JPS59126758A - Martensitic stainless cast steel for casting strain inducing body of load cell - Google Patents

Abstract

PURPOSE:To provide a titled cast steel which yields a strain inducing body having good dimensional accuracy and a desired shape when adequately machined by incorporating C, Si, Mn, Ni, Cr, Mo, Cu and Nb respectively at prescribed proportions, and the balance composed of the Fe and unavoidable impurities. CONSTITUTION:A titled martensitic stainless cast steel consists of 0.02-0.1% C, 0.4-2.0% Si, 0.2-1.5% Mn, 4.5-8.5% Ni, 8.5-10.5% Cr, 1.0-3.0% Mo, 1.0- 3.0% Cu, 0.2-0.5% Nb, and the balance Fe and unavoidable impurities. The production of a strain inducing body of a load cell by using such cast steel is accomplished by making a casting having a desired shape by an ordinary casting method, and homogenizing the same by heating and holding at 1,050-1,150 deg.C then subjecting the casting to furnace cooling. The furnace cooled casting is subjected to a solution heat-treatment consisting of holding at 900-1,100 deg.C and oil cooling and to a heat treatment consisting of holding at 400-600 deg.C and air cooling after an aging treatment. As a result, the strain inducing body of the load cell provided with various good characteristics such as strength, impact resistance, linearity within the elastic limit, hysteresis or the like is obtd.

Description

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

A load cell strain body is a weight sensor that converts the applied load into an electrical signal proportional to it.
39 (0,4C-0,25Si-0,75Mn-1
,8Ni-0,8Cr-0,23Mo-Fe)
It is manufactured by using forged press material as a material and cutting it into a predetermined shape by machining it, or by assembling several press parts into a predetermined shape by tightening bolts. However, the disadvantage of the machining method is that the processing cost is extremely high, while with the assembly method, the manufacturing process is complicated, the shape of the strain-generating body becomes large, and the weight inevitably increases. Tightening medium bolts has drawbacks such as a decrease in accuracy due to torque loosening. In addition, in either method, there is a limit to the shape that can be manufactured, and it is 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 conventional load cell strain bodies made of alloys such as SNCM439 have different characteristics as a strain body, especially linearity, hysteresis, and micro- Creep properties are significantly different, and the properties of cast products are inferior to the amount of forging. For example, a strain body made of SNCM439 with a forging amount can achieve an accuracy of 178,000, whereas a cast product made from the same alloy has an accuracy of only 1/1.
In the end, it was impossible to manufacture a highly accurate strain body by casting.

In order to deal with the above-mentioned situation, the present inventors have provided an alloy in which a strain-generating body having an accuracy equivalent to the amount of forging can be manufactured by casting in a previous application (Japanese Patent Application No. 57-1402;
? No. 3).

In order to further improve the properties of the above-mentioned alloy, the present invention has conducted various studies on the chemical composition. By reducing the amount of Cr, residual austenite remaining in the material structure has been eliminated, and the linearity in the lower part of the elastic limit has been improved. It has improved hysteresis and microcreep characteristics.

The alloy of the present invention is a precipitation hardening stainless steel cast steel having a martensitic structure, containing Co, 02 to 0.1%, and Si.
O, 4-2.0%, Mn O12-1.5%, Ni 4
．． 5-8.5%, Cr 8.5-10.5%, Mo1.
0~3.0%, Cu 1.0~3.0%, Nb0.2~
It has a chemical composition consisting of 0.5%, the balance Fe and unavoidably mixed impurities.

After casting, the alloy of the present invention can be heat-treated as described below to provide the necessary properties as a strain-generating body for a load cell.
Accuracy reaching 1"0,000 can be guaranteed. The composition of the alloy of the present invention was determined taking into consideration mechanical properties, corrosion resistance, etc., so that it can correspond to various usage conditions of load cell strain bodies. It is something.

The reasons for limiting the components of the alloy of the present invention will be explained below.

Note that "%" is % by weight.

C: 0.02-0.1% C increases the hardness of the material, but if it is less than 0.02%, its effect is insufficient. Hardness increases as the amount of C increases, but if it is too large, impact resistance, workability, etc. will deteriorate, so
．． 1% or less.

Si: 0.4-2.0% Si is added as a deoxidizing agent during alloy melting.

If the content is less than 0.4%, the deoxidizing effect will be insufficient, while if it exceeds 2.0%, impact resistance and toughness will be impaired.

Mn: 0.2-1.5% Mn cleans the molten alloy and improves the material quality.

If the content is less than 0.2%, the effect will not be exhibited,
On the other hand, if it exceeds 1.5%, impact resistance decreases.

Ni: 4.5-8.5% High elastic limit 1. A content of at least 4.5% is required to ensure high tensile strength. However, containing a large amount not only increases cost but also deteriorates castability.
．． The upper limit is 5%.

Cr: 8.5-10.5% In order to obtain a high elastic limit and high tensile strength, 8.5% or more is required, but if it is too large, a martensitic structure cannot be obtained and the lower part of the elastic limit This causes deterioration of linearity, hysteresis, and microcreep characteristics in the 1.
The upper limit is 0.5%.

Mo: 1.0 to 3.0% Mo is effective in improving the elastic limit and tensile strength. However, if the concentration is less than 1.0%, the effect will be insufficient;
If it exceeds %, impact resistance, elongation, and drawing capacity decrease.

Cu: 1.0 to 8.0% Cu (Cu') improves the elastic limit and tensile strength through precipitation hardening due to the thick layer. In order to obtain this effect, a content of 1.0% or more is required, but if the content exceeds 3.0%, impact resistance decreases, elongation, and aperture decrease.

Nb: 0.2 to 0.5% Nb contributes to improving mechanical properties, especially the elastic limit, but if it is less than 0.2%, the effect is insufficient, while if it exceeds 0.5%, impact resistance decreases. descend.

The alloy of the present invention is accompanied by impurities that are unavoidable due to ordinary melting technology, but in order to improve mechanical properties, Po, 0
It is desirable to regulate it to 3% or less and 80.03% or less.

To manufacture a load cell strain body using the alloy of the present invention,
A cast product having the desired shape is obtained by a normal casting method, homogenized by heating and holding at a temperature of 1050 to 1150°C, and then furnace cooled at a cooling rate of approximately 0.6 to 1.2
°C/min), then solution treatment by holding at 900-1100°C and oil cooling (approx. 15-45°C/sec), then aging treatment by holding at 400-600°C, followed by air cooling. (approximately 3-7°C/sec). The above heat treatment imparts good properties such as strength, impact resistance, linearity within elastic limits, and hysteresis.

Furthermore, the cast product made of the alloy of the present invention can be subjected to additional working steps as necessary during the heat treatment process.

In the case of a cast product of SNCM439, which is a conventional material, if processing is applied during the heat treatment stage, large distortions occur, making it impossible to achieve the required dimensional accuracy. Furthermore, even if one attempts to process the material after all heat treatments have been completed in order to avoid distortion, the material is hard and extremely difficult to process. 1. The alloy of the present invention is easy to process and has very little distortion even during heat treatment after processing, so by applying appropriate machining, it can be finished into a strain-generating body having a desired shape with good dimensional accuracy.

Next, examples of the present invention will be described.

EXAMPLE A box-type load cell strain body (L: 14 (h++m, W
: 67mm, T: 50mm, hole diameter (Dt)
: 20M, hole diameter (D2): 20mm).

Flavoring (1) to (3) are examples of the present invention, (10) and (11).
) is a comparative example. Comparative example (10) is one in which the Cr amount deviates from the upper limit stipulation of the present invention, and (11) is SNCM43
It is a 9NC phase.

The above heat treatment was performed at r1100°C for 2 hours, furnace cooling → 1000° for fragrance (1) to (3) and (10).
C x 2 hours, oil cooling -480°C x 2 hours, air cooling], and the fragrance (11) is JIS' for SNCM439.
Quenching and tempering according to regulations Quenching temperature 870°C1
The tempering temperature is 580°C).

Table 1 shows the measurement results of the accuracy of each test strain body as a weight sensor. Incense made of cast SNCM439 (
The accuracy of the flexure element 11) is only 1/1000, and the accuracy of the flexure element 10, which has a high Cr content, is 1/80.
00, whereas the strain-generating bodies (1) to (3) made of cast products of the alloy of the present invention have an accuracy of 1/9000 m6. This accuracy sufficiently exceeds the accuracy (approximately 1/8.000) of the conventional strain body made of SNC'M439 pressed product.

In addition, each test casting product (2), (10) and (11) (
Table 2 shows the results of mechanical tests on test pieces prepared from the above-mentioned heat-treated materials. The alloy of the present invention is similar to conventional S
Although it has lower elongation and aperture than NCM439 etc., it is clear that it has the performance necessary as a load cell strain body and is particularly strong.

As described above, the alloy of the present invention can be made by casting the conventional S
It is possible to manufacture a load cell strain body having a higher precision than that made of NCM439 pressed product. Therefore, compared to conventional manufacturing methods that use forged presses as raw materials, there is a greater degree of freedom in design, and the process can be simplified by reducing the number of machining operations.
Brings down manufacturing costs. Further, since processing in the heat treatment process is easy and distortion caused by processing is small, a strain-generating body having an optimal shape according to a desired shape can be finished with high dimensional accuracy by machining. Of course, since it can be 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 has excellent mechanical properties such as strength as described above, and also has high corrosion resistance as cast stainless steel, so it is suitable for various structural materials that require these properties.

[Brief explanation of the drawing]

FIG. 1 [1] is a plan view showing the shape of a load cell strain body related to an embodiment, and [II] is a side view. Figure 1 288-

Claims (1)

[Claims] +l) CO, 02~0.1%, S i O, 4~-
2.0%, Mn0, 2-1.5%, Ni 4.5-8.
5%, Cr8.5-10.5%, Mo 1.0-3.0
%, Cu 1.0-8.0%, NbO, 2-0.5%,
A martensitic precipitation-hardening stainless steel cast steel for casting a load cell strain body, the balance being Fe and unavoidable impurities.