Prise winners list

Development of high-strength lead-free micro alloying steel for a cranking con rod

Kokurakita-ward, Kitakyusyu-City
Sumitomo Metals (Kokura), Ltd.
Other award winners
Sumitomo Metals (Kokura), Ltd. / Michikazu Koga, Takeshi Sato, Sai Matumoto
Sumitomo Metal Industries, Ltd. / Naoyuki Sano, Koji Watari
Honda R&D Co., Ltd. / Tetsuya Asai, Yoshitsugu Iida, Ryosuke Kogure, Kentaro Takada
Recommended by
The Japan Iron and Steel Federation

Hasegawa, Tatsuya  (40)
Product Development Dept., Product Development No.1 Room, Manager

"Produce a con rod that can be cracked easily but has high fatigue strength." They satisfied these two conflicting requirements like a Buddhist riddle by conducting experiments repeatedly

A con rod for automobile is a part that converts the up-and-down movement of piston into the rotational movement. Since the con rod was connected to the crankshaft, conventionally its rod and cap were manufactured separately and joined later. However, Sumitomo Metals (Kokura), Ltd. focused on the manufacturing method called "cracking con rod" that was widely used in Europe. In this method, the con rod was manufactured as one piece and later force was applied and it was cracked into the rod and cap. However, European products did not meet the high quality standards of Japanese carmakers. Therefore, jointly with Honda, this company developed a new steel that had two conflicting properties. Namely, the new steel is easy to fracture, but easy to grind and has high metallic fatigue strength.


In this method, a con rod is cracked into two pieces and later joined again

A con rod is installed in a car engine to convert the up-and-down movement of piston into the rotational movement of crankshaft. The con rod can be compared to "human feet" in a bicycle. 
In manufacturing of a con rod, conventionally a rod and cap were manufactured separately because a crankshaft was inserted between them and fixed with bolts later. However, European manufacturers began to use a new manufacturing method called "racking con rod" in the late 1980s and early 1990s. In this method, a con rod is manufactured as one piece and then it is cracked into the rod and cap. 
For people who has knowledge about steel, this method may seem shocking, but simplifies the production process drastically. In addition, since the two surfaces of cracked rod matches with each other perfectly, the two pieces can be joined well and high strength can be obtained. 
"However, ordinary steels are tenacious and cannot be cracked easily. The products developed by European manufacturers contained a large amount of carbon to make them harder. The harder a steel product was, the easier it could be cracked, but a hard steel product could not be ground easily and its metallic fatigue strength was low. Those products did not meet the quality standards of Japanese carmakers."
This company thought that the cracking con rod had good potential and started development of for it in the late 1990s. The con rods and steel materials for crankshaft were major products for this company, and so it decided to focus on development of them. Mr. Hasegawa became the leader of development team in 2000.
"When I started development, our team could crack a hard steel into two pieces only occasionally. Therefore, I had to find the condition to crack the rods correctly and its mechanism and a method to manufacture con rods in mass-production stably.

Finally developed a product that satisfied the high-quality standards of Japanese carmakers

A con rod is pulled and pushed several thousand times a minute as the piston moves up and down, and so metal fatigue is caused and finally it breaks when even a weak force is applied. Therefore, the con rod is required to be cracked easily for manufacturing and to be ground easily to drill holes for the bolts, but must have high metallic fatigue strength at the same time. They had to satisfy these conflicting requirements like a Buddhist riddle.
"A joint researcher at Sumitomo Metal Industries, Ltd. found that when a steel material was mixed with titanium, it could be cracked easily in a certain condition. And we knew that when a steel material was mixed with a large quantity of vanadium, it could have high metallic fatigue strength. However, if too much titanium and vanadium were mixed, a steel material became too hard and it could not be drilled easily. In addition, since titanium and vanadium were expensive, we had to reduce use of them as much as possible."
While changing the composition of these two substances, they conducted a break test with patience repeatedly to check the fracture surfaces and fatigue strength. 
They conducted experiments to crack con rods as follows. A part that looked like a split cylinder was inserted into the hole of con rod, into which the crankshaft was to be inserted later, and a wedge was put into the center hole of the part. Subsequently a weight was dropped just above it freely to forcibly widen the hole and crack the ring of the con rod.
"The two positions of the ring were not cracked at the same time. If fact, one position was cracked first and then the other position was cracked. The broken surface of the first cracked position was clean and even, but that of the second position was not because the tenacious steel was torn off. We had to solve this problem."
After conducting a break test several hundred times, they found the optimal results. Based on these results, Honda, the partner of joint development, conducted a break test many times and completed a technology for mass production.
"Our new product is 13% lighter in weight than the conventional one, and has 30% higher metallic fatigue strength. Since the weight of engine, especially the parts that convey power, is reduced, fuel efficiency is improved and CO2 emission is reduced accordingly."
In addition, the engine itself was downsized because of thinner steel wall. 
The new cracking con rod was first used for Legend commercialized by Honda in 2004, has already been installed in the engines of more than 2.5 million cars. It is also used for Insight, a hybrid car that became very popular last year.

Sumitomo Metals (Kokura), Ltd.

Apr. 2004
27 billion yen
1226 (as of Mar. 2009)
Brief information:
This company is specialized in manufacturing of special high-performance steels in one continuous production process from its blast furnace. The Kokura company aims to establish a reputation for reliability and quality".

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This company is a manufacturer of blast furnaces in Kitakyushu, manufacturing high-quality steels from iron ores and selling them to carmakers and other manufacturers.


A part that looks like a split cylinder is inserted into the hole of con rod and a wedge is inserted into the center of the part. A weight is dropped from just above the wedge to crack the con rod.


One part is cracked into two pieces and after putting a crankshaft between the split two pieces, they are joined again and fixed by tightening the bolts. The production process was simplified drastically and the strength was increased significantly.


"Steel bars are one of major products of this company. They are pressed to form car parts.