Gouging and sliding abrasion of austenitic manganese steels reinforced by hard phases

Boron in austenitic manganese steels leads to the formation of (Fe,Mn)₃(B,C) carboborides arranged in a cell-type microstructure.Gouging abrasion tests with a modified 300 J Charpy impact tester (copy of the “Uppsala pendulum”) reveal that these carboborides do not improve the wear resistance. This originates from their relatively low hardness compared with the work-hardened matrix, from a weak bonding to the austenite as well as from favourable conditions for unimpeded crack propagation and crack branching within the carboboride cell walls.However, pin abrasion tests on flint abrasive paper show that carboborides, hardened, for example, by additions of vanadium, substantially increase the abrasive wear resistance. This results from a supporting effect of the hard phase cell structure on the abrasive agent which consequently impedes wear of the softer matrix.     

Mechanisms of dry wear of some martensitic steels

The basic wear mechanisms operating when two identical steel surfaces are rubbed against each other were studied to determine material parameters essential for wear resistance. Three simple model alloys, with the same basic properties as tool steels, were developed, containing three different predetermined volumes of M₇C₃ carbide, having approximately the same hardnesses after hardening and annealing, and approximately the same composition of the matrix.Unlubricated sliding wear tests were performed in air, using a pin-on-ring type machine. Normal force, sliding speed and sliding distance were varied. Friction force and temperature were recorded during the test and changes in weight of specimens were measured. The worn surfaces were carefully examined by scanning electron microscopy, in an attempt to classify the different wear mechanisms.It was found that corrosive wear dominates at low sliding speeds (2 m/min). Material annealed to a lower hardness had a lower wear resistance, irrespective of carbide content. The wear is characterized as mild.At high sliding speed (100 m/min) and especially for high normal forces, the wear was dominantly by a severe adhesive mechanism. Tempering to a lower hardness gave better wear resistance, which indicates that the room temperature hardness is not significant when a high contact temperature is reached. The influence of the carbide content was complex. The results indicate that a carbide free material is the most wear resistant, because of the more extensive occurrence of corrosive wear. Abrasives such as carbides in the more carbide rich alloys may possibly tear up protective corrosive layers and expose the steel to adhesive wear.     

Phase transformations in austenitic stainless steels during low temperature tribological stressing

The tribological behaviour at low temperatures is unknown for many materials even for those widely used in cryogenic engineering. Because of the extension of applications of low temperature technologies there is a need for investigations in this field. It is the aim to study the stability of the austenitic structure of FeCrNi alloys under these harsh conditions. This paper deals with tribological experiments with alloys of different stability of the austenitic structure in the temperature range between room and liquid helium temperature. It was found that alloys stable at room temperature show martensitic transformation under tribological stressing and decreased service temperature. The obtained transformation behaviour does not exhibit a linear tendency down to liquid helium temperature. A maximum could be stated.     

Corrosive wear of carbon and austenitic stainless steels in NaCl solution

The wear rates of an AISI 52100 carbon steel and a type 316 austenitic stainless steel and the corrosion current I from the rubbing steels were measured in NaCl solution to study the interrelationship between the corrosion and wear of the steels. An on-off cyclic loading test was also conducted to examine the effect of static corrosion during an unloading period on the corrosive wear of the steels.

It was found that the wear rates of the carbon steel and the type 316 stainless steel reach a maximum at NaCl concentrations of about 3% and 0.1% respectively. The on-off cyclic test has shown that corrosive wear of the steels is influenced by static corrosion during an unloading period. The increment †I of the corrosion current due to sliding was associated with the corrosive wear rate of the steels.     

Corrosion-wear mechanisms of hard coated austenitic 316L stainless steels

Austenitic stainless steels like 316L are amongst the most commonly selected structural alloys for use in corrosion environments. Unfortunately, their resistance to surface degradation caused during sliding contacts with other materials, in such environments is poor. Here, a synergistic combination of mechanical (wear) and chemical (corrosion) processes, known as corrosion-wear processes, are responsible for causing surface material loss. Accordingly, efforts are being made to identify surface treatments that can enhance the corrosion-wear resistance of 316L and similar alloys. One plausible solution is to apply thin hard coatings (∼5-10 μm thick) using various plasma-based technologies. In practice, this is often fraught with difficulty because of the complex nature of the pervading corrosion-wear mechanisms. This paper presents our recent work that has identified three major corrosion-wear mechanisms that must be minimised if a successful surface engineering design is to be achieved for corrosion-wear protection. These are: Type I—the removal of the coating passive film during sliding contact; Type II—galvanic attack of the substrate resulting in blistering of the coating and; Type III—galvanic attack of the counterface material leading to abrasion of the coating during subsequent sliding contact.     

Comparison of radiation-induced segregation in ultrafine-grained and conventional 316 austenitic stainless steels

Due to a high number density of grain boundaries acting as point defect sinks, ultrafine-grained materials are expected to be more resistant to irradiation damage. In this context, ultrafine-grained 316 austenitic stainless steel samples have been fabricated by high pressure torsion. Their behavior under ion irradiation has been studied using atom probe tomography. Results are compared with those obtained in an ion irradiated conventional coarse-grained steel. The comparison shows that the effects of irradiation are limited and that intragranular and intergranular features are smaller in the ultrafine-grained alloy. Using cluster dynamic modeling, results are interpreted by a higher annihilation of point defects at grain boundaries in the ultrafine-grained steel.     

Elastoplastic phase-field simulation of martensitic transformation with plastic deformation in polycrystal

The martensitic transformation with plastic deformation in polycrystal is investigated by the elastoplastic phase-field model. The model can capture not only spatiotemporal change of martensitic microstructure, but also plastic deformation behavior to accommodate transformation-induced stress. In this paper, fcc→bcc martensitic transformation in Fe-Ni polycrystalline alloy is simulated in two-dimensions. The effects of self- and plastic accommodations on the transformation kinetics and morphology of microstructure are studied. The simulation results demonstrate that the martensite phase nucleates near crystal defects and grows into the parent phase. The morphology of the growing martensite phase presents a plate-like shape to minimize the elastic strain energy. The present simulation clearly shows that stress relaxation behavior is dominant factor which characterizes the morphology of martensite phase. The martensitic transformation only with the self-accommodation produces fine multivariant lamellar microstructure which accommodates internal stress-field. The high stress-field in the microstructure prevents completion of the transformation and causes formation of retained parent phase. In the martensitic transformation with the self- and the plastic accommodations, since the plastic deformation largely reduces the elastic strain energy, the self-accommodation driven by reduction of the elastic strain energy is suppressed. As a result, coarse multi-variant microstructure emerges in the grain where large amount of plastic strain is introduced. Furthermore, the parent phase can transform into the martensite phase completely.     

Improvement of indentation technique for measuring general biaxial residual stresses in austenitic steels

Investigations on engineering structures show that residual stresses in combination with external loads can cause failure in loads that are less than the design threshold. Due to the applicability of austenitic steel in important industries (such as oil pipelines), accurate measurement of residual stress in this material is very important. Indentation is a new method for estimating residual stress. In this paper, by performing a large number of finite element simulations, the accuracy of residual stress measurements in austenitic stainless steels using indentation was studied by performing a large number of finite element simulations. Three different models (Suresh's, Wang's and Lee and Kwon's model) were investigated and it was found that the Lee and Kwon's model has a more accurate prediction of residual stress values in austenitic steels.Based on these numerical simulations and by studying how the residual stress measurement error of Lee and Kwon's model changes according the stress ratio, a method is suggested to correct this error and calculate the real amount of non-equibiaxial residual stresses in austenitic steels. The procedure is significantly reducing the error of residual stress measurement (from about 50% to less than 10%) and has been verified by conducting experimental test on a sample made from austenitic steel.     

The effect of nitrogen on the scratch resistance of austenitic stainless steels

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N₂+Ar) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress–strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too.     

Machining of austenitic stainless steels using CVD multi-layer coated cemented carbide tools

This paper presents the results of experimental work in dry turning of austenitic stainless steels (AISI 304 and AISI 316) using CVD multi-layer coated cemented carbide tools. The turning tests were conducted at four different cutting speeds (120, 150, 180 and 210 m/min) while feed rate and depth of cut were kept constant at 0.16 mm/rev and 1 mm, respectively. The cutting tools used were TiC/TiCN/TiN and TiCN/TiC/Al₂O₃ coated cementide carbides. The influences of cutting speed, cutting tool coating top layer and workpiece material were investigated on the machined surface roughness and the cutting forces. The worn parts of the cutting tools were also examined under scanning electron microscope (SEM). The results showed that cutting speed significantly affected the machined surface roughness values. With increasing cutting speed, the surface roughness values decreased until a minimum value is reached beyond which they increased.     

The unlubricated adhesive wear resistance of metastable austenitic stainless steels containing silicon

The unlubricated adhesive wear resistance of metastable austenitic stainless steels can be improved by silicon additions. At low surface temperatures (under the M_d temperature) metastability appears helpful in maintaining the alloy in a state of mild wear. Silicon was not found to promote alloy metastability but did tend to strengthen the alloy by solid solution hardening. At lower temperatures the silicon had little effect on the mild wear rates of metastable alloys but did act to lower the severe wear rates of stable alloys. At high surface temperatures (above the M_d temperature) the silicon additions (2–4%) were found very beneficial in promoting mild wear rates while metastability had little or no effect. Silicon additions were also found to be beneficial to the oxidation resistance and did not increase the running-in period for the alloys. Improving the oxidation resistance of these alloys is more effective in promoting mild wear than is increasing the hardness through metastability.     

Using magnetic testing to optimize the technology of manufacturing stain-proof austenitic steels

Some results are presented that are concerned with the use of magnetic methods and tools for nondestructive testing of articles made of OAO Izhstal’ austenitic chrome-nickel steels. It is shown that modern magnetic-testing techniques help significantly in optimizing the industrial process while improving the technical specs of the produce.     

Performance of cryogenically treated M35 HSS drills in drilling of austenitic stainless steels

In this study, performance of cryogenically treated M35 high speed steel (HSS) twist drills in drilling of AISI 304 and 316 stainless steels was evaluated in terms of thrust force, surface roughness, tool wear, tool life, and chip formation. To present the differences in tool performance between untreated and treated drills, and machinability between AISI 304 SS and AISI 316 SS, a number of experiments were performed at different combinations of cutting speed, and feed rate. As the results of the conducted experiments, the treated drills showed better performance than untreated drills in terms of thrust force, surface roughness, and tool wear and tool life for both types of stainless steels. Tool lives of treated HSS drills in drilling of AISI 304 SS and AISI 316 SS improved 32% and 14%, respectively, when compared with untreated drills. Experimental results also showed that machinability of AISI 304 SS was harder than the machinability of AISI 316 SS.     

Tribological investigation of commercially sintered steels under dry sliding conditions against austenitic steel

In this study the wear and friction of uncoated sintered steels, their relationship with microstructure and toughness when tested against austenitic steel were investigated. The metallographic investigation and the quantitative testing are interrelated in such a way that one can explain the other, and together they explain the wear behaviour of the sintered parts. The paper identifies the main wear mechanisms in this particular type of testing for the investigated materials. For the same materials, the paper also proves in quantitative terms (for the first time) the correlation between material fracture toughness and its wear behaviour - a correlation demonstrated before for other materials by theoretical studies.     

Behavior of austenitic stainless steels at high speed turning using specific force coefficients

Turning operation has been widely studied, and it is a well-known process. However, still today some limitations exist in the processing of some materials, mainly due to the poor or inexistent characterization. Such is the case of austenitic stainless steels, which in spite of being materials of high economic and technological value, their behavior to machining is still not well understood in some aspects. There are not reliable and updated technological data about austenitic stainless steels at industry. This fact is especially significant when considering technological development conducted by a continuous increment of cutting speeds. Nowadays, there is not a reliable mechanistic model for austenitic stainless steels turning adjusted for high cutting speeds. In this paper, a mechanistic model for cutting force prediction is presented. This model was developed for machining with nose radius tools considering the effect of the edge force due to the rounded cutting edge. In addition, a set of machining tests were carried out to obtain the specific force coefficients expressions for austenitic stainless steels using the mechanistic approach at high cutting speeds. The specific cutting coefficients were obtained applying the force model as an inverse model. This paper presents expressions for shearing and edge cutting coefficients which are valid for a wide range of cutting conditions. Results were validated by comparing the values estimated by the model with the ones obtained by experimentation.     

Cryogenic fracture toughness evaluation for austenitic stainless steels by means of unloading compliance method

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch (SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.     

Adhesive and abrasive wear behaviour of TiC alloyed,sintered, austenitic stainless steels

Abstract

This study examines abrasive and adhesive wear behaviour of austenitic stainless steel and its TiC alloyed composite produced through powder metallurgy technique. Abrasive wear tests have been carried out using a pin on disc wear tester under loads of 10, 20 and 30 N. For adhesive wear tests, a block on ring wear tester has been used under loads of 20, 40, 60 and 80 N. A possible correlation between the hardness, microstructure and wear behaviour of the samples has been investigated. The abrasive wear tests have revealed that the highest rate of mass loss occurred in the austenitic matrix stainless steel sample; also, mass losses decreased with an increased rate of reinforcing material in the composite. In adhesive wear tests, interparticle spacing developed from severe wear and extreme plastic deformation under heavy loads; however, at low loads, oxidation type wear was shown to be dominant.     

Atom probe tomography investigation of assisted precipitation of secondary hardening carbides in a medium carbon martensitic steels

A medium carbon martensitic steel containing nanometer scale secondary hardening carbides and intermetallic particles is investigated by field ion microscopy and atom probe tomography. The interaction between the concomitant precipitations of both types of particles is investigated. It is shown that the presence of the intermetallic phase affects the nucleation mechanism and the spatial distribution of the secondary hardening carbides, which shifts from heterogeneous on dislocations to heterogeneous on the intermetallic particles.     

Improved work-hardening ability and wear resistance of austenitic manganese steel under non-severe impact-loading conditions

An investigation into the work-hardening mechanism and the method of improving the work-hardening ability and the wear resistance of austenitic manganese steel, under non-severe impact-loading conditions, by means of transmission electron microscopy and X-ray diffraction has been conducted in this project. The results indicate that the work-hardening effects result from increased dislocation density and stacking faults for the manganese steel with higher austenite stability, while they result from the combined effects of dislocation strengthening and strain-induced martensite for manganese steel with lower austenite stability. By comparison with Hadfield steel, the work-hardening ability and the wear resistance of the austenitic medium manganese steel increase by 60%–120% (the highest surface hardness up to 700 HV) and 50%–140% respectively, if the chemical compositions and technology are properly controlled, to obtain suitable austenite stability and secondary phase hard particles.     

TiN涂层刀具切削高锰钢的磨损破损研究

研究奥氏体高锰钢切削过程中TiN涂层硬质合金刀具的磨损、破损机制,测量了切削温度并得出后刀面磨损量与 切削时间和切削速度的关系曲线,以及刀具前、后刀面显微磨损、破损形貌和化学变化。结果表明,TiN涂层硬质合金刀 具切削奥氏体高锰钢时耐磨性优于单一硬质合金刀具,且适于低速切削(小于30m/min)。