JPS581165B2 - Method for imparting carburization resistance to austenitic stainless steel - Google Patents

Description

Detailed Description of the Invention The present invention relates to an austenitic stainless steel with excellent carburization resistance, and in particular, to a general-purpose heat-resistant and oxidation-resistant austenitic stainless steel that does not require component adjustment to improve carburization resistance. This invention relates to a method for obtaining carburizing-resistant austenitic stainless steel by subjecting steel to simple processing.

Generally, austenitic stainless steel has better oxidation resistance than other steel types, so it is often used in high temperature ranges, but it requires continuous heating or repeated heating and cooling in relatively high temperature ranges. It is also commonly used in places with carburizing atmospheres.

An example of this is the use of high carbon steel in annealing boxes and inner covers.

However, under such carburizing atmosphere conditions, a general-purpose austenitic stainless steel such as SUS304 diffuses and absorbs carbon from its surface and becomes carburized, causing expansion and deformation, which may lead to breakage.

In order to suppress such carburization, that is, to improve carburization resistance, it is generally desirable to increase the amount of Si or Ni-Cr in the steel.

However, increasing the Ni-Cr content increases material costs, and manufacturing austenitic stainless steel by adjusting the components for the purpose of improving carburization resistance is burdensome in terms of operation, leading to an increase in manufacturing costs.

Therefore, if carburization resistance can be imparted to general-purpose oxidation-resistant or heat-resistant austenitic stainless steel without adjusting its composition, its uses will expand and it will be economical.

The present invention was conceived in view of the above circumstances, and an object of the present invention is to impart carburization resistance to a general-purpose heat-resistant, oxidation-resistant austenitic stainless steel.

In other words, the present inventors have discovered that carburization resistance can be significantly improved by forming a layer with a large amount of plastic deformation on the surface of austenitic stainless steel through cold working treatment.

It has also been found that forming such a layer with a large amount of plastic deformation on the surface can be easily achieved by work hardening treatment that causes tensile deformation or compressive deformation on the steel surface.

Therefore, the present invention provides a carburizing-resistant austenitic stainless steel having a layer with a large amount of cold plastic deformation on its surface, and a method for producing this steel in which a work-hardened layer is formed on the surface by tensile deformation or compression deformation. Provided is a method for producing carburization-resistant austenitic stainless steel.

Cold plastic deformation means plastically deforming the surface through cold working, and in the case of rolled steel sheets, plastic deformation occurs only on the surface, meaning that the amount of plastic deformation is greater on the surface than inside the steel sheet. do.

Tensile deformation processing means bending deformation or rolling processing, and means processing by applying tensile force to the surface.

For example, in a corrugated steel plate, the amount of plastic deformation on the surface is large at the bent portion.

Compression deformation processing means subjecting the surface to compression processing, such as shot blasting or shot peening.

This amount of tensile and compressive deformation is sufficient to cause surface hardening, and a structure with a high degree of surface hardening also has high carburization resistance.

By processing temperature is meant the cold working temperature as used in conventional surface hardening methods.

Tensile deformation processing and compression deformation processing depend on the type of steel used (material, shape,
The most suitable processing method is selected depending on the dimensions), but in some cases, both processing methods may be used in combination.

Next, the present invention will be explained with reference to Examples.

Example 1 A general-purpose austenitic stainless steel sheet having the composition shown in Table 1 was rolled at a rolling rate of 10% and 5% using a four-high roll mill.
Cold rolled at 0%.

The rolling conditions for four-high rolling of this steel plate are as follows.

Rolling speed: 60 m/min When rolling rate is 10%: 1 bath 5%, 2 bath 3%, 3 bath 2%.

When rolling rate is 50%; 1 bath 20%, 2 baths 10%,
3 buses 10%, 4 buses 8%, 5 buses 2%.

Next, each of the cold-rolled austenitic stainless steels was exposed to a carburizing atmosphere at 800°C, 900°C, and 1000°C.

However, this carburizing treatment was carried out under a gas atmosphere of CO+CO2 while maintaining each temperature for 60 hours.

After this carburizing treatment, the surface carbon concentration (
The concentration (concentration) and surface hardness (Pickas) at a position 10 μm below the surface were measured by spectroscopic analysis.

A high surface hardness indicates a high degree of carburization.

The results obtained are shown in Table 2.

The materials shown as comparative examples in the table are materials that were not cold rolled but were carburized under the same carburizing conditions as above.

From the results in Table 2, it can be seen that the cold-worked material has improved carburization resistance compared to the control material that is not cold-worked.

In particular, the carburization resistance of the 10% cold-worked steel is better than that of the 50% cold-worked steel, and it can be seen that there is an optimum range for the degree of working when cold rolling is used.

Example 2 The same austenitic stainless steel plate as Example 1 (Table 1
glass beads were sprayed onto the surface of the steel plate) using a dry honing machine.

The conditions for this shot blasting treatment are as follows.

Spraying pressure: 5kg/cm2 Spraying distance: 5cm Spraying time: 3 minutes 00 seconds Glass bead diameter: 210-500μ SUS surface hardened by this shot blasting treatment
The surface hardness of No. 304 and the hardness distribution of the hardened surface layer are shown in the attached FIG. 1.

As shown in Figure 1, the surface hardening layer is about 0.4 mm in the surface layer.
The surface is hardened.

This shot-blasted steel plate was exposed to a carburizing atmosphere under the same conditions as in the example.

After the carburizing treatment, the carbon content and surface hardness of the carburized portion were measured in the same manner as in Example 1, and the obtained results are shown in Table 3.

For comparison, the measurement results of a material that was carburized without shot blasting are also listed as a control example.

From the results in Table 3, it can be seen that when the surface of austenitic stainless steel is compressed and deformed, the carburization resistance is significantly improved, and the effect is even more excellent than that obtained by cold rolling.

The attached photograph is a micrograph (magnification x 200) showing the surface condition of SUS304 steel treated according to Example 2.

The photo in Figure 2 shows SUS304 steel surface-hardened using a dry honing machine in a CO+CO2 atmosphere.
This shows the surface exposed to a carburizing atmosphere at 00°C for 60 hours, with almost no carburized layer visible.

The photograph in Figure 3 shows the surface of the same SUS304 steel carburized under the same conditions without surface hardening, and it can be seen that the carburized layer has spread to the deep part.

[Brief explanation of the drawing]

FIG. 1 shows the hardness distribution in the cross-sectional direction of a sheet of SUS304 steel whose surface layer is work-hardened by shot blasting. Figure 2 is a micrograph of a cross section of an austenitic sterless steel having a layer with a large amount of cold plastic deformation according to the present invention (
Magnification x 200), and shows the state after being exposed to a carburizing atmosphere according to Example 2. Figure 3 is a micrograph (magnification x 200) of a cross section of a conventional austenitic stainless steel, showing the same type of steel as in Figure 1 exposed to the same carburizing atmosphere, showing that the carburized part extends deep. shows.

Claims (1)

[Claims] 1. Add carburization resistance to austenitic stainless steel by forming a work-hardened layer with a large amount of cold plastic deformation on the surface of the austenitic stainless steel by subjecting it to cold tensile deformation or compression deformation. Method.