JPH04362154A - Machine elemental parts - Google Patents

Abstract

PURPOSE:To obtain machine element parts improved in the properties of impact value from stock with a thickness higher than that of the conventional article by subjecting the stock with a specified thickness or below of a boron steel contg. specified amounts of B and Ti to austempering treatment. CONSTITUTION:The stock with <=11mm sheet thickness of a boron steel cocntg. 0.40 to 0.65% C, 0.0005 to 0.0030% B and 0.020 to 0.050% Ti is subjected to austempering treatment. By the use of the baron steel having the above components, the region B at the time of the austempering treatment deviates to the long time side, so that the austempering treatment for the stock of a sheet with a thickness higher than that of the conventional one can be executed in the region A.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mechanical components, such as fastener products (industrial fastening products), which have been subjected to austempering treatment (a method of heat treatment of steel utilizing the austenitic temperature range).

0002

2. Description of the Related Art Mechanical components such as fastener products that require spring properties are usually quenched and tempered or austempered to provide spring properties, hardness, and toughness. FIG. 5 shows the time-temperature-structure relationship due to conventional heat treatment. In FIG. 5, region A is an austenite region, region B is a pearlite or bainite region, and C is a martensite region. The normal quenching and tempering curve is curve c
The normal thin plate material (thickness of 2.5 mm or less) austempering process curve is shown as curve b. As can be seen from the comparison between curves b and c, in the austempering process, the same springiness and toughness as in normal quenching and tempering can be obtained just by quenching in a salt bath, and there is no need for tempering. Therefore, the heat treatment time was shorter than that of quenching and tempering, and it was suitable for heat treatment of large quantities of fastener products and the like.

0003

[Problems to be Solved by the Invention] However, in the austempering process, the inside of the product must be rapidly cooled to prevent it from getting caught in the nose of area B. The problem was that it could only be applied to That is, a thicker workpiece cannot be austempered to the core, which limits the scope of its application. In addition, research on conventional austempering methods has focused exclusively on making the gradient of the cooling curve b steeper, that is, increasing the cooling rate, in order to avoid snagging in the area B, and this is no longer the case. Improvements since then have reached their limits.

[0004] The present invention prevents the cooling curve from getting caught in the nose by shifting the nose of the pearlite or carbide region, and thereby the mechanical element which is austempered and given properties such as hardness, regardless of its thickness. The purpose is to provide parts.

[0005]

[Means for Solving the Problems] According to the present invention, the above object is achieved by a mechanical component having the following requirements. The chemical composition of mechanical component parts material is 0.40.
- be made of boron steel containing 0.65% carbon, 0.0005-0.0030% boron, and 0.020-0.050% titanium; the mechanical component material shall have a plate thickness of 11 mm or less; and the above The machine element part must be manufactured by austempering the machine element part material.

[0006]

[Function] By containing 0.0005-0.030% boron, the pearlite nose shifts to the long-term side, making it possible to perform austempering treatment without rapid cooling as in the conventional method. In terms of plate thickness, austempering is possible if the plate thickness is 11 mm or less. 0.020-0.050%
Titanium is added to boron to effectively produce the above effects. If you want to give hardness to a plate with a thickness of 2.5 mm or more and 11 mm or less, conventionally austempering is 2.
．． Since it cannot be applied to products with a thickness of 5 mm or more, quenching and tempering, which has a higher cooling ability than austempering, is used. However, quenching and tempering does not produce as much impact value as austempered products. Furthermore, quenching and tempering requires an extra tempering process compared to austempering, and is not suitable for mass production. According to the present invention, these problems are solved.

[0007]

[Examples] Examples of the present invention will be described below. First, we will examine the material conditions to expand the conditions under which austempering can be performed by shifting the pearlite nose toward the long-term side. Currently, fastener products are made from JIS, SK5, and SAE1075 medium carbon steel. In order to achieve almost the same hardness and heat treatability, we selected a material with boron added to JIS S48C.

[0008] Figure 2 shows the relationship between plate thickness and cross-sectional average hardness when this JIS S48CB boron steel commercially available product with a diameter of 38 mm was heated to 830°C and then rapidly cooled to 330°C and austempered. Shown below. As shown in Figure 2,
The hardness decreases as the plate thickness increases, but at a plate thickness of 10 mm.
The effective hardness from front to back satisfies the Vickers hardness of Hv450 or higher. The reason for this is thought to be that boron steel shifts the nose of pearlite and bainite regions to the long-term side due to the action of boron, and can be hardened even at a low cooling rate.

[0009] Boron steel has 0 boron B in JISS48C.
．． 0020%, but the amount of boron added is 0.
．． A content in the range of 0.0005 to 0.0030% by weight is effective for long-term transition of pearlite nose. Here, 0
．． 0.0005% is the limit below which the effect of boron addition is weakened, and 0.0030% is the limit when the carbon content is 0.40 to 0.
．． In the case of high carbon steel with a content of 0.0030% or more, this is the limit at which the boron effect does not increase even if boron is added to 0.0030% or more, and adding more than this will result in an unnecessary increase in cost.

[0010] Furthermore, in order to stably produce the effect of adding boron, it is desirable to add titanium Ti in an amount of 0.020 to 0.050%. As a result of the above, the chemical composition of the material for the mechanical component parts according to the present invention is 0.40-0.
．． 65% carbon, 0.0005-0.0030% boron,
It was decided to use boron steel with 0.020-0.050% titanium.

Next, consideration will be given to expanding the plate thickness conditions that allow austempering. JIS for conventional fastener product materials,
SK5 and boron steel S48 included in the selected materials of the present invention
Figure 3 shows the relationship between plate thickness and cross-sectional hardness when a CB round bar with a diameter of 38 mm is austempered at 330°C as a test material.
Shown below. For example, the effective hardness is Vickers hardness Hv5
00, the limit plate thickness is 2 mm for SK5 and 7 mm for boron steel S48CB, and it was found that the present invention can increase the plate thickness by about three times or more compared to the conventional one. In other words, as the thickness of the plate increases, the cooling rate of the core cannot be fast enough and the hardness cannot be achieved, but compared to the conventional material SK
5 is austempered to achieve a hardness of about Hv450, the maximum thickness is 2.5 mm, but if boron steel like the one of the present invention is used, the pearlite nose will shift to the long-term side. Even if the cooling rate of the core portion becomes slower due to the increase in plate thickness, austempering treatment is possible up to a plate thickness of about 11 mm. Therefore, the material plate thickness of the machine element component according to the present invention is set to a maximum of 11 mm.

FIG. 1 shows an austempering curve according to the present invention. In Fig. 1, region A is an austenite region, region B is a pearlite and carbide region of boron steel, and region C is a carbide region.
is the martensitic region. Also, the dotted line is the conventional SK
The pearlite and bainite regions of the 5 materials are shown, and the pearlite nose of boron steel is shifted to the long-term side.

Further, in FIG. 1, curve a is the austempering curve for the boron steel of the present invention with a plate thickness of 10 mm, curve b is the austempering curve for the normal fastener material SK5 and the plate thickness is 2 mm. c shows a quenching and tempering curve for a conventional fastener material SK5 with a plate thickness of 10 mm. With conventional materials, austempering cannot be applied to plates with a thickness of 2.5 mm or more, so hardness was achieved through quenching and tempering with high cooling capacity, but in the present invention, by applying boron steel, austempering can be achieved by shifting the pearlite nose. You can see that processing is possible.

[0014] In the case of quenching and tempering, the tempering toughness is not achieved,
Further improvements have been desired in terms of heat treatment for fastener products that are used under harsh conditions. In order to investigate the impact property improvement effect of the present invention, we used the conventional method J
IS, SK5 quenched and tempered products and boron steel J of the present invention
A comparison test was conducted on the Charpy impact values of IS and S48CB austempered products. The results are shown in Figure 4. In Figure 4,
The horizontal axis represents Rockwell hardness C scale HRC, and the vertical axis represents impact value Joule J/cm2. Figure 4
As is clear from the above, the product of the present invention is approximately 3 times lower than the conventional product.
It shows twice the superior impact value.

[0015]

Effect of the invention: According to the present invention, 0.0005-0.0
Machine element parts were created by austempering materials up to 11mm thick using boron steel containing 0.30% boron, allowing for mass production compared to quenching and tempering, which allows austempering even for thicknesses of 2.5mm or more. suitable for
Effects such as improved impact value characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram of an austempering process for manufacturing machine element parts according to the present invention.

FIG. 2 is a diagram showing the relationship between hardness and plate thickness in austempering of boron steel.

FIG. 3 is a hardness vs. plate thickness relationship diagram in austempering for conventional materials JIS, SK5 and JIS, S48CB included in the present invention materials.

FIG. 4 is a Charpy impact value comparison diagram between conventional JIS and SK5 quenched and tempered products and the present invention product.

FIG. 5 is a time-temperature-structure relationship diagram in conventional heat treatment of fastener materials.

[Explanation of symbols]

A Austenite region B Pearlite, bainite area C Martensite region a Austempering curve

Claims (1)

[Claims] Claim 1: Chemical components are 0.40-0.65% carbon, 0.0005-0.0030% boron, 0.020-
Made of 0.050% titanium boron steel, 11m thick.
A machine element part characterized in that it is produced by austempering a material with a size of less than m.