corrosion was the same as the rate of sample with no cobalt. But when the cobalt content was more than 0.3 percentage, the rate of point corrosion increased significantly.For the forging 304 stainless steel was the state of heat treatment solution, the different mass fraction of cobalt inhibited the formation of ferrite, reduced the grain size of austenite. When the cobalt content was less than or equal to 0.5 percentage, with the cobalt content increasing, the tensile strength of steel was not changed significantly, the yield strength and hardness was slight increased, the shrinkage of section was reduced, but the plastic is still very good. The different mass fraction of cobalt little affected the inter-granular corrosion resistance. The cobalt increased the pitting sensitivity of steel. With increasing of the cobalt, the performance of the pitting corrosion resistance trended downward.