Low-nitriding and deformation-free process method for thin-wall template

Abstract

A thin-wall template part is subjected to stress relief tempering in the machining process, then the thin-wall template is placed in a groove of a special clamp tool, a bolt on one side is tightened to make close contact with the outer surface of the part in the width direction, no pressing stress exists, and nitriding treatment is conducted. According to the method, stress relief tempering with the temperature higher than the nitriding temperature is adopted, machining and internal stress are eliminated to the maximum extent, a special clamp tool for nitriding deformation prevention is designed and manufactured, two-time stepped heating and heat preservation and one-section heat preservation nitriding are conducted in nitriding, and the treatment process of furnace discharging and air cooling is conducted after furnace cooling is conducted to a certain temperature. Through trial-manufacture research of the thin-wall template nitriding process method, the hardness, the layer depth and the brittleness of a nitriding layer meet the technical requirements of parts, nitriding treatment with little or no deformation is achieved, and it is guaranteed that the size deformation of a nitriding part is within the process range.

Description

Technical Field

[0001] The invention belongs to the field of heat treatment technology, and specifically relates to a process method for nitriding a thin-walled template with little deformation, and in particular to a gas nitriding process for manufacturing a thin-walled template part with a material and strength grade of 42CrMo-Q640-III-WJ533-1997 with little deformation. Background Art

[0002] The material and strength grade of a thin-walled template forging part is 42CrMo-Q640-Ⅲ-WJ533-1997. The finished product appearance size (length*width*thickness) is about: 1600mm*270mm*90mm. There are many "U"-shaped grooves in the thickness direction, among which there is a groove with a length of about 1200mm, a depth of about 65mm, and a width of 89H9 along the length direction. Nitriding treatment is required on both the upper and lower sides of the width 89H9 direction. After nitriding treatment, the template parts manufactured were tested and found that the width 89H9 had an out-of-tolerance deformation with the mouth opening outward, which could not meet the technical requirements of the parts. Due to the large size of the parts, long processing cycle and high manufacturing cost, the normal delivery of the products has been affected. Summary of the invention

[0003] The invention provides a process method for nitriding a thin-wall template with little deformation, and the technical problem to be solved is: reducing and controlling the deformation tolerance problem of the thin-wall template parts of forgings after gas nitriding treatment.

[0004] In order to solve the above technical problems, the present invention provides a process for nitriding a thin-walled template with little deformation, characterized in that the steps are as follows:

[0005] 1) Thin-walled formwork parts are subjected to stress relief tempering during processing;

[0006] 2) Place the thin-walled template in the groove of the special fixture, and tighten the bolts on one side to make it in close contact with the outer surface of the part width without compressive stress;

[0007] 3) Carry out nitriding treatment.

[0008] Beneficial effects: In order to reduce and control the deformation tolerance problem of thin-walled template parts of forgings after gas nitriding treatment, improve the qualified rate of nitriding treatment, and meet the technical requirements and product production delivery of parts after nitriding, the present invention conducts trial research on the nitriding anti-deformation process of thin-walled template parts. During the processing of thin-walled template parts, stress relief tempering higher than the nitriding temperature is used to eliminate processing and internal stress to the greatest extent. Special fixtures and tools for nitriding anti-deformation are designed and manufactured. The nitriding process includes two steps of heating and heat preservation and one section of heat preservation nitriding, and the furnace is cooled to a certain temperature and then air-cooled. Through the trial research of the thin-walled template nitriding process method, the hardness, layer depth and brittleness of the nitriding layer meet the technical requirements of the parts and the nitriding treatment with little or no deformation is achieved, ensuring that the dimensional deformation of the nitrided part is within the process range.

[0009] After the finished thin-walled template parts are nitrided, the hardness, layer depth and brittleness of the nitrided layer meet the technical requirements of the parts, achieving less deformation during nitriding and ensuring that the groove width deformation is ≤30μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Nitriding anti-deformation special fixture tooling diagram

[0011] Figure 2 Nitriding less deformation heat treatment process curve. DETAILED DESCRIPTION

[0012] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0013] The present invention proposes a thin-wall template nitriding process with little deformation, taking a thin-wall template with a material and strength grade of 42CrMo-Q640-Ⅲ-WJ533-1997 (appearance size (length*width*thickness) is about: 1600mm*270mm*90mm), and a groove with a length of about 1200mm along the length direction (width is 89H9 (+0.0740), depth is about 65mm) and nitriding treatment on the upper and lower sides as an example, the steps are as follows:

[0014] 1) During the processing of thin-walled template parts, stress relief tempering is carried out at a temperature higher than the nitriding temperature but lower than the Q640 tempering performance temperature to eliminate processing and internal stress to the greatest extent. The tempering process is (530±10)℃*(4-6)h, and the parts are air-cooled to room temperature after being taken out of the furnace. Subsequently, the width 89H9 finishing dimension is controlled to 89(+0.0440).

[0015] 2) Design and manufacture a special fixture for nitriding to prevent deformation. The special fixture consists of a main body and bolts. Place the thin-walled template in the groove of the special fixture, tighten the bolts on one side to make close contact with the outer surface of the part width, but without compressive stress.

[0016] The special fixture tool is provided with a groove matching the outer shape of the thin-wall template, and a threaded hole is provided on one side of the special fixture tool along the length direction for installing bolts.

[0017] 3) Perform nitriding treatment: Two step heating and heat preservation and one heat preservation nitriding are used in nitriding, which can reduce the temperature difference between the furnace temperature and the nitriding workpiece, reduce the stress deformation of the parts, and reduce the brittleness of the nitriding layer. Then, the furnace is cooled to a certain temperature and then air-cooled to avoid surface oxidation of the parts, reduce the brittleness of the nitriding layer and deformation of the parts;

[0018] The specific nitriding process is as follows: the first step heating temperature is (400±10)℃, the heating rate is ≤100℃, and the holding time is (1.5-2)h; the second step heating temperature is (500±10)℃, the holding time is (1.5-2)h, and then the nitriding is carried out at (520±10)℃ for (15-20)h, and the furnace is cooled to below 250℃ and then air-cooled.

[0019] Three thin-walled template parts were treated by nitriding trial production. The nitriding hardness was 600-650HV, the layer depth was 0.23-0.28mm, the nitriding layer brittleness was ≤2 levels, and the groove width dimension 89H9 deformation was ≤30μm. The performance technical indicators of the nitriding layer met the technical requirements of the parts; the width of the nitriding part 89H9 (+0.0740) was within the tolerance range. The nitriding process method achieved nitriding treatment of thin-walled template parts with little deformation.

[0020] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A process for nitriding thin-walled templates with little deformation. It is characterized in that Here are the steps: 1) Thin-walled formwork parts are subjected to stress relief tempering during processing; 2) Place the thin-walled template in the groove of the special fixture, and tighten the bolts on one side to make it in close contact with the outer surface of the part width without compressive stress; 3) Carry out nitriding treatment.

2. A process for nitriding thin-walled templates with little deformation according to claim 1, Features: The material and strength grade of the thin-wall template are 42CrMo-Q640-III-WJ533-1997.

3. A process for nitriding thin-walled templates with little deformation according to claim 1, Features: During the processing of thin-walled template parts, stress relief tempering is performed at a temperature higher than the nitriding temperature but lower than the Q640 tempering performance temperature.

4. A process for nitriding thin-walled templates with little deformation according to claim 1, Features: The tempering process is 530±10℃, the holding time is 4-6h, and then it is air-cooled to room temperature after being taken out of the furnace.

5. A process for nitriding thin-walled templates with little deformation according to claim 1, Features: The subsequent width finishing dimension is guaranteed to be 89 (+0.0440).

6. A process for nitriding thin-walled templates with little deformation according to claim 1, Features: During nitriding, two steps of heating and insulation and one stage of insulation nitriding are adopted, and then the furnace is cooled to a certain temperature and then air-cooled.

7. A process for nitriding thin-walled templates with little deformation according to claim 6, Features: The first step heating temperature is (400±10)℃, the heating rate is ≤100℃, and the holding time is (1.5-2)h.

8. A process for nitriding thin-walled templates with little deformation according to claim 6, Features: The second step heating temperature is (500±10)℃, and the holding time is (1.5-2)h.

9. A process for nitriding thin-walled templates with little deformation according to claim 6, Features: Carry out heat-insulating nitriding at (520±10)℃ for (15-20)h.

10. A process for nitriding thin-walled templates with little deformation according to claim 6, Features: After nitriding, the furnace is cooled to below 250℃ and then air-cooled.

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