Metal sheet to be heated by radiant heat transfer and method of manufacturing the same, and metal processed product having portion with different strength and method of manufacturing the same
On part of a surface of a metal sheet that is to be heated by radiant heat transfer with a near-infrared ray, a region where reflectance for a radiant ray is made lower than that of the original surface of the metal sheet is formed. As reflectance reducing treatment, painting or thermal spraying in a blackish color, plating in a blackish color, treatment for increasing roughness of the surface of the metal sheet, blasting, etching, blackening, surface layer quality changing treatment of the metal sheet, or the like can be adopted. The metal sheet is turned into a heated metal sheet partially having a different temperature by being heated by radiant heat transfer, and thereafter, the heated metal sheet is subjected to thermal processing accompanied by cooling, for example, by hot stamping.
1. A metal sheet comprising a reflectance-reduced region where reflectance for a radiant ray is reduced formed only on a part of a surface of the metal sheet that is to be heated by radiant heat transfer, and wherein the reflectance-reduced region comprises Al 2 O 3 —TiO 2 -based thermal spray material.
2. The metal sheet according to claim 1 , wherein the reflectance of the reflectance-reduced region is 40% or less of radiation directed at the region.
3. The metal sheet according to claim 1 , wherein the metal sheet is a plated steel sheet.
4. A metal processed product formed by processing the metal sheet according to claim 1 , the metal processed product having a portion with different strength, wherein a portion where reflectance for a radiant ray is reduced is formed only on a part of a surface of the metal processed product, and a difference in Vickers hardness between the portion of the metal processed product where the reflectance for the radiant ray is reduced and the other portion of the metal processed product is HV180 or more, and wherein bending portions are co-existent with the portion where reflectance for the radiant ray is reduced.
5. The metal processed product having the portion with different strength according to claim 4 , wherein the difference in Vickers hardness between the portion where the reflectance for the radiant ray is reduced and the other portion is HV200 or more.