1. Field of the Invention
The present invention relates to an alloy steel from which rolls of a cold rolling mill, in particular, work rolls are made. More specifically, the invention relates to a roll steel for rolls used in a cold rolling mill and this steel has extremely high wear resistance without any deterioration of resistance to thermal cracking, spalling resistance, and other mechanical characteristics.
2. Description of the Prior Art
As a prior steel from which rolls of a cold rolling mill, in particular, work rolls are made, the industry has adopted a kind of steel which contains 0.70 to 1.20 wt% of C, 0.15 to 1.00 wt% of Si, 0.15 to 1.00 wt% of Mn, 1.30 to 6.00 wt% of Cr, 0.20 to 0.50 wt% of Mo, and 0.40 wt% or less of V and has a Shore hardness (Hs) of 80 to 100. Recently, however, materials to be rolled become harder and the market trend is toward much thinner products This situation makes the rolling requirements severer, requiring the roll manufacturers to supply rolls with higher wear resistance.
To meet these requirements, the manufacturers tend to use high alloy materials to allow rolls of a cold rolling mill to have sufficiently high wear resistance in preference to other characteristics.
JIS SKD 11 steel, JIS SKH 57 steel, or improved roll steel derived therefrom are used to make rolls for Sendzimir or Cluster mills. If the roll diameter exceeds 300 mm, the manufacturing method thereof is under various restrictions. In addition, during rolling operation, the roll surface suffers many problems with its macroscopic or microscopic structure, including segregation associated with high alloying and coarse carbides dropped out of the surface. These problems are possible factors which may impair the surface of materials to be rolled.