Cold-rolled Stainless Steel Research Articles

Simulation of the Temperature, Microstructure and Mechanical Properties of Cold-Rolled Stainless Steel Sus430 During Continuous Annealing

Mathematical models of variation of the temperature, microstructure and mechanical properties of cold-rolled steel SUS340 in a continuous annealing furnace are derived using experimental results and numerical methods. The results obtained are used for computing the mechanical properties of SUS340 under continuous annealing and for developing new annealing modes with the help of the model suggested.

Comparison of Laser-Engraved Hole Properties between Cold-Rolled and Laser Additive Manufactured Stainless Steel Sheets

Laser drilling and laser engraving are common manufacturing processes that are found in many applications. With the continuous progress of additive manufacturing (3D printing), these processes can now be applied to the materials used in 3D printing. However, there is a lack of knowledge about how these new materials behave when processed or machined. In this study, sheets of 316L stainless steel produced by both the traditional cold rolling method and by powder bed fusion (PBF) were laser drilled by a nanosecond pulsed fiber laser. Results were then analyzed to find out whether there are measurable differences in laser processing parts that are produced by either PBF (3D printing) or traditional steel parts. Hole diameters, the widths of burn effects, material removal rates, and hole tapers were measured and compared. Additionally, differences in microstructures of the samples were also analyzed and compared. Results show negligible differences in terms of material processing efficiency. The only significant differences were that the PBF sample had a wider burn effect, and had some defects in the microstructure that were more closely analyzed. The defects were found to be shallow recesses in the material. Some of the defects were deep within the material, at the end and start points of the laser lines, and some were close to the surfaces of the sample.

Study on Fatigue Crack Propagation Behavior in Corrosion Environment of a Cold-Rolled Austenitic Stainless Steel

Fatigue crack growth testing and measurement of fracture toughness with single edge notch tension (SENT) specimens of American Iron and Steel Institute (AISI) 301L-MT stainless steel were performed in the air, distilled water, and 3.5% and 9% NaCl solutions. Type 301L-MT steel exhibited the same resistance to corrosion for various environments in near-threshold region. The crack growth in the Paris region could be accelerated in a [Cl−] containing environment by decreasing the threshold of stress corrosion KISCC, but independent of [Cl−] concentration. When specimens were fatigue precracked in different conditions, it was found that the fracture toughness of SENT specimens in the aqueous environment decreased 23% to 30% compared with that in the air. The normalized formula was established to describe the behavior of fatigue crack propagation of type 301L-MT steel. Three parameters, ΔKthcf, β, and JIQ, were used to clarify the effect of H-embrittlement mechanism on fatigue crack propagation.

Strain-Induced Martensite Detection Methods in Cold-Rolled Duplex Stainless Steels

Duplex stainless steels (DSS) are biphasic austeno-ferritic steels, whose favorable combination of mechanical strength and corrosion-resistance properties makes them highly suitable for structural applications in chemical, petrochemical, and nuclear industries. DSS are high-alloyed steels and their interesting features derive from the presence of an almost equal volume fraction of ferrite and austenite, obtained from a suitable balance of the alloying elements and after a proper post-forming heat treatment (solubilization). However, DSS suffer from ferrite instability when heating the material within certain temperature ranges that can cause the precipitation of harmful secondary phases, which consequently limits their utility to below 250°C. Moreover, owing to austenite metastability at room temperature, a diffusionless martensitic transformation can occur after cold deformation, which leads to the formation of the so-called strain-induced martensite (SIM), especially when the phase is not adequately stabilized by a suitable amount of γ-stabilizing elements. In the present work, cold rolling was adopted as a cold deformation process, and four different DSS grades (SAF 2101, 2304, 2205, and 2507) were subjected to thickness reductions from 15 to 85 %. The developed microstructural features were analyzed by means of various characterization techniques (optical and electron metallography, hardness tests, X-ray and neutron time-of-flight diffraction, magnetic measurements, and critical pitting temperature determination), in order to detect and evaluate the amount of transformed austenite and to observe associated changes in properties induced by the occurrence of SIM. The experimental results revealed that the low-alloyed Lean DSS (2101 and 2304) seem to be more prone to SIM formation, whereas 2205 and 2507 grades were found to be more stable, even after large deformations. Nevertheless, the performed analyses pointed out that SIM detection in DSS is not a straightforward process as in austenitic grades, owing to similar crystallographic and magnetic properties of SIM and ferrite.

Heterogeneous nanostructure developed in heavily cold-rolled stainless steels and the specific mechanical properties

Stainless steels were cold rolled to 92% reduction. The microstructure developed in a stable austenitic stainless steel was complicated heterogeneous nanostructure composed of lamellar-twin domains, shear bands and low-angle lamellar boundaries. Cold-rolled duplex stainless steel, however, exhibited more complicated and mixed microstructure where ferritic lamellar and the heterogeneous nanostructure of austenite were alternatively stacked. The heavily cold-rolled stainless steels followed by ageing exhibited marvelous high tensile strength over 2.6GPa perpendicular to the rolling direction, although around 2GPa along the rolling direction. Even while such high strength, moderate plastic elongation over 5% was attained.

単純強圧延オーステナイト系ステンレス鋼中のヘテロナノ組織が集合組織と延性に及ぼす影響

単純強圧延オーステナイト系ステンレス鋼中のヘテロナノ組織が集合組織と延性に及ぼす影響

Reverse Martensitic Transformation and Resulting Microstructure in a Cold Rolled Metastable Austenitic Stainless Steel

The reverse martensitic transformation in cold-rolled metastable austenitic stainless steel has been investigated via heat treatments performed for various temperatures and times. The microstructural evolution was evaluated by differential scanning calorimetry, X-ray diffraction and microscopy. Upon heat treatment, both diffusionless and diffusion-controlled mechanisms determine the final microstructure. The diffusion reversion from α′-martensite to austenite was found to be activated at about 450°C and the shear reversion is activated at higher temperatures with Af′ ∼600°C. The resulting microstructure for isothermal heat treatment at 650°C was austenitic, which inherits the α′-martensite lath morphology and is highly faulted. For isothermal heat treatments at temperatures above 700°C the faulted austenite was able to recrystallize and new austenite grains with a low defect density were formed. In addition, carbo-nitride precipitation was observed for samples heat treated at these temperatures, which leads to an increasing Ms-temperature and new α′-martensite formation upon cooling.

The influence of hot band annealing on recrystallization kinetics and texture evolution in a cold-rolled Nb-stabilized ferritic stainless steel during isothermal annealing

Abstract

Intergranular Stress Corrosion Cracking growth perpendicular to fatigue pre-cracks in T–L oriented compact tension specimens in simulated Pressurized Water Reactor primary water

Intergranular Stress Corrosion Cracking (IGSCC) growth observed perpendicular to the plane of fatigue pre-cracks in T–L oriented compact tension specimens made of highly cold-rolled Type 316 stainless steel has been investigated metallurgically. One-directional cold rolling resulted in significant lamellar local strains on the plane parallel to the rolling plane. Oxide was detected along intergranular crack. It is deduced that intergranular cracking was due to selective oxidation and enhanced high diffusivity at grain boundaries coupled with lamellar local strains. It is argued that strain-induced oxidation could be a possible mechanism for IGSCC in cold-rolled stainless steels in simulated Pressurized Water Reactor environment.

Formability of adhesive-bonded steel sheets with artificial finite adhesive defects

In this investigation, the influence of artificial finite adhesive defects with different shapes and sizes, characterized by (1) aspect ratios, a/ b = 0.5, 1 and 1.5 (where a is transverse axis length of defect; b is longitudinal axis length of defect), (2) number of defects and (3) different locations, in the epoxy adhesive layer on the formability of adhesive-bonded blanks, is analysed. The deep drawing quality cold-rolled steel and stainless steel (SS 316L) sheets were used as base materials. The increase in aspect ratio of adhesive defect reduces the ductility of adhesive layer and thereby decreases the formability of adhesive-bonded blanks. This is due to the early failure of adhesive layer at the location of defect where strain is locally concentrated. The strain hardening exponent ( n) of adhesive-bonded blanks has decreased with increase in aspect ratio of adhesive defect in all the regions of deformation. The limit strain of deep drawing quality and SS 316L sheets constituting adhesive-bonded blanks shows decrement with increase in aspect ratio of adhesive defect. It is postulated that the aspect ratio of the finite adhesive defect influences significantly the formability of adhesive-bonded blanks, but not shape of the finite adhesive defects. There is no considerable effect of number of adhesive defects and different locations of adhesive defects on the formability of adhesive-bonded blanks.

Mechanical Behaviors of Friction Stir Spot Welded Joints of Dissimilar Ferrous Alloys under Opening-Dominant Combined Loads

Mechanical properties and failure behaviors of friction stir spot welded (FSSW) joints of two dissimilar ferrous alloys, cold-rolled carbon steel (SPCC) and 409L stainless steel (SUS 409L), are investigated under opening-dominant combined loads. The texture of dissimilar FSSW joints depends on the upper sheet material. The failure contours for the FSSW joints under combined loads are constructed in terms of the axial load and shear load by modifying existing failure criteria for resistance spot welds. The shape of the failure contour also depends on the upper sheet material. The failure contours are nearly elliptic in shape when the upper sheet is SPCC and are relatively straight lines when the upper sheet is SUS 409L.

Dislocation characterization in cold rolled stainless steel using nonlinear ultrasonic techniques: A comprehensive model

Both dislocation density and character in cold rolled stainless steel cause the change of acoustic nonlinearity. An analytical model considering the different oscillating motion of edge and screw dislocations is presented for the generation of ultrasonic harmonic wave during the process of multiplication and motion of dislocation. Results reveal that the edge dislocation induces stronger acoustic nonlinearity response than screw dislocation. The new model is certified by the application to the cold rolled stainless steel.

Studies on Martensite Transformation in a Metastable Austenitic Cr-Mn Stainless Steel

The influences of the heating rate and annealing duration on martensite formation and its reversion to austenite have been investigated in a 60% cold-rolled metastable high-manganese austenitic Type 204Cu stainless steel. A Gleeble 3800 thermomechanical simulator was used for dilatometric measurements. Cold-rolled steel pieces were either heated up to 1000 °C at various heating rates between 5 °C/s and 150 °C/s followed by quenching to room temperature, or heated and held at temperatures in the range of 450 620 °C for different durations between 0.1 600 s. In heating experiments, dilatation curves revealed an expansion of a specimen starting around 550 °C followed by contraction, both processes depending on the heating rate. These dimensional changes could be correlated to the formation and reversion of a ferromagnetic phase, α-martensite. Some martensite was also formed during isothermal holding in connection with tempering of the pre-existing α-martensite before the following reversion, as established by magnetic measurements. Tempering of martensite was revealed by microhardness behaviour, X-ray diffraction analysis and transmission electron microscopy.

Deformation-Induced Martensitic Transformation Behavior in Cold-Rolled AISI304 Stainless Steels

AISI 304 stainless steels have been cold-rolled to different thickness reduction degrees, and consequently a deformation-induced martensite phase transformation takes place in the specimens. Metallurgical microscopy was used to study the microstructure and morphology of the specimens. X-ray diffraction was also used to investigate deformation-induced transformation. Martensite phase content was determined using a Ferrite Content Measuring Instrument. The evolution of the microstructure change and the mechanism of phase transformation by varying cold-rolled thickness reduction degree were discussed.

Evaluation of Internal Stress in Individual Grains of Cold-Rolled Stainless Steel by Energy Dispersive X-ray Diffraction

Evaluation of Internal Stress in Individual Grains of Cold-Rolled Stainless Steel by Energy Dispersive X-ray Diffraction

Evolutions of texture and grain boundary plane distributions in a ferritic stainless steel

The grain size, textures and grain boundary plane distributions in a cold-rolled and annealed ferritic stainless steel were investigated by means of EBSD techniques. The results show that, following cold rolling with the thickness reduction of 85%, relatively low temperature (780°C) annealing brings an extremely sluggish grain growth and no grain texture develops when the annealing time varies from 5 min to 480 min. The free energy reduction of the system is mainly caused by the grain boundary plane re-orientation in addition to minor grain growth because the distributions of grain boundary planes are moderately preferred on {100} according to the five parameter analyses (FPA) concerning the grain boundary plane characteristics. However, in the case of high-temperature (1 000 °C) annealing, the average grain size does not increase until annealing time is prolonged to 90 min, after which extensive grain growth occurs and strong {100} 〈hkl〉 texture emerges whereas nearly random grain boundary plane distributions are observed. The free energy reduction of the system is most likely attributed to the selective growth.

Measurements of Residual Stresses in Cold-Rolled 304 Stainless Steel Plates Using X-Ray Diffraction with Rietveld Refinement Method

The determination of the residual stresses using X-ray powder diffraction in a series of cold-rolled 304 stainless steel plates, deforming 0, 34, 84, 152, 158, 175 and 196 % reduction in thickness has been carried out. The diffraction data were analyzed using the Rietveld structure refinement method. The analysis shows that for all specimens, the martensite particles are closely in compression and the austenite matrix is in tension. Both the martensite and austenite, for a sample reducing 34% in thickness (containing of about 1% martensite phase) the average lattice strains are anisotropic and decrease approximately exponential with an increase in the corresponding percent reduction (essentially phase content). It is shown that this feature can be qualitatively understood by taking into consideration the thermal expansion mismatch between the martensite and austenite grains. Also, for all cold-rolled stainless steel specimens, the diffraction peaks are broader than the unrolled one (instrumental resolution), indicating that the strains in these specimens are inhomogeneous. From an analysis of the refined peak shape parameters, the average root-mean square strain, which describes the distribution of the inhomogeneous strain field, was predicted. The average residual stresses in cold-rolled 304 stainless steel plates showed a combination effect of hydrostatic stresses of the martensite particles and the austenite matrix. Received: 14 March 2008; Revised: 13 October 2008; Accepted: 6 November 2008

Mechanical Bending Simulation of Thin Stainless Steel by Using Isotropic and Orthotropic Properties

The most important factors in hard disk drive suspension manufacturing is the suspension preload, so call “gram load”. The suspensions were generally made from cold rolled stainless steel (SUS304). The suspensions were formed by mechanical forming and gram load was adjusted by mechanical bending until reached a specification. The material properties in mechanical bending simulation of thin stainless steel were usually as isotropic for simple calculation. But the properties of thin stainless steel should be defined as orthotropic materials. Therefore, this work aimed to study gram load results of using isotropic and orthotropic properties. The thin stainless sheet was cut and test for mechanical properties in rolling and transverse directions. The properties of the thin sheet were applied to simulation model. It was found that orthotropic material properties shows a good agreement with the experimental results more than using isotropic material properties. Therefore, the results of this work could be used to explain and predict the mechanical response on the suspension manufacturing.

염분분사환경에서 냉연 304 스테인레스강의 부식거동

염분분위기에서의 부식은 사용후핵연료의 중간저장 기간동안 304 스테인레스 강재 건식저장용기의 주 열화기구들 중 하나다. 본 연구에서는 감소정도가 서로 다른 냉연 304 스테인레스 강 시편들에 0.5wt.%의 염화나트륨 연무를 분사시키면서 느린 변형속도시험(SSRT)과 중성염 분사시험(NSS)을 <TEX>$85^{\circ}C$</TEX>와 <TEX>$200^{\circ}C$</TEX> 에서 수행하였다. <TEX>$85^{\circ}C$</TEX>에서 2000 시간 동안 시험한 NSS시편의 무게 변화는 <TEX>$200^{\circ}C$</TEX>에서 시험한 시편의 무게 변화와 크게 달랐다. NSS 시편의 <TEX>$85^{\circ}C$</TEX>에서 무게 감량은 미미하였지만, 냉연 감소율이 증가함에 따라서 무게 변화는 점진적으로 감소하였다. <TEX>$85^{\circ}C$</TEX>와 <TEX>$200^{\circ}C$</TEX>에서 그리고 염분분사 환경에서 가볍게 냉연 가공된 시편의 SSRT 시험으로부터 얻은 항복강도와 극한 인장응력의 값은 공기 중의 값보다 약간 낮았다. 그러나 염분 분위기에서 부식으로 인한 20% 감소 냉연시편의 강도는 더 이상 변화하지 않았다. 예비결과는 냉연 304 스테인레스 강의 질과 성능이 건식저장용기의 제작을 위한 조건에 맞는다는 것을 증명하였다. 그러나 냉연 스테인레스 강의 장기적인 성능을 더 잘 이해하기 위해서는 염분분위기에서 이 재질의 부식거동에 관한 더 많은 연구가 필요하다. Saline corrosion is one of the major degradation mechanisms for stainless steel type 304 (SS304) dry storage cask during the spent fuel interim storage period. Slow strain rate test (SSRT) and neutral salt spray test (NSS) were performed at <TEX>$85^{\circ}C$</TEX> and <TEX>$200^{\circ}C$</TEX> with 0.5 wt% sodium chloride mist sprayed on the cold-rolled SS304 specimens of different degrees of reduction in this study. The weight changes of the NSS specimens tested at <TEX>$85^{\circ}C$</TEX> for 2000 hours differed greatly from those at <TEX>$200^{\circ}C$</TEX>. The weight loss of NSS specimens was not significant at <TEX>$85^{\circ}C$</TEX> but the weight gain decreased gradually with increasing the cold-rolled reduction. The yield strength (YS) and ultimate tensile stress (UTS) values obtained from the SSRT tests for lightly cold-rolled specimens in the salt spray environment at <TEX>$85^{\circ}C$</TEX> and <TEX>$200^{\circ}C$</TEX> are slightly lower than in air. But for those with 20% reductions, the specimen strengths were no longer changed by the saline corrosion. The preliminary results demonstrated that the quality and performance of cold-rolled SS304 is acceptable for fabrication of dry storage casks. However, more work on the corrosion behavior of cold-rolled stainless steel in the saline atmosphere is needed to better understand its long-term performance.

Microstructure and Deformation Behavior of Cold-Rolled Super-Duplex Stainless Steel

The present examination is a part of project concerning a deformation behavior of duplex type ferritic-austenitic stainless steels. The investigations included the analysis of ferrite and austenite microstructures formed in cold-rolled sheet of super-duplex stainless steel, major deformation mechanisms operating in both constituent phases and changes in morphology of two-phase structure after the thermo-mechanical treatment and subsequent cold-rolling. Duplex type stainless steels develop the band-like ferrite-austenite morphology in the course of hot- and cold-rolling. This specific two-phase structure creates different conditions for plastic deformation in comparison to single phase steels. The interaction of both phases upon deformation exerts fairly significant influence on structure and texture formation in both constituent phases and in consequence affects the material properties and its behavior upon further processing.