WO2019169548A1

WO2019169548A1 - Low-strength cast steel micro-alloyed with rare earth

Info

Publication number: WO2019169548A1
Application number: PCT/CN2018/078146
Authority: WO
Inventors: 高海艇
Original assignee: 高海艇
Priority date: 2018-03-06
Filing date: 2018-03-06
Publication date: 2019-09-12

Abstract

A low-strength cast steel micro-alloyed with rare earth. The cast steel has a chemical composition mainly comprising C, Si, Mn, Nb, Ti, Re, La, Ce, P, S, iron and trace impurities, wherein the contents of C, Si, Mn, Nb, Ti, Re, P and S, in mass percentage, are 0.40%-0.5% of C, 0.20%-0.30% of Si, 1.5%-1.69% of Mn, 0.1%-0.8% of Nb, 0.05%-0.12% of Ti, 0.02%-0.22% of Re, 0.2%-0.44% of La, 0.1%-0.29% of Ce, P ≥ 0.045%, and S ≥ 0.020%, respectively, and the total contents of Nb, Ti, La and Ce are less than or equal to 0.6%. The low-strength cast steel micro-alloyed with rare earth can greatly increase the yield strength and tensile strength without significantly reducing the plasticity and toughness. Compared to a common 35SiMn steel, the yield strength of the low-strength cast steel micro-alloyed with rare earth is increased by more than 60MPa and the tensile strength thereof is increased by more than 95MPa.

Description

Low-strength microalloyed rare earth cast steel

Technical field

The invention relates to a cast steel material, in particular to a low-strength micro-alloyed rare earth cast steel suitable for large pressure parts in mines, cement, coal, petroleum and the like, and a smelting and heat treatment process thereof.

Background technique

Large-scale steel castings are characterized by relatively easy forming and low production cost, so they are widely used in mining, cement, petroleum, shipbuilding, etc., but large steel castings are prone to shrinkage, shrinkage, porosity and cracks during the forming process. Such defects, which affect the mechanical properties and service life of large steel castings, cause great losses to enterprises and the national economy. In addition, due to the low cost of intermediate frequency furnace steelmaking, many enterprises in China still use intermediate frequency furnace steelmaking. The steelmaking process generally adopts a non-oxidation method, and the molten steel cannot be dephosphorized and desulfurized, so the quality of the molten steel is poor, which causes the large steel castings to be more prone to structural defects such as casting cracks and pores during the casting process. Its mechanical properties and service life are further reduced.

In addition, silicon and manganese have very rich resources in China, and manganese steel and silicon-manganese steel have high strength, hardness and wear resistance. Therefore, manganese steel and silicon-manganese steel are commonly used materials in large steel castings. . When smelting manganese steel and silicon-manganese steel, ferrosilicon and ferromanganese are often used as alloying elements, while ferrosilicon and ferromanganese have more phosphorus elements, and when using medium frequency furnace steelmaking, it is not possible to dephosphorize and desulfurize molten steel, thereby making manganese steel, The content of phosphorus in silicon-manganese steel is high, even exceeding national standards, and the performance of manganese steel and silicon-manganese steel is not fully utilized.

Chinese patent document CN100999800A (Application No. 200610155704.1) discloses a cast steel containing rare earth elements and a production method thereof, wherein the chemical composition and mass percentage are: C0.24% to 0.32%, Si 1.0% to 1.6%, Mn 1.0% to 1.6%, Cr 0.2% to 0.5%, Re 0.01% to 0.20%, Ni ≤ 0.05%, Mo ≤ 0.01%, P ≤ 0.035%, S ≤ 0.010%, B ≤ 0.05%, The amount is iron and inevitable impurities. The content of Si in the cast steel is high, which tends to cause deterioration in the ductility, toughness and cutting performance of the steel casting. At the same time, the total content of P plus S is relatively high, thereby further reducing the plasticity and toughness of the steel casting.

Therefore, there is an urgent need to develop a low-strength microalloyed rare earth cast steel capable of lowering the contents of P and S elements and a preparation method thereof, and no technical solutions identical or similar to those of the present invention have been found by searching.

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-strength microalloyed rare earth cast steel capable of reducing the content of P and S elements and a method for preparing the same, which solves one or more of the above problems of the prior art.

According to the invention, a low-strength micro-alloyed rare earth cast steel is innovative in that the main chemical components of the cast steel include C, Si, Mn, Nb, Ti, Re, La, Ce, P, S, iron and trace amounts. The impurity content, the mass percentages of the C, Si, Mn, Nb, Ti, Re, P, and S are respectively C0.40% to 0.5%, Si 0.20% to 0.30%, and Mn 1.5% to 1.69%. Nb 0.1% to 0.8%, Ti 0.05 to 0.12%, Re 0.02% to 0.22%, La 0.2% to 0.44%, Ce 0.1% to 0.29%, P ≥ 0.045%, and S ≥ 0.020%.

Preferably, the total content of Nb, Ti, La, Ce is less than or equal to 0.6%.

A smelting method for low-strength microalloyed rare earth cast steel, which is smelted by an intermediate frequency induction furnace, and the smelting process comprises the following steps:

1) Pretreatment: bake steel, alloying elements and ladle before smelting, reduce the content of water and gas, and remove mud and rust on the surface of scrap steel;

2) Ingredients: The yield of alloying elements C, Si and Mn is calculated according to the yield of C, Si and Mn in ZG35SiMn low alloy cast steel. The content of microalloying elements Nb, Ti, La and Ce is based on the chemical composition of steel. Request a ratio;

3) Loading and feeding: large, medium and small metal charge is added according to about 1:4:2 when charging, large metal charge is put into the bottom of the furnace, and small metal charge is put into the large metal charge and the bottom of the furnace. The gap between the furnaces ensures that the charge in the furnace body is tightly closed; the added charge is made of small pieces of metal;

4) Adding alloy: After the scrap steel in the furnace is melted, some ferromanganese and ferrosilicon alloys are pre-added. After the chemical composition of the molten steel before the furnace is detected, the final required ferromanganese and ferrosilicon alloys are added according to the test results, and the first Adding ferromanganese and adding ferrosilicon in sequence; Nb, Ti, La, Ce and other alloying elements are pre-added to the bottom of the ladle after drying; when the steel is tapped, carbon powder is poured into the molten steel to increase carbon;

5) tapping: according to step 4), the chemical composition in the molten steel is adjusted, and the tapping temperature is controlled at 1650 ° C ~ 1680 ° C. Immediately after tapping, a proper amount of slag forming agent is sprinkled on the ladle liquid surface;

6) Final deoxidation: the final deoxidation is carried out with pure aluminum during tapping. The pure aluminum block is added to the bottom of the ladle in advance. When the molten steel impacts the bottom of the ladle, the pure aluminum is melted and reacted with the oxygen in the molten steel for deoxidation. The amount of pure aluminum added is The quality of the molten steel is 0.050% to 0.125%, and the residual aluminum content in the low strength microalloyed rare earth cast steel is 0.03% to 0.08%;

7) Casting: The molten steel in the step 6) is poured into the pre-prepared mold, and the pouring temperature is controlled at 1550 ° C ~ 1580 ° C. After cooling and removing the mold, the low-strength micro-alloyed rare earth cast steel is obtained. Pieces.

Preferably, the ferromanganese, the ferrosilicon alloy and the rare earth Nb, Ti, La, Ce, etc. are baked and dried for 2 to 5 hours before the addition, and the baking drying temperature is 100 to 300 °C.

Preferably, the temperature range of the pre-manganese iron and the ferrosilicon alloy is controlled at 1640 ° C to 1660 ° C. After the chemical composition of the molten steel in front of the furnace is detected, the final required ferromanganese or ferrosilicon alloy is added; First, a ferromanganese alloy is added, and after the manganese-iron alloy is completely melted and the slag is completed, a ferrosilicon alloy is added.

Preferably, the microalloying elements such as Nb, Ti, La, Ce, etc. are added to the bottom of the ladle in the form of a metal powder.

Preferably, the normalizing treatment and the tempering treatment are two parts; the normalizing treatment process is: heating in a box type electric resistance furnace at a speed of 80 ° C / h to 120 ° C / h to 860 ° C ~ 960 ° C, the holding time is The thickness of the steel casting (mm) × 1.5 ~ 1.8min / h, and then the steel castings are cooled to room temperature in air;

The tempering heat treatment process is: heating in a box type electric resistance furnace at a speed of 80 ° C / h to 120 ° C / h to 600 ° C ~ 650 ° C, the holding time is the thickness of the steel casting (mm) × 1.8 ~ 2.2 min / h, The steel castings are then cooled to room temperature in air; the time between normalizing and tempering does not exceed 6 h.

Preferably, after the heat treatment of the steel casting, the tensile strength is greater than or equal to 720 MPa, the yield strength is greater than or equal to 480 MPa, the elongation is greater than or equal to 12%, the area shrinkage is greater than or equal to 14%, and the impact test temperature is 4 ° C. The work is greater than or equal to 9J.

An advantage of the present invention is that the low strength microalloyed rare earth cast steel of the present invention can significantly improve yield strength and tensile strength without significantly reducing plasticity and toughness. Compared with ordinary 35SiMn steel, the low-strength micro-alloyed rare earth cast steel can increase the yield strength by more than 60 MPa, and the tensile strength can be increased by more than 95 MPa.

Detailed ways

A low-strength microalloyed rare earth cast steel, the main chemical composition of the cast steel includes C, Si, Mn, Nb, Ti, Re, La, Ce, P, S, iron and trace impurity elements, the C, Si, The mass percentages of Mn, Nb, Ti, Re, P, and S are C0.40% to 0.5%, Si 0.20% to 0.30%, Mn 1.5% to 1.69%, and Nb 0.1% to 0.8%, respectively. Ti 0.05 to 0.12%, Re 0.02% to 0.22%, La 0.2% to 0.44%, Ce 0.1% to 0.29%, P ≥ 0.045%, S ≥ 0.020%; total of Nb, Ti, La, Ce The content is less than or equal to 0.6%.

A smelting method for low-strength microalloyed rare earth cast steel is carried out by using an intermediate frequency induction furnace for smelting, and the smelting process comprises the following steps: pretreatment: baking scrap steel, alloying elements and ladle before smelting, reducing the content of water and gas therein, And remove the dirt and rust on the surface of the scrap steel; ingredients: the yield of alloying elements C, Si, Mn is calculated according to the yield of C, Si, Mn in ZG35SiMn low alloy cast steel, microalloying elements Nb, Ti, La, The content of Ce is proportioned according to the chemical composition requirements of steel; charging and feeding: large, medium and small metal charge is added according to about 1:4:2 during charging, and bulk metal charge is put into the bottom of the furnace, small piece of metal The charge is placed in the gap between the bulk metal charge and the bottom of the furnace to ensure that the charge in the furnace body is tightly closed; the added charge is made of small metal; the alloy is added: after the steel is melted in the furnace, a portion of ferromanganese and silicon are pre-added. Ferroalloy, after the chemical composition of the molten steel in front of the furnace is detected, the final required ferromanganese and ferrosilicon alloy are added according to the test results, and the ferromanganese is added first, followed by the addition of ferrosilicon; Nb, Ti, La, Ce, etc. After the alloying elements are dried First, add the bottom of the ladle; when the steel is tapped, pour the carbon powder into the molten steel to increase the carbon; tapping: adjust the chemical composition in the molten steel according to the previous step, and tap the steel. The tapping temperature is controlled at 1650 ° C ~ 1680 ° C, tapping Immediately afterwards, sprinkle an appropriate amount of slag-forming agent on the ladle surface; final deoxidation: final deoxidation with pure aluminum during tapping, pre-adding pure aluminum block to the bottom of the ladle, and molten steel melts the bottom of the ladle to melt the pure aluminum and the molten steel The oxygen is reacted for deoxidation, and the amount of pure aluminum added is 0.050% to 0.125% of the quality of the molten steel, and the residual aluminum content in the low-strength microalloyed rare earth cast steel is 0.03% to 0.08%; pouring: step 6) ladle The molten steel is poured into a pre-prepared mold, and the pouring temperature is controlled at 1550 ° C to 1580 ° C. After cooling and removing the mold, the low-strength micro-alloyed rare earth cast steel piece is obtained.

Ferromanganese, ferrosilicon and rare earth Nb, Ti, La, Ce, etc. should be baked and dried for 2~5h before baking, the baking drying temperature is 100~300°C, and the temperature range of pre-added ferromanganese and ferrosilicon alloy is controlled at 1640°C. ~1660 ° C, after the chemical composition of the molten steel in front of the furnace is to be tested, the final required ferromanganese and ferrosilicon alloy are added; the order of the two alloys is first added with ferromanganese alloy, after all the ferromanganese alloy is melted and the slag is completed, Further, a ferrosilicon alloy is added, and microalloying elements such as Nb, Ti, La, and Ce are added to the bottom of the ladle in the form of a metal powder.

Normalizing treatment and tempering treatment; the normalizing treatment process is: heating in a box type resistance furnace at a speed of 80 ° C / h ~ 120 ° C / h to 860 ° C ~ 960 ° C, holding time for the steel castings Thickness (mm) × 1.5 ~ 1.8min / h, and then the steel castings are cooled to room temperature in air; tempering heat treatment process: in a box-type resistance furnace at 80 ° C / h ~ 120 ° C / h speed to 600 ° C ~ 650 ° C, holding time is the thickness of the steel castings (mm) × 1.8 ~ 2.2min / h, and then the steel castings are cooled to room temperature in air; normalizing and tempering time interval not more than 6h, cast steel After heat treatment, the tensile strength is greater than or equal to 720MPa, the yield strength is greater than or equal to 480MPa, the elongation is greater than or equal to 12%, the area shrinkage is greater than or equal to 14%, and the impact absorption at 4°C is greater than or equal to 9J.

The low-strength microalloyed rare earth cast steel of the present invention can significantly improve the yield strength and the tensile strength without significantly reducing the plasticity and toughness. Compared with ordinary 35SiMn steel, the low-strength micro-alloyed rare earth cast steel can increase the yield strength by more than 60 MPa, and the tensile strength can be increased by more than 95 MPa.

The above is only a preferred mode of the present invention, and it should be noted that various similar modifications and improvements can be made by those skilled in the art without departing from the inventive concept. Within the scope of protection of the present invention.

Claims

A low-strength microalloyed rare earth cast steel characterized in that: the main chemical components of the cast steel include C, Si, Mn, Nb, Ti, Re, La, Ce, P, S, iron and trace impurity elements, The mass percentages of C, Si, Mn, Nb, Ti, Re, P, and S are respectively C 0.40% to 0.5%, Si 0.20% to 0.30%, Mn 1.5% to 1.69%, and Nb 0.1% to 0.8. %, Ti 0.05 to 0.12%, Re 0.02% to 0.22%, La 0.2% to 0.44%, Ce 0.1% to 0.29%, P ≥ 0.045%, and S ≥ 0.020%.
A low-strength microalloyed rare earth cast steel according to claim 1, wherein the total content of the Nb, Ti, La, and Ce is less than or equal to 0.6%.
The smelting method for a low-strength microalloyed rare earth cast steel according to claim 1, wherein the smelting process is performed by using an intermediate frequency induction furnace, wherein the smelting process comprises the following steps:

1) Pretreatment: bake steel, alloying elements and ladle before smelting, reduce the content of water and gas, and remove mud and rust on the surface of scrap steel;

2) Ingredients: The yield of alloying elements C, Si and Mn is calculated according to the yield of C, Si and Mn in ZG35SiMn low alloy cast steel. The content of microalloying elements Nb, Ti, La and Ce is based on the chemical composition of steel. Request a ratio;

3) Loading and feeding: large, medium and small metal charge is added according to about 1:4:2 when charging, large metal charge is put into the bottom of the furnace, and small metal charge is put into the large metal charge and the bottom of the furnace. The gap between the furnaces ensures that the charge in the furnace body is tightly closed; the added charge is made of small pieces of metal;

4) Adding alloy: After the scrap steel in the furnace is melted, some ferromanganese and ferrosilicon alloys are pre-added. After the chemical composition of the molten steel before the furnace is detected, the final required ferromanganese and ferrosilicon alloys are added according to the test results, and the first Adding ferromanganese and adding ferrosilicon in sequence; Nb, Ti, La, Ce and other alloying elements are pre-added to the bottom of the ladle after drying; when the steel is tapped, carbon powder is poured into the molten steel to increase carbon;

5) tapping: according to step 4), the chemical composition in the molten steel is adjusted, and the tapping temperature is controlled at 1650 ° C ~ 1680 ° C. Immediately after tapping, a proper amount of slag forming agent is sprinkled on the ladle liquid surface;

6) Final deoxidation: the final deoxidation is carried out with pure aluminum during tapping. The pure aluminum block is added to the bottom of the ladle in advance. When the molten steel impacts the bottom of the ladle, the pure aluminum is melted and reacted with the oxygen in the molten steel for deoxidation. The amount of pure aluminum added is The quality of the molten steel is 0.050% to 0.125%, and the residual aluminum content in the low strength microalloyed rare earth cast steel is 0.03% to 0.08%;

7) Casting: The molten steel in the step 6) is poured into the pre-prepared mold, and the pouring temperature is controlled at 1550 ° C ~ 1580 ° C. After cooling and removing the mold, the low-strength micro-alloyed rare earth cast steel is obtained. Pieces.
The method for smelting low-strength microalloyed rare earth cast steel according to claim 3, characterized in that the ferromanganese, the ferrosilicon alloy and the rare earths Nb, Ti, La, Ce, etc. are baked before being added. Dry for 2 to 5 hours, and the baking drying temperature is 100 to 300 °C.
The method for smelting a low-strength microalloyed rare earth cast steel according to claim 3, wherein the temperature range of the pre-manganese iron and the ferrosilicon alloy is controlled at 1640 ° C to 1660 ° C, and the molten steel before the furnace is to be detected After the chemical composition, the final required ferromanganese and ferrosilicon alloys are added; the order of the two alloys is first added with ferromanganese alloy. After the ferromanganese alloy is completely melted and the slag is completed, the ferrosilicon alloy is added.
The method for smelting a low-strength microalloyed rare earth cast steel according to claim 3, wherein the microalloying elements such as Nb, Ti, La, and Ce are added to the bottom of the ladle in the form of a metal powder.
A heat treatment method for a low-strength microalloyed rare earth cast steel according to claim 1, comprising: a normalizing treatment and a tempering treatment; the normalizing treatment process is: in a box type resistor The furnace is heated at a rate of 80 ° C / h ~ 120 ° C / h to 860 ° C ~ 960 ° C, the holding time is the thickness of the steel casting (mm) × 1.5 ~ 1.8min / h, and then the steel castings are cooled in air to Room temperature

The tempering heat treatment process is: heating in a box type electric resistance furnace at a speed of 80 ° C / h ~ 120 ° C / h to 600 ° C ~ 650 ° C, the holding time is the thickness of the steel casting (mm) × 1.8 ~ 2.2 min / h, then the steel castings are cooled to room temperature in air; the time between normalizing and tempering does not exceed 6 h.
The method for heat-treating a low-strength microalloyed rare earth cast steel according to claim 7, wherein the steel casting has a tensile strength of 720 MPa or more and a yield strength of 480 MPa or more after heat treatment. The rate is greater than or equal to 12%, the area shrinkage is 14% or more, and the impact absorption at 4°C is greater than or equal to 9J.