Since “The Big Twist” Essay Example for Free

Since The Big Twist EssaySince The Big Twist failure that killed multiple people, an investigation of the wheel and prepare deviations from the derailed railroad car has been carried out in score to determine what course of action should be taken to prevent similar catastrophes from occurring. In order to achieve safety, the rails of the newly designed car were vatic to be composed of 4130 steel. A heat treatment process involving a water quench and tempering was also required to modify the rail to a desired correspondence between ductility and hardness. The final Rockwell C-scale hardness was supposed to be 35-40.The failed rail was found to have a Rockwell C hardness of unless 4. 8. In our own reference experiment, we were able to produce specimens similar to the failed specimen, with a Rockwell C hardness of 3. 7. Our similar sample was austenized and air cooled, which leads to the conclusion that the failed rail was not quenched or tempered at all, but merely annealed and left to cool. The resulting pearlite crystallization structure of the material was soft and ductile, bending easily under assay and causing the car to derail and plummet to the ground.Introduction A new roller coaster in Florida called The Big Twist killed four people when one of the cars unconnected from the track and fell to the ground 120 feet below. It was discovered that the outer left wheel assembly was bent more than 30 degrees from its normal vertical orientation due to twisting of the support beam that connected the wheels to the car. Our research was performed to discover why the rail was weak enough to bend. The characteristics of steel can be greatly modified by changing the phase (or crystal structure).The first step in heat treating steel is the process of annealing and austenizing. When the steel is heated to a high enough temperature (annealing), carbon is dissolved into the metal solution (austenizing) by fitting into the interstitial vacancies in the high t emperature-induced face-centered cubic structure of iron (austenite). The near step in heat treating is to quench the steel in water or oil, quickly cooling the steel to room temperature in order to ambush the carbon in the crystal structure (even at the reduced temperature).This new phase is called martensite, intermediate to the face-centered and body-centered cubic structures. The internal stress caused by the distorted crystal structure causes the metal to be exceedingly hard and brittle. Finally, the heat treating is completed by heating the material once again (tempering) to gain a balance between strength and ductility. During tempering, nucleation of cementite occurs along with a growth in grain size, both reducing internal stress and restoring ductility. The resulting metal can be both harder and stronger than it can be without treatment.Essentially, if the metal contains as well much pearlite (it is only annealed or tempered too long or hot), it will be too ductile and soft to withstand the forces on the rail of the roller-coaster car, for example. Conversely, if the metal contains too much untempered martensite (it is only annealed and quenched without a tempering), it will be extremely hard but utterly brittle. Experimental Procedures and Results Using seven samples of 4130 steel as references, it was possible to determine what was wrong with the received sample of roller coaster rail with comparative analysis.Seven reference specimens were placed in an austenitizing furnace at 844C for one hour. After austenitizing, six of the samples were immediately quenched in water at room temperature and four of them were placed in tempering furnaces at 205C, 370C, 482C, and 677C for one hour. The other ii were left at room temperature. The samples were next sanded with abrasive material paper to remove surface discoloration and tested for Rockwell C-scale hardness, with three tests each to be averaged. After the hardness tests were completed, Charpy Imp act Tests were performed on each specimen.A flurry of results can be seen below. Obviously the crashed car rail was not tempered correctly, if at all, since its properties are almost identical to the austenized, air-cooled sample of 4130 steel. Also, a crashed car rail specimen was prepared and examined under the microscope to study the microstructure. The preparation included cutting, hot mounting, rough and delightful grinding, and beautify of the specimen. After the specimen was cut into two pieces of appropriate sizes, hot mounting was carried out using a press which molded a thermoplastic around the samples on three sides.Rough and fine grinding involved using a silicon carbide abrasive on a belt sander with 120, 240, 400, and 600 grit papers. Polishing was performed with rotating wheels covered by polishing cloths soaked in alumina slurrys (1mm, . 3? m, and . 05? m alumina respectively). Finally, the samples were chemically etched with nitric acid, one for 8 and one for 15 seconds. The samples were examined under a microscope at 400x, the images of which are shown below.