Wyniki wyszukiwania - Biblioteka Nauki

1

Hydrogen embrittlement in low carbon steel

100%

Siddiqui R. A. , Abdul-Wahab S. A. , Pervez T. , Qamar S. Z.

|

2007

|

tom Vol. 28, nr 1-4

136-142

EN

Many metals and alloys absorb hydrogen and diffusion of hydrogen under certain conditions can seriously weaken and produces embrittlement in steel. Hydrogen embrittlement is a type of metal deterioration that is related to stress corrosion cracking. Although steels are well known for their susceptibility to hydrogen embrittlement, the mechanism of transportation of hydrogen is not very clear in low carbon steels. Standard tensile steel specimens were hydrogenated from 1 to 5 hours and deformed by cold worked to 50%, 60%, 70% and 80% and were investigated for mechanical properties.

2

Experimental investigation of effects of external loads on erosive wear

100%

Imrek H. , Bagci M. , Khalfan O. M.

|

2009

|

tom Vol. 32, nr 1

18-22

EN

Purpose: The purpose of the paper is to investigate effects of external loads on erosive wear. Design/methodology/approach: In this experimental study, specimens were placed on specially designed a specimen holder and then, external tensile loads corresponding to 0%, 20%, 40% and 60% of the specimen’s yield strength were applied on the specimens. For every load step, the specimens were subjected to 15ş, 30ş, 45ş, 60ş, 75ş and 90ş of erodent impact angles. At the end of the tests, effects of external loads and impingement angles on erosive wear were studied. In the experimental set, dry and compressed air was used to impinge erodents onto the test specimens and subsequent wear was investigated. During the tests, the impingement angles were adjusted by turning the specimen holder around its axis. Erodent particles used were SAE G40 having internal uniform martensitic structure and angular geometry. Determination of erodents speed was achieved with the help of the Rotating Double Disc Method. The speed used in the tests was 30 m/s. Findings: At the end of the tests, erosive wear rates were obtained as functions of stresses and impingement angles. Graphs showing variations of erosive wear rates for load values obtained against every impingement angle and yield stress were drawn. Critical impingement angle and load values at which maximum erosion rate was obtained were determined. Research limitations/implications: In researches made on erosive wears so far; there are only few studies dealing with the effects of external loads on the specimens subjected to erosive wear. By considering that stresses may affect the erosive wear, the stress state around contact area as well as material properties, this experimental study has thus, investigated likely effects of stresses on the erosive wear. With the help of the designed special specimen holder, the specimens were subjected to tensile stresses that are lower than the yield strength of the material and then the erosive wear was investigated. Originality/value: The investigations of effects of external loads on erosive wear.

3

Computer simulation of working stress of heat treated steel specimen

100%

Smoljan B. , Iljkic D. , Smokvina Hanza S.

|

2009

|

tom Vol. 34, nr 2

152-156

EN

Purpose: In this paper, the prediction of working stress of quenched and tempered steel has been done. The working stress was characterized by yield strength and fracture toughness. The method of computer simulation of working stress was applied in workpiece of complex form. Design/methodology/approach: Hardness distribution of quenched and tempered workpiece of complex form was predicted by computer simulation of steel quenching using a finite volume method. The algorithm of estimation of yield strength and fracture toughness was based on steel hardness, HV. Yield strength and fracture toughness distributions have been predicted using the Hahn-Rosenfield approach. Findings:It can be concluded that working stress of quenched and tempered steel can be successfully predicted by proposed method. The further experimental investigations are needed for final verification of established model. Research limitations/implications: For efficient estimation of fracture toughness from hardness, additional data about microstructure are needed. Practical implications: Estimation of hardness distribution can be based on time, relevant for structure transformation, i.e., time of cooling from 800 to 500 şC (t8/5). The prediction of distribution of microstructure composition, yield strength, and fracture toughness, can be based on steel hardness. Originality/value: Hardness distribution is predicted by involving the results of simple experimental test, i.e., Jominy-test in numerical modelling of steel quenching.

4

Computer simulation of mechanical properties of quenched and tempered steel specimen

80%

Smoljan B. , Iljkić D. , Tomašić N.

|

2010

|

tom Vol. 40, nr 2

155-159

EN

Purpose: The computer simulation of mechanical properties of quenched and tempered steel was investigated. The established method of computer simulation was applied in prediction of mechanical properties of workpiece with complex form. Design/methodology/approach: The method of computer simulation of mechanical properties of quenched and tempered steel was established by theoretical analysis of relevant properties which have influence on hardness of quenched and tempered steel, and by regression analysis based on experimental results. Findings: The new method of prediction of mechanical properties of quenched and tempered steel was established. Proposed method of computer simulation of mechanical properties of quenched and tempered steel is based on predicted steel hardness. Hardness distribution of quenched and tempered workpiece of complex form was predicted by computer simulation of steel quenching using a finite volume method. It was found out that mechanical properties of quenched and tempered steel can be successfully predicted by proposed method. Research limitations/implications: The investigation was done on carbon and low alloyed steel. The further experimental investigations are needed for final verification of established model. Practical implications: The established method could be applied in industrial practice. Originality/value: As-quenched hardness distribution is predicted by involving the results of simple Jominy-test in numerical modelling of steel quenching. Estimation of hardness distribution is based on time, relevant for structure transforma- tion, i.e., time of cooling from 800 to 500°C (t8/5). The distribution of mechanical properties in quenched and tempered steel workpiece is estimated based on as-quenched steel hardness, tempering temperature and Jominy-test results.

5

Mechanical properties dependency of the pearlite content of ductile irons

80%

Gonzaga R. A. , Martinez Landa P. , Perez A. , Villaneuva P.

|

2009

|

tom Vol. 33, nr 2

150-158

EN

Purpose: In this work, it is pretended to make a comparison of different pearlite contents in pieces with similar shape and dimensions and to analyze the variation of mechanical properties as pearlite content increases. The three pieces used had form of stair made of ductile cast iron. Design/methodology/approach: The present study was based on an adequate balance of alloying elements. None heat treatment was used to obtain different pearlite contents in the microstructures. Many specimens taken from the cast were mechanized to be polished and swabbed with nital to analyze the microstructure. To study the mechanical properties these casts present many tests were done such as Charpy impact test, done at different temperatures. Fracture toughness and tensile strength tests were done, as well. Findings: This study gave evidences that heat treatments are not necessary to obtain different pearlite content in the microstructure. Good mechanical properties are obtained by an appropriate balance of alloying elements. Research limitations/implications: They are that of natural sources. Besides, high and precision technology must be applied to get the present results better. Practical implications: Cast iron productions are focussed straight on machine building and automotive industries and constructions. The low cost production of ductile cast iron, its mechanical properties and low cost transformations are the tempting for application. Originality/value: The whole experimental work and the appropriate results obtained as consequences of the analysis carried out are novel, although applied methods are well known. Values presented in tables are given as new results of our experiments. This work is of great importance for the development of new economical methods for ductile iron production. This study is directed to researchers and metallurgy centres.

6

Formability modelling of aluminium base PM alloys.

61%

Bagaviev A. , Durisin J. , Dybiec H. , Klein K. , Mandziej S. , Ziaja G.

|

1998

|

tom R. XIX, nr 4

1153-1158

EN

The paper presents the results investigations carried out in the frame of the Project CT 96-0750 MicroAlu of Inco-Copernicus program. The investigated materials are PM aluminium alloys with high contents of silicon. The aim of this part is a comprehensive characterisation of microstructure features and specific parameters at the example of an AlSi27Ni6 alloy. The experiments on the plastic and viscoplastic behaviour of this alloy (compressive and tensile tests) at different temperatures and strain rates were done to identify the material properties. The evolution of the microstructure of the tested specimens due to temperature rise and deformation process was investigated with optical and electron microscopy as well as with X-ray analysis technique. The alloy was compacted by a PM extrusion process to a preform and then forged to a final product -connecting rod. From the performed experiments the constitutive parameters were identified and the connecting rod forging process has been simulated by means of a general purpose FEM program.