阅读说明：本技术 一种对片状石墨铸铁的片状石墨进行尖端钝化的生产方法 (Production method for performing tip passivation on flake graphite of flake graphite cast iron ) 是由 李路峰 刘怀阳 李振豪 郑世佐 郑世佑 李晶晶 陈冠呈 张诗民 于 2019-10-22 设计创作，主要内容包括：本发明公开了一种对片状石墨铸铁的片状石墨进行尖端钝化的生产方法,包括以下步骤：第一步,熔炼,采用中频感应熔炼炉进行熔炼,依次将废铁及废钢进行熔化,同时加入增碳剂和合金元素,炉料熔化后扒净炉渣；第二步,升温,(1)升温至1420-1450℃保温,用炉前热分析铁水成分管理仪进行成分分析,调整成分达到工艺要求；(2)升温至1500-1510℃,铁水包内加入0.3%氮化铬和0.3%蠕化剂,然后覆盖0.5%硅锶合金；第三步,钝化及孕育,铁水出炉并采用冲入法进行钝化处理,浇注时用随流孕育剂进行随流孕育,孕育量为0.1-0.15%；第四步,成型；本发明的对片状石墨铸铁的片状石墨进行尖端钝化的生产方法,能够提高片状石墨铸铁的抗拉强度和减小石墨尖端的缺口敏感性。(The invention discloses a production method for tip passivation of flake graphite cast iron, which comprises the following steps: smelting, namely smelting by adopting a medium-frequency induction smelting furnace, sequentially melting scrap iron and scrap steel, simultaneously adding a carburant and alloy elements, and completely removing furnace slag after furnace burden is melted; secondly, heating up, (1) heating up to 1420-; (2) heating to 1500-1510 ℃, adding 0.3 percent of chromium nitride and 0.3 percent of vermiculizer into the foundry ladle, and then covering 0.5 percent of silicon-strontium alloy; thirdly, passivating and inoculating, namely discharging molten iron and passivating by adopting a flushing method, and carrying out stream inoculation by using a stream inoculant during pouring, wherein the inoculation amount is 0.1-0.15%; fourthly, molding; the production method for passivating the tip of the flake graphite cast iron can improve the tensile strength of the flake graphite cast iron and reduce the notch sensitivity of the graphite tip.)

1. A production method for performing tip passivation on flake graphite of flake graphite cast iron is characterized by comprising the following steps of:

in the first step, smelting is carried out,

smelting by adopting a medium-frequency induction smelting furnace, sequentially smelting 20-50 wt% of scrap iron and 50-80 wt% of scrap steel, simultaneously adding silicon carbide, a recarburizing agent and alloy elements into the medium-frequency induction smelting furnace, and completely removing slag after furnace burden is molten;

in the second step, the temperature is increased,

(1) heating to 1420-;

(2) heating to 1500-1510 ℃, adding 0.3 weight percent of chromium nitride and 0.3 weight percent of vermicular agent into the ladle, and then covering 0.5 weight percent of silicon-strontium alloy;

the third step, passivation and inoculation,

tapping molten iron, passivating by adopting a flushing method, and carrying out stream inoculation by using a stream inoculant during pouring, wherein the inoculation amount is 0.1-0.15%;

the fourth step, the forming,

and cooling and boxing and cleaning the cast iron to finally obtain the iron casting.

2. The method for producing graphite flakes for cast iron graphite flakes according to claim 1, wherein the second step of adjusting the composition to meet process requirements comprises the following steps: and according to the analysis and detection result of the stokehole thermal analysis molten iron composition management instrument, adding alloy elements with required components into the medium-frequency induction smelting furnace until the components detected by the stokehole thermal analysis molten iron composition management instrument are qualified.

3. The method for producing tip-passivated flake graphite of flake graphite cast iron according to claim 1, wherein the passivation in the third step is mainly used for treating cast iron having a carbon content of 3.4-3.6% and a final silicon content of 1.5-2.0%, and the passivation rate of graphite after passivation reaches 30-50%.

4. The method for producing graphite tip passivation for graphite flake cast iron as claimed in claim 1, wherein the inoculation pretreatment is carried out by adding silicon carbide and is 0.8-1% by weight.

5. The method for producing graphite flakes for cast iron flake according to claim 1, wherein the stream inoculant is a rare earth silico-calcium alloy or a rare earth ferrosilicon alloy.

6. The method for producing graphite flakes for use in a cast flake iron of claim 1, wherein said cast iron member has a tensile strength greater than or equal to 25MPa greater than that of cast iron of equivalent composition.

Technical Field

The invention relates to a cast iron production method, in particular to a production method for performing tip passivation on flake graphite of flake graphite cast iron, and belongs to the technical field of brake cast iron production.

Background

The carbon content of the gray cast iron is high (2.7-4.0%), the carbon mainly exists in a flake graphite form, fractures are gray, and the abrasion resistance is good due to the existence of the flake graphite. In gray cast iron, flake graphite is long and thin, has a flat surface and sharp ends, and when subjected to a load, the sharp portions tend to cause stress concentration, which becomes a starting point of breakage of gray cast iron, resulting in a decrease in strength of the cast. In the existing gray cast iron production method, the strength of gray cast iron is often improved by reducing carbon equivalent and increasing alloy elements, the inoculation treatment process is relatively extensive, and the common inoculant in the existing production is ferrosilicon, but the stress concentration of the sharp corner of flake graphite is not improved. Therefore, in order to solve the above problems, it is desired to devise a production method for tip-passivating graphite of flake graphite cast iron.

Disclosure of Invention

In order to solve the problems, the invention provides a production method for carrying out tip passivation on flake graphite of flake graphite cast iron, which reduces stress concentration generated by sharp corners of graphite by passivating the flake graphite; can improve the tensile strength of the flake graphite cast iron and reduce the notch sensitivity of the graphite tip.

The invention relates to a production method for tip passivation of flake graphite cast iron, which comprises the following steps:

in the first step, smelting is carried out,

smelting by adopting a medium-frequency induction smelting furnace, sequentially smelting 20-50 wt% of scrap iron and 50-80 wt% of scrap steel, simultaneously adding silicon carbide, a recarburizing agent and alloy elements into the medium-frequency induction smelting furnace, and completely removing slag after furnace burden is molten;

in the second step, the temperature is increased,

(1) heating to 1420-;

(2) heating to 1500-1510 ℃, adding 0.3 weight percent of chromium nitride and 0.3 weight percent of vermicular agent into the ladle, and then covering 0.5 weight percent of silicon-strontium alloy;

the third step, passivation and inoculation,

tapping molten iron, passivating by adopting a flushing method, and carrying out stream inoculation by using a stream inoculant during pouring, wherein the inoculation amount is 0.1-0.15%;

the fourth step, the forming,

and cooling and boxing and cleaning the cast iron to finally obtain the iron casting.

Further, the specific operation steps for adjusting the components in the second step to meet the process requirements are as follows: and according to the analysis and detection result of the stokehole thermal analysis molten iron composition management instrument, adding alloy elements with required components into the medium-frequency induction smelting furnace until the components detected by the stokehole thermal analysis molten iron composition management instrument are qualified.

Further, the passivation treatment in the third step is mainly used for treating cast iron with the carbon content of 3.4-3.6% and the final silicon content of 1.5-2.0%, and the passivation rate of graphite after passivation reaches 30-50%.

Further, the inoculation pretreatment is carried out by silicon carbide, and the inoculation pretreatment accounts for 0.8 to 1 percent of the total weight.

Furthermore, the stream inoculation agent is rare earth silicon calcium alloy and rare earth silicon iron alloy.

Furthermore, the tensile strength of the iron casting is higher than that of cast iron with the same composition by more than 25 MPa.

Compared with the prior art, the production method for passivating the tips of the flake graphite cast iron has the advantages that nitrogen (N) and Rare Earth (RE) elements are added into molten metal in a certain proportion, so that the two ends of the graphite are passivated, stress concentration is reduced, strength is improved, and the sensitivity of the tip notches of the graphite is reduced; the cast iron produced by the production method is used for the brake drum of the transport vehicle, under the condition that other components are the same, the tensile strength can be improved by more than 25MPa, and meanwhile, because the notch sensitivity is reduced, the phenomena of cracking and cracking of the brake drum can be reduced in frequent braking and large-distance braking, the service life of the brake drum is effectively prolonged, and the after-sale claim rate is reduced.

Detailed Description

The invention relates to a production method for tip passivation of flake graphite cast iron, which comprises the following steps:

in the first step, smelting is carried out,

smelting by adopting a medium-frequency induction smelting furnace, sequentially smelting 20-50 wt% of scrap iron and 50-80 wt% of scrap steel, then adding silicon carbide, a recarburizing agent and alloy elements into the medium-frequency induction smelting furnace, and completely removing furnace slag after furnace burden is molten;

in the second step, the temperature is increased,

(1) heating to 1420-;

(2) heating to 1500-1510 ℃, adding 0.3 weight percent of chromium nitride and 0.3 weight percent of vermicular agent into the ladle, and then covering 0.5 weight percent of silicon-strontium alloy;

the third step, passivation and inoculation,

tapping molten iron, passivating by adopting a flushing method, and carrying out stream inoculation by using a stream inoculant during pouring, wherein the inoculation amount is 0.1-0.15%;

the fourth step, the forming,

and cooling and boxing and cleaning the cast iron to finally obtain the iron casting.

The specific operation steps for adjusting the components in the second step to meet the process requirements are as follows: and according to the analysis and detection result of the stokehole thermal analysis molten iron composition management instrument, adding alloy elements with required components into the medium-frequency induction smelting furnace until the components detected by the stokehole thermal analysis molten iron composition management instrument are qualified.

The passivation treatment in the third step is mainly used for treating cast iron with the carbon content of 3.4-3.6% and the final silicon content of 1.5-2.0%, and the passivation rate of graphite after passivation reaches 30-50%.

The inoculation pretreatment is carried out by silicon carbide, and the silicon carbide accounts for 0.8 to 1 percent of the total weight.

The stream-following inoculant is rare earth silicon-calcium alloy, rare earth silicon-iron alloy or silicon-barium-calcium alloy.

The tensile strength of the iron casting is higher than that of cast iron with the same components by more than 25 MPa.

According to the production method for passivating the tips of the flake graphite cast iron, disclosed by the invention, the stress concentration generated by the sharp corner of the graphite is reduced by passivating the flake graphite; the tensile strength of the flake graphite cast iron can be improved, and the notch sensitivity of the graphite tip can be reduced;

in the flake graphite cast iron, graphite exists in a disordered blade shape, the end part is sharp, stress concentration can be formed, and the two ends of the graphite are passivated by adding a certain proportion of nitrogen (N) and Rare Earth (RE) elements into molten metal, so that the stress concentration is reduced, the strength is improved, and the notch sensitivity of the tip of the graphite is reduced;

the cast iron produced by the production method is used for the brake drum of the transport vehicle, under the condition that other components are the same, the tensile strength can be improved by more than 25MPa, and meanwhile, because notch sensitivity is reduced, the phenomena of cracking and cracking of the brake drum can be reduced in frequent braking and large-distance braking, the service life of the brake drum is effectively prolonged, and the after-sale claim rate is reduced.

The above-described embodiments are merely preferred embodiments of the present invention, and all equivalent changes or modifications of the structures, features and principles described in the claims of the present invention are included in the scope of the present invention.