阅读说明：本技术 易切削铁素体不锈钢及其铸造方法 (Free-cutting ferritic stainless steel and casting method thereof ) 是由 车德会 李建民 张增武 张威 杨红岗 李欢 于 2021-08-03 设计创作，主要内容包括：本发明属于钢铁冶炼技术领域,涉及一种易切削铁素体不锈钢及其铸造方法。本发明的一种易切削铁素体不锈钢,按重量百分比计,包括：0.005％≤C+N≤0.05％,Si 0.3％-0.8％,Mn 0.5％-2.0％,P 0.025％-0.05％,S0.15％-0.40％,Cr 18％-25％,Mo 1.0％-3.5％,Bi 0.05％-0.20％,其余为铁及不可避免的杂质。本发明的易切削铁素体不锈钢,钢锭碳含量低,钢锭内部缺陷少,表面质量佳,避免了开裂问题,可大幅提高后续轧制的成材率,其中开坯成材率提高可至85％,盘条轧制成材率可提高至93％。(The invention belongs to the technical field of steel smelting, and relates to free-cutting ferritic stainless steel and a casting method thereof. The invention relates to free-cutting ferritic stainless steel, which comprises the following components in percentage by weight: 0.005% or more and less than or equal to 0.05% of C and N, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities. The free-cutting ferritic stainless steel has low carbon content in steel ingots, few internal defects in the steel ingots, good surface quality, avoids cracking, and can greatly improve the yield of subsequent rolling, wherein the cogging yield can be improved to 85 percent, and the rolling yield of wire rods can be improved to 93 percent.)

1. A free-cutting ferritic stainless steel characterized by comprising, in weight percent: 0.005% or more and less than or equal to 0.05% of C and N, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities.

2. The free-cutting ferritic stainless steel of claim 1, characterized by comprising, in weight percent: 0.015 percent or more of C and 0.035 percent or less of N, 0.35 to 0.6 percent of Si, 1.0 to 1.5 percent of Mn, 0.03 to 0.04 percent of P, 0.26 to 0.32 percent of S, 19 to 21 percent of Cr, 1.6 to 2.0 percent of Mo and 0.08 to 0.16 percent of Bi.

3. The free-cutting ferritic stainless steel of claim 2, characterized by comprising, in weight percent: c and N are more than or equal to 0.02 percent and less than or equal to 0.03 percent, Si is 0.4 to 0.6 percent, Mn is 1.05 to 1.25 percent, P is 0.03 to 0.04 percent, S is 0.27 to 0.31 percent, Cr is 19.5 to 20.5 percent, Mo is 1.7 to 1.9 percent, Bi is 0.1 to 0.15 percent, and the balance is iron and inevitable impurities.

4. The method of casting a free-cutting ferritic stainless steel as set forth in any of claims 1 to 3, characterized by comprising:

(1) smelting molten steel;

wherein the tapping temperature of the molten steel is 85-120 ℃ higher than the liquidus temperature;

(2) under the protection of argon, pouring molten steel into an ingot mold according to the flow rate of 1.5-2.5 t/min;

(3) standing for 3-6 hours.

5. The method of casting a free-cutting ferritic stainless steel as set forth in claim 4 wherein the molten steel comprises, in weight percent: 0.005% or more and less than or equal to 0.05% of C and N, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities.

6. The method for casting a free-cutting ferritic stainless steel as set forth in claim 4, wherein the flow rate of argon gas is not less than 5m³/min。

7. The method of casting a free-cutting ferritic stainless steel as set forth in claim 4, characterized in that the molten steel is protected with a low-carbon mold flux having a carbon content of 2% or less at the time of casting.

8. A casting method of a free-cutting ferritic stainless steel as set forth in claim 4 wherein the ingot mold is a 5.8 ton square ingot or an 8.4 ton square ingot.

9. A method of casting a free-cutting ferritic stainless steel as set forth in claim 4 wherein the ingot mold is maintained at a temperature of 60 ℃ or higher before casting.

10. The casting method of a free-cutting ferritic stainless steel as set forth in claim 8, wherein the length of the standing time of the 5.8 ton square ingot is 3 to 4.5 hours and the length of the standing time of the 8.4 ton square ingot is 4.5 to 6 hours after completion of the casting.

Technical Field

The invention belongs to the technical field of steel smelting, relates to free-cutting ferritic stainless steel and a casting method thereof, and particularly relates to high-sulfur high-corrosion-resistance ferritic free-cutting stainless steel and a casting method thereof.

Background

The free-cutting stainless steel generally needs to be subjected to cold machining treatment when a precision device is machined, so that the dimensional precision, the mechanical property and the like meet the machining requirements. The super-free-cutting ferritic stainless steel generally adopts a multiphase composite mode to improve the cutting performance of the steel, the S element is a traditional free-cutting element, and when the S element of the steel is more than 0.15%, the cutting performance of the steel is obviously improved. The S element and the Mn element added into the steel form MnS inclusions to break the continuity of matrix tissues, stress concentration and easy chip breaking are generated under the action of a cutter in the cutting process, the cutting force is reduced, and the condition that the winding of filament-shaped chips, the chip removal difficulty and the influence on the cutting process are avoided. In the field, in order to improve the machinability of the free-cutting stainless steel material, Pb is added into the stainless steel material, but because Pb has toxicity, potential harm is generated to a human body in the production process and the product using process.

In addition, the production of ferritic stainless steels has been a problem, and there are few reports on die casting methods for such steels because of the high risk of cracking. Moreover, high sulfur content further deteriorates the toughness of the steel. The surface of the cast steel billet is easy to form steel ingot surface cracks or even fracture, which causes serious influence on the following hot working or even cannot be processed, thereby causing waste products. The high-sulfur ferrite type free-cutting stainless steel has the problems that the control of carbon and nitrogen cannot meet the component requirements of products by adopting high-carbon protective slag and low-flow nitrogen control, and the corrosion resistance of subsequent finished products is greatly influenced.

Disclosure of Invention

The invention aims to provide free-cutting ferritic stainless steel and a casting method thereof aiming at the defects of the prior art.

Specifically, the free-cutting ferritic stainless steel comprises the following components in percentage by weight: 0.005% or more and less than or equal to 0.05% of C and N, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities.

The free-cutting ferritic stainless steel comprises the following components in percentage by weight: 0.015 percent or more of C and 0.035 percent or less of N, 0.35 to 0.6 percent of Si, 1.0 to 1.5 percent of Mn, 0.03 to 0.04 percent of P, 0.26 to 0.32 percent of S, 19 to 21 percent of Cr, 1.6 to 2.0 percent of Mo and 0.08 to 0.16 percent of Bi.

The free-cutting ferritic stainless steel comprises the following components in percentage by weight: c and N are more than or equal to 0.02 percent and less than or equal to 0.03 percent, Si is 0.4 to 0.6 percent, Mn is 1.05 to 1.25 percent, P is 0.03 to 0.04 percent, S is 0.27 to 0.31 percent, Cr is 19.5 to 20.5 percent, Mo is 1.7 to 1.9 percent, Bi is 0.1 to 0.15 percent, and the balance is iron and inevitable impurities.

In another aspect, the present invention provides a method for casting a free-cutting ferritic stainless steel, comprising:

(1) smelting molten steel;

wherein the tapping temperature of the molten steel is 85-120 ℃ higher than the liquidus temperature;

(2) under the protection of argon, pouring molten steel into an ingot mold according to the flow rate of 1.5-2.5 t/min;

(3) standing for 3-6 hours.

According to the casting method of the free-cutting ferritic stainless steel, the molten steel comprises the following components in percentage by weight: 0.005% or more and less than or equal to 0.05% of C and N, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities.

In the casting method of the free-cutting ferritic stainless steel, the flow of the argon is more than or equal to 5m³/min。

According to the casting method of the free-cutting ferritic stainless steel, when the free-cutting ferritic stainless steel is poured, the molten steel is protected by low-carbon protective slag with the carbon content of less than or equal to 2%.

In the casting method of the free-cutting ferritic stainless steel, the ingot mould is a 5.8-ton square ingot or an 8.4-ton square ingot.

In the casting method of the free-cutting ferritic stainless steel, the ingot mold is required to be kept at a temperature of more than 60 ℃ before casting.

According to the casting method of the free-cutting ferritic stainless steel, after the casting is finished, the standing time of the 5.8-ton square ingot is 3-4.5 hours, and the standing time of the 8.4-ton square ingot is 4.5-6 hours.

The technical scheme of the invention has the following beneficial effects:

(1) according to the casting method of the free-cutting ferritic stainless steel, the low-carbon covering slag is adopted to avoid excessive carburization in the casting process, and the high-flow argon is adopted for protection, so that excessive nitrogen increase in the casting process is avoided; by controlling the pouring temperature and the standing time and adopting a large ingot mold and a high riser for pouring, the feeding capacity is enhanced, the cooling speed of the steel ingot is reduced, the cooling stress of the steel ingot is reduced, and the surface cracking caused by the over-quick temperature drop of the steel ingot is avoided;

(2) the free-cutting ferritic stainless steel has low carbon content in steel ingots, few internal defects in the steel ingots, good surface quality, avoids cracking, and can greatly improve the yield of subsequent rolling, wherein the cogging yield can be improved to 85 percent, and the rolling yield of wire rods can be improved to 93 percent;

(3) the free-cutting ferritic stainless steel does not cause use problems such as micro cracks on the surface and in the interior in the subsequent cutting process, and the rejection rate of machined products due to raw material problems can be reduced to be below 0.03%;

(4) the invention has the advantages that when the square slab can not be produced during the slab continuous casting of the slab continuous casting machine with the integral square slab, the die casting production can be unlimited and flexible, and the delivery date can be ensured.

Detailed Description

The present invention will be described in detail with reference to the following embodiments in order to fully understand the objects, features and effects of the invention. The process of the present invention employs conventional methods or apparatus in the art, except as described below. The following noun terms have meanings commonly understood by those skilled in the art unless otherwise specified.

The terms "the," "said," "an," and "an" as used herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. In addition, all ranges disclosed herein are inclusive of the endpoints and independently combinable.

In particular to free-cutting ferritic stainless steel which comprises the following components in percentage by weight,

the method comprises the following steps: 0.005% or more of C + N and 0.05% or less, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities; preferably, the method comprises the following steps: 0.015 percent or more of C and 0.035 percent or less of N, 0.35 to 0.6 percent of Si, 1.0 to 1.5 percent of Mn, 0.03 to 0.04 percent of P, 0.26 to 0.32 percent of S, 19 to 21 percent of Cr, 1.6 to 2.0 percent of Mo, 0.08 to 0.16 percent of Bi and the balance of iron and inevitable impurities; most preferably, it comprises: c and N are more than or equal to 0.02 percent and less than or equal to 0.03 percent, Si is 0.4 to 0.6 percent, Mn is 1.05 to 1.25 percent, P is 0.03 to 0.04 percent, S is 0.27 to 0.31 percent, Cr is 19.5 to 20.5 percent, Mo is 1.7 to 1.9 percent, Bi is 0.1 to 0.15 percent, and the balance is iron and inevitable impurities.

The free-cutting ferritic stainless steel of the present invention has a high S, P element content, which is close to the allowable upper limit of steel. Since the S element forms an MnS phase with Mn in the steel, the S element is a cutting phase with excellent effect commonly used in free-cutting stainless steel. The P element is an element with cold brittleness, and the addition of the P element can reduce the plasticity of steel, so that the steel is more brittle in the cutting process, and the problem of plastic deformation, namely tool sticking, is reduced.

Cr and Mo are typical additive elements of the high-corrosion-resistance ferritic stainless steel, and the Cr and the Mo are matched to form a high PREN value, so that the ferritic stainless steel is better corrosion-resistant.

Bi element is a low-melting point element, plays a role in assisting cutting in the free-cutting stainless steel material, and can soften or melt in the high-speed cutting process, lubricate a cutter, reduce the cutting force, reduce the temperature of the cutter and the like. The product has the similar effect as the traditional Pb element, but has no Pb toxicity, the production process is safe, and the product can not generate potential harm to human bodies in the use process.

In the free-cutting ferritic stainless steel, the ferritic stainless steel has high corrosion resistance and free-cutting property through the synergistic effect of the elements with specific contents, the cogging yield and the wire rod rolling yield are improved, and the use problems of microcracks and the like on the surface and in the interior cannot be caused in the subsequent cutting process.

The free-cutting ferritic stainless steel of the invention is used for producing bloom, bar or wire rod with different specifications.

The free-cutting ferritic stainless steel has very high S content, so that the free-cutting ferritic stainless steel has very excellent cutting performance, has high Cr and Mo content, has corrosion resistance equivalent to that of 304 stainless steel, and belongs to steel grade with excellent corrosion resistance in super-free-cutting ferritic stainless steel.

In another aspect, the present invention provides a method for casting a free-cutting ferritic stainless steel, comprising:

(1) and smelting molten steel.

Wherein, by weight percentage, the molten steel comprises: 0.005% or more of C + N and 0.05% or less, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities; preferably, the method comprises the following steps: 0.015 percent or more of C and 0.035 percent or less of N, 0.35 to 0.6 percent of Si, 1.0 to 1.5 percent of Mn, 0.03 to 0.04 percent of P, 0.26 to 0.32 percent of S, 19 to 21 percent of Cr, 1.6 to 2.0 percent of Mo, 0.08 to 0.16 percent of Bi and the balance of iron and inevitable impurities; most preferably, it comprises: c and N are more than or equal to 0.02 percent and less than or equal to 0.03 percent, Si is 0.4 to 0.6 percent, Mn is 1.05 to 1.25 percent, P is 0.03 to 0.04 percent, S is 0.27 to 0.31 percent, Cr is 19.5 to 20.5 percent, Mo is 1.7 to 1.9 percent, Bi is 0.1 to 0.15 percent, and the balance is iron and inevitable impurities.

The method comprises the following steps: 0.005% or more and less than or equal to 0.05% of C and N, 0.3% -0.8% of Si, 0.5% -2.0% of Mn, 0.025% -0.05% of P, 0.15% -0.40% of S, 18% -25% of Cr, 1.0% -3.5% of Mo, 0.05% -0.20% of Bi, and the balance of iron and inevitable impurities.

Wherein the tapping temperature of the molten steel is 85-120 ℃ higher than the liquidus temperature. When the tapping temperature is less than the minimum of this range, the risk of freezing of the steel during casting may occur, and when the tapping temperature is greater than the maximum of this range, solidification is too slow. Therefore, when the tapping temperature is not in this range, the pouring is rejected.

In a specific embodiment, the liquidus temperature of the molten steel is 1490 ℃ and the tapping temperature of the molten steel is 1575-1610 ℃.

(2) Under the protection of argon, the molten steel is poured into an ingot mould according to the flow rate of 1.5-2.5t/min, and the casting height of a riser is not less than 330 mm.

The ingot mould is kept at a temperature above 60 ℃ before casting.

Preferably, the pouring process adopts argon protection, and the flow of the argon is not less than 5m³Min, thereby avoiding nitrogen increase of the molten steel.

Preferably, during pouring, the molten steel is protected by low-carbon covering slag with carbon content less than or equal to 2%, so that the carbon content is prevented from increasing in the pouring process.

According to the invention, the casting height of the riser is limited to be more than 330mm, so that the heat preservation and feeding effects of the steel ingot can be improved, the temperature drop speed of the steel ingot is reduced, and the stress of the steel ingot is reduced.

Preferably, the ingot mould is a 5.8 ton square ingot or an 8.4 ton square ingot. The square ingot mould with the weight of more than 5.8 tons has higher efficiency, faster pouring and smaller temperature drop of molten steel. And the large steel ingot has slower temperature drop and smaller internal stress.

(3) Standing for 3-6 hours.

The casting method of the free-cutting ferritic stainless steel has the advantages that the standing time after casting is 3-6 hours, the solidification is waited, the solidification time is very short and is less than 50% of the standing time of other steel grades.

Preferably, after the pouring is finished, the standing time of the 5.8-ton square ingot is 3-4.5 hours, and the standing time of the 8.4-ton square ingot is 4.5-6 hours. The short standing time can cause incomplete solidification of molten steel, the long standing time is lower in efficiency, the steel ingot cracking risk can be caused after the standing time is too long, and the steel ingot cracking can be avoided after the steel ingot is charged in a furnace within 6 hours.

The casting method of the free-cutting ferritic stainless steel adopts the low-carbon covering slag to avoid excessive carburization in the casting process, and adopts the high-flow argon protection to avoid excessive nitrogen increase in the casting process. By controlling the pouring temperature and the standing time and adopting a large ingot mold and a high riser for pouring, the feeding capacity is enhanced, the cooling speed of the steel ingot is reduced, the cooling stress of the steel ingot is reduced, and the surface cracking caused by the over-quick temperature drop of the steel ingot is avoided.

Examples

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. Experimental procedures without specifying specific conditions in the following examples were carried out according to conventional methods and conditions.

Example 1

The casting molten steel comprises the following chemical components (in percentage by mass) except iron and inevitable impurity elements:

C+N	Si	Mn	P	S	Cr	Mo	Bi
								0.022	0.42	1.20	0.031	0.30	20.05	1.86	0.15

(1) controlling the tapping temperature of the molten steel to be poured to be in the range of liquidus temperature plus 120 ℃.

(2) The ingot mould adopts a 5.8 ton square ingot, the temperature of the ingot mould is required to be kept above 80 ℃ before casting, and the flow rate of the molten steel is controlled to be 2.1 ton/minute.

(3) The pouring process adopts argon gas sealing protection, and the flow of the argon gas is not less than 7.5m³And/min, adopting low-carbon covering slag with carbon content not more than 1.5% as the casting covering slag.

(4) And (5) standing for 5 hours after pouring, and then performing motor car.

The detection proves that the surface of the steel ingot is good and has no cracks, and the total amount of the components C and N of the steel ingot is 0.024%. The cogging yield is 85 percent, and the wire rod rolling yield is 92.5 percent. The stainless steel bright steel wire with the diameter of 2.3mm produced by the steel ingot is continuously sprayed for 120 hours at 35 ℃ by 5 percent sodium chloride solution, a small amount of rust spots exist, and the rust area is less than 10 percent.

The phi 2.3mm steel wire produced by the steel ingot is used for processing the ball-point pen point on a MULTISTER high-speed machine tool of Mikron, after 500 ten thousand steel wires are continuously processed, the abrasion of a cutter is slight, the produced ball-point pen point still meets the requirements of dimension specifications, the cutter does not need to be replaced, and the cutting performance is excellent.

Example 2

The casting molten steel comprises the following chemical components (in percentage by mass) except iron and inevitable impurity elements:

C	Si	Mn	P	S	Cr	Mo	Bi
								0.035	0.69	1.01	0.031	0.19	18.2	1.2	0.05

(1) controlling the tapping temperature of the molten steel to be poured to be in the range of liquidus temperature plus 100 ℃.

(2) The ingot mould adopts a 5.8 ton square ingot, the temperature of the ingot mould is required to be kept above 80 ℃ before the ingot mould is poured, and the flow rate of the molten steel is controlled at 2.5 ton/minute.

(3) The pouring process adopts argon gas sealing protection, and the flow of the argon gas is not less than 6m³And/min, adopting low-carbon covering slag with carbon content not more than 1.8% as the casting covering slag.

(4) And (5) standing for 5 hours after pouring, and then performing motor car.

The detection proves that the surface of the steel ingot is good and has no cracks, and the total amount of the steel ingot components C and N is 0.037%. The cogging yield is 84.5 percent, and the wire rod rolling yield is 93 percent.

The stainless steel bright steel wire with the diameter of 2.3mm produced by the steel ingot is continuously sprayed for 120 hours at 35 ℃ by 5 percent sodium chloride solution, more rust spots and partial blocks are rusted, and the rusted area is less than 40 percent.

The phi 2.3mm steel wire produced by the steel ingot is used for processing the ball-point pen point on a MULTISTER high-speed machine tool of Mikron, after 300 ten thousand steel wires are continuously processed, the cutter is slightly worn, the position of the cutter needs to be finely adjusted, the continuously produced ball-point pen point still meets the requirements of dimension specifications, the cutter does not need to be replaced, and the cutting performance is good.

Example 3

The casting molten steel comprises the following chemical components (in percentage by mass) except iron and inevitable impurity elements:

C+N	Si	Mn	P	S	Cr	Mo	Bi
								0.015	0.39	1.28	0.038	0.35	24.5	3.1	0.3

(1) controlling the tapping temperature of the molten steel to be poured to be in the range of the liquidus temperature plus 85 ℃.

(2) The ingot mould adopts a 5.8 ton square ingot, the temperature of the ingot mould is required to be kept above 100 ℃ before casting, and the flow rate of the molten steel is controlled to be 1.6 ton/minute.

(3) The pouring process adopts argon gas for sealing protection, and the flow of the argon gas is not less than 9m³And/min, adopting low-carbon covering slag with carbon content not more than 1.1% as the casting covering slag.

(4) And (5) standing for 4 hours after pouring and then performing motor car movement.

The detection proves that the surface of the steel ingot is good and has no cracks, and the total amount of the steel ingot components C + N is 0.017%. The cogging yield is 85.5 percent, and the wire rod rolling yield is 93.5 percent.

The stainless steel bright steel wire with the diameter of 2.3mm produced by the steel ingot is continuously sprayed for 120 hours at 35 ℃ by a 5% sodium chloride solution, a small amount of rust spots exist, and the rust area is less than 5%.

The phi 2.3mm steel wire produced by the steel ingot is used for processing the ball-point pen point on a MULTISTER high-speed machine tool of Mikron, after 500 ten thousand steel wires are continuously processed, the abrasion of a cutter is slight, the produced ball-point pen point still meets the requirements of dimension specifications, the cutter does not need to be replaced, and the cutting performance is excellent.

The present invention has been disclosed in the foregoing in terms of preferred embodiments, but it will be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that all changes and substitutions that are equivalent to these embodiments are deemed to be within the scope of the claims of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined in the claims.