Why don't use stainless steel in aircraft carrier produce

Isn't stainless steel really rusting? There are many kinds of chloride components in the seawater such as sodium chloride and magnesium chloride. Ordinary stainless steel is basically not resistant to chloride ions, as long as it is soaked in seawater for ten days and a half. The Surface must also be devastated, while ordinary steel is less resistant to chloride ion corrosion, but it is only a difference between five days and ten days. For an aircraft carrier that needs to sail in seawater all the year round, it is not as good as a Liaoning ship. The aircraft carrier is regularly derusted, and then a layer of good anti-rust paint is applied!

In addition to stainless steel is not resistant to seawater corrosion, it has another fatal weakness, that is, poor welding performance! Both martensite and ferritic stainless steel have problems of low-temperature embrittlement cracking and toughness reduction. Therefore, pre-weld preheating and post-weld heat treatment are required, and it is necessary to maintain a constant temperature of 800 degrees or more during welding. To avoid cracks, to increase the strength.

However, although austenite does not have low temperature cracking, it does not need to be preheated and heat treated during welding. However, when the welding temperature exceeds 800 °C, some high alloy stainless steels with high nickel and molybdenum content will inevitably exhibit high temperature stress. The phenomenon of cracking also seriously affects the welding performance. Moreover, austenitic stainless steel generally contains about 18% of chromium element. After high temperature carbonization, it is easy to form a layer of chromium-depleted layer in the welding head, which will cause serious intergranular corrosion effect and greatly reduce the service life of the steel.

The aircraft carrier is a giant with a displacement of more than 10,000 tons. The size between the various components is several tens of meters. If the welding performance is not good, it will seriously affect the performance of the aircraft carrier and even endanger the safety of the aircraft carrier! Therefore, the poor welding performance has already shattered the life dream of most stainless steel avatar aircraft carriers!

However, in stainless steel, there are also outstanding people. This is a duplex stainless steel with half of austenite and ferrite. Duplex stainless steel is not only resistant to chloride ion pitting, but also has excellent welding performance, and no additional heat treatment is required. The plasticity of the double-body stainless steel is also good. It can be easily rolled and cut into various complicated parts. More importantly, its yield strength is above 400MPA, which is fully qualified for the flight deck of the aircraft carrier.

But why is duplex stainless steel not used as a large number of aircraft carriers? Mainly due to cost considerations, stainless steel itself is much more expensive than ordinary carbon iron. Duplex stainless steel has more alloying elements, and the refining process is more complicated. The cost is 20% higher than that of stainless steel. An aircraft carrier Need to use tens of thousands of tons of steel, the cost is definitely a high price! Therefore, duplex stainless steel is currently used mostly in heat exchangers, condensers and other key components of nuclear power plants or chemical plants!

Isn't it expensive to use steel for aircraft carriers? It's not expensive! In fact, the steel for aircraft carriers is a low-cost steel that meets the basic performance requirements. As long as the basic data such as corrosion resistance, weldability, yield strength and tensile strength can reach the standard, the cheaper the better. For example, the US Ford uses HSLA-105. In fact, the performance is similar to that of the Nimitz-class HSLA-100. It only improves the welding and cutting performance. The purpose of this is to reduce the cost of the Ford-class aircraft carrier. Therefore, aircraft steel can not be high-end, but it must be cheap!