CN114481006A

CN114481006A - Carburizing method capable of adjusting nitrogen-methanol atmosphere proportion

Info

Publication number: CN114481006A
Application number: CN202011268908.2A
Authority: CN
Inventors: ***; 黄勇; 卞凯强; 陈慧清
Original assignee: Shanghai Automobile Gear Works
Current assignee: Shanghai Automobile Gear Works
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2022-05-13

Abstract

A carburizing method capable of adjusting nitrogen methanol atmosphere proportion is characterized in that under the condition of keeping methanol flow rate unchanged at 4.0L/h, the introduction amount of nitrogen is controlled to be 4.5m³The/h is reduced to 3.4m³H, i.e. the composition of the cracked gas is changed from CH₃OH and N₂The ratio of (1: 1.1) is adjusted to 1: 0.9; meanwhile, the CO value of the oxygen probe is adjusted to be 23%, then variable oxygen measurement is carried out, and the carbon potential is controlled by adding propane or air. The invention can save the nitrogen consumption by more than 30 percent on the premise of ensuring the original carburizing speed.

Description

Carburizing method capable of adjusting nitrogen-methanol atmosphere proportion

Technical Field

The invention relates to a technology in the field of carburizing, in particular to a method for adjusting the proportion of a medium introduced into a heat treatment carburizing atmosphere in a part carburizing process.

Background

The nitrogen-methanol atmosphere carburizing is widely applied to the field of carburizing and quenching, and has the advantages that the generated atmosphere is stable, and the defects that equipment needs to consume a large amount of nitrogen and the production cost is high. Thermodynamically, when the temperature exceeds 700 ℃, the main medium methanol cracking equation is: CH (CH)₃OH－→CO+2H₂The introduced methanol is liquid, and the gas production per liter of liquid methanol is 1.67m³. According to the usual CH₃OH：N₂1:1.1 (methanol 4.0L/h, nitrogen 4.5 m)³H) nitrogen-methanol atmosphere, the gas composition in the actual high-temperature cracked furnace is as follows: CO: 40.. 1.67/3 ═ 2.2, H₂：2*4.0*1.67/3＝4.4，N₂: 4.4; the gas composition ratio is CO: h₂：N₂1: 2: 2, namely the standard composition of 40 percent nitrogen and 60 percent methanol mixed gas, and the CO value in furnace gas is 20 percent.

The nitrogen does not participate in the cracking reaction of the atmosphere in the hearth, and the nitrogen mainly has the functions of adjusting the proportion of CO in the furnace, increasing the air exchange rate and reducing the formation of carbon black. The nitrogen introduction amount is properly reduced, the carburization speed and effect are not influenced, and resources can be saved.

Disclosure of Invention

The invention provides a carburizing method capable of adjusting the proportion of a nitrogen-methanol atmosphere, aiming at the defect that nitrogen and methanol in a nitrogen-methanol atmosphere furnace in the prior art are used as constant flux and account for larger consumption proportion of chemicals in a carburizing furnace, and the using amount of nitrogen can be saved by more than 30% on the premise of ensuring the original carburizing speed.

The invention is realized by the following technical scheme:

the invention keeps the methanol flow rate unchanged at 4.0L/h, and the nitrogen is introduced from 4.5m³The reaction time/h is reduced to 3.4m³H, i.e. the composition of the cracked gas is changed from CH₃OH and N₂The ratio of (1: 1.1) to (1: 0.9); meanwhile, the CO value of the oxygen probe is adjusted to be 23%, then variable oxygen measurement is carried out, and the carbon potential is controlled by adding propane or air.

The gas composition in the hearth after pyrolysis comprises: CO: 4.0 x 1.67/3 ═ 2.2 (m)³)，H₂：2*4.0*1.67/3＝4.4(m³)，N₂：3.4(m³) The gas composition ratio is CO: h₂：N₂1: 2: 1.6, namely 34 percent of nitrogen and 66 percent of methanol mixed gas, wherein the CO value in furnace gas is close to 23 percent.

The reaction equation of the variable oxygen amount is as follows:

the CO value correction refers to the following steps: according to the comparison table of the output potential of the oxygen probe and the carbon potential, when the CO value is 20%, the carbon potential is 1.00% at the temperature of 900 ℃, and the output potential of the corresponding oxygen probe is 1142 MV; 1.00% carbon potential at 900 ℃ corresponding to an oxygen probe output potential of 1135 MV. After the nitrogen-methanol ratio is adjusted, correspondingly correcting the CO set value of the oxygen probe, which specifically comprises the following steps: the set value of the carbon control instrument is corrected by 7 MV values.

Preferably, the pressure in the furnace chamber may be slightly reduced due to the decrease of the nitrogen gas introduction amount, and the weight of the exhaust port needs to be adjusted to maintain the pressure range of 300pa in the furnace chamber 250.

Preferably, the carbon atoms lose activity after staying in the furnace for a long time, and are replaced by new ones appropriately. The current controllable carburizing furnace has greatly improved tightness and carbon potential control means, and the hearth ventilation frequency is ensured to be more suitable for 2.5-5 times/h.

Technical effects

Compared with the prior art, the method has the advantages that the use amount of the nitrogen in the nitrogen-methanol atmosphere and the CO set value of the oxygen probe are adjusted, the use of enriched gas is not increased, the carburizing speed is not influenced, and the consumption of the nitrogen is greatly reduced.

Detailed description of the invention

In the embodiment, a transmission gear is selected as a test part, the material of the part is 20MnCr5, and the depth requirement of a carburized layer is as follows: 550HV1 of 0.50-0.80mm, the metallographic structure of the carburized layer is 1-4 level carbide, 1-5 level residual austenite, and the non-martensitic structure is less than or equal to 0.020 mm.

In the carburizing process of the embodiment, an Aichelin VKEES 2/4 type box type multipurpose furnace is adopted, propane is used as a carburizing and enriching agent, and HOUGHTON quenching oil is adopted.

In the specific carburizing method of the embodiment, 4.0L/h of the existing methanol and 4.5m of nitrogen are added³H; adjusting to the following steps: methanol 4.0L/h, nitrogen 3.4m³The oxygen probe CO value was corrected from 20% to 23%. After the nitrogen flow rate decreased, the furnace pressure showed a decrease from 300pa to 290pa, and the carburized enriched propane did not change. The whole carburizing process has stable carbon potential without increasing fluctuation, and the carburizing process time is kept consistent with the original carburizing process time.

The correction is carried out by correcting the carbon potential by using a carbon fixing sheet and finely adjusting millivolts.

The air exchange rate of the hearth atmosphere is as follows: the furnace volume of the VKES2/4 box type multipurpose furnace is 3.5m3, and the furnace volume is measured according to the flow: before adjustment: (4.0 × 1.67+4.5)/3.5 ═ 3.2 times/h; after adjustment: (4.0 × 1.67+3.4)/3.5 ═ 2.9 times/h.

The nitrogen flow is reduced by more than 30 percent, and the furnace gas exchange rate is still in a reasonable range.

The same process (temperature, time, carbon potential and other parameters), the same part and the same furnace are selected and respectively tested in 2 groups. Data comparisons were performed using 20% CO values for group I and 23% CO values for group II. Each group of 9 samples are separately placed according to the 9-point uniformity position of the multipurpose furnace.

The surface carbon content is tested by a stripping spectrum method, two groups of metallographic measurement results have no obvious difference, and the data is as follows:

through observation, the hearth has no obvious carbon deposition aggravation phenomenon, namely, the same nitrogen methanol atmosphere equipment of the multipurpose furnace is adopted, the atmosphere proportion of the hearth is changed by the same parts and the same process (temperature, time, carbon potential and the like) parameters, and the parts have no obvious difference in the aspects of surface hardness, hardened layer depth, carburized layer metallographic structure and the like.

Compared with the prior art, the method does not change the introduction amount of the activated carbon atoms, only reduces the introduction amount of nitrogen and changes the proportion of the nitrogen methanol atmosphere on the premise of not influencing the carburizing speed and the carburizing quality, reduces the nitrogen consumption by more than 30 percent, and effectively reduces the production cost.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A carburizing method capable of adjusting the proportion of nitrogen methanol atmosphere is characterized in that under the condition of keeping the flow rate of methanol unchanged at 4.0L/h, the introduction amount of nitrogen is controlled to be 4.5m³The reaction time/h is reduced to 3.4m³H, i.e. the composition of the cracked gas is changed from CH₃OH and N₂The ratio of (1: 1.1) to (1: 0.9); meanwhile, the CO value of the oxygen probe is adjusted to be 23%, then variable oxygen measurement is carried out, and the carbon potential is controlled by adding propane or air.

2. The carburizing method capable of adjusting the proportion of the methanol-nitrogen atmosphere as claimed in claim 1, wherein the weight of the exhaust port is adjusted to maintain the pressure range of the furnace chamber of 250 Pa and 300 Pa.

3. The method of carburizing with an adjustable nitrogen-methanol atmosphere ratio according to claim 1, characterized in that the furnace chamber is ventilated at a frequency of 2.5 to 5 times/h.