Train axles are key components that bear the weight of the vehicle and are subjected to multiple complex stresses such as rotating bending and impact during operation, directly relating to the speed and safety of vehicle operation. So which is better, 40 steel or 50 steel? This topic has been debated for 30 years without a result. And another concern has surfaced with a widely reprinted report.

　　Some media reports say that the service life of 50 steel should be 13 years. Our country uniformly adopted 50 steel axles in 2001, so by this calculation, it is exactly today that 50 steel axles have reached the critical point. The lifespan of the axles is about to end. Are the trains we ride every day still safe?

　　An axle refers to the cylindrical part that goes through the wheel hub and bears the weight of the vehicle body. This steel axle determines the train's speed and is also a crucial link in operational safety. Should axle material be 40 steel or 50 steel? Within the China Academy of Railway Sciences, this issue has sparked fierce debate for over 30 years and remains unresolved today. Kang Xiong, vice president of the academy, politely but firmly declined to comment.

　　Kang Xiong: This matter has been over for many years; those who should retire have retired. We really cannot say.

　　Historically, 40 steel, 45 steel, and 50 steel have all been used as axle steel in our country. In the mid-1950s, due to frequent accidents, our country stopped using 50 steel axles and began developing and producing 40 steel axles according to Soviet standards. Until 1973, 40 steel axles that had been in operation for five or six years were found to have cracks, affecting safety and transportation. "Improving 40 steel" and "restoring 50 steel" became the two options at the time.

　　Ultimately, 50 steel, once abandoned, returned to center stage. Since 2001, 50 steel axles have been uniformly used in our country's trains. China National Radio reached an anonymous figure in the railway science community who has participated in multiple core railway technology research projects. Regarding 40 steel and 50 steel, he said there is no absolute difference in superiority between the two. Railway expert: The difference between 40 steel and 50 steel, from the grade designation, is just a difference in carbon content in the steel—one is 0.4 carbon, the other is 0.5 carbon.

　　Reporter: What difference does it make when used as an axle?

　　Railway expert: Under the same process, 50 steel has higher strength because of its higher carbon content, and carbon content is one of the key factors determining strength in steel.

　　Reporter: Why don't other countries use 50 steel?

　　Railway expert: While strength increases, toughness decreases. Maintaining a balance between strength and toughness is a highly technical matter.

　　Is 50 steel safe? Supporters of 50 steel cite multiple replies from the former Ministry of Railways Science and Technology Department, which fully affirm the performance and legality of technical appraisal of 50 steel axles. Opponents present a technical appraisal from the Association of American Railroads, in which the qualification of China-developed 50 steel axles is completely denied. Regarding the US "unqualified" conclusion, core team members who initially developed 50 steel axles speculate that because the US did not want to import steel axles from China at the time, they could only reject them by verifying them as unqualified.

　　With the 13-year lifespan limit approaching, what is the prospect of the 50 steel axles currently in use? If the axles are nearing retirement, is "replacing axles" imperative, and will the feared "axle breaking while the train is running" happen?

　　On the eve of the 2014 Spring Festival travel rush, the debate over 40 steel and 50 steel seems even more meaningful. After reading the statement that "50 steel's lifespan is about to expire," some inevitably have doubts: Is it safe to take the train? In response, railway science community members said that 40 steel and 50 steel are generally used for freight trains. In addition, regardless of the material, axles have a service life issue, and replacement upon expiration is a routine process, so there is no need to panic.

　　Railway expert: The axle materials for passenger and freight trains are different. Passenger trains are divided by speed; for example, EMU high-speed trains have different axles, including different materials and processing techniques. 40 steel and 50 steel are for freight train axles. For high-speed rail, the axles and wheels are directly imported from abroad; domestically we do not yet produce these. But for lower-speed trains, we do. Currently, train axles are the same—they must be replaced after a certain period. If metallurgical quality is well controlled in 50 steel axles, actually from their existing design life, there should not be major problems.

　　Experts revealed that improving axle safety is indeed one of the current tasks of railway research departments, but saying "50 steel is unsafe" based on this is clearly unfair.

　　Railway expert: Under the current domestic conditions of extremely high traffic volume and high speed—equivalent to high-speed and heavy-haul development—how to further adjust to suit our railway development is the question, rather than saying there are definitely hidden dangers. In fact, since the year before last, the China Academy of Railway Sciences has been leading the supply of an alternative material for 50 steel freight axles. From what I understand, the physical axles made with the new material, after testing, show improvements over 50 steel axles.