KR920010532B1 - Making process for chisel steels - Google Patents

Abstract

The method for chisel steel, which composition is 0.35-0.60 C, 0.70-1.50 Si, 0.62-1.20 Mn, <= 0.030 S, <= 0.03 Cu, <= 0.25 Ni, 0.70- 1.60 Cr, 0.15-0.50 Mo, 0.05-0.20 V, 0.10-0.20 Nb, 0.020-0.040 Al, and the remainder of Fe in wt.%, is produced by the following; (1) quenching the steel piece from 800-900 deg.C, and (2) tempering it at 350-550 deg.C. The chisel steel has a good wear resistance because of hardening to chisel's center evenly, compared with Cr-steel or Mo-steel.

Description

High toughness chisel steels and manufacturing method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a chisel steel having a unique wear resistance and impact resistance as a chisel for a brake car of an excavator used for civil construction such as rock excavation, dismantling crushing of concrete structures, quarrying, and the like.

As a material of the chisel used in the related art, chromium, molybdenum steel (SCM440), chromium, nickel, and molybdenum steel (SNCM8) have been mainly used. In use, the steel is machined into a predetermined shape and then subjected to heat treatment. However, the chisel chisel end is severely worn by use, and the life is short, and it is uneconomical because the maintenance work is complicated when the shape is used repeatedly. On the other hand, another problem of the conventional chisel is that frequent breakage accidents occur in the hanger area of the chisel due to continuous hitting (impact) of the hydraulic brake car during the excavation or crushing of the rock. Because of this, the replacement work takes a long time and the continuity of the work is not maintained, resulting in inefficient work. This problem is due to the general properties of the steel is good to increase the strength in order to increase the wear resistance, but the toughness is weak to impact and the toughness is lowered strength is worse wear resistance.

The present invention is to provide a chisel steel excellent in impact resistance by solving the above problems of the conventional steel to obtain the required hardness and at the same time maintain the toughness. First chemical composition and second heat treatment were devised and designed to satisfy the two opposing quality conditions. The design contents are as follows.

(1) As chemical composition weight ratio, C 0.35-0.60%, Si 0.70-1.50%, Mn 0.60-1.20%, p 0.030% or less, s 0.030% or less, Cu 0.30% or less, Ni 0.25% or less, Cr 0.70-1.60 %, Mo 0.15-0.50%, V 0.05-0.20% or Nb 0.01-0.20%, Ai 0.020-0.040%, and the remaining Fe. That is, the steel of the present invention is uniformly quenched to the center of the chisel as compared with the conventional chromium and molybdenum steel, and has good abrasion resistance.

Next, the reason for limitation of chemical composition of this invention steel is demonstrated. C is quenched and added to obtain the required hardness, and carbides are formed to improve wear resistance. However, if the C content is increased, the upper limit is set to 0.60% or less because there is a risk of breakage during use due to the decrease in toughness. Si improves abrasion resistance and softening resistance at high temperatures, and in the case of Cr and Mo amounts, it adds 0.70% or more, but it adds 0.50% or less for the purpose of improving so-called softening resistance because it lowers the ratio and raises the quenching temperature. Mn is an element that improves the hardenability, and improves the homogeneity of heat treatment and high temperature strength, so that 0.60% or more is required in order to obtain the required hardness of chisel HRC 47 or more. However, Mn increases the brittleness and retained austenite. The risk of breakage during use is 1.20% or less. Cr forms carbides and improves abrasion resistance, and has the effect of uniform hardness distribution, strength improvement and softening due to frictional heat during use. The upper limit was made 1.6% because it increased and the hardening work was complicated. Mo is added in the range of 0.15-0.50% because it is effective in imparting hardenability, antifriction resistance, high temperature characteristics, precipitation secondary hardening ability, and preventing loose brittleness, but Mo is expensive and stable carbide when added in large amounts The upper limit was limited to 0.50% because the added effect was reduced to decrease the effect of addition. Nb belongs to the most powerful carbide-forming element and forms hard stable carbides, resulting in immobilization of carbon. On the other hand, since the effect of miniaturization and growth suppression of grains is great, the quenching property and the quenching hardness are lowered, but the wear resistance and toughness are improved. However, excessive addition forms coarse Nb carbide and degrades the material of the steel, so it is 0.01-0.20%.

V prevents softening accompanying heat rise during chisel use and simultaneously forms carbonitrides in combination with C and N to improve wear resistance. However, even if it contained more than 0.30%, since the effect was small, the upper limit was made into 0.20%. In addition to the effect similar to Mn, Ni is added to improve toughness and fatigue strength to prevent chisel breakage, but when the addition amount is large, the particle size decreases and machinability decreases, so the upper limit is 0.25%. Al was limited to 0.02-0.04% because it has an effect of miniaturizing grains. P, S, Cu, and the like have only an upper limit of inhibition as impurities.

(2) Heat treatment design: In order to obtain satisfactory mechanical properties by showing sufficient properties of materials with chemical composition as above, the following heat treatment is performed. That is, the material is heated to 800-900 ° C. in a heat treatment furnace and then annealed at a temperature of 350-550 ° C. to have toughness, thereby making a product having excellent toughness.

EXAMPLE

Next, the characteristic of this invention steel is revealed with the Example compared with the conventional steel.

[Table 1]

After melting and tapping with the same components as those in the first table in the electric furnace, degassing and secondary refining were carried out in the ladle, followed by injection into steel ingots. The ingot was heated to 1250 ° C. in a heating furnace and rolled or forged into various circular steels before processing. The steel thus produced was heated to 850 ° C. in a heat treatment furnace and then quenched at 500 ° C. to give toughness. In order to compare the mechanical properties with conventional steel, the sample was made by adjusting the sowing temperature, and the mechanical properties as shown in the second table were obtained.

[Table 2]

Table 2 shows that when the heat treatment conditions of the inventive steel samples C, D and the conventional steel sample (A) were performed in the same manner, the hardness and tensile strength of the inventive steel were superior to those of the conventional steel by about 15-25%. When the heat treatment conditions are adjusted to adjust the hardness to a level similar to that of the inventive steel (B, C, D samples), the elongation or impact value of the inventive steel is about 70% or more superior to that of the conventional steel.

As described above, the present invention steel is designed to the optimum conditions of chemical composition and heat treatment conditions to obtain the high hardness required for wear resistance of the chisel material, to make toughness and to maintain high elongation and impact value, which is actually mounted on the excavator In the case of the chisel, the returned cases were drastically reduced, and the lifespan was extended by 1.5 times to 2 times as compared to the conventional chisel, thereby demonstrating excellent impact resistance to wear, thereby improving the continuity and efficiency of the work.

Claims (2)

As weight ratio C 0.35-0.60%, Si 0.70-1.50%, Mn 0.60-1.20%, P 0.030%, S 0.030%, Cu 0.30%, Ni High toughness wear-resistant chisel steel characterized by having a component of 0.25%, Cr 0.70-1.60%, Mo 0.15-0.50%, V 0.05-0.20% or Nb 0.01-0.20%, AI 0.020-0.040%, remaining Fe. A method for producing a high toughness wear-resistant chisel steel having the component of claim 1, wherein the heat treatment temperature is quenched at 800-900 ° C and reduced at 350-550 ° C.