CN86107204A

CN86107204A - The high-frequency isothermic quenching of spheroidal graphite cast iron

Info

Publication number: CN86107204A
Application number: CN 86107204
Authority: CN
Inventors: 何宁; 黄其华
Original assignee: RESEARCH INSTITUTE OF CASTING ELECTRO-MACHINERY ACADEMY BEIJING CHINA
Current assignee: RESEARCH INSTITUTE OF CASTING ELECTRO-MACHINERY ACADEMY BEIJING CHINA
Priority date: 1986-10-15
Filing date: 1986-10-15
Publication date: 1988-05-04

Abstract

本发明提供一种新的球墨铸铁的热处理方法以及相应的球墨铸铁材料。其特点是：用高频加热、等温淬火的方法获得表面层为贝氏体组织，其余部分为铁素体基体或铁素体—珠光体混合基体的球墨铸铁。由于表面组织为贝氏体，所以表面韧性比马氏体高，裂纹倾向较小。方法是表面加热，节省了能耗，缩短了生产周期。由于内部不淬硬，所以比普通等温淬火又具有心部易加工，减噪性好的特点。因此这种材料对于仅仅表面受接触载荷的工件，从性能和经济方面考虑都是适用的。The invention provides a new heat treatment method for ductile iron and corresponding ductile iron material. Its characteristics are: using high-frequency heating and austempering to obtain ductile iron whose surface layer is bainite structure, and the rest is ferrite matrix or ferrite-pearlite mixed matrix. Since the surface structure is bainite, the surface toughness is higher than that of martensite, and the crack tendency is smaller. The method is surface heating, which saves energy consumption and shortens the production cycle. Since the inside is not hardened, it has the characteristics of easy processing of the core and good noise reduction than ordinary austempering. Therefore, this material is suitable for workpieces that are only subjected to contact loads on the surface, both in terms of performance and economy.

Description

High-frequency isothermal quenching of nodular cast iron

The invention relates to a surface heat treatment process of nodular cast iron, in particular to a surface heat treatment process of quenching in an isothermal tank by rapid cooling after high-frequency heating.

The conventional induction hardening of spheroidal graphite cast iron is mainly to obtain a hardened layer having a martensitic structure on the surface, as disclosed in Japanese patent application J53-106322, manufactured by JP ャソマ - デイ - ゼル. The process comprises the following steps: the nodular cast iron of a mixed matrix of ferrite and pearlite is subjected to high-frequency heating to the surface of an element to about 900 ℃, and then is quenched to room temperature. A surface hardened layer of martensite is obtained, the remainder being a mixed matrix of ferrite and pearlite. The surface of such parts has extremely high hardness and wear resistance. And because a large amount of ferrite exists in the parts, the parts have high plasticity and bending resistance.

The problems with this approach are: in the transformation process from austenite to martensite, the specific volume of martensite is larger than that of austenite and is much larger than that of the original structure, which causes large volume expansion and causes increase of internal stress, especially in a high carbon region around graphite. This causes not only a decrease in toughness at the surface of the workpiece, but also a great tendency to crack around martensite or at austenite crystals.

The invention aims to provide a novel heat treatment method of nodular cast iron so as to obtain a nodular cast iron material which has high toughness, high wear resistance, low energy consumption and economic price.

The method provided by the invention comprises the following steps: rapidly heating the ductile cast iron part to over 900-6000 ℃ by high frequency, rapidly immersing the ductile cast iron part into a nitrate medium at 250-400 ℃ after the heating layer is completely austenitized, and preserving the temperature for 30-60 minutes. So as to obtain the material with bainite on the surface of the part and ferrite or ferrite-pearlite on the rest part.

Compared with the technology provided by the Japanese J53-106322 patent, the nodular cast iron material obtained by the method provided by the invention eliminates the tendency that the martensite layer obtained by high-frequency quenching is easy to generate internal stress. Thereby improving the toughness of the casting surface and reducing the formation of cracks. Compared with the common bainite austempering, the method has lower energy consumption and smaller part thermal deformation. This is economical for parts where the surface requires a high toughness and the rest requires a low toughness. On the other hand, the surface induction hardening of spheroidal graphite cast iron is lower in surface hardness (from HRC50 or higher to HRC40 or so) than that of steel, and therefore, it is excellent in workability and has excellent noise reduction properties.

As an application example of the invention, a ductile iron gear with a ferrite matrix is rapidly heated to 900-920 ℃ by a high-frequency heater, and then rapidly quenched into an isothermal nitrate medium with 280 ℃ and kept for 30-60 minutes. Thus, a complete bainite layer of 1 to 4 mm thickness is obtained on the surface of the part. The adjacent bainite layer is an incomplete bainite layer with the thickness of 3-4 mm, and the rest is ferrite.

Claims

1. A surface heat treatment method for nodular cast iron is characterized in that nodular cast iron parts are rapidly heated to 900-1000 ℃ by high frequency. The method is characterized in that after the heating layer is completely austenitized, the parts are quickly put into an isothermal salt tank at 250-400 ℃, and the temperature is kept for 30-60 minutes at the temperature.

2. The article of ductile iron of claim, wherein the surface comprises a bainite structure and the remainder comprises a ferrite matrix or a ferrite-pearlite mixture.

3. The ductile iron part according to claims 1 and 2, wherein the surface of the ductile iron part is a bainite layer with a thickness of 1 to 4 mm, the adjacent bainite layer is an incomplete bainite layer with a thickness of 3 to 4 mm, and the rest is ferrite or a ferrite-pearlite mixed structure.