JP2011074455A - Method for manufacturing corrosion-resistant stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a corrosion-resistant stainless steel which has enhanced corrosion resistance by reducing a remaining amount of undissolved chromium carbide as much as possible. <P>SOLUTION: The manufacturing method includes: a heat treatment step of hot-rolling, annealing and then cold-rolling stainless steel; a quenching treatment step of heating the heat-treated stainless steel in an inert gas atmosphere at 950°C or higher for a predetermined period of time and then quenching the steel to control the amount of chromium carbide to less than 0.3 wt.%; and a tempering treatment step of tempering the quenched stainless steel in an inert gas atmosphere at 450°C or lower for a predetermined period of time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heat treatment method for stainless steel that requires wear resistance, characterized in that the chromium carbide in the stainless steel is suppressed to less than 0.3% by weight to impart corrosion resistance to the stainless steel. It is a manufacturing method of steel.

The loom parts such as wings and healds that are installed in the automatic loom water jet loom (hereinafter referred to as WJL) operate at a high speed of 300 to 800 rpm in contact with the fibers during weaving, and therefore wear resistance. Is required. In particular, when weaving polyester yarn containing titanium oxide or the like, abrasion damage occurs at the fiber contact portion, and early replacement of the loom parts is necessary to cause yarn breakage and fluffing. In addition, since the loom parts are used in a wet environment due to splashing with weft insertion, corrosion resistance to WJL water (ground water, tap water) is necessary. In WJL stainless steel component heald, crevice corrosion has been reported to occur between the resin deposit that is the yarn sizing agent and the heald (Non-patent Document 1). Similar to the above-mentioned wear damage, this corrosion damage also causes yarn breakage and fluffing during weaving and causes warp streaks in the woven fabric product.

Conventionally, austenitic stainless steel SUS301 has been used for wings, and martensitic stainless steel SUS420J2 has been used for healds. However, SUS301 wears quickly, and SUS420J2 is prone to rust and has a problem in corrosion resistance. Various stainless steels have been developed to solve this problem. For example, there are ferritic stainless steel, duplex stainless steel (Patent Document 1), and austenitic stainless steel (Patent Document 2) in which the amount of Cr is increased and corrosion resistance elements such as Mo and Ni are added. However, these are not popular because they do not satisfy the corrosion resistance, wear resistance and low cost required for loom parts. Recently, resin healds developed for the purpose of metal corrosion countermeasures have enabled high-speed operation of the loom due to the weight reduction of the parts, but the through-hole (hereinafter referred to as mail) that allows the warp to pass through is elongated. There's a problem.

In stainless steel that requires abrasion resistance, a material that improves corrosion resistance and can be supplied at low cost as a fiber part is desired. Therefore, we focused on martensitic stainless steel with excellent wear resistance that has been used for heald materials. Martensitic stainless steel is a stainless steel that is hardened by heating to the temperature range of the austenite phase and then quenching (quenching). In order to impart wear resistance, the material having an increased amount of C in the chemical composition is heat-quenched and martensitic transformation is used to improve the hardness. On the other hand, Cr is an element that improves the corrosion resistance of stainless steel, but depending on the heat treatment conditions, it combines with C and precipitates chromium carbide, which lowers the corrosion resistance.

JP-A-10-110647 JP 2003-105504 A JP-A-9-87944

Nakatsu Michiyo et al .: Zairyo-to-Kankyo, 55, 495 (2006)

When we conducted a material survey of the martensitic stainless steel weaving machine parts heald currently on the market, it contained a large amount of chromium carbide at 1 to 2% by weight. It was found to be undissolved chromium carbide. When undissolved chromium carbide remains, the effective amount of chromium in the stainless steel is reduced and a chromium-deficient layer is formed, resulting in a significant decrease in corrosion resistance. Therefore, an object of the present invention is to provide a method for producing a corrosion-resistant stainless steel in which the residual amount of undissolved chromium carbide is suppressed as much as possible to improve the corrosion resistance.

  As a result of intensive studies to solve the above problems, the present inventor has found that the corrosion resistance of stainless steel can be improved with the following contents, and has led to the present invention. The invention according to claim 1 includes a heat treatment step of hot rolling stainless steel, cold rolling after annealing, and heating and quenching the heat treated stainless steel in an inert gas atmosphere at a temperature of 950 ° C. or more for a predetermined time. And a tempering process for tempering the quenched stainless steel at a temperature of 450 ° C. or lower for a predetermined time in an inert gas atmosphere; It is provided with.

The invention according to claim 2 is the manufacturing method according to claim 1, wherein the stainless steel before the heat treatment has a chemical composition of C0.16 to 0.40 wt%, Cr 11.5 to 14 wt%. Si is contained in an amount of 0.5% by weight or less and Mn is 0.5% by weight or less, and the balance is Fe and inevitable impurities.

The invention according to claim 3 is the manufacturing method according to claim 1 or 2, wherein the chromium carbide is chromium carbide that is insoluble, and is M ₂₃ C ₆ type carbide mainly composed of chromium. It is characterized by being.

The invention according to claim 4 is characterized by comprising a part forming step of forming the part using the stainless steel tempered by the manufacturing method according to any one of claims 1 to 3.

The invention according to claim 5 is a loom part manufactured by the manufacturing method according to claim 4.

A heat treatment step of hot rolling stainless steel, cold rolling after annealing, and heat treating the stainless steel in an inert gas atmosphere at a temperature of 950 ° C. or higher for a predetermined time, followed by quenching to a chromium carbide content of 0.3 It has excellent corrosion resistance by having a quenching treatment step of less than% by weight and a tempering treatment step of tempering the quenched stainless steel in an inert gas atmosphere at a temperature of 450 ° C. or less for a predetermined time. Corrosion resistant stainless steel can be manufactured. When quenching and tempering processes are performed in the atmosphere without gas replacement (Patent Document 3), an oxide film is formed on the surface of the stainless steel, resulting in a reduction in coloration and corrosion resistance. Therefore, it is necessary to remove the oxide film. That is, complicated steps of polishing and chemical treatment are required. However, the present invention in which these heat treatment steps are performed in an inert gas atmosphere does not produce an oxide film, can make the production process more efficient, and can use conventional heat treatment equipment as it is. Therefore, low-cost production is possible, and the price of the product can be reduced. The present invention can prevent corrosion of stainless steel parts mounted on a loom, and greatly contributes to cost reduction of woven fabric production and improvement of quality control technology.

In the present invention, martensitic stainless steel is a stainless steel that has a martensitic structure by heat quenching in the quenching process.

In the present invention, the inert gas atmosphere includes a gas of nitrogen, argon, helium, or a mixed gas thereof, and a mixture of these with a reducing gas of hydrogen gas. The inert gas can prevent the generation of scale such as an oxide film generated on the stainless steel surface during the heat treatment.

In the present invention, the M ₂₃ C ₆ type carbide mainly composed of chromium is a carbide in which M is a chromium or iron atom, and includes a carbide in which both atoms are mixed.

In the present invention, heating for a predetermined time is a time required for the undissolved chromium carbide to be less than 0.3% by weight, and is limited by the size, shape and weight of the stainless steel material and the shape of the heat treatment furnace. Is done.

In the present invention, the quenching treatment step means that the stainless steel is heated in an inert gas atmosphere at a temperature of 950 ° C. or more for 10 minutes or more, preferably 1000 ° C. or more for 15 to 30 minutes, and then immediately after water or oil It is to cool rapidly by putting heated stainless steel in liquid nitrogen. This rapid cooling includes indirect cooling using water, oil, and liquid nitrogen as a medium. The processing equipment can be a batch vacuum furnace or a continuous electric furnace. Tempering is performed after the quenching process. However, at 450 ° C. or less, which is the temperature condition for tempering, undissolved chromium carbide does not decrease. Therefore, chromium carbide is made less than 0.3% by weight in the quenching process. There is a need. In addition, quenching is a heat treatment applied to martensitic stainless steel, where the steel is heated to the austenitizing temperature, and chromium carbide in the steel is dissolved in a metal matrix and then rapidly cooled. The temperature at which this austenite phase is formed is determined from the chemical composition of carbon and chromium in the steel. With a chemical composition C of 0.16 to 0.40% by weight and Cr of 11.5 to 14% by weight of the stainless steel before the heat treatment of the present invention, a heating temperature of 950 ° C. or higher is considered to be an austenitized region.

In the present invention, the tempering step is a process in which stainless steel is heated in an inert gas atmosphere at a temperature of 450 ° C. or lower for less than 10 minutes, preferably at a temperature of 300 ° C. or lower for 30 seconds to 10 minutes, and then immediately cooled. It is. Cooling also includes indirect cooling using stainless steel as water, oil, liquid nitrogen, air, or these as a medium. In the heating temperature range of 500 to 650 ° C., sensitization occurs in which chromium carbide is precipitated in the material and a chromium-deficient region is generated, and the corrosion resistance is remarkably lowered. In order to avoid this, it is necessary to set the heating temperature to 450 ° C. or lower. A heating temperature of 700 ° C. to 800 ° C. is not suitable as a method for manufacturing a loom part because wear resistance decreases.

In the present invention, even if the undissolved chromium carbide after heating and quenching is less than 0.3% by weight, M ₂₃ C ₆ , M ₇ C ₃ , M ₃ C (M is chromium) Or, a carbide mainly composed of chromium of an iron metal atom may reprecipitate. However, when expecting the crevice corrosion resistance of the loom parts, it is desirable that the chromium carbide content after tempering is within 0.5% by weight. In order to keep the amount of chromium carbide within 0.5% by weight, a tempering treatment step of tempering in an inert gas atmosphere at a temperature of 300 ° C. or lower for 1 to 5 minutes is desirable.

In the present invention, the part forming step is to make the shape of the intended loom part, and includes the steps of pressing, polishing, and surface treatment.

The following examples illustrate the invention in detail.

Each alloy component shown in Table 1 was melted in vacuum, and a stainless steel plate having a thickness of 2 mm was produced through hot forging, hot rolling, and cold rolling. This was cut into a test piece of 50 mm × width 5 mm × thickness 2 mm. This was heated at 1050 ° C. for 10 minutes in an alumina tube furnace substituted with argon gas, then cooled with water, and further tempered at 400 ° C. for 1 minute. The amount of chromium carbide deposited on the test piece after heating and cooling with water was determined by performing electrolytic extraction in a maleic anhydride methanol solution and collecting the insoluble component with a 0.2 μm membrane filter. Hardness was measured using a Vickers hardness tester. After the heat treatment, the test piece was polished, washed with pure water and acetone in this order, and a corrosion test was conducted. In the corrosion test, a test piece was immersed in a 1000 ppm chloride ion solution, and the presence or absence of corrosion after 48 hours was visually observed.

Each alloy component shown in Example 2 of Table 1 was processed and heat-treated in the same manner as in Example 1. Further, the chromium carbide content, hardness measurement, and corrosion test were performed in the same manner as in Example 1.
[Comparative Example 1]
Each alloy component shown in Comparative Example 1 in Table 1 was subjected to the same processing and heat treatment as in Example 1. Further, the chromium carbide content, hardness measurement, and corrosion test were performed in the same manner as in Example 1.
[Comparative Example 2]
Each alloy component shown in Comparative Example 2 in Table 1 was processed and heat-treated in the same manner as in Example 1. Further, the chromium carbide content, hardness measurement, and corrosion test were performed in the same manner as in Example 1.
[Comparative Example 3]
Each alloy component shown in Comparative Example 3 in Table 1 was processed and heat-treated in the same manner as in Example 1. Further, the chromium carbide content, hardness measurement, and corrosion test were performed in the same manner as in Example 1.

The amount of chromium carbide in the test piece was less than 0.3% by weight in Example 1, Example 2, and Comparative Example 2. In Comparative Example 1 and Comparative Example 3, it was considered that pitting corrosion occurred in the corrosion test because the chromium carbide amount was 0.3% by weight or more. In Comparative Example 2, the amount of chromium carbide was 0.27% by weight and less than 0.3% by weight, but pitting corrosion occurred. It was thought that the corrosion resistance was lowered because chromium of the alloy composition was as low as 11%.

A stainless steel plate having a thickness of 2 mm was prepared by processing each alloy component shown in Example 2 in Table 1 in the same manner as in Example 1. This was cut into a test piece of 50 mm × width 5 mm × thickness 2 mm. Under the conditions shown in Table 2, this test piece was subjected to a heat treatment in a quenching process and then in a tempering process. The heat treatment was performed in an alumina tube furnace in an argon gas atmosphere. The test piece after the heat treatment was subjected to a corrosion test after being polished and then washed in the order of pure water and acetone. In the corrosion test, immersion was carried out in a 6.8% nitric acid solution at 20 ° C. for 56 hours, and the erosion depth was measured. The amount of chromium carbide was analyzed in the same manner as in Example 1.
[Comparative Example 4]
Each alloy component shown in Example 2 of Table 1 was subjected to a heat treatment in a quenching treatment step and then a tempering treatment step under the conditions shown in Table 2. The test piece after the heat treatment was subjected to a corrosion test and an analysis of the chromium carbide amount in the same manner as in Example 3.
[Comparative Example 5]
Each alloy component shown in Example 2 of Table 1 was subjected to a heat treatment in a quenching treatment step and then a tempering treatment step under the conditions shown in Table 2. The test piece after the heat treatment was subjected to a corrosion test and an analysis of the chromium carbide amount in the same manner as in Example 3.
[Comparative Example 6]
Each alloy component shown in Example 2 of Table 1 was subjected to a heat treatment in a quenching treatment step and then a tempering treatment step under the conditions shown in Table 2. The test piece after the heat treatment was subjected to a corrosion test and an analysis of the chromium carbide amount in the same manner as in Example 3.
[Comparative Example 7]
Each alloy component shown in Example 2 of Table 1 was subjected to a heat treatment in a quenching treatment step and then a tempering treatment step under the conditions shown in Table 2. The test piece after the heat treatment was subjected to a corrosion test and an analysis of the chromium carbide amount in the same manner as in Example 3.

Example 3 showed excellent corrosion resistance with a chromium carbide content of 0.22 wt% and an erosion depth of 0 μm. In Comparative Example 4, the amount of chromium carbide was 1.6% by weight, and the corrosion was 50 μm. This was thought to be due to the fact that undissolved chromium carbide remained and the corrosion resistance was lowered because the heating time was as short as 2 minutes. In Comparative Example 5, since the heating temperature was as low as 900 ° C., undissolved chromium carbide remained and the corrosion resistance decreased. In Comparative Example 6, the amount of chromium carbide after the quenching process was 0.25% by weight, but because the heating temperature was 550 ° C. in the tempering process, the specimen became sensitized and the erosion deepened. it was thought. In Comparative Example 7 in which heat treatment was performed in the air instead of the inert gas atmosphere, a surface oxide film was formed, and chromium nitride was also generated in addition to chromium carbide, resulting in a decrease in corrosion resistance.

Each alloy component of Example 2 shown in Table 1 was melted in vacuum, and a stainless steel plate having a thickness of 0.3 mm was produced through hot forging, hot rolling, annealing, and cold rolling. Next, after the quenching process and the tempering process of Example 3 in Table 2, it was pressed into a heald (length 300 mm × width 2 mm × thickness 0.3 mm). Each 15,000 of these healds were mounted on a WJL actual machine, and a weaving test of polyester cloth was performed at a room temperature of 70% humidity and 25 degrees. WJL operates continuously for 24 hours for 2 months, and the water used for WJL is tap water. Two months later, the heald was removed from the WJL, and after removing the resin on the heald surface and attached dirt, visual observation was performed to confirm the occurrence of crevice corrosion. The test results are shown in Table 3.
[Comparative Example 8]
A stainless steel plate having a thickness of 0.3 mm processed in the same manner as in Example 4 was subjected to a heald (length 300 mm × width 2 mm × thickness 0.3 mm) after the quenching process and tempering process of Comparative Example 4 in Table 2. Press processed. The manufactured heald was subjected to a weaving test using an actual WJL machine in the same manner as in Example 4. The test results are shown in Table 3.

From the results in Table 3, it was confirmed that the occurrence of crevice corrosion was suppressed by making the chromium carbide content of the stainless steel heald less than 0.3% by weight.

None

Claims (5)

A heat treatment step of hot rolling stainless steel, cold rolling after annealing, and heat treating the stainless steel in an inert gas atmosphere at a temperature of 950 ° C. or higher for a predetermined time, followed by quenching to a chromium carbide content of 0.3 Corrosion resistance comprising: a quenching treatment step of less than% by weight; and a tempering treatment step of tempering the quenched stainless steel in an inert gas atmosphere at a temperature of 450 ° C. or lower for a predetermined time. Stainless steel manufacturing method. The stainless steel before the heat treatment includes C 0.16-0.40 wt%, Cr 11.5-14 wt%, Si 0.5 wt% or less, and Mn 0.5 wt% or less. The manufacturing method according to claim 1, wherein the balance consists of Fe and inevitable impurities. The method according to claim 1, wherein the chromium carbide is chromium carbide that is insoluble, and is M ₂₃ C ₆ type carbide mainly composed of chromium.   A method for manufacturing a loom component, comprising a component forming step of forming the component using the stainless steel tempered by the manufacturing method according to claim 1. A loom part manufactured by the manufacturing method according to claim 4.