A WEAR-RESISTANT STEEL WITH EXCELLENT SURFACE QUALITY AND A PRODUCTION METHOD THEREOF

Abstract

The invention relates to a wear-resistant steel with excellent surface quality, which is composed of C: 0.12-0.20%, Si: ≤0.1%, Mn: 0.6-1.20%, Nb: 0.010-0.040%, V: ≤0.01%, Ti: 0.010%-0.030, Al: ≤0.04%, Ni: ≤0.1%, Cu: ≤0.1%, Cr: 0.10-0.40%, Mo: ≤0.1%, B: 0.001-0.005%, Ca: 0.0010-0.0050%, P: ≤0.010%, S: ≤0.0015%, O: ≤0.0012%, N: ≤0.0035%, H: ≤0.0002%, the balance is Fe, and the carbon equivalent CEV≤0.4; PCM≤0.25. The production process flow is: converter smelting->LF refining->VD or Rh high vacuum degassing->continuous casting->heating->rolling->shot blasting->quenching->tempering. The wear-resistant steel of the invention has better surface quality, and there are no surface defects such as air pit, inclusion, hemp pit and pressed iron oxide scale. The depth of surface spots caused by the peeling off iron oxide scale is ≤0.1 mm, and the surface grinding of steel plate cannot be carried out. Based on element design, non-preheating welding and excellent toughness can be further realized.

Claims

1. A wear-resistant steel with excellent surface quality, characterized in that chemical constituents by mass percentage are C: 0.12-0.20%, Si: ≤0.1%, Mn: 0.6-1.20%, Nb: 0.010-0.040%, V: ≤0.01%, Ti: 0.010-0.030%, Al: ≤0.04%, Ni: ≤0.1%, Cu: ≤0.1%, Cr: 0.10-0.40%, Mo: ≤0.1%, B: 0.001-0.005%, Ca: 0.0010-0.0050%, P: ≤0.010%, s: ≤0.0015%, O: ≤0.0012%, N: ≤0.0035%, H: ≤0.0002%, and the balance is Fe and unavoidable impurity elements.

2. The wear-resistant steel with excellent surface quality according to claim 1, characterized in that its chemical constituents meet that the carbon equivalent value CEV is ≤0.40 according to a formula CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15; according to a formula PCM=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B, the welding crack sensitivity coefficient PCM≤0.25.

3. The wear-resistant steel with excellent surface quality according to claim 1, characterized in that when the product is a steel plate, the thickness of the steel plate is 4-20 mm.

4. The wear-resistant steel with excellent surface quality according to claim 1 or 2 or 3, characterized in that the surface quality of the steel is good, and there are no surface defects such as pores, inclusions, pits, or pressed iron oxide scales; the steel plate needs not to be polished, and the depths of surface spots caused by peeling off iron oxide scales are ≤0.1 mm.

5. The wear-resistant steel with excellent surface quality according to claim 1 or 2 or 3, characterized in that the tensile strength is ≥1200 MPa, the elongation is ≥12%, and the Charpy V-shaped longitudinal impact energy at −40° C. is ≥30J; Brinell hardness meets 360-460 HB.

6. A method for producing wear-resistant steel with excellent surface quality, which is characterized by comprising the following steps: (1) Smelting smelting by converter, controlling basicity of final slag R (CaO/SiO.sub.2)≥3, conducting slag cut-off, and the slag per ton of steel is controlled to be ≤3 kg; sending molten steel to LF refining furnace for refining, the content of FeO+MnO in the slag is controlled to be ≤2%, and SiO.sub.2 content ≤8%, Al.sub.2O.sub.3 content ≤15%-35%; the refining time ≤1 hour; sending the refined molten steel to VD or RH for vacuum treatment, where the degree of vacuum is ≤0.5 mbar, and the time is no lower than 30 min; using calcium iron wires to replace traditional silicon calcium wires for Ca treatment; inclusions are so controlled that a sum of the Grades of Group A, B, C and D is ≤2.5; (2) Continuous casting pouring at low overheat and under argon protection during the whole process, and adopting a dynamic soft reduction control; (3) Heating and rolling slab heating temperature is controlled at 1100-1180° C.; controlling that the soaking period of slab in the furnace does not exceed 1 hour; conducting high pressure water descaling before starting a steel plate rolling, carrying out high pressure descaling at the first pass and the last two passes of rough rolling; controlling the temperature of a head and a tail of an intermediate slab after the rough rolling ≤1000° C.; increasing a finish-rolling start temperature to >930° C.; in order to quickly reduce the rolling temperature, high-pressure water descaling is used before the finishing rolling, the total number of the passes with descaling during the finish rolling is not less than 3 passes, and controlling the final rolling temperature at >800° C.; for the rolled steel plate, an accelerated cooling, such as water cooling, is prohibited; (4) Shot blasting the steel plate must be shot blasted before heat treatment, to remove a complete and dense oxide scale on the surface of the steel plate; (5) Quenching & tempering the steel plate is quenched at 880-940° C., and the holding time is 20-60 min after the furnace temperature reaches the desired temperature; the steel plate is tempered at a low temperature, the tempering temperature is 150-250° C., and the holding time is 30-60 min after the furnace temperature reaches the desired temperature.

7. The method for producing wear-resistant steel with excellent surface quality according to claim 6, characterized in that in step (3), the overheat of the molten steel is controlled at 5-20° C., and the center segregation is not higher than grade C1.0.

8. The method for producing wear-resistant steel with excellent surface quality according to claim 6, characterized in that in step (4), when descaling with high-pressure water, the descaling pressure at the nozzle is >21 MPa.

9. The method for producing wear-resistant steel with excellent surface quality according to claim 6, characterized in that the accuracy of temperature control for quenching and tempering in step (5) is ±10° C.

10. The method for producing wear-resistant steel with excellent surface quality according to claim 6, characterized in that: in step (3), for the rolled steel plate, water cooling is strictly prohibited, and stacking slow cooling or covering slow cooling or air cooling is adopted for cooling.

Description

DESCRIPTION OF THE ATTACHED DRAWINGS

[0041] FIG. 1 shows the surface quality of steel plate with 0.25% Si.

[0042] FIG. 2 shows the surface quality of steel plate with 0.15% Si.

[0043] FIG. 3 shows the surface quality of steel plate with 0.05% Si.

[0044] FIG. 4 shows the constituents analysis of iron oxide scale on the surface of steel plate with 0.25% Si.

[0045] FIG. 5 shows the surface quality of a 12 mm thick steel plate of embodiment 1.

DETAILED DESCRIPTION OF EMBODIMENTS

[0046] The invention is described in further detail below in combination with embodiments.

[0047] Taking the steel plate as an example, the production process of the wear-resistant steel of the invention is: converter smelting->LF refining->VD or RH high vacuum degassing->continuous casting->heating->rolling->shot blasting->quenching->tempering.

[0048] The invention is further described below in combination with embodiments 1-2. See Table 1 for specific chemical constituents of embodiment 1-2. Steel plate carbon equivalent CEV≤0.4 and welding crack sensitivity coefficient PCM≤0.25 can realize non-preheating welding.

[0049] The production method of low alloy easy welding wear-resistant steel plate with excellent surface quality according to embodiments 1-2 of the invention comprises the following steps:

[0050] (1) Smelting: Adopt 150-ton converter for smelting. Control basicity of final slag from converter R (CaO/SiO.sub.2)>3.0, produce molten steel from converter, and control slag dropping per ton of steel ≤2 kg; Refer to Table 2 for detailed process parameters of converter smelting. Send steel to LF refining furnace for refining, and control the content of FeO+MnO≤2.0%, SiO.sub.2 content ≤8%, Al.sub.2O.sub.3 content ≤15%-35%; Ensure the refining time at 30-60 min; Send the refined molten steel to RH for degassing. The pressure is 0.5 mbar, and the time is 30-50 min. See Table 3 for specific refining process parameters.

[0051] (2) Continuous casting: Cast molten steel into 150 mm thick continuous casting slab. Control the casting temperature at 5-20° C. above the liquidus. Implement dynamic soft reduction in the casting process, and control the plate at C05-C1.0

[0052] (3) Rolling: Put the continuous casting slab obtained in step (2) into a walking beam heating furnace with a heating temperature of 1100-1180° C. and a soaking period of 30-60 min; After the slab is discharged from the furnace, it is descaled by high-pressure water with a descaling pressure of 21 MPa; Rough rolling is carried out after treatment. High pressure descaling shall be carried out for the first and last two passes of rough rolling (i.e. high pressure water descaling shall be matched for the passes with high reduction rate), and the waiting temperature of steel plate shall be 930-1000° C. Final temperature of finish rolling >800° C. The passes with descaling during finish rolling shall not be less than 3 passes. See Table 4 for specific process parameters related to rolling.

[0053] (4) Shot blasting: put the steel plate obtained in step (3) into the shot blasting equipment for shot blasting to completely remove the dense oxide scale on the surface of the steel plate.

[0054] (5) Quenching+tempering: the steel plate is quenched after shot blasting, the quenching temperature is 910° C., the holding time is 40 min, and the quenching medium is water. After quenching, the steel plate is tempered at low temperature. The tempering temperature is 200° C. and the holding time is 40 min.

[0055] See Table 5 for the steel plate properties corresponding to examples 1-2. The results show that the steel plate has excellent mechanical properties, tensile strength >1200 MPa, elongation >12%, Charpy V-shaped longitudinal impact energy >30J at −40° C.; Brinell hardness shall meet 360-460HB.

[0056] See FIG. 3 and FIG. 5 for the steel plate surface of the embodiment. The results show that the surface quality of the steel plate is good, there are no defects such as pores, inclusions, pits and oxide scale spots. There is no need for grinding treatment, and the surface quality is excellent. For comparison, the surface quality of steel plates with different Si content is shown in FIGS. 1 and 2. FIGS. 1 and 2 show the surface quality of steel plate obtained when the Si content of traditional wear-resistant steel is greater than 0.1%.

[0057] The invention reasonably designs the alloy constituents such as C and Si and their ratio, reduces the alloy cost, and reasonably designs the smelting, steel rolling and heat treatment processes, so that the obtained steel plate has excellent mechanical properties and welding properties; At the same time, the surface quality of steel plate is excellent, which provides feasibility for the production of engineering equipment with high standard surface quality requirements, and has the advantages and prospects of mass production and application.

TABLE-US-00001 TABLE 1 chemical constituents of wear resistant steel plate in embodiment (wt %) Embodiment C Si Mn P S Cr Nb Al B O N H CEV Pcm 1 0.13 0.05 1.00 0.009 0.001 0.40 0.015 0.025 0.0020 0.0008 0.0030 0.0001 0.38 0.21 2 0.17 0.05 1.10 0.008 0.0008 0.20 0.020 0.030 0.0015 0.0010 0.0025 0.00015 0.39 0.24

TABLE-US-00002 TABLE 2 Smelting process parameters of converter in embodiment SiO.sub.2 CaO Basicity Slag Embodiment % % R Kg/ton 1 13.58 45.26 3.33 2 2 13.16 45.13 3.43 1.8

TABLE-US-00003 TABLE 3 Refining process parameters of embodiment Em- Refining Degassing bodi- FeO MnO FeO + SiO.sub.2 Al.sub.2O.sub.3 time, time, ment % % MnO % % % min min 1 1.3 0.53 1.83 6.78 24.62 35 40 2 1.2 0.67 1.87 7.31 30.18 40 40

TABLE-US-00004 TABLE 4 Rolling process control Finish Product slab Descaling rolling Descaling Final thickness heating Soaking passes of waiting passes of temperature specification, temperature, time, finish temperature, finish of finish Embodiment mm ° C. min rolling ° C. rolling rolling, ° C. 1 12 1160 40 3 950 3 820 2 20 1170 50 3 940 4 810

TABLE-US-00005 TABLE 5 Mechanical properties of embodiments of the invention Transverse tension Yield Tensile Thickness Surface strength strength Embodiment mm hardness Pa MPa Elongation % Impact energy Akv, J 1 12 378 1123 1247 15.5 −40° C. 47 54 48 2 20 456 1294 1434 14.0 −40° C. 52 56 46

[0058] In addition to the above embodiments, the invention also includes other embodiments. Any technical scheme formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the claims of the invention.