¶ … Engineering Materials: High Strength Steel and Bus Seat Frames The purpose of this paper is to conduct research and the review the findings. This paper seeks an understanding of the engineering material of high strength steel, the process in which it is made and the items it is used to build specifically that of bus seat frames. Over the course of the research, it is has been determined that high strength steel is effective when used in building lightweight yet safe and sturdy bus seat frames. This construct lends to the overall safety of buses using this material, specifically in existing models found in buses designed by a company called Fainsa located in Barcelona, Spain. This paper explores the process and design of these seats by looking at the process in which high strength steel is created. By understanding how high strength steel is made, one can better understand its unlimited uses an applications when it comes to designing safer vehicles used for mass transit around the world. This means doing in depth research of the process and investigating recent data regarding bus seat frames. What are the implications of using this material? Does it better the safety of bus seats or cause other problems? This paper will investigate international case studies that show different outcomes of use high strength steel as a material.

Background

The Process of Making High Strength Steel

As technology continues to change, the possibilities for application become endless. Researchers in the automotive industry are constantly looking for stronger components that weight than before. This in turn, has given birth new categories of steel grades so that the industry can meet higher strength to weight ratio requirements. The development of high- and ultra high-strength steel or UHSS grades in thin strips has progressed in recent years. The process begins by taking the original high-strength but low alloy or HSLA materials to treat with a dual phase process and fully martensitic grades in various levels (Basta and Hoon 2004). Steels can be categorized as dual-phase, HSLA and Martensitic depending on what level the process is stopped. HSLA steels vary depending on the levels of carbon and manganese. Dual-phase combine high strength and ductility through a soft ferrite microstructure with varying levels of hard martensite. By baking the steel, this makes these elements harden for structural applications. Martensitic steels are completely made of martensite and these steels are the highest strength used commercially. The fully martensitic microstructure brings steel to the hardest phase. A post quench process can be applied to make this steel more ductile and have greater formability. How these steels are handled and cut during the process also plays a part in the resulting strength. For higher grade steel and thicker gauges the coil processor will need to limit the number of cuts per coil and possibly use a two-pass preslit/final slit schedules to avoid exceeding the slitting machines capacity (Basta and Hoon 2004). This means paying attention to the knives used in cutting the steel.

The idea behind the heat treated process is that ultrahigh strength steels can be used in applications where high strength can be converted to a weight-saving advantage over other steels. Usually once the heat treatment is concluded, the steel need no further treatment. There are over twenty types of high-strength alloy steels. Some have been developed to combine improved welding characteristics along with high strength. Most have good impact properties in addition to high strength. Ultrahigh-strength steels start with a grade of 4340 and are modifications of alloy. They can be further modified depending on applications, for instance, when these steels are used for aerospace components, they are put through a vacuum-arc-re-melt process. These steels considered ultra strength because they can endure strengths greater than 180,000 psi. Once again the measure of strength is based upon the steels chemical composition. Greg Olson and his group of researchers reflect, "steel is heavy but sometimes it is the only thing that can do the job. If you can push the strength up so you use less f it, you can save a lot of weight" (2005). His team does this by combining quantum theory with supercomputing. Tests run on steel using these tools brings new insight about the effects of impurities on grain-boundary cracking in steel. This results in a steel that can be used on the space shuttle, a steel that withstands "pressure, corrosion and high temperature beyond previous steel" (Olsen 2005). Olson does this by examining...

The higher electron density, the stronger the steel, the lighter the weight. It was found that upon the steel cracking, phosphorus was present along the seam. The team is working to minimize its presence. In the paragraphs below, this paper will explore how ultra high strength steel improves the design of bus seats by improving safety.
Fainsa

Fainsa is a small Spanish company that designs seats. The company started in 1930s as company that designed seats for bicycle, motorcycle and other passenger vehicles for the public. Recently the rules and regulations mandating seat safety in buses for the European Union have changed to include a three point seat belt system and a whiplash restraint system. This meant that the design of the seat would need to be changed. The older seat frame would work as a design for the new seat belt as it did not allow for the three point system to work without putting the occupant in greater danger. Fainsa answered the challenge by changing the materials used to design the seat. Along with the choice of the new high-strength steel came new ways of working, involving close collaboration between Fainsa and several of its suppliers. This has opened the door to new thinking. The demands for light weight and improved safety were met with a design that combines extruded and pressed components of ultra-high strength steel. This forward thinking has lead to new relationships for Fainsa and greater exposure to new markets. By implementing cutting edge materials has brought Fainsa design to the top of the market and won them many design awards including the Swedish Steel Prize.

Bus Seat Frames and Safety

When it comes to seat frames used in buses or motor coaches, it appears there are many different types of materials that can be used to optimize investment. Recently the European Union has changed regulations, making the old bus seat frame obsolete. Aluminum and magnesium were debated before ultrahigh strength steel was decided. Research found that using ultra high strength steel created a more durable chair that also was comfortable for the passenger. The paragraph below describes the new seat design created by Fainsa. This design took into account major changes to safety protection as warranted by the new regulations.

Sawyer writes, "the seat bottom is a hollow section made from ultra-high-strength cold rolled two phase steel with a minimum tensile strength of 800 N/m [m.sup. 2]" (2005). This cold-rolled two-phase steel with this grade of strength is used for the rest of the frame as well. This makes the average double seat version with the new three point seatbelts installed capable of withstanding an impact of more than two tons (Sawyer 2005). The backrest of the seat is also able to be hollow, tubular steel that includes whiplash protection. The legs and brackets are also made of this steel material. Fainsa claims that this frame weighs "30% lighter than previous designs" (Sawyer 2005). The company hopes to adapt the design to fit seat on the EuroRail system and also aircraft. This will mean tremendous growth for the company as its chosen material allows them to diversify the product for numerous applications in the transportation industry. This has lead the company to researching new ways of allowing the steel to resist cracking. With this type of steel being used for seat frames, one can imagine the applications within other parts of the vehicle. This can mean stronger, reinforced compact cars that can be built in fewer steps. The key is creating an ultrahigh strength steel that does not crack under pressure and can be reshaped over and over. Companies working with Fainsa like the Swedish steel company SSAB Tunnplat alongside Bemo Systems, a German company has found a new method of roll-forming high-strength steel into previously impossible curved sections. This works with computer driven rollers that adjust consistently depending on conditions within the steel's composition. This steel can be used for bumper and side impact bars in cars.

Research suggests that the European Union is at the forefront of using ultra high strength steel components in public vehicles. This is mainly due to a change in regulations adopted by the EU to adapt seat belting use to the bus seat. As discussed earlier, this meant redesigning the existing seat to account for modifications. At this time that while there are no standards in the North America for the manufacture of bus seats, magnesium is widely used in the production of automobile seats which…