Rolled Stainless Steel Research Articles

Tribological Aspects of Advanced Roll Material in Cold Rolling of Stainless Steel

Tribological Aspects of Advanced Roll Material in Cold Rolling of Stainless Steel

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part II: Thermal stress analysis by FEA

A martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used as a glass roller failed prematurely after six rolling campaigns. A previous fractographic investigation showed that the failure of the roll was caused by thermal stresses associated with microstructural embrittlement of the steel casting. Crack nucleation took place on the internal surface of the roll and the crack propagated by ductile intergranular mode. In the present work, the thermal stresses distribution was investigated by a thermal elastic–plastic model using finite element analysis in order to associate the crack growth with the thermal history of the roll during service. The proposed methodology based on the assessment of thermal stresses by finite element analysis together with coupled thermal–mechanical non-linear modelling and calculations using non-linear elastic–plastic fracture mechanics allowed a better understanding of the stable and unstable growth of a longitudinal crack until the premature failure of the roll during its cooling to room temperature after the sixth campaign. The stable and unstable crack growth and the thermal history of the roll (heating up, glass rolling and cooling operations during the six campaigns of the roll) could be related using the proposed calculation.

Comparison of reduction ability between multi-stage cold drawing and rolling of stainless steel wire – Experimental and numerical investigations of damage

The present paper deals with the comparison between two multi-stage cold forming processes on an austenitic stainless steel, wire drawing and wire rolling, in terms of reduction ability. In the first step, experimental tests are carried out and reveal that, starting from an identical initial wire, higher reduction can be obtained with the drawing process. In the second step, numerical simulations are employed to investigate ductile damage in these two processes, using the phenomenological fracture criterion proposed recently by Bai and Wierzbicki (2008) and the coupled Lemaitre model in the framework of continuum damage mechanics (CDM). For the applications to forming processes, the models’ parameters are identified first based on different mechanical tests at different loading configurations. Applications to wire drawing and rolling processes show the validity of these two models in fracture prediction both quantitatively and qualitatively. These two damage models are capable of predicting accurately the instant of fracture and also confirm the experimental comparative results between the reduction abilities of the two processes. Between the two studied forming processes, the results suggest the use of the drawing process instead of the rolling process to reduce wire section with minimum damage. It also shows that numerical simulations with the two developed damage models could be an effective tool to investigate ductile damage in other forming configurations or processes.

Surface Crack and Organization of Hot Rolled S31803 Duplex Stainless Steel Bars

In bar rolling of S31803 duplex stainless steel, the surface crack is easy to appear. Through the observation on the microstructure, ferrite and austenite morphology and phase ratio were analyzed. The surface cracks of S31803 duplex stainless steel bar is mainly because of the dual phase microstructure softening mechanism of different in thermal processing, and the double phase stainless steel heat plasticity decrease. When the ferrite and austenite proportion close, and the heating temperature is too high, to reduce the binding force between the grains of billet surface, easy to cause the crack surface of a bar.

Surface Roughness and Friction in Hot Rolling of Stainless Steels

An experimental method was developed to examine oxidations of austenitic and martensitic stainless steels. The results show that the surface roughness along both rolling and transverse directions decreases with an increase of reduction. When the reheating time is increased, the average thickness of oxide scales of stainless steels increases, which results in relatively rough surface after hot rolling. The effects of oxide scale on the friction condition and surface roughness transfer in hot rolling depend on the oxide scale generated during reheating. The calculated surface roughness is close to the experimental results, which verifies the developed FEM model.

Rolling of 316L Stainless Steel with Rough Rolls to Potentially Obtain Superficial Nanograins

316L stainless steel plates of 5-mm thickness, normalized at 900 °C, were cold rolled with different reductions and number of passes using rolls with three different surface roughnesses: grain heights of 0.17 and 0.33 mm and rhomboid-shaped grains of 1.5-mm height. Subsequently, the rolled samples were annealed at 275 °C for 1 h in an effort to achieve superficial nanograins. The plates laminated using low-roughness rolls had continuous superficial microcrystallization when they were rolled for at least 26 passes. For samples made with rougher rolls, the recrystallized superficial grains formed on the surface (sized ~10-15 μm) were smaller than those below the surface; this behavior was caused by the major deformation induced by repeated indentations. The superficial recrystallization of the sample also tended to be more continuous for higher number of passes; micrographs of the penetration profiles of indentation in the samples rolled with high-roughness rolls revealed that a sample rolled 24 times had not yet reached the steady surface topology. As a conclusion, in order to successfully form superficial nanograins, very low-roughness rolls must be used as well as a small absolute reduction per pass, followed by annealing. These rolling conditions generate a continuous field of highly superficial deformations, which act as nucleation centers for nanograins during annealing.

Development of Smart Contact Backup Rolls in Ultra-wide Stainless Strip Rolling Process

In order to solve the serious backup roll spalling of roughing mill during ultra-wide stainless steel rolling process, a 3D elastic deformation finite element model of 4-high roll stacks was established for simulating the mechanical behavior during the hot rolling process. The asymmetric contact pressure between backup and work rolls is the key factor for the frequent roll spalling accidents. Based on the principle of homogenizing contact pressure between rolls, minimizing harmful contact zone in different strip widths and considering roll wearing as a whole, SCR (Smart Contact Backup Rolls) was developed. The simulation reveals when using the SMS200 backup roll contour, the peak position of contact pressure keeps consistent with the practical spalling position. Instead, the peak value of the roll contact pressure with SCR technology decreases significantly with various strip widths. The unevenness coefficients of roll contact pressure with SCR technology decline sharply from 1.36 and more to less than 1.18 with different strip widths. The roll consumption decreases from 0.1254kg/t to 0.055kg/t. During the continuous strip production of 20 million tons and more, non-occurring backup roll spalling, uniform roll wear and remarkable decrease in roll consumption have been validated by long-term industrial applications of the 2250 hot strip mill.

Prove of hydrogen formation through direct potential measurements in the rolling slit during cold rolling

In this work, direct potential measurements during cold rolling of zinc and X20Cr13 stainless steel were carried out in the rolling slit to follow the tribologic and galvanic mechanisms of hydrogen formation and absorption on the surface of the working rolls made of DHQ1 grade steel. An Ag/AgCl in 3.5 M KCl reference microelectrode was used to record the open circuit potential of the electrochemical system roller-product immersed into commercially relevant electrolyte (rolling emulsion) with a pH value of 4.5 and an electric conductivity 46 mS cm-1. The potential shift into either negative or positive direction of the rolls-product system gives information on the processes taking place at the surface in the course of the friction. A detailed discussion of the in-situ potentiometry experiments reveals a stationary situation established between the destruction and repassivation of the surface structures during continuous cold rolling accompanied with intensive hydrogen evolution. Galvanic coupling of the working rolls with the product significantly intensifies the hydrogen embrittlement related problems of the rolls. Atomic hydrogen is adsorbed on the surface and exhibits a pressure supported absorption into the rolls during their whole lifetime.

Estimation of Roles of Matrix and NbC Particles Dispersed in Surface Layer of Tool by PTA Welding

Investigation has been carried out to estimate the roles of the matrix and NbC particles in the reinforced layer of a tool surface. In the last decade of the last century/In the 1990s it was reported that the reinforced layer of a tool surface by plasma-transferred-arc (PTA) welding using coarse NbC particles showed 10 times longer tool life in hot rolling of stainless steel and titanium. However, the roles of the matrix and NbC particles have not been investigated separately until now. In order to maximize the performance of the tool, it is important to optimize the structure of the welded surface layer, and for this purpose an optimum set of welding parameters of PTA should be selected. In the present work, major welding parameters are changed to clarify the roles of the matrix and NbC particles. The parameters changed are the size of NbC particles in the parent powder, the weight fraction of NbC in the parent powder, and the times of re-melting after PTA welding. For evaluation two types of sliding test are carried out: sliding tests under room temperature and at elevated temperature.

Initiation of Sticking during Hot Rolling of Stainless Steel Plate

Hot rolling of stainless steel is one of the most important steps in manufacturing process regarding surface quality of the product. Stabilised ferritic stainless steels are widely used in automotive and cosmetic appliances but are also concerned by sticking phenomenon. These grades, having high dry corrosion and creep resistance, are enriched in specific chemical elements such as Cr, Nb or Ti, limiting also slab oxidation during hot rolling. Nevertheless, the mastered oxidation of slab surface is a way to protect metal surface from direct contact with rolls. In order to better understand initiation of sticking, a first campaign was based on topography and rolls surface state wear analysis. This study revealed that sticking initiation is not due to the presence of roll scratches which depth is higher than oxide layer thickness. Indeed, the probability that roll scratches are deeper than oxide layer thickness is very low. In a second time, a pilot was designed, reproducing tribological conditions of a roll bite, to better understand mechanisms that initiate sticking. Keeping in mind the importance of rolls and slab surface state, this pilot is able to use specimen taking from industrial products, having the original oxide layer surface. This second study highlighted the major role of silicon oxides on scale adherence and the high heterogeneity of this scale layer in thickness and in chemical composition.

Effects of Contact Pressure, Plastic Strain and Sliding Velocity on Sticking in Cold Forging of Aluminium Billet

Hot rolling of stainless steel is one of the most important steps in manufacturing process regarding surface quality of the product. Stabilised ferritic stainless steels are widely used in automotive and cosmetic appliances but are also concerned by sticking phenomenon. These grades, having high dry corrosion and creep resistance, are enriched in specific chemical elements such as Cr, Nb or Ti, limiting also slab oxidation during hot rolling. Nevertheless, the mastered oxidation of slab surface is a way to protect metal surface from direct contact with rolls. In order to better understand initiation of sticking, a first campaign was based on topography and rolls surface state wear analysis. This study revealed that sticking initiation is not due to the presence of roll scratches which depth is higher than oxide layer thickness. Indeed, the probability that roll scratches are deeper than oxide layer thickness is very low. In a second time, a pilot was designed, reproducing tribological conditions of a roll bite, to better understand mechanisms that initiate sticking. Keeping in mind the importance of rolls and slab surface state, this pilot is able to use specimen taking from industrial products, having the original oxide layer surface. This second study highlighted the major role of silicon oxides on scale adherence and the high heterogeneity of this scale layer in thickness and in chemical composition.

GS10 SUS304ステンレス鋼圧延材の破壊強度異方性

Stainless steel is mainly used as structural materials under severe environment. Therefor clarifying the fracture strength of stainless steel is important. The purpose of this study is to clarify the fracture toughness anisotropy of rolled stainless steel. Inclusion distribution is influenced by the rolling process. The stable crack grows by coalescence of voids which occur as nuclear inclusions. Therefore the distribution of inclusions affects the fracture strength of the material. In this study rolled SUS304 stainless steel with the thickness of 30mm was used. Specimens in the crack direction of the six were produced from this material. The fracture toughness values of these specimens were evaluated by direct current potential difference method. As a result, the fracture toughness of this material showed anisotropy. The specimen of which crack plane was parallel to the rolling plane showed lowest fracture toughness value. This tendency was the same as other the rolled metal material having ductile properties. As a result the orientation relationship between crack plane and rolled surface affects the fracture toughness. In addition, in case the large dimples are present in the fracture surface, the fracture toughness values of the specimens were low.

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part I: Material and fractographic characterization

The failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used in cast glass rolling was carried out by means of traditional characterization techniques (optical metallography, SEM, EDX microanalysis, tensile testing and XRD). The roll was in the as-cast condition and its microstructure featured large proportion of δ ferrite (between 20% and 27%) in a martensitic (α′) matrix, with the δ/α′ interfaces presenting an intergranular network of M23C6 carbides. The crack propagation began in the internal surface of the roll, with δ/α′ intergranular and transgranular cleavage in the “equiaxed region” of the casting, progressing to δ/α′ intergranular ductile fracture in the “columnar” and “chilled regions”. Tensile thermal stresses in the internal surface of the roll associated with microstructural embrittlement (network of interfacial carbide and microporosities) are thought to be the main causes for the premature failure of the roll. Finally, materials selection was performed to replace the CA-15M stainless steel with another class of stainless steel for centrifugal casting.

Cancer incidence among Finnish ferrochromium and stainless steel production workers in 1967–2011: a cohort study

ObjectivesThe aim of the study was to assess the risk of cancer among workers employed in the Finnish ferrochromium and stainless steel industry since the beginning of production in 1967.MethodsThe...

Mechanical modeling of macroscopic behavior for anisotropic and heterogeneous metal alloys

The present investigative work was focused on modeling the effect of through-thickness texture gradients on the global mechanical behavior of a rolled ferritic stainless steel sheet. The material was experimentally characterized according to the needs of the analysis. First, a homogeneous rolled sheet was analytically described, based on Hill’s formalism of generalized materials. Then, a heterogeneous sheet was analyzed through two analytic approaches. The predictive capability of the resulting approaches was also proven in relation to the choice of the pseudo-anisotropic coefficients selected from fictitious materials. Finally, the application of a simple method, called continuum mechanics of textured polycrystals, taking into account crystallographic considerations, was adopted. As a result, this method was found to be an effective way to model the mechanical behavior of an anisotropic and heterogeneous sheet, replicating the evolution of experimental yield stress and plastic strain ratio either in terms of evolution or in those of level values. An attempt to estimate the impact of low-texture gradients on the heterogeneity of any industrial metal sheet is also made.

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.

Analysis of Microstructures and XRD of a Gradient Boron Alloyed Composite Material

A new type of gradient boron alloyed composite material, containing boron alloyed core layers and stainless steel coatings around the core, were designed and prepared by composite casting and hot rolling. The evolution of microstructures, phases and precipitations, as well as their influence on hot rolling process and performance are investigated. A mixture of austenitic matrix and uniformly distributed borides are obtained in the hot rolled stainless steel with 2-2.5 % boron, while massive borides are in the length of 80-120 μm together with micro gaps at the interface between the borides, and the matrix is remained after hot rolling for the core layers with higher boron contents. Hot deformation would be hindered since more precipitations of these orthorhombic or tetragonal phases occur with an increase of the boron concentration in the core layers.

Role of microstructural constituents on surface crack formation during hot rolling of standard and low nickel austenitic stainless steels

The effect of alloy segregation and delta (δ) ferrite contents on surface cracking of three standard (i.e. AISI 304L, AISI 310S and AISI 321) and two low nickel (i.e. LNi-1 and LNi-0.3) austenitic stainless steels (ASS) during hot rolling was investigated using optical microscopy (OM), automatic image analyzer, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electron probe micro analyzer (EPMA). It was observed that the amount of δ-ferrite varied among different grades and also distributed heterogeneously across the width of the steel plates. In general, low nickel ASS showed higher amount of δ-ferrite compared to the standard ASS grades. The tendency to surface cracking during hot rolling gradually increased with increasing δ-ferrite content. Interestingly, carbon and nitrogen exerted maximum effect on δ-ferrite formation. The higher carbon and nitrogen content in the steel decreased δ-ferrite content. In addition, the segregation of Cu and Mn plays significant role in low nickel ASS and Ni-Cr in case of standard ASS has profound effect on surface cracking of the steel plates. A possible cause of surface crack formation/origination in steel plates during hot rolling was discussed.

Recovery of Lubricating Oil for Cold Strip Rolling

A lot of lubricating oil is consumed in the process of the cold rolling of stainless steel. The oil recovery is very important due to some reasons, such as the cost of production and environmental pollution. A set of lubricating oil recovery system is designed and constructed, which is equipped with a set of expanded size recovery oil pan for recycling splashed oil, a high efficiency two-level mist recovery system for recycling the oil mist, and an oil collection platform for recycling the oil rolled. The system is effectively to recovery more of lubricating oil through actual use and measurement.

Spatially Inhomogeneous Recrystallization in Ferritic Stainless Steels

The kinetics of static recrystallization in cold rolled ferritic stainless steel sheet tends to slow drastically over the last 10-20% of recrystallization. This has its origins in both the microstructure (deformed grain shape, precipitates) and in the local deformation texture. In this work we have sought to provide a physical explanation for the slow last stages of recrystallization through a texture dependent JMAK model which is informed by the microstructure of the partially recrystallized microstructure. The geometrical assumptions made in developing this JMAK model have been compared to phase field simulations using experimental observations as the source of their starting configuration.