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 declaim deviations from the derailed machine has been motorcarried bug out in lay out 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 supposed to be composed of 4130 steel. A heat treatment process involving a water slop and tempering was also required to modify the rail to a desired balance between ductileness and callosity. The final Rockwell C-scale asperity was supposed to be 35-40.The failed rail was found to have a Rockwell C hardness of only 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 mashed or tempered at all, but merely anneal ed and left to cool. The resulting pearlite crystal structure of the material was soft and ductile, bending easily nether stress and causing the car to derail and plummet to the ground.Introduction A new curler coaster in Florida called The Big Twist killed four people when one of the cars separated from the track and fell to the ground one hundred twenty feet below. It was discovered that the outer left wheel assembly was bent more than 30 degrees from its normal just 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 stagecoach (or crystal structure).The first step in heat treating steel is the process of annealing and austenizing. When the steel is modify to a high enough temperature (annealing), carbon is dissolved into the coat solution (austenizing) by fitting into the interstitial vacancies i n the high temperature-induced face-centered cubic structure of iron (austenite). The succeeding(a) step in heat treating is to quench the steel in water or oil, quickly cooling the steel to room temperature in order to trap the carbon in the crystal structure (even at the reduced temperature).This new phase is called martensite, medium 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(prenominal) 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 too much pearlite (it is only annealed or tempered too long or hot), it wil l 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 unannealed martensite (it is only annealed and quenched without a tempering), it will be extremely hard but utterly brittle. observational 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(prenominal) 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 two were left at room temperature. The samples were next sanded with abrasive paper to remove surface discoloration and tested for Rockwell C-scale hardness, with three tests each to be averaged. aft(prenominal) the har dness tests were completed, Charpy Impact Tests were performed on each specimen.A table 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 low the microscope to study the microstructure. The preparation included cutting, hot mounting, techy and fine grinding, and polishing 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 out and fine grinding involved using a silicon carbide abrasive on a charge 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 n itric 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.