Steel material for hot forming, hot-formed member, and manufacturing method therefor

Abstract

A steel material for hot forming including, by weight: 0.04 to 0.45% of carbon (C); 1.5% or less of silicon (Si) (excluding 0%); 0.2 to 2.5% of manganese (Mn); 0.05% or less of phosphorous (P); 0.02% or less of sulfur (S); 0.01 to 0.1% of aluminum (Al); 0.01 to 5.0% of chromium (Cr); 0.02% or less of nitrogen (N), and a balance of iron (Fe) and inevitable impurities. A surface roughness factor calculated by the following [Relationship 1] is 1.8 μm or less: where Rt is defined as a vertical distance between a highest peak and a deepest valley in a random measurement section on a surface of a steel sheet, and Rdq is a root mean square of a slope of the peak in a random measurement section on the surface of the steel sheet.