Stainless steels were invented by Krupp Stahl in 1912 Richard J. Choulet, 1997. Stainless steels are iron metals in which little measures of C are added to its composing. Besides that, stainless steel contains about 10.5 % Cr that signifier thin, transparent and lasting chrome protective inactive oxide beds that contributes to its corrosion opposition feature. The corrosion opposition of steel and the stableness of the inactive bed additions with increasing chrome content in the metal. This protective oxide movie is self-healing in which regardless of how much of the surface is removed ; the steel is still corrosion resistant. In contrast to instances where C or low metal steels are protected from corrosion by metallic coatings such as Zn or Cd or by organic coatings such as pigment ( Technical Handbook of Stainless Steels, 2008 ) . The corrosion opposition of chromium steel steels is besides dependent on the metallurgical and processing variables. Although unstained steel possibly costlier than other metals with similar mechanical features yet it is normally used due to the chief proof of its improved corrosion opposition. The presence of Cr ( 16-28 % wt. ) and nickel ( 3.5-32 % wt. ) near to the little contents of the C ( normally below 0.1 % wt. ) assures a stable austenitic construction in the whole scope of the temperature ( from the temperature of bezant to the room temperature ) ( W. Ozgowicz & A ; A. Kurc, 2009 ) .
Stainless steels can be chiefly categorized into five distinguishable groups ; austenitic, ferritic, martensitic, duplex and precipitation hardening. Austenitic chromium steel steels are the most common and familiar types of chromium steel steel ( Michael F. McGuire, 2008 ) . Austenitic chromium steel steels have many advantages such as the easiness of its formability in which they can be made soft plenty to be easy formed utilizing similar tools that work with C steel, nevertheless they can besides be made improbably strong as they increase in hardness after traveling through cold working. At elevated temperatures, austenitic chromium steel steels do non lose their strength every bit quickly as ferritic Fe based alloys. The least corrosion-resistant versions of austenitic steels are able to defy the normal caustic onslaught of the day-to-day environment experienced by worlds, while the most corrosion-resistant classs is able to defy boiling saltwater. While holding so many advantages, austenitic steels do hold some disadvantages every bit good. Austenitic chromium steel steels are less immune to cyclic oxidization compared to ferritic classs due to their greater thermic enlargement coefficient that has the inclination to do the protective oxide surfacing to spall. Other than that, they may see emphasis corrosion checking if used under an environment to which they have deficient corrosion opposition.
Ferritic chromium steel steels can be considered the simplest and lowest cost class of chromium steel steels. They contain sufficient sums of Cr to get the better of their built-in degree of C dross and hit the minimal 11 % of Cr that gives it the unstained feature. The mechanical belongingss of ferritic chromium steel steels appear similar to austenitic steels in footings of strength, yet they lack the ductileness of austenitic steels and are limited at lower temperatures by crispness and softness at high temperatures. The corrosion opposition of ferritic chromium steel steels are hindered by their inability to use N. Ferritic chromium steel steels are basically free from stress-corrosion checking as they are below the threshold hardness for H embrittlement in body-centred three-dimensional ferric metals.
Duplex chromium steel steels are the newest and fastest-growing metal class of chromium steel steels. They are called semidetached house because they consist of ferrite and austenite stages at room temperature. Duplex chromium steel steels are exceptionally strong, have first-class stamina and corrosion opposition. Besides that, they besides exhibit exceeding opposition to stress-corrosion snap and corrosion weariness. Their restrictions are in their deficiency of cryogenic stamina and their inability to defy temperatures above 300AA°C without organizing embrittling stages. However, between temperatures of -100 and 300AA°C they are exceeding stuffs.
Martensitic chromium steel steels are the most marginally corrosion resistant among all the classs of chromium steel steel metals. The demand that they can be to the full austenizable bounds the sum of corrosion-resisting Cr and Mo that they can incorporate. Martensitic chromium steel steels are ever susceptible to stress-corrosion checking when their hardness exceeds Rockwell hardness of Rc 22. These restrictions combine to do their first-class belongingss useable in merely mild environments compared to other unstained steels. Their high strength and hardness for their comparatively low cost ensures that they are really utile technology stuffs.
The precipitation-hardenable classs of chromium steel steels are a extremely specialised household of chromium steel steels. The being of this class of chromium steel steel comes from the demand for a really high-strength stuff with good corrosion opposition. The precipitation-hardenable chromium steel steels exploit the low austenite stableness possible in the Cr and nickel chromium steel steels by doing the metal every bit thin as possible in composing that they are able to transform about wholly to martensite by thermic or mechanical intervention. The advantage that the precipitation-hardenable chromium steel steels have over the purely martensitic chromium steel steels is that they attain great strength with higher stamina and corrosion opposition than can be obtained through the hardening of martensite through C add-on. In add-on to that, they can be fabricated in a comparatively soft province and so hardened with really small alterations in dimension.
Martensitic and ferritic steels have magnetic features. Martensitic steels have low formability and are normally hardened by heat intervention. Duplex grades unstained steels are tougher than ferritic class steels and are more immune to emphasize corrosion checking than austenitic steels. Austenitic steels have a face-centered three-dimensional crystal construction which is really tough and malleable whereas martensitic steels crystallize in body-centered three-dimensional construction at low C concentrations. Martensitic steels are harder and stronger compared to austenitic steels.
Figure 1.1: Comparative Properties of the Stainless Steel Alloy Families
( Reprinted from the Technical Handbook of Stainless Steels, p.10, 2008 )
Stainless steel class 316L is made up of a composing of different elements such as C, Cr, Ni, Mo, etc. Stainless steel class 316L is a type of austenitic chromium steel steel which is widely used in many applications in the industry such as surgical and medical tools and implants, chemical and pharmaceutical industry, crude oil refinement equipment and fabric tube. This is due to its first-class opposition to corrosion and phosphates, sulfates and other salts, good formability and welding ability. 316L chromium steel steels have high work indurating rate during distortion and is by and large accepted that high work indurating rate is related to stacking mistake energy which controls the easiness of cross-slip, so that different distortion mechanisms can be activated at the different phases of distortion.
Figure 1.2: Composition of 316L Stainless Steel
( Reprinted from the American Society for Testing and Materials, F139-86, p.61, 1992 )
The chief aim of this undertaking is to analyze the consequence of mechanical intervention which in this research is turn overing procedure on 316L chromium steel steel. This undertaking is besides conducted to look into the mechanical belongingss of 316L unstained steel under cold working. Besides that, microscopic observation is besides conducted to qualify the microstructure of the stuff before and after mechanical intervention.
The chief range of this undertaking is to analyze and analyze the consequence of turn overing on the mechanical belongingss such as bending and tensile strength of 316L unstained steel.
1.3 PROBLEM STATEMENT
Metallic stuffs are frequently used to replace structural constituents of the human organic structure because they surpass plastic or ceramic stuffs in footings of tensile strength, fatigue strength, and break stamina ( M. Sumita & A ; S. H. Teoh, 2004 ) . Stainless steels are inferior to other implant metals due to its ductileness, easiness of machinability and besides its cost. However, under those machining procedures, the mechanical belongingss such as strength and hardness of the chromium steel steel may be affected.