摘要:

For the reliable determination of carbon contents of a few μg/g in low and ultra‐low carbon steels by the combustion method with commercially available carbon analyzers special measures as surface cleaning by chemical etching, pre‐treatments of crucible and accelerator materials, or in‐situ desorption of contaminations have to be taken. A new technique including firstly, the pre‐burning of copper for degassing the ceramic crucible and, secondly, the desorption of carbonaceous contaminations from the surface of the sample and the Cu‐accelerator by placing together into the still hot crucible yields a detection limit of about 0.5 μg/g carbon. The technique was checked with granular and compact iron samples, and the results were compared with those of investigations with special devices for fractionated, temperature controlled combustion.

ISSN:0003-8962    

DOI:10.1002/srin.199501154

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The present work presents mathematical model for the estimation of sulphide capacities. The sulphide capacity,CSis expressed as(1)whereΔG0is the standard Gibbs energy change for the reaction,(2)ξ, being a function of both temperature and composition, is characterized by the system under consideration. By optimizingξ, the sulphide capacities could be estimated as functions of temperature and composition. The slag composition is described using a modified Temkin approach, where complex polymeric ions are considered as dissociated to simple species. The model has been applied to the binary systems CaO‐SiO2, MnO‐SiO2as well as the CaO‐MnO‐SiO2ternary system. The results show that reliable predictions of the sulphide capacities can be obtained using the present model.

ISSN:0003-8962    

DOI:10.1002/srin.199501155

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

For the first time, hot direct rolling was applied in ferrite region in the mill and the resulting quality of the cold rolled and annealed sheet steel was as good as that hot direct rolled in austenite region with respect to microstructure and mechanical properties. In case of ferrite phase rolling, microstructure of the hot strip reveals abnormal grains and deformation bands in the grains, and elongation andrvalue are not so good as those rolled in the austenite phase. However, these abnormal grains left no traces and appeared to be equiaxed grains like the austenite phase rolled microstructure after 75 % cold rolling and continuous annealing at 830°C. This is attributed to the deformation bands which provide nucleation sites for recrystallization during annealing so that recrystallization occurs uniformly in the matrix. (111) texture was well developed andrvalue thus appeared high.

ISSN:0003-8962    

DOI:10.1002/srin.199501156

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The determination of the microstructural and forming parameters of rods and wire from low to medium‐alloy quenched and tempered as well as spring steel grades is a prerequisite for the mathematical modelling and optimization of the technology on the basis of process and material criteria. Using the boundary, heat balance and finite difference methods as well as visioplastic investigations, the most important forming parameters were determined in high‐speed rolling. The rolling of such steel grades allowed to determine the material constants for the dynamic and static equations of recrystallization. Due to the inhibitive effect of the alloying elements (Mo, V) the investigated steel grades display a comparatively pronounced recrystallization inertia. Accordingly, the austenitic post‐recrystallization grain size is very fine and relatively independent of the temperature. Temperature control during rod and wire rolling allows to influence and adjust the austenitic microstructure prior to phase transformation.

ISSN:0003-8962    

DOI:10.1002/srin.199501157

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

A mathematical model has been developed to predict the thermal and phase transformation behaviour of plain carbon steel rebars having mass contents of carbon in the range of 0.10 to 0.18 %, during quenching and self tempering process. The model takes into account the operating parameters such as rebar diameter, rolling speed, finishing temperature of rebar leaving the last stand of hot rolling mills. The design features of cooling tube and water flow rate have also been included in the model. The phase transformation kinetics from austenite to martensite at the surface, bainite beneath the surface and ferrite and pearlite in the core has been incorporated in the model. An attempt has been made to predict the yield strength of rebars as a function of chemical composition and volume fractions of different phases.In‐plant trials were conducted at Visakhapatnam Steel Plant for 10 and 18 mm diameter rebars. Tempering temperature was measured and volume fractions of different phases and mechanical properties were determined. A very good agreement was found between measured and predicted volume fractions of martensite, bainite and ferrite + pearlite. Comparison between predicted and measured yield strength values show a reasonably good agreement under industrial conditions.

ISSN:0003-8962    

DOI:10.1002/srin.199501158

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

A numerical model is presented which describes the growth rate of ferrite during the decomposition of austenite in Fe‐C alloys. The growth rate is modelled assuming carbon diffusion in austenite as the rate determining mechanism. The effect of the definition of the diffusion coefficient of carbon in austenite on the growth rate is shown. The model is used to examine the effects of initial carbon concentration, the local carbon concentration in austenite at the interface and the initial austenite grain size on the growth rate. Good agreement between theoretical results and both new and existing experimental data was observed.

ISSN:0003-8962    

DOI:10.1002/srin.199501159

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The mechanism of austenite reversion in 18 Ni Co‐free maraging steel (250 grade) has been established by conducting extensive X‐ray diffraction (XRD) and transmission electron microscopy (TEM) under differently aged conditions. It has been proposed that contrary to the precipitate dissolution mechanism suggested for the initiation of austenite reversion in 18Ni‐8Co‐5Mo type maraging steels, the initiation of transformation of martensite to austenite in this type of maraging steel is due to the diffusion of Ni from matrix to the dislocations and other defect structures on prolonged/high temperature ageing. This results in local enrichment of Ni which lowers both ASand MStemperatures of the region. Lowering of these transformation temperatures is responsible for the early reversion of martensite to Ni‐enriched stable austenite which, on subsequent cooling to room temperature, does not transform back to martensite.

ISSN:0003-8962    

DOI:10.1002/srin.199501160

出版商:Wiley    

年代:2016

数据来源: WILEY

摘要:

The effect of cryoforming at 77 K on the flow and work‐hardening characteristics was investigated considering the martensitic transformation behaviour in austenitic Cr Ni steels with different nickel contents. The test steels can be divided into two groups relating to the flow and work‐hardening characteristics and martensitic transformation behaviour at 77 K. The first group comprises steels with less than 16 % nickel, the second group those with more than 16 % nickel. The flow curves of the first‐group steels show two inflection points on the basis of γ → α'‐transformation. αγ'‐martensite is observed and∊‐and α∊'‐martensite too. The flow curves of the second‐group steels do not show any inflection points. The γ → α'‐martensitic transformation is not induced, ∊‐ and α∊'‐martensite are provable by light and scanning microscopy. The stress‐strain intervals were determined for the individual martensite transformations at 77 K in the test steels. They are dependent from the nickel content. The stress which specifies the first inflection point on the flow curve and the minimum of the work‐hardening rate, respectively, characterizes the stress for initiating the deformation‐induced αγ'‐martensite formation. Transformation of the austenite toα'martensite will end in achieving a stress of 1200 to 1400 MPa, i.e. in achieving the second inflection point of the flow curve and the maximum of the work‐hardening rate, respectively. The stress interval is not dependent from the nickel content.

ISSN:0003-8962    

DOI:10.1002/srin.199501161

出版商:Wiley    

年代:2016

数据来源: WILEY