Libun Chamur
28. A utensil used in fire, e.g., a skewer on which chametz was roasted, must be kashered in fire to the point that sparks shoot out of it (שו"ע סי' תנא ס"ד ). This standard was relevant to the utensils used in Chazal's times; nowadays, even when subject to intense heat, sparks do not shoot out due to different utensil material (יד אהרן להגר"א פפויפר ).
29. Several poskim hold that 400 °C is enough for libun chamur (יד אהרן שם ).
Libun Kal
30. There is another type of libun called "libun kal." The Rama (שם ) characterizes this as heating the utensil to the point that straw placed on the outside of it, would burn. The poskim say this is 250 °C. The consensus of the poskim is that libun kal does not work where libun chamur is needed, because chametz is primarily treated as absorbed issur. Therefore, libun chamur is required (מ"ב סקכ"ח ). Where the libun is just a chumra, one can rely on libun kal (רמ"א ס"ד ).
31. There are several instances given where one can rely on libun kal. For example: 1. Something which needs hag'alah but may get ruined through the hag'alah, may undergo libun kal. 2. Where one needs to do libun on grooves and crevices in a utensil (רמ"א שם ). 3. Bedieved if, where libun chamur should have been done, libun kal was done, and to fix it would cause significant losses or prevent Yom Tov joy, and it did not absorb chametz in the last 24 hours (פמ"ג, מ"ב סקל"ב ), one can rely on the opinion that chametz is treated as absorbed heter.
