Intrinsic Workability Research Articles

Dynamic recrystallisation behaviour and intrinsic workability of 12%Cr USC rotor steel during hot deformation

ABSTRACT Hot deformation of 12%Cr USC rotor steel was investigated by hot compression testing over a temperature range of 900 °C to 1,200 °C at strain rates of 0.001 s−1–1 s−1 with the use of a Gleeble–1500D thermal-mechanical simulator. The true stress–strain curves were obtained and showed that the stress increased with a decrease in temperature, an increase in strain rate, or both. Based on the stress–strain curves, processing maps of 12%Cr USC rotor steel under various strains were established, and the Zener-Hollomon (Z) parameter was calculated, it increased with decreasing temperature or increasing strain rate. Combining the values of the Z parameter and the microstructure after thermal compression, it was found that dynamic recovery was the main softening mechanism at lnZ > 39.09, and dynamic recrystallisation (DRX) became the main softening mechanism at 39.09 > lnZ > 32.56. When lnZ < 32.56, DRX occurred completely, and a small amount of recrystallised grains formed. The deformed microstructures showed that 12%Cr USC rotor steel incurred a continuous dynamic recrystallisation mechanism, a discontinuous dynamic recrystallisation mechanism, and a geometric dynamic recrystallisation mechanism during the hot deformation process. The intrinsic workability of 12%Cr USC rotor steel was explored by analysing the processing maps. It was found that the best forging process parameters range of the material in the actual production process was a deformation temperature range of 1,100 °C to 1,200 °C and a strain-rate range of 0.01 s−1–0.1 s−1.

Design and Fabrication of a One Stand Hot Tandem Rolling Mill

Over the years, metalworking processes have emerged as a promising paradigm to modify materials' intrinsic workability and microstructural evolution. However, due to the stringent requirement of the state-of-the-art, non-uniform original grain structure of the metal ingot comprising large columnar grains growth in the direction of solidification, resulting in brittleness, weak grain boundaries, shrinkage, porosity, etc. remain a major bottleneck. This paper proposes a novel metalworking process to overcome this challenge. In particular, a one-stand hot tandem rolling mill that can break the grain structure and destroy the boundaries having uniform grain structures is developed. The proposed one-stand hot tandem rolling mill was constructed using 60 mm diameter work rolls, 150 mm diameter backup rolls, 120 mm diameter spur gears, a 3 hp electric motor, and a 50 mm diameter shaft. The components were installed, and the roll was fixed at a roll gap of 60 mm. Experimental investigations using a 65 mm aluminium sheet metal at a draft of 5 mm per pass after heating the metal sheet above its re-crystallization temperature were performed to validate the superiority of the proposed model. Available results indicate a robust improvement in the toughness, strength, and resistance of materials. Specifically, the results showed an efficiency of 86 % at an average draft of 4.3mm per pass.

Hot Deformation Behavior and Microstructure Evolution of 2219/TiB2 Al-matrix Composite

Hot compression tests for 2219/TiB2 Al-matrix composite were conducted on a Gleeble-3500 isothermal simulator in the temperature range of 300~500°C and strain rates of 0.01, 0.1, 1, 10s-1 to obtain true stress strain curves. The original Johnson-Cook model was calculated and used to describe the constitutive relationship of hot deformation behavior of this composite. After precision evaluation and analysis, a new modified Johnson-Cook model was proposed. Comparing with the original model, the new model has a lower absolute average relative error (AARE) of 6.4415% and a higher relative error (R) of 0.9852, which indicates better prediction precision. Meanwhile, to understand the intrinsic workability of this composite, processing map based on dynamic materials model was constructed. Two stable regions locating at 300~400°C&0.01~0.1s-1 and 420~500°C &0.01~1s-1 were identified by the processing map and the instable microstructure in the instability region validated the reliability of the processing map. Furthermore, the microstructure evolution was analyzed and the results revealed that the θ-phase reduced with the increasing temperature.

Shape Rememorization of an Organosuperelastic Crystal through Superelasticity–Ferroelasticity Interconversion

AbstractAs altering permanent shapes without loss of material function is of practical importance for material molding, especially for elastic materials, shape‐rememorization ability would enhance the utility of elastic crystalline materials. Since diffusionless plastic deformability can preserve the crystallinity of materials, the interconversion of diffusionless mechanical deformability between superelasticity and ferroelasticity could enable shape rememorization of superelastic single crystals. This study demonstrates the shape rememorization of an organosuperelastic single crystal of 1,4‐dicyanobenzene through time‐reversible interconversion of superelasticity–ferroelasticity relaxation by holding the mechanically twinned crystal without heating. The shape‐rememorization ability of the organosuperelastic crystal indicates the compatibility of superelasticity (antiferroelasticity) and ferroelasticity as well as the intrinsic workability of organic crystalline materials capable of recovering their crystal functions under mild conditions.

Shape Rememorization of an Organosuperelastic Crystal through Superelasticity-Ferroelasticity Interconversion.

As altering permanent shapes without loss of material function is of practical importance for material molding, especially for elastic materials, shape-rememorization ability would enhance the utility of elastic crystalline materials. Since diffusionless plastic deformability can preserve the crystallinity of materials, the interconversion of diffusionless mechanical deformability between superelasticity and ferroelasticity could enable shape rememorization of superelastic single crystals. This study demonstrates the shape rememorization of an organosuperelastic single crystal of 1,4-dicyanobenzene through time-reversible interconversion of superelasticity-ferroelasticity relaxation by holding the mechanically twinned crystal without heating. The shape-rememorization ability of the organosuperelastic crystal indicates the compatibility of superelasticity (antiferroelasticity) and ferroelasticity as well as the intrinsic workability of organic crystalline materials capable of recovering their crystal functions under mild conditions.

Characterization on hot deformation behavior of Ti-22Al-25Nb alloy using a combination of 3D processing maps and finite element simulation method

In hot deformation behavior, two indispensable parameters which are power dissipation efficiency (η) and flow instability domains (ξ) in the processing maps have been exploited in most of literatures. However, rarely caught sight of dynamic distribution of η and ξ. In this study, hot deformation behavior of Ti-22Al-25Nb alloy was investigated by using a combination of three-dimensional (3D) processing maps and finite element (FE) simulation to unveil the variations of η and ξ with temperature, strain and strain rate during hot forming process. The hot compression tests were performed in the temperatures range of 995–1075 °C and strain rates from 0.001 to 1.0s−1. According to the basic experimental data of isothermal compression tests, the intrinsic workability relevant to this alloy was evaluated comprehensively on the basis of true stress-strain curves and 3D processing maps. Moreover, the recommended processing domains are predicated to be within the temperatures range of 1050–1065 °C and strain rates range of 0.01–0.1s−1, with a peak efficiency of 55%. The results of FE simulation show spatial distribution regularities of η and ξ in the specimens corresponding to the three characteristic districts during compressive deformation process. In addition, microstructure observations indicate a reasonable correspondence between hot processing parameters and microstructure evolution.

On the increase of intrinsic workability and hot working temperature range of M42 ledeburitic super high steel in as-cast and wrought states

In order to remain competitive to powder metallurgy and spray forming, further improvements of a classical production route are needed and desired. This paper describes the means by which the intrinsic hot deformability may be improved and the temperature range of the safe hot working extended for AISI M42 super high speed steel, one of the most challenging materials with respect to hot deformability. A special hot compression procedure is described to determine appropriate soaking temperatures of as-cast and semi-wrought states. Moreover, conventional hot compression tests in the extended temperature range (850–1150°C) and strain rates range 0.001–5s−1 were carried out. The complex behaviour of carbides is discussed, which depends on the soaking temperature and time, deformation temperature and strain rate. Deformation conditions for improved crushing of initial eutectic carbides networks during the first stages of hot working are identified. Apparent activation energies for hot working in two temperature ranges and constants of the hyperbolic sine function are determined. The microstructure and respective carbides are characterised by field emission scanning electron microscope, optical microscopy, X-ray diffraction and the results compared to equilibrium thermodynamic calculations using ThermoCalc.

Study on hot deformation behavior and intrinsic workability of 6063 aluminum alloys using 3D processing map

Hot deformation in 6063 aluminum alloys was investigated by hot compression testing over the temperature range of 573–723 K with strain rates of 0.01–10 s−1 using a Gleeble 3500 thermal-mechanical simulator. Based on the experimental results, constitutive equations compensated with strain were developed to model the hot deformation behavior. The intrinsic workability was further analyzed by establishing three-dimensional processing maps. These maps were constructed based on dynamic materials model to delineate variations in power dissipation efficiency and flow instability domains. Combined with microstructure observation, recommended processing domains are predicated to be within the temperatures range of 673–723 K and strain rates range of 0.01–0.1 s−1. Under such conditions, the main softening mechanism is dynamic recrystallization. The results from these processing maps agree well with microstructure observation.

Hot Deformation Behavior and Intrinsic Workability of Carbon Nanotube-Aluminum Reinforced ZA27 Composites

Using a controlled thermal simulator system, hybrid carbon nanotube-aluminum reinforced ZA27 composites were subjected to hot compression testing in the temperature range of 473-523 K with strain rates of 0.01-10 s−1. Based on experimental results, a developed-flow stress model was established using a constitutive equation coupled with strain to describe strain softening arising from dynamic recrystallization. The intrinsic workability was further investigated by constructing three-dimensional (3D) processing maps aided by optical observations of microstructures. The 3D processing maps were constructed based on a dynamic model of materials to delineate variations in the efficiency of power dissipation and flow instability domains. The instability domains exhibited adiabatic shear band and flow localization, which need to be prevented during hot processing. The recommended domain is predicated to be within the temperature range 550-590 K and strain rate range 0.01-0.35 s−1. In this state, the main softening mechanism is dynamic recrystallization. The results from processing maps agree well with the microstructure observations.

Theoretical study on Cold Open Die Forging Process Optimization for Multipass Workability

Cold Workability limits strength enhancement of austenitic materials through cold deformation. The intrinsic workability is the material characteristic whereas state-of-stress workability is governed by nature of applied stress, strain rate and geometry of deformation zone. For Cold Open Die Forging (CODF), multipass workability is essential. In this work, FEM tool FORGE-3 is used to optimize CODF on hydraulic press by analysis of stress-strain profiles and use of Latham-Cockroft damage criterion. Study recommends optimized process parameters, die combinations and pass-schedules.

Flow characteristics and intrinsic workability of IN718 superalloy

This study focuses on deformation characteristics of superalloy IN718 by formulation of a new flow stress model and detailed evaluation of intrinsic workability through the generation of three-dimensional (3D) processing maps with the support of optical microstructural observations. Based on thermomechanical simulation tests using a Gleeble-1500 machine, the flow stress model for superalloy IN718 was built and the flow stress throughout the entire deformation process was described by a peak stress only depending on Zener–Hollomon parameter and strain. The developed model exhibited the strain softening due to dynamic recrystallisation (DRX). The intrinsic workability was further investigated by constructing 3D processing maps. The 3D processing maps described the variations of the efficiency of power dissipation and flow instability domains as a function of strain rate, temperature and strain, from which the favourite deformation conditions for thermomechanical processing of IN718 can be established.

Material driven workability simulation by FEM including 3D processing maps for magnesium alloy

The three-dimensional (3D) processing maps considering strain based on the two-dimensional (2D) processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element (FE) simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress (SOS) workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the appropriate process parameters.

Identification of optimal deforming parameters from a large range of strain, strain rate and temperature for 3Cr20Ni10W2 heat-resistant alloy

The intrinsic workability of 3Cr20Ni10W2 was investigated using processing maps constructed from the stress–strain data generated by isothermal compression tests with a height reduction of 60% over a temperature range of 1203–1403K and a strain rate range of 0.01–10s−1. As the true strain was −0.3, −0.5, −0.7 and −0.9, the responses of strain rate sensitivity (m-value), power dissipation efficiency (η-value) and instability parameter (ξ-value) to temperatures and strain rates were evaluated respectively. By the superimposition of power dissipation and instability maps, the stable regions with higher power dissipation efficiency (⩾0.3) and unstable regions were clarified clearly. As the true strain was −0.3, −0.5, −0.7 and −0.9, respectively, the area of instability regions decreased with increasing true strain from −0.3 to −0.7, while it increased with increasing true strain from −0.7 to −0.9. In further, in the stable area, on the basis of determination for domains with dynamic recrystallization (DRX) microstructural evolution, the DRX-predominant regions with higher power dissipation efficiency were identified and recommended. Then not only DRX-predominant domains were validated by the stable microstructures refined by DRX, but also the regimes of flow instabilities were validated by the microstructures involving cracks. The identification of optimal deforming parameters from a large range of strain, strain rate and temperature for 3Cr20Ni10W2 heat-resistant alloy contributes to designing reasonable hot deforming processes without resorting to expensive and time-consuming trial-and-error methods.

Hot workability characteristics of as-cast titanium alloy Ti–6Al–2Zr–1Mo–1V: A study using processing map

The intrinsic workability of as-cast Ti–6Al–2Zr–1Mo–1V alloy was investigated by using processing maps constructed from the stress–strain data generated by isothermal compression tests with a height reduction of 60% over a range of temperatures 1073–1323K and strain rates 0.01–10s−1. As the true strain was 0.3, 0.5, 0.7, and 0.9, respectively, the responses of strain rate sensitivity (m-value), power dissipation efficiency (η-value) and instability parameter (ξ-value) to temperature and strain rate were evaluated. By the superimposition of power dissipation and instability maps, the stable and unstable regions were clarified clearly. In further, in the stable area the regions have the highest efficiency of power dissipation (≥0.2) were identified and recommended. On the basis of determination for domains with dynamic recrystallization (DRX) microstructural evolution, the full DRX regions were identified in the processing map at true strain 0.3–0.9. Then not only the domains optimized were validated by DRX refined microstructures, but also the regimes of flow instabilities were validated by the microstructures involving wedge cracking and deformation twinning. The optimal working parameters identified by processing maps and validated by microstructure observations contribute to designing the reasonable hot forming process of Ti–6Al–2Zr–1Mo–1V alloy without resorting to expensive and time-consuming trial-and-error methods.

Identification for the optimal working parameters of as-extruded 42CrMo high-strength steel from a large range of strain, strain rate and temperature

Abstract The intrinsic workability of as-extruded 42CrMo high-strength steel was investigated by using processing maps constructed from the stress–strain data generated by hot compression tests with a height reduction of 60% over a range of temperatures 1123–1348 K and strain rates 0.01–10 s −1 . As the true strain was −0.3, −0.5, −0.7, and −0.9, respectively, the responses of strain rate sensitivity ( m -value), power dissipation efficiency ( η -value) and instability parameter ( ξ -value) to temperature and strain rate were evaluated. By the superimposition of power dissipation and instability maps, the stable and unstable regions were clarified clearly, and furthermore in the stable area the regions with higher power dissipation efficiency (≥0.2) were identified and recommended. As the true strain is −0.3, −0.5, −0.7, and −0.9, respectively, three domains were identified at each strain. The whole area of the domains increased with increasing true strain from −0.3 to −0.7, while it decreased with increasing true strain from −0.7 to −0.9. On the basis of determination for domains with dynamic recovery (DRV) or dynamic recrystallization (DRX) microstructural evolution, the full DRX regions were identified in the processing map at true strain −0.5 to −0.9, and the full DRV regions at true strain −0.2 to −0.9. Then not only the domains optimized were validated by DRX refined microstructures without any wedge crack, but also the regimes of flow instabilities were validated by the microstructures involving intercrystalline cavity, dynamic strain aging (DSA), deformation twinning. The optimal working parameters identified by processing maps and validated by microstructure observations contribute to designing the reasonable hot forming process of as-extruded 42CrMo high-strength steel without resorting to expensive and time-consuming trial-and-error methods.

Optimization of hot working parameters for thermo-mechanical processing of modified 9Cr–1Mo (P91) steel employing dynamic materials model

Intrinsic workability of modified 9Cr–1Mo steel has been studied in a wide range of temperatures (1123–1373 K) and strain rates (0.001–10 s −1). Using the experimental data obtained from isothermal hot compression tests, processing map at 0.5 true strain has been developed employing dynamic material model (DMM) approach. The activation energy map has been developed to substantiate the results obtained from processing map and to finalize the optimum processing parameters. Microstructural studies have been carried out to validate the domains of the processing map. The material shows localized deformation bands in the temperature range of 1150–1373 K at strain rates above 1 s −1 and exhibits abnormally elongated martensite laths at higher temperature (1373 K) and lower strain rates (0.001–0.01 s −1). The optimum domain for the hot deformation is found to be in the temperature ranges of 1250–1350 K and strain rate ranges 0.015–0.3 s −1 with a peak efficiency of 38%. In this domain, apparent activation energy is found to be 400 kJ/mol. The microstructure of the specimens deformed in this region exhibits defect free equiaxed grains.

Analysis of metal workability by integration of FEM and 3-D processing maps

Workability consists of two independent parts: state-of-stress (SOS) workability and intrinsic workability. The traditional processing maps proposed by Prasad on the base of dynamic material model (DMM) demonstrate the intrinsic workability depending on the material properties. The three-dimensional (3-D) processing maps including strain are put forward in this paper, which describe the variations of the efficiency of power dissipation and flow instability domains with strain rate, temperature and strain. The Gleeble-1500 thermo-mechanical tests of magnesium alloy AZ31B were conducted. The hot deformation behaviors in the temperature range of 250–400 °C and strain rate range of 0.001–1 s −1 are studied. According to the 3-D processing maps, the optimum domain of hot deformation is in the temperature range of 250–325 °C and the strain rate range of 0.1–1 s −1. For metals characterized by dynamic recrystallization (DRX) such as magnesium alloys, the 3-D processing maps are able to deal with the sensitivity of the workability to strain at elevated temperature. By integration of the 3-D processing maps and finite element simulation (FEM), the distributions and variations of stress, strain, strain rate, temperature and flow instability domains are obtained under different hot deformation conditions. This method demonstrates both SOS workability and intrinsic workability and can be considered as an effective way to analyze the workability of metal deformation.

Effect of alloying elements and microstructure on the processing parameters of α 2 aluminide alloys

The intrinsic workability of five Ti 3Al base aluminide alloys was studied using power dissipation (PD) maps. The effects of aluminium, niobium and molybdenum on the workability were studied. In one of the alloys, the effect of starting microstructure on workability was also studied. While increase of Al beyond about 24 at% considerably reduced the workability, increase of Mo even beyond 1 at% embrittled the alloy. The workability went through a maximum at around 16–17 at% Nb. The MA structure consisting of equiaxed α 2 exhibited better workability in comparison to cast structure consisting of widmanstatten α 2. Through dynamic recrystallization (DRX) of α 2 was readily observed in all the alloys, recrystallization of β/B2 could be achieved only statically.

Strategy for the design of thermomechanical processes for AISI type 304L stainless steel using dynamic materials model (DMM) stability criteria and model for the evolution of microstructure

The dynamic materials model (DMM) [1] is a proven technique for studying constitutive behavior of materials. In this model, the efficiency of power dissipation through microstructural changes, given by η = 2m/(m + 1), where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a DMM processing map. The different domains exhibited by the map are correlated with specific microstructural processes occurring during hot working. Prasad [1] has shown that flow instability will occur during hot deformation if ξ (e) = {∂ ln[m/(m + 1)]/ ∂ ln e} + m < 0, where e, is the strain rate. The variation of the instability parameter, ξ (e) with temperature and strain rate, constitutes an instability map, which may be superimposed on the processing map for delineating the regimes of flow instability. The optimal domains predicted by the DMM processing maps are quite wide. In practice, in a wide domain it is very difficult to control the microstructure of the product. Hence, some refining procedure needs to be established for the precise control of the microstructure during working. Malas and Seetharaman [2] proposed stability criteria based on DMM. According to them the optimal processing windows for safe working are: 0 < m ≤ 1, ṁ < 0, s ≥ 1, and ṡ < 0, where ṁ = ∂m/∂ ln e, s = ∂ log σ/∂(1/T ), ṡ = ∂s/∂ log e and T = temperature in K . The apparent activation energy Q = sRT/m, where R = gas constant. In this methodology the reasonable “safe” processing range corresponds to the processing condition where a desirable and fairly constant value of Q is operative. These criteria can be used to refine the safe processing window to achieve better microstructural control during processing. In order to control the development of microstructure during hot working, a new strategy for systematically calculating near-optimal control parameters for hot deformation process has been proposed [3]. This approach involves developing state-space models from available material behavior and hot deformation process models. The control system design consists of two basic stages, and analysis and optimization are critical in both stages. In the first stage, the kinetics of certain dynamic microstructural behavior and intrinsic hot workability of the material are used, along with an approximately chosen optimality criterion, to calculate the optimum strain (e(t)), strain-rate (e(t)), and temperature (T (t)) trajectories for processing. A suitable process simulation model is then used in the second stage to calculate process control parameters, such as ram velocity, die profiles, and billet temperature, which approximately achieve the strain, strain-rate, and temperature trajectories calculated in the first stage. This process design approach treats the deforming material as a dynamic system and involves developing statespace models from available material behavior and hot deformation process models. The design approach requires three basic components for defining and setting up the optimization problem: (1) a dynamic system model, (2) physical constraints, and (3) an optimality criterion. The system models of interest are material behavior and deformation process models. Constraints include the hot workability of the workpiece and the limitations of the forming equipment. Optimality criteria could be related to achieving a particular final microstructure (grain size), regulating temperature, and/or maximising deformation speeds. Fig. 1 describes the steps involved in the proposed new approach [3]. The microstructure development optimization determines optimal trajectories of strain, strain rate, and temperature. From these optimal trajectories, the process optimization stage determines optimal process control parameters, namely the die shape, the ram velocity profile and billet temperature. Goals of the first stage are to achieve enhanced workability and prescribed microstructural parameters. In the second stage, a primary goal is to achieve the thermo-mechanical conditions obtained from stage one for predetermined regions of the deforming workpiece. In the first stage, models of material behavior that describe the kinetics of primary metallurgical mechanisms such as dynamic recovery, dynamic recrystallization, and grain growth during hot working are required for analysis and optimization of material system dynamics. The objective is to define the acceptable ranges of temperature and strain rate over which the material exhibits a “safe” processing window. The complete details of this approach are available elsewhere [3]. The aim of the present investigation is to evaluate the constitutive flow behavior of austenitic stainless steel

Modelling of hot deformation for microstructural control

Bulk metal working processes are carried out at elevated temperatures where the occurrence of simultaneous softening processes would enable the imposition of large strains in a single step or multiple steps. Hot working also causes a significant change in the microstructure of the material and this contributes to one part of workability generally referred to intrinsic workability, which is sensitive to the initial conditions of the material and the process parameters. The other part, related to the state of stress existing in the deformation zone, is specific to a metal working process and may be controlled by changing the applied state of stress and/or the geometry of the deformation zone. An understanding of the constitutive behaviour of the material is essential for the optimisation of the intrinsic workability and control of microstructural evolution during hot working. In recent years, modelling techniques have been developed for this purpose and these are critically reviewed. These include: (1) the kinetic model, (2) the atomistic model, (3) the dynamic materials model, and (4) other models including activation energy maps with stability criteria and polar reciprocity model. Since the first two models do not lead to workability optimisation directly and are not useful for commercial alloys, the dynamic materials model has been developed. This model forms a bridge between the continuum mechanics and the microstructural mechanisms occurring during hot deformation, and consists of principles of irreversible thermodynamics of large plastic flow. The dissipated power is related to the rate of entropy production due to metallurgical processes obtained by partitioning the total power between that due to the temperature rise and the microstructural change. In view of the viscoplastic nature of hot deformation, the strain rate sensitivity of flow stress has been found to be the power partitioning factor. The development of processing maps using this model, their interpretation and application for optimising hot workability and control of microstructure are reviewed. The development of activation energy maps and their use in the control of microstructure are useful for obtaining robust process control for microstructural optimisation, while the use of the stability criteria puts undue restrictions on the processing regimes. Several mechanisms of hot deformation, with special reference to dynamic recrystallisation, are discussed in the light of results from processing maps obtained on a wide range of materials. Finally, the application of the processing maps in designing bulk metal working processes is briefly explained.