**2. Mechanisms for generating residual stresses in electric arc welding**

The importance of this study is based on the principle that the most widespread concept of residual stresses (RS) refers to stresses that remain in the component even though the external forces applied on the body are removed [1]. Otherwise, residual stresses are those that are not necessary to maintain the balance between the body and its environment [2].

The state of stresses causes a residual deformation that is self-balancing and, therefore, the resulting forces and moments that tend to zero [Eqs. (1) and (2)]. These equations describe the state of residual stresses considering a generic volume of the material and the moment of the forces acting on the material, respectively. Here, dV is the volume and dM is the resulting moment.

Mainly regarding metallic materials, residual stresses are a consequence of the interactions between time/temperature, stress/strain, and microstructure, that is, residual stresses arise from misfits *(eigentrains)* between different regions or different phases within the material, or even in different layers of atomic arrangements [3].

The material or characteristics related to this that influence the development of residual stresses include thermal conductivity, calorific capacity, thermal expansivity, modulus of elasticity and Poisson coefficient, thermodynamics and kinetics of transformations, transformation mechanisms and transformation plasticity [3].

$$
\Box \sigma \, dV = 0 \tag{1}
$$

$$\mathbb{L}\,dM = 0\tag{2}$$

**235**

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

temperature, heating time, stress-strain, and microstructure, that is, residual stresses arise from mismatches between different regions or different phases within the material, or still, in different layers of atomic arrangements [3]. Regarding the intrinsic characteristics of these materials, which influence the suggestion of RS, there are thermal conductivity, heat capacity, thermal expansiveness, elasticity modulus and Poisson's coefficient, in addition to the thermodynamics and kinetics of transformations, of the mechanisms of transformations and transformation plasticity [3]. Hence, therefore, the importance of studying residual stresses in

Another important problem surrounding the RS is its classification, and this is not yet well established, however, some of these classifications will be presented

a.The most common occurs according to the scale to which they self-balance:

• Type II: They correspond to the average stresses within each phase, are almost homogeneous in all microscopic areas, of a grain or parts of it in a material and are balanced through enough grains. This type of stress is also

• Type III: They are heterogeneous in the submicroscopic areas of a material, can be caused by accumulations of displacements (variations in interatomic distances) within a grain or elastic stresses around precipitates and are balanced

containing this type of stresses may change its dimensions.

b.According to their origins, that is, by the causes as they arose [2];

levels of residual stresses as do electric arc welding processes.

following phenomena occur almost simultaneously:

c.Or according to the effect on the behavior of the welded structure [4]

However, it is known that metal components need to go through at least one manufacturing process, even considering current processes, such as additive or more traditional manufacturing such as lamination, casting, forging, machining, thermal sprinkling or welding, each generates its pattern of residual stresses in the product, which is intended to produce [1]. However, few influences or generate high

Thus, the joining of metallic parts using the electric arc as a heat source brings together many welding processes used on a large scale in the industry. These arc welding processes cause abrupt thermal changes through the local heat source at different scales giving rise to the known residual welding stresses, that is, the consequent mismatch between different parts (base metal—BM, zone affected by heat—HAZ and weld metal—WM), different phases (microstructures) or different regions of the same part (different grains in the HAZ) contributing to their formation [2]. However, the phenomenology of this process is complex and the

1.In the heating occurs the formation of the weld pool (until the weld pool forms the piece heats up a lot, varying for each material) that expands and generates compressive flow from the neighborhood and when the weld pool cool causes

• Type I: These are stresses that act on macroscopic scales, involving several adjacent grains of the material, having an almost homogeneous character. Each interference in the balance of forces and moments of a volume

metallic materials, due to their great generation complexity.

below, according to the point of view of some areas [4]:

known as pseudo-macrostresses [5].

through small parts of a grain.

The RS are present in all materials that go through manufacturing processes, and in general, in metallic materials they are more evident and extremely studied, a fact that is due to the great use of these materials in the industrial one. Thus, in metallic materials, residual stresses are a consequence of the interactions between

## *Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

*Welding - Modern Topics*

no standardized system for the distribution of residual stresses, each author uses what suits him, there is no right or wrong way to observe the RS. But a main point can be considered, being the consensus of many authors is the magnitude of the RS, whether it is compressive or tensile, each type of stress has a specific attribute, which may be beneficial or not for the evaluated component. A methodology worth mentioning for the evaluation of RS is the ultrasonic technique of acoustic birefringence (AB), with this technique it is possible to evaluate a metallic component in a nondestructive and entirety. This line of research, presents an interesting approach, but not much explored. The use of different RS measurement and control technologies, widen the options for existing assessment, with the combination of these technologies it is possible to achieve a reduction in RS levels or even almost its complete elimination. Countless welding processes have been used to control RS. Recently a process has been introduced, the CW-GMAW process (Cold Wire—Gas Metal Arc Welding), showing promising results. The premise of the process is to reduce the temperature of the fusion arc/weld pool. In this context, this work addresses a review of the concepts of residual stresses generated by arc welding, as well as their magnitude and implications for welded structures. However, ways of measuring them are also explored, so that more efficient control methodologies, welding processes are developed, which together with the welding procedures, promote significant results

in reducing the values of residual stresses and deformations generated.

the body and its environment [2].

arrangements [3].

Here, dV is the volume and dM is the resulting moment.

**2. Mechanisms for generating residual stresses in electric arc welding**

The importance of this study is based on the principle that the most widespread concept of residual stresses (RS) refers to stresses that remain in the component even though the external forces applied on the body are removed [1]. Otherwise, residual stresses are those that are not necessary to maintain the balance between

The state of stresses causes a residual deformation that is self-balancing and, therefore, the resulting forces and moments that tend to zero [Eqs. (1) and (2)]. These equations describe the state of residual stresses considering a generic volume of the material and the moment of the forces acting on the material, respectively.

Mainly regarding metallic materials, residual stresses are a consequence of the interactions between time/temperature, stress/strain, and microstructure, that is, residual stresses arise from misfits *(eigentrains)* between different regions or different phases within the material, or even in different layers of atomic

The material or characteristics related to this that influence the development of residual stresses include thermal conductivity, calorific capacity, thermal expansivity, modulus of elasticity and Poisson coefficient, thermodynamics and kinetics of trans-

> ∫ = σ

The RS are present in all materials that go through manufacturing processes, and in general, in metallic materials they are more evident and extremely studied, a fact that is due to the great use of these materials in the industrial one. Thus, in metallic materials, residual stresses are a consequence of the interactions between

.*dV* 0 (1)

∫ = *dM* 0 (2)

formations, transformation mechanisms and transformation plasticity [3].

**234**

temperature, heating time, stress-strain, and microstructure, that is, residual stresses arise from mismatches between different regions or different phases within the material, or still, in different layers of atomic arrangements [3]. Regarding the intrinsic characteristics of these materials, which influence the suggestion of RS, there are thermal conductivity, heat capacity, thermal expansiveness, elasticity modulus and Poisson's coefficient, in addition to the thermodynamics and kinetics of transformations, of the mechanisms of transformations and transformation plasticity [3]. Hence, therefore, the importance of studying residual stresses in metallic materials, due to their great generation complexity.

Another important problem surrounding the RS is its classification, and this is not yet well established, however, some of these classifications will be presented below, according to the point of view of some areas [4]:

a.The most common occurs according to the scale to which they self-balance:


b.According to their origins, that is, by the causes as they arose [2];

c.Or according to the effect on the behavior of the welded structure [4]

However, it is known that metal components need to go through at least one manufacturing process, even considering current processes, such as additive or more traditional manufacturing such as lamination, casting, forging, machining, thermal sprinkling or welding, each generates its pattern of residual stresses in the product, which is intended to produce [1]. However, few influences or generate high levels of residual stresses as do electric arc welding processes.

Thus, the joining of metallic parts using the electric arc as a heat source brings together many welding processes used on a large scale in the industry. These arc welding processes cause abrupt thermal changes through the local heat source at different scales giving rise to the known residual welding stresses, that is, the consequent mismatch between different parts (base metal—BM, zone affected by heat—HAZ and weld metal—WM), different phases (microstructures) or different regions of the same part (different grains in the HAZ) contributing to their formation [2]. However, the phenomenology of this process is complex and the following phenomena occur almost simultaneously:

1.In the heating occurs the formation of the weld pool (until the weld pool forms the piece heats up a lot, varying for each material) that expands and generates compressive flow from the neighborhood and when the weld pool cool causes

the formation of contraction forces [6]; more particularly, the mass of the heated volume with the restrictive combinations and the contraction of the weld metal originate the thermal stresses.


One way to study the mechanism of generation of residual stresses in welded structures beyond experimentation and measurement is based on thermomechanical processes associated with computational mathematics and simulation with specific software. It is possible to obtain satisfactory results that help in the prediction, control and relief of the real state of residual stresses caused in the structure after welding in a qualified manner, that is, to perceive the effect that each factor or parameter alone has on the magnitude of such stresses. The starting principle is based on the models of [9, 10] referring to the effects of the temperature distribution of the heat source during welding and through these models the possible effects on residual stresses originated as proposed by [11, 12].

However, the great predominance of studies today has been consolidated with residual stresses being influenced by four groups of interrelated welding technology parameters.


**237**

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

vessels when in operation.

for local fusion of the weld.

*• Application parameters of operational techniques*: welding sequence, welding passes (continuous, intermittent, alternating, reverse, tensioning), pre and

*• Primary operating parameters:* such as I (current), U (voltage), welding speed (mm/s). These are, however, the most used, because they constitute the energy involved and used for metal fusion, its formula is described according to Eq. (3). Known as heat input (Hp), generic term of welding energy, usually in KJ/mm.

> =η

> > υ

*U I Hp* (3)

. . *s*

First, due to the greater constraints of safety criteria, the design of a conscious welded structure currently involves the skills of welding engineers and designers, considering not only the structure itself, but also the prior knowledge of complex interactions between metallurgical phenomena, aspects related to the mechanisms of connections and the mechanical behavior of all materials involved [13]. Where residual stresses, distortions and failures are perceived to be costly and complex control phenomena. Thus, considering that some areas of industrial production, for example, shipbuilding do not all projects quantify the initial welding imperfections explicitly, but these imperfections reduce the strength of the structure, besides being accumulative [14] and dangerous in the case of

In a way, the control of welding residual stresses starts from the choice of the type of material to be welded, that is, carbon steel, because it presents a composition basically formed by Fe and C and few alloying elements that interfere in phase transformations, it is considered in practice that this mechanism has negligible participation in the generation of RS in the weld metal of this type of material. Unlike medium and high alloy steels, stainless steel, Monel, Stellite, etc. these will have their inherent stress levels affected by chemical composition [15]. Thus, welding processes were developed through the formulation and manufacture of special consumables produced with this objective based on the principle of phase transformations at low temperatures (LTTW—low temperature transformation welding), where compressive residual stress formations and distortion reduction are induced [16, 17]. Other characteristics intrinsic to the material such as physicochemical properties (thermal conductivity, thermal expansion, density, specific heat, etc.), may favor for the generation or need preheating to relieve RS, such as copper and aluminum and their alloys, because they are good heat conductors, dissipate it quickly, most often requiring more intense localized sources, due to the difficulty

Other factors, very relevant that are correlated to the formation or increase of RS in welded components, refer to the parameters of joint geometry such as thickness (plate, pipes, flanges, etc.), type and angle of bevel. The temperature gradient is what differentiates the origin of residual stresses into a thin and coarse component. Where, in thin thicknesses, the weld pool can be considered 2D and in thick thicknesses, 3D, changing the process of heat transfer of the part and, consequently, the distribution of temperature that directly influences the process of RS formation [18]. The geometry of the joint in the form of butt weld, fillet weld, superimposed, among others also affects this distribution, by the way the heat is distributed, being

the T-joint is the one with the highest heat removal coefficient [19].

post heating, structure with or without restrictions.

Which also interfere in the shape and volume of the weld bead.

*Welding - Modern Topics*

welded joint.

defects [7].

GMAW, FCAW, SAW, etc.).

originated as proposed by [11, 12].

metal originate the thermal stresses.

the formation of contraction forces [6]; more particularly, the mass of the heated volume with the restrictive combinations and the contraction of the weld

2.The heat transfer and the flow of the liquid metal generate thermal gradients in the welded joint, besides actively acting in the shape and size of the melting pool, that is, in the volume of liquid metal. The measurement of heat transfer through the cooling rate helps in the prediction of Thermal Stresses (TS) that will affect the level of residual stresses formed in the

3.The volume of the liquid metal depends on the interaction of the welding parameters and the displacement of the electric arc that subjects the welded joint to various thermal cycles, can be differentiated when: (a) if the welding process uses only the electric arc to fuse the parts to be joined, i.e. when only the base metal is melted, autogenous welding (e.g. GTAW) or (b) if transfer of molten metal from the consumable occurs, mixing with the molten base metal simultaneously with the movement of the arc, the weld is deposition (SMAW,

4.Thermal stresses are stresses formed during the thermal cycle, both in heating and cooling, not existing in liquid metal; however, these stresses until they reach room temperature become the forms of residual stresses, distortions and/or

5.During the solidification of the weld pool, phase transformations occur influencing or not the formation of residual deformations, depending on the chemical composition of the metal alloy, there is less or greater influence on

One way to study the mechanism of generation of residual stresses in welded structures beyond experimentation and measurement is based on thermomechanical processes associated with computational mathematics and simulation with specific software. It is possible to obtain satisfactory results that help in the prediction, control and relief of the real state of residual stresses caused in the structure after welding in a qualified manner, that is, to perceive the effect that each factor or parameter alone has on the magnitude of such stresses. The starting principle is based on the models of [9, 10] referring to the effects of the temperature distribution of the heat source during welding and through these models the possible effects on residual stresses

However, the great predominance of studies today has been consolidated with residual stresses being influenced by four groups of interrelated welding technology

*• Welded structure design parameters*: the thickness of the plate or pipes (thin, medium or coarse), joint geometry (butt weld, fillet, double fillet, etc.) and type of chamfer (V, X, K, U, etc.), pass numbers, chemical composition of the

• *Available choice parameters*: Welding processes (autogenous process), such as GTAW or with metal deposition such as GMAW, FCAW, SAW, SMAW, PAW;

the mode used for welding (manual, mechanized, automated), etc.

the formation of residual welding stresses [8].

base metal and consumable (wire or rod).

**236**

parameters.


$$Hp = \eta \cdot \frac{U.I}{\nu\_s} \tag{3}$$

First, due to the greater constraints of safety criteria, the design of a conscious welded structure currently involves the skills of welding engineers and designers, considering not only the structure itself, but also the prior knowledge of complex interactions between metallurgical phenomena, aspects related to the mechanisms of connections and the mechanical behavior of all materials involved [13]. Where residual stresses, distortions and failures are perceived to be costly and complex control phenomena. Thus, considering that some areas of industrial production, for example, shipbuilding do not all projects quantify the initial welding imperfections explicitly, but these imperfections reduce the strength of the structure, besides being accumulative [14] and dangerous in the case of vessels when in operation.

In a way, the control of welding residual stresses starts from the choice of the type of material to be welded, that is, carbon steel, because it presents a composition basically formed by Fe and C and few alloying elements that interfere in phase transformations, it is considered in practice that this mechanism has negligible participation in the generation of RS in the weld metal of this type of material. Unlike medium and high alloy steels, stainless steel, Monel, Stellite, etc. these will have their inherent stress levels affected by chemical composition [15]. Thus, welding processes were developed through the formulation and manufacture of special consumables produced with this objective based on the principle of phase transformations at low temperatures (LTTW—low temperature transformation welding), where compressive residual stress formations and distortion reduction are induced [16, 17]. Other characteristics intrinsic to the material such as physicochemical properties (thermal conductivity, thermal expansion, density, specific heat, etc.), may favor for the generation or need preheating to relieve RS, such as copper and aluminum and their alloys, because they are good heat conductors, dissipate it quickly, most often requiring more intense localized sources, due to the difficulty for local fusion of the weld.

Other factors, very relevant that are correlated to the formation or increase of RS in welded components, refer to the parameters of joint geometry such as thickness (plate, pipes, flanges, etc.), type and angle of bevel. The temperature gradient is what differentiates the origin of residual stresses into a thin and coarse component. Where, in thin thicknesses, the weld pool can be considered 2D and in thick thicknesses, 3D, changing the process of heat transfer of the part and, consequently, the distribution of temperature that directly influences the process of RS formation [18]. The geometry of the joint in the form of butt weld, fillet weld, superimposed, among others also affects this distribution, by the way the heat is distributed, being the T-joint is the one with the highest heat removal coefficient [19].

Using models through the application of finite element methods (FEM) applied to the butt weld, with the decrease in thickness the RS increase [20]. A possible argument to describe the fact is that the absorption energy per unit of volume in thin plates is higher than in the thick ones, causing the inverse relationship between the thickness of the plate and the residual stresses. However, in T-joint welds, with the increase in plate thickness, the non-uniformity of the temperature alters the thermal expansion and the contraction during cooling, consequently, increases the RS. In this same type of joint, the increase in flange thickness strengthens the internal restriction by increasing these stresses in T joints [21]. The number of passes also influences the distribution of residual stresses, in fillet weld in T joint, a single pass on one side generates more stresses than when welding both sides [22]. The measurement of stresses at each weld pass was simulated in a joint containing six passes in plates of 16 mm thick hardened steel, where it was observed that the first 3 passes tend to generate more compressive stresses and the following passes 4, 5 and 6 showed the tendency to tensile stresses.

The choice of process also affects the magnitude of RS of electric arc welding, one of the studies that most involves processes with this type of local source, used four of these processes (SAW, DC GMAW, GMAW pulsed and CMT Fronius) and two more laser (one autogenous and one hybrid) applying in naval carbon steel (ASTM A131), where it was observed that the processes showed very similar peaks (near to 400 MPa) proportional to temperature peaks, differing by the width of the peaks, where the SAW has wider peaks [10]. On the other hand, the process and RS can present unexpected results, using the SMAW, FCAW and GTAW processes in ballistic steel butt welds, it was observed that the HAZ when subjected to projectile penetration testing, the SMAW process with higher residual stresses, withstood the test, and the others even with lower stress levels were penetrated [23].

Regarding the application parameters of the techniques, the two most researched are the constraints of the welded structure and the welding sequence. The degree of restriction refers to the resistance of the welded joint to the contraction and thermal expansion free of the heated material [24]. The constraint of the welded joint has a strong influence on the level of residual stresses, so much so that it can be considered that there are the inherent residual stresses produced naturally by the internal misfit and auto equilibrium and the reaction stresses that are a consequence of welded parts usually trapped by mechanical mechanisms. However, the basic principle for good welding practices reveals that longitudinal constraints more efficiently decrease residual welding stresses [25]. Otherwise, the deposition sequence of the welds also has a direct impact on the distribution of RS and distortions in the most varied forms and welded geometries. In studies involving the simulation of butt welds in plates and circumferential welds in pipes, this influence became notorious [26]. Simulating the J bevel deposition sequence in austenitic stainless steel tube-block joints (SUS304), the results indicated that this sequence has not only significant influence on the gradient of RS, but the last pass has a more significant gradient at the end [27].

Finally, no class of factors is further studied than the primary parameters of electric arc welding (U, I and νs), the interaction between these parameters generates the energy required for arc opening, producing thermal cycles and temperature peaks that generate thermal stresses and are the driving force of phase transformations during weld pool cooling. From this arc energy only part of it participates effectively in the fusion that generates the weld metal. It is important to mention that heat input has been erroneously referenced in many articles as synonymous with welding energy, which are not equal. However, its quantification is difficult due to numerous experimental difficulties [7, 28]. The basic relationship of the heat input with RS refers to its origin from the conversion of thermal stresses, as already mentioned.

**239**

**Figure 1.**

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

transformation in the case of ferrous alloys.

**3.1 Directions and magnitudes**

gradients on the z axis [25, 31].

Thus, any change in the primary parameters will change the formation settings of the residual stresses. That is, when the welding speed growth, the heat input decreases and residual stresses increase by producing a strait isotherm [12, 29]. In addition, the increase in welding energy is directly proportional to the magnification in RS present in the welded joint, also causing an enlargement the peak of tensile stresses [9, 24]. Otherwise, welding energy is so important by controlling the transformation temperature of weld pool phases that it is possible to combine the microstructure with acceptable resistance and toughness with low tensile or even compressive residual stresses. These transformations are governed almost entirely by austenitic

**3. Evaluation and measurement of residual stresses in welded structures**

The evaluation of RS states is often uncertain and the reason for this is related to several specific aspects that should be considered in the measurement of residual stress, since analyses are sometimes problematic and dubious and that residual stress notation is not always used adequately by some authors [30]. Because there is no standardization system that convinces and guides the distribution of residual stresses, each author uses what suits him. However, this point is paramount for proper understanding and knowing the possible effects that can cause on a welded part or structure. Thus, considering that there is no right or wrong way, the criterion used is based on the one most referenced by the specialized academic community, according to the model in **Figure 1**. Generally, the analyses are performed two-dimensionally, considering the longitudinal (σy) and transverse (σx) directions studied, always having as reference the weld bead. The stresses of the normal plane (σz) are less measured, but should not be discarded in any hypothesis, even though the thickness of the plate is conditioned. Finally, it is important mentioning that, in practice, the most significant component is composed of longitudinal stresses, and generally equals, on average, three times the transverse stresses to the weld bead, where welds of a single pass are considered and that there are no temperature

Still, within the study of residual stress generated by arc welding two parameters are essential for understanding it: (i) the behavior of this RS (in MPa), that is, if it

*Schematic representation of the distribution of RS directions on a three-dimensional plate.*

### *Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

*Welding - Modern Topics*

Using models through the application of finite element methods (FEM) applied to the butt weld, with the decrease in thickness the RS increase [20]. A possible argument to describe the fact is that the absorption energy per unit of volume in thin plates is higher than in the thick ones, causing the inverse relationship between the thickness of the plate and the residual stresses. However, in T-joint welds, with the increase in plate thickness, the non-uniformity of the temperature alters the thermal expansion and the contraction during cooling, consequently, increases the RS. In this same type of joint, the increase in flange thickness strengthens the internal restriction by increasing these stresses in T joints [21]. The number of passes also influences the distribution of residual stresses, in fillet weld in T joint, a single pass on one side generates more stresses than when welding both sides [22]. The measurement of stresses at each weld pass was simulated in a joint containing six passes in plates of 16 mm thick hardened steel, where it was observed that the first 3 passes tend to generate more compressive stresses and the

following passes 4, 5 and 6 showed the tendency to tensile stresses.

test, and the others even with lower stress levels were penetrated [23]. Regarding the application parameters of the techniques, the two most researched are the constraints of the welded structure and the welding sequence. The degree of restriction refers to the resistance of the welded joint to the contraction and thermal expansion free of the heated material [24]. The constraint of the welded joint has a strong influence on the level of residual stresses, so much so that it can be considered that there are the inherent residual stresses produced naturally by the internal misfit and auto equilibrium and the reaction stresses that are a consequence of welded parts usually trapped by mechanical mechanisms. However, the basic principle for good welding practices reveals that longitudinal constraints more efficiently decrease residual welding stresses [25]. Otherwise, the deposition sequence of the welds also has a direct impact on the distribution of RS and distortions in the most varied forms and welded geometries. In studies involving the simulation of butt welds in plates and circumferential welds in pipes, this influence became notorious [26]. Simulating the J bevel deposition sequence in austenitic stainless steel tube-block joints (SUS304), the results indicated that this sequence has not only significant influence on the gradient of RS, but the last pass has a more

The choice of process also affects the magnitude of RS of electric arc welding, one of the studies that most involves processes with this type of local source, used four of these processes (SAW, DC GMAW, GMAW pulsed and CMT Fronius) and two more laser (one autogenous and one hybrid) applying in naval carbon steel (ASTM A131), where it was observed that the processes showed very similar peaks (near to 400 MPa) proportional to temperature peaks, differing by the width of the peaks, where the SAW has wider peaks [10]. On the other hand, the process and RS can present unexpected results, using the SMAW, FCAW and GTAW processes in ballistic steel butt welds, it was observed that the HAZ when subjected to projectile penetration testing, the SMAW process with higher residual stresses, withstood the

Finally, no class of factors is further studied than the primary parameters of electric arc welding (U, I and νs), the interaction between these parameters generates the energy required for arc opening, producing thermal cycles and temperature peaks that generate thermal stresses and are the driving force of phase transformations during weld pool cooling. From this arc energy only part of it participates effectively in the fusion that generates the weld metal. It is important to mention that heat input has been erroneously referenced in many articles as synonymous with welding energy, which are not equal. However, its quantification is difficult due to numerous experimental difficulties [7, 28]. The basic relationship of the heat input with RS refers to its origin from the conversion of thermal stresses, as already mentioned.

**238**

significant gradient at the end [27].

Thus, any change in the primary parameters will change the formation settings of the residual stresses. That is, when the welding speed growth, the heat input decreases and residual stresses increase by producing a strait isotherm [12, 29]. In addition, the increase in welding energy is directly proportional to the magnification in RS present in the welded joint, also causing an enlargement the peak of tensile stresses [9, 24]. Otherwise, welding energy is so important by controlling the transformation temperature of weld pool phases that it is possible to combine the microstructure with acceptable resistance and toughness with low tensile or even compressive residual stresses. These transformations are governed almost entirely by austenitic transformation in the case of ferrous alloys.
