Kati Valtonen

The Deformation, Strain Hardening, and Wear Behavior of Chromium-Alloyed Hadfield Steel in Abrasive and Impact Conditions

Abstract The alloying of Hadfield steels aims at enhanced mechanical properties and improvements in the wear resistance. In this work, the impact and abrasive properties of a chromium-alloyed high-manganese Hadfield steel were experimentally studied using a wide variety of testing techniques and characterization methods. In addition, an in-service sample was characterized to identify the wear and hardening mechanisms in a real application (jaw crusher). The dynamic mechanical behavior of the steel was determined using the Hopkinson split bar technique. The abrasion properties were studied with three-body abrasion tests using several different natural abrasives. The effects of existing plastic strain and normal loading on the surface hardening and wear rate were further investigated with scratch testing. High-velocity impact testing was performed to evaluate the effect of pre-strain on the impact wear behavior of the material. It was shown that the dynamic loading affects both the yield behavior and the strain hardening rate of the studied steel. The connection between pre-strain, hardness, and wear rate in abrasion was established. In impact conditions, plastic straining of the surface layer first has a positive effect on the wear resistance, but when strain hardening reached the observed ductility limit, it showed an adverse effect on the material’s performance. The addition of chromium and an increase in the manganese content from the nominal ASTM Hadfield composition provided some improvements in the strength, ductility, and surface hardening of the studied steel.

Effect of test parameters on large particle high speed slurry erosion testing

Abstract A high speed slurry-pot wear tester was developed for close-to-reality heavy-duty wear testing of materials used in mineral applications. The samples are attached on four levels in a pin mill configuration. The tester and the developed sample rotation test method deliver reproducible results. This study focuses on the effects of testing parameters in large particle slurry testing. Parameters such as the speed, particle size and slurry concentration were varied. The effect of test duration was also examined. Round steel samples and slurry of water and granite gravel were used for testing. The test parameter variations were 4 to 10 mm for particle size, up to 23 wt-% for concentration and up to 20 m s−1 for the sample tip speed. The relationships between the parameters are discussed. The kinetic energy of the large abrasive particles is also considered. Wear surfaces studied with optical and electron microscopy are also presented and discussed.

Impact-abrasion wear of wear-resistant steels at perpendicular and tilted angles

Earth moving and processing machinery has to withstand heavy wear caused by impacts and scratching by the soil. Especially, the edges are subjected to heavy wear. To simulate these conditions, impeller–tumbler impact-abrasion wear testing equipment was used to determine the wear resistance of four steel grades at perpendicular and tilted sample angles. The angles were selected to simulate the loading conditions. Natural granite rock was used as abrasive. The amount of wear was clearly smaller in the harder materials. The significance of hardness was quite similar at both sample angles in the steady-state wear of wear-resistant steels. On the initial state wear, hardness had a slightly greater effect at the perpendicular angle due to more severe wear in sample edges already at the beginning of the test. Overall, the largest differences in wear were observed in the sample edges. At the perpendicular sample angle, the sample edges were much more rounded. Some small differences were observed in the surface formations due to dissimilar movement of the abrasive. Deformed surfaces and fractured lips indicated that wear occurred mainly by the deformation of material followed by the removal of the deformed areas through impacts. In addition, scratches and dents were observed. It was found that larger sized abrasives caused higher mass loss than abrasives of similar mass but smaller size. Moreover, same amount of abrasive particles in each test reduces the scatter of the results.

Effect of Multiple Impacts on the Deformation of Wear-Resistant Steels

More durable materials enable reducing the downtime and maintenance costs by decreasing the number of replaced core components in various industrial applications. In this study, the behavior of three wear-resistant quenched martensitic steel grades and the S355 structural steel was examined in controlled impact conditions. The materials’ impact behavior was investigated by several methods including residual stress measurements and electron backscatter diffraction. For all studied materials, the size and depth of the impact marks correlate via a logarithmic function to the number of impacts mostly due to work hardening. The underlying deformation behavior of the material depends on the mechanical properties and microstructure of the material. At high impact counts, softer martensitic steel was found to behave differently when compared to the other tested materials as it underwent severe changes in its microstructure and exhibited marked hardening.

Modelling and testing of elastomer impact deformation under high strain rates

Abstract Elastomers are frequently used in applications involving repeated impacts of hard abrasive particles on surfaces at high or moderate strain rates. Operational conditions of components experiencing erosive and impact type wear are sometimes difficult to mimic in laboratory conditions, and as such, it is common to approach behaviour and lifetime predictions by meticulously studying different types of single impacts. This is particularly true for characterising and modelling of high strain rate impact events between hard particles and a wearing elastomer surface. This work presents and applies such a methodology for two specific elastomer materials: a natural rubber (NR) and styrene–butadiene rubber (SBR) compounds. The elastomer materials are subjected to quasistatic and dynamic testing conditions for determination of hyper- and viscoelastic material properties. The results are used in an iterative calibration procedure for establishing related constitutive models by applying the Ogden and Prony series models.

Correlation of wear and work in dual pivoted jaw crusher tests

A laboratory sized jaw crusher with uniform movement of the jaws, the dual pivoted jaw crusher, was used to determine the relationship between wear and work. Wear was concentrated on the jaw plates opposing each other and was measured as mass loss of the specimens. Work was measured directly from the force and displacement of the instrumented jaw, which allowed work to accumulate only from the actual crushing events. The tests were conducted with several jaw geometries and with two motional settings, where the relation of compressive and sliding motion between the jaws was varied. The tests showed that the relation between wear and work was constant in many of the tested cases. In certain tests with larger lateral and faster contact speed, wear occurred at relatively lower amounts of work. This behavior was more definite when the relation of wear and work was investigated using modified Archards wear equation. The results indicate that the lower amount of needed work could stem from the material reaching a dynamic situation, where the flow stress becomes increasingly strain-rate dependent.

Effect of quartzite and granite in wear surfaces on dry sliding

Abstract The wear surfaces abraded with quartzite and granite were subjected to scratch tests. Sharp and blunt indenters were used with various constant loads to produce controlled abrasive wear tracks. The characteristics of deformation mechanisms and material removal were further studied using a scanning electron microscope to determine the differences in the tribological behaviour between the quartzite and granite wear surfaces. The results indicate that quartzite residues are more uniformly distributed as individual particles on the wear surfaces and therefore provide more stable frictional forces. In the case of granite the abrasive residues are rather non-uniformly collected into piles of abrasives.

Tribological Testing and Modeling of Elastomeric Materials

In applications which experience repeated impacts by hard abrasive particles at high or moderate strain rates, elastomers are commonly used. The goal of the current work is to develop a methodology involving scratch testing and modeling which would be simple and cost effective for capturing the failure and wear behavior of elastomeric materials. The high failure strains as well as the extremely good wear resistance of elastomers make this task a formidable challenge. Modeling of a scratch test, however, seems to be promising in this regard.