**1. Introduction**

Austenitic stainless steels, particularly 316L grade, have received much attention because of their good mechanical properties and high corrosion resistance [1]. This material contains a maximum carbon content of 0.03 by weight, which provides an extra level of corrosion resistance as well as the high rate of weldability. Several domains, notably marine and petrochemical industry, architecture, chemical production, and also biomedical sector, use this stainless steel due to its superior tensile strength, fracture toughness, and good formability [2]. 316L is non-magnetic and has excellent biocompatibility, which makes him a good candidate in the production of biomedical parts such as knee joints of total hip replacements [3]. In addition, 316L became very attractive to the industry owing to its low-cost and easy fabrication.

In almost engineering applications, an important interest is directed to the aspect of surface as it strongly influences the functional properties of mechanical parts such as their corrosion resistance, tribological behavior, and fatigue durability. Most failures of manufactured parts initiate from the outer layers which are exposed to the environmental conditions of service [4]. Mechanical, metallurgical, or chemical changes are the most common causes of the initiation of alterations in the surface [5]. In the case of wear, repeated contact actions between surfaces lead to the abrasion and/or delamination of the superficial layer which causes a loss in material quantity as well as in wear resistance. This loss is also produced in the case of corrosion where chemical changes in the surface are provoked after the contact between the surface and the environment under which the material operates. As a result, of these phenomena, the properties of surfaces become poor and unacceptable to fulfill the intended requirements of service. Some examples of components because of surface damages are: (a) environmental stress cracking of plastics by some chemical environments [6], (b) turbine vane and blade material surface deterioration caused by erosion [7], (c) surface corrosion [8], etc. The surface quality of materials therefore greatly needs attention to guarantee a good longevity of manufactured products.

The surface integrity notion, as it is understood is manufacturing processes, was defined by Field and Kahles [9] as *the inherent or enhanced condition of a surface produced in machining or other surface generation operation*. This term concerns many parameters:


Among the aforementioned parameters, surface roughness and microhardness are the major ones influencing the functional properties of parts. By far, the two parameters are remaining extensively studied to achieve better surface integrity. Surface roughness is a measurement of surface texture. A lower surface roughness indicates a smaller contact area with other materials, which is advantageous to improve corrosion resistance, frictional resistance, and fatigue life. Generally, the high quality of surface roughness is highlighted by the low values of amplitude parameters of surface topography. These parameters clarify the aspect of the topography which is related to the distance of a point on the surface from the mean plane, i.e., it gives information about the height or depth of a surface [10]. Hardness is the ability of a material to resist deformation. It is commonly preferred to produce surfaces with high values of microhardness as it prevents failures by wear and fatigue.

One way of improving the surface roughness and microhardness of parts is by applying surface treatments during the finishing step. Ball burnishing is a common mechanical surface treatment that has been widely applied on engineering parts for the finishing of their functional surfaces. This post-machining process is based on causing plastic deformation of the superficial layers through compressing a hard ball on the surface of the workpiece (**Figure 1**). As the ball is continuously moving, it transfers a material flow from peaks to valleys of superficial asperities. As a result, surface irregularities are reduced and compressive residual stresses are induced in the deformed layer. These two simultaneous actions improve the physical and mechanical characteristics of the surface which becomes smoother and also harder. Ball burnishing is easy, simple, and fast process which enhance the long-term properties of materials with low energy and almost no environmental pollution.

At present, there are rich literature sources about the effect of ball burnishing on surface roughness and microhardness of materials and also on the service performance of manufactured parts. The positive effect of this treatment in reducing the surface roughness [12–16] and raising the microhardness [12, 15–18] was widely reported. As a result, of these changes caused in surface characteristics, wear delamination was restricted as the interlocking movements of micro-irregularities were limited during friction [4, 19]. Fatigue resistance, yield and tensile strength, and also corrosion resistance were improved [20, 21].

*Surface Integrity of Ball Burnished 316L Stainless Steel DOI: http://dx.doi.org/10.5772/intechopen.101782*

**Figure 1.** *Ball burnishing concept [11].*

High surface finishing after ball burnishing is dependant on whether appropriate parameters of the process were well chosen or not. While the penetration depth and the initial state of the surface play a secondary role in obtaining good surface integrity, other parameters such as the burnishing force, the feed rate, and the number of passes contribute fundamentally to the final aspect of the treated surface [22]. Thus, it is very necessary to choose the right combination of process parameters and to master their effect on the surface integrity.

This research tackles the surface integrity of 316L after being subjected to the ball burnishing process. The effect of the number of burnishing passes, as an important process parameter, will be investigated. The results will be analyzed in terms of surface texture and microhardness after processing. At the sight of the results, an appropriate combination between burnishing force, feed rate, ball size, and a number of passes shall be proposed to execute the operation according to the right objective. This is important for 316L to confer its parts the special properties intended in the different industrial applications.
