CN1207429C

CN1207429C - Metals surface heat treatment method

Info

Publication number: CN1207429C
Application number: CN 03113705
Authority: CN
Inventors: 刘长乐
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-01-24
Filing date: 2003-01-24
Publication date: 2005-06-22
Anticipated expiration: 2023-01-24
Also published as: CN1431337A

Abstract

The present invention discloses a heat processing method for metal surfaces. In the method, ammonia gas at certain pressure is let in a furnace tank in a rotational flow mode; simultaneously, the furnace is heated; nitrogen atoms starts to permeate through alpha-Fe interstitial voids on the surface of steel pieces along with the raise of the furnace temperature; when the furnace temperature reaches needed holding temperature of 410 to 620 DEG C, oxygen is added in the furnace, simultaneously, certain pressure is applied to the furnace tank, and heated oxygen performs a catalyst function at this time, for causing nitrogen atoms to permeate through the deep parts of the tissues of the steel pieces for reaching the solid-solution strengthening function for enhancing the tissue density of metal surfaces; through heat preservation for 15 to 20 hours, electricity is cut off, temperature is lowered, and oxygen is cut off; when furnace temperature is lowered at 480 to 450 DEG C, ammonia gas is cut off, and workpieces are taken out from the furnace. Under the premise that the present invention controls deformation to be micro, the present invention enhances combination properties such as hardness, strength, wear resistance, toughness, corrosion resistance, etc., of metal surfaces and solves ubiquitous technological problems such as deformation, brittleness, depth, corrosion prevention, environment protection, etc., in heat processing industries.

Description

Metal surface heat treatment method

The invention relates to the technical field of metal material surface engineering, in particular to the technical field of improving the mechanical property and the chemical property of iron-carbon alloy (including various steel products, cast iron, powder metallurgy and the like) materials, parts made of the iron-carbon alloy materials and various die surfaces by a heat treatment method.

Background art iron and steel materials, i.e. iron-carbon alloys, are the most basic industrial raw materials, and the quality and quantity of the iron and steel materials are directly related to industrial production, national civilization and technical progress. From iron ore to steel and from manufacturing parts to assembling a machine is a very complicated, heavy and costly production process with long cycle times. How to improve the surface properties of parts and moulds and prolong the service life is a valuable work.

The more durable a machine or die is for a user, the better the machine or die is, the higher the hardness, strength, wear and corrosion resistance of the part, but the hardness of various steels is not required to be too high for the part to be machined, so as to facilitate cutting. However, the current numerous heat treatment processes generally have the defects of deformation, brittleness and easy corrosion, and cause troubles in production and use, such as integral quenching, surface quenching, high frequency, medium frequency treatment, carburization and the like. Although the deformation amount is small at lower temperature such as nitriding, plasma nitriding and the like, the hardness layer is too shallow (0.05-0.06 mm, more than 0.100 mm) due to the inert nature of nitrogen atom penetration, and the practical value is not good. In the prior art, a hard nitriding method is adopted to achieve a depth of 0.50-0.60 mm by greatly prolonging the treatment time (5-7 days and nights), but the method causes the surface of a workpiece to be damaged and integrally deformed due to long-time heating of the part in a furnace, and the workpiece can be put into use after being corrected and ground again. In addition, some new surface treatment techniques such as: metal element diffusion, vapor vacuum ion implantation, and the like are mostly limited in practical use due to the defects of complex equipment, high technical difficulty, high cost, and the like. Therefore, the defects of easy deformation, embrittlement, insufficient depth hardness of a treatment layer and the like generally exist in the prior metal heat treatment technology, and the requirements of rapid development of machinery and die industry are not met.

The invention aims to provide a metal heat treatment process which has the advantages of small deformation of the treated metal, high hardness, good toughness, deep hardness layer of 0.3-0.5 mm and good corrosion resistance.

The invention comprises the following steps:

A. purifying a non-metal gas ammonia medium and then introducing the purified medium into a furnace tank;

B. heating the furnace, and when the temperature is raised to about 350 ℃, ammonia gas begins to separate out nitrogen ions;

C. when the temperature reaches the required heat preservation temperature of 410-620 ℃, adding oxygen through the mixer, and applying a certain atmospheric pressure to the furnace tank;

D. after the heat preservation is carried out for 15-20 hours, the power is cut off to cool, and the oxygen is turned off;

E. when the furnace temperature is reduced to 480-450 ℃, closing ammonia gas, discharging the workpiece, cooling the air, and cleaning the workpiece.

The ammonia gas in the step A is introduced into the furnace pot from the bottom.

The ammonia gas in the step A is introduced into the furnace pot from the bottom after obtaining the rotational flow through the spiral pipeline.

The mixer in the step C is in the form of a tee pipe with two air inlets and one air outlet.

And D, mixing the oxygen and the ammonia in the step C in a three-way pipe, performing electromagnetic ultrasonic vibration and heating to obtain certain energy, introducing the energy into the furnace tank from the bottom through a spiral pipeline, and filling the periphery of the workpiece to be processed in the furnace tank at a low speed from bottom to top by swirling flow and forming vortex.

The flow rate of the ammonia gas in the step A is 60-1400L/h.

The flow rate of the oxygen in the step C is 20-120 ml/min.

The certain pressure applied to the furnace pot in the step C is 0.01-0.5 atmospheric pressure.

The invention achieves the purpose of improving the comprehensive properties of metal surface hardness and strength, wear resistance, toughness, corrosion resistance and the like on the premise of controlling the deformation to be extremely tiny, the hardness layer reaches 0.3-0.5 mm, the technical problems of deformation, brittleness, depth, corrosion resistance, environmental protection and the like which are generally existed in the heat treatment industry at present are solved, and the invention has the following advantages:

the method meets the requirement of environmental protection and has advanced process. The process flow does not contain toxic components, does not use oil or water for cooling, is clean and sanitary, and can greatly reduce the workload of electroplating in industry and reduce the pollution to the environment.

And (II) the surface treatment of the plastic (rubber) mould with complex shape and structure is solved, the toughness of the punching shear forming hardware mould is improved, and the capability of resisting thermal stress damage of the die-casting mould is improved. In a word, improve mould quality, extension mould life-span satisfies the demand of industry development to the mould.

And (III) the cheap domestic alloy quenched and tempered steel-40 Cr can be used for replacing the expensive imported die steel, so that the die cost is reduced, and the steel import is reduced.

And (IV) in the aspect of machining mechanical parts, the working procedures can be reduced, and the machining is convenient. Because the deformation is very small, the workpiece is required to be processed in place without allowance. The product can be installed for use after being treated by the process, and is popular. (for a hole-like part, it is difficult to find a center of the part which is deformed after heat treatment after the part is removed from a jig and the deformed center is to be retrieved in order to remove a machining allowance.)

(V) the anticorrosive performance is good, and the outward appearance is beautiful. Can replace electroplating, phosphorization, blackening and the like, and is once and for all.

And (VI) the applicability is wide. The mechanical parts and dies made of carbon steel, alloy steel, castings, powder metallurgy, stainless steel and other materials and with complex shapes, sizes and structures can be suitable.

And (seventhly), the automation degree is high. The operation is simple, stable and reliable. High productionefficiency and considerable economic benefit.

Drawings

FIG. 1 is a schematic view of the structure of a furnace tank in the embodiment.

FIG. 2 is a metallographic structure of the treated metal.

FIG. 3 is a metallographic representation of the treated metal.

Detailed Description

In fig. 1, it can be seen that the main equipment required by the process, i.e. the heat treatment furnace, is a furnace body which is composed of a furnace shell 1, a refractory lining 2, and components provided with resistance wires and electric heating elements and provides a heat source and heat preservation. The furnace body made of stainless steel is used for placing a workpiece to be treated and creating a container, namely a furnace tank 3, of an atmosphere required by treatment, the air inlet pipe 4 is wound on the wall of the furnace tank 4 in a spiral shape and enters from the bottom, and the waste gas pipe 5 purifies and discharges redundant waste gas.

Fig. 2 and 3 are metallographic structure diagrams of the treated metal. The metallographic structure in the figure is point-shaped or strip-shaped nitride (Fe)₃N and Fe₂N) and fine lamellar carbonitride.

In the embodiment, the process is different from the laggard method of the general nitriding surface treatment method, in which ammonia is dropped to take nitrogen, and then a fan is used to blow air downwards, but ammonia gas is introduced into a furnace from the bottom after being purified by a purifier and a spiral pipeline (obtaining a rotational flow), the flow rate is controlled according to the amount of a workpiece, the furnace is heated, when the temperature is increased to about 350 ℃, the ammonia gas begins to separate out nitrogen ions, nitrogen atoms gradually permeate into gaps of α -Fe crystal lattices along with the increase of the furnace temperature, and when the temperature is increased to the required heat preservation temperature of 410-620 ℃ (determined according to the size of the workpiece and the charging amount), oxygen gas is introduced into the furnace from the bottom through a mixer (a three-way pipe type), the flow rate is 20-120ml/min, the size of the ammonia gas is referred to the flow rate of the workpiece, the oxygen gas and the ammonia gas are mixed in a three-way pipe, after electromagnetic ultrasonic vibration and heating to obtain certain energy, the certain energy is introduced into the furnace from the bottom through the spiral pipeline, the furnace is rotated and forms a vortex to fill the periphery of the workpiece to be treated in the furnace slowly from the bottom, and the furnace is applied to the atmospheric pressure of the steel tissue, so that the oxygen gasTo improve the density of the metal surface structure. While part of the nitrogen atoms are combined with iron atoms to form Fe₃N and Fe₂The metallographic structure of the N compound is the pearlite of the punctiform or strip-shaped nitride and the fine flake-shaped carbide, so that the surface of the steel part has a compact structure and a deep permeable layer, and therefore, on the premise of extremely small deformation, the high mechanical properties such as high hardness, low brittleness, toughness, wear resistance, corrosion resistance and the like are obtained.

After heat preservation (also determined by the size of the workpiece and the charging amount) for 15-20 hours, power is cut off to reduce the temperature, oxygen is turned off, ammonia gas is turned off when the furnace temperature is reduced to 480-450 ℃, the workpiece is taken out of the furnace, air is cooled, the workpiece is cleaned, and the process is finished.

The main chemical reaction process in the furnace is as follows:

(1)

(2)

the small part of oxygen and hydrogen are combined to generate water vapor which is discharged along with the waste gas, thereby reducing the generation of hydride caused by the action of the hydrogen and the surface of the steel part and reducing the occurrence of surface brittleness.

The metallographic structure can be seen from the drawing.

Therefore, the process can ensure that the surface of the steel part in a deeper range has higher hardness, toughness, corrosion resistance and oxidation resistance, the strength is correspondingly improved, and the whole process is carried out at a lower temperature (under a eutectoid temperature line) and does not generate austenite transformation, so the deformation amount is extremely small. Meanwhile, the process is irrelevant to the main means of improving the metal hardness through conventional heat treatment, namely a method for obtaining hard and brittle martensite through high-temperature phase transformation, so that the process has better toughness.

Claims

1. A metal surface heat treatment method is characterized by comprising the following steps:

C. when the temperature reaches the required heat preservation temperature of 410-620 ℃, adding oxygen through the mixer, and simultaneously applying 0.01-0.5 atmospheric pressure to the furnace tank;

2. The heat treatment method according to claim 1, wherein the ammonia gas is introduced into the furnace pot from the bottom in the step A.

3. The heat treatment method according to claim 2, wherein the ammonia gas is introduced into the furnace through the spiral pipe and introduced into the furnace from the bottom.

4. The heat treatment method according to claim 1, 2 or 3, wherein the mixer in step C is in the form of a tee pipe having two inlets and one outlet.

5. The heat treatment method according to claim 4, wherein in the step C, the oxygen and the ammonia are mixed in a tee pipe, subjected to electromagnetic ultrasonic vibration and heating to obtain certain energy, and then introduced into the furnace from the bottom through a spiral pipeline to swirl and form a vortex to slowly fill the periphery of the workpiece to be treated in the furnace from bottom to top.

6. The heat treatment method according to claim 1, 2 or 3, wherein the flow rate of the ammonia gas in the step A is 60 to 1400L/h.

7. The thermal processing method according to claim 5, wherein the flow rate of the ammonia gas in step A is 60-1400L/h.

8. The heat treatment method according to claim 1, 2 or 3, wherein the flow rate of oxygen in the step C is 20 to 120 ml/min.

9. The heat treatment method according to claim 5, wherein the flow rate of oxygen in the step C is 20 to 120 ml/min.