• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.834-835
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• 2006

Manganese is an alloying element that improves the hardenability of steels. It could be a valid substitute in sintered steels, increasing mechanical properties. The hardenability of three low alloy Mn steels was studied to establish the influence of manganese on the heat treatments. The Grossmann approach was adopted, which uses cylinders with different diameters to induce different gradients of cooling rate in the cross section. The correlation of microstructure and microhardness to the actual cooling rate makes the results independent on the process parameters and applicable to each industrial condition, once the actual cooling rate in the parts is known.

• Journal of the Korean Society for Heat Treatment
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• v.3 no.4
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• pp.23-40
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• 1990

This study has been carried out to investigate into some effects of Mn content with varying amounts and austenite grain size on hardenability in boron-added Fe-C-Cr-Mo alloy systems. (1) Austenite grains have been found to hardly grow in the temperature range of $900^{\circ}C$ to $950^{\circ}C$, whereas they grow rapidly in the temperature range of $975^{\circ}C$ to $1100^{\circ}C$. (2) Austenite grain growth is considerably small with increasing holding time at a given austenitizing temperature and is, in particular, hardly found to occur at a temperature of $900^{\circ}C$. (3) The hardenability improves ramarkably as Mn content is increased at three different austenitizing temperatures $900^{\circ}C$, $1000^{\circ}C$ and $1100^{\circ}C$. (4) The maximum hardenability is obtained from steels A, B and C austenitized at the $900^{\circ}C$, although Mn content is varied in each specimen.

• Korean Journal of Metals and Materials
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• v.49 no.3
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• pp.203-210
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• 2011

Bake hardening steels have to resist strain aging to prevent the yield strength increment and stretcher strain during press process and to enhance the bake hardenability during baking process after painting. The bake hardening steels need to control the solute carbon and the solute nitrogen to improve the bake hardenability. Ti and/or Nb alloying for nitride and carbide precipitation and low carbon content below 0.003% are used to solve strain aging and formability problem for automotive materials. However, in the present study, the effect of micro-precipitation of copper sulfide on the bake hardenability and fatigue properties of extremely low carbon steel has been investigated. The bake hardenability of Cu-alloyed bake hardening (Cu-BH) steel was slightly higher (5 MPa) than that of Nb-alloyed bake hardening (Nb-BH) steel, but the fatigue limit of Cu-BH steel was far higher (45 MPa) than that of Nb-BH steel. All samples showed the ductile fracture behavior and some samples revealed distinct fatigue stages, such as crack initiation, stable crack growth and unstable crack growth.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.781-789
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• 2019

The prediction of Jominy hardness curves and the effect of alloying elements on the hardenability of boron steels (19 different steels) are investigated using multiple regression analysis. To evaluate the hardenability of boron steels, Jominy end quenching tests are performed. Regardless of the alloy type, lath martensite structure is observed at the quenching end, and ferrite and pearlite structures are detected in the core. Some bainite microstructure also appears in areas where hardness is sharply reduced. Through multiple regression analysis method, the average multiplying factor (regression coefficient) for each alloying element is derived. As a result, B is found to be 6308.6, C is 71.5, Si is 59.4, Mn is 25.5, Ti is 13.8, and Cr is 24.5. The valid concentration ranges of the main alloying elements are 19 ppm < B < 28 ppm, 0.17 < C < 0.27 wt%, 0.19 < Si < 0.30 wt%, 0.75 < Mn < 1.15 wt%, 0.15 < Cr < 0.82 wt%, and 3 < N < 7 ppm. It is possible to predict changes of hardenability and hardness curves based on the above method. In the validation results of the multiple regression analysis, it is confirmed that the measured hardness values are within the error range of the predicted curves, regardless of alloy type.

• Journal of the Korean institute of surface engineering
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• v.34 no.3
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• pp.247-257
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• 2001

In an effort to improve the dent resistance of exterior body panels at a reduced steel thickness, the bake hardenable steels added Ti or Nb with tensile strength of 35Kgf/$\textrm{mm}^2$ were investigated. The bake hardenability increased with the annealing temperature and solute carbon content. Bake hardening of 3 to 5Kgf/$\textrm{mm}^2$ was obtained in steels with a controlled solute carbon concentration range from 6 to 10ppm. The galvannealing temperature and time had little influence on the bake hardenability. The Fe-Zn alloying reaction of 35Kgf/$\textrm{mm}^2$ BH steel was remarkably retarded due to a 0.07%P addition. The optimum galvannealing temperatures of 35Kgf/$\textrm{mm}^2$ BH steel were ranged from 520 to 56$0^{\circ}C$ in view of the Fe content and powdering resistance. The cross-section and planar views of the galvannealed coatings to characterize morphology development were discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.37-44
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• 2004

Automotive company has been endeavoring to develop high strength steels to get higher fuel efficiency of car since the oil shortage in 1970s and to cope with the recent strict environmental regulation. Outer panels(Hood, Roof, Door and Fender) for automobile require higher dent resistance. Bake-hardenable(BH) steels are known as useful for their high deep drawability and high dent resistance. Recently BH steels are increasingly adapted for outer panel use due to their high drawability and high dent resistance. In this study effect of temper rolling on formability (textures, r value) and bake hardenability is investigated fur improving characteristic of bake-hardenable steels.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.325-328
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• 2005

Bainitic microalloyed steels have drawn a lot of attention because of high strength combined with high toughness. In order to process the alloys easily , it is necessary to get the alloys of high hardenability. Mo and B were added to enhance the hardenability, which was demonstrated by TTT simulation and microstructures. It was also identified using BNCT that B, hardenability raising element, was distributed more evenly as cooling rate went up. Examination of grain coarsening temperature depending upon austenitizing temperature revealed that V and Ti effectively inhibited the grain growth up to $1000^{\circ}C\;and\;1050^{\circ}C$ respectively.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.1
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• pp.17-28
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• 2019

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.4
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• pp.161-172
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• 2020

The tensile property of A5082 and A6060 aluminium wrought alloys was investigated, in terms of the strain rate sensitivity on alloy conditions by heat treatment and bake hardenability on pre-strain prior to strain ageing. The tensile test was carried out in a range of strain rate of 4.17 × 10^-5 s^-1 ~ 4.17 × 10^-5 s^-1 in room temperature and the nominal range of pre-strain was 3.0 ~ 10.5%. The tensile deformation of A5082 alloys is characterized as typical case of dynamic strain ageing with negative strain rate sensitivity for all conditions, and the tensile strength indicates a similar level regardless of alloy conditions, except only in full annealed condition. The stress-relief annealing on A6060 alloys can induce practical decrease in strength level of over approximately 100 MPa without any ductility loss, compared to as-rolled condition, while a full annealed and aged condition leads remarkable strengthening effect with the decrease of tensile elongation. Additionally, the bake hardenability of A5082 alloy by strain ageing indicates a negative dependence upon the increase of pre-strain, while A6060 alloy exhibits a positive sign even in low level relatively compared with conventional SPCC.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.93-100
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• 1996

Effect of a flux composition on weld metal toughness in submerged arc welding with 60kgf/$\textrm{mm}^2$ grade C-Mo type wires was investigated and interpreted in terms of weld metal microstructure and hardenability. Flux workability was also studied by characterizing a weld bead profile. Compared to other weld metals, .weld metal used alumina basic flux with nickel showed lowest oxygen content, highest hardenability and the most acicular ferrite. The highest impact toughness of that weld metal, however, was attributed to the tough matrix due to the nickel rather than to the larger amount of acicular ferrite. Manganese silicate flux had better workability than alumina basic flux, showing broader welding conditions resulting in a depth-to-width ratio of 0.5. The composition of oxides in the weld metal was dependent on the flux composition, showing MnO-SiO$_2$-TiO in manganese silicate flux and MnO-SiO$_2$-Al$_2$O$_3$-TiO in alumina basic flux. MnO-SiO$_2$composition in both oxides was similar to a tephroite.