Tribological characteristics of high strength steel sheets under hot stamping conditions

A process of one-step hot stamping-forging for increasing the tensile strength of the hole-flanging of the high-strength steel sheets with flange thickening was developed. In this proposed method, the high-strength steel sheet is directly formed within the designed die, which is simultaneously accompanied with a resistance heating, a hole punching, and the flanging and forging processes. The electrode material is SKD61. This material is not only used as the forming of the high-strength steel sheet but also directly served as the heating of the high-strength steel sheet within the die. The experimental results indicated that the high-strength steel sheet could be heated to 850 °C in 30 s by the SKD61 die. It demonstrates the successful completion of heating, hole punching, flanging and forging in a one-step process. Furthermore, it is found that the tensile strength of M18 tapped hole with forged part is increased by about 7.4% than that without forged part, and the breaking toughness is increased by about 33%.

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Prevention of Oxidation in Hot Stamping of Ultra High Strength Steel Sheets

Journal of the Japan Society for Technology of Plasticity ◽

10.9773/sosei.48.318 ◽

2007 ◽

Vol 48 (555) ◽

pp. 318-322 ◽

Cited By ~ 6

Author(s):

Ken-ichiro MORI ◽

Seijiro MAKI ◽

Shoichi SAITO ◽

Makoto KISHIMOTO ◽

Tatsushi HAYASHI ◽

...

Keyword(s):

High Strength Steel ◽

Hot Stamping ◽

High Strength ◽

Steel Sheets ◽

Ultra High Strength Steel

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Prevention of Oxidation in Hot Stamping of Ultra High Strength Steel Sheets

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.410-411.255 ◽

2009 ◽

Vol 410-411 ◽

pp. 255-261 ◽

Cited By ~ 1

Author(s):

Kenichiro Mori ◽

Seijiro Maki ◽

Shouichi Saito

Keyword(s):

High Strength Steel ◽

Elevated Temperatures ◽

Hot Stamping ◽

High Strength ◽

Shape Accuracy ◽

Steel Sheets ◽

Ultra High Strength Steel ◽

Bending Load ◽

Formed Product ◽

Very High

Oxidation in hot stamping of ultra high strength steel sheets was prevented by coating the sheets with an oxidation preventive oil. For four types of oxidation preventive oil, the degree of oxidation under natural cooling of the heated sheets without forming was first evaluated. The oil that forms a liquefied film at elevated temperatures exhibited high oxidation prevention, and this oil was chosen for a hot bending experiment. Hot hat-shaped bending of the coated sheets using resistance heating was carried out to examine the properties of the products. The bending load was markedly decreased, the shape accuracy of bent products was very high, the surface roughness was similar to that of the sheet, and the hardness was about 1.5 times larger than that of the sheet before the bending due the die quenching. In addition, the layer remaining on the surface of the formed product could be removed using phosphoric acid. It was found that the hot stamping operation using the oxidation preventive oil is effective in the precision forming of ultra high strength steel sheets.

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Trend of Standardization Works on Resistance Spot Welding of High and Ultra-High Strength Steel Sheets

JOURNAL OF THE JAPAN WELDING SOCIETY ◽

10.2207/jjws.84.462 ◽

2015 ◽

Vol 84 (6) ◽

pp. 462-466

Author(s):

Kin-ichi MATSUYAMA

Keyword(s):

Resistance Spot Welding ◽

High Strength Steel ◽

Spot Welding ◽

High Strength ◽

Resistance Spot ◽

Steel Sheets ◽

Ultra High Strength Steel

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Mechanical clinching and self-pierce riveting for sheet combination of 780-MPa high-strength steel and aluminium alloy A5052 sheets and durability on salt spray test of joints

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-020-06545-7 ◽

2021 ◽

Vol 113 (1-2) ◽

pp. 59-72

Author(s):

Yohei Abe ◽

Ken-ichiro Mori

Keyword(s):

Aluminium Alloy ◽

High Strength Steel ◽

Salt Spray ◽

High Strength ◽

Alloy Sheet ◽

Galvanized Steel ◽

Load Reduction ◽

Minimum Thickness ◽

Steel Sheets ◽

Mechanical Clinching

AbstractTo increase the usage of high-strength steel and aluminium alloy sheets for lightweight automobile body panels, the joinability of sheet combinations including a 780-MPa high-strength steel and an aluminium alloy A5052 sheets by mechanical clinching and self-pierce riveting was investigated for different tool shapes in an experiment. All the sheet combinations except for the two steel sheets by self-pierce riveting, i.e., the two steel sheets, the two aluminium alloy sheets, and the steel-aluminium alloy sheets, were successfully joined by both the joining methods without the gaps among the rivet and the sheets. Then, to show the durability of the joined sheets, the corrosion behaviour and the joint strength of the aged sheets by a salt spray test were measured. The corrosion and the load reduction of the clinched and the riveted two aluminium alloy sheets were little. The corrosion of the clinched two steel sheets without the galvanized layer progressed, and then the load after 1176 h decreased by 85%. In the clinched two galvanized steel sheets, the corrosion progress slowed down by 24%. In the clinched steel and aluminium alloy sheets, the thickness reduction occurred near the minimum thickness of the upper sheet and in the upper surface on the edge of the lower aluminium alloy sheet, whereas the top surface of the upper sheet and the upper surface of the lower sheet were mainly corroded in the riveted joint. The load reduction was caused by the two thickness reductions, i.e., the reduction in the minimum thickness of the upper sheet and the reduction in the flange of the aluminium alloy sheet. Although the load of the clinched steel without the galvanized coating layer and aluminium alloy sheets decreased by about 20%, the use of the galvanized steel sheet brought the decrease by about 11%. It was found that the use of the galvanized steel sheets is effective for the decrease of strength reduction due to corrosion.

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