Machine Structural Steel Material Having Low Heat-Treatment Deformation

Abstract

There is provided a steel material with small heat treatment deformation, comprising a machine structural steel used for components for power transmission, such as gears and shafts used in automobiles, industrial machines, and the like. In the steel material, the Ms point of the steel material comprising a machine structural steel, comprising in mass %: C: 0.20 to 0.30%; Si: 0.10 to 1.50%; Mn: 0.10 to 1.20%; P: 0.030% or less; S: 0.030% or less; Cr: 1.30 to 2.50%; Cu: 0.30% or less; Al: 0.008 to 0.300%; O: 0.0030% or less; and N: 0.0020 to 0.0300%; and the balance Fe and unavoidable impurities, is 460° C. or less; a ratio (J9 / J1.5) of hardness J9 at a distance of 9 mm from the quenched end of the steel material to hardness J1.5 at a distance of 1.5 mm from the quenched end of the steel material, as measured by Jominy end quenching method, is in a range of from 0.70 to 0.85; and a ratio (J11 / J1.5) of hardness J11 at a distance of 11 mm from the quenched end of the steel material to hardness J1.5 is in a range of from 0.67 to 0.78.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority to Japanese Patent Application No. 2012-193763 filed on Sep. 4, 2012, the entire content of which is incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to machine structural steels, for example, used for power transmission components such as gears and shafts used in automobiles, industrial machines, and the like, and particularly relates to a machine structural steel with small heat treatment deformation.BACKGROUND ART[0003]It is known that deformation of a steel material occurs due to heat treatment such as quenching (hereinafter referred to as “heat treatment deformation”). Such heat treatment deformation has such an adverse effect that the number of production steps is increased in order to correct the deformation, the percentage of defective components is increased when the deformation is too large to correct, or noise or vibration is caused by the deformation in the cas...

AI Technical Summary

Benefits of technology

The present invention provides a machine structural steel material with small heat treatment deformation. This is achieved by controlling the chemical constituents of the steel, the martensitic transformation start temperature, and the hardness of the steel material. The steel material has a martensitic transformation start temperature of 460°C or less, and a value of (J9 / J1.5) calculated by equation (1) using hardness J1.5 at a distance of 1.5 mm and hardness J9 at a distance of 9 mm from a quenched end of the steel material, as measured by Jominy end quenching method, is in a range of from 0.70 to 0.85, and a value of (J11 / J1.5) calculated by equation (2) using hardness J1.5 at a distance of 1.5 mm and hardness J11 at a distance of 11 mm, as measured by Jominy end quenching method, is in a range of from 0.67 to 0.78. The steel material has a hardness of 40 to 45 HRC and a hardness of 4 to 7 HRC. The invention provides a solution for reducing heat treatment deformation in machine structural components, which is important for their strength and durability.

Problems solved by technology

However, the conventional methods proposed as described above have not always been able to be general-purpose means.

This is because, for example, the technology of Patent Literature 1 may involve introduction of the soft phase with low strength into a component; the technology of Patent Literature 2 requires a modification of a heat treating furnace itself; and the technology of Patent Literature 3 requires treatment to an individual component to be heat-treated, so that it has been difficult to consider that the conventional methods are general-purpose means.

In contrast, the inventors have extensively researched a steel of which the heat treatment deformation can be reduced to a low level even when cooling of a component is non-uniform under a common technique such as oil quenching, while securing the sufficient strength of the steel material without relying on generation of a ferrite morphology which is soft and may result in reduced component strength.

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