JPS59126757A - Stainless cast steel of precipitation hardening type for casting strain inducing body of load cell - Google Patents

Abstract

PURPOSE:To provide an alloy which yields a strain inducing body of a load cell having excellent accuracy and mechanical property when cast by incorporating C, Si, Mn, Ni, Cr, Mo, Cu, V, and Nb respectively at prescribed proportions and composing of the balance Fe and unavoidable impurities. CONSTITUTION:A stainless cast steel of a precipitation hardening type for casting a strain inducing body of a load cell consists of 0.05-0.3% C, 1.0-3.0% Si, 0.2-1.5% Mn, 4.5-8.5% Ni, 11.0-14.0% Cr, 1.0-3.0% Mo, 1.0-3.0% Cu, 0.2- 0.5% Nb, 0.1-0.5% V, and the balance Fe and unavoidable impurities. A casting having a required shape is made by an ordinary casting method to manufacture the strain inducing body of the load cell consisting of such cast steel. The casting is subjected to a solution heat-treatment consisting of homogenizing at 1,000-1,200 deg.C, furnace cooling, holding at 800-1,000 deg.C then oil cooling. The treated casting is subjected to a heat treatment consisting of holding at 400- 600 deg.C, and air cooling after an aging treatment, whereby the above-described intended stainless cast steel is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a precipitation hardening stainless cast steel used for casting a load cell strain body.

A load cell strain body used as a load sensor in truck scales and other weight measuring devices converts the applied load into an electrical signal proportional to it, and its material properties include mechanical properties that can withstand the load. hand,
It must have excellent linearity, hysteresis, and microcreep properties necessary for a sensor.

Conventionally, the load cell strain body is SNCM439 (0,4
C-0,25Si-0,75Mn-1,8Ni-0,
8Cr-0,23Mo-Fe) is used as a raw material, and is manufactured by cutting it into a predetermined shape by machining, or by assembling a few pressed parts into a desired shape by tightening bolts. However, the machining method requires extremely high processing costs, while the assembly method requires a complicated manufacturing process and the shape of the strain-generating body becomes large.
Further, there are drawbacks such as the weight increase, and the accuracy of bolt tightening during use is reduced due to loosening of torque. In addition, with either method, there is a limit to the shape that can be manufactured, and it is either impossible to obtain a load cell strain body with an optimal shape, or extremely complicated machining steps are required. .

If the strain-generating body could be manufactured by casting, the above problems would be solved all at once, and it would also be possible to expand the variety of designs.

However, the characteristics of strain-generating bodies made of alloys such as SNCM439, which have been used in the past, vary significantly depending on whether they are forged or cast. Generally, the properties of the strain-generating body of cast products are inferior to those of forged products. By the way, in a strain body made of a forged product of SNCM439, 1
While an accuracy of 78,000 was obtained, the accuracy of the cast product was only about 171,000, which was poor, and in the end, it was not possible to put a high-accuracy strain element made by casting into practical use.

The present invention addresses the above-mentioned circumstances and provides an alloy that allows a load cell strain body with excellent precision and mechanical properties to be manufactured by casting.

The alloy of the present invention is a precipitation hardening stainless steel cast steel, and its chemical composition is C0.05~0.3%, Si1.0~0.
3.0%, Mn 0.2-1.5%, Ni 4.5-8.
5%, Cr 11.0-14.0%, Mo 1.0-8
．． 0%, Cu 1.0-10%, NbO, 2-0.5%
, Vo, 1 to 0.5%, the remainder being Fe and unavoidably mixed impurities.

A cast product made of the alloy of the present invention is given mechanical characteristics necessary as a load cell strain body by the heat treatment described below, and its accuracy is superior to that made of a conventional forged product of SNCM439. It also has good mechanical properties and high strength.

The reasons for limiting the components of the alloy of the present invention are as follows.

In addition, in the specification, all "%" indicating chemical component compositions are weight %.

C: 0.05-03% C increases the hardness of the material and also improves linearity, hysteresis, and microcreep properties in the lower part of the elastic limit. To achieve this effect, at least 0
．． 05% is required. These effects increase as the content increases. Preferably, it is 0.1% or more. However, if the content is too large, impact resistance and workability will deteriorate, so the upper limit is set at 0.3%.

si: t, o~3.0% Si is an element effective in improving the linearity, hysteresis, and microcreep properties of materials within the elastic limit, but if it is less than 1.0%, the effect is insufficient. The effect increases as the content increases, but if the content increases too much, the impact resistance and toughness will drop significantly. Therefore, 1.0 to 3.0
%, preferably 1.5 to 3.0%.

Mn: 0.2-1.5% Mn cleans the molten alloy by deoxidizing and desulfurizing effects. 0
．． If it is less than 2%, the effect is insufficient; on the other hand, 1.5
If it exceeds %, impact resistance deteriorates.

Ni: 4.5-8.5% Ni is required to be 4.5% or more in order to ensure a high elastic limit and high tensile strength. However, since the inclusion of a large amount not only increases cost but also impairs castability, the upper limit is set at 8.5%.

Cr: 11.0 to 14.0% Cr is effective in improving the elastic limit and tensile strength. It should be at least 11.0% to obtain a sufficient effect. However, if the amount is too large, a martensitic structure cannot be obtained, which results in a decrease in strength, and also causes deterioration of linearity, hysteresis, and microcreep characteristics in the lower part of the elastic limit. Therefore, the upper limit is set at 14.0%.

Mo: 1.0-8.0% Mo increases the elastic limit and tensile strength. For this purpose, at least 1.0% is required, but if it exceeds 3.0%, the impact resistance will be reduced, and the elongation and drawing area will be reduced.

Cu: 1.0-8.0% Cu increases the elastic limit and tensile strength by precipitation hardening of the Cu-rich layer. For this purpose, a content of 1.0% or more is required, but if it exceeds 30%, impact resistance, elongation, and drawing properties deteriorate.

Nb: 0.2-05% Nb contributes to improving the mechanical properties, especially the elastic limit.

If the content is less than 0.02%, the effect will be insufficient; on the other hand, 0.5
If it exceeds %, impact resistance is poor.

v20.1-0.5% (2) strengthens the pinning of dislocations by precipitation of fine precipitates such as carbides, increasing the elastic limit and tensile strength.

0.1% or more is required to obtain this effect. Tazoshi,
Containing a large amount will reduce impact resistance, elongation, and aperture, so 0
．． The upper limit is 5%.

The alloy of the present invention is accompanied by impurities that are inevitably mixed in due to the melting technology, but in order to improve the material quality, Po, 0.3% or less, 50%
．． It is preferable to regulate it to 0.3% or less.

To manufacture a load cell strain body made of the alloy of the present invention,
A cast product having the desired shape is obtained by a normal casting method, homogenized at a temperature of 1000 to 1200°C, cooled in a furnace at a cooling rate of about 0.6 to 1.2°C/min), and then heated to 800°C.
After being maintained at ~1000°C, oil cooling (approx. 15~45°C)
/second) and then further heated at 400 to 600°C.
After aging treatment by keeping at
/second).

The cast product of the alloy of the present invention may be subjected to appropriate working steps in the heat treatment process described above. SNC, a conventional material
For M439 castings, when processed at the heat treatment stage,
Large distortions occur, making it impossible to achieve the required dimensional accuracy, and even if attempts are made to process the material after all heat treatments have been completed to avoid distortion, the material is hard and extremely difficult to process.

The alloy of the present invention does not have such disadvantages, has good workability, and exhibits very little distortion even after subsequent heat treatment. Therefore, by performing appropriate machining, a strain-generating body having a desired shape and high dimensional accuracy can be obtained.

Next, examples of the present invention will be described.

Example A box-type load cell strain body (L: 140 mm, W:
6'7mm, T: 50mm, hole diameter (DI): 2
0 sea bream, hole diameter (D2): 20 mm).

Flavoring (1) to (4) are examples of the present invention, (10) and (11).
) is a comparative example (comparative example (11) is S N CM4
39 equivalent material).

The above heat treatment conditions are as follows for flavoring (1) to (4):
1100°C x 2 hours, Furnace cooling - 900°C x 2 hours, Oil cooling - 500°C x 2 hours, Air cooling", fragrance (10) is r
1100°C x 2 hours, furnace cooling → 1040°C x 2 hours, oil cooling - 480°C x 2 hours, air cooling.

In addition, the fragrance (11) is quenched and tempered at a quenching temperature of 870°C1 in accordance with JIS regulations for SNCM439 material.
A tempering temperature of 580°C was applied.

Table 1 shows the accuracy of each test strain body as a weight sensor. The accuracy of the strain elements (1) to (4) made of the alloy of the present invention is 1/100001 - e4'''g.This accuracy is higher than that of the conventional pressed strain body of SNCM439 (about
8000). On the other hand, SNCM4
The accuracy of the incense stick (11), which is a cast product of 39, is only 1/1
It is only 1,000, and the incense (10) is also 178,000.
This is not as good as the example of the present invention.

Table 2 shows the mechanical properties of each sample material. The alloy of the present invention is
It can be seen that it has particularly excellent tensile strength and yield strength, and also has the required impact properties.

As described above, the alloy of the present invention can be used to obtain a load cell strain body with excellent performance by casting.

Its accuracy exceeds that of the conventional strain body made of SNCM439 pressed product. It also has excellent mechanical properties such as strength and elastic limit. The casting method has a greater degree of freedom in design than conventional manufacturing methods that use pressed products as raw materials, and the process is simplified by reducing the number of machining operations, making it possible to reduce manufacturing costs. In addition, machining during the heat treatment process is easy and less distortion occurs, so a strain-generating body having an optimal shape according to the desired shape and good dimensional accuracy can be obtained. Furthermore, since it is formed as a single piece by casting, it can be made smaller and lighter than the conventional assembly method using bolts.

The alloy of the present invention not only has excellent mechanical properties such as strength as described above, but also has high corrosion resistance as cast stainless steel, so it is suitable for structural members and mechanical parts that require these properties. .

[Brief explanation of the drawing]

FIG. 1 [I] is a plan view showing the shape of the box-type load cell strain body related to the embodiment, and [11F is a side view]. Agent Patent Attorney Shinhachibe Miyazaki

Claims (1)

[Claims] (L) C0.05-0.3%, Si 1.0-3.
0%, Mn0, 2-1.5%, Ni4.5-8.5%,
Cr11. O ~ 14.0%, Mo 1.0 ~ 3.0%,
Cu 1. O' ~ 3.0%, V 0.1 ~ 0.5%,
A precipitation hardening stainless steel cast steel for casting a load cell strain body, consisting of 0.2 to 0.5% Nb, the remainder Fe and unavoidable impurities.