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Performance and microstructure of stainless steel 1
Mar 23, 2017

Performance and microstructure of stainless steel 1

At present, there are more than 100 kinds of chemical elements  as known, and there are about more than and 20 kinds of chemical elements in the iron and steel materials commonly used in industry,also contained stainless steel. For the practice of people in the long struggle with the corrosion phenomenon and the formation of the stainless steel special steel series, the most common elements of a dozen, in addition to the basic elements of the iron steel, The greatest impact elements to affects the microstructure and properties of stainless steel is the carbon, chromium, nickel, manganese, silicon, molybdenum, titanium, niobium, cobalt, copper, nitrogen, etc.. In addition to carbon, silicon and nitrogen, these elements are the elements in the periodic table of chemical elements.

In fact, the industrial application of the stainless steel are exist at the same time and several dozen elements, when several elements coexist in a single entity in the stainless steel, their impact is much more complicated than when they are alone, because in this case should not only consider the elements of its function, but also pay attention to their influence each other therefore, the organization decided to stainless steel sum of effects of various elements.

1.The effect of various elements on the properties and microstructure of stainless steel

1-1. Cr in stainless steel the determinded effects

There is only one element that determines the nature of the stainless steel, which is chromium, each containing a certain amount of chromium. So far, there is no chromium free of stainless steel. Chromium has become the main factor to determine the performance of stainless steel, the fundamental reason is that the addition of chromium to the steel as an alloying element, to promote its internal contradiction movement to the development of resistance to corrosion damage. This change can be explained from the following aspects:

Chromium enhances the electrode potential of Fe based solid solution

Chromium absorbs iron electrons and make the iron passivation

Passivation is caused by the improvement of the corrosion resistance of metals and alloys due to the anodic reaction. There are many theories about the formation of metal and alloy passivation.

1-2. carbon in stainless steel the double abilities

Carbon is one of the main elements of industrial steel. The properties and microstructure of steel are largely determined by the content and distribution of carbon in steel. Effect of carbon on microstructure in stainless steel is mainly manifested in two aspects, one is the stable austenite carbon element, and the extent of a large (approximately 30 fold of nickel), on the other hand, because of the great affinity of carbon and chromium, the formation of a series of complex carbides and chromium. Therefore, from the two aspects of the strength and the performance of the corrosion resistance, the role of carbon in stainless steel is contradictory.

Understanding the impact of the rules, we can start oru actual usage of requirements , and choose the different carbon content of stainless steel.

For example, the most widely used in industry, the standard provisions of chromium content is at least 0Crl3 ~ 4Cr13 of the five stainless steel grades 12 to 14%, is the factors of carbon to form chromium carbide and chromium into consideration before deciding, aims to make carbon and chromium combined chromium carbide, chromium content the solution of chromium was in no less than 11.7% of the minimum.

In market,the 304 stainless steel angle is the most contains 0.1%,it is not accordance with the ASTM standard A479/484/276 max C0.08% though the angle stainless steel price is cheaper than the standard stainless steel 304 angle,so when buy stainless steel bars,not only stainless steel angle iron,please also note the carbon contents.

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