Steel is valued for its reliability, but not when it gets cold. Most forms of steel abruptly(突然) become brittle （脆的）at temperatures below about -25℃ unless they are mixed with other metals. Now, though, a novel type of steel has been developed that resists fractures(断裂) at much lower temperatures, while retaining its strength and toughness—without the need for expensive additives(添加剂）.Steel's fragility at low temperatures first became a major concern during the Second World War. After German U-boats torpedoed （用鱼雷攻击）numerous British ships, a 2,700-strong fleet of cheap- and-cheerful "Liberty ships" was introduced to replace the lost vessels, providing a lifeline for the besieged(被围困的) British. But the steel shells of hundreds of the ships cracked(破裂) in the icy north Atlantic, and 12 broke in half and sank.Brittleness remains a problem when building steel structures in cold conditions, such as oil rigs in the Arctic. So scientists have strived(努力) to find a solution by mixing it with expensive metals such as nickel.Yuuji Kimura and colleagues in Japan tried a more physical approach(方法). Rather than adding other metals, they developed a complex mechanical process involving repeated heating and very severe mechanical deformation, known as tempforming.The resulting steel appears to achieve a combination of strength and toughness that is comparable(类似的) to that of modem steels that are very rich in alloy content and, therefore, very expensive.Kimura's team intends to use its tempformed steel to make ultra-high strength parts, such as bolts. They hope to reduce both the number of components(部件) needed in a construction job and their weight—by replacing solid supports with hollow(空心的) tubes, for example. This could reduce the amount of steel needed to make everything from automobiles to buildings and bridges.