Smelting method of 42CrMo4 + HH round steel for ship engine connecting rod

Abstract

The invention discloses a smelting method of 42CrMo4 + HH round steel for a connecting rod of a ship engine, which comprises the following steps: smelting by adopting the working procedures of electric furnace smelting, LF furnace refining, VD refining and die casting, and before the electric furnace smelting, determining the chemical component content of the 42CrMo4 + HH round steel according to the hardenability requirement; during LF furnace refining, a nickel raw material is added, the nickel content in steel is controlled to be 0.05%-0.07%, during die casting, argon protection casting is adopted, low-superheat-degree fast casting solidification is adopted, the casting temperature ranges from 1542 DEG C to 1552 DEG C, the casting superheat degree ranges from 50 DEG C to 55 DEG C, molten steel in each furnace is cast in multiple discs, multiple ingots are arranged in each disc, the ingot body casting speed is controlled to be 0.05 t / min to 0.06 t / min, and the riser casting speed is controlled to be 0.06 t / min to 0.08 t / min. The 42CrMo4 + HH round steel prepared through the method can meet the performance requirements of high hardenability, high strength and high toughness at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for smelting 42CrMo4+HH round steel for a ship engine connecting rod. Background Art

[0002] At present, the connecting rod of PA6 diesel engine for ship is mainly made of 42CrMo4+HH. As one of the key moving parts of diesel engine, the engine connecting rod is subjected to complex alternating loads during operation. The structural strength and reliability of the engine connecting rod have a great impact on the diesel engine. The reliability of the engine connecting rod directly affects whether the whole diesel engine can work normally. The current PA6 diesel engine for ship is a low-speed diesel engine. Different from other medium- and high-speed diesel engines, its connecting rod parts have a complex structure and large size. The stress state and magnitude of the connecting rod during operation are different from those of the connecting rods of other diesel engines. The structural fatigue strength of the connecting rod is required to be higher. Therefore, the 42CrMo4+HH material used to manufacture the engine connecting rod is required to have high hardenability, high strength and high toughness.

[0003] Hardenability refers to the ability of steel to accept quenching to form martensite, which is controlled by the kinetics of the transformation of supercooled austenite of steel into non-martensitic structure. The more stable the supercooled austenite of steel, the smaller its critical cooling rate, the stronger the ability of steel to obtain martensite, and the higher the hardenability. High hardenability is an important indicator to ensure the deformation stability and processability of 42CrMo4+HH after heat treatment. The size of the hardenability bandwidth greatly affects the heat treatment deformation. The narrower the hardenability bandwidth and the smaller the discreteness, the more conducive to the processing of the material. The structural fatigue strength of 42CrMo4+HH connecting rod mainly depends on the strength and toughness of 42CrMo4+HH material. When the strength and toughness of 42CrMo4+HH material are higher, the structural fatigue strength of 42CrMo4+HH connecting rod is also higher.

[0004] However, the 42CrMo4+HH round steel currently produced with conventional composition and conventional process is difficult to simultaneously meet the performance requirements of high hardenability, high strength and high toughness, resulting in poor strength of the engine connecting rod prepared based on the produced 42CrMo4+HH round steel. Summary of the invention

[0005] In order to solve part or all of the technical problems existing in the above-mentioned prior art, the present invention provides a smelting method of 42CrMo4+HH round steel for ship engine connecting rod.

[0006] The technical solution of the present invention is as follows:

[0007] Provided is a method for smelting 42CrMo4+HH round steel for ship engine connecting rods, the method comprising:

[0008] The smelting process is electric furnace smelting + LF furnace refining + VD refining + die casting;

[0009] Before electric furnace smelting, the chemical composition content of 42CrMo4+HH round steel is determined according to the hardenability requirements of 42CrMo4+HH round steel;

[0010] During electric furnace smelting, molten iron and scrap steel are used as raw materials, the proportion of molten iron is controlled to be greater than 70%, slag is strictly prohibited during electric furnace steelmaking, the carbon content of the electric furnace steelmaking is controlled to be 0.22% to 0.25%, the phosphorus content in the steel is controlled to be [P] ≤ 0.012%, and the temperature of the electric furnace steelmaking is controlled to be 1640 to 1660°C;

[0011] During LF furnace refining, calcium-free refining slag with high basicity and high Al2O3 content is used for deep deoxidation and desulfurization, the basicity of the refining slag is controlled to CaO / SiO2=6-7, the Al2O3 content in the refining slag is controlled to 25%-35%, nickel raw materials are added and the nickel content in the steel is controlled to [Ni]=0.05%-0.07%, the oxygen content in the steel is controlled to [O]≤0.0015%, and the sulfur content in the steel is controlled to [S]≤0.002%;

[0012] During VD refining, the holding time under high vacuum is controlled to be 16 to 22 minutes, and hydrogen is determined online. The hydrogen content in the steel is controlled to be [H] ≤ 1.5 ppm, and the calcium content in the steel is controlled to be [Ca] = (7 to 12) × 10 -4 %, Argon soft stirring time is controlled to be 16 to 20 minutes;

[0013] During mold casting, argon gas is used to protect the pouring, and low superheat fast pouring solidification is adopted. Then the steel ingot is sent red, demolded, and cooled in a slow cooling pit. The pouring temperature is controlled at 1542-1552°C, and the pouring superheat is controlled at 50-55°C. Each furnace of molten steel is poured in multiple trays, and each tray has multiple ingots. The pouring speed of the ingot body is controlled at 0.05-0.06t / min, and the pouring speed of the riser is controlled at 0.06-0.08t / min.

[0014] In some optional embodiments, according to the hardenability requirement of 42CrMo4+HH round steel, the chemical composition content of 42CrMo4+HH round steel is determined, including:

[0015] Determine the carbon content in the steel based on the hardness requirement at 1.5mm from the quenched end of the 42CrMo4+HH round steel;

[0016] According to the hardness requirements at 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm and 50mm from the quenching end of 42CrMo4+HH round steel, the content of other chemical components in the steel is determined.

[0017] In some optional embodiments, the carbon content in the steel is determined using the following formula according to the hardness requirement at 1.5 mm from the quenched end of the 42CrMo4+HH round steel:

[0018] J 1.5 (HRC)=35.395+6.990C+312.330C 3 -821.744C 2 +1015.479C 4 -538.346C 5 ;

[0019] Among them, J 1.5 (HRC) represents the hardness value at 1.5 mm away from the quenched end, and the unit is HRC. C represents the mass fraction of carbon content in steel, and the unit is %.

[0020] In some optional embodiments, according to the hardness requirements at 3 mm, 5 mm, 7 mm, 9 mm, 11 mm, 13 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm and 50 mm from the quenched end of the 42CrMo4+HH round steel, the contents of other chemical components in the steel are determined in the following manner:

[0021] According to the required ideal critical diameter, the following formula is used for iterative optimization to determine the content of other chemical components in the steel;

[0022] D I =25.4×f GZ ·f C ·f Mn ·f Si ·f Ni ·f Cr ·f Mo ·f Cu ·f V ;

[0023] Among them, D I Indicates the ideal critical diameter in mm, f GZ Represents the calculation factor corresponding to the grain size, f C Indicates the calculation factor corresponding to the carbon element, f Mn represents the calculation factor corresponding to the manganese element, f Si represents the calculation factor corresponding to silicon, f Ni represents the calculation factor corresponding to the nickel element, f Cr represents the calculation factor corresponding to the chromium element, f Mo represents the calculation factor corresponding to the molybdenum element, f Curepresents the calculation factor corresponding to the copper element, f V represents the calculation factor corresponding to the vanadium element;

[0024] The various calculation factors are determined using the following table:

[0025]

[0026] Among them, the grain size is 7 levels.

[0027] In some optional embodiments, 42CrMo4+HH round steel includes the following chemical components by mass percentage:

[0028] C: 0.41%-0.44%, Si: 0.25%-0.36%, Mn: 0.75%-0.88%, Cr: 1.13%-1.20%, Mo: 0.21%-0.25%, Ni: 0.05%~0.07%, and the balance is Fe and inevitable impurity elements.

[0029] In some optional embodiments, 42CrMo4+HH round steel includes the following chemical components by mass percentage:

[0030] C: 0.41%, Si: 0.26%, Mn: 0.77%, P: 0.008%, S: 0.001%, Cr: 1.15%, Mo: 0.22%, Ni: 0.06%, Cu: 0.01%, and the balance is Fe and inevitable impurity elements.

[0031] In some optional embodiments, the method comprises:

[0032] Before electric furnace smelting, according to the hardenability requirements of 42CrMo4+HH round steel, the chemical composition content of 42CrMo4+HH round steel is determined as follows: C=0.41%, Si=0.26%, Mn=0.77%, P=0.008%, S=0.001%, Cr=1.15%, Mo=0.22%, Ni=0.06%, Cu=0.01%;

[0033] During the electric furnace smelting, 15.3 tons of scrap steel and 69.90 tons of molten iron are used as raw materials for charging the electric furnace, oxygen is blown to melt, foam slag is made, carbon and phosphorus are reduced, and the molten chemical composition is: C=0.21%, Si=0.04%, Mn=0.05%, P=0.008%, S=0.022%, Cr=0.04%, Mo=0.005%, Cu=0.01%, and the electric furnace is tapped. The molten steel temperature is 1658°C. 460kg of lime, 400kg of synthetic slag, 655kg of silicon manganese, 206kg of ferromolybdenum, 1000kg of high chromium, and 253kg of aluminum shot are added with the steel flow.

[0034] During LF furnace refining, the LF station is entered, the molten steel temperature is 1535℃, and the electrochemical slag is sent. The molten steel composition is sampled and analyzed: C=0.25%, Si=0.20%, Mn=0.65%, P=0.009%, S=0.003%, Cr=0.69%, Cu=0.01%, Al=0.030%, Mo=0.010%, Ni=0.01%, slag adjustment and composition adjustment, adding 580kg of high aluminum refining slag, 200kg of high manganese, 49kg of ferrosilicon, 544kg of high chromium, 194kg of micro chromium, 295kg of ferromolybdenum, 103kg of ferronickel, and 68kg of aluminum shot. The molten steel composition is sampled and analyzed: C=0.37%, Si=0.23%, Mn=0.72%、P=0.010%、S=0.001%、Cr=0.77%、Cu=0.01%、Al=0.067%、Mo=0.20%、Ni=0.06%、adjust slag and composition, add 32kg aluminum shot, 49kg high manganese, 12kg ferrosilicon, 13kg micro chromium and 15kg ferromolybdenum, sample and analyze the composition of molten steel: C=0.42%、Si=0.26%、Mn=0.75%、P=0.010%、S=0.001%、Cr=1.01%、Cu=0.01%、Al=0.052%、Mo=0.21%、Ni=0.06%、LF exits the station, and the molten steel temperature is 1660℃;

[0035] During VD refining, the molten steel temperature was 1645°C at the VD station, and the vacuum was evacuated to 60Pa. After 17 minutes, the vacuum was broken. The hydrogen content in the steel was controlled to [H] = 0.5ppm, and the calcium content in the steel was controlled to [Ca] = 7×10 -4 %, argon soft stirring was carried out, the argon soft stirring time was controlled to be 20 minutes, the ladle was added with covering agent and discharged from the station, and the composition of the molten steel discharged from the VD station was: C=0.41%, Si=0.26%, Mn=0.77%, P=0.008%, S=0.001%, Cr=1.15%, Cu=0.01%, Al=0.021%, Mo=0.22%, Ni=0.06%;

[0036] During mold casting, the mold casting station is entered, the molten steel temperature is 1546℃, the sampling argon seal protection pouring, 1.3 tons of pre-flow steel is poured, and 2.1 tons are poured. The mold casting ingot is 5.8t electrode blank. Each furnace of molten steel is poured in three trays, the first tray has 6 ingots, the ingot body is poured for 9 minutes and 5 seconds, and the cap is poured for 7 minutes and 35 seconds, the second tray has 6 ingots, the ingot body is poured for 8 minutes and 22 seconds, and the cap is poured for 8 minutes and 4 seconds, the third tray has 2 ingots, the ingot body is poured for 8 minutes and 52 seconds, and the cap is poured for 5 minutes and 35 seconds. The steel ingots are sent red, demolded, and put into the slow cooling pit for cooling for 24 hours and 10 minutes.

[0037] The main advantages of the technical solution of the present invention are as follows:

[0038] The 42CrMo4+HH round steel prepared by the smelting method of 42CrMo4+HH round steel for ship engine connecting rod of the present invention can simultaneously meet the performance requirements of high hardenability, high strength and high toughness, meet the end quenching performance of 15 points at different distances from the quenching end and meet the high-level hardenability requirements of +HH grade, and the mechanical properties after quenching+tempering heat treatment simultaneously meet the high-strength and high-toughness requirements of yield strength RP0.2≥650MPa, tensile strength Rm≥900MPa, and impact KV≥35J, and can ensure the safety of the connecting rod of a ship diesel engine during use. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] The technical solution provided by the embodiments of the present invention is described in detail below.

[0041] The embodiment of the present invention provides a smelting method of 42CrMo4+HH round steel for ship engine connecting rods, which adopts the process of electric furnace smelting+LF furnace (ladle refining furnace) refining+VD (vacuum degassing refining furnace) refining+die casting to smelt 42CrMo4+HH round steel, wherein:

[0042] Before electric furnace smelting, the chemical composition content of 42CrMo4+HH round steel is determined according to the hardenability requirements of 42CrMo4+HH round steel;

[0043] During electric furnace smelting, molten iron and high-quality scrap steel are used as raw materials, with the proportion of molten iron controlled to be greater than 70%. The content of S, P and other harmful elements is strictly controlled, and the raw and auxiliary materials and alloys are fully baked. It is strictly forbidden to add oxidized slag when tapping steel from an electric furnace. When tapping steel from an electric furnace, the oxidized slag not only has a high oxygen content, but also has a large number of oxidation products. If the oxidized slag from the electric furnace enters the molten steel, it will increase the oxygen content of the molten steel and the total amount of inclusions in the subsequent refining process. The composition and temperature of the steel tapping from the electric furnace are stably controlled, specifically controlling the carbon content of the steel tapping from the electric furnace to be 0.22% to 0.25%, the phosphorus content in the steel to be controlled to be [P] ≤ 0.012%, and the tapping temperature of the electric furnace to be controlled to be 1640 to 1660°C.

[0044] During LF furnace refining, a reasonable refining slag system and deoxidation and desulfurization processes are selected. In the LF refining process, a calcium-free special refining slag with high basicity and high Al2O3 content is used for deep deoxidation and desulfurization to achieve ultra-low oxygen and ultra-low sulfur content control. The oxygen content in the steel is controlled to [O]≤0.0015%, the sulfur content in the steel is controlled to [S]≤0.002%, the refining slag basicity is controlled to R (CaO / SiO2) = 6 to 7, and the alumina (Al2O3) content is controlled to 28% to 40%; Ni microalloying technology is used to improve the high strength and toughness of round steel products, and 0.05%-0.07% Ni is added;

[0045] During VD refining, the VD furnace is kept at high vacuum for 16 to 22 minutes, and hydrogen is determined online. The hydrogen content in the steel is controlled to be [H] ≤ 1.5 ppm, and the calcium content in the steel is controlled to be [Ca] = (7 to 12) × 10 -4 %, Argon soft stirring time is controlled to be 16 to 20 minutes, and the soft stirring effect is preferably such that the slag surface shows obvious creeping and the molten steel is not exposed;

[0046] During mold casting, argon gas is used to protect the pouring, and the pouring temperature and pouring speed are controlled. Low superheat fast pouring solidification is adopted, and then the steel ingot is red-fed, demolded, and cooled in a slow cooling pit. The pouring temperature is controlled at 1542-1552°C, and the pouring superheat is controlled at 50-55°C. Each furnace of molten steel is poured in multiple trays, and each tray has multiple ingots. The ingot body pouring speed is controlled at 0.05-0.06t / min, and the riser pouring speed is controlled at 0.06-0.08t / min. This reduces segregation, realizes uniform control of chemical composition, and controls carbon segregation in the product cross section below 0.05%.

[0047] Further, in the embodiment of the present invention, according to the hardenability requirement of 42CrMo4+HH round steel, the chemical composition content of 42CrMo4+HH round steel is determined, including:

[0048] Determine the carbon content in the steel based on the hardness requirement at 1.5mm from the quenched end of the 42CrMo4+HH round steel;

[0049] According to the hardness requirements at 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm and 50mm from the quenching end of 42CrMo4+HH round steel, the content of other chemical components in the steel is determined.

[0050] Further, in the embodiment of the present invention, according to the hardness requirement at 1.5 mm from the quenched end of the 42CrMo4+HH round steel, the carbon content in the steel is determined using the following formula:

[0051] J 1.5(HRC)=35.395+6.990C+312.330C 2 -821.744C 3 +1015.479C 4 -538.346C 5 ;

[0052] Among them, J 1.5 (HRC) represents the hardness value at 1.5 mm away from the quenched end, and the unit is HRC. C represents the mass fraction of carbon content in steel, and the unit is %.

[0053] Further, in the embodiment of the present invention, according to the hardness requirements at 3 mm, 5 mm, 7 mm, 9 mm, 11 mm, 13 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm and 50 mm from the quenched end of the 42CrMo4+HH round steel, the contents of other chemical components in the steel are determined in the following manner:

[0054] According to the required ideal critical diameter, the following formula is used for iterative optimization to determine the content of other chemical components in the steel:

[0055] D I =25.4×f GZ ·f C ·f Mn ·f Si ·f Ni ·f Cr ·f Mo ·f Cu ·f V ;

[0056] Among them, D I Indicates the ideal critical diameter in mm, f GZ represents the calculation factor corresponding to the grain size, f C Indicates the calculation factor corresponding to the carbon element, f Mn represents the calculation factor corresponding to the manganese element, f Si Represents the calculation factor corresponding to silicon, f Ni represents the calculation factor corresponding to the nickel element, f Cr represents the calculation factor corresponding to the chromium element, f Mo represents the calculation factor corresponding to the molybdenum element, f Cu represents the calculation factor corresponding to the copper element, f V represents the calculation factor corresponding to the vanadium element;

[0057] The various calculation factors are determined using the following table:

[0058]

[0059]

[0060] The grain size is selected according to the actual level. In the embodiment of the present invention, the grain size is level 7.

[0061] Further, in the embodiment of the present invention, the 42CrMo4+HH round steel includes the following chemical components by mass percentage:

[0062] C: 0.41%-0.44%, Si: 0.25%-0.36%, Mn: 0.75%-0.88%, Cr: 1.13%-1.20%, Mo: 0.21%-0.25%, Ni: 0.05%~0.07%, and the balance is Fe and inevitable impurity elements.

[0063] To make the above technical solution of the present invention clearer, the technical solution of the present invention will be described clearly and completely in combination with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0064] Example 1

[0065] In this embodiment 1, the performance requirements for 42CrMo4+HH are as follows: 42CrMo4+HH hardenability meets 15 points and meets the high-level hardenability requirements of +HH grade, specifically requiring J1.5mm=56-61HRC, J3mm=56-61HRC, J5mm=55-61HRC, J7mm=54-60HRC, J9mm=52-60HRC, J11mm=48-59HRC, J13mm=46-59HRC, J15mm=44-58HRC RC, J20mm=41-56HRC, J25mm=39-53HRC, J30mm=38-51HRC, J35mm=36-48HRC, J40mm=36-47HRC, J45mm=35-46HRC, J50mm=34-45HRC, the mechanical properties of 42CrMo4 after HH quenching + tempering heat treatment meet the high strength and high toughness requirements of yield strength RP0.2≥650MPa, tensile strength Rm≥900MPa, and impact KV≥35J.

[0066] Before electric furnace smelting, according to the hardenability requirements of 42CrMo4+HH round steel, the chemical composition content of 42CrMo4+HH round steel is determined as follows: C=0.41%, Si=0.26%, Mn=0.77%, P=0.008%, S=0.001%, Cr=1.15%, Mo=0.22%, Ni=0.06%, Cu=0.01%;

[0067] During the electric furnace smelting, 15.3 tons of scrap steel and 69.90 tons of molten iron are used as raw materials for charging the electric furnace, oxygen is blown to melt, foam slag is made, carbon and phosphorus are reduced, and the molten chemical composition is: C=0.21%, Si=0.04%, Mn=0.05%, P=0.008%, S=0.022%, Cr=0.04%, Mo=0.005%, Cu=0.01%, and the electric furnace is tapped. The molten steel temperature is 1658°C. 460kg of lime, 400kg of synthetic slag, 655kg of silicon manganese, 206kg of ferromolybdenum, 1000kg of high chromium, and 253kg of aluminum shot are added with the steel flow.

[0068] During LF furnace refining, the LF station is entered, the molten steel temperature is 1535℃, and the electrochemical slag is sent. The molten steel composition is sampled and analyzed: C=0.25%, Si=0.20%, Mn=0.65%, P=0.009%, S=0.003%, Cr=0.69%, Cu=0.01%, Al=0.030%, Mo=0.010%, Ni=0.01%, slag adjustment and composition adjustment, adding 580kg of high aluminum refining slag, 200kg of high manganese, 49kg of ferrosilicon, 544kg of high chromium, 194kg of micro chromium, 295kg of ferromolybdenum, 103kg of ferronickel, and 68kg of aluminum shot. The molten steel composition is sampled and analyzed: C=0.37%, Si=0.23%, Mn=0.72%、P=0.010%、S=0.001%、Cr=0.77%、Cu=0.01%、Al=0.067%、Mo=0.20%、Ni=0.06%、adjust slag and composition, add 32kg aluminum shot, 49kg high manganese, 12kg ferrosilicon, 13kg micro chromium and 15kg ferromolybdenum, sample and analyze the composition of molten steel: C=0.42%、Si=0.26%、Mn=0.75%、P=0.010%、S=0.001%、Cr=1.01%、Cu=0.01%、Al=0.052%、Mo=0.21%、Ni=0.06%、LF exits the station, and the molten steel temperature is 1660℃;

[0069] During VD refining, the steel enters the VD station, the temperature of the molten steel is 1645°C, and the steel is evacuated to a vacuum degree of 60Pa. After 17 minutes, the steel is broken. The hydrogen content in the steel is controlled to be [H]=0.5ppm, and the calcium content in the steel is controlled to be [Ca]=7×10-4%. Argon soft stirring is performed, and the argon soft stirring time is controlled to be 20 minutes. The ladle is added with a covering agent and leaves the station. The composition of the molten steel leaving the VD station is: C=0.41%, Si=0.26%, Mn=0.77%, P=0.008%, S=0.001%, Cr=1.15%, Cu=0.01%, Al=0.021%, Mo=0.22%, and Ni=0.06%;

[0070] During mold casting, the mold casting station is entered, the molten steel temperature is 1546℃, the sampling argon seal protection pouring, 1.3 tons of pre-flow steel is poured, and 2.1 tons are poured. The mold casting ingot is 5.8t electrode blank. Each furnace of molten steel is poured in three trays, the first tray has 6 ingots, the ingot body is poured for 9 minutes and 5 seconds, and the cap is poured for 7 minutes and 35 seconds, the second tray has 6 ingots, the ingot body is poured for 8 minutes and 22 seconds, and the cap is poured for 8 minutes and 4 seconds, the third tray has 2 ingots, the ingot body is poured for 8 minutes and 52 seconds, and the cap is poured for 5 minutes and 35 seconds. The steel ingots are sent red, demolded, and put into the slow cooling pit for cooling for 24 hours and 10 minutes.

[0071] The composition and performance of the 42CrMo4+HH round steel prepared by the smelting method of the 42CrMo4+HH round steel for the ship engine connecting rod provided by the embodiment of the present invention were verified, and the results were as follows:

[0072] Chemical composition: C = 0.41%, Si = 0.26%, Mn = 0.77%, P = 0.008%, S = 0.001%, Cr = 1.15%,

[0073] Mo=0.22%, Ni=0.06%, Cu=0.01%;

[0074] Gas content: [H] = 0.88 × 10 -4 %, [O] = 0.0016%;

[0075] Macrostructure level: general looseness 0.5 level, central looseness 0.5 level, ingot-shaped segregation 0 level, point-shaped segregation 0 level;

[0076] Inclusion level: Class A: 0 for fine series and 0 for coarse series; Class B: 0 for fine series and 0 for coarse series; Class C: 0 for fine series and 0 for coarse series; Class D: 0.5 for fine series and 0 for coarse series; Class DS: 0;

[0077] Mechanical properties: yield strength RP0.2=672MPa, tensile strength Rm=952MPa, room temperature impact KV2=51J end quenching test results: 15 points meet the high-level hardenability requirements of +HH grade at the same time, specifically J1.5mm=60HRC, J3mm=60HRC, J5mm=59HRC, J7mm=58HRC, J9mm=57HRC, J11mm=55HRC, J13mm=54HRC, J15mm=53HRC, J20mm=52HRC, J25mm=45HRC, J30mm=45HRC, J35mm=44HRC, J40mm=42HRC, J45mm=38HRC, J50mm=38HRC.

[0078] In summary, compared with the prior art, the smelting method of 42CrMo4+HH round steel for ship engine connecting rod provided by the embodiment of the present invention has the following advantages and beneficial effects:

[0079] The prepared 42CrMo4+HH round steel can simultaneously meet the performance requirements of high hardenability, high strength and high toughness, meet the end quenching performance of 15 points at different distances from the quenching end and meet the high-level hardenability requirements of +HH grade, and the mechanical properties after quenching + tempering heat treatment meet the high strength and high toughness requirements of yield strength RP0.2≥650MPa, tensile strength Rm≥900MPa, and impact KV≥35J, which can ensure the safety of the connecting rod of a marine diesel engine during use.

[0080] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A smelting method of 42CrMo4+HH round steel for ship engine connecting rod, characterized in that: The smelting process is electric furnace smelting + LF furnace refining + VD refining + die casting; Before electric furnace smelting, the chemical composition content of 42CrMo4+HH round steel is determined according to the hardenability requirements of 42CrMo4+HH round steel; During electric furnace smelting, molten iron and scrap steel are used as raw materials, the proportion of molten iron is controlled to be greater than 70%, slag is strictly prohibited during electric furnace steelmaking, the carbon content of the electric furnace steelmaking is controlled to be 0.22% to 0.25%, the phosphorus content in the steel is controlled to be [P] ≤ 0.012%, and the temperature of the electric furnace steelmaking is controlled to be 1640 to 1660°C; During LF furnace refining, calcium-free refining slag with high basicity and high Al2O3 content is used for deep deoxidation and desulfurization, the basicity of the refining slag is controlled to CaO / SiO2=6-7, the Al2O3 content in the refining slag is controlled to 25%-35%, nickel raw materials are added and the nickel content in the steel is controlled to [Ni]=0.05%-0.07%, the oxygen content in the steel is controlled to [O]≤0.0015%, and the sulfur content in the steel is controlled to [S]≤0.002%; During VD refining, the holding time under high vacuum is controlled to be 16 to 22 minutes, and hydrogen is determined online. The hydrogen content in the steel is controlled to be [H] ≤ 1.5 ppm, and the calcium content in the steel is controlled to be [Ca] = (7 to 12) × 10 -4 %, Argon soft stirring time is controlled to be 16 to 20 minutes; During mold casting, argon gas is used to protect the pouring, and low superheat fast pouring solidification is adopted. Then the steel ingot is sent red, demolded, and cooled in a slow cooling pit. The pouring temperature is controlled at 1542-1552°C, and the pouring superheat is controlled at 50-55°C. Each furnace of molten steel is poured in multiple trays, and each tray has multiple ingots. The pouring speed of the ingot body is controlled at 0.05-0.06t / min, and the pouring speed of the riser is controlled at 0.06-0.08t / min.

2. The smelting method of 42CrMo4+HH round steel for ship engine connecting rod according to claim 1, characterized in that: According to the hardenability requirements of 42CrMo4+HH round steel, the chemical composition content of 42CrMo4+HH round steel is determined, including: Determine the carbon content in the steel based on the hardness requirement at 1.5mm from the quenched end of the 42CrMo4+HH round steel; According to the hardness requirements at 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm and 50mm from the quenching end of 42CrMo4+HH round steel, the content of other chemical components in the steel is determined.

3. The smelting method of 42CrMo4+HH round steel for ship engine connecting rod according to claim 2, characterized in that: According to the hardness requirement at 1.5mm from the quenched end of 42CrMo4+HH round steel, the carbon content in the steel is determined using the following formula: J 1.5 (HRC)=35.395+6.990C+312.330C 2 -821.744C 3 +1015.479C 4 -538.346C 5 ; Among them, J 1.5 (HRC) represents the hardness value at 1.5 mm away from the quenched end, and the unit is HRC. C represents the mass fraction of carbon content in steel, and the unit is %.

4. The smelting method of 42CrMo4+HH round steel for ship engine connecting rod according to claim 3, characterized in that: According to the hardness requirements at 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm and 50mm from the quenched end of 42CrMo4+HH round steel, the content of other chemical components in the steel is determined by the following method: According to the required ideal critical diameter, the following formula is used for iterative optimization to determine the content of other chemical components in the steel; D I =25.4×f GZ ·f C ·f Mn ·f Si ·f Ni ·f Cr ·f Mo ·f Cu ·f V ; Among them, D I Indicates the ideal critical diameter in mm, f GZ Represents the calculation factor corresponding to the grain size, f C Indicates the calculation factor corresponding to the carbon element, f Mn represents the calculation factor corresponding to the manganese element, f Si represents the calculation factor corresponding to silicon, f Ni represents the calculation factor corresponding to the nickel element, f Cr represents the calculation factor corresponding to the chromium element, f Mo represents the calculation factor corresponding to the molybdenum element, f Cu represents the calculation factor corresponding to the copper element, f V represents the calculation factor corresponding to the vanadium element; The various calculation factors are determined using the following table: Among them, the grain size is 7 levels.

5. The smelting method of 42CrMo4+HH round steel for ship engine connecting rod according to claim 1, characterized in that: 42CrMo4+HH round steel includes the following chemical components by mass percentage: C: 0.41%-0.44%, Si: 0.25%-0.36%, Mn: 0.75%-0.88%, Cr: 1.13%-1.20%, Mo: 0.21%-0.25%, Ni: 0.05%~0.07%, and the balance is Fe and inevitable impurity elements.

6. The smelting method of 42CrMo4+HH round steel for ship engine connecting rod according to claim 1, characterized in that: 42CrMo4+HH round steel includes the following chemical components by mass percentage: C: 0.41%, Si: 0.26%, Mn: 0.77%, P: 0.008%, S: 0.001%, Cr: 1.15%, Mo: 0.22%, Ni: 0.06%, Cu: 0.01%, and the balance is Fe and inevitable impurity elements.

7. The smelting method of 42CrMo4+HH round steel for ship engine connecting rod according to claim 1, characterized in that: include: Before electric furnace smelting, according to the hardenability requirements of 42CrMo4+HH round steel, the chemical composition content of 42CrMo4+HH round steel is determined as follows: C=0.41%, Si=0.26%, Mn=0.77%, P=0.008%, S=0.001%, Cr=1.15%, Mo=0.22%, Ni=0.06%, Cu=0.01%; During the electric furnace smelting, 15.3 tons of scrap steel and 69.90 tons of molten iron are used as raw materials for charging the electric furnace, oxygen is blown to melt, foam slag is made, carbon and phosphorus are reduced, and the molten chemical composition is: C=0.21%, Si=0.04%, Mn=0.05%, P=0.008%, S=0.022%, Cr=0.04%, Mo=0.005%, Cu=0.01%, and the electric furnace is tapped. The molten steel temperature is 1658°C. 460kg of lime, 400kg of synthetic slag, 655kg of silicon manganese, 206kg of ferromolybdenum, 1000kg of high chromium, and 253kg of aluminum shot are added with the steel flow. During LF furnace refining, the LF station is entered, the molten steel temperature is 1535℃, and the electrochemical slag is sent. The molten steel composition is sampled and analyzed: C=0.25%, Si=0.20%, Mn=0.65%, P=0.009%, S=0.003%, Cr=0.69%, Cu=0.01%, Al=0.030%, Mo=0.010%, Ni=0.01%, slag adjustment and composition adjustment, adding 580kg of high aluminum refining slag, 200kg of high manganese, 49kg of ferrosilicon, 544kg of high chromium, 194kg of micro chromium, 295kg of ferromolybdenum, 103kg of ferronickel, and 68kg of aluminum shot. The molten steel composition is sampled and analyzed: C=0.37%, Si=0.23%, Mn=0.72%、P=0.010%、S=0.001%、Cr=0.77%、Cu=0.01%、Al=0.067%、Mo=0.20%、Ni=0.06%、adjust slag and composition, add 32kg aluminum shot, 49kg high manganese, 12kg ferrosilicon, 13kg micro chromium and 15kg ferromolybdenum, sample and analyze the composition of molten steel: C=0.42%、Si=0.26%、Mn=0.75%、P=0.010%、S=0.001%、Cr=1.01%、Cu=0.01%、Al=0.052%、Mo=0.21%、Ni=0.06%、LF exits the station, and the molten steel temperature is 1660℃; During VD refining, the molten steel temperature was 1645°C at the VD station, and the vacuum was evacuated to 60Pa. After 17 minutes, the vacuum was broken. The hydrogen content in the steel was controlled to [H] = 0.5ppm, and the calcium content in the steel was controlled to [Ca] = 7×10 -4 %, argon soft stirring was carried out, the argon soft stirring time was controlled to be 20 minutes, the ladle was added with covering agent and discharged from the station, and the composition of the molten steel discharged from the VD station was: C=0.41%, Si=0.26%, Mn=0.77%, P=0.008%, S=0.001%, Cr=1.15%, Cu=0.01%, Al=0.021%, Mo=0.22%, Ni=0.06%; During mold casting, the mold casting station is entered, the molten steel temperature is 1546℃, the sampling argon seal protection pouring, 1.3 tons of pre-flow steel is poured, and 2.1 tons are poured. The mold casting ingot is 5.8t electrode blank. Each furnace of molten steel is poured in three trays, the first tray has 6 ingots, the ingot body is poured for 9 minutes and 5 seconds, and the cap is poured for 7 minutes and 35 seconds, the second tray has 6 ingots, the ingot body is poured for 8 minutes and 22 seconds, and the cap is poured for 8 minutes and 4 seconds, the third tray has 2 ingots, the ingot body is poured for 8 minutes and 52 seconds, and the cap is poured for 5 minutes and 35 seconds. The steel ingots are sent red, demolded, and put into the slow cooling pit for cooling for 24 hours and 10 minutes.

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