CN113604734A

CN113604734A - Ultra-thick gauge low residual stress forklift steel and preparation method thereof

Info

Publication number: CN113604734A
Application number: CN202110789241.9A
Authority: CN
Inventors: 李艳; 王中学; 麻衡; 杜传治; 于全成; 霍孝新; 倪凯; 李文强; 王月香; 何康; 刘俊宝
Original assignee: Laiwu Steel Group Yinshan Section Steel Co Ltd
Current assignee: Laiwu Steel Group Yinshan Section Steel Co Ltd
Priority date: 2021-07-13
Filing date: 2021-07-13
Publication date: 2021-11-05

Abstract

The invention provides ultra-thick gauge low residual stress steel for a forklift and a preparation method thereof, wherein the steel for the forklift with the low residual stress comprises the following chemical components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.15 percent, Si is more than or equal to 0.30 percent and less than or equal to 0.30 percent, Mn is more than or equal to 1.45 percent and less than or equal to 0.010 percent and less than or equal to 0.018 percent and less than or equal to 0.012 percent, Nb is more than or equal to 0.035 percent and less than or equal to 0.020 percent, Cr is more than or equal to 0.030 percent and less than or equal to 0.010 percent and less than or equal to 0.020 percent, Als is more than or equal to 0.040 percent and the balance is iron and inevitable impurities, wherein the Als is acid soluble aluminum, and the low residual stress ensures that a steel plate does not deform when a user cuts and welds.

Description

Ultra-thick gauge low residual stress forklift steel and preparation method thereof

Technical Field

The invention relates to the field of steel smelting, in particular to ultra-thick gauge low residual stress forklift steel and a preparation method thereof.

Background

Residual Stress (Residual Stress) refers to the internal Stress of self-equilibrium that remains in the object after the action of external force or uneven temperature field, etc. is eliminated. Both machining and strengthening processes can cause residual stresses such as cold drawing, bending, machining, rolling, shot blasting, casting, forging, welding, and heat treating the metal. Residual stresses are generally detrimental, as they can cause warping or distortion, and even cracking, of the part after improper heat treatment, welding, or machining of the part. The presence of residual stresses sometimes does not immediately manifest itself as a defect, but cracks and breakages occur when the total stress exceeds the strength limit during operation due to the superposition of operating stresses and residual stresses. The residual stress of the part can be largely eliminated by appropriate heat treatment.

The forklift matching parts need to weld the steel plate after cutting, and in order to avoid deformation after cutting and welding, the steel plate needs to be subjected to heat treatment to eliminate residual stress. The user provides the chemical composition and mechanical property requirements of the steel for the forklift, and the thickness specification of the steel for the forklift with low residual stress is that h is more than 60mm and less than or equal to 100mm, as shown in tables 1 and 2.

TABLE 1 chemical composition (wt%)

C	Si	Mn	P	S
					≤0.18	≤0.55	≤1.70	≤0.020	≤0.020

TABLE 2 mechanical Property requirements

In Table 2, No. 4 is a bar-shaped sample.

In practical application, various additional requirements are provided due to different use conditions and application fields, and the product performance needs to be further improved on the basis of the product given by a user.

At present, ultra-thick steel plates with low specification and residual stress for forklifts and a manufacturing method thereof are rarely reported. Through review, the patent number ZL201510645919.0 and the patent name 'a special steel plate for forklift beams with 500MPa grade yield strength and a preparation method thereof' are mentioned: the steel plate with the thickness of 50-120 mm can be produced by adopting the controlled rolling and controlled cooling and normalizing process, but low residual stress is not mentioned, and whether the steel plate is deformed or not during cutting in the using process is also mentioned.

Disclosure of Invention

The invention aims to provide steel for a forklift with an ultra-thick specification and low residual stress and a preparation method thereof, so as to solve the problems. The invention provides a low residual stress steel plate for a forklift with excellent comprehensive performances such as high product strength, high impact toughness, high elongation after fracture and the like, and the steel plate for the forklift with low residual stress can be obtained by adding and controlling various alloy elements, performing thermomechanical rolling (TMCP) and quenching and tempering (quenching and tempering) processes, wherein the performance qualification rate reaches 100%, and producing the low residual stress steel plate with the thickness specification of 60mm < h < 100 mm.

In order to achieve the above purpose, the invention provides the following technical scheme:

the steel for the forklift with the ultra-thick specification and the low residual stress is characterized by comprising the following chemical components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.15 percent, Si is more than or equal to 0.30 percent and less than or equal to 0.30 percent, Mn is more than or equal to 1.45 percent and less than or equal to 0.010 percent and less than or equal to 0.018 percent and less than or equal to 0.012 percent and less than or equal to 0.035 percent, Cr is more than or equal to 0.020 percent and less than or equal to 0.030 percent, Ti is more than or equal to 0.010 percent and less than or equal to 0.020 percent, Als is more than or equal to 0.040 percent and the balance is iron and inevitable impurities, and the Als is acid-soluble aluminum.

The invention also provides a preparation method of the steel for the forklift with the ultra-thick specification and the low residual stress, which comprises the following steps:

(1) pretreating, namely desulfurizing molten iron;

(2) smelting, namely smelting the pretreated molten iron;

(3) refining, namely LF refining and RH refining;

(4) continuous casting, which adopts full-process protection casting;

(5) rolling by adopting TMCP;

(6) cooling, namely adopting laminar flow cooling;

(7) quenching, namely water cooling quenching is adopted;

(8) and (4) tempering, namely adopting high-temperature tempering.

In the step (1), the sulfur content in the molten iron is controlled to be below 0.010 percent by mass, and the desulfurization temperature is 1250-1320 ℃.

In the step (2), the pretreated molten iron enters a converter for smelting, the slag forming materials are added within 1-5 min before the molten iron enters the end point of the converter, the alkalinity of the final slag is controlled to be 3.0-3.5, the gun pressing time at the end point is 65-120 s, aluminum manganese iron is adopted for deoxidation, the adding amount of the aluminum manganese iron is 2.0-3.5 kg/t, when the molten steel is discharged to 1/4-2/5, low-phosphorus low-carbon manganese silicon, medium-carbon manganese iron, medium-carbon ferrochrome and ferrocolumbium are added in batches, and when the molten steel is discharged to 3/5-3/4, the adding is completed.

The low-phosphorus low-carbon manganese silicon is an iron alloy containing 0-0.06 wt% of phosphorus, 0-0.20 wt% of carbon, 68-72 wt% of manganese and 14-18 wt% of silicon, and the addition amount of the low-phosphorus low-carbon manganese silicon is 10.8kg/t-17.7 kg/t;

the medium carbon ferromanganese is an iron alloy containing 0.5 to 2 weight percent of carbon and 75 to 82 weight percent of manganese, and the addition amount of the medium carbon ferromanganese is 2.0kg/t to 8.5 kg/t;

the medium carbon ferrochrome is ferroalloy containing 0.5 to 2 weight percent of carbon and 52 to 85 weight percent of chromium, and the adding amount of the medium carbon ferrochrome is 3.5kg/t to 5.5 kg/t;

the ferrocolumbium is an iron alloy containing niobium with the weight percentage of 60-70%, and the adding amount of the ferrocolumbium is 0.2kg/t-0.6 kg/t.

In the step (3), the LF refining is stirred by bottom blowing argon in the whole process, argon is softly blown for 10-15 min, aluminum particles, calcium carbide and aluminum slag are used for slagging, yellow white slag or white slag is kept for 10-30 min, and the alkalinity of final slag is controlled to be 2.5-4.0; the vacuum degree in the RH refining process is controlled to be 10Pa-30Pa, the vacuum time is 15min-25min, the pure degassing time is more than or equal to 5min, the soft blowing time is more than or equal to 12min, the RH refining period is controlled to be 45min-60min, the adding amount of the aluminum wire is 1.2m/t-2.3m/t, and the adding amount of the titanium wire is 0.7m/t-1.6 m/t.

In the step (4), the whole-process protective casting means that a long water gap is adopted from a large ladle to a middle ladle and argon sealing protection is carried out; the tundish is covered by a covering agent combined with the carbonized rice hulls; the tundish to the crystallizer adopts an immersion type water gap and adopts argon seal protection; the liquid level of the crystallizer adopts peritectic steel covering slag;

the peritectic steel casting powder comprises SiO with the weight percentage of more than or equal to 21.0 percent₂≤31.0％、32.7％≤CaO≤42.7％、0≤MgO≤5％、6.5％≤Al₂O₃Less than or equal to 12.5 percent. The pulling speed is stabilized to 0.85m/min-0.90m/min, the casting superheat degree is controlled to be 15-25 ℃, the height of the liquid level of the tundish is controlled, the height of the liquid level of the tundish is not less than 600mm during casting, the height of the liquid level is 800mm-1000mm during normal casting, and the straightening temperature of a casting blank is controlled to be above 900 ℃.

In the step (5), the tapping temperature of the steel billet is controlled to be 1150-1220 ℃, the initial rolling temperature of rough rolling is 1130-1180 ℃, the final rolling temperature of rough rolling is 1050-1130 ℃, the total compression ratio of rough rolling is more than 50%, and the ratio of the thickness of the intermediate billet to the thickness of the finished product is 1.35-1.6; the initial rolling temperature of the finish rolling is 855-885 ℃, and the finish rolling temperature of the finish rolling is 825-855 ℃.

In the step (6), the cooling starting temperature is 785-835 ℃, the cooling finishing temperature is 625-675 ℃, and the cooling speed is 5 ℃/s-7 ℃/s.

In the step (7), the quenching temperature is controlled to be 905-915 ℃, the quenching heat preservation time is controlled to be 22-33 min, and the final cooling temperature is 20-25 ℃.

Quenching is adopted to convert the super-cooled austenite into martensite or bainite to obtain martensite or bainite tissues, and then tempering at different temperatures is matched to obtain tempered sorbite, so that the rigidity, hardness, wear resistance, fatigue strength, toughness and the like of the steel can be greatly improved, and different use requirements of various mechanical parts and tools are met. The mechanical property of the material is better than that of a normalized sorbite tissue with the same hardness. The strength and toughness of the steel plate can be improved by the quenching and tempering heat treatment process, and the strength and toughness of the steel plate can be greatly reduced and improved by the normalizing process; during use, the parts experience varying degrees of wear, and wear and fatigue resistance is also critical. In order to take the strength, toughness, wear resistance and fatigue resistance into consideration, the quenching and tempering process is adopted.

In the step (8), the tempering temperature is controlled to be 500-510 ℃, and the tempering heat preservation time is controlled to be 20-30 min.

Compared with the prior art, the invention has the following beneficial effects:

1) the steel is based on C, Si, Mn, P and S elements in chemical component design, Nb, Cr and Ti alloy elements are added in an auxiliary manner, other noble elements are not added, and therefore the alloy cost is reduced.

2) The invention meets the requirements that the thickness specification is more than 60mm-100mm, the yield strength is more than or equal to 510MPa, the tensile strength is more than or equal to 620MPa, the elongation after fracture is more than or equal to 25 percent, and the longitudinal V-shaped impact power value at minus 5 ℃ is more than or equal to 150J.

3) The steel plate is delivered in a hardened and tempered state, residual stress can be effectively eliminated, and deformation of the steel plate is avoided during cutting and welding.

4) The product is mainly applied to the field of manufacturing of forklift matching parts, can replace part of section steel after being machined, further improves the material utilization rate, reduces the purchasing cost and generates good economic and social benefits.

5) The invention provides a low residual stress steel plate for a forklift, which has excellent low-temperature impact toughness and excellent comprehensive properties such as product strength, elongation after fracture, cold bending property and the like, and the steel plate for the forklift with low residual stress can be obtained by adding and controlling various alloy elements, directly adopting TMCP (thermal mechanical control processing) and quenching and tempering processes, producing the steel plate with the performance qualification rate of 100 percent, producing the steel plate with the thickness of 60mm-100mm and the thickness of 60mm unequal.

Detailed Description

The present invention will be further described with reference to the following specific examples.

According to embodiments of the present invention, ultra-thick gauge low residual stress steel for forklifts and a method of making the same are provided. The steel for the forklift comprises the following components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.15 percent, Si is more than or equal to 0.30 percent and less than or equal to 0.30 percent, Mn is more than or equal to 1.45 percent and less than or equal to 0.010 percent and less than or equal to 0.018 percent and less than or equal to 0.012 percent and less than or equal to 0.035 percent, Cr is more than or equal to 0.020 percent and less than or equal to 0.030 percent, Ti is more than or equal to 0.010 percent and less than or equal to 0.020 percent, Als is more than or equal to 0.040 percent and the balance is iron and inevitable impurities, and the Als is acid-soluble aluminum. The steel for the forklift is excellent in low-temperature impact toughness and excellent in comprehensive properties such as product strength, elongation after fracture, cold bending property and the like. And the microalloying component design of low C + Nb, Cr and Ti is adopted, so that the steel plate is ensured to have easy weldability.

The control of the content of components and the action of the low residual stress steel for a fork truck of the present invention will be further described below.

Based on the components provided by the user, the contents of Nb, Cr, Ti and Al are reasonably designed. Nb: the fine grain strengthening effect of Nb is fully exerted, and the steel plate is ensured to have enough strength; cr: the small amount of the additive can improve the strength and the hardenability of the steel; ti: on one hand, free nitrogen in steel is eliminated, the anti-aging performance is improved, on the other hand, crystal grains are refined, segregation is reduced, the level of a banded structure is reduced, and the toughness is improved; al: on one hand, the crystal grains can be refined, the strength is improved, and on the other hand, the combination of Al and N can prevent strain aging.

On the other hand, the invention also provides a preparation method of the steel for the forklift with the low residual stress, which comprises the following steps: pretreatment, smelting, refining, continuous casting, rolling, cooling, quenching and tempering.

In order to ensure the requirement of low residual stress of the steel for the forklift, on one hand, the addition amount of each alloy element is fully considered during component design, on the other hand, a TMCP rolling process is adopted in the rolling process, and simultaneously, quenching and tempering heat treatment is adopted to meet the requirement on the product performance.

The pretreatment refers to molten iron desulphurization, and the process procedures are strictly executed in the molten iron desulphurization, the sulfur content in the molten iron is controlled to be below 0.010 percent (such as 0.001 percent, 0.002 percent, 0.003 percent, 0.004 percent, 0.005 percent, 0.006 percent, 0.007 percent, 0.008 percent, 0.009 percent and 0.010 percent) according to the mass percentage, the desulphurization temperature is 1250 ℃ -1320 ℃ (such as 1250 ℃, 1255 ℃, 1258 ℃, 1260 ℃, 1263 ℃, 1267 ℃, 1270 ℃, 1275 ℃, 1280 ℃, 1290 ℃, 1300 ℃, 1305 ℃, 1310 ℃, 1315 ℃ and 1320 ℃), and the slag on the molten iron surface is completely removed after the desulphurization. In general, sulfur is a harmful element, causes hot brittleness of steel, reduces ductility and toughness of steel, causes cracks at the time of rolling, and is disadvantageous in welding performance. In the invention, KR method desulfurization is adopted to control the desulfurization temperature during pretreatment, and the sulfur content in the molten iron is effectively reduced to be below 0.010 percent, so that the desulfurization is thorough, and the purity of steel is ensured.

Smelting, the pretreated molten iron enters a converter for smelting, the addition of slag forming materials is finished within 1-5 min before the molten iron enters the end point of the converter, the alkalinity of the final slag is controlled to be 3.0-3.5, the end point gun pressing time is 65-120 s (such as 65s, 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s, 120s and the range between any two numerical values), the end point gun pressing time is within 65s-120s, the chemical reaction of the added alloy components in the molten steel is exactly finished, and the complete homogenization of the components is achieved. If the time is shorter than 65s, the reaction is not sufficiently completed; if the time is longer than 120s, no effect on the components is exerted, and the production efficiency is adversely affected.

And (3) deoxidizing by adopting aluminum-manganese-iron, wherein the adding amount of the aluminum-manganese-iron is 2.0kg/t-3.5kg/t, adding low-phosphorus and low-carbon manganese-silicon, medium-carbon ferromanganese, medium-carbon ferrochromium and ferrocolumbium in batches when the molten steel is discharged to one fourth, and finishing adding when the molten steel is discharged to three fourths. The key points of converter smelting control are to reduce the phosphorus and sulfur content at the end point as much as possible, reasonably control the carbon content and ensure the purity of steel.

The low-phosphorus low-carbon manganese silicon is an iron alloy containing 0-0.06 wt% of phosphorus, 0-0.20 wt% of carbon, 68-72 wt% of manganese and 14-18 wt% of silicon, and the addition amount of the low-phosphorus low-carbon manganese silicon is 10.8kg/t-17.7 kg/t; the medium carbon ferromanganese is an iron alloy containing 0.5 to 2 weight percent of carbon and 75 to 82 weight percent of manganese, and the addition amount of the medium carbon ferromanganese is 2.0kg/t to 8.5 kg/t; the medium carbon ferrochrome is ferroalloy containing 0.5 to 2 weight percent of carbon and 52 to 85 weight percent of chromium, and the adding amount of the medium carbon ferrochrome is 3.5kg/t to 5.5 kg/t; the ferrocolumbium is an iron alloy containing niobium with the weight percentage of 60-70%, and the adding amount of the ferrocolumbium is 0.2kg/t-0.6 kg/t.

And refining, namely LF refining and RH refining.

Wherein, LF refining adopts bottom argon blowing and stirring in the whole process, argon is blown softly for 10min-15min, lime is added for slagging, aluminum grain deoxidizer is adopted for deoxidation, yellow and white slag is kept for 10min-30min (such as 10min, 12min, 17min, 19min, 20min, 22min, 25min, 27min, 29min and 30min), the yellow and white slag is kept for too short time, and the final slag is not melted; the retention time of the yellow and white slag or the white slag is too long, which affects the production efficiency. Controlling the alkalinity of the final slag to be 2.5-4.0, finely adjusting the components by adopting ferrocolumbium and ferrovanadium, feeding an aluminum wire for increasing aluminum, and feeding a titanium wire for increasing titanium. The LF refining can further perform desulfurization, deoxidation and inclusion removal, and adjust the components and temperature of molten steel to obtain a good refining effect.

The RH refining adopts a deep processing mode, the vacuum degree is controlled to be 10Pa-30Pa, and the smaller the vacuum degree is, the smaller the content of gaseous inclusions such as nitrogen, hydrogen, oxygen and the like in the molten steel is, namely clean steel smelting is carried out. The value of the ideal state vacuum degree is 0Pa, but the vacuum degree is controlled to be 10Pa-30Pa to achieve unrealistic, which shows that the content of gaseous inclusions such as nitrogen, hydrogen, oxygen and the like in the molten steel is very small and is close to clean steel smelting. The vacuum time is controlled at 15min-25min (such as 15min, 17min, 19min, 20min, 22min, 25min), the vacuum degree retention time is too short, and gas impurities cannot be removed; and the production efficiency is influenced on the contrary because the product is not used any longer. The pure degassing time is controlled to be more than or equal to 5min, and the soft blowing time is controlled to be more than or equal to 12 min. The RH refining period is controlled to be 40min-60min, the adding amount of aluminum particles in each furnace is 0-4kg (when the adding amount of aluminum wires is enough to achieve the deoxidation effect in LF refining, the aluminum particles can not be added in RH refining), and the adding amount of ferrotitanium in each furnace is 0-3 kg. The main purposes of RH refining are to perform vacuum degassing, reduce the gas content in steel, reduce the defects caused by gas in the steel plate, and improve the purity, alloying and homogenization of molten steel.

Continuous casting, wherein in the slab continuous casting process, whole-process protective casting is adopted, namely, a long water gap is adopted from a large ladle to a middle ladle, and argon sealing protection is carried out; the tundish is covered by combining a covering agent with the carbonized rice hulls, so that the liquid level is well covered, the molten steel is isolated from air, and secondary oxidation is avoided; the tundish to the crystallizer adopts an immersion type water gap and adopts argon seal protection; the liquid level of the crystallizer adopts peritectic steel covering slag, so that the pulling speed is stable. The peritectic steel casting powder comprises SiO with the weight percentage of more than or equal to 21.0 percent₂≤31.0％、32.7％≤CaO≤42.7％、0≤MgO≤5％、6.5％≤Al₂O₃≤12.5％。

In the continuous casting process, the casting is slowly and uniformly started, the pulling speed is increased to the target pulling speed, automatic control is carried out, the fluctuation condition of the liquid level of the crystallizer is closely observed, the pulling speed is gradually stabilized to 0.85m/min-0.90m/min, the pulling speed is determined according to the size of the section, and the 300-section is adopted. The size of the cross section is the thickness specification of the cast slab.

When the casting temperature and the superheat degree are fixed, the liquid can be more fully solidified according to the speed set by the section, more non-uniform nucleation cores are reserved in the liquid, the nucleation rate is improved, and the development of a columnar crystal area is prevented, so that more equiaxial crystals are obtained, and the effect of refining the crystal grains is achieved.

The drawing speed is determined according to the section size of the casting blank. According to the speed increasing curve, the speed is increased in a step mode, the speed is increased by 0.05m every 30s, the speed is maintained for a certain time after the speed is increased to a numerical value, the specific operation is that the speed is maintained for 1min at 0.4m/min, the speed is maintained for 2min at 0.6m/min, and the speed is increased to the required pulling speed finally in the mode. The large section drawing speed is small, the small section drawing speed is large, and the casting blank drawing speed is determined according to the casting period and the solidification law, so that the internal defects of the casting blank are avoided. If the section is large and the drawing speed is high, the molten steel is not solidified and the steel is directly drawn, thereby generating steel leakage.

The continuous casting process mainly reduces the central segregation degree of the casting blank through controlling the casting superheat degree, reduces or avoids surface cracks of the continuous casting blank through reasonably controlling the cooling water and the straightening temperature, thereby improving the surface and internal quality of the casting blank and providing powerful guarantee for the quality of a final product. The degree of superheat of the casting is determined by the difference between the tundish temperature and the liquidus temperature, with a target of 15 ℃ to 25 ℃ (e.g., 15 ℃, 20 ℃, 25 ℃ and any range between the two values). Controlling the height of the liquid level of the tundish, wherein the height of the liquid level of the tundish is not less than 600mm when casting is started, the height of the liquid level of the tundish is between 800mm and 1000mm in the normal casting process, and strictly prohibiting low-liquid-level casting to prevent slag entrapment. On one hand, the casting temperature is reduced by water cooling to obtain fine grain size; on one hand, the vibration of a crystallizer and dynamic soft pressure are adopted to refine grains. The straightening temperature of the casting blank is controlled to be above 900 ℃. And rolling, wherein in the rolling process, the wide and thick plate rolling adopts thermomechanical rolling, namely TMCP rolling, which is divided into rough rolling and finish rolling, and the rough rolling and the finish rolling adopt a four-roller reversing mill. The billet is heated before rolling, the tapping temperature of the billet is controlled to be 1150-1220 ℃ (such as 1150 ℃, 1155 ℃, 1160 ℃, 1170 ℃, 1175 ℃, 1180 ℃, 1190 ℃, 1200 ℃, 1205 ℃, 1210 ℃, 1215 ℃, 1220 ℃ and the range between any two values), and the purpose of heating the billet is to improve the plasticity of steel, reduce the deformation resistance and improve the internal structure and performance of metal. The steel is generally heated to a temperature within the range of the austenite single phase solid solution structure and a relatively high temperature and sufficient time are ensured to homogenize the structure and dissolve carbides, but the temperature should not be too high. The heating temperature is too high, so that on one hand, the defects of strong oxidation, decarburization, overheating, overburning and the like of the steel can be caused; the viscosity of iron scale contacted with a casting blank matrix is increased, and the descaling effect is influenced; on the other hand, the prior austenite grains are too coarse, and the grains of the finished product are also coarse according to the grain inheritance principle, so that the performance of the finished product is not facilitated. If the heating temperature is too low, the final rolling temperature is reduced, the rolling passes are increased, the rolling force is increased, the rolling rhythm and the control of the final finished product plate shape are influenced, the quality of steel is reduced, and even waste products can be caused.

After the billet is taken out of the furnace and before rough rolling, high-pressure water descaling is carried out, namely, the iron oxide scale on the surface of the casting blank is removed, so that the follow-up high surface quality is ensured. Therefore, the slab roughing start temperature is lowered as compared with the slab tapping temperature. The initial rolling temperature of the rough rolling of the billet is 1130-1180 ℃ (such as 1130 ℃, 1135 ℃, 1140 ℃, 1145 ℃, 1150 ℃, 1155 ℃, 1160 ℃, 1165 ℃, 1170 ℃, 1175 ℃, 1180 ℃ and the range between any two values), the final rolling temperature of the rough rolling is 1050-1130 ℃ (such as 1050 ℃, 1055 ℃, 1060 ℃, 1065 ℃, 1070 ℃, 1075 ℃, 1080 ℃, 1085 ℃, 1090 ℃, 1095 ℃, 1000 ℃, 1005 ℃, 1010 ℃, 1015 ℃, 1020 ℃, 1125 ℃, 1130 ℃ and the range between any two values), the higher rolling temperature can provide good temperature conditions for recrystallization, reduce deformation resistance in the rolling process, reduce damage to rolling mill equipment, facilitate implementation of high-temperature low-speed high-pressure processes, further facilitate elimination of defects such as cracks, looseness, pores and the like and spheroidization of inclusions, facilitate deformation to penetrate to the center, enable deformation to be more uniform, and improve the plasticity of the slab, is beneficial to rolling so as to ensure the total compression ratio in the rough rolling stage.

The rough rolling total compression ratio is more than 50%, and the ratio of the thickness of the intermediate blank to the thickness of the finished product is 1.35-1.6 (such as 1.35, 1.5, 1.6 and the range between any two values); the initial rolling temperature of the finish rolling is 855-885 ℃ (855 ℃, 865 ℃, 875 ℃, 885 ℃ and the range between any two values), and the final rolling temperature of the finish rolling is 825-855 ℃ (825 ℃, 835 ℃, 845 ℃, 855 ℃ and the range between any two values).

And (3) cooling, wherein in the cooling process, ACC cooling is adopted, the cooling starting temperature is 785-835 ℃, the cooling finishing temperature is 625-675 ℃, and the cooling speed is 5 ℃/s-7 ℃/s.

Quenching, adopting water cooling quenching, controlling the quenching temperature at 905-915 ℃, controlling the quenching heat preservation time at 22-33 min, and controlling the final cooling temperature at 20-25 ℃.

Tempering at high temperature of 500-510 deg.c for 20-30 min.

The control of each parameter in the production process can refine grains and improve the structure of the core of the steel plate to the maximum extent, and the steel plate with the final thickness, performance and surface quality meeting the requirements can be obtained.

The invention adopts thermo-mechanical rolling (TMCP), which is a technology for obtaining good texture by reasonably controlling parameters such as heating temperature, rolling temperature, deformation rate, finish rolling temperature, cooling process after rolling and the like of a billet so as to obviously improve the toughness of a material.

The invention adopts water cooling quenching, which is a heat treatment process method for heating steel to above critical temperature, preserving heat for a certain time, and cooling by adopting a surface water spraying mode, thereby obtaining an unbalanced structure mainly comprising martensite.

The high-temperature tempering is adopted in the invention, and the high-temperature tempering refers to the tempering of the steel plate at the temperature of 500-650 ℃, so that the residual stress can be effectively reduced or eliminated, and the deformation of the steel plate in the cutting and welding processes can be avoided.

The processes or parameters not specified in the process of the present invention are conventional in the art of steels for forklifts.

Example 1

The steel for the forklift comprises the following components in percentage by weight: c: 0.135%, Si: 0.19%, Mn: 1.38%, P: 0.016%, S: 0.004%, Nb: 0.022%, Cr: 0.24%, Ti: 0.010%, Als: 0.016% and the balance of iron and inevitable impurities.

The manufacturing method of the forklift steel containing the components comprises the following steps:

1) and (3) preprocessing, strictly executing the technological process of molten iron desulphurization, controlling the sulfur content of the molten iron to be 0.008 percent and the temperature to be 1250 ℃, and completely skimming the slag on the surface of the molten iron after the desulphurization is finished.

2) Smelting, wherein the pretreated molten iron enters a converter for smelting, the slag forming materials are added 3min before the end point, the alkalinity of the final slag is controlled to be 3.0, and the end point gun pressing time is 65 s. The aluminum manganese iron is adopted for deoxidation, and the adding amount of the aluminum manganese iron is 2.5 kg/t. When the molten steel is discharged to one fourth, low-phosphorus low-carbon manganese silicon, medium-carbon ferromanganese, medium-carbon ferrochromium and ferrocolumbium are added in batches, and when the molten steel is discharged to three fourths, the molten steel is added.

3) Refining, wherein molten steel smelted in the converter enters an LF refining furnace, lime is added according to actual conditions for slagging, yellow and white slag or white slag is kept for 13min, bottom argon blowing stirring is adopted in the whole process, and argon is blown softly for 11 min.

And (3) after LF refining, feeding the molten titanium into an RH refining furnace, and controlling the vacuum degree to be 10Pa, the vacuum time to be 18min, the pure degassing time to be 10min, the soft blowing time to be 15min, the RH refining period to be 45min, wherein the adding amount of the titanium wire is 0.8 m/t.

4) And continuous casting, wherein the whole-process protective pouring is adopted, peritectic steel protective slag is adopted as the protective slag, a casting blank with a 300-section is adopted, and the casting speed in the stationary period is set to be 0.85 m/min.

5) Rolling, wherein the rolling temperature is controlled to ensure that rolling is carried out in a specified temperature range, (1) the tapping temperature of a billet is 1190 ℃; (2) the average temperature of rough rolling and initial rolling of the billet is 1175, the average temperature of final rolling is 1125 ℃, the total compression ratio of rough rolling is more than 50 percent, and the thickness of the intermediate billet/the thickness of the finished product is 1.6; (3) the initial rolling temperature of finish rolling is 875 ℃, and the final rolling temperature is 840 ℃.

6) And cooling, wherein the cooling starting temperature is 800 ℃, the cooling finishing temperature is 640 ℃, and the cooling rate is 5 ℃.

7) Quenching, wherein the quenching temperature is 910 ℃, the quenching heat preservation time is 25min, and the final cooling temperature is 20 ℃.

8) Tempering at 500 deg.c for 20 min.

The properties of the steel sheet of this example are shown in Table 3, and the property test method was carried out by the International general method.

Example 2

The steel for the forklift comprises the following components in percentage by weight: c: 0.140%, Si: 0.21%, Mn: 1.40%, P: 0.015%, S: 0.003%, Nb: 0.020%, Cr: 0.25%, Ti: 0.015%, Als: 0.025%, and the balance of iron and inevitable impurities.

2) Smelting, wherein the pretreated molten iron enters a converter for smelting, the addition of a slagging material is finished 3min before the end point, the alkalinity of the final slag is controlled to be 3.5, and the end point gun pressing time is 70 s. The aluminum manganese iron is adopted for deoxidation, and the adding amount of the aluminum manganese iron is 2.0 kg/t. When the molten steel is discharged to one fourth, low-phosphorus low-carbon manganese silicon, medium-carbon ferromanganese, medium-carbon ferrochromium and ferrocolumbium are added in batches, and when the molten steel is discharged to three fourths, the molten steel is added.

3) Refining, wherein molten steel smelted in the converter enters an LF refining furnace, lime is added according to actual conditions for slagging, yellow and white slag or white slag is kept for 15min, bottom argon blowing stirring is adopted in the whole process, and argon is blown softly for 13 min.

And (3) after LF refining, feeding the molten titanium into an RH refining furnace, controlling the vacuum degree to be 10Pa, the vacuum time to be 17min, the pure degassing time to be 12min, the soft blowing time to be 17min, the RH refining period to be 50min, and controlling the adding amount of the titanium wires to be 1.0 m/t.

4) And continuous casting, wherein the whole-process protective pouring is adopted, peritectic steel covering slag is adopted as the covering slag, a casting blank with a 300-section is adopted, and the casting speed in the stationary period is set to be 0.90 m/min.

5) Rolling, wherein the rolling temperature is controlled to ensure that rolling is carried out in a specified temperature range, (1) the tapping temperature of a billet is 1180 ℃; (2) the average temperature of the rough rolling of the billet is 1165 ℃, the average temperature of the final rolling is 1115 ℃, the total compression ratio of the rough rolling is more than 50%, and the thickness of the intermediate billet/the thickness of the finished product is 1.5; (3) the initial rolling temperature of finish rolling is 870 ℃, and the final rolling temperature is 830 ℃.

6) And cooling, wherein the cooling starting temperature is 815 ℃, the cooling finishing temperature is 660 ℃, and the cooling rate is 6 ℃/s.

7) Quenching, wherein the quenching temperature is 910 ℃, the quenching heat preservation time is 30min, and the final cooling temperature is 20 ℃.

8) Tempering, wherein the tempering temperature is 505 ℃, and the tempering heat preservation time is 25 min. The properties of the steel sheet of this example are shown in Table 3, and the property test method was carried out by the International general method.

Example 3

The steel for the forklift comprises the following components in percentage by weight: c: 0.135%, Si: 0.25%, Mn: 1.38%, P: 0.013%, S: 0.002%, Nb: 0.016%, Cr: 0.22%, Ti: 0.015%, Als: 0.030%, the balance being iron and unavoidable impurities.

The manufacturing method of the wind power steel containing the components comprises the following steps:

1) and (3) preprocessing, strictly executing the technological process of molten iron desulphurization, controlling the sulfur content of the molten iron to be 0.005 percent and the temperature to be 1290 ℃, and completely removing slag on the surface of the molten iron after the desulphurization is finished.

2) Smelting, wherein the pretreated molten iron enters a converter for smelting, the addition of a slagging material is finished 3min before the end point, the alkalinity of the final slag is controlled to be 3.5, and the end point gun pressing time is 100 s. The aluminum manganese iron is adopted for deoxidation, and the adding amount of the aluminum manganese iron is 3.0 kg/t. When the molten steel is discharged to one fourth, low-phosphorus low-carbon manganese silicon, medium-carbon ferromanganese, medium-carbon ferrochromium and ferrocolumbium are added in batches, and when the molten steel is discharged to three fourths, the molten steel is added.

3) Refining, wherein molten steel smelted in the converter enters an LF refining furnace, lime is added according to actual conditions for slagging, yellow and white slag or white slag is kept for 13min, bottom argon blowing stirring is adopted in the whole process, and argon is blown softly for 15 min. Deoxidizing by using aluminium particle deoxidant. The components are finely adjusted by adopting ferrocolumbium, aluminum wire is fed for increasing aluminum, and titanium wire is fed for increasing titanium.

And (3) after LF refining, feeding the molten aluminum into an RH refining furnace, controlling the vacuum degree to be 20Pa, the vacuum time to be 25min, the pure degassing time to be 15min, the soft blowing time to be 20min, and the RH refining period to be 60min, wherein the adding amount of the aluminum wire is 1.5m/t, and the adding amount of the titanium wire is 2.0 m/t.

5) Rolling, wherein the rolling temperature is controlled to ensure that rolling is carried out in a specified temperature range, (1) the tapping temperature of a billet is 1200 ℃; (2) the average temperature of the rough rolling of the billet is 1180 ℃, the average temperature of the final rolling is 1130 ℃, the total compression ratio of the rough rolling is more than 50%, and the thickness of the intermediate billet/the thickness of the finished product is 1.35; (3) the initial rolling temperature of finish rolling is 880 ℃, and the final rolling temperature is 850 ℃.

6) And cooling, wherein the cooling starting temperature is 820 ℃, the cooling finishing temperature is 650 ℃, and the cooling rate is 7 ℃/s.

7) Quenching at 9910 deg.c for 33min and final cooling at 20 deg.c.

8) Tempering, wherein the tempering temperature is 510 ℃, and the tempering heat preservation time is 30 min.

The properties of the steel sheet of this example are shown in Table 3, and the property test method was carried out by the International general method. In Table 3, d is the radius of the bend and a is the thickness of the sample.

Table 3: steel sheet Properties in examples 1 to 3

According to the low residual stress forklift steel, the structure transformation and the phase proportion are accurately controlled by adjusting the components and the manufacturing process of the steel, and the low residual stress forklift steel with special mechanical properties is finally obtained. Accordingly, exemplary embodiments of the present invention provide a steel for a forklift with low residual stress, and thus can prevent deformation of a steel plate when cutting and welding.

According to the exemplary embodiment of the present invention, it is possible to provide a low residual stress steel for a forklift with an ultra-thickness of 60mm to 100mm, which is not equal to 60 mm. The invention relates to a steel for a forklift, which is suitable for forklift parts with TMCP + quenched and tempered state and low residual stress requirements, and does not deform in the using process.

Conventional technical knowledge in the art can be used for the details which are not described in the present invention.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. The steel for the forklift with the ultra-thick specification and the low residual stress is characterized by comprising the following chemical components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.15 percent, Si is more than or equal to 0.30 percent and less than or equal to 0.30 percent, Mn is more than or equal to 1.45 percent and less than or equal to 0.010 percent and less than or equal to 0.018 percent and less than or equal to 0.012 percent and less than or equal to 0.035 percent, Cr is more than or equal to 0.020 percent and less than or equal to 0.030 percent, Ti is more than or equal to 0.010 percent and less than or equal to 0.020 percent, Als is more than or equal to 0.040 percent and the balance is iron and inevitable impurities, and the Als is acid-soluble aluminum.

2. The steel for the forklift with the ultra-thick specification and the low residual stress as claimed in claim 1, wherein the thickness specification of the steel for the forklift is 60mm & lt h & lt 100mm, the yield strength is not less than 510MPa, the tensile strength is not less than 620MPa, the elongation after fracture is not less than 25%, and the longitudinal V-shaped impact power value at-5 ℃ is not less than 150J.

3. A method for preparing the steel for the ultra-thick gauge low residual stress forklift as claimed in claim 1, comprising the following steps:

1) pretreatment: desulfurizing the molten iron; controlling the sulfur content in the molten iron to be below 0.010 percent by mass; the desulfurization temperature is 1250-1320 ℃;

2) smelting: smelting the pretreated molten iron; adding the slag-making materials within 1-5 min before the molten iron enters the end point of the converter, and controlling the alkalinity of the final slag to be 3.0-3.5; the gun pressing time at the end point is 65-120 s;

3) refining: the method comprises LF refining and RH refining; the period of LF refining is controlled to be 45min-60min, the adding amount of the aluminum wire is 1.2m/t-2.3m/t, and the adding amount of the titanium wire is 0.7m/t-1.6 m/t; the RH refining period is controlled to be 45-60 min;

4) continuous casting: adopting whole-process protective casting; controlling the casting superheat degree at 15-25 ℃; controlling the height of the liquid level of the tundish, wherein the height of the liquid level of the tundish is not less than 600mm during casting, and the height of the liquid level is between 800mm and 1000mm during normal casting; controlling the straightening temperature of the casting blank to be more than 900 ℃;

5) rolling: rolling by adopting TMCP; the initial rolling temperature of rough rolling is 1130-1180 ℃, and the final rolling temperature of rough rolling is 1050-1130 ℃; the total reduction ratio of rough rolling is more than 50 percent, the initial rolling temperature of finish rolling is 855-885 ℃, and the finish rolling temperature is 825-855 ℃;

6) and (3) cooling: laminar cooling is adopted;

7) quenching: water cooling quenching is adopted; the quenching temperature is controlled to be 905-915 ℃, the quenching heat preservation time is controlled to be 22-33 min, and the final cooling temperature is 20-25 ℃;

8) tempering: high-temperature tempering is adopted; the tempering temperature is controlled to be 500-510 ℃, and the tempering heat preservation time is controlled to be 20-30 min.

4. The preparation method according to claim 3, wherein in the step 2), aluminum manganese iron is adopted for deoxidation, the adding amount of the aluminum manganese iron is 2.0kg/t-3.5kg/t, when the molten steel is discharged to 1/4-2/5, low-phosphorus low-carbon manganese silicon, medium-carbon manganese iron, medium-carbon ferrochrome and ferrocolumbium are added in batches, and when the molten steel is discharged to 3/5-3/4, the addition is finished;

5. The preparation method according to claim 3, wherein in the step 3), the LF refining is stirred by bottom blowing argon in the whole process, argon is softly blown for 10-15 min, and aluminum particles, calcium carbide and aluminum slag are used for slag adjustment; keeping the yellow and white slag for 10-30 min, and controlling the final slag alkalinity at 2.5-4.0.

6. The preparation method according to claim 3, wherein in the step 3), the degree of vacuum in the RH refining process is controlled to be 10Pa to 30Pa, and the vacuum time is 15min to 25 min; the pure degassing time is more than or equal to 5min, and the soft blowing time is more than or equal to 12 min; the adding amount of the aluminum particles in each furnace is 0kg-4kg, and the adding amount of the ferrotitanium in each furnace is 0kg-3 kg.

7. The preparation method according to claim 3, wherein in the step 4), the tundish is covered by a covering agent combined with the carbonized rice hulls; the tundish to the crystallizer adopts an immersion type water gap and adopts argon seal protection; the liquid level of the crystallizer adopts peritectic steel covering slag; the peritectic steel casting powder comprises SiO with the weight percentage of more than or equal to 21.0 percent₂≤31.0％、32.7％≤CaO≤42.7％、0≤MgO≤5％、6.5％≤Al₂O₃Less than or equal to 12.5 percent; the pulling speed is stabilized to 0.85m/min-0.90 m/min.

8. The preparation method according to claim 3, wherein in the step 5), the tapping temperature of the steel billet is controlled to be 1150-1220 ℃; the ratio of the thickness of the intermediate blank to the thickness of the finished product is 1.35-1.6.

9. The production method according to claim 3, wherein in the step 6), the cooling start temperature is 785 ℃ to 835 ℃, the cooling end temperature is 625 ℃ to 675 ℃, and the cooling rate is 5 ℃/s to 7 ℃/s.