TOKYO - Mitsubishi Motors Corp. has developed a lightweight, high-strength steel sheet for use in chassis parts.
The sheet is used in about 80 parts in the new Pajero sport-utility (known as the Montero in the United States), which was launched in early September. The new steel reduced the weight of those parts by about 13 percent, or 31 pounds.
Nippon Steel Corp., Sumitomo Metal Industries Ltd. and Kobe Steel Ltd. helped to develop the steel.
Generally, the greater the tensile strength of steel sheet, the easier it is to reduce weight by using thinner sheets.
However, a steel sheet is harder to shape with increasing tensile strength, so that sheets then often crack or split when being pressed into parts. Thinner sheets also soften due to the 'heat effect' during welding, resulting in weaker welded joints.
Up to now, that has put a limit on the thinness of the steel that can be used to make formed parts.
In the newly developed steel sheet, the sulfur content and the retained austenite content has been reduced. This has made it possible to provide the stretchability required for the pressing process.
Also, the steel's high silicon and manganese content prevents softening during welding and realizes a much higher welded joint fatigue strength.