China’s technological breakthrough in bearing steel: solving a major industry problem

The material used to make high-speed rail bearings is bearing steel which is known as "king of steel". It is one of the most demanding types of steel in high-speed rail smelting process. However, how to forge bearing steel with "high purity" and "high uniformity" and keep the oxygen content in the steel to a minimum has always been a difficult problem faced by iron and steel enterprises in China.

(Finished products using PTR)

In recent years, the PTR technology developed by Professor Liu Dong and his team from the School of Materials Science and Engineering of Northwestern Polytechnical University of China has broken the technology monopoly of foreign giants and solved a major industry problem for China.

1. Small part, big problem

The working environment for bearings is severe and complicated: it not only needs to keep a high-speed and stable rotation, but also withstand strong extrusion, friction, and even ultra-high temperature. Therefore, more stringent requirements are put forward on quality and reliability of bearing steel.

(The left picture using traditional technology, the right-hand side picture using PTR, PTR makes the particles more fine and dispersed)

Then how to improve the quality of bearing steel? Professor Liu Dong told us that first of all, the interiors should be pure enough, that is, the less foreign matter within the material the better; and secondly, the material should be evenly distributed, and the particles in the material are as fine and dispersed as possible.

"Unfortunately, the quality of bearing steel produced in China has been far behind the international advanced level. Take inclusions as an example, the size of inclusions of foreign products is completely less than or equal to 10μm, while in China the particle size reaches 50- 52μm, which is almost five times larger than that of the foreign products."

Many companies can not find bearing steel that meets high demand from domestic manufacturers and have to import them at high prices from other countries. Because the research and development, manufacturing and sales of high-end bearing steel have long been monopolized by bearing giants in the United States, Sweden and other countries, and the core technology has always been strictly classified business information. This also means that every time we manufacture a set of products, we need to buy bearings from abroad.

2. With years of research, the problem has finally been conquered

With the dream of developing the country to a “World Steel power”, Professor Liu Dong and his team have been through a lot of trials and overcome difficulties along the way to the present point. He proudly said, “With decades years efforts by our own country, problems with oxygen content, inclusions, segregation and other various technical problems have been effectively resolved. The carbide problem, which remained the last biggest problem in the industry, was finally overcome by our team! "Bearing steel is a high-carbon steel, and its carbon content is relatively high among all steels. If the carbides are unevenly distributed in forms of large blocks, it will seriously affect the quality of the steel.

3. PTR technology may bring new changes to the automotive manufacturing industry

According to Mr. Liu Dong, China's bearing industry has grown to a large market with sales up to 200 billion yuan, and the annual growth rate keeps going at 12%-15%; but the bearings produced are still mainly low-end ones and small/medium-sized products, among which, automotive bearings account for about 40%. Fortunately, with the PTR technology, such harsh reality will be significantly and effectively changed to a favorable status in the years to come.

(The left picture’s grain size is 80μm using traditional way; the middle picture averages 11 μm after using PTR; the third picture, from the left to right respectively presents the hardness in rolled, annealed and quenched and tempered state)

Laboratory data shows that with the use of PTR technology, the grain size is refined from the original 50μm to the present 10μm, and the carbide size is only 1/10 of the original size. The hardness of GCr15 bearing steel, stagnating at 600-700HV in the past 100 years, now has been increased above 900HV, making it a leading edge technology in the world. In addition, the bearing life and reliability have been greatly improved after adopting the PTR technology, and the average life span has reached 26 times the calculated life, and the reliability has reached 99.9%.

At present, the bearing steel modified by PTR technology has been used in many projects and can fully meet the high-end quality requirements. The technology has been applied to other materials and achieved very good results. And it is the first time being used in titanium alloys and high temperature alloys in the world.

"The performance of bearing steel produced with our technology is very impressive. This year, many companies have contacted us, hoping that the technology would bring innovation to the automobile manufacturing industry." When it comes to the future application of the new technology, Professor Liu Dong is full of confidence, he believes that a new and vast market is at hand.

China has been through lots of hardships in the development and innovation with bearing, now we have advanced to a certain level in the industry. It is a fact that our country is indeed inferior to the West in terms of industrial accuracy, but as time goes by, we keep doing better and better. When the Vision of Industrial Manufacturing of China 2025 was formulated a few years back, the rise of China’s industry is bound to make greater achievements under the strong support of the government.

Industry is not merely about making an advanced precision bearing or make a breakthrough in some technology, but building a whole set of equipment-manufacturing ability and technologies with which to sustain further progress, just like Japan does; then China will surely be among top bearing-making countries in the world.

(Source: Northwestern Polytechnical University)