"...or art thou a dagger of the mind, a false creation
proceeding from heat oppressed brain?"
MacBeth II, i.33
The effects of heat on weapons and armour is very much a reality.
I agree with Chris, Gav's observation is very well placed. I do know that many edged weapons had steel hilts covered with leather for this, as one reason. In the 19th century, many of the steel hilts on the sabres worn by horsemen in the heat of the Mexican deserts were covered with sewn leather covers. This is also true of British 'colonial' swords, in desert regions of India such as the Punjab and Sind, the steel hilts also had leather covers. I once had a British WWI pattern 1908 cavalry sword with a huge steel bowl hilt. This was one used by General Allenby's cavalry in the campaigns in the Middle East, and the hilt was covered in sewn leather.
It is also suggested that the purpose of these leather covered hilts was to prevent accidental glints or reflection from the sun revealing positions of cavalry, however that seems unlikely as the clatter of horse trappings and thunder of hooves in mass, the dust stirred not withstanding, would be more likely to reveal such presence.
As to armour in the Crusades and Middle East, in fact to ancient times, the effects of heat on the wearer is a very real, however not often discussed, reality.
"...the heat of summer made the armour insupportable and exposed the wearer to the dangers of suffocation and apoplexy, or produced at least, such debility as to disable him from wielding his weapons".
"The History of Chivalry and Armour"
Dr. F.Kottenkamp, 1850
"...the real problem with armour was not its weight but the way it trapped heat. Body heat resulting from battle exertion could prove fatal. At the Battle of Agincourt (1415) the Duke of York seems to have died of a heart attack brought on by 'the heat of battle'.
"Brasseys Book of Body Armour"
Robert Wasasnam-Savage,2000, p.70
"...it is one of the mysteries in the history of armour, how the crusaders can have fought under the scorching sun of the East in thick quilted garments covered with excessively heavy chain mail".
-Brittanica, p.392
None of these resources reveals any particular means of resolving the obviously well established problem of heat and its effect on the armoured individual, but these references do acknowledge awareness of it.
As for the sword, the covering of the hilt in leather does seem to be intended to reduce the obvious effects of hot steel in these cases.However with the leather covered hilts of the takouba swords of the Tuareg, the purpose is basically apotropaic, as it is a taboo for them to touch iron.
A very interesting perspective, and well represented by this 'mummified' sword
All best regards,
Jim