High carbon steel pipe having excellent cold workability, machinability, and quenching properties, and method for manufacturing same

Abstract

Provided are a high carbon resistance-welded steel pipe having excellent cold workability, machinability, and quenching properties; and a method for manufacturing the same. Specifically, a high carbon steel pipe having a composition containing, by mass, 0.25 to 0.60% of C, 0.01 to 2.0% of Si, 0.2 to 3.0% of Mn, 0.001 to 0.1% of Al, 0.001 to 0.05% of P, 0.02% or less of S, 0.0010 to 0.0100% of N, 0.0003 to 0.0050% of B, and 0.0001 to 0.0050% of Ca, with the remainder made up by residual Fe and unavoidable impurities, is used as a material steel pipe. Heating and soaking is performed to Ac3 transformation point or above, and diameter-reducing rolling is subsequently performed at a rolling finishing temperature of 900°C or above (Ac1 transformation point) and a cumulative diameter reduction ratio of 30 to 70% in a temperature range no greater than 900°C. This makes it possible to obtain, without performing spheroidizing annealing, a structure in which cementite particles having an average particle diameter (d) from 0.1 mum to less than 0.5 mum and in which the average distance (L) between the surfaces of adjacent cementite particles is 0.5 to 10 mum are dispersed in a ferrite phase. In particular, machinability is significantly improved.

Description

technical field [0001] The present invention relates to a steering rack bar, a steering shaft, and a drive shaft suitable for being assembled in a rack and pinion type steering device of an automobile or the like. A high carbon steel tube for automotive parts and a method for manufacturing the same, especially relating to improving cold workability, machinability and hardenability. Background technique [0002] In recent years, from the viewpoint of conservation of the global environment, improvement of automobile mileage has been strongly desired, and weight reduction of automobile bodies has been promoted. Due to the lightweight requirements of such automobile bodies, the associated parts of steering, such as steering racks and steering shafts, are assembled in the steering device that transmits the movement of the steering wheel of the automobile to the wheels; Or for associated parts of drive shafts such as drive shafts that transmit the power of the engine to the wheel...

AI Technical Summary

Problems solved by technology

However, spheroidizing annealing is a long-term heat treatment at about 700° C. for several hours, and there are problems such as a decrease in productivity and an increase in production cost.

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