Oxide scale characterization of ferritic stainless steel and its deformation and friction in hot rolling

The oxidation kinetics of ferritic stainless steel 430 was studied in dry and humid air at 1090 °C by Thermo Gravimetric Analysis (TGA). Different atmospheres and heating times were adopted for reheating to obtain different compositions and thickness of the oxide scale. Hot rolling was performed on a 2-high Hille 100 experimental rolling mill at various reductions. Oxide scale thickness and composition were analysed with optical microscopy (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The surface profiles were examined by a digital microscope, and the topographic features of the thin oxide scale surface were examined with an atomic force microscope (AFM) before and after rolling. The oxide scale surface and steel/oxide interface roughness were measured after rolling. Inverse calculation of the coefficient of friction was employed to analyse and the effect of oxide scale on friction in hot rolling. The coefficient of friction depends not only on the thickness of the oxide scale, but also on its composition and surface topography before hot rolling.     

Sliding wear of 304 and 310 stainless steels

Blocks of 304 (metastable) and 310 (stable) austenitic stainless steels were tested in argon against M2 tool steel rings. Scanning, transmission and scanning transmission electron microscopy analysis, together with microhardness measurements, showed that the strain-induced martensite transformation in 304 steel affects the form and composition of the wear debris and the nature of the transfer layer. The hardness of the transfer layer relative to the hardness of the adjacent deformed base material is also important, as shown in earlier work on Cu-Be. During early stages of sliding, the friction values for both alloys are similar, but whereas the friction continues to rise smoothly to a steady state value for 310 steel, the formation of α'-martensite in 304 steel gives a lower average value of friction coefficient with large fluctuations.     

Wear and corrosion wear of medium carbon steel and 304 stainless steel

Wear and corrosive wear involve mechanical and chemical mechanisms and the combination of these mechanisms often results in significant mutual effects. In this paper, tribological behavior, X-ray peak broadening, and microstructure changes of carbon steel AISI 1045 and stainless steel AISI 304 samples under simultaneous wear and corrosion were investigated and the results were compared with those obtained from dry wear tests. 3.5 wt.% NaCl solution was used as the corrosion agent and a pin-on-disk tribometer was employed to perform wear and corrosive wear tests.X-ray diffraction measurements have shown that by increasing the applied load, the worn surfaces of carbon steel samples reached a constant strain at which fracture and wear occurred. Whereas in 304 stainless steel samples, by increasing the applied load, broadening of X-ray diffraction peaks was decreased.Wear tests of carbon steel and stainless steel samples have shown smaller weight losses and lower friction coefficient in the presence of corrosive environment. Study of worn surfaces suggested that depending on wear environment and applied load, different features of wear mechanisms were involved.     

SUS304亚稳奥氏体不锈钢在耦合摩擦和变形条件下的磨损行为研究

在自制的耦合摩擦和变形的试验机上初步研究了SUS304亚稳奥氏体不锈钢带的磨损变形行为,分析了在耦合摩擦和变形条件下的形变量、磨痕表面的马氏体转变以及磨痕形貌与试验条件的关系。结果表明:研制的试验机实现了SUS304亚稳奥氏体不锈钢带的摩擦和塑性变形的耦合行为;不仅带试样摩擦表面的形貌随正压力增加变化明显,而且其形变量和诱发转变的马氏体量均增大,但马氏体量增加对SUS304奥氏体不锈钢的磨损无明显影响。     

Analysis of tribological feature of the oxide scale in hot strip rolling

In this paper, the effects of the flow stress of the scale and steel, and the friction coefficients at the scale-steel and the roll-scale interfaces on the final surface roughness have been studied. The surface roughness increases for both oxide scale and steel with an increasing friction coefficient at the roll-scale interface. However, the roughness increment is limited. The calculated roughness is close to the measured value. The temperature affects the scale roughness transfer, and the maximum difference is about 25% when the temperature is 850-1025 °C for rolling speeds 0.12-0.72 m/s. The developed model is applicable in hot strip mills.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Lubrication in steel strip rolling in Japan

Research into, and the state of technology for, lubrication in steel strip rolling in Japan are reviewed. Both cold and hot strip rolling are discussed. Subjects covered include coefficient of friction and oil film thickness, friction pick-up, and roll wear.     

The effects of casting and forging processes on joint properties in friction-welded AISI 1050 and AISI 304 steels

The aim of the present study was to investigate the effects of investment casting and forging process on the microstructure and mechanical properties of friction weldments, AISI 1050–AISI 304. A continuous-drive friction welding device with the automatic control ability of friction time and forging pressure was designed and constructed. Factorial design of experiments was performed to join investment cast AISI 1050 steels and forged AISI 1050 steels with AISI 304 austenitic stainless steel with respect to the optimized process parameters. The joint performance was evaluated by tensile and hardness tests performed parallel and perpendicular to the weld interface. Microstructure of forged parts under friction welding was examined using optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. Results of microstructural studies were compared with those of friction welding of investment cast parts. The results reveal that a recrystallized region or a mechanically mixed layer was formed on the AISI 304 side near the weld interface, depending on friction time and friction pressure. Friction welding of forged parts always exhibited higher tensile strength, lower hardness, and more upset than the cast parts.     

基于黏结-滑移摩擦模型的304不锈钢切削力仿真研究*

通过预测加工304不锈钢时产生的切削力,从而对切削参数和刀具几何参数进行优化,是提高304不锈钢的加工精度、切屑控制及保障刀具寿命的基础。建立304不锈钢切削仿真模型,为提高模型的精确性,选择Johnson-Cook本构方程和黏结-滑移摩擦模型。结果表明：采用黏结-滑移摩擦模型的切削力预测结果更为准确,表明相对于纯剪切摩擦与库仑摩擦模型,黏结-滑移摩擦模型能更准确地描述刀-屑摩擦特性。展开不同参数下的切削力研究,研究发现：切削力随着刀具前角、后角和切削速度的增大而减小,随切削刃钝圆半径和切削厚度、宽度的增大而增大,其中切削宽度、厚度及前角对切削力大小影响较大。研究结果为304不锈钢切削效率的提高和切削机制的研究提供了理论依据。     

Evolution of friction-induced microstructure of SUS 304 meta-stable austenitic stainless steel and its influence on wear behavior

The microstructure evolution of the worn surface and sub-surface layer of SUS 304 austenitic stainless steel (ASS) disc against Al₂O₃ ceramic ball were studied on the basis of the tribological behaviors in the tests performed using a Cameron-Plint TE67 pin-on-disc tester. The microstructure after friction test was observed by optical and scanning electron microscope. The possible phase transformation of meta-stable austenite to martensite was detected by X-ray diffractometer. Results showed that friction-induced deformation led to finer grain at the subsurface beneath the worn surface. Furthermore, white layer was observed on some worn surface layers after higher normal loads. Transformed martensite from the austenite appeared on the worn surface under both low and high normal-loading conditions. Absence of transformed martensite was detected at the site about 25 μm below the worn surface although the grains at the site were still intensive and fine. In addition, the specific wear rate of SUS 304 stainless steel specimens was measured, and the possible reasons affecting the wear behavior were analyzed and discussed.     

Investigation of mechanical properties of friction-welded AISI 304 with AISI 1021 dissimilar steels

Austenitic stainless steel and low alloy steels are extensively used in various automotive, aerospace, nuclear, chemical, and other general purpose applications. Joining of dissimilar metals is one of the challenging tasks and most essential need of the present-day industry. It has been observed that a wide range of dissimilar materials can be easily integrated by friction welding. The objectives of the present investigation were obtaining weldments between austenitic stainless steel (AISI 304) with low alloy steel (AISI 1021) and optimizing the friction welding parameters in order to establish the weld quality. In the present study, an experimental setup was designed in order to achieve friction welding of plastically deformed austenitic stainless steel and low alloy steel. AISI 304 and AISI 1021 steels were welded by friction welding using five different axial pressures at 1,430 rpm. The joining performances of friction-welded dissimilar joints were studied, and influences of these process parameters on the mechanical properties of the friction-welded joints were estimated. The joint strength was determined with tensile testing, and the fracture behavior was examined by scanning electron microscopy (SEM) and was supported and backed by energy dispersive spectroscopy (EDS) analysis. Furthermore, the proposed joints were tested for impact strength, and the microhardness across the joint was also evaluated.     

Effect of Extreme Pressure Additives on the Deformation Behavior of Oxide Scale during the Hot Rolling of Ferritic Stainless Steel Strips

High-speed steel (HSS) materials are universally used as work rolls for the hot rolling of stainless steels. Their use has increased the output of the rolling mill and decreased roll material consumption and grinding. Sticking defects often occur, however, during the hot rolling process. In this article, extreme pressure (EP) additives were dropped on the HSS samples at high temperature. Zinc dialkyl dithiophosphate (ZDDP) was chosen as the most effective EP additive by scratch tests on the HSS samples. In order to determine the optimum proportion of ZDDP in the lubricant, two reduction rates were tested on a Hille 100 experimental rolling mill by hot rolling ferritic stainless steel 445J1M at five different concentrations of ZDDP. The mechanism of EP additive action during the hot rolling process was also investigated. By analyzing the deformation behavior of the oxide scale of samples after hot rolling using different proportions of ZDDP, it was found that 20% ZDDP in the lubricant is the preferred concentration for industrial application.     

Influence of oxides on friction in hot rolling: Experimental investigations and tribological modelling

In a hot strip mill, the contact established between the hot strip and the work rolls in the first times of running has to be oxide on oxide to allow the strip to be pulled in the roll bite. The oxide scale formed on the roll is submitted to thermo-mechanical stresses and grows up. From a critical thickness, the scale spalls and causes some superficial damage to the rolls and to the strip.For the roll manufacturers as well as for the steel makers, it is essential to understand the influence of the creation and the growth of such a scale on friction in order to control the antagonist superficial damage and consequently to reduce the running cost of the mill.The present work aims to study the interaction between the oxides formed on a work roll grade and the coefficient of friction established with a strip steel usually rolled by this roll grade. A high temperature tribometer was set up in a pin-on-disc configuration. A previous part of study showed that friction was dependent on the nature of antagonist materials and the thermal transfer. We observed the establishment of a running-in period in the case of a metal-on-oxide initial contact between the pin and the disc which corresponds to the creation of an oxide layer on the pin.The mechanisms that allowed the formation of this scale were determined. SEM observations in conjunction with EDS analysis, both inside and outside the contact area on both antagonists, led to the development of a phenomenological model explaining the creation and the movement of oxide debris in the contact.     

Friction and rolling–sliding wear of DC-pulsed plasma nitrided AISI 410 martensitic stainless steel

In the present work, industrial-scale DC-pulsed plasma nitriding for 20 h at 673 K was used to improve the wear resistance of an AISI 410 martensitic stainless steel. The tribological behaviour was studied and compared to the behaviour of the same steel in as-received condition.Pin-on-disc dry tests, using an alumina ball as counter-body, were carried out to determine the evolution of the friction coefficient. The wear resistance was investigated using an Amsler-disc-machine, employing a dry combined contact of rolling–sliding with three different applied loads. The wear mechanisms involved during rolling–sliding of unnitrided and plasma nitrided steels were investigated by microscopic observation of the surfaces, the corresponding cross-sections and the produced wear debris.The combination of different wear mechanisms taking place in the wear process of unnitrided and nitrided materials were discussed and analyzed. In contrast to the unnitrided steel, DC-pulsed plasma nitrided samples presented an improvement in the friction coefficient and the wear rate.     

A multi-scale model for friction in cold rolling of aluminium alloy

A simple and robust friction model is proposed for cold metal rolling in the mixed lubrication regime, based on physical phenomena across two length scales. At the primary roughness scale, the evolution of asperity contact area is associated with the asperity flattening process and hydrodynamic entrainment between the roll and strip surfaces. The friction coefficient on the asperity contacts is related to a theoretical oil film thickness and secondary-scale roll surface roughness. The boundary friction coefficient at the “true” asperity contacts is associated with tribo-chemical reactions between fresh metal, metal oxide, boundary additives, the tool and any transfer layer on the tool. The asperity friction model is verified by strip drawing simulations under thin film lubrication conditions with a polished tool, taking the fitting parameter of the boundary lubrication friction factor on the true contact areas equal to 0.1. Predicted values of average friction coefficient, using a boundary friction factor in the range 0.07–0.1, are in good agreement with measurements from laboratory and industrial rolling mill trials.     

Tribological property of self-lubricating PM304 composite

PM304 composite has been prepared by high-energy ball milling and powder metallurgy. The composition of the PM304 composite is the same as that of PS304, but the microstructure is quite different. The microstructure of PM304 composite was fine and dense, the size of self-lubricating particles in the composite was very small. The tribological properties of PM304 composites against Inconel X-750 were examined in the temperature range from room temperature to 800 °C. The friction coefficient of PM304 was ranged from 0.32 to 0.41. At room temperature, brittle fracture occurred on the worn surface. With the increase of temperature up to 200 °C, a protective layer consisting of fluorides and Ag existed on the worn surface and led to a low wear rate. The wear resistance of the PM304 was superior to that of the PS304 in the temperature range from room temperature to 650 °C. The improvement in wear resistance of the PM304 was discussed in the terms of its microstructural characteristics.     

冷却方式对不锈钢板翅结构强度和微观组织的影响

对采用镍基钎料BNi-2的304不锈钢板翅结构进行真空钎焊试验,讨论冷却方式对结构强度和微观组织的影响。利用扫描电镜（SEM）对钎焊接头微观组织进行观察;利用能谱分析（EDS）对接头化学成分进行研究。研究结果表明,在其它钎焊工艺参数不变的情况下,冷却方式对304不锈钢板翅结构的强度影响很大。采用现有文献使用的充氮快速冷却的方式,导致钎焊接头产生了较多的裂纹和孔洞,绽得强度降低;采用改进的缓慢冷却方式,即从钎焊温度到620℃,让其自由冷却,当炉中温度降到620℃时,向炉内充氮气并同时启动风机快速冷却。利用高温蠕变松弛原理,释放部分钎焊残余应力,减少了裂纹等缺陷的产生,极大提高了304不锈钢板翅结构的强度。     

高性能不锈钢冷轧轧制油的研制：Ⅰ基础油和助剂的筛选

不锈钢冷轧轧制生产工艺和工况(高速、高温、高压)比较苛刻,轧制不锈钢板带质量要求甚高,因而对不锈钢冷轧轧制油的性能要求很高。研究高性能不锈钢冷轧轧制油基础油和添加剂的配伍性,基于挥发性、表面张力和抗氧化能力3个指标筛选出最佳的基础油,基于抗老化性和黏度2个指标筛选出最佳的抗氧剂,基于磨斑直径与摩擦因数2个指标筛选出最佳的润滑剂;基于最大无卡咬负荷、烧结负荷和摩擦因数3个指标筛选出最佳的助剂。在此基础上,筛选得到了最佳的不锈钢冷轧轧制油配方。     

Wear of metals at high sliding speeds

High speed sliding wear of AISI 1020 steel, AISI 304 stainless steel and commercially pure titanium (75A) was studied using a pin-on-ring geometry. All the tests were carried out in air without any lubricant. The sliding speed was 0.5–10.0 m s^?1 and the normal force was 49.0 N (5 kgf).The friction coefficient of all the materials tested decreased with the sliding speed; this appears to be a consequence of oxide formation. The wear rate of 304 stainless steel increased monotonically with speed, whereas the wear rate of 1020 steel and titanium first decreased and then increased and again decreased, with a maximum occurring at about 5 m s^?1. The complex variation of the wear rate as a function of speed is explained in terms of the dependence of the friction coefficient, hardness and toughness of the materials on temperature. Microscope examinations of the wear track, the sub-surface of worn specimens and the wear particles indicate that the wear mode was predominantly by subsurface deformation, crack nucleation and growth processes, i.e. the delamination process, similar to the low speed sliding wear of metals. Oxidative and adhesion theories proposed in the past to explain the high speed sliding wear of metals are found to be incompatible with the experimental observations.     

Tribology and surface mechanical properties of the oxide film formed by excimer laser surface treatment of AISI 304 stainless steel

The surface hardness and tribological properties of the surface oxide formed by excimer laser surface processing of AISI 304 stainless steel have been examined. It is found that laser processing initially anneals the stress-induced martensite on the surface of the stainless steel, resulting in a softening of the surface. After more than 100 cycles of melting and resolidification, a surface oxide film develops which is harder than the austenite of the annealed substrate and comparable in hardness to the stress-induced martensite. The thickness of the oxide film is dependent on the number of laser pulses, so that arbitrarily thick films can be produced. The dry-sliding friction of the oxide film against a steel pin is substantially lower than that of the untreated polished surface with only the native oxide film and there is substantially less damage in both the wear track and the pin. The hard surface oxide is underlain by relatively soft austenite. The tribological behavior is thus not obviously the result of the surface mechanical properties of the film-substrate combination but is ascribed to changes in the chemical interaction between the pin and the disk.