CN103088283B - Sectional type pressurizing solid solution nitriding accelerating method of austenitic stainless steel - Google Patents

Abstract

A stepwise pressurized solid solution nitriding and catalytic infiltration method for austenitic stainless steel, which mainly includes: placing austenitic stainless steel in the patent titled "a pressurized high-temperature nitriding device with a double-pressure balance structure" No. 201210530358.6 solid solution nitriding furnace, and NH ₃ is passed into the furnace at a flow rate of 0.5-2L/min until the pressure in the furnace reaches the range of 0.1-1.0MPa, and NH ₃ nitriding pretreatment is carried out at a temperature of 500-700°C for 5- 10h; then completely discharge the NH ₃ in the above-mentioned solid solution nitriding furnace and feed N ₂ at a flow rate of 1-5L/min until the pressure in the furnace reaches the range of 0.1-1.0MPa, and then rapidly raise the furnace temperature to 900-1200°C, Under these conditions, _N2 solid solution nitriding treatment is carried out for 1 to 20 hours, followed by rapid water cooling to room temperature to form a solid solution nitriding layer on the surface of austenitic stainless steel. The invention can improve the nitriding efficiency, increase the overall nitrogen content of the nitriding layer, and effectively slow down or even avoid the grain coarsening of the nitriding part during the nitriding process.

Description

A method for catalyzing and catalyzing austenitic stainless steel by segmented pressurized solid solution nitriding

technical field

The invention relates to a metal surface chemical heat treatment method, in particular to a solid solution nitriding method for austenitic stainless steel.

Background technique

As a new surface chemical heat treatment technology, solid solution nitriding has been widely used in the production of medicine, chemical industry, machinery manufacturing and so on. Traditional solid solution nitriding is generally realized at high temperature (1050-1200°C) and a certain pressure of nitrogen atmosphere. In order to increase the thickness and nitrogen content of the solid solution nitriding layer, it is necessary to carry out a long-term heat preservation treatment in a high-temperature _N2 environment to ensure that _N2 decomposes a large amount of active N atoms and obtains a higher diffusion rate, which inevitably leads to The grain coarsening and overall performance deterioration of austenitic stainless steel will increase the wear rate of equipment in industrial production. Therefore, the length of the solid solution nitriding cycle will directly affect the overall quality of the parts.

Through the retrieval of the prior art, it was found that the article "Solid Solution Nitriding Technology of 15Cr-7.5Mn-2.6Mo Duplex Stainless Steel" published by the author Fu Rui-dong used high-temperature multi-stage solid solution nitriding, but the temperature of each stage of the process Both are greater than 1050°C, and the solid solution nitriding temperature has not been fundamentally reduced. In the document "Ammonia Nitriding Treatment of Austenitic Stainless Steel", a three-stage nitriding process is adopted. The temperature of the three stages is different, but the nitriding medium is NH ₃ , and the N atoms are not solid-dissolved in the surface of the stainless steel, and nitrides are precipitated.

Contents of the invention

The object of the present invention is to provide a segmental pressurized solid solution nitriding of austenitic stainless steel which can improve the nitriding efficiency, increase the overall nitrogen content of the permeated layer, and effectively slow down or even avoid the grain coarsening of the permeated parts during the nitriding process. Infiltration method. The present invention mainly comprises: using different media to sequentially carry out nitriding treatment in two sections of low temperature and high temperature, and then quickly water cooling to room temperature to form a solid solution nitriding layer on the surface of the austenitic stainless steel.

Technical scheme of the present invention is as follows:

(1) Place the austenitic stainless steel in the solid solution nitriding furnace with the patent name "A pressurized high-temperature nitriding device with dual-pressure balance structure" and the application number 201210530358.6, and flow at a flow rate of 0.5-2L/min Introduce NH ₃ until the pressure in the furnace reaches the nitriding pressure range of 0.1-1.0 MPa, and carry out NH ₃ nitriding pretreatment at a temperature of 500-700°C for 5-10 hours.

(2) Completely discharge the _NH3 in the solid solution nitriding furnace with the above application number 201210530358.6 and feed _N2 until the pressure in the furnace reaches the range of 0.1-1.0MPa. The _N2 flow rate is 1-5L/min, and then the furnace The temperature is rapidly raised to 900-1200°C for N ₂ solid solution nitriding treatment for 1-20 hours, and then rapidly cooled to room temperature with water to form a solid solution nitriding layer on the surface of austenitic stainless steel.

Compared with the prior art, the present invention has the following advantages:

1. It has a relatively high permeation rate throughout the nitriding process. The low-temperature and high-speed strong permeation is due to the fact that _NH3 decomposes into active N atoms at a relatively low temperature (500-700°C), and high nitrogen is obtained by pressurizing and increasing the flow rate. Potential, on the surface of austenitic stainless steel, first prepare the surface nitrogen-rich area or make the surface produce a higher N concentration gradient, so as to ensure that the diffusion of N atoms can be effectively promoted in the high-temperature nitriding stage, and the N content and the thickness of the infiltrated layer can be increased.

2. Using this staged process to treat austenitic stainless steel with solid solution nitriding treatment, the thickness of the infiltrated layer is greater than the superimposition of the depth of the nitrided layer obtained by the separation of the two stages of technology. The accelerated nitriding effect is remarkable, and not only a higher N content and hardness, and greatly improve the efficiency of solid solution nitriding, significantly reducing the tendency of grain growth of infiltrated parts.

3. Under the same nitrogen content and thickness requirements of the infiltrated layer, this process can effectively shorten the nitriding time in the high temperature section (or reduce the nitriding temperature), improve the efficiency of solid solution nitriding, shorten the process cycle of solid solution nitriding, and reduce costs and equipment loss.

Description of drawings

Figure 1 is a microstructure diagram of the solid solution nitrided layer obtained in Example 1 of the present invention.

Fig. 2 is a microstructure diagram of the solid solution nitrided layer obtained in Example 2 of the present invention.

Fig. 3 is a microstructure diagram of a solid solution nitrided layer obtained in Example 3 of the present invention.

The specific way:

Example 1:

Process 304 austenitic stainless steel into a thin plate and hang it in a solid solution nitriding furnace with the patent name "A pressurized high-temperature nitriding device with a double-pressure balance structure" and application number 201210530358.6, and pass it at 0.5L/min Inject NH ₃ gas, raise the temperature to 500°C, and nitriding for 10h under the pressure condition of 0.25MPa. Then discharge the NH ₃ in the solid solution nitriding furnace with the above application number 201210530358.6 and feed N ₂ at a flow rate of 5L/min, rapidly raise the temperature to 1150°C, and perform solid solution nitriding under 0.25MPa pressure for 10 hours, and then quickly Water cooled to room temperature. The solid solution nitrided layer obtained in this example has a thickness of about 311 μm, as shown in FIG. 1 .

Example 2:

Process 304 austenitic stainless steel into a thin plate and hang it in the solid solution nitriding furnace with the patent name "A pressurized high-temperature nitriding device with a double-pressure balance structure" patent number 201210530358.6, and feed NH ₃ at 1L/min gas, heated to 700°C, and nitrided for 5h under the pressure of 0.1MPa. Then discharge the NH ₃ in the solid solution nitriding furnace with the above application number 201210530358.6 and feed N ₂ at a flow rate of 3L/min, rapidly raise the temperature to 1050°C, and perform solid solution nitriding under 0.15MPa pressure for 10 hours, and then quickly Water cooled to room temperature. The solid solution nitrided layer obtained in this embodiment has a thickness of about 160 μm, as shown in FIG. 2 .

Example 3:

Process 316 austenitic stainless steel into a thin plate and hang it in the solid solution nitriding furnace with the patent name "A pressurized high-temperature nitriding device with a double-pressure balance structure" patent number 201210530358.6, and feed NH ₃ at 1L/min gas, the temperature was raised to 600°C, and nitriding was carried out for 5 hours under the pressure of 1.0MPa. Then discharge the NH ₃ in the solid-solution nitriding furnace with the above application number 201210530358.6 and feed N ₂ at a flow rate of 5L/min, rapidly raise the temperature to 900°C, perform solid-solution nitriding under 1.0MPa pressure for 1 hour, and then quickly Water cooled to room temperature. The solid solution nitrided layer obtained in this embodiment has a thickness of about 90 μm, as shown in FIG. 3 .

Claims (1)

1. A method for catalyzing austenitic stainless steel segmented pressurized solid solution nitriding, is characterized in that: (1) Austenitic stainless steel is placed in a solid solution nitriding furnace. The main structure of the solid solution nitriding furnace includes a furnace cover, a furnace furnace and a furnace shell. The cover is equipped with an inflatable pipeline connected to the _NH3 bottle and the _N2 bottle, the inflatable pipeline extends to the furnace reaction chamber, the furnace reaction chamber is nested by the heating furnace tube, and the bottom of the heating furnace tube is supported by a ceramic base , the temperature measuring device is introduced through the ceramic base and the center hole at the bottom of the heating furnace tube, the upper end of the furnace is provided with a vacuum pump and an exhaust pipe, the exhaust end of the furnace is connected with a flow monitor, and the upper and lower flanges of the furnace are provided with Circulating water jacket, the lower end of the furnace shell is equipped with an inflatable pipe connected to the Ar bottle, the upper end of the furnace shell is equipped with an exhaust pipe connected to the exhaust gas collection system, and the furnace and the exhaust end of the furnace shell are respectively equipped with pressure measuring devices , and feed NH3 at a flow rate of 0.5-2L/min until the pressure in the furnace reaches the range of 0.1-1.0MPa, and carry out _NH3 nitriding pretreatment at a temperature of 500-700°C for 5-10 hours; (2) Completely discharge the NH ₃ in the above-mentioned solid solution nitriding furnace and feed N ₂ until the pressure in the furnace reaches the range of 0.1-1.0 MPa. The N ₂ flow rate is 1-5 L/min, and then the furnace temperature is rapidly raised to 900 _N2 solid solution nitriding treatment is carried out in the range of ~1200°C for 1 ~ 20h, followed by rapid water cooling to room temperature to form a solid solution nitriding layer on the surface of austenitic stainless steel.