the melt spun method includes any of the processes such as single roll chill block casting , double roll quenching , melt - extraction , melt drag etc ., where a thin layer of liquid metal is brought in contact with a solid substrate . other rapidly solidified powder processing methods such as forced convective cooling of atomized droplets known in the art , can be used to make rapidly solidified powders of the present alloys and such powders can be subsequently powder metallurgically consolidated into bulk parts and / or heat treated for optimised microstructure , mechanical properties etc . in accordance with the present invention iron base alloys containing 20 to 40 atom percent aluminum are further alloyed with 5 to 17 atom percent of boron . the alloys are optionally alloyed with one or more of the following elements ; 0 to 10 % of cu , ni and cr , either singly or combined , 0 to 10 % of mo , w , nb , ta and v , either singly or combined , and 0 - 5 % of si . the alloys may also contain limited amounts of other elements which are commercially found in iron base alloys without changing the essential behavior of the alloys . typically examples include fe 48 al 35 b 17 , fe 50 al 33 b 17 , fe 50 al 35 si 5 b 10 , fe 45 al 30 mo 5 ni 5 si 5 b 10 , fe 40 al 30 cu 5 ni 5 mo 2 v 3 si 5 b 10 and fe 50 al 25 ni 10 mo 2 ta 1 nb 1 w 1 b 10 . the alloys of the present invention , upon rapid solidification processing from the melt by melt spin chill casting at cooling rates of the order of 10 5 to 10 7 ° c / sec , form brittle ribbons consisting predominantly of a single solid solution phase with high degree of compositional uniformity . the brittle ribbons are readily pulverised into powders having particle size less than 100 u . s . mesh using standard comminution techniques . the powder is consolidated into bulk parts , e . g . disks , plates , bars , etc . using powder metallurgical techniques ( e . g .) hot extrusion , hot isostatic pressing , hot forging , hot rolling , etc ., optionally followed by heat treatment for optimised properties . the bulk alloys contain finely dispersed borides and / or silicides within an iron - rich matrix , such material being tough and having high hardness and strength compared to conventional iron - base alloys . when the alloys within the scope of the present invention are solidified by conventional slow cooling processes , they have relatively coarse grains and hence lesser mechanical properties . in contrast , when the alloys are made using rsp techniques followed by heat treatment at high temperatures , preferably between 800 ° to 950 ° c . for 0 . 1 to 100 hrs . the precipitation of ultrafine borides takes place , these borides having an average particle size of ˜ 0 . 5 micron , preferably 0 . 05 micron , being finely dispersed both intergranularly and intragranularly . typically , the matrix grains have a size less than 10 microns , preferably less than 2 microns . the fully heat treated rsp alloys of the present invention exhibit high hardness and high strength . the alloys of the present invention have hardness values of 350 to 720 kg / mm 2 corresponding to 150 to 300 ksi . in comparison , the standard stainless and heat resisting steels have a maximum hardness of 350 kg / mm 2 . the boron content of the present alloys is critical . when the boron content is less than 5 % the alloys are difficult to form as rapidly solidified ribbons by the method of melt deposition on a rotating chill substrate ( i . e .) melt spinning . this is due to the inability of the alloy melts with low boron contents to form a stable molten pool on the quench surface . such alloys do not readily spread into a thin layer on a rotating substrate as required for melt spinning . when the boron content is greater than 17 % it becomes difficult to form a solid solution phase . the heat treated alloys are very brittle containing excessive amounts of brittle boride phases exhibiting poor mechanical properties . of particular interest in these alloys are the increased strength and hardness combined with good corrosion and oxidation resistance . also , these alloys do not contain chromium which is in short supply because of limited mineral reserves . the alloys of the system fe - al - b with b contents between 13 to 17 atom percent prepared in accordance with the present invention belong to a preferred group of alloys . these alloys are described by the formula fe 48 - 62 al 25 - 35 b 13 - 17 . examples include fe 48 al 35 b 17 , fe 55 al 30 b 15 , fe 50 al 35 b 15 , and fe 60 al 25 b 15 . the above alloys upon rapid quenching by melt spinning form extremely brittle ribbons consisting of single solid solution phase . the quenched alloys may additionally contain borides dispersed in the matrix . upon heat treatment at 900 ° c . for 2 hrs . the precipitation of ultrafine borides takes place both intergranularly and intragranularly . after such heat treatment the above alloys exhibit improved toughness i . e . ductility and possess relatively high hardness values between 350 to 400 kg / mm 2 . another preferred class of alloys is based on the system fe - al - si - b . this class is defined by the general formula fe 50 - 68 al 25 - 35 si 2 - 5 b 5 - 10 . typical examples include fe 50 al 35 si 5 b 10 . fe 60 al 25 si 5 b 10 , fe 60 al 30 si 5 b 5 and fe 65 al 25 si 5 b 5 . the ribbons obtained by melt spinning are brittle which upon heat treatment at 900 ° c . shown significantly improved ductility with typical hardness values ranging between 520 to 640 kg / mm 2 . another preferred class of alloys which is obtained by the addition of molybdenum to fe - al - si - b alloy is described by the formula , fe 40 - 60 al 25 - 35 mo 5 - 10 si 0 - 5 b 10 - 15 , with the provisos that the sum of ( b + si ) may not exceed 15 . typical examples include fe 45 al 35 mo 5 si 5 b 10 , fe 50 al 30 mo 10 b 10 , fe 50 al 25 mo 10 si 5 b 10 , and fe 55 al 30 mo 5 b 10 . the above alloys when processed by the method described in the present invention exhibit very high hardness , up to 720 kg / mm 2 and hence high tensile strength . alloys of the present invention upon melt spinning form very brittle ribbons which become tough upon heat treatment at high temperatures . the toughness of melt - spun ribbons can be readily characterized by the bend test wherein the metallic ribbon is bent to form a loop and the diameter of the loop is gradually reduced until the ribbon fractures . the smaller the breaking diameter for a given ribbon thickness , the toughness the ribbon is considered to be . table 1 gives compositions of selected alloys along with the typical values of hardness and breaking diameters of the ribbons in as - quenched state and after heat treatment . table 1______________________________________ heat treated ( 900 ° c . for 2 hrs ) as - quenched ribbonex - alloy ribbon hardnessam - composition hardness breaking ( kg / breakingple ( atom percent ) kg / mm . sup . 2 dia ( inch ) mm . sup . 2 ) dia ( inch ) ______________________________________1 fe . sub . 52 al . sub . 35 b . sub . 13 972 0 . 30 352 0 . 022 fe . sub . 48 al . sub . 32 mo . sub . 8 b . sub . 12 840 0 . 20 450 0 . 023 fe . sub . 60 al . sub . 30 si . sub . 3 b . sub . 7 600 0 . 15 520 0 . 01______________________________________ selected fe - al alloys were alloyed with boron , silicon and molybdenum . typical examples are given in table 2 . these alloys were melt spun as brittle ribbons having thicknesses of 25 to 75 microns by rsp method of melt spinning using a cu - be cylinder having a quench surface speed of ˜ 5000 ft / min . the ribbons were found by x - ray diffraction analysis to consist predominantly of a single solid solution phase . the brittle ribbons were pulverized into powder under 100 mesh or staple using a rotating hammer mill . table 2______________________________________ alloy compositionexample ( atom percent ) ______________________________________4 fe . sub . 55 al . sub . 30 b . sub . 155 fe . sub . 55 al . sub . 32 b . sub . 136 fe . sub . 48 al . sub . 35 b . sub . 177 fe . sub . 53 al . sub . 30 b . sub . 178 fe . sub . 48 al . sub . 30 mo . sub . 7 b . sub . 159 fe . sub . 45 al . sub . 30 mo . sub . 10 si . sub . 3 b . sub . 1210 fe . sub . 43 al . sub . 35 mo . sub . 8 si . sub . 2 b . sub . 1211 fe . sub . 55 al . sub . 35 si . sub . 2 b . sub . 812 fe . sub . 60 al . sub . 30 si . sub . 5 b . sub . 5______________________________________ a number of iron - aluminum alloys containing boron were prepared as brittle rsp ribbons in 50 to 100 grams quantity in accordance with the present invention . typical compositions of the alloys are given in table 3 . upon heat treatment at 900 ° c . for 2 hours the melt spun ribbons became tough i . e . exhibited smaller breaking diameter in bend test and had hardness values ranging from 350 to 720 kg / mm 2 . table 3______________________________________ alloy composition hardness of heat treatedexample ( atom percent ) ribbon ( kg / mm . sup . 2 ) ______________________________________13 fe . sub . 52 al . sub . 35 b . sub . 13 35014 fe . sub . 53 al . sub . 32 b . sub . 15 38015 fe . sub . 50 al . sub . 35 b . sub . 15 40016 fe . sub . 50 al . sub . 33 mo . sub . 5 b . sub . 12 72017 fe . sub . 48 al . sub . 32 mo . sub . 8 b . sub . 12 45018 fe . sub . 56 al . sub . 32 si . sub . 3 b . sub . 9 64019 fe . sub . 60 al . sub . 30 si . sub . 3 b . sub . 7 520______________________________________ a number of alloy ribbons were subjected to corrosion and oxidation tests . the tests and the results are tabulated in table 4 . the compositions of the alloys investigated are ( i ) fe 52 al 35 b 13 ( ii ) fe 53 al 32 b 15 ( iii ) fe 60 al 30 si 3 b 7 ( iv ) fe 56 al 32 si 3 b 9 ( v ) fe 50 al 33 mo 5 b 12 and ( vi ) fe 48 al 32l mo 8 b 12 . table 4______________________________________test results______________________________________ ( a ) exposure to indoor atmosphere had excellent resistance for 1000 hours without sign of discoloration or tarnish ( b ) exposure to outdoor had excellent resistance atmosphere for 1000 hours without sign of discoloration or tarnish ( c ) exposed at 900 ° c . for 16 did not show any trace of hours oxidation as evidenced by lack of oxide scale formation ( d ) kept in 5 wt % sodium did not show any corrosion as chloride solution for 120 hours evidenced by the clear surface______________________________________ the following example illustrates an economical method of production of rsp powder of the boron modified iron - aluminum alloys of the composition indicated in ( a ) with the present invention . the iron base alloys are melted in any of the standard melting furnaces . the melt is transferred via a ladle into a tundish having a series of orifices . a multiple number of jets are allowed to impinge on rotating water cooled copper - beryllium drums whereby the melt is rapidly solidified as ribbons . the ascast brittle ribbons are directly fed into a hammer mill of appropriate capacity wherein the ribbons are ground into desirable size ranges . while the invention has been described with particular reference to the specific embodiments , numerous modifications thereto will appear feasible to those skilled in the art .