Daido Tokushuko Kabushiki Kaisha

Nissan Motor Company Limited

Kenji Isokawa

Sadayuki Nakamura

Kimihiro Shibata

Masahide Ike

Hideaki Inaba

Toshimitsu Fujii

Katsunori Takada

Hisashi Ohta

Toshio Yanagiya

A steel shaft material having desirable cuttability and induction hardenability even in the form of milled stock without being subjected to any heat treatment, such as annealing, and a method for manufacturing the same. A steel ingot is prepared containing 0.38 to 0.45 wt. % of carbon, 0.15 wt % or less of silicon, 0.3 to 1.0 wt % of manganese, 0.0005 to 0.0030 wt % of boron, 0.01 to 0.05 wt % of titanium, 0.01 to 0.06 wt % of aluminum, 0.010 wt % or less of nitrogen, optionally at least one of chromium in an amount of 0.3 wt % or less and molybdenum in an amount of 0.10 wt % or less, and optionally at least one of 0.005 to 0.30 wt % of sulfur, 0.0002 to 0.005 wt % of calcium, 0.005 to 0.30 wt % of lead and 0.005 to 0.10 wt % of tellurium, and the remainder being iron and unavoidable impurities. After the ingot is heated to 1,100.degree. C. or less, the ingot is milled at a finishing temperature of 950.degree. C. or below and an area reduction rate of 70% or higher, and then cooled in the atmosphere. The steel material of the present invention has a microstructure formed of ferrite and lamellar pearlite (the amount which remains bainite being %5 or less) and having a ferrite grain size number of 6 or higher, as determined by JISG0552, a HRB hardness of 80 to 90, as determined by JISZ2245, and a DM-T decarbonized depth of 0.20 mm or less, as determined by JISG0558.

Steel shaft material which is capable of being directly cut and

A case hardening steel which consists essentially of 0.03-0.2 wt % of C, 1.0-3.0 wt % of Si, 0.2-2.0 wt % of Mn, 0.05-0.5 wt % of V and the balance of Fe. The primary advantage of this steel is fineness of grain size after carburizing at relatively high temperatures. Even when carburizeed at or above 950.degree. C., the grain size number is not smaller than 6 in both the hardened case and the core. Optionally the steel may contain up to 2.0 wt % of Ni, up to 2.0 wt % of Cr and/or up to 0.5 wt % of Mo for the reinforcing purpose, and/or up to 0.1 wt % of Al, up to 0.3 wt % of Ti, up to 0.1 wt % of Zr, up to 0.03 wt % of N and/or up to 0.5 wt % of Nb+Ta for the purpose of depressing the grain growth.

Manufacturing process for high temperature carburized case harden steel

An improved steel for cold forging for machine structural use, particularly, case hardening steel, contents of Al, N and Nb are selected to satisfy a specific corelation therebetween, and the amounts of O and S are controlled. The steel is resistant to cracking at the cold forging, and growth of austenite crystals to coarse grains during carburizing or carbonitriding is prevented. Disclosed are preferable structure of the steel and rolling conditions to obtain the structure, and conditions for continuous casting of the steel.

Steel for cold forging and method of making

Growing community of inventors

Aichi, Japan

Kenji Isokawa