In 1798 stainless steel was invented. It was cheaper than carbon steel, stronger, easier toaintain but it became dull very easily.
The sabres (swords used by hussars and other cavalry) were well used from early modern warfare until World War One. So, this means swords and stainless steel co-existed for 100 years.
My question is, were there any instance of stainless steel sabres in those era? As i reason, poorer soldiers that couldnt afford carbon steel would order stainless steel blades from blacksmith as it was cheaper and easier to maintain. Even if it is harder to avoid dullness, sabre charges were only were one of two times in the combat and rest of the melee charges were made by bayonets and lancers. Also it is better than nothing.
1798 is when reasonably pure chromium metal was first produced (chromium was discovered the previous year, 1797). The first investigation of chromium steels appears to have been in 1820, by Michael Faraday and James Stodart. Stodart brought a lot of practical experience to the team - not only was he a scientist (and Fellow of the Royal Society), he was also a cutler and maker of surgical instruments. While Faraday and Stodart found that chromium steels were useful for cutting tools due to higher hardness and wear resistance, they only studied steels with low chromium content, below 3%, which are not stainless.
A big step towards stainless steel was in the following year, 1821. Pierre Berthier produced ferrochromium, a very high chromium iron-chromium alloy produced by reduction of a combination of chromium and iron ores. His ferrochromium had a very high carbon content, which meant that it wasn't yet useful for making stainless steel, since adding enough chromium (in the form of ferrochromium) to iron to reach the level needed for stainless steel would also add a lot of carbon, which would (a) make the carbon content too high for the usual uses of steel, and (b) stop the steel from being stainless (since the carbides resulting from the very high carbon content prevent passivation of the surface). Like Faraday and Stodart, Berthier only studied low-chromium alloys. Like Faraday and Stodart, he noted higher hardness and wear resistance, and that these alloys were useful for cutting tools. He also noticed improved corrosion resistance, but his chromium contents of about 1-1.5% were too low for the alloy to be stainless.
Next, in 1872, an acid-resistant high-chromium alloy, about 31% chromium, 2% tungsten, and the remainder steel, was developed. Next, in 1892, Robert Hadfield (of Hadfield manganese steel fame) studied chromium steels with chromium in the stainless range. His carbon contents were high, from 1-2% (which would make these alloys difficult to use for swords). He tested for corrosion resistance with sulphuric acid, and concluded that the corrosion resistance was poor. It was later found that testing such alloys with sulphuric acid doesn't reveal their real-world corrosion resistance - Hadfield missed a discovery.
Next, in 1895, Hans Goldschmidt developed a method for producing low-carbon ferrochromium (and also chromium metal). Now, chromium steels could be made with whatever carbon content was desired.
Next, from 1904-1906, Léon Guillet made and investigated a wide range of low-carbon and high-carbon stainless steels, including alloys similar to many modern martensitic, ferritic, and austenitic stainless steels. These alloys included some that are suitable for sword-making.
While these early steps towards sword-capable stainless steel were going on in the 19th century, steel metallurgy became much better understood, and the metallurgy of swords was put on a reasonably scientific basis. In 1889, two British engineers made what was perhaps the first modern metallurgical study of sword blades, including the effect of different alloys and heat treatments. They recommended to the British Army that a high-carbon low alloy steel be used (approximately corresponding to the modern 1095 standard), and the Army chose this as their specification. No suitable stainless alloy had yet been developed, and they saw no significant advantage from using a low-chromium chromium steel.
The significant commercial use of stainless steel was begun by Harry Brearly in 1913, with the manufacture of stainless steel cutlery. He started work on stainless steel the previous year, investigating wear-resistant alloys for lining gun barrels. Research on stainless steels was reduced by the effect of WWI, but large-scale research started again after the war, and many of the common alloys we use today were developed between 1920 and 1935 (in particular chromium-nickel-steels hadn't been studied much before; Krupp appears to have developed the first such steels in 1914).
Essentially, the age of stainless steel arrived as swords were disappearing from the battlefield. The only sword intended for the battlefield I know of that used a stainless alloy was the stainless version of the Japanese kai-gunto (Navy sword). An example:
Today, many replica swords are made from stainless steel. 420J2 is a common alloy for decorative swords (and is widely used for cheap bottom-end kitchen knives). In principle, 420J2 could be used to make functional swords, with excellent corrosion resistance, and a hardness of about 45-50HRC. This is a rather low hardness compared to late 19th century swords, but was not unusual earlier in the 19th century. Higher-carbon alloys such as 440A would provide somewhat higher hardnesses.
It is commonly said that stainless steel is too brittle to be used for swords. One commonly cited example of "too brittle" is this home-shopping channel accident:
Generally, stainless alloys only have about 1/2 to 2/3 of the fracture energy (as measured, e.g., by the Charpy or Izod impact tests) of a low-alloy carbon steel of similar hardness. The above accident was with a sword made with 440C, with a very high carbon content - if the heat treatment is not perfect, 440C is easily too brittle for swords. However, this doesn't mean that lower-carbon stainless alloys will be too brittle. For example, the above-mentioned 440A, with about 0.65% carbon, hardened to the same hardness one would use for a sword made with 1065, will only be about as tough as a 1095 sword. But this is within the acceptable range of toughness, rather than being too brittle. An even lower carbon alloy, such as 420J2, will result in a quite tough sword (although compromising on hardness and therefore edge retention). Almost all swords made today with 420J2 are unfit for use - not the result of the choice of alloy, but the result of being made as a cheap decorative sword, rather than being made as a properly-functional sword.
It was cheaper than carbon steel
I haven't seen any data for stainless steel prices from before 1900, but I see that stainless steel prices fell by about 70% from 1900 to 1920, compared with carbon steel prices falling by about 30% (the price had peaked in about 1900). This suggests that what stainless steel was available before 1900 was more expensive than carbon steel.
For more on the history of stainless steel, see: