CN113234992A - High-hardenability medium-carbon MnCrMoB steel for engineering machinery transmission part and manufacturing method thereof - Google Patents

Abstract

The invention relates to high-hardenability medium carbon MnCrMoB steel for an engineering machinery transmission part, which comprises the following chemical components in percentage by weight: 0.30-0.38%, Si: 0.10 to 0.35%, Mn: 1.25-1.50%, Cr: 0.40-0.65%, Ti: 0.020-0.050%, B: 0.0015-0.0040%, Mo: 0.08-0.15 percent of Fe, less than or equal to 0.020 percent of S, less than or equal to 0.025 percent of P, less than or equal to 0.20 percent of Cu, less than or equal to 0.04 percent of Al, less than or equal to 0.0020 percent of O, and the balance of Fe and inevitable impurities. The invention greatly reduces the content of Cr and Mo in the alloy or eliminates the content of Ni by adding a proper amount of B, and the hardenability of the important performance index can meet the requirement of large torsion of the steel for the transmission system of the engineering machinery while reducing the production cost.

Description

High-hardenability medium-carbon MnCrMoB steel for engineering machinery transmission part and manufacturing method thereof

Technical Field

The invention relates to high-hardenability medium-carbon MnCrMoB steel for an engineering machinery transmission part and a manufacturing method thereof. Belongs to the technical field of ferrous metallurgy.

Background

The engineering machinery mainly comprises parts such as excavating machinery, shovel soil transportation machinery, engineering hoisting machinery, forklifts, industrial vehicles and the like. The material for welded structural parts required for manufacturing these machines is generally called steel for construction machines. The engineering machinery has various steel types, except various grades of plates, the steel is used for manufacturing hot rolled bars such as track sections, chain plates, transmission parts, pin shafts and the like, and the hot rolled bars have a plurality of steel types with different components according to different requirements.

In order to meet the severe environment and heavy load in the use of large-scale engineering machinery, the hot-rolled round steel for the engineering machinery is mainly made of common alloy structural steel and carbon steel, the strength of the hot-rolled round steel is further improved by adding V, Ti, Nb and the like on the basis of the existing carbon steel or bonded steel, and in recent years, the hardenability is greatly improved by utilizing B, the performance is improved, the cost is greatly reduced, and a large amount of B-containing steel is developed.

Patent No. CN201110412321.9 provides a quenched and tempered steel for engineering machinery with yield strength of 800MPa grade and a production method thereof, wherein the quenched and tempered steel comprises the following chemical components (by weight): 0.10 to 0.15 percent; si: 0.10 to 0.40 percent; mn: 1.00% -1.60%; cr: 0.10 to 0.50 percent; mo: 0.10 to 0.30 percent; ni: 0.00% -0.20%; b: 0.0010 to 0.0030 percent; nb: 0.000 to 0.030 percent; v: 0.010% -0.050%; ti: 0.010% -0.020%; and (3) Alt: 0.010% -0.050%; p: less than or equal to 0.020%; s: less than or equal to 0.010 percent; the produced 800MPa grade quenched and tempered steel for engineering machinery has good plasticity and toughness matching by optimizing rolling and cooling control and adopting a proper quenching and tempering heat treatment process. However, the steel is expensive and poor in surface quality because of V, Nb and the like.

Patent No. CN201210087346.0 discloses a high-strength wear-resistant steel for engineering machinery and a preparation method thereof. The steel comprises the following components in parts by weight: c: 0.15 to 0.30%, Si: 0.20 to 0.65%, Mn: 1.20-1.60%, S is less than or equal to 0.010%, P is less than or equal to 0.020%, B: 0.0010-0.0040%, Cr: 0.30-1.00%, V: 0.030-0.080%, Al: 0.015-0.050%, [ N ]: 80-200 x 10 < -6 >, less than or equal to 2 x 10 < -6 > for [ H ], lessthan or equal to 40 x 10 < -6 > for [ O ], and the balance of Fe and inevitable impurities. The steel can be used for manufacturing mechanical products in the industries of engineering, mining, construction, agriculture, cement production, ports, electric power, metallurgy and the like which require high strength and high wear resistance. For example, it can be used as steel balls and lining plates of ball mills, bucket teeth of excavators, rolling mortar walls, toothed plates and hammers of various crushers, track shoes of tractors and tanks, scraper blades for bulldozers, shovel teeth, etc. But is not suitable for manufacturing steel for transmission parts of engineering machinery.

Disclosure of Invention

The invention aims to solve the technical problem of providing high-hardenability medium-carbon MnCrMoB steel for engineering machinery transmission parts and a manufacturing method thereof, which aim to solve the technical problem that the high-hardenability medium-carbon MnCrMoB steel for the engineering machinery transmission parts can greatly reduce the contents of Cr and Mo alloys or eliminate the content of Ni by adding a proper amount of B, reduce the production cost and simultaneously meet the requirement of large torsion of the steel for the engineering machinery transmission systems on the hardenability which is an important performance index.

The technical scheme adopted by the invention for solving the problems is as follows: a high-hardenability medium carbon MnCrMoB steel for engineering machinery transmission parts comprises the following chemical components in percentage by weight: 0.30-0.38%, Si: 0.10 to 0.35%, Mn: 1.25-1.50%, Cr: 0.40-0.65%, Ti: 0.020-0.050%, B: 0.0015-0.0040%, Mo: 0.08-0.15 percent of Fe, less than or equal to 0.020 percent of S, less than or equal to 0.025 percent of P, less than or equal to 0.20 percent of Cu, less than or equal to 0.04 percent of Al, less than or equal to 0.0020 percent of O, and the balance of Fe and inevitable impurities.

The main functions and design basis corresponding to each element of the steel chemical composition are as follows:

c is the most basic element in steel and is also the most economic strengthening element. In order to ensure that the transmission part produced by the steel has good obdurability after quenching and tempering and is suitable for surface induction quenching to improve the surface strength, the carbon content range of the steel is determined.

Si as a deoxidizing element increases the hardness, strength, and hardenability of steel in the form of solid solution strengthening. In addition, Si reduces oxidation during frictional heating and increases the cold deformation hardening rate of steel to improve the wear resistance of the material. However, when the Si content is high, the toughness of the steel is lowered, and the Si increases the susceptibility to overheating, cracking, and decarburization tendency in the steel. The invention controls the content of Si to be 0.10-0.35%.

Mn plays a role in solid solution strengthening on steel, and the steel content range is determined by utilizing the characteristics that Mn strongly improves the hardenability of the steel and has low cost.

Cr plays a role in solid solution strengthening on steel, and the content range of the steel is determined by utilizing the principle that Cr is matched with Mo to improve the hardenability of the steel and considering the cost.

Mo is a carbide forming element and can improve the hardenability of steel, refine grains and improve toughness, but the Mo price is high, so the Mo content is determined to be 0.08-0.15% to improve the stability after tempering.

B is a surface active element, boron which is dissolved in austenite in a solid state is adsorbed on a grain boundary to reduce the grain boundary energy, inhibit the proeutectoid ferrite and pearlite nucleation rate, slow down the decomposition of undercooled austenite, delay the transformation of ferrite and improve the hardenability of steel. The hardenability of the steel can be remarkably improved by 1.2 to 2.2 times by adding a trace amount of B (0.0005 to 0.005%) into the steel. According to the existing research results, the effect is equivalent to adding 1.6 percent of Ni, 0.7 percent of Cr, 0.6 percent of Mn or 0.50 percent of Mo, so that the alloy can replace part of precious alloy elements. In order to ensure that the steel has enough effective B, the content of B is controlled to be 0.0015 to 0.0040 percent in the design of the invention

Ti is both a strong carbide former and a strong nitride former. Ti in the steel is combined with C and N to form TiN or Ti (C, N) particles, and the grain growth can be effectively prevented by pinning the grain boundary, so that the effect of refining the grains is achieved. In the invention, Ti must be combined with N in the steel to form TiN so as to play a role of fixing N and protecting B, and meanwhile, the content of Ti cannot be over high, so that on one hand, the cost is higher, and on the other hand, massive TiN compounds can be formed, which is very unfavorable for the quality and refined grains of the steel; therefore, the invention considers the consumption of Ti by the N, O content in the steel, and controls the Ti content to be 0.020-0.050% under the condition that the Ti content in the steel is controlled to be 6.0 ≥ Ti/(N + O) ≥ 5.5.

Generally, P, S is an impurity element and a harmful element, is harmful to the mechanical property and the hot workability of steel and steel balls, and easily forms the defects of segregation, inclusion and the like, thereby causing the obvious reduction of plasticity and impact toughness; the content thereof should be minimized. Considering the cost factors of reducing the P content and the S content, the invention controls the P content to be less than or equal to 0.025 percent and the S content to be less than or equal to 0.020 percent.

Al is an element which is very effective in deoxidation, Al can also be jointed with N to form AlN, and can refine grains, but the temperature of AlN refined grains is limited, and the AlN refined grains cannot refine the grains after the temperature generally exceeds 1000 ℃, and Ti is adopted to refine the grains when the temperature is further increased, so that the method is a very effective measure, and because the heating temperature of the steel rolling and the heating temperature of the steel rolling are far above 1000 ℃, the Al has the main function of deoxidation in the invention; on the other hand, too high an Al content results in the formation of a large amount of brittle inclusions (e.g., Al) in the steel₂O₃Etc.) contamination of molten steel, resulting in a decrease in toughness; further, too high Al content causes deterioration of hot workability of the steel. The invention controls the Al content to be below 0.040%.

The oxygen content represents the total amount of oxide inclusions, the limitation of the oxide brittle inclusions influences the service life of a finished product, and a large number of tests show that the reduction of the oxygen content is obviously beneficial to improving the purity of steel, particularly reducing the content of the oxide brittle inclusions in steel. The oxygen content of the invention is determined to be less than or equal to 0.0020 percent.

The invention relates to a process flow of the high-hardenability medium carbon MnCrMoB steel for the transmission part of the engineering machinery, which comprises the following steps: preparing smelting raw materials according to the chemical element composition of the steel, and sequentially adding molten iron and preferred scrap steel → electric furnace primary smelting → LF furnace refining → VD furnace vacuum degassing → continuous casting 300X 340mm continuous casting blank → continuous heating furnace heating → high-pressure water descaling → rolling → bar slow cooling → finishing and detection-warehousing.

The method comprises the following specific steps:

(1) strengthening the deoxidation of the molten steel in the refining process of an LF furnace, adding FeSi powder and SiC powder into the slag surface for diffusion deoxidation, and strengthening the forced deoxidation of the molten steel by using an Al wire feeding method, wherein Al in the steel is enough to ensure that the vacuum degassed Al is controlled within a target range; (2) after the treatment is carried out for 5-8 minutes under a lower vacuum degree, the molten steel is offline and is subjected to soft argon blowing for more than 30 minutes, and Ti and B are sequentially added to the internal control range 5 minutes before the ladle is hung; (3) in order to reduce component segregation, the continuous casting process adopts crystallizer electromagnetic stirring and secondary cooling section electromagnetic stirring technologies; carrying out anti-oxidation protection pouring on molten steel in the whole continuous casting process; (4) the rolled steel is put into a slow cooling pit for heat preservation at the temperature of over 600 ℃ so as to reduce the hardness and improve the steel structure.

Compared with the prior art, the invention has the advantages that:

1) the steel type is different from CrMo used for a conventional engineering mechanical transmission system or CrNiMo steel which contains high content of Cr and Mo and contains noble element Ni, the content of Cr and Mo is reduced by canceling noble alloy element Ni, B is added, the technical means that Mn and B elements can strongly improve the hardenability is fully utilized, Mn in the steel is improved and the influence effect of Cr and Mo on different depths of the hardenability of the steel is combined, the hardenability depth of the steel is further improved after B is added, so that the hardenability requirement of the steel used for the engineering mechanical transmission system is met, and the steel has higher market competitiveness and popularization value.

2) The steel of the invention adopts the key control technologies of aluminum deep deoxidation, slag high-alkalinity control, increased soft argon blowing time for more than 30 minutes after VD vacuum treatment, protective pouring in the whole continuous casting process and other processes for the electric furnace tapping terminal [ C ] and LF refining process, is different from the limitation of VD high-vacuum degree and vacuum treatment time, ensures the oxygen content in the steel by prolonging the soft argon blowing time, adds FeTi after 5 minutes before ladle lifting, improves the recovery rate of Ti and B, reduces the addition amount, and better plays a role in fixing N and protecting B.

Detailed Description

The present invention will be described in further detail with reference to examples.

First, smelting in an electric furnace

1) The molten iron in the raw materials fed into the furnace accounts for 40-50%, and the balance is selected high-quality scrap steel;

2) the key point control of the electric furnace smelting and tapping process is as follows: controlling the end point tapping carbon of the electric furnace, wherein the end point of [ C ] is not less than 0.10%, and the content of [ P ] is not more than 0.015%; the steel ladle is partially alloyed, and slag-making materials and other deoxidizing agents are quantitatively added, so that lower oxidizing slag is prevented in the EBT tapping process.

Refining in LF furnace

1) Adding 150kg of lime after the LF furnace is powered on for 10 minutes, reinforcing the forced deoxidation of the molten steel by using an Al wire feeding method, adding FeSi powder and SiC powder on the surface of the refined slag for diffusion deoxidation, making higher-alkalinity slag for reinforcing the deoxidation effect, and adding a slag diluting agent to keep good fluidity of the slag;

2) refining and taking a 1 st chemical component sample, adjusting Cr, Mn and Mo to an internal control lower limit, analyzing a 2 nd sample, finely adjusting all components to enter a target value, and tapping at least 5 minutes after the temperature is qualified; the LF refining time is controlled to be 40-50 minutes.

Third, VD vacuum degassing and soft argon blowing

1) Keeping for 5-8 minutes under proper vacuum degree (less than or equal to 500 Pa);

2) after the air is broken, the steel ladle is hung away from the VD tank and the soft argon blowing time is more than or equal to 30 minutes.

3) Sampling and analyzing after soft blowing for 30 minutes, adding FeTi according to the calculated ratio of the contents of Al and N, adding FeB to adjust the content of B to the target content, continuing to soft blow argon for more than 5 minutes, and hoisting to the continuous casting operation.

Fourthly, continuous casting

1) Protecting the casting in the whole continuous casting process, and setting the electromagnetic stirring parameters of a crystallizer and a secondary cooling section;

2) the superheat degree target of the continuous casting molten steel is controlled to be 10-30 ℃, the superheat degree of a first furnace is allowed to be 10 ℃ higher than that of a continuous casting furnace, and the pulling speed is controlled to be 0.5-0.85 m/min;

3) continuous casting blank hot delivery rolling or putting the continuous casting blank into a slow cooling pit at the temperature of more than 500 ℃ for heat preservation for more than 24 hours.

Fifth, rolling

1) Heating the continuous casting billet in a heating furnace in a low-oxidizing atmosphere, controlling the temperature of a preheating section at 400-750 ℃, controlling the temperature of a heating section and the temperature of a soaking section at 1100-1200 ℃, and preserving heat for 3.5-5 hours;

2) the initial rolling temperature is 1000-1100 ℃, and the final rolling temperature is more than or equal to 850 ℃.

3) The steel cooling process comprises the following steps: the steel is put into a pit and slowly cooled to below 200 ℃ at the temperature of above 600 ℃.

Test results in examples of the Steel of the present invention

1) The chemical compositions (wt%) of the examples and comparative examples of the present invention are shown in Table 1.

TABLE 1

Steel grade	C	Si	Mn	P	S	Cr	Ni	Mo	Al
										Example 1	0.34	0.20	1.36	0.015	0.005	0.55	0.03	0.12	0.016
Example 2	0.32	0.25	1.42	0.014	0.002	0.50	0.02	0.13	0.018
										Example 3	0.35	0.19	1.32	0.012	0.003	0.52	0.02	0.10	0.020
Comparative example 1	0.42	0.25	0.68	0.015	0.003	1.05	0.04	0.20	0.025
										Comparative example 2	0.41	0.21	0.65	0.012	0.002	0.75	1.35	0.19	0.023

TABLE 1 (continuation)

Steel grade	Ti	B	Cu	O
					Example 1	0.031	0.0025	0.05	0.0009
Example 2	0.035	0.0035	0.04	0.0010
					Example 3	0.028	0.0018	0.05	0.0070
Comparative example 1	0.005	0.0001	0.04	0.0010
					Comparative example 2	0.003	0.0002	0.06	0.0080

2) The results of hardenability tests for the steel materials of the examples and the comparative examples are shown in Table 2.

TABLE 2

Steel grade	Rolled stock specification, mm	J15,HRC	Quenching temperature of DEG C
				Example 1	φ90	52	850
Example 2	φ80	53	850
				Example 3	φ100	50	850
Comparative example 1	φ80	49	850
				Comparative example 2	φ70	51	850

In addition to the above embodiments, the present invention also includes other embodiments, and any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of the claims of the present invention.

Claims (9)

1. The utility model provides an engineering machine tool transmission part is with medium carbon MnCrMoB steel of high hardenability which characterized in that: the steel grade comprises the following chemical components in percentage by weight: 0.30-0.38%, Si: 0.10 to 0.35%, Mn: 1.25-1.50%, Cr: 0.40-0.65%, Ti: 0.020-0.050%, B: 0.0015-0.0040%, Mo: 0.08-0.15 percent of Fe, less than or equal to 0.020 percent of S, less than or equal to 0.025 percent of P, less than or equal to 0.20 percent of Cu, less than or equal to 0.04 percent of Al, less than or equal to 0.0020 percent of O, and the balance of Fe and inevitable impurities.

2. The high-hardenability medium-carbon MnCrMoB steel for the engineering machinery transmission part according to claim 1, characterized in that: the hardenability of the steel meets that J15 is more than or equal to 46 HRC.

3. The high-hardenability medium-carbon MnCrMoB steel for the engineering machinery transmission part according to claim 1, characterized in that: the Ti content in the steel meets the requirement that the Ti/(N + O) is more than or equal to 6.0 and more than or equal to 5.5.

4. A method for manufacturing high hardenability medium carbon MnCrMoB steel for a transmission member of construction machinery according to claim 1, characterized in that: the method comprises electric furnace smelting → LF furnace refining → VD furnace vacuum degassing → continuous casting → continuous heating furnace heating → high-pressure water descaling → rolling → bar slow cooling → finishing and detecting-warehousing.

5. The manufacturing method of high hardenability medium carbon MnCrMoB steel for engineering machinery transmission parts according to claim 4, characterized by comprising the following steps: the electric furnace smelting specifically comprises the following steps:

1) the molten iron in the raw materials fed into the furnace accounts for 40-50%, and the balance is selected high-quality scrap steel;

2) controlling the end point tapping carbon of the electric furnace, wherein the end point of [ C ] is not less than 0.10%, and the content of [ P ] is not more than 0.015%; the steel ladle is partially alloyed, and slag-making materials and other deoxidizing agents are quantitatively added, so that lower oxidizing slag is prevented in the EBT tapping process.

6. The manufacturing method of high hardenability medium carbon MnCrMoB steel for engineering machinery transmission parts according to claim 4, characterized by comprising the following steps: the LF furnace refining specifically comprises the following steps:

1) replenishing lime after the LF furnace is powered for 10 minutes, strengthening the forced deoxidation of the molten steel by using an Al wire feeding method, adding FeSi powder and SiC powder into the surface of the refined slag for diffusion deoxidation, and adding a slag diluting agent to keep the good fluidity of the slag;

2) refining and taking a 1 st chemical component sample, adjusting Cr, Mn and Mo to an internal control lower limit, analyzing a 2 nd sample, finely adjusting all components to enter a target value, and tapping at least 5 minutes after the temperature is qualified; the LF refining time is controlled to be 40-50 minutes.

7. The manufacturing method of high hardenability medium carbon MnCrMoB steel for engineering machinery transmission parts according to claim 4, characterized by comprising the following steps: the vacuum degassing of the VD furnace specifically comprises the following steps:

1) keeping the vacuum degree less than or equal to 500Pa for 5-8 minutes;

2) after the air is broken, the steel ladle is hung away from the VD tank, and the soft argon blowing time is more than or equal to 30 minutes;

3) sampling and analyzing after soft blowing for 30 minutes, adding FeTi according to the calculated ratio of the contents of Al and N, adding FeB to adjust the content of B to the target content, continuing to soft blow argon for more than 5 minutes, and hoisting to the continuous casting operation.

8. The manufacturing method of high hardenability medium carbon MnCrMoB steel for engineering machinery transmission parts according to claim 4, characterized by comprising the following steps: the continuous casting is protected in the whole process, the superheat degree of the continuous casting molten steel is controlled to be 10-30 ℃, the superheat degree of the first furnace is allowed to be 10 ℃ higher than that of the continuous casting furnace, and the pulling speed is controlled to be 0.5-0.85 m/min.

9. The manufacturing method of high hardenability medium carbon MnCrMoB steel for engineering machinery transmission parts according to claim 4, characterized by comprising the following steps: the rolling process specifically comprises:

1) heating the continuous casting billet in a heating furnace in a low-oxidizing atmosphere, controlling the temperature of a preheating section at 400-750 ℃, controlling the temperature of a heating section and the temperature of a soaking section at 1100-1200 ℃, and preserving heat for 3.5-5 hours;

2) the initial rolling temperature is 1000-1100 ℃, and the final rolling temperature is more than or equal to 850 ℃;

3) after rolling, the rolled steel enters a pit at the temperature of above 600 ℃ and is slowly cooled to below 200 ℃.