High-hardness, high-toughness steels and crawler components, earth wear resistant components, fastening bolts, high-toughness gears, high-toughness, high contact pressure resistance gears, and wear resistant steel plates using the same

Abstract

In order to provide a high-hardness, high-toughness steel, Si, Al, Cr, Mo, V, W, Ni, and Co are more appropriately added so that the steel can have an HRC hardness of 50 or higher and a Charpy impact value of 5 kgf m/cm 2 or more by tempering at a high temperature of 600° C. or higher. The steel is a martensite steel containing at least C: 0.15 to 1.2% by weight and Si: 0.05 to 1.8% by weight, wherein Si is partially replaced by 0.15 to 1.6% by weight of Al. The steel further contains Ni: 0.3 to 2.5% by weight; Cr: 0.1 to 3.5% by weight; Mo: 0.1 to 1.7% by weight, wherein the amount of Mo is not more than the upper limit determined by the relation formula: Mo(% by weight)=1.7−0.5×(Si(% by weight)+Al(% by weight)); one or both of V: 0.05 to 0.40% by weight and W: 0.1 to 1.0% by weight; at least one alloying element of Mn, Co, Cu, Ti, B, and Nb; inevitable impurities including P, S, N, and O; and the balance consisting essentially of Fe.

What is claimed is:  
     
         1 . A high-hardness, high-toughness steel containing at least C: 0.15 to 0.60% by weight, Si: 0.05 to 1.8% by weight, and Cr: 0.1 to 3.5% by weight, which comprises: Mo in an amount of 0.1 to 1.7% by weight, wherein the amount of Mo is not more than the upper limit determined by the relation formula: Mo(% by weight)=1.7−0.5×Si(% by weight); one or both of V: 0.10 to 0.40% by weight and W: 0.1 to 1.0% by weight; at least one alloying element of Mn, Ni, Co, Cu, Al, Ti, B, Nb, Zr, Ta, Hf, and Ca; inevitable impurities including P, S, N, and O; and the balance consisting essentially of Fe, wherein the steel is a quenched and tempered martensite steel.  
     
     
         2 . The steel according to  claim 1 , wherein Si is in an amount of 0.8 to 1.60% by weight, Cr is in an amount of at least 0.1% by weight and less than 1.0% by weight, Mo is in an amount of 0.5 to 1.3% by weight, and B is added in an amount of 0.0005 to 0.005% by weight.  
     
     
         3 . The steel according to  claim 1 , wherein the amount of each alloying element is adjusted to satisfy the relation formula: 26.2≦5.8×(Si(% by weight)+Al(% by weight))+2.8×Cr(% by weight)+11×Mo(% by weight)+25.7×V(% by weight)+7.5×W(% by weight)≦36.2.  
     
     
         4 . The steel according to  claim 1 , wherein Co is added in an amount of 1 to 20% by weight.  
     
     
         5 . The steel according to  claim 1 , wherein the steel contains at least one of Nb, Ti, Zr, Ta, and Hf in a total amount of 0.005 to 0.2% by weight.  
     
     
         6 . The steel according to  claim 1 , wherein the steel provides an HRC hardness of 50 to 60 and a Charpy impact value of at least 5 kgf m/cm 2  after quenching and following tempering at a high temperature of at least 600° C.  
     
     
         7 . The steel according to  claim 1 , wherein the steel is a tempered martensite steel quenched and then tempered and has an HRC hardness of at least 45 and a Charpy impact value that satisfies the relation formula: log(Charpy impact value (kgf m/cm 2 ))≧−0.0263×HRC+2.225 where its HRC hardness is in the range from 45 to 55, or has an HRC hardness of at least 55 and a Charpy impact value of at least 6 kgf m/cm 2 .  
     
     
         8 . A high-hardness, high-toughness steel containing at least C: 0.10 to 1.20% by weight and Si: 0.05 to 1.8% by weight, which comprises: 0.15 to 1.6% by weight of Al partially replacing Si; 0.3 to 2.5% by weight of Ni; at least one alloying element of Mn, Cr, Mo, V, W, Co, Cu, Ti, B, Nb, Zr, Ta, Hf, and Ca; inevitable impurities including P, S, N, and O; and the balance consisting essentially of Fe, wherein the steel is a quenched and tempered martensite structure steel.  
     
     
         9 . The steel according to  claim 8 , wherein the steel contains Cr in an amount ranging from 0.1 to 3.5% by weight.  
     
     
         10 . The steel according to  claim 8 , wherein Mo is added in an amount of less than 1.7% by weight and the amount of Mo is not more than the upper limit determined by the relation formula: Mo(% by weight)=1.7−0.5×(Si(% by weight)+Al(% by weight)) depending on the amount of Si and Al.  
     
     
         11 . The steel according to  claim 8 , wherein one or both of V: 0.05 to 0.40% by weight and W: 0.1 to 1.0% by weight are added to the steel.  
     
     
         12 . The steel according to  claim 8 , wherein the steel satisfies one or both of limitation (1): Al is in an amount of 0.15 to 0.75% by weight and Ni is in an amount of 0.3 to 2.0% by weight and limitation (2): B is added in an amount of 0.0005 to 0.005% by weight.  
     
     
         13 . The steel according to  claim 8 , wherein the amount of each alloying element is adjusted to satisfy the relation formula: 21.2≦5.8×(Si(% by weight)+Al(% by weight))+2.8×Cr(% by weight)+11×Mo(% by weight)+25.7×V(% by weight)+7.5×W(% by weight)≦41.2.  
     
     
         14 . The steel according to  claim 8 , wherein Co is added in an amount of 1 to 20% by weight.  
     
     
         15 . The steel according to  claim 8 , wherein the steel contains at least one of Nb, Ti, Zr, Ta, and Hf in a total amount of 0.005 to 0.2% by weight.  
     
     
         16 . The steel according to  claim 8 , wherein the steel provides an HRC hardness of 50 to 60 and a Charpy impact value of at least 5 kgf m/cm 2  after quenching and following tempering at a high temperature of at least 600° C.  
     
     
         17 . The steel according to  claim 8 , wherein the steel is a tempered martensite steel quenched and then tempered and has an HRC hardness of at least 45 and a Charpy impact value that satisfies the relation formula: log(Charpy impact value (kgf m/cm 2 ))≧−0.0263×HRC+2.225 where its HRC hardness is in the range from 45 to 55, or has an HRC hardness of at least 55 and a Charpy impact value of at least 6 kgf m/cm 2 .  
     
     
         18 . A high-hardness, high-toughness steel containing at least C: 0.25 to 0.55% by weight, Si: less than 0.8% by weight, and Cr: 3.5 to 5.5% by weight, which comprises: Mo in an amount of 0.3 to 1.0% by weight; one or both of V: 0.10 to 0.40% by weight and W: 0.1 to 1.0% by weight; at least one alloying element of Mn, Ni, Co, Cu, Al, B, Ti, Nb, Zr, Ta, Hf, and Ca; inevitable impurities including P, S, N, and O; and the balance consisting essentially of Fe, wherein the steel has a quenched and tempered martensite structure.  
     
     
         19 . The steel according to  claim 18 , wherein the steel contains Al in an amount of 0.15 to 1.0% by weight and Ni in an amount of 0.3 to 2.5% by weight so that it has an improved resistance to temper softening and an improved toughness.  
     
     
         20 . The steel according to  claim 19 , wherein the amount of each alloying element is adjusted to satisfy the relation formula: 21.2≦3×(Si(% by weight)+Al(% by weight))+2.8×Cr(% by weight)+11×Mo(% by weight)+25.7×V(% by weight)+7.5×W(% by weight)≦41.2.  
     
     
         21 . The steel according to  claim 18 , wherein Co is added in an amount of 1 to 20% by weight.  
     
     
         22 . The steel according to  claim 18 , wherein the steel contains at least one of Nb, Ti, Zr, Ta, and Hf in a total amount of 0.005 to 0.2% by weight.  
     
     
         23 . The steel according to  claim 18 , wherein the steel provides an HRC hardness of 50 to 60 and a Charpy impact value of at least 5 kgf m/cm 2  after quenching and following tempering at a high temperature of at least 600° C.  
     
     
         24 . The steel according to  claim 18 , wherein the steel is a tempered martensite steel quenched and then tempered and has an HRC hardness of at least 45 and a Charpy impact value that satisfies the relation formula: log(Charpy impact value (kgf m/cm 2 ))≧−0.0263×HRC+2.225 where its HRC hardness is in the range from 45 to 55, or has an HRC hardness of at least 55 and a Charpy impact value of at least 6 kgf m/cm 2 .  
     
     
         25 . A crawler component including a crawler bush, a crawler link, a top or bottom tracker roller for a crawler, and a crawler shoe for a crawler vehicle, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is a quenched and tempered martensite steel having an HRC hardness of at least 52 and a Charpy impact value of at least 6 kgf m/cm 2 .  
     
     
         26 . An earth wear-resistant component including a tunneling shank, a tunneling disk cutter, a chisel tool, and a stirring blade for soil improvement, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is a quenched and tempered martensite steel having an HRC hardness of at least 50 and a Charpy impact value of at least 8 kgf m/cm 2 .  
     
     
         27 . A fastening bolt for use in a construction machine, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is a quenched and tempered martensite steel having an HRC hardness of at least 40 and a Charpy impact value that satisfies the relation formula: log(Charpy impact value (kgf m/cm 2 ))≧−0.0263×HRC+2.225.  
     
     
         28 . A high-toughness gear, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is formed into a gear shape and then carburized, quenched, and tempered to have a surface carbon concentration of 0.6 to 1.0% by weight, a surface carburizing depth of at least 0.4 mm, and an adjusted HRC hardness of 55 to 64 and to provide a Charpy test piece with an equivalent depth and a Charpy impact value of at least 8 kgf m/cm 2 .  
     
     
         29 . A high-toughness, high contact pressure-resistance gear, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is formed into a gear shape and then carburized to have a surface carbon content of 0.8 to 1.3% by weight, temporarily cooled to the Al transformation temperature or lower, and then heated again, quenched, and tempered to have a surface carburized case depth of at least 0.4 mm, to contain cementite particles with an average particle diameter of at most 1 μm dispersed in its quench-hardened case, to have an adjusted HRC hardness of 59 to 65, and to provide a Charpy test piece with its equivalent depth and a Charpy impact value of at least 4 kgf m/cm 2 .  
     
     
         30 . A high-toughness gear, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is formed into a gear shape and then induction-hardened and tempered to have an adjusted surface HRC hardness of 52 to 64 and to provide a Charpy test piece having a hardened depth equivalent to that of the steel and a Charpy impact value of at least 5 kgf m/cm 2 .  
     
     
         31 . A wear-resistant steel plate, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel is quenched and tempered to have a high tension of at least 50 kgf/mm 2  and/or an adjusted HRC hardness of at least 50, and weldable use of the steel plate includes a bucket and a bulldozer blade.  
     
     
         32 . An earth wear-resistant component for use in earth excavation including a ripper point, an end bit, bucket tooth, an edge, and a tunneling disk cutter, which comprises the high-hardness, high-toughness steel according to any one of  claims 1  to  24 , wherein the steel contains less than 3.5% by weight of Cr and alloying elements each in a controlled amount that satisfies the relation formula: 26.2≦5.8×(Si(% by weight)+Al(% by weight))+2.8×Cr(% by weight)+11×Mo(% by weight)+25.7×V(% by weight)+7.5×W(% by weight)≦41.2 so that the steel can have an HRC hardness of at least 50 by tempering at 600° C.