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Vacuum Heat Treatment Furnace

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Chain link vacuum quenching and tempering

The chain rail section of the bulldozer is the support of the crawler shoe of the construction machinery bulldozer, and the current market demand is very large. Hot forging die for chain link

The lifespan is the bottleneck restricting production and occupies a very important position in production. In this paper, the advantages of vacuum quenching and tempering are analyzed, and the heat treatment process of vacuum high pressure gas quenching and vacuum positive pressure tempering is determined through experiments, and the hot forging die after vacuum heat treatment is tested. It has been proved by practice that vacuum quenching and tempering can significantly improve the life of H13 hot forging die.

1.Introduction

The chain rail links of bulldozer track shoes are formed by hot die forging. The hot forging die material is H13 (ASM steel grade). The die size is 540mm long x 220mm wide x 80mm thick and weighs about 80kg.

The process route of the mold is: forging → annealing CNC machining (rough machining) → quenching and tempering → CNC machining (finishing) → put into use → CNC machining (finishing, removing the failed cavity) → reuse.

2.General heat treatment process and usage of H13 mold

The general heat treatment process of H13 mold is ordinary box furnace + well-type tempering furnace quenching and tempering, charcoal + methanol atmosphere protection, quenching oil, cooling to about 150C, and immediately entering the well-type tempering furnace for tempering three times. The disadvantages of this process mainly include: although there are charcoal protection + methanol protection and anti-oxidation paint to protect the cavity, the surface of the cavity is still prone to oxidation and decarburization or carbon increase, the crack tendency is large, and improper cooling control is prone to quenching cracks; quenching quality is not good. Stable, the hardness of the mold fluctuates greatly, and the phenomenon of early failure of the mold occurs from time to time.

The economic loss is relatively large; due to the long time to assemble and disassemble the mold, the life of the mold restricts the improvement of production efficiency.

The dies that have undergone ordinary heat treatment are used on 2500t and 4000t mechanical hot die forging presses. The forging material is 35MnB and weighs 4.8kg. The forging temperature is 1150~1250℃. The preheating temperature of the mold cavity is 150~250℃, the working temperature is about 600℃, and it is cooled with an environmentally friendly mold release agent; the mold is repaired by removing the failed mold cavity and continues to use, a total of 4 times, and the service life of the mold is 6000 pieces each time (2500t press), 9000 pieces (4000t press).Due to the harsh use conditions of hot forging dies, which are subjected to impact force, friction force and high operating temperature, the die is required to have good high temperature strength, tempering resistance stability, wear resistance, heat treatment fatigue resistance and its good cooperation. The main failure modes of ordinary heat treatment molds are early overall cracking and early thermal fatigue cracks in the mold cavity, which are mainly caused by insufficient toughness when the hardness of the mold is high, and insufficient strength and wear resistance when the hardness is low.

3.Advantages and equipment performance of vacuum quenching and tempering

Vacuum quenching and tempering mainly have the following advantages: small deformation, about 1/6~1/8 of salt bath heat treatment; improve mechanical properties, prolong service life; save resources, reduce energy consumption, high economic benefits; reduce pollution ,protect environment.

4.Determination of process parameters

With reference to the relevant information, according to the material hardenability, external dimensions, cavity size and equipment performance of the mold, through multiple tests, the heating rate, holding time, working vacuum, cooling pressure, furnace installation and heating rate of vacuum quenching and tempering are finally determined. method and cooling medium and other heat treatment parameters. The vacuum high pressure gas quenching process curve and the vacuum positive pressure tempering process curve are shown in the figure below.

5.Hardness and metallographic inspection

The hardness and metallographic structure of the vacuum quenched and vacuum tempered molds were tested. Hardness test: cut the vacuum heat treated workpiece with wire EDM, take part A and use HR-150A Rockwell hardness tester to test the hardness along the dotted line shown, the result is 45±1HRC, which meets the technical requirements of 44~48HRC . Metallographic structure inspection: After the hardness test of part A, take two small samples for metallographic inspection. The inspection results show that the structure is diffused crypto-needle martensite + a very small amount of retained austenite. According to the relevant information, the martensite grade is rated as 2, which is ideal.

6.Summary

The one-time investment of vacuum quenching and tempering equipment is large, and the production cost is higher than that of ordinary heat treatment, but the overall economic benefits are significant. Practice has proved that the H13 hot forging die after vacuum quenching and tempering has significantly improved the service life and significantly reduced the amount of deformation. H13 hot forging die adopts vacuum quenching and tempering process, which has important value for promotion.

Selection of vacuum tempering equipment: The RVT series vacuum tempering furnace produced by SIMUWU is a high-quality product for vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum tempering process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.