这艘偌大的游轮究竟为什么会沉于海底呢？由于技术上的原因，直至1991年。科学考察队才开始到水下对残骸进行考察，并收集了残骸的金属碎片供科研用。这些碎片以及沉船在海底的状况使人们终于???开了巨轮“泰坦尼克号”罹难之谜。考察队员们发现了导致“泰坦尼克号”沉没重要细节。

造船工程师只考虑到要增加钢的强度，而没有想到要增加其韧性。把残骸的金属碎片与如今的造船钢材作一对比试验，发现在“泰坦尼克号”沉没地点的水温中，如今的造船钢材在受到撞击时可弯成V形，而残骸上的钢材则因韧性不???而很快断裂。由此发现了钢材的冷脆性，即在-40℃至0℃的温度下，钢材的力学行为由韧性变成脆性，从而导致灾难性的脆性断裂。而用现代技术炼的钢只有在-70℃至60℃的温度下才会变脆。不过不能责怪当时的工程师，因为当时谁也不知道，为了增加钢的强度而往炼钢原料中增加大量硫化物会大大增加钢的脆性，以致酿成了“泰坦尼克号”沉没的悲剧。

另据美国《纽约时报》报导，一个海洋法医专家小组对打捞起来的“泰坦尼克号”船壳上的铆钉进行了分析，发现固定船壳钢板的铆钉里含有异常多的玻璃状渣粒，因而使铆钉变得非常脆弱、容易断裂。

这一分析表明：在冰山的撞击下，可能是铆钉断裂导致船壳解体，最终使“泰坦尼克号”葬身于大西洋海底。

有人说：泰坦尼克号所用钢材追求强度加入大量硫，导致韧性变差，脆性转变温度高，否则在0度左右海水中撞击时会变成v形而不断裂。
另外采用铆接，而不是焊接，导致船身截断。

我查阅了一些相关的情况，往钢材里加硫来提高强度的说法是不太可靠的，关键是当时使用的是一种叫做酸性平炉法的技术，但是在万方上没查到什么相关文献，而且冷脆性和P相关，硫是热脆性呀。
在当时的钢种冶炼当中，硫和磷已经是备受关注的对象，因此，为了避免这两个元素对冷脆性的影响，已做了足够的努力。其实导致钢出现低温脆性的主要原因是由于当时人们对N在钢种行为的不理解以及高强度微合金钢冶炼技术不太成熟所致。当时主要是以锰钢为主，而不过多考虑微合金元素对钢种低温脆性的影响，更重要的是在钢种由于没有足够的合金元素与钢中的N结合，导致了钢中自由N过多而增加了低温脆性的敏感度，因此后来的冶金就开始添加了Al来固氮，再后来就是添加微合金元素了。

这个有专题报道的。。。
见下文（转自sciencedaily）：
Olympic and Titanic were built using Siemens-Martin formula steel plating throughout the shell and upper works. This type of steel was first used in the armed merchant cruisers, Teutonic and Majestic in 1889/90. This steel was high quality with good elastic properties, ideal for conventional riveting as well as the modern method (in 1912) of hydraulic riveting. Each plate was milled and rolled to exact tolerances and presented a huge material cost to both yard and ship owner. The steel was not a new type, as already stated, but shows that yard and owner only put material and equipment into these two giants that was tried and tested. Reports of Teutonic's and Majestic's hull condition 20 years after they entered service showed that both were in remarkable condition. The excellent properties of this steel and resistance to corrosion made it the natural choice for the new sisters.

Yard workers at the time referred to this steel as "battleship quality." I had several conversations with retired shipbuilders at Harland and Wolff and they confirm this. Harland and Wolff used larger sized plates to reduce the amount of butts and overlaps. The shells themselves were generally 6 feet wide and 30 feet long weighing between 2 1/2 and 3 1/2 tons depending on thickness. The double bottom plating was 1 1/2 inches thick and hydraulically riveted up to the bilge. Some of the largest plates were 6 feet wide and 36 feet long and weighed 4 1/2 tons.

White Star gave Harland and Wolff complete freedom to build the very best ships they could, adding a percentage profit to the final cost of the building. The so-called "cost-plus" arrangement was used on all but one of the company's ships. From 1869 until 1919, it was said that there was never a single day that Harland and Wolff was not working on one of the White Star Line's ships. White Star was Harland and Wolff's best customer and they undertook to build Olympic and Titanic on the same basis as before, cost-plus. The ships were the largest in the world and would require numerous calculations as to the strength of hull required at this size. Much of the ships' arrangement was tried and tested basic shipbuilding design -- just larger with greater added strength. The strength was entirely provided by the ship's shell plating and rivets. Hydraulic riveting was used for much of the 3 million rivets, in some places the hull quadruply riveted.

Titanic's impact with an iceberg caused the rippling and springing of the joints between plates. Rivet heads ripped off would not cause massive flooding, rather the long leaking that is recorded to have happened in her forward compartments. Science tells us that in order for steel of this quality to fracture due to cold and impact would mean the steel being brought down to below the temperature of liquid nitrogen. As the water in Titanic's ballast tanks had not frozen on the night she struck the iceberg, it's safe to say the steel was above the freezing point of ordinary seawater.

We discovered on the Arabic (White Star liner of 1903) dive the ship's shell plating was in remarkable condition, but the rivets had "let go." That is to say, sprung -- allowing the plates to come apart. In places the ship was like a stack of playing cards not relating to any structure. I have some of these and I'm organizing a scientific study of them and will keep you apprised of the results.

I think -- and this is just a theory -- the rivets were heated so they could be riveted into place by hand or by hydraulic riveter. The steel would have to be capable of easy heating, malleable, and perhaps weaker by design. Is this the Achilles' heel of the Titanic? So much time is spent looking at the steel but I think these 3 million mild steel rivets might hold the secret.