Thermal tool steel

Abstract

A hot toolsteel comprises 0.10 to 0.70% C, 0.10 to 0.80% Si, 0.30 to 1.00% Mn, 0.007 to 0.020% P, 3.00 to 7.00% Cr, W and Mo in 0.20 to 12.00% in terms of (1 / 2W+Mo) alone or in combination, 0.10 to 3.00% V, 0.05 to 0.80% Ni, <=6.50% Co and <=0.150% S, and the balance substantially Fe with inevitable impurities. The cleanliness of nonmetallic inclusions is <=0.020%, and, on annealing, the area ratio of carbides and nonmetallic inclusions having particle diameters of >1.0 mu m is <=0.004%. The hot tool steel has improved heat check and erosion resistances, and has remarkably improved machinability by the above technical measure.

Description

Technical field

[0001] The invention relates to a hot tool steel used for hot forging dies, extrusion dies, die-casting dies, etc., in particular to a hot tool steel for controlling carbides and non-metallic inclusions and improving machinability, thermal cracking resistance and melting loss resistance. Background technique

[0002] In the past, a technique for improving the toughness of hot tool steel by improving the purity of non-metallic inclusions has been disclosed (Japanese Patent No. 2809622, Patent Application Publication No. 61331 / 1999). In addition, some people have proposed a technology to improve the machinability by increasing the number of inclusions and making the shape of the inclusions spherical (Electric Steel, Vol. 64, No. 3, pages 191 to 201, Figures 2 and 4, Japanese No. 61331 / 1999, 60585 / 1998 Invention Patent Application Publication). However, the above-mentioned prior art evaluates inclusions based on standards such as JISGO555 or ASTM E45-76, and therefo...