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Technical Paper

Trend toward weight reduction of automobile body in Japan

2000-06-12
2000-05-0240
With society demanding automobiles that provide higher fuel efficiency, safety of occupants in collisions and that at the end of their service life can be recycled with low environmental impact, the steel industry is tackling the needs of the automobile industry by developing ever-higher performance steel materials and simulation technologies that can demonstrate the performance of steel materials at the development stage without the need for costly prototype testing. In this paper, weight reduction of automobile body in Japan will be discussed. The main items will be as follows: (1) Development of Automobile Steel Sheets, (2) Materials for Automobile Bodies, (3) Materials and Technologies (Tailored Blanks, Hydroforming and Locally Quenching) for Reducing the Weight of Panels and Reinforcing members, (4) Future Prospects.
Technical Paper

Perforation Corrosion of Automobiles - Field Car and Laboratory Investigation

1993-10-01
932367
In order to clarify the effect of design and materials of the hem as well as the climatic factors on perforation corrosion of the automobile doors, field car and laboratory investigation has been carried out Field car investigation revealed that corrosion of the hem can be minimized by using two side galvanized steel plus adhesives. The ratio of wet/dry environment was evaluated in laboratory on hemmed sample, and it was found that the design of the hem in conjunction with the various wet/dry ratio affected the corrosion rate differently.
Technical Paper

Application of Vibration Damping Steel Sheet for Autobody Structural Parts

1992-02-01
920249
As a demand for vehicles of higher functionality grows, automakers and material suppliers are devoting increasing efforts to develop technologies for greater safety, lighter weight, higher corrosion resistance, and enhanced quietness. The resin-sandwiched vibration damping steel sheet (VDSS), developed as a highly functional material for reducing vehicle vibration and noise, has been used for oil pans1) and compartment partitions2). First applied for a structural dash panel of the new Mazda 929, a Zn-Ni electroplated VDSS which allows direct electric welding has contributed to greater weight reduction as well as improved quietness.
Technical Paper

Study of Formable High Strength Steel Sheets for Automotive Panels

1992-02-01
920247
Weight reduction of automobiles is one of the most highlighted subjects in automobile industry from the energy saving and clean environment points of view. A typical approach for the purpose is to use high strength steel sheets as well as optimizing designs and using low density materials. It is not, however, easy to apply high strength steel sheets to automotive panels because of their strict requirement for the shape-fixability although a high dent resistance is also required. Besides the use of bake hardening steels, two different high strength steel sheets, which are a continuously annealed extra-low carbon titanium-added IF steel and a low carbon TRIP steel which contains about six volume% of austenite, were assessed for the application to automotive panels in combination with a tension-controled press-forming technique and showed as good shape-fixability as a conventional box-annealed aluminum-killed DDQ steel sheet when high blank-holding-forces were applied.
Technical Paper

Properties of a Newly Developed Organic Composite Coated Steel Sheet for Automotive Use

1992-02-01
920172
The newly developed sheet steel lightly coated with an organic composite is as follows. Zn-Ni alloy plated sheet steel with a coating weight of 30 g/m2 and average Ni concentration of 11.5 ∼12.0 % is chromated through electrolysis. The coating weight of chromate film is 50 ∼90 mg/m2 in Cr. Furthermore, emulsified olefin-acrylic acid copolymer resin mixed with colloidal silica of particle size 7 ∼8 nm applied to a thickness of 1.0 ∼1.8 μm. Olefin-acrylic acid copolymer resin and colloidal silica are mixed at the rate of 100 and 30 (parts by weight). It maintains excellent corrosion resistance even after forming, C-ED paint corrosion resistance and paint adhesion. Furthermore, it has excellent perforation resistance. The product has excellent weldability and is well suited to continuous forming, too.
Technical Paper

Development of an Inexpensive, Highly Wear-Resistant Ceramic Cam Follower - Part 1 Engine Test Results

1993-11-01
931933
This paper describes the development of an inexpensive ceramic cam follower that uses a silicon nitride material and is more wear and scuff resistant than the sinter alloy cam follower. A thin ceramic disk is directly brazed on a steel cam follower body without using any stress-relief materials which makes the grinding for crowning unnecessary, reducing the production cost. We performed a material screening test using an abrasion tester to determine the optimum type of silicon nitride and the optimum surface roughness. Engine endurance tests proved its excellent wear and scuff resistance. Consequently, it has been adopted in the 1993 series production engines as the first ceramic cam follower.
Technical Paper

Development of an Inexpensive, Highly Wear-Resistant Ceramic Cam Follower - Part 2 Brazing Technology

1993-11-01
931934
Ceramic materials such as silicon nitride and sialon are known for their excellent wear-resistance and scuffing-resistance even under high contact pressure and poor lubrication1. However, ceramic materials, which have excellent sliding properties, are not widely adopted for valve train components, at present. A main reason for this is their high cost. A ceramic cam follower, newly developed by utilizing the direct brazing technology, has the following features and can be produced at the lowest cost: (1) Parts are only three. -A thin ceramic disc, a steel body, and an active brazing foil. (2) No grinding is necessary after brazing. -A crowning at the cam sliding surface is formed by the difference of the thermal expansion coefficients between silicon nitride and steel. (3) No hardening is necessary after brazing. -The steel body is hardened by the heat treatment of brazing.
Technical Paper

The Development of Vibration Damping Steel Sheet For Automotive Use

1989-02-01
890708
Vibration Damping Steel Sheet (VDSS) for automotive use, which has a three layer structure of steel/viscoelastic resin/steel, has been studied. For automotive body panels, VDSS is required to have not only high vibration damping capability but also other properties such as bonding strength, formability, weldability and durability. In this research, the effect of resin layer on these properties was studied. It is found that VDSS which satisfies these properties can be made from thermosetting resin involving metal particles.
Technical Paper

High-Strength Cold-Rolled Steels Produced by Continuous Annealing and Their Automotive Applications

1981-02-01
810028
In continuous annealing, accelerated cooling methods have recently found practical application in addition to conventional gas jet cooling or water jet quenching method. Moderate cooling rate of gas jet cooling or accelerated cooling makes it possible to utilize new high-strength steels with excellent properties. The faster cooling rate deteriorates ductility of steels. These newly developed steels are improved rephosphorized steels with high r̄-value and high bake hardenability, dual phase steels with superior ductility, Ti-stabilized high-strength steels with very high r̄-value, grain boundary hardening steels employing low temperature annealing, and unique ultra high-strength steels. This paper describes properties and process factors of these steels, and their applications to automotive.
Technical Paper

Effect of Strengthening Mechanism on Fatigue Properties of Hot-Rolled Sheet Steels

2002-03-04
2002-01-0042
The influence of tensile strength on fatigue strength and the effect of strengthening mechanism on fatigue notch factor were investigated into conventional mild steels, HSLA steels, DP steels and TRIP steels. The grade of studied steels was altered from 440MPa to 780MPa. Not only smooth fatigue specimens with side surface ground and smooth fatigue specimens with laser-cut side surface but also fatigue specimens with a pierced hole were prepared for each of steel sheets. Fatigue tests were conducted in an axial load method. These experiments made it clear that the fatigue limits of smooth specimen increase along the tensile strength approximately independent of strengthening mechanism but those of notched specimen do not necessarily increase along the tensile strength. Namely, fatigue limits of DP steels and TRIP steels with notch increase in proportion to tensile strength although those of HSLA steels with notch do not increase.
Technical Paper

Comparison between Experiments and FEM Simulation of High Velocity Tensile Test Methods to Clarify Test Method's Influence of High Strength Steel

2000-10-03
2000-01-2725
In order to examine the compatibility of improvement of crashworthiness with weight-saving of automobiles by using high strength steel, a combination analysis of Finite Element Method and Dynamic Mechanical Properties has been established. The material properties used in this analysis have been measured by “one bar method” high velocity tensile tests, which can examine the deformation behaviour of materials at an actual crash speed range (∼55km/h). As for the accuracy of this system, comparison between experiments and FEM simulation both of this test machine and other high-velocity-tensile-test machines have clarified the feature of one bar method and the metallurgical features of high velocity deformation. It was confirmed that the stress-strain curve measured by the one bar method agreed with that measured by the modified Split Hopkinson pressure bar method.
Technical Paper

Forming Performance of Aluminum Alloy Sheets for Automobile Body Panels

1995-02-01
950924
Improvement of material characteristic values, adjustment of forming conditions as well as introduction of new forming technics are necessary to promote wide application of aluminum alloy sheets into automotive parts. 5000 series and 6000 series aluminum alloy sheets are concerned about the relationship between material characteristic values and fundamental forming ability required to apply them to automobile body parts as well as the effect of lubricant on their formability. The hardening parameters, n values, of them are larger than those of cold-rolled steel sheets. However, the r values and the local elongations are extremely small. The improvement of stretch formability owing to increase of n value is smaller than that of the steel sheets. Inferior deep drawability of the aluminum alloy sheets is due to low fracture resistance force caused by low r value.
Technical Paper

Analysis of Dry Cylinder Liner Behavior During Engine Operation

1996-02-01
960059
Engine manufactures are continuing to develop new engine designs that provide higher power output, lower fuel consumption and lower engine weight. In order to achieve significant engine weight reduction, the light weight cylinder block structure employs dry cylinder liners rather than wet cylinder liners. The cast iron dry liner structure is utilized because of the superior wear and scuff resistance of the cast iron. Thin wall dry cast iron liners are being employed in both gasoline and diesel engines. Dry cylinder liners with wall thickness of 1.5mm are in production for Japanese automotive diesel engines. In the case of the dry thin wall cast iron liners, two(2) design configurations are employed: Loose-fit type having a specified clearance between the outer liner surface and the cylinder bore surface. Press-in type having an interference fit between the outer surface of liner and the cylinder bore surface.
Technical Paper

Development of High Strength Steel Sheet with Excellent Stretch Flange Formability for Automobile Application

1994-03-01
940943
With the aim of improving stretch-flange formability by further reducing carbides in steel, the authors studied the hole expansion ratio of a steel consisting entirely of ferrite and the factors governing the hole expansion ratio. Ultra low carbon steels adding Ti and/or Nb showed a higher hole expansion ratio than conventional steels, but their hole expansion ratio was not higher than the hole expansion ratio of bainitic steel reported before1). On the other hand, it was found from study of the relationship between hole expansion ratio and r-value of various steels, including cold-rolled interstitial-free steels, that the hole expansion ratio of a steel consisting only of the ferrite phase is strongly influenced by the minimum r-value and n-value and that it improves as the r- and n-values increase. The steel added Ti and/or Nb has a strong anisotropy of r-value, hence its minimum r-value is small. This is disadvantageous to hole expansion ratio.
Technical Paper

Strengthening of Surface Induction Hardened Parts for Automotive Shafts Subject to Torsional Load

1994-03-01
940786
The purpose of this study is twofold: to clarify the factors governing the torsional strength of surface induction hardened parts and, to present a method for strengthening automotive shaft parts for their weight reduction. The torsional strength against Mode III fracture can be expresssed by a new indicator, “equivalent hardness” defined as an average hardness weighted with the radius squared. If the equivalent hardness is continuously increased, the fracture mode change from Mode III to Mode I. The torsional strength against Mode I fracture is governed by grain boundary strength. Accordingly, the key-points in increasing the torsional strength of surface induction hardened parts are to raise the equivalent hardness and increase the grain boundary strength of the steel. By application of this method, the torsional strength of steel can be raised by 50%, which, in turn, enables about a 25% weight reduction for shaft parts.
Technical Paper

Extremely Formable Cold Rolled Sheet Steel with Ultra-High Lankford and n Values - Metallurgy and Formabilities

1993-03-01
930783
Extremely formable cold sheet steel with an ultra-high Lankford value of more than 2.5 and an n value of more than 0.27 has been developed. This steel is obtained due to the following factors; using extremely pure IF (Interstitial free) steel, immediate rapid cooling upon completion of rolling in the hot rolling process, a high reduction in the cold rolling process, and a high soaking temperature in the continuous annealing process. This steel sheet shows excellent deep drawability and stretch formability compared with conventional steel sheet (former IF steel and low carbon aluminum-killed steel) as a result of evaluating the limiting drawing ratio and limiting dome height, respectively. This excellent formability is also shown by the model forming tests for simulating the actual stamping of an oilpan and a side-panel. Furthermore, this steel shows the same spot-weldability as that of former IF steel, and zinc phosphatability similar to that of low carbon aluminum-killed steel.
Technical Paper

Recent Developments in Press Formability of Aluminum Alloy Sheets for Automotive Panels

1993-03-01
930705
Aluminum alloy sheets are used for automotive body-panels, but their small Young's modulus results in inferior shape-fixability than conventionally-applied steel sheets with similar strengths. Smaller radius of curvature, indicating better shape-fixability, is found at the center of a panel press-formed with higher blank holder force (BHF). Higher force can be applied for press-forming of alloy sheets with larger strain-hardening exponent (n value) induced by an increased addition of Mg. Recently-developed 5000 series alloy sheets containing 5.5 pct Mg and 0.3 pct Cu have an elongation over 33 pct at an ultimate tensile strength of 270 MPa and can be press-formed with better shape-fixability.
Technical Paper

Crashworthiness Improvement of the Side Crash by the Work Hardening Effect of Pre-Strained High Strength Steel

2001-10-16
2001-01-3112
In order to examine the compatibility of improvement of crashworthiness with weight saving of automobiles by using high strength steel, a combination analysis of Finite Element Method and Dynamic Mechanical Properties has been established. Material properties used in this analysis have been measured by “one bar method” high velocity tensile tests, which can examine the deformation behavior of materials at a bend crush speed range (∼55km/h). It was confirmed that the strength of steel measured by one bar method was raised remarkably after press and hydro forming of high strength steels. It was also confirmed by FEM analysis and load drop test that absorbed energy of bend crush was improved by pre-strain effect. Further, we proved that absorbed energy of bend crush was also improved by appropriate design of thickness and the ratio of bend span and plate length. These effects are applicable to respective high strength steels.
Technical Paper

Evaluation of the Corrosion Durability of Steel Systems for Automobile Fuel Tanks.

2005-04-11
2005-01-0540
The Strategic Alliance for Steel Fuel Tanks (SASFT), an international group of steel producers and manufacturing companies, recently completed a major corrosion study of various steel ‘systems’ for automobile fuel tanks. The ten steel systems included low carbon steels (either pre-painted or post-painted with protective coatings) and stainless steels. The 2-year corrosion test program included testing in salt solutions to simulate road environments for the exterior of a fuel tank. Special test specimens were designed to represent a manufactured tank. The external tests used were the Neutral Salt Spray test (ASTM B117) with exposures up to 2000 hours and the Cyclic Corrosion test (SAE J2334) with exposures up to 120 and 160 cycles to represent vehicle lives of 15 years and 20 years, respectively. Additionally, the resistance to an aggressive ethanol-containing fuel (internal tank corrosion) was assessed by using uniquely designed drawn cups of the various steel systems.
Technical Paper

An Evaluation of Fatigue Strength for Various Kinds of Spot-Welded Test Specimens

1988-02-01
880375
Eight kinds of the spot-welded test specimens were studied to obtain the basic fatigue data on steel sheets for car bodies. Analytical methods such as the strain amplitude at outside and inside plates close to the nugget, the maximum nominal stress and Kθmax criteria of fracture mechanics were used. The authors propose that the ratio of strains at two points around the nugget can provide evaluation of the bending load and estimation of the fatigue strength.
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