Effect Of Steel Composition Research Articles

Effect of Steel Composition and Processing Parameters on the Penetration Depth of Microcracks in ZnFe‐Coated Boron Steels

Liquid metal assisted cracking (LMAC) and so‐called microcracking are limiting the application of hot‐dip galvanized boron steels in the direct press hardening process. This study addresses the role of steel hardenability on the microcracking behavior of ZnFe‐coated (galvannealed) boron steels 22MnB5 and 22MnMoB8. Several soaking times and forming start temperatures in the range of 800–520 °C are examined using a laboratory press hardening equipment with a hat‐profiled forming tool. The results indicate that the penetration depth of microcracks can be reduced by improving the hardenability of steel, which enables hot forming in austenitic state at exceptionally low temperatures even without accelerated cooling procedures. The austenite decomposition of 22MnB5 leads easily to heterogeneous microstructure (ferrite + austenite/martensite) below the coating/steel interface, which promotes the penetration of microcracks. The crack depth is generally reduced with a conversion‐delayed 22MnMoB8 steel; however, a crucial reduction is attained only at lowest hot forming temperatures of 550 and 520 °C. The results of 22MnMoB8 uncouple the effect of high‐temperature ferrite formation from the microcracking mechanisms and suggest that the embrittling effect from zinc or zinc‐rich intermetallic phases plays a crucial role at conventional hot forming temperatures of 800–600 °C.

Prediction of the failure mode of automotive steels resistance spot welds

ABSTRACT In this study, the critical nugget size, at which the failure state in tensile shear test changed from the interfacial failure mode to the pull-out failure one, was estimated as a function of nugget and base metal hardness. The proposed approach could address the effect of various parameters involved in resistance spot welding process, such as sheet thickness, base metal chemical composition and physical properties of electrodes and sheets. The reliability of the present model was evaluated using independent experimental results. Based on the obtained results, the effect of steel composition on critical nugget diameter was found to be more important, especially for the sheets thicker than about 1 mm, whereas predicted nugget sizes by previous models could not guarantee the pull-out failure mode.

Effect of steel composition and slag properties on NMI in clean steel production

The modern steel plants for clean steel production depend to large extent on the efficiency of the refining processes that applied for the production. Refining processes that applied for low alloy and alloyed steel production include degassing via vacuum or ladle and ladle furnace units. This technique could help in producing homogeneous steel with low gas content and minimum internal defects. In certain grades of steel for tools and penetration and impact resistance uses, non-metallic inclusions (NMI) and sulphur content are the key factors for the steel performance and applications. ESR, Electro-salg refining (or remelting), is the technique that can efficiently produce clean steel with minimum content of NMI and sulphur due to the special nature and mechanism of this technique. In this study, the effect of initial chemical composition of steel and slag properties on the efficiency of ESR process in removal of NMI and sulphur from steel are evaluated. Different grades of steels were refined using ESR process. The efficiency of ESR in modifying and enhancing NMI shape, size and counts as well as removal of sulphur in different steel grades was evaluated at different slag composition and physical properties. The effect of chemical composition of steel on the efficiency of ESR process was studied. It was found that ESR process has a great effect in producing clean steel where both viscosity and initial composition of steel have influence on the final NMI status and sulphur content in the produced steel.

Mathematical Modeling of Nitrogen Removal from the Vacuum Tank Degasser

The removal of nitrogen from an industrial vacuum tank degasser depends on a series of operational parameters, steel composition, and contents of surface‐active elements in liquid steel, e.g., oxygen and sulfur. The effect of some specific elements on nitrogen removal in the vacuum degasser has been (well) examined. Still, it is quite challenging to assess the overall effect of the whole steel composition on the process. The focus of the present work was to predict nitrogen removal from the vacuum degasser specially taking into account the multi‐component effect of steel composition. An integrated computational fluid dynamics (CFD) model for simulating nitrogen (and hydrogen) removal in industrial vacuum tank degassers was therefore developed based on theories and methods that are relatively separate in the literature. In order to include the multi‐component effect, the model is coupled with an in‐house thermodynamics code that can be used to determine the activity coefficient of nitrogen, oxygen, or sulfur as a function of steel composition and temperature. The code was verified by comparing the calculated activity coefficients against experimental measurements from various sources. Efforts were also put into developing an on‐line use concept to control the nitrogen removal. The gas plume, flow field, and evolutions of nitrogen and hydrogen during vacuum treatment were predicted and the on‐line concept was demonstrated by presenting two operating diagrams. The results showed that the final nitrogen content decreases with an increase in the chemical reaction rate constant and a decrease in the initial nitrogen content. By contrary, the final nitrogen content increases with a decrease in the chemical reaction rate constant and an increase in the initial nitrogen content. Finally, the operating diagrams were validated by industrial data and observations.

Simulation of precipitation of secondary carbides in hot work tool steels

Precipitation of secondary carbides in hot work tool steels during tempering heat treatments has been investigated using simulations based on a thermodynamic description coupled with kinetic parameters through multicomponent nucleation and growth models. The simulations reproduce the measured effects of steel composition on the precipitation of secondary carbides. Both Si and V increase the volume fraction of fine secondary carbides precipitated during tempering provided that the austenitising temperature is adjusted to give the same fraction of retained primary carbides. The most important effect of Si in 5%Cr steels is its influence on the primary carbide stability at austenitisation temperatures, but increasing the V contents has a strong effect on the fraction of secondary carbides, without increasing the size, and can thus improve the yield strength. The most critical input to the calculations is the thermodynamic description of the individual phases.

Improvement of Crystallographic Texture of High Strength Interstitial Free Steels by the Control of Steel Chemistry and Coiling Temperature

Effects of steel composition and coiling temperature on textures of a series of high strength IF steels were studied. An intermediate coiling temperature (6200C), instead of a high coiling temperature (7100C), was found most beneficial for the steels containing moderate to high phosphorus content. On the other hand, high coiling temperature was found beneficial for the steels containing low amount of phosphorus.

System for on/offline prediction of mechanical properties and microstructural evolution in hot rolled steel strip

A comprehensive computer based system for online prediction of mechanical properties and offline prediction of the microstructure of hot rolled C–Mn and microalloyed steel strip of has been developed. The approach used was based on two types of model: a neural model that predicts the mechanical properties and a physically based semiempirical model that predicts the microstructural features. The mechanical properties of the hot rolled strip are calculated online, but it is also possible to simulate the effects of steel composition and process parameters on the mechanical properties. The microstructural model is an offline tool for use in research and development, product planning and production. It can be applied to the study of microstructural evolution during hot rolling or to estimate changes caused by process conditions or by the steel composition. The system provides information that has not been available before, thus enabling more precise process planning, improvement of the consistency of products and better opportunities for future steel development.

Effect of Steel Composition on Iron Dissolution in Molten Zinc and Development of Fe–Zn Phases on Steel Surface

The effect of steel composition on iron solubility in molten zinc and coating microstructure was studied by immersing test coupons of four different steel grades in zinc bath for 20 min at 470°C. The amount of iron dissolved in the molten zinc depends upon the steel composition. The coating was characterized by energy dispersive spectroscopy, X-ray diffraction and galvanostatic methods. The coating consists of mainly ζ (zeta) and δ (delta) phases along with zinc layer at the top, irrespective of the steel composition. The presence of a thin layer of gamma phase has also been confirmed by XRD and galvanostatic analysis. However, the proportion and distribution of the coating phases varies with the steel chemistry.

The Effects of Steel Composition on the Oxidation Kinetics, Scale Structure, and Scale-Steel Interface Adherence of Low and Ultra-Low Carbon Steels

The oxidation behaviors of several commercial low and ultra low carbon steels in air at 700-950°C were studied. Under isothermal oxidation conditions, the oxidation kinetics, scale structure and scale-steel interface adherence were significantly affected by the steel composition.

Mould investigations on a thick slab caster

As regards conditions in the mould, Continuous Casting of 400 mm thick slabs can differ from conventional slab casting. Specific features of thick slab casting are reported, concerning heat fluxes, both integral and local. Local heat flux has been determined through an instrumented mould along with thermal modeling of the copper plate. Integral heat withdrawal data are compared with data from conventional slab casting. The effect of steel composition on integral and local heat extraction has been evaluated and interpreted in relation to residence times in the mould and to the relevant thermal resistances. The influence of tundish temperature on superheat in the mould and on heat removal was quantified. Oscillation mark depth and mould powder consumption have been related to heat withdrawal. Cracking defects were characterized in dependence on mould heat flux densities.

Modelling of retained austenite in carburized layers

In this paper, modelling of the phase composition of the carburized case produced on steel alloys containing chromium, manganese and nickel will be discussed. In particular, the effect of steel composition on the amount of retained austenite and carbide structure will be discussed. These microstrucures were selected because they exhibit the greatest influence on the correlation between structure and properties of hardened carburized case. The thermal process largely influences the formation of carbides quantity of residual austenite in structure of hardened carburized elements. Properties evaluated include: hardness, micro-hardness, and impact resistance. The model can be applied to carburized 20H (20Cr4), 15HN (17CrNi6-6) and 16HG (16MNCr5) steel although data for 20H (20Cr4) steel is provided here.

Effects of Steel Composition on Pitting Resistance

Effects of Steel Composition on Pitting Resistance

Effect of steel composition on failure of oxide scales in tension under hot rolling conditions

The differences in failure of oxide scales formed on mild, Si‐Mn, Mn‐Mo and stainless steels were investigated using a high‐temperature tensile test technique over the range of test parameters near to the hot rolling conditions at entry into the roll gap. Temperature, strain and strain rates were 783 – 1200 °C, 2.0 – 5.0 % and 0.2 – 4.0 s−1 respectively. The scale thickness was maintained within 5 – 250 μm. Mild steel has the highest oxidation rate throughout the temperature range. A slightly thicker scale for the Mn‐Mo steel compared with Si‐Mn steel was observed. The stainless steel has shown the highest resistance to oxidation. Although through‐thickness cracks and sliding were competitive mechanisms for oxide scale failure for the mild steel, the other steel oxides failed only by through‐thickness cracking or were delaminated over the whole temperature range 783 ‐ 1200 °C. Modelling based on the finite‐element method was applied for better understanding of the micro‐events both during uni‐axial tension and just before contact with the rolls. The part of the model related to oxide scale failure has been upgraded taking into account experimental evidence concerning differences in scale failure, due to the steel chemical content, which were observed in the hot tensile tests.

A new empirical formula for the calculation of M S temperatures in pure iron and super-low carbon alloy steels

It has often been observed that when the experimentally determined M S (the upper limit of the martensite transformation, or the practical start temperature of martensite transformation) temperatures are extrapolated to pure iron from binary Fe–C, Fe–Ni, Fe–Cr, Fe–Mn, Fe–Co alloys, anomalous temperatures, e.g. 520, 680, 700–750, 800–900°C, or even as high as the equilibrium γ→α temperature of 912°C, are obtained. In order to shed light on these conflicting results, a new empirical formula M S (° C)= 795−25 ,000 C 1−45 Mn−35 V( Nb+ Zr+ Ti)−30 Cr−20 Ni−16 Mo−8 W−5 Si+6 Co+15 Al 525−350( C 2−0.005)−45 Mn−35 V( Nb+ Zr+ Ti)−30 Cr−20 Ni−16 Mo−8 W−5 Si+6 Co+15 Al, where C 1<0.005, 0.005≤ C 2<0.02 is proposed to predict the M S temperature of pure iron and super-low carbon alloy steels. The effect of steel composition on the M S temperature is discussed. The validity of this new equation together with 11 other existing empirical formulae for the calculation of M S temperature in pure iron and super-low carbon alloy steels is examined. For more than 80% of super-low carbon alloy steels, the M S temperatures can be predicted by this new formula to within ±25°C. The new formula indicates an M S temperature of 795°C for a steel without carbon or other alloying elements (“pure” iron). This is a better approximation to the experimental result of 750°C than for other formulae when the cooling rates exceed 35,000°C/s, and the carbon content is lower than 0.0017 wt.%.

A new empirical formula for the bainite upper temperature limit of steel

The definition of the practical upper temperature limit of the bainite reaction in steels is discussed. Because the theoretical upper temperature limit of bainite reaction, B 0, can neither be obtained directly from experimental measurements, nor from calculations, then, different models related to the practical upper temperature limit of bainite reaction, B S, are reviewed and analyzed first in order to define the B 0 temperature. A new physical significance of the B S and B 0 temperatures in steels is proposed and analyzed. It is found that the B 0 temperature of the bainite reaction in steels can be defined by the point of intersection between the thermodynamic equilibrium curve for the austenite→ferrite transformation by coherent growth (curve Z $$\gamma \to \overrightarrow \alpha $$ ) and the extrapolated thermodynamic equilibrium curve for the austenite→cementite transformation (curve ES in the Fe-C phase diagram). The B S temperature for the bainite reaction is about 50–55 °C lower than the B 0 temperature in steels. Using this method, the B 0 and B S temperatures for plain carbon steels were found to be 680 °C and 630 °C, respectively. The bainite reaction can only be observed below 500 °C because it is obscured by the pearlite reaction which occurs prior to the bainite reaction in plain carbon steels. A new formula, B S(°C) =, 630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W, is proposed to predict the B S temperature of steel. The effect of steel composition on the B S temperature is discussed. It is shown that B S is mainly affected by alloying elements other than carbon, which had been found in previous investigations. The new formula gives a better agreement with experimental results than for 3 other empirical formulae when data from 82 low alloy steels from were examined. For more than 70% of these low alloy steels, the B S temperatures can be predicted by this new formula within ±25°C. It is believed that the new equation will have more extensive applicability than existing equations since it is based on data for a wide range of steel compositions (7 alloying elements).

A re-examination of the B0 and BS temperatures of steel

A new explanation of the physical significance of the B 0 (the theoretical upper temperature limit) and the B S (the practical upper temperature limit) temperatures in steel is proposed. It is found that the B 0 temperature of the bainite reaction in steel should be defined by the point of intersection between the thermodynamic equilibrium curve of austenite→ferrite transformation by coherent growth (curve Z γ→ α → ) and the thermodynamic equilibrium curve of austenite→cementite transformation (curve ES in the Fe–C phase diagram). The B S temperature for the bainite reaction is approximately 50∼55°C lower than the B 0 temperature. Using this method, the B S and B 0 temperatures for plain carbon steel were found to be 630°C and 680°C, respectively. The effects of steel composition on the B S temperature are discussed. The formula B S (°C)=630−45 Mn−40 V−35 Si−30 Cr−25 Mo−20 Ni−15 W can be used to predict the B S temperature of a wide range of commercial steels.

急冷途中の大ひずみ加工による結晶粒超微細化挙動に及ぼす合金元素の影響

急冷途中の大ひずみ加工による結晶粒超微細化挙動に及ぼす合金元素の影響

特集 工具鋼 工具鋼のＡｌ溶損挙動に及ぼす鋼組成の影響

Dissolution behavior of four kinds of tool steels in molten Al alloy was investigated to know the effect of steel composition. Results obtaind are as follows.1) In standard dissolution condition (1023°K, 0.49m/sec), dissolution rate of SKD61 was larger than the estimation by the diffusion control of Fe in molten Al alloy, because of acceleration by flaking of compound layer.2) Dissolution rate of other three steels was smaller than SKD61, and flaking of compound layer was not observed. But dissolution rate was smaller than the estimation by the diffusion control, that means no flaking of compound layer is unsufficient to explain of small dissolution rate.3) Strong enrichment of Cr and V was observed at the front part of compound layer, which is caused by smaller diffusion coefficient of Cr and V than Fe in molten Al.4) Enrichment of Cr and V was thought to retard the transfer of Fe from solid to liquid phase, therefore low dissolution rate of other three steels is explained by high content of Cr and V than SKD61.5) In case of steels with high content of V, some of V-carbides also pile up at the front of compound layer, which is also thought to retard the transfer of Fe to liquid phase.

Solidification microstructure of electrodischarge machined surfaces of tool steels

Abstract Some recent advances made in the understanding of the solidification behaviour of molten metal during electrodischarge machining (EDM) of a range of commonly used tool steels are presented. In general, the recast layers produced by EDM can be classified into three structural types: thick multilayer, intermediate single layer, and thin featureless. The discharge energy affects the average thickness of the recast layer, and hence the distribution of the different types of recast layer formed during EDM. Detailed microstructural studies have shown that during EDM, solidification of the molten metal takes place simultaneously from the top interface with the dielectric and the bottom interface with the underlying metal into the melt, as well as from within the melt towards both interfaces. This leads to the formation of three distinctive sublayers withing each recast layer resolidified from a given pool of molten metal. The effects of steel composition and thermal properties on the solidification micr...

Effects of steel composition and production technology on hydrogen-induced cracking sensitivity and hydrogen sulfide corrosion cracking: Survey of foreign research

Low-carbon microalloyed steels containing niobium, vanadium, molybdenum, and copper can be made with low levels of sulfur, phosphorus, and oxygen and with optimum shapes for the nonmetallic inclusions to give high resistance to hydrogeninduced cracking and sulfide stress corrosion cracking.