Strain-induced Precipitation Research Articles

Effect of Niobium Supersaturation in Austenite on the Static Recrystallization Behavior of Carbon Structural Steels

This work describes the effect of Nb supersaturation in austenite on the suppression of static recrystallization of austenite during an isothermal holding period following hot deformation. The investigation involved three carbon structural steels with varying Nb concentration at constant C (0.20 pct) and N (0.007 pct) levels. The isothermal double-hit deformation technique led to the determination of T5 pct and T95 pct (recrystallization-stop and full recrystallization temperatures, respectively) as a function of a true strain and interpass time. The results indicate that the T5 pct increases with increasing Nb supersaturation in austenite at a rate of 40 °C per 0.006 pct Nb supersaturation for a true stain ε=0.40. At each respective T5 pct, all tested steels exhibited an Nb supersaturation ratio ≥ 7.5 in austenite. A high, localized strain-induced precipitation of Nb(CN) was observed at the austenite subgrain boundaries in the unrecrystallized microstructure. This translated into higher values for local precipitate-pinning forces (FPIN), which were significantly higher than that predicted from equilibrium thermodynamics. The critical FPIN for retardation of static recrystallization was found to be 1.6 MPa at the respective T5 pct for each steel. The present study has contributed to advancing our knowledge of the interplay between Nb solute supersaturation and volume fraction of Nb(CN) precipitation in particular for carbon structural steels. It has also highlighted an opportunity to apply niobium, even an ultra-low addition (i.e., < 100 ppm) to commodity-grade structural steels to reduce overall alloying costs.

Effects of rolling deformation on precipitation behavior and mechanical properties of Al–Zn–Mg–Cu alloy

The effects of cold rolling (CR) with different hot rolling (HR) reductions on the precipitation behavior and mechanical properties of Al–Zn–Mg–Cu (AA7050) alloy are investigated by synchrotron small angle X-ray scattering (SAXS) and transmission electron microscope (TEM). With increasing HR reduction, the refinement degree of recrystallized structure increases, the dissolution and fragmentation of the second phase particles, and ultrafine sub-grains in shear bands occur. The number of spherical strain-induced precipitates (SIP) and ultrafine sub-grains increase due to high dislocation density before T6 heat treatment. After T6 heat treatment, the morphology of nanoprecipitates changes from rod-like to globular, the mean size of nanoprecipitates decreases, and the volume fraction increases with growing HR reduction. The 7050 alloy with 80 % HR reduction presents the highest yield strength of ∼513 MPa, the tensile strength of ∼571 MPa and elongation of ∼13.6 %. The strength increment is mainly ascribed to the contribution of precipitation strengthening and dislocation strengthening relevant to the small mean size and large volume fraction of nanoprecipitates. The improved ductility attributes to the refined recrystallized structure and multi-scale and multi-morphology particles. This investigation can guide further designing novel aluminum alloys by tailoring refined grain, highly dispersed nanoprecipitate structures for a preeminent combination of mechanical properties.

Effect of Nb and Mo on Austenite Microstructural Evolution During Hot Deformation in Boron High Strength Steels

This work has focused on the study of hot working behavior of boron high strength steels microalloyed with different combinations of Nb and/or Mo. The role of Nb and Mo during the hot deformation of low carbon steels is well known: both mainly retard austenite recrystallization, leading to pancaked austenite microstructures before phase transformation and to refined room temperature microstructures. However, the design of rolling schedules resulting in properly conditioned microstructures, requires microstructural evolution models that take into account the effect of the different alloying elements. In this specific case, the effect that high levels of molybdenum (0.5 pct) have in the recrystallization delay was evaluated. In that respect, hot torsion tests were performed in this work to investigate the microstructural evolution during hot deformation of four boron steels, with different Nb (0.025 pct) and Mo (0.5 pct) combinations. The retardation in recrystallization kinetics was modeled in all cases and measured kinetics agree with those predicted by equations previously developed for Nb–Mo microalloyed steels with lower Mo concentrations (< 0.3 pct). The strain-induced precipitation in the Nb and Nb–Mo bearing steels was also characterized. Finally, the fractional softening evolution during multipass rolling simulations was compared with MicroSim® model predictions, showing a good agreement with experimental results.

Achieving Superior High-Temperature Strength and Oxidation Resistance of TiAl Nanocomposite through In Situ Semicoherent MAX Phase Precipitation.

Increasing the service temperature of TiAl intermetallics is the main challenge for the development of next-generation aircraft. Dispersion-strengthening, an effective means to further improve the high-temperature performance of metals, fails to implement in TiAl intermetallics due to difficulties in interface optimization. Here, we successively fabricate a TiAl naocomposite with fully lamellar microstructures and homogeneously dispersed Ti2AlC nanoprecipitates via spark plasma sintering. The composite consisted of semicoherent interfaces among γ-TiAl/Ti2AlC precipitates/α2-Ti3Al, in addition to continuous polysynthetic nanotwins. Strong pinning effects as well as strain-induced nanoscale TiCr2 precipitation uplift the operation temperature of TiAl nanocomposites by more than 50 °C. Furthermore, we experimentally proved that semicoherent interfaces among in situ Ti2AlC precipitates and its surrounding matrix serve as oxygen diffusion barrier during isothermal oxidization and significantly drop down the mass gain of TiAl nanocomposites during operation, making the present nanocomposite a highly potential candidate for use as light-weight structural materials in automotive and aerospace industries.

Physical simulation of finish rolling of microalloyed steels in isothermal conditions

The aim of this work was to establish a temperature of finish rolling stage of Nb/Ti microalloyed steel containing 0.06 wt.% C, 0.77 wt.% Mn, 0.039 wt.% Nb and 0.015 wt.% Ti, using physical simulation. Samples were subjected to laboratory simulation at a twist plastometer at high temperatures, i.e. between 825 and 950?C. Five pass deformation and interpass times were selected in accordance with a processing parameters at five stand finishing hot strip mill. Restoration (recovery and/or recrystallization) behavior was evaluated by calculation of Fraction Softening (FS) and Area Softening Parameter (ASP) values. At 950?C all individual pass stress-strain curves, FS and ASP show full recrystallization in all interpass intervals. On the other hand, with a decrease in temperature to the interval of 875-825?C, the extent of restoration is decreasing, leading to recovery as a sole softening mechanism at 825?C, which was confirmed by the stress-strain curve shape, and values of FS and ASP. It is assumed that, due to high supersaturation, strain-induced precipitation promoted pinning of grain and subgrain boundaries and suppressed recrystallization. Therefore, the critical temperature for finish rolling was estimated to be 825?C.

Evolution of strain-induced precipitates in Inconel 617B alloy and their effect on flow behavior

Strain-induced precipitation was systematically investigated in austenitic Inconel 617B superalloy (IN617B) after deformation of 0.2 true strain in its service temperature range (700–850 °C). The precipitation-time-temperature (PTT) curves obtained by stress relaxation experiments showed a classic C-shape with the nose temperature of 800 °C, and a minimum incubation period of 30 s, and the main strain-induced precipitate was M23C6 carbide. After specimens deformed at 800 °C to a strain of 0.2 were held between 10 and 1000 s, they underwent a second-pass strain test, during which the M23C6 precipitates evolved and influenced the flow stress; this behavior was investigated. During the nucleation, growth, and coarsening of the strain-induced precipitates, the morphology of the M23C6 particles gradually changed from spherical to polygonal with increasing size, but the precipitates always maintained their cube-on-cube orientational relationship with the austenitic matrix. During the nucleation stage before 30 s, many pre-precipitation clusters and weak static recovery softening led to low second-deformation flow stress, which persisted at approximately 630 MPa. In the precipitation growth phase before 360 s, recovery softening balanced precipitation hardening. The strain-induced precipitates grew larger, and they were able to pin dislocations. In addition, some complex microstructures resulting from particle collisions were observed. This resulted in the maximum rate of increase of the second deformation flow stress, which quickly reached almost 700 MPa. When the holding time was extended to 1000 s, the recovery softening effect further increased, while the M23C6 particles gradually coarsened; this weakened the increasing trend of the second deformation flow stress, which increased to only 715 MPa at 1000 s

Low cycle fatigue response of differently aged AA6063 alloy: Statistical analysis and microstructural evolution

Understanding the dynamic structural changes during cyclic deformation of Al-alloys is a discipline of great interest to material technologists. The primary objective of this report is to assess the low cycle fatigue (LCF) behaviour of AA6063 alloy in under-aged (UA), peak-aged (PA) and over-aged (OA) states and to understand the energetic aspects of cyclic plastic behaviour in the background of the nature and density of the dislocations. Two parameters Weibull distribution analyses, for the first time, establish that despite inferior monotonic strength, LCF life of UA alloy is twice compared to PA alloy at higher (≥0.5%) strain amplitudes. This corroborates well with the fact that the cumulative dissipated plastic strain energy density (CPSED) values exhibit reverse variation with applied strain amplitude in the case of UA alloy as compared to PA and OA alloys. TEM analyses confirm that strain-induced vacancy-driven dynamic precipitation causes dramatic cyclic hardening in UA alloy resulting in improved fatigue life. One can also evidence this from the fivefold increase in the plastic strain energy dissipation and 2-times increased of post-fatigue hardness. In contrast, fracture surface analyses and XRD-based dislocation density measurements coupled with TEM examinations reveal that the shearing or by-passing of precipitates by the dislocations in the PA or OA alloys, respectively, lead to strain localization and cyclic softening, and consequently, reduce the plastic strain energy dissipation and lower fatigue life. The study provides important guidelines for the development of high strength Al-alloys with improved fatigue performance.

Effect of strain-induced precipitation on microstructure and properties of titanium micro-alloyed steels

Effect of strain-induced precipitation on microstructure and properties of titanium micro-alloyed steels

Constitutive Equation for Flow Stress in Superalloy 718 by Inverse Analysis under Hot Forming in a Region of Precipitation

The purpose of this study is to obtain a constitutive equation of high-accuracy flow stress in superalloy 718, which allows fabrication of highly reliable disks for gas turbine engines. Hot compression tests using superalloy 718 at deformation temperatures from 850 to 1100 °C, a 67% height reduction, and strain rates of 1, 10, and 25 s−1 were performed to investigate the flow stress behavior, which excludes environmental effects during hot working by inverse analysis. The effects of dynamic recrystallization and strain-induced dynamic precipitation on the flow stress were also investigated. The dynamically precipitated δ phases deformed at 1050 °C and γ″ phases deformed at 950 °C might affect the increase in the plastic modulus F1 and the decrease in the critical strain εc, deteriorating the accuracy of regression in terms of, for example, the strain rate sensitivity m and the temperature sensitivity A. A constitutive equation for a generalized flow curve for superalloy 718 is proposed by considering these effects.

Effect of Strain-Induced Precipitation on the Recrystallization Kinetics in a Model Alloy

The effects of Nb addition on the recrystallization kinetics and the recrystallized grain size distribution after cold deformation were investigated by using Fe-30Ni and Fe-30Ni-0.044 wt pct Nb steel with comparable starting grain size distributions. The samples were deformed to 0.3 strain at room temperature followed by annealing at 950 °C to 850 °C for various times; the microstructural evolution and the grain size distribution of non- and fully recrystallized samples were characterized, along with the strain-induced precipitates (SIPs) and their size and volume fraction evolution. It was found that Nb addition has little effect on recrystallized grain size distribution, whereas Nb precipitation kinetics (SIP size and number density) affects the recrystallization Avrami exponent depending on the annealing temperature. Faster precipitation coarsening rates at high temperature (950 °C to 900 °C) led to slower recrystallization kinetics but no change on Avrami exponent, despite precipitation occurring before recrystallization. Whereas a slower precipitation coarsening rate at 850 °C gave fine-sized strain-induced precipitates that were effective in reducing the recrystallization Avrami exponent after 50 pct of recrystallization. Both solute drag and precipitation pinning effects have been added onto the JMAK model to account the effect of Nb content on recrystallization Avrami exponent for samples with large grain size distributions.

Analysis of strain-induced precipitates by delta-processing in Inconel 718 superalloy

Delta-Processing (DP) is a suitable heat treatment process aiming at controlling grain growth during hot deformation of the well-known Ni-base superalloy Inconel 718 (IN718). DP is often applied by heating up to 900 °C for 24 h in order to promote δ-phase saturation prior to deformation. In addition to the δ-phase, Mo and Cr-rich carbides in the form of M23C6 may also precipitate during the subsequent hot deformation of this alloy in the range of 950–1000 °C These carbides are induced by deformation and can affect the static and dynamic recrystallization of the matrix.The objective of the current work is to understand the precipitation of M23C6 carbides when the material has been saturated with δ-phase precipitation, as well as their interaction with recrystallization phenomena. For this purpose, a series of double-strain hot compression test (double-hit) were carried out. Several holding times were applied between the first and the second hit in order to derive the softening/hardening fraction progress with time. Microstructural characterization of the samples was performed through Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) in order to identify the precipitating/dissolving phases under each testing condition.

Effect of Processing Parameters on Interphase Precipitation and Mechanical Properties in Novel CrVNb Microalloyed Steel

Novel steel microalloyed with 0.73 (Cr + V + Nb) has been subjected to thermomechanical processing (TMP) with varying parameters to simultaneously maximise the steel strength and ductility. Optical and electron microscopy studies coupled with uniaxial tensile testing were carried out to analyse the processing-microstructure-properties relationship. For the suggested steel composition, the simultaneously highest yield stress (960 MPa), ultimate tensile strength (1100 MPa), and elongation to failure (25%) were achieved following simulated coiling at 650 °C and holding for 30 min. The variation in the finish rolling temperature affects the ferrite grain size and the ratio of precipitates formed in austenite and ferrite. If a significant amount of solute is consumed for precipitation in austenite and during subsequent growth of strain-induced precipitates, then a lower fraction of interphase and random precipitates forms in ferrite resulting in a lower strength. Extended time at a simulated coiling temperature resulted in the growth of interphase precipitates and precipitation of random ones in ferrite. Fine tuning of TMP parameters is required to maximise the contribution to strength arising from different microstructural features.

Recrystallization–precipitation interaction of a Ti microalloyed steel with controlled rolling process

The interaction between austenite static recrystallization and strain induced precipitation of a Ti microalloyed steel deformed in the non-recrystallization region was investigated by two-stage interrupted compression method and transmission electron microscopy (TEM). The softening rate curves of austenite were obtained by the true stress-strain curves of the two-pass of deformation. Results showed that the softening rates increased with increasing deformation temperatures. The softening rate curve exhibited a “S” shaped, and the static recrystallization was completed in 300 s when deformed at 1000°C, while deformed temperatures were lower than 950°C, the softening rates dropped sharply and increased very slowly as pass inter time increased. At 975°C or below, platforms appeared in softening curves, which implied strain-induced precipitates occurred during the isothermal process after the first deformation. The shortest incubation time of strain-induced precipitates was about 78 s when deformed at 925°C. Based on TEM results, strain-induced precipitates were found to be mainly distributed at dislocations and the diameters of the particles precipitated at dislocations were obviously larger than those of precipitated in other nucleation sites due to the effective route for the diffusion of Ti element. Evolution of austenite grains morphologies showed that the static recrystallization of deformed austenite was strongly inhibited by strain-induced precipitation and occurred again after the strain-induced precipitation finished.

Strain-induced precipitation in Ti microalloyed steel by two-stage controlled rolling process

Strain-induced precipitation kinetics and precipitates' characteristics in a Ti microalloyed steel subjected to a two-stage controlled rolling process, simulating rough and finish rolling process of industrial production, were quantitatively investigated by stress relaxation experiments and transmission electron microscopy (TEM), as well as inductively coupled plasma-atomic emission spectroscopy (ICP-AES). In the present work, precipitation during the cooling stage after rough rolling was taken into consideration for the first time. It was found that a small amount of Ti-bearing precipitates, consuming about 10% of the elemental Ti, were formed on dislocations after rough rolling and cooling to 900 °C. The obtained precipitation-time-temperature (PTT) curves exhibited a classic C shape with a nose temperature of 900 °C and the shortest incubation time of 60 s. The PTT curves moved to the lower left by the introduction of 20% deformation at 1050 °C, which was attributed to more nucleation sites for strain-induced precipitation and the decrease of Ti concentration in deformed austenite. During the stress relaxation stage, strain-induced precipitates preferentially nucleated on dislocations and sub-boundaries and were identified as TiC particles. The mean size of precipitated TiC particles increased from 10.2 ± 2.1 to 25.2 ± 2.8 nm, as the holding time was increased from 100 to 1800 s at 900 °C. When the holding time exceeded 600 s the migration of austenite grain boundaries could not be completely inhibited due to the coarsening of precipitates. Isothermal treatment at 900 °C with a holding time of 60–100 s is suggested here as a viable combination for the processing of the 0.05C-0.21Si-1.05Mn-0.13Ti (wt. %) steel due to the shortest incubation time period and effective pinning of grain boundaries by strain-induced precipitates.

Hot deformation mechanisms, mechanical properties and microstructural evolution of a HP-Nb steel

In this study hot deformation mechanisms, mechanical properties and microstructural evolution of a HP-Nb steel used as reformers tube in oil and gas industries was examined. Hot tensile tests were performed on the as-cast samples in temperature range from 700 °C to 1000 °C with 100 °C interval and under various strain rates. Microstructural analyses of the hot tensile samples were performed using optical microscope and Field Emission Scanning Microscope (FE-SEM). Constitutive equations were constructed to define deformation regimes. In that regard, and based on apparent activation energy, strain rate sensitivity and Zener-Hollomon parameters were calculated. Results showed that increasing temperature after 800 °C substantially reduced the flow stress. Such an effect was a little offset by increasing the strain rate. Strain rate sensitivity was remarkably increased at 800 °C and again at 1000 °C which indicated an increase in ductility due to the occurrence of dynamic recrystallization (DRX) at these temperatures. Strain rate sensitivity was relatively low at 700 °C and 900 °C with the latter being higher than 700 °C. It was seen that increasing the deformation temperature to 900 °C led to a decrease in the possibility of DRX due mainly to strain induced precipitation (SIP) and solute drag effect of Nb element. It was also observed that increasing the engineering strain rate from 0.002 s−1 significantly increased the flow stress due probably to the domination of work hardening over restoration phenomena, particularly at 700 °C. As well, it was found that when deformation temperature increased, particularly at lower strain rate regimes, more dynamically recrystallized grains were developed. A contour map of Zener-Hollomon parameter together with the strain rate and temperature is constructed which defined the deformation regime under various combinations of strain rates and temperatures.

Effect of Processing Conditions on the Microstructure, Mechanical Properties, and Corrosion Behavior of Two Austenitic Stainless Steels for Bioimplant Applications

Hot torsion tests were carried out to simulate the industrial thermomechanical processing of two austenitic steels for bioimplant applications, namely ISO 5832-9 and ASTM F138. The former has Ti, Nb, and V in the composition, being N-rich. However, the latter is Ni-richer and without extra alloying element additions. Special attention was paid to the effect of interpass times, particularly to the soaking temperature, which was reduced to decrease processing times and costs. Optical and electron microscopy, corrosion tests, and hardness measurements were used to characterize the effect of the above processing parameters on both alloys. No significant increase in processing loads was noticed after the reduction of the reheating temperature. This was explained in terms of the balance between partial particles dissolution and the increment in the solute drag effect provided by the elements put into solution. Such an increment in solid solution favored the dynamic recovery process, delaying the dynamic recrystallization one. However, strain-induced precipitation took place at lower temperatures, by using the extra N and Cr delivered to the matrix, and limiting the recrystallization softening. The rolling schedule promoted abundant grain refinement. The final grain size ranged from 2.5 to 11 µm, depending on reheating temperature, interpass time, presence of alloying elements, and N. In general terms, the corrosion resistance of the ISO steel soaked at the lowest temperature (1200 °C) was better than when reheated to the highest one (1250 °C). On the contrary, the F138 steel had worse corrosion behavior.

Effects of dynamic recrystallization and strain-induced dynamic precipitation on the corrosion behavior of partially recrystallized Mg–9Al–1Zn alloys

Abstract The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed (ECAPed) Mg–9Al–1Zn (AZ91) alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupled with high resolution techniques such as scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). During ECAP, dynamic recrystallization (DRX) and strain-induced dynamic precipitation (SIDP) simultaneously occurred, resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grains with a large volume fraction of β-Mg17Al12 precipitates. Corrosion preferentially initiates and propagates in the DRXed grains, owing to the greater microchemistry difference between the β-Mg17Al12 precipitates formed at the DRXed grain boundaries and the adjacent α-Mg matrix, which induces a strong microgalvanic coupling between these phases. Additionally, the weaker basal texture of the DRXed grains also makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains. The influence of dynamic recrystallization and dynamic precipitation was also studied in ECAPed alloys with different levels of deformation strain through corrosion and electrochemical techniques. Increasing the strain level led to a more uniform corrosion with a shallow penetration depth, lower corrosion rate values, and higher protective ability of the oxide film. Furthermore, higher levels of strain resulted in greater hardness values of the ECAPed alloys. The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination of smaller DRXed grain size, higher DRX ratio, and higher volume fraction of uniformly distributed fine β-Mg17Al12 precipitates.

Development of precipitation model with the use of the Lattice Boltzmann Method and its application for the rolling process

A new precipitation model based on the Lattice Boltzmann Method with elements of Cellular Automata is presented in the paper. The model consists of three submodels: nucleation, precipitation growth, and diffusion of niobium and carbon.The nucleation model used classical nucleation theory and considers homo- and heterogeneous nucleation. The nucleation rate depends on the number of possible nucleation sites, which are defined by dislocation density, i.e. deformation conditions. The nucleation rate depends also on the Zeldowicz parameter, the factor of condensation rate, precipitation work, temperature, and other variables. The nucleation rate is realized in the model by calculating the probability of nucleon appearance in every cell, free of precipitation, and depends on the nucleation rate, the cell volume, and the time step.The growth or dissolution of the precipitation depends on the model on particle size and prevailing local conditions near the particle. The temperature and concentration define the equilibrium size of the particle.LBM model is applied to solve the Fourier equation for niobium and carbon diffusion. Near the precipitations equilibrium concentration of niobium and carbon is established according to precipitations size and temperature, while free diffusion is considered in the other space.Strain-induced precipitation at different temperatures and with the different constant cooling rate was simulated. Results are coincident with theory and experimental researches reported in the scientific literature.Modeling of precipitation during the rolling process with consideration of recrystallization shows an ability of the model to simulate and study the more complex processes that strain-induced precipitation in single deformation. It can be applied for multi-stages deformation processes to design or optimize them in view of precipitation and microstructure evolution.

Thermal Mechanisms of Grain Refinement in Steels: A Review

Thermal mechanisms of microstructural refinement in steels were reviewed. These include thermal cycling, martensite process, and static recrystallization (SRX), in which the dominant stage of microstructural refinement is governed by an annealing treatment of a deformed or an undeformed material. Recent progress in grain refinement by thermal cycling for the body-centered cubic, face-centered cubic, and dual phase (DP) steels was introduced. The application of the cold rolling and subsequent annealing of a martensite starting structure (martensite process) for grain refinement of low-carbon and DP steels was reviewed. The formation and reversion of strain-induced martensite in metastable austenitic stainless steels and their effects on the microstructural evolutions were critically discussed. Moreover, the repetition of the martensite process and its limitations were explained. Important findings on the SRX of ferrite and austenite for grain refinement as well as the recrystallization kinetics were presented. Finally, the concepts of controlled rolling for grain refinement and the interaction of austenite recrystallization and strain-induced precipitation in microalloyed steels during thermomechanical processing were also reviewed. This short overview presents the opportunities that the conventional and innovative processing routes can offer for grain refinement of steels.

The Interdependence of the Degree of Precipitation and Dislocation Density during the Thermomechanical Treatment of Microalloyed Niobium Steel

In this paper, thermomechanical processing of niobium microalloyed steel was performed with the purpose of determining the interaction between niobium precipitates and dislocations, as well as determining the influence of the temperature of final deformation on the degree of precipitation and dislocation density. Two variants of thermomechanical processing with different final rolling temperatures were carried out. Samples were studied using electrochemical isolation with an atomic absorption spectrometer, transmission electron microscopy, X-ray diffraction analysis, and universal tensile testing with a thermographic camera. The results show that the increase in the density of dislocations before the onset of intense precipitation is insignificant because the recrystallization process takes place simultaneously. It increases with the onset of strain-induced precipitation. In this paper, it is shown that niobium precipitates determine the density of dislocations. The appearance of Lüders bands was noticed as a consequence of the interaction between niobium precipitates and dislocations during the subsequent cold deformation. In both variants of the industrial process performed on the cold deformed strip, Lüders bands appeared.