Tool steel for hot working, tool for hot working and plug for producing seamless pipe

Abstract

The present invention is a tool steel for hot working, and the oxide scale formed on the surface thereof has good adhesion and lubricity and high strength. The tool steel contains C: 0.05-0.5%, Si: 0.1-1%, Mn: 1.6-3.5%, Ni: 0.05-0.5%, Mo: 2-5%, W: 2-5%, Cu: 0.05- 0.5%, and the remainder is substantially composed of Fe. One or more of Cr, Co, REM, Ti, Nb, V, Zr, and B may also be contained. The surface of a tool made of this steel is covered with an oxide scale with a thickness of 50 to 1500 μm. A typical example of the tool is a piercing plug for seamless pipe production.

Description

technical field [0001] The invention relates to a tool steel for hot working and a tool for hot working. The tool steel of the present invention is suitable as a raw material for a plug of a piercing calender (for example, a Mannesmann piercer) used in the production of a seamless pipe made of a high-Cr alloy steel and a Ni-based alloy. The so-called high-Cr alloy steel is steel represented by stainless steel containing 13% or more of Cr. Background technique [0002] At present, the calenders used to manufacture seamless steel pipes, among them, the plugs for the piercing and calendering machines represented by the Mannesmann piercing machine are made of steel with a basic composition of 3%Cr-1%Ni-the rest of Fe. Plugs are used after heat treatment to form scale on the surface. The plug is used for piercing when ordinary steel is used to make seamless steel pipes. [0003] However, when piercing and rolling seamless pipes made of high-Cr alloy steel represented by stainl...

AI Technical Summary

Problems solved by technology

[0016] However, the plug in (a) has insufficient high-temperature strength of the base metal and adhesion of scale, and cannot ensure a sufficient life when piercing a long billet, that is, when piercing and rolling with a long piercing length.

[0017] For plugs (a) to (c), the scale on the front end of the plug with the highest surface pressure and increased temperature melts during the piercing process, losing the heat insulation effect and wear resistance, and the front end of the plug is prone to melting loss and deformation.

[0018] The plugs (d) to (e) have the disadvantage that the front end of the plug is prone to melting loss and deformation due to the high content of Cr, which not only deteriorates the welding resistance, but also has insufficient high-temperature strength.