CN115572910B - High-strength non-quenched and tempered steel for automobile crankshafts and preparation method thereof - Google Patents

Abstract

The invention discloses non-quenched and tempered steel for a high-strength automobile crankshaft and a preparation method thereof, wherein the non-quenched and tempered steel comprises the following elements in percentage by mass: 0.35 to 0.45 percent of C, 0.25 to 0.35 percent of Si, 0.50 to 0.80 percent of Mn, 0.015 to 0.03 percent of Ta, 0.001 to 0.003 percent of B, 0.005 to 0.008 percent of S, less than or equal to 0.0013 percent of O, less than or equal to 0.023 percent of N and the balance of Fe and unavoidable impurities. The processing process of the non-quenched and tempered steel adopts the processes of converter, LF furnace, VD furnace, continuous casting and hot rolling. The invention can avoid the problems of large energy consumption, easy oxidation, cracking and the like in the hardening and tempering process, and solves the problems of poor hardenability and low strength of non-hardened and tempered steel.

Description

A kind of non-quenched and tempered steel for high-strength automobile crankshaft and its preparation method

technical field

The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a high-strength non-quenched and tempered steel for automobile crankshafts and a preparation method thereof.

Background technique

In recent years, the automobile industry has developed rapidly, and the competition in manufacturing costs among various enterprises has become increasingly fierce. At the same time, the industry's requirements for automotive safety, that is, the performance of automotive structural materials, are also getting higher and higher. At present, the traditional quenched and tempered structural material with complex production process, high energy consumption and serious heat treatment defects is gradually being replaced by non-quenched and tempered steel with simple production process, low energy consumption and few defects. The use of non-quenched and tempered technology for the production of structural steel for automobiles has become an important breakthrough to improve the market competitiveness of automobile manufacturers.

The crankshaft is one of the core parts of the automobile engine, and its performance determines the reliability and life of the engine to a large extent. The service conditions of the crankshaft are very harsh, and it bears impact load and inertial force for a long time during work, and its parts produce alternating stresses such as torsion, bending, tension and compression, and shearing. Therefore, the crankshaft must have good appearance quality and microstructure to ensure that the crankshaft has sufficient strength, stiffness, toughness, wear resistance and good balance. For quenched and tempered steel crankshafts, a large amount of energy is consumed during the heat treatment process, and problems such as oxidation, deformation, and even cracking during the heating process of parts will also be brought about. When the crankshaft is heat-treated and quenched, it often bends and twists. It is difficult to meet the requirements of the parts through the straightening process, which will cause insufficient precision of the crankshaft after processing, resulting in noise and vibration of the engine. Non-quenched and tempered steel is more and more widely favored by crankshaft manufacturers for its low cost, energy saving and environmental protection. Among them, hardenability is one of the important indicators of non-quenched and tempered steel, which has a great influence on the uniformity and performance of the structure. However, the hardenability of medium and low carbon manganese non-quenched and tempered steels is low, which is not enough to meet the increasing requirements of automobile companies for material properties. Based on the above requirements, it is imperative to develop non-quenched and tempered steels for automobiles with high hardenability. In addition, due to the harsh working environment of crankshafts, further improvement of the mechanical properties of materials is an inherent requirement of the automotive industry for non-quenched and tempered steels.

Contents of the invention

In order to solve the problems existing in the prior art, the object of the present invention is to provide a kind of non-quenched and tempered steel for high-strength automobile crankshaft and its preparation method. The present invention can avoid the problems of high energy consumption, easy oxidation and cracking in the quenching and tempering process. It also solves the problems of poor hardenability and low strength of non-quenched and tempered steel.

The technical scheme that the present invention adopts is as follows:

A high-strength non-quenched and tempered steel for automobile crankshafts, in terms of mass percentage, its elemental composition includes:

C is 0.35%~0.45%, Si is 0.25%~0.35%, Mn is 0.50%~0.80%, Ta is 0.015%~0.03%, B is 0.001%~0.003%, S is 0.005%~0.008%, O≤ 0.0013%, N≤0.023%, the balance is Fe and unavoidable impurities.

The preparation method of the above-mentioned high-strength automobile crankshaft non-quenched and tempered steel of the present invention comprises the following steps:

Step (1), high-drawing carbon smelting: controlling the carbon content of the converter tapping to 0.15% to 0.25%; controlling the tapping temperature to 1620 to 1650°C;

Step (2), tapping pretreatment: control the amount of slag in the converter during tapping; bake the ladle to 1150-1200°C before tapping, add 1/3 to 1/2 of the total slagging auxiliary materials into the ladle, and continue to bake Bake to 1150～1200℃; add deoxidizer A when tapping to 1/4～1/3 liquid level; add deoxidizer B when tapping to 1/2～3/4;

Step (3), low-oxygen-nitrogen alloying: remove oxygen from the steel to 30ppm-50ppm and add tantalum-iron alloy for alloying; remove N in the steel to 30ppm-40ppm and add ferroboron for alloying; after alloying is completed billet;

Step (4), deformation strengthening treatment: rolling the cast slab, the rolling is divided into two stages, wherein, during the first stage of rolling: the deformation temperature is 950-1100°C, and the deformation is 70%-75% of the total deformation %; during the second stage of rolling: the deformation temperature is 850-900°C, and the deformation is 25%-30% of the total deformation; After air cooling to room temperature, the processing is completed.

Preferably, the amount of slag discharged from the converter in step (2) is controlled at 3-5 kg/t steel.

Preferably, the deoxidizer A is aluminum alloy ash.

Preferably, the deoxidizer B is a silicon-manganese alloy, wherein the ratio of Si content to Mn content is 2-4.

Preferably, the alloying temperature of tantalum iron in step (3) is 1640-1650°C.

Preferably, the tantalum-iron alloying process is carried out in an LF furnace.

Preferably, the boron-iron alloying temperature in step (3) is 1610-1620° C., and the alloying process is carried out after the VD breaks the vacuum.

The present invention has following beneficial effects:

In the non-quenched and tempered steel for the high-strength automobile crankshaft of the present invention, in order to improve the hardenability of the steel, B is added in the composition design, which can significantly improve the hardenability of the steel. In order to improve the strength of the steel, Ta is introduced into the steel. Ta can not only dissolve in the steel to achieve the effect of solid solution strengthening, but also Ta is a strong carbonitride forming element; because the mass fraction of Ta is relatively large, its The diffusion coefficient of Ta is small, so the nucleation work of Ta-containing carbonitrides is large, so the size of the precipitates is very small.

In the preparation method of the non-quenched and tempered steel for high-strength automobile crankshafts of the present invention, the use of high-drawing carbon smelting can effectively reduce the oxygen content in the steel and reduce the burden of subsequent deoxidation; the oxygen content in the steel is reduced, and the added deoxidizer is relatively reduced. The amount of non-metallic inclusions in the steel due to deoxidation is also reduced, which is conducive to the purification of molten steel. The reduction of the amount of oxygen blowing will lead to insufficient molten steel temperature, so a certain molten steel temperature should be guaranteed during the high-drawing carbon smelting process. The addition of slag to steel will lower the temperature of molten steel. Due to the carbon pulling operation, the slag should be baked. Baking the ladle temperature to 1150-1200°C, after reaching the temperature, add some slag-making auxiliary materials, and then bake, this is to prevent the slag from being heated together with the ladle for a long time to cause erosion of the refractory material of the ladle; put the slag Another advantage of baking to 1150-1200°C is that it can quickly slag, and the speed of slag formation is the key to smelting. In addition to a large amount of metal aluminum, aluminum alloy ash also contains some fluorides and oxides, which have a low melting point. Adding it to molten steel can not only effectively reduce the oxygen content in molten steel, but also can be used as a flux to accelerate other Melting of additives. Aluminum deoxidation will produce large-sized Al ₂ O ₃ inclusions, and the fluorides and oxides in aluminum alloy ash will quickly adsorb Al ₂ O ₃ to avoid remaining large-sized inclusions in steel. Silico-manganese deoxidation will form complex silicates, and oxides in the liquid phase in molten steel are easier to remove. Using the composition ratio designed in the present invention can ensure that the inclusions in the liquid phase are generated after silicomanganese deoxidation and are absorbed and removed by slag. The purpose of deoxidizing the aluminum alloy ash first and then deoxidizing the silicomanganese is also to increase the yield of the silicomanganese alloy. As an important rare metal, tantalum is also very active and will combine with oxygen in steel to form oxides; after controlling the oxygen in steel at a lower level, alloying is to prevent its oxidation. The present invention hopes to It exists in steel in the form of alloys. The chemical properties of boron are also very active. It will not only combine with oxygen in steel to form boron oxide, but also combine with nitrogen in steel to form boron nitride. The above-mentioned boron oxides and nitrides will deteriorate the performance of steel. Only solid solution The boron element existing as an interstitial atom in steel can effectively improve the hardenability of steel, so the present invention carries out corresponding process design. The reasons for the two-stage rolling are as follows: the first-stage rolling is to change the size of the steel, the second-stage rolling is to deform and induce nucleation of tantalum carbonitrides, and the heat preservation treatment just after rolling is to make The tantalum-containing carbonitrides in the steel are fully separated to improve the overall performance of the steel.

Detailed ways

The present invention will be further described below in conjunction with the embodiments.

In the non-quenched and tempered steel for the high-strength automobile crankshaft of the present invention, its elemental composition includes:

C is 0.35%~0.45%, Si is 0.25%~0.35%, Mn is 0.50%~0.80%, Ta is 0.015%~0.03%, B is 0.001%~0.003%, S is 0.005%~0.008%, O≤ 0.0013%, N≤0.023%, the balance is Fe and unavoidable impurities.

The overall scheme of the preparation method of the above-mentioned high-strength non-quenched and tempered steel for automobile crankshafts of the present invention adopts the process of converter→LF furnace→VD furnace→continuous casting→hot rolling, which specifically includes the following steps:

Step (1), high-drawing carbon smelting: controlling the carbon content of the converter tapping to 0.15% to 0.25%; controlling the tapping temperature to 1620 to 1650°C;

Step (2), tapping pretreatment: control the amount of slag in the converter during tapping; bake the ladle to 1150-1200°C before tapping, add 1/3 to 1/2 of the total slagging auxiliary materials into the ladle, and continue to bake Bake to 1150-1200°C; add deoxidizer A (using aluminum alloy ash) when tapping to 1/4-1/3 liquid level; add deoxidizer B (using silicon ash) when tapping to 1/2-3/4 Manganese alloy, wherein the ratio of Si content to Mn content is 2-4); the amount of slag discharged from the converter is controlled at 3-5kg/t steel;

Step (3), low-oxygen-nitrogen alloying: Remove oxygen from the steel to 30ppm-50ppm and add tantalum-iron alloy for alloying. The tantalum-iron alloying temperature is 1640-1650°C. The tantalum-iron alloying process is carried out in an LF furnace; N is removed to 30ppm~40ppm and ferroboron is added for alloying. The alloying temperature of ferroboron is 1610~1620℃. The alloying process is carried out after VD breaks the vacuum; after the alloying is completed, it is made into a billet;

Step (4), deformation strengthening treatment: rolling the cast slab, the rolling is divided into two stages, wherein, during the first stage of rolling: the deformation temperature is 950-1100°C, and the deformation is 70%-75% of the total deformation %; during the second stage of rolling: the deformation temperature is 850-900°C, and the deformation is 25%-30% of the total deformation; After air cooling to room temperature, the processing is completed.

Example 1

In the non-quenched and tempered steel for high-strength automobile crankshafts in this embodiment, the elemental composition includes:

C is 0.35%, Si is 0.25%, Mn is 0.50%, Ta is 0.015%, B is 0.001%, S is 0.005%, O is 0.0012%, N is 0.023%, and the balance is Fe and unavoidable impurities.

The preparation method of the non-quenched and tempered steel for the high-strength automobile crankshaft of the present embodiment comprises the following steps:

Step (1), high-drawing carbon smelting: controlling the carbon content of the converter tapping to 0.15%; controlling the tapping temperature to 1620-1650°C;

Step (2), tapping pretreatment: controlling the amount of slag in the converter during tapping; baking the ladle to 1150°C before tapping, adding 1/3 of the total slagging auxiliary materials to the ladle, and continuing to bake to 1150°C; When the steel reaches 1/3 of the liquid level, add deoxidizer aluminum alloy ash; when the steel reaches 1/2, add deoxidizer silicomanganese alloy, wherein the ratio of Si content to Mn content is 2; the amount of slag discharged from the converter is controlled at 3kg/t steel;

Step (3), low-oxygen-nitrogen alloying: Remove oxygen from the steel to 30ppm and add tantalum-iron alloy for alloying. The tantalum-iron alloying temperature is 1640-1650°C. The tantalum-iron alloying process is carried out in an LF furnace; Add ferroboron to 40ppm for alloying, the alloying temperature of ferroboron is 1610～1620℃, the alloying process is carried out after VD breaks the vacuum; after the alloying is completed, it is made into a billet;

Step (4), deformation strengthening treatment: rolling the slab, the rolling is divided into two stages, wherein, during the first stage rolling: the deformation temperature is 980-1100°C, and the deformation amount is 75% of the total deformation amount; During the two-stage rolling: the deformation temperature is 850-890°C, and the deformation is 25% of the total deformation; after the rolling, the rolled material is kept at 650°C for 3 hours, and after the heat preservation, it is air-cooled to room temperature, and the processing is completed.

Example 2

In the non-quenched and tempered steel for high-strength automobile crankshafts in this embodiment, the elemental composition includes:

C is 0.45%, Si is 0.35%, Mn is 0.80%, Ta is 0.03%, B is 0.003%, S is 0.008%, O is 0.0009%, N is 0.020%, and the balance is Fe and unavoidable impurities.

The preparation method of the non-quenched and tempered steel for the high-strength automobile crankshaft of the present embodiment comprises the following steps:

Step (1), high-drawing carbon smelting: controlling the carbon content of the converter tapping to 0.25%; controlling the tapping temperature to 1620-1650°C;

Step (2), tapping pretreatment: controlling the amount of slag in the converter during tapping; baking the ladle to 1200°C before tapping, adding 1/2 of the total slagging auxiliary materials into the ladle, and continuing to bake to 1200°C; When the steel reaches 1/4 liquid level, add deoxidizer aluminum alloy ash; when tapping reaches 3/4, add deoxidizer silicon-manganese alloy, wherein the ratio of Si content to Mn content is 4; the amount of slag discharged from the converter is controlled at 5kg/t steel;

Step (3), alloying with low oxygen and nitrogen: remove the oxygen in the steel to 50ppm and add tantalum iron alloy for alloying. The alloying temperature of tantalum iron is 1640-1650°C. Add ferroboron to 30ppm for alloying, the alloying temperature of ferroboron is 1610～1620℃, the alloying process is carried out after VD breaks the vacuum; after the alloying is completed, it is made into a slab;

Step (4), deformation strengthening treatment: rolling the slab, and the rolling is divided into two stages, wherein, during the first stage of rolling: the deformation temperature is 950-1080°C, and the deformation amount is 70% of the total deformation amount; During two-stage rolling: the deformation temperature is 860-900°C, and the deformation is 30% of the total deformation; after rolling, the rolled material is kept at 700°C for 2 hours, and after the heat preservation, it is air-cooled to room temperature, and the processing is completed.

The specific performance is shown in Table 1.

Example 3

In the non-quenched and tempered steel for high-strength automobile crankshafts in this embodiment, the elemental composition includes:

C is 0.40%, Si is 0.30%, Mn is 0.65%, Ta is 0.020%, B is 0.002%, S is 0.0065%, O≤0.0013%, N≤0.023%, and the balance is Fe and unavoidable impurities.

The preparation method of the non-quenched and tempered steel for the high-strength automobile crankshaft of the present embodiment comprises the following steps:

Step (1), high-drawing carbon smelting: controlling the carbon content of the converter tapping to 0.20%; controlling the tapping temperature to 1620-1650°C;

Step (2), tapping pretreatment: controlling the amount of slag in the converter during tapping; baking the ladle to 1180°C before tapping, adding 2/5 of the total slagging auxiliary materials to the ladle, and continuing to bake to 1170°C; When the steel reaches the liquid level of 7/12, add deoxidizer aluminum alloy ash; when the steel reaches 5/8, add deoxidizer silicon-manganese alloy, wherein the ratio of Si content to Mn content is 4; the amount of slag discharged from the converter is controlled at 4kg/t steel;

Step (3), alloying with low oxygen and nitrogen: remove the oxygen in the steel to 45ppm and add the tantalum iron alloy for alloying. The alloying temperature of the tantalum iron is 1640-1650°C. Add ferroboron to 36ppm for alloying. The alloying temperature of ferroboron is 1610-1620℃. The alloying process is carried out after VD breaks the vacuum; after the alloying is completed, it is made into a billet;

Step (4), deformation strengthening treatment: rolling the slab, the rolling is divided into two stages, wherein, during the first stage of rolling: the deformation temperature is 960-1090°C, and the deformation is 74% of the total deformation; During the two-stage rolling: the deformation temperature is 852-897°C, and the deformation is 26% of the total deformation; after the rolling, the rolled material is kept at 680°C for 2.6 hours, and after the heat preservation, it is air-cooled to room temperature, and the processing is completed.

The specific performance is shown in Table 1.

Example 4

In the non-quenched and tempered steel for high-strength automobile crankshafts in this embodiment, the elemental composition includes:

C is 0.42%, Si is 0.33%, Mn is 0.68%, Ta is 0.025%, B is 0.0025%, S is 0.0075%, O is 0.0010%, N is 0.019%, and the balance is Fe and unavoidable impurities.

The preparation method of the non-quenched and tempered steel for the high-strength automobile crankshaft of the present embodiment comprises the following steps:

Step (1), high-drawing carbon smelting: controlling the carbon content of the converter tapping to 0.23%; controlling the tapping temperature to 1620-1650°C;

Step (2), tapping pretreatment: controlling the amount of slag in the converter during tapping; baking the ladle to 1180°C before tapping, adding 1/2 of the total slag-making auxiliary materials to the ladle, and continuing to bake to 1175°C; When the steel reaches 1/3 of the liquid level, add deoxidizer aluminum alloy ash; when the steel reaches 3/4, add deoxidizer silicomanganese alloy, wherein the ratio of Si content to Mn content is 3.5; the amount of slag discharged from the converter is controlled at 4.3kg/ t steel;

Step (3), low-oxygen-nitrogen alloying: Remove oxygen from the steel to 38ppm and add tantalum-iron alloy for alloying. The tantalum-iron alloying temperature is 1640-1650°C. The tantalum-iron alloying process is carried out in an LF furnace; Add ferroboron to 36ppm for alloying. The alloying temperature of ferroboron is 1610-1620℃. The alloying process is carried out after VD breaks the vacuum; after the alloying is completed, it is made into a billet;

Step (4), deformation strengthening treatment: rolling the slab, the rolling is divided into two stages, wherein, during the first stage of rolling: the deformation temperature is 950-1100°C, and the deformation amount is 73% of the total deformation amount; During the two-stage rolling: the deformation temperature is 850-900°C, and the deformation is 27% of the total deformation; after the rolling, the rolled material is kept at 675°C for 2.6 hours, and after the heat preservation, it is air-cooled to room temperature, and the processing is completed.

The specific performance parameters of the non-quenched and tempered steel prepared in each embodiment are shown in Table 1.

Table 1

As can be seen from Table 1, the non-quenched and tempered steel for high-strength automobile crankshafts prepared by the present invention can effectively avoid problems such as large energy consumption, easy oxidation and cracking caused by quenching and tempering without quenching and tempering treatment, and the crankshaft steel has excellent Excellent hardenability, the depth of the fully hardened zone is 4627-5153μm; high mechanical properties, the microhardness is 340-366HV, the yield strength is 871-890MPa, the tensile strength is 997-1117MPa, and the elongation is 23%-27%. .

Claims (6)

1. a preparation method for high-strength automobile crankshaft non-quenched and tempered steel, characterized in that, in mass percentage, the element composition of described high-strength automobile crankshaft non-quenched and tempered steel comprises: C is 0.35%~0.45%, Si is 0.25%~0.35%, Mn is 0.50%~0.80%, Ta is 0.015%~0.03%, B is 0.001%~0.003%, S is 0.005%~0.008%, O≤ 0.0013%, N≤0.023%, the balance is Fe and unavoidable impurities; The preparation method comprises the following steps: Step (1), high-draw carbon smelting: control the carbon content of the converter tapping at 0.15%~0.25%; control the tapping temperature at 1620~1650°C; Step (2), tapping pretreatment: control the amount of slag in the converter during tapping; bake the ladle to 1150~1200°C before tapping, add 1/3~1/2 of the total slagging auxiliary materials into the ladle, and continue to bake Bake to 1150~1200℃; add deoxidizer A when tapping to 1/4~1/3 liquid level; add deoxidizer B when tapping to 1/2~3/4; Step (3), low oxygen and nitrogen alloying: remove oxygen from steel to 30 ppm~50 ppm and add tantalum iron alloy for alloying; remove N in steel to 30 ppm~40 ppm and add ferroboron for alloying; alloying After completion, it is made into a billet; Step (4), deformation strengthening treatment: rolling the slab, the rolling is divided into two stages, wherein, during the first stage of rolling: the deformation temperature is 950~1100°C, and the deformation is 70%~75% of the total deformation %; during the second stage of rolling: the deformation temperature is 850~900°C, and the deformation is 25%~30% of the total deformation; After air cooling to room temperature, the processing is completed; Deoxidizer A is aluminum alloy ash; Deoxidizer B is silicon-manganese alloy, wherein the ratio of Si content to Mn content is 2~4. 2. The method for preparing high-strength non-quenched and tempered steel for automobile crankshafts according to claim 1, characterized in that the amount of slag discharged from the converter in step (2) is controlled at 3-5 kg/t steel. 3 . The method for preparing a high-strength non-quenched and tempered steel for automobile crankshafts according to claim 1 , wherein the tantalum-iron alloying temperature in step (3) is 1640-1650° C. 4. the preparation method of a kind of high-strength automobile crankshaft non-quenched and tempered steel according to claim 3, is characterized in that, tantalum-iron alloying process is carried out in LF furnace. 5. The method for preparing non-quenched and tempered steel for high-strength automobile crankshafts according to claim 1, characterized in that the ferroboron alloying temperature in step (3) is 1610-1620°C, and the alloying process is carried out at VD After vacuum. 6. A high-strength non-quenched and tempered steel for automobile crankshafts, characterized in that the non-quenched and tempered steel for high-strength automobile crankshafts is produced by the preparation method described in any one of claims 1-5.