Joel R. Teodósio

Mechanical properties of a quenched and tempered dual phase steel

Low carbon steels can be properly heat treated to produce a high strength dual phase structure of ferrite plus martensite. The heat treatment may consist of an intercritical annealing (between A{sub 3} and A{sub 1}) followed by rapid cooling to promote the austenite{r_arrow}martensite transformation. In this paper, mechanical properties of a heat treated dual phase steel were investigated as a function of the martensite volume fraction. The changes promoted by tempering at 100 C, 200 C and 300 C were measured and investigated. Residual stresses introduced by quenching from the intercritical temperature and the changes occurred during the tempering were also measured.

Analysis of residual stress state in speed gears for automotive vehicles

The residual stress profiles in speed gears for automotive vehicles were determined. The profiles were measured at the root between two teeth of the gears by x-ray tensometry without the necessity of cutting the pieces. The gears were cemented, quenched and annealed. After this heat treatment, compressive residual stresses were introduced by shot-peening. The profiles indicate the maximum residual stress of -950 MPa (compressive) at a depth of 0.05 mm. The stresses are zero at a depth of 0.25 mm. In the gears without shot-peening the maximum residual stress at the surface is -600 MPa (compressive) and is zero at a depth of 0.30 mm.

Magnetic and mechanical hardening of Fe-based alloys

Abstract The aim of this work was the analysis of the influence of precipitates on the magnetic and mechanical properties, during the thermal treatment of a duplex stainless steel at 475 and 550°C, as well as during the thermal aging at 610°C of a Fe–20Mo–5Ni–0.12C alloy. In the duplex stainless steel it was verified that the precipitation of the α′ phase inside the α phase increases the coercive force, H c , and increases the mechanical hardness of the α phase, for the heat treatment at 475°C. In this process the mechanical hardness of the γ phase remains constant. After the heat treatment at 550°C the mechanical hardness of the α phase and the coercive force of the stainless steel remain practically constant. For the Fe–20Mo–5Ni–0.12C alloy the thermal aging at 610°C results in simultaneous magnetic and mechanical hardening. In both cases (steel and alloy) the magnetic and mechanical hardening curves are similar.

Magnetic properties and thermomagnetic analysis of a Fe-20Mo-5Ni-0.075C alloy

A Fe-20Mo-5Ni-0.075C (wt %) alloy for magnets was prepared by induction melting under vacuum. The material was hot rolled, solution treated and aged at 610°C for different periods of time. The magnetic properties (Hc, Br, Bs and (BH)max) were measured and compared with some commercial alloys containing cobalt. The precipitation of Mo-rich phases and the decrease of the ferrite lattice parameter during ageing were detected by X-ray diffraction. The thermomagnetic analysis (TMA) was carried out in the solution treated samples and aged samples. The behaviour of TMA curves was explained with the help of X-ray analysis.

Magnetic hardening in a hot-rolled Fe-20Mo-5Ni-0.12C alloy

Abstract The magnetic properties in an Fe-20Mo-5Ni-0.12C alloy, hot-rolled, solution treated at 1230°C and aged at 610°C for different times were measured. These properties were compared with those of the same alloy previously cold-rolled, solution treated at the same temperature and aged under the same conditions. The results for the same alloy without carbon, obtained by other authors, have also been considered. The alloy presented magnetic hardening during aging, reaching a H c value of 401 Oe after 240 min. of aging. The precipitation hardening was accompanied by thermomagnetic analysis (TMA) in the range 25–800°C and X-ray diffraction.

Texture development and magnetic anisotropy in semi-hard magnetic Fe20Mo5Ni alloys

This work analyzes the crystallographic texture of cold rolled and magnetic aged samples of Fe20Mo5Ni with 0.020, 0.057 and 0.092% of carbon. Results were compared with the increase of magnetic anisotropy represented by the relation between remanence (B{sub r}) and saturation induction (B{sub s}). Results show that these alloys have a sharp {l_brace}100{r_brace} texture component after magnetic hardening that increases with rolling reduction. Magnetic anisotropy increases with this component.

Microstructural features of a Fe-20Mo-5Ni-0.12C magnetic alloy

The Fe-20Mo-5Ni-0.12C alloy after hot rolling presented coarse precipitates with the following approximated composition: 56.30%Mo, 35.96%Fe, 1.68%C, 2.01%Ni and traces of W (0.54%). One may deduce that, in agreement with the chemical analysis, that the coarse precipitates are carbides of type M{sub 6}C where M is Fe or Mo. Ni and W are present as solid solution elements, and are preferentially dissolved in the {alpha} matrix. The precipitates are stable at temperatures as high as 1,250 C. They are ferromagnetic carbides and are responsible for the high Hc values of the alloy.

Portable x-ray apparatus for stress measurements

Portable apparatus presented in this paper is an x-ray equipment permitting to carry out traditional stress determination by x-ray diffraction method both in-laboratory and in-field conditions. The portability of apparatus is achieved by construction of compact and light high voltage source coupled with special x-ray tube and using of coordinate sensitive detector. Other distinctive characteristic of apparatus is an absence of a goniometer. Special collimator and simple meter of incidence angle permit to substitute the goniometer and to carry out the stress measurements of different industrial equipments such as pipelines, tanks. Software program executes a control of measurement procedure and carries out data processing experimental results.

Residual stress state behaviour under fatigue loading in pipeline welded joints

Compressive residual stress state behaviour under fatigue of the welded joints of a pipeline were investigated. The regions on the intersection between the welded joints of the longitudinal pipe manufacturing seam and the circumferential welded joints of the pipeline construction were investigated. Stress-controlled fatigue loading was carried out at various stress ratios of the yield strength of the base metal. Surface residual stresses were introduced in samples by shot-peening treatment and were measured using X-ray diffraction techniques. The results showed that compressive residual stresses which, unless they are relieved or inverted during the process of fatigue loading, make crack initiation difficult.

Secondary recrystallization and magnetic properties of an Fe-50Ni-1.26Mn alloy

Abstract A complete survey of the crystallographic texture of an Fe-50Ni-1.26Mn alloy, secondarily recrystallized (S.R.), was undertaken by means of the Three-Dimensional Function of the distribution of Crystallographic Orientations (TDFCO). Comparing this texture to that of the same alloy primarily recrystallized (P.R.), it was confirmed that secondary recrystallization takes place via the inhibition of grain growth because of cube texture {100} 〈100〉 during primary recrystallization. Using the Kossel technique, the crystallographic orientation { hkl } 〈 uvw 〉 of eleven secondary recrystallization grains with an average diameter 3 mm, was determined. All grains presented {100} 〈100〉 orientations. Experimental measurements indicate that the alloy presents low levels of magnetic loss (from 60 to 500 Hz) due to the reduction of the lattice defects.